Influence of High Cutting Speeds

114
Report No. ERC/NSM - S-96-19 INFLUENCE OF HIGH CUTTING SPEEDS ON THE QUALITY OF BLANKED PARTS by Martin Grünbaum, Visiting Scholar University of Stuttgart, Germany and Jochen Breitling, Staff Engineer, ERC/NSM Taylan Altan, Professor and Director, ERC/NSM NSF Engineering Research Center for Net Shape Manufacturing The Ohio State University 1971 Neil Avenue Columbus, Ohio 43210 May, 1996 Advanced Copy For Limited Distribution Only (This report is an advance copy subject to modification and is distributed only to members of the ERC for Net Shape Manufacturing. Approval must be requested from the ERC prior to distribution to other organizations or individuals.)

Transcript of Influence of High Cutting Speeds

Page 1: Influence of High Cutting Speeds

Report No. ERC/NSM - S-96-19

INFLUENCE OF HIGH CUTTING SPEEDS ON THE QUALITY OF

BLANKED PARTS

by

Martin Grünbaum, Visiting Scholar

University of Stuttgart, Germany

and

Jochen Breitling, Staff Engineer, ERC/NSM

Taylan Altan, Professor and Director, ERC/NSM

NSF Engineering Research Center for

Net Shape Manufacturing

The Ohio State University

1971 Neil Avenue

Columbus, Ohio 43210

May, 1996

Advanced Copy

For Limited Distribution Only

(This report is an advance copy subject to modification and is distributed only to

members of the ERC for Net Shape Manufacturing. Approval must be requested

from the ERC prior to distribution to other organizations or individuals.)

Page 2: Influence of High Cutting Speeds

i

FOREWORD

This document has been prepared for the Engineering Research Center for Net

Shape Manufacturing (ERC/NSM). The Center was established on May 1, 1986

and is funded by the National Science Foundation and the member companies.

The focus of the Center is net shape manufacturing with emphasis on cost-

effective manufacturing of discrete parts. The research concentrates on

manufacturing from engineering materials to finish or near finish dimensions via

processes that use dies and molds. In addition, to conduct industrially relevant

engineering research, the Center has the objectives to

a) establish close cooperation between industry and the university,

b) train students and

c) transfer the research results to interested companies.

This report summarizes experimental and simulation work, investigating the

effects of very high cutting speeds. The goal of the first part of the project was to

monitor and analyze the velocity profile obtained with a Lourdes

electromagnetic impact press. For that purpose the press was equipped with a

velocity and proximity sensor in order to monitor the velocity-stroke curve. In

addition, the influence of material properties, cutting velocity and punch-die

clearance on the quality of the part edge was investigated.

Information about the ERC for Net Shape Manufacturing can be obtained from

the office of the Director, Taylan Altan, located at the Baker Systems Engineering

Building, 1971 Neil Avenue, Columbus, Ohio 43210-1271, phone 614/292-5063.

Page 3: Influence of High Cutting Speeds

ii

INFLUENCE OF HIGH CUTTING SPEEDS ON THE QUALITY OF

BLANKED PARTS

Martin Grünbaum, Visiting Scholar

Report No. ERC/NSM - S-96-19

EXECUTIVE SUMMARY

This report summarizes the influences of different parameters on the part edge

quality of blanked parts. Experiments have been conducted using different

materials, punch-die clearances and cutting speeds. In order to determine the

reachable cutting speeds and to calculate the energy required for blanking,

velocity-stroke curves were obtained. In addition, blanking simulations with

DEFORM 2D have been performed. The results of these simulations have then

been compared with the results obtained by the experiments.

The evaluation of the part edges shows that higher cutting speeds can improve

the part edge quality, resulting in smaller burr height and rollover, and a larger

shear zone. Furthermore, it could be observed that the part quality improvement

when blanking with high cutting speeds (up to 12 ft/sec) is much more distinct

for steel than for copper or aluminum. According to theory, this improvement

was expected because copper and aluminum have much higher heat conduction

coefficients. Therefore, the heat dissipates faster and the desired stress relief

effect does not take place to the same degree as for steel.

ERC/Net shape Manufacturing

339 Baker Systems / 1971 Neil Avenue

Columbus, OH 43210 ph: 614-292-9267 fax: 614-292-7219

Page 4: Influence of High Cutting Speeds

iii

TABLE OF CONTENTS

FOREWORD.................................................................................................................. i

EXECUTIVE SUMMARY............................................................................................. ii

TABLE OF CONTENTS.............................................................................................. iii

LIST OF TABLES.......................................................................................................... v

LIST OF FIGURES....................................................................................................... vi

CHAPTERS PAGE

1. INTRODUCTION.....................................................................................................................................1

2. THE BLANKING PROCESS ..................................................................................................................2

2.1 DEFINITION OF SHEARING AND BLANKING .................................................................................................2

2.2 INFLUENCES ON THE BLANKING PROCESS ...................................................................................................2

2.3 PHASES OF THE BLANKING PROCESS ..........................................................................................................3

2.4 STRESS CONDITIONS IN SHEARING ..............................................................................................................6

2.5 FORMATION OF THE PART EDGE..................................................................................................................8

2.6 HIGH SPEED BLANKING.............................................................................................................................10

3. EQUIPMENT USED...............................................................................................................................13

3.1 THE LOURDES PRESS 100-OH ..................................................................................................................13

3.2 EXPERIMENTAL SETUP .............................................................................................................................17

3.2.1 Punches and Dies ............................................................................................................................17

3.2.2 Stock materials ................................................................................................................................19

3.2.3 Sensors.............................................................................................................................................20

3.2.3.1 Analog Proximity Sensor ..........................................................................................................................20

3.2.3.2 Linear velocity transducer .........................................................................................................................20

3.2.4 Data Acquisition and Signal Analysis .............................................................................................21

3.3 TECHNIQUES FOR EVALUATING THE PART EDGE .......................................................................................22

3.3.1 Measuring the penetration depth, the shear zone and the rollover .................................................22

3.3.2 Technique for burr height measuring..............................................................................................23

3.3.2.1 Definition of the burr height......................................................................................................................23

3.3.2.2 Requirements and design of the device .....................................................................................................24

Page 5: Influence of High Cutting Speeds

iii

4. EXPERIMENTAL PROCEDURE ........................................................................................................27

4.1 INVESTIGATION OF PRESS CHARACTERISTICS............................................................................................28

4.2 VELOCITY INVESTIGATIONS......................................................................................................................29

4.3 PART QUALITY INVESTIGATIONS...............................................................................................................30

5. EXPERIMENTAL RESULTS ...............................................................................................................31

5.1 PRESS CHARACTERISTICS AND PRELIMINARY RESULTS .............................................................................31

5.2 VELOCITY INVESTIGATIONS......................................................................................................................33

5.3 PART QUALITY INVESTIGATIONS...............................................................................................................41

5.3.1 Experiments with low carbon steel ..................................................................................................42

5.3.2 Experiments with high strength steel ...............................................................................................50

5.3.3 Experiments with aluminum ............................................................................................................57

5.3.4 Experiments with copper .................................................................................................................64

5.3.5 Material comparison .......................................................................................................................71

6. FEM SIMULATIONS WITH DEFORM 2D........................................................................................78

6.1 THE FINITE ELEMENT CODE DEFORM 2D ..............................................................................................78

6.1.1 Pre-processor ..................................................................................................................................78

6.1.2 Simulation engine ............................................................................................................................78

6.1.3 Post-processor .................................................................................................................................79

6.2 SIMULATIONS OF THE HIGH SPEED BLANKING PROCESS ............................................................................79

6.2.1 Simulation settings...........................................................................................................................79

6.2.2 Simulation results ............................................................................................................................81

6.2.3 Comparison of the experimental and simulated results...................................................................82

7. SUMMARY AND CONCLUSIONS......................................................................................................84

8. LIST OF REFERENCES .......................................................................................................................87

APPENDIX A

APPENDIX B

APPENDIX C

APPENDIX D

Page 6: Influence of High Cutting Speeds

v

LIST OF TABLES

CHAPTERS PAGE

TABLE 1: INFLUENCES ON THE FORMATION OF THE CUTTING EDGE /10/, /4/, /8/, /11/, /12/................................10

TABLE 2: HEAT CONDUCTION COEFFICIENTS FOR DIFFERENT MATERIALS /19/ ..................................................11

TABLE 3: LOURDES 100-OH PRESS SPECIFICATIONS (ACCORDING TO THE MANUFACTURER) .............................14

TABLE 4: CLEARANCES IN PERCENT FOR DIFFERENT PUNCH DIAMETERS AND MATERIAL THICKNESSES (DIE

BUTTON DIAMETER: 0.500")...................................................................................................................19

TABLE 5: CLEARANCES IN PERCENT FOR DIFFERENT PUNCH DIAMETERS AND MATERIAL THICKNESSES (DIE

BUTTON DIAMETER: 0.514")...................................................................................................................19

TABLE 6: CUTTING SPEEDS AT DIFFERENT POWER LEVELS OF THE PRESS FOR DIFFERENT MATERIALS.................32

TABLE 7: CUTTING FORCE FOR DIFFERENT MATERIALS.....................................................................................38

TABLE 8: ENERGY LEVEL AT DIFFERENT CUTTING SPEEDS.................................................................................40

TABLE 9: CUTTING ENERGY FOR THE STOCK MATERIALS ...................................................................................41

TABLE 10: CROSS SECTION AND SIDE VIEW FOR LOW CARBON STEEL. CLEARANCE: 3/4%. ..................................47

TABLE 11: CROSS-SECTION AND SIDE VIEW FOR LOW CARBON STEEL. CLEARANCE: 15%. ..................................48

TABLE 12: CROSS-SECTION AND SIDE VIEW FOR LOW CARBON STEEL. CLEARANCE: 21/24%. .............................49

TABLE 13: CROSS-SECTION AND SIDE VIEW FOR HIGH STRENGTH STEEL. CLEARANCE: 3%. ................................54

TABLE 14: CROSS-SECTION AND SIDE VIEW FOR HIGH STRENGTH STEEL. CLEARANCE: 14%. ..............................55

TABLE 15: CROSS-SECTION AND SIDE VIEW FOR HIGH STRENGTH STEEL. CLEARANCE: 20/24%..........................56

TABLE 16: CROSS-SECTION AND SIDE VIEW FOR ALUMINUM. CLEARANCE: 5%. .................................................61

TABLE 17: CROSS-SECTION AND SIDE VIEW FOR ALUMINUM. CLEARANCE: 15%. ...............................................62

TABLE 18: CROSS-SECTION AND SIDE VIEW FOR ALUMINUM. CLEARANCE: 21%. ...............................................63

TABLE 19: CROSS-SECTION AND SIDE VIEW FOR COPPER. CLEARANCE: 6%. ......................................................68

TABLE 20: CROSS-SECTION AND SIDE VIEW FOR COPPER. CLEARANCE: 13%. ....................................................69

TABLE 21: CROSS-SECTION AND SIDE VIEW FOR COPPER. CLEARANCE: 19%. ....................................................70

TABLE 22: INPUT DATA OF THE LOW CARBON STEEL SHEET AND THE PUNCH......................................................80

TABLE 23: INPUT DATA OF THE DIE BUTTON AND THE BLANK HOLDER...............................................................80

TABLE 24: COMPARISON OF THE EXPERIMENTAL AND SIMULATED RESULTS (LOW CARBON STEEL) ......................83

Page 7: Influence of High Cutting Speeds

vi

LIST OF FIGURES

CHAPTERS PAGE

FIGURE 1: SCHEMATIC ILLUSTRATION OF THE SHEARING PROCESS.......................................................................3

FIGURE 2: PHASES OF THE BLANKING PROCESS /6/ ............................................................................................6

FIGURE 3: SHEARING FORCES ............................................................................................................................7

FIGURE 4: STRESS CONDITIONS IN THE SHEARING ZONE ......................................................................................8

FIGURE 5: DIFFERENT ZONES OF THE PART EDGE ...............................................................................................9

FIGURE 6: THE LOURDES PRESS 100-OH ........................................................................................................13

FIGURE 7: POSITION OF MATERIAL STRIP IN THE PRESS .....................................................................................14

FIGURE 8: SCHEMATIC PICTURE OF THE LOURDES PRESS 100 - OH ..................................................................15

FIGURE 9: PUNCH VELOCITY VERSUS THE POWER LEVELS OF THE PRESS DEPENDING ON THE STROKE LENGTH. NO

CUTTING CONDITION. .............................................................................................................................17

FIGURE 10: STRIPPER, DIE BUTTON AND PUNCH ...............................................................................................18

FIGURE 11: SENSOR WIRING (SCHEMATICALLY).................................................................................................22

FIGURE 12: MICROSCOPE PICTURE SHOWING THE CROSS SECTION OF A SLUG /4/...............................................23

FIGURE 13: BURR HEIGHT MEASUREMENT DEVICE............................................................................................24

FIGURE 14: METHOD OF WORKING OF THE BURR HEIGHT MEASURING DEVICE...................................................25

FIGURE 15: VELOCITY/DISPLACEMENT-TIME CURVE FOR NO CUTTING CONDITION AT POWER LEVEL 5 OF THE

PRESS ....................................................................................................................................................28

FIGURE 16: VELOCITY-STROKE CURVE FOR NO CUTTING CONDITION. POWER LEVEL 5. ......................................29

FIGURE 17:MAXIMUM CUTTING SPEED FOR DIFFERENT PUNCH-DIE CLEARANCES AND STOCK MATERIALS...........31

FIGURE 18: UNIFORMITY OF PART EDGE (LOW CARBON STEEL, 14% CLEARANCE, 4 FT/SEC)...............................33

FIGURE 19: VELOCITY/DISPLACEMENT-TIME CURVE. MATERIAL: LOW CARBON STEEL. POWER LEVEL 3, STROKE

LENGTH 0.5"..........................................................................................................................................34

FIGURE 20: VELOCITY/DISPLACEMENT-TIME CURVE. MATERIAL: LOW CARBON STEEL. POWER LEVEL 9, STROKE

LENGTH 1.5"..........................................................................................................................................35

FIGURE 21: PUNCH VELOCITY VERSUS DISPLACEMENT. MATERIAL: LOW CARBON STEEL. POWER LEVEL 3, STROKE

LENGTH 0.5"..........................................................................................................................................36

FIGURE 22: PUNCH VELOCITY VERSUS DISPLACEMENT. MATERIAL: LOW CARBON STEEL. POWER LEVEL 9, STROKE

LENGTH 1.5"..........................................................................................................................................37

FIGURE 23: BURR HEIGHT VERSUS PUNCH-DIE CLEARANCE (LOW CARBON STEEL)..............................................42

FIGURE 24: % SHEAR VERSUS PUNCH-DIE CLEARANCE (LOW CARBON STEEL) .....................................................43

FIGURE 25: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE (LOW CARBON STEEL)...............................................45

FIGURE 26: % PENETRATION VERSUS PUNCH-DIE CLEARANCE (LOW CARBON STEEL)..........................................46

FIGURE 27: BURR HEIGHT VERSUS PUNCH-DIE CLEARANCE (HIGH STRENGTH STEEL) .........................................50

Page 8: Influence of High Cutting Speeds

vi

FIGURE 28: % SHEAR VERSUS PUNCH-DIE CLEARANCE (HIGH STRENGTH STEEL) ................................................51

FIGURE 29: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE (HIGH STRENGTH STEEL) ..........................................52

FIGURE 30: % PENETRATION VERSUS PUNCH-DIE CLEARANCE (HIGH STRENGTH STEEL) .....................................53

FIGURE 31: BURR HEIGHT VERSUS PUNCH-DIE CLEARANCE (ALUMINUM) ..........................................................57

FIGURE 32: % SHEAR VERSUS PUNCH-DIE CLEARANCE (ALUMINUM)..................................................................58

FIGURE 33: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE (ALUMINUM)............................................................59

FIGURE 34: % PENETRATION VERSUS PUNCH-DIE CLEARANCE (ALUMINUM).......................................................60

FIGURE 35: % SHEAR VERSUS PUNCH-DIE CLEARANCE (COPPER) ......................................................................65

FIGURE 36: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE (COPPER) ................................................................66

FIGURE 37: % PENETRATION VERSUS PUNCH-DIE CLEARANCE (COPPER) ...........................................................67

FIGURE 38: BURR HEIGHT VERSUS PUNCH-DIE CLEARANCE, 0.5 FT/SEC.............................................................71

FIGURE 39: BURR HEIGHT VERSUS PUNCH-DIE CLEARANCE, 12 FT/SEC..............................................................71

FIGURE 40: % SHEAR VERSUS PUNCH-DIE CLEARANCE, 0.5 FT/SEC....................................................................73

FIGURE 41: % SHEAR VERSUS PUNCH-DIE CLEARANCE, 12 FT/SEC.....................................................................73

FIGURE 42: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE, 0.5 FT/SEC..............................................................75

FIGURE 43: % ROLLOVER VERSUS PUNCH-DIE CLEARANCE, 12 FT/SEC...............................................................75

FIGURE 44: % PENETRATION VERSUS PUNCH-DIE CLEARANCE, 0.5 FT/SEC.........................................................76

FIGURE 45: % PENETRATION VERSUS PUNCH-DIE CLEARANCE, 12 FT/SEC..........................................................76

Page 9: Influence of High Cutting Speeds

1

1. Introduction

Since raw-material as well as energy will become scarce and hence more

expensive in the future, the costs in the production industry will increase.

Despite the pressure of rising costs, it is very important to stay competitive in the

market. Therefore it is essential to think about economic production and high

productivity during the early part of the design phase.

Netshape or near netshape manufacturing is becoming more important to

decrease the costs of production. The final part has to be produced with fewer

manufacturing processes and natural resources. Many sheet metal parts are

produced by a blanking operation or include blanking within their

manufacturing process. In particular, when blanking with high punch velocities

it is possible to manufacture near netshape parts by improving the part edge

quality. The burr height, the rollover and the penetration depth are decreased

and the shear zone is increased when blanking at high speeds /1/. The overall

goal is to improve the blanking process in such a way that the produced part

does not need to be reworked. Therefore, the process parameters have to be

optimized carefully.

In order to determine the influence of different parameters on the part edge

quality, investigations have been made by varying process parameters, like the

punch-die clearance and the cutting speed for different materials. The punch

velocity and displacement was continously monitored by means of a velocity and

proximity sensor. Based on these two values it was possible to calculate the

required energy for blanking a part.

Page 10: Influence of High Cutting Speeds

2

2. The blanking process

The following sections provide general information about the blanking process,

the different phases of the cutting operation and the various parameters that

influence the process. In addition, the formation of the resulting part edge will be

discussed.

2.1 Definition of Shearing and Blanking

Shearing is defined as the cutting of a workpiece between two die components. The

material is stressed between two cutting edges to the point of fracture or beyond

its ultimate strength. During this process, the material is subjected to tensile as

well as compressive stresses /2/.

Various metal forming operations are based on the shearing process. Blanking is

cutting of parts out of sheet material to a predetermined contour. The contour is

defined by the punch and the die (Figure 1). The ejected slug is the part and the

remaining skeleton is considered scrap, in contrast with punching where the

sheared slug is discarded and the rest is the part /2/.

2.2 Influences on the blanking process

The cutting process is influenced by many parameters. The primary variables

affecting the cutting process are listed below /3/, /4/:

• punch - die clearance

• punch velocity

• stock material (thickness, mechanical properties, chemical

composition, microstructure and grain size)

• cutting tools (materials, cutting edge, tool wear)

• lubrication

Page 11: Influence of High Cutting Speeds

3

• alignment of the tools and

• strain rate.

punch motion

punchstripper

d ie

workpiece

Figure 1: Schematic illustration of the shearing process

Figure 1 shows the shearing process in principle. In industrial applications a

stripper or blankholder is used to strip or remove the material from the punches.

The simpliest type of stripper is the fixed one, in which the material is guided in

a gap between the die and stripper plate (fixed channel stripper) /5/.

2.3 Phases of the Blanking Process

The different phases of the cutting process are shown schematically in Figure 2.

Schüssler explains the process in terms of the following steps /6/, /7/:

Phase1: The punch moves downwards in the direction of the sheet with a

certain velocity. There is no contact between punch and die.

Page 12: Influence of High Cutting Speeds

4

Phase 2: The punch reaches the stock. Due to elastic and plastic deformation,

the contact area increases until enough force is applied for material

deformation.

Phase 3: The applied forces deform the stock elastically. The amount of the

bending moment and the elastic bending of the sheet depends on the

clearance between punch and die. The bending force consists of

tension and compression.

Phase 4: As the cutting elements penetrate further into the material, the

stresses within the deformation zone reach the shearing strength of

the material. The material starts yielding into the die. In this phase,

the draw in zone/rounded edge of the final part is created.

Phase 5: The material is sheared along the cutting edge. During this phase the

material which flows into the cutting gap is strain hardened within

the deformation area. The maximum cutting force is reached in this

step.

Phase 6: As soon as the shear stress reaches the tensile strength of the

material, material rupture starts. Due to high radial and tangential

stresses rupture starts behind the cutting edge on the surface area of

the die and spreads out to the surface area of the punch. This phase is

completed when the maximum rupture force of the material is

reached.

Phase 7: The blanked part is separated from the stock. If the incipient cracks

which start at the cutting edge of punch and die are not aligned and

Page 13: Influence of High Cutting Speeds

5

do not meet, the material is still not completely separated. In this case

the complete material separation occurs after the cutting elements

move further together.

Phase 8: The two parts are now separated and the shape of the shear area is

fully developed. Due to the elastic springback effects, the diameter of

the slug increases and the diameter of the skeleton decreases. The

result is a pressure on the surface of the cutting elements.

Phase 9: The punch moves down to the bottom dead center and ejects the

blanked part. During this phase, the surface pressure is still effective.

Phase 10: At the bottom dead center, the direction of motion is inverted. Due to

the friction between the stock and the surface of the punch, the

surface pressure is intensified. A stripper or blank holder has to strip

the blank from the punch.

Page 14: Influence of High Cutting Speeds

6

Figure 2: Phases of the Blanking Process /6/

2.4 Stress conditions in shearing

The cutting forces do not act linearly at the cutting edge. Instead, the vertical

force FV and horizontal force FH act in a small area near the cutting edge (Figure

3). The distribution of those compressive forces is nonuniform. The distance l

between the forces causes a moment which either bends or tilts the workpiece.

This moment has to be compensated by a counterbending moment which results

in bending stresses and horizontal normal stresses on the workpiece and tool

/4/, /8/. In addition to the above forces, frictional forces also act on the tooling.

The horizontal forces result in the frictional forces µFH and µF'H and the shearing

forces in µFV and µF'V .

Page 15: Influence of High Cutting Speeds

7

Figure 3: Shearing forces

The stress condition in the shearing zone during crack formation is triaxial.

According to Tresca, the flow criterion is given by (Figure 4) /9/:

τσ σ σ

max =−

=1 3

2 2f (1)

σ1 principal tensile stress

σ3 principal compressive stress

σf flow stress

τ max maximum shear stress

During the process, the shear yield stress increases because of the strain

hardening effect. As shown in Figure 4, the principal stress circle enlarges until

the shearing strength is reached /8/.

Page 16: Influence of High Cutting Speeds

8

As described in chapter 2.3, the stress condition changes throughout the

deformation process. The cracks propagate in the direction of the maximum

shear stresses /9/.

tensioncompression normal stress

shear stress

shearing strength

shear yield stress

fractureshearing

σ σ3 1

τmax

Figure 4: Stress conditions in the shearing zone

2.5 Formation of the part edge

The part edge is characterized by distinct regions as shown below (Figure 5) /4/.

The smooth and shiny area created by shearing the material is called shear zone.

The rough surface of the rupture zone is caused by material fracture/3/. The

penetration depth of the cracks depends on the material and the clearance between

punch and die. If the cracks do not run towards each other, secondary shear

formation may occur /8/. Stresses between the tool and the workpiece, and

between the two sheared surfaces, generate friction that stretches the metal into a

thin, ragged protrusion called a burr (see also 2.4). The side opposite the burr

Page 17: Influence of High Cutting Speeds

9

develops a rounded edge called rollover, as material is drawn away from the

surface /1/. The rollover is caused by plastic deformation, which is mainly

affected by material ductility, tool wear and clearance.

The quality of the part edge (ratio of the different zones) is mainly influenced by

the punch-die clearance, material properties, material thickness, cutting speed

and tool wear (see also chapter 3.2.1). The burr height, for instance, increases

with increasing clearance and increasing ductility of the material. Previous

investigations have shown that the cutting speed can have a remarkable

influence on the formation of the part edge (see also chapter 2.6) /6/. The

influences on the formation of the different zones of the part edge are

summarized in Table 1.

rollover

shear zone

rupture zone

burr

secondary shear

depth of the crackpenetration

Figure 5: Different zones of the part edge

Page 18: Influence of High Cutting Speeds

10

zone mainly influenced by:

burr ductility of the material, clearance, tool

wear, cutting speed

rollover material properties, clearance, tool

wear,

penetration depth tool wear, material properties,

clearance

shear zone material properties, tool wear, cutting

speed, clearance

secondary shear ductility of the material, clearance,

sheet thickness

Table 1: Influences on the formation of the cutting edge /4/, /8/, /10/, /11/, /12/

2.6 High speed blanking

Blanking at high speeds could mean that the process speed/stroke rate is high or

that the punch speed is high, or both. In this study, high speed blanking is

refered to as blanking with high punch velocities. The result are high strain rates

within the material. The strain rate within a deforming material describes the

variation of strain over time. The strain rate (dimension: [ s−1]) affects the

temperature of the workpiece as well as of the tool. Huml found out that as

much as 95% of all the work performed when forming and cutting materials is

converted into heat /13/.

This means that an increase in cutting velocity results in a temperature increase

in the forming zone and the tool surface. Since the heat is generated faster than it

can dissipate into the material (depending on the heat conduction coefficient,

Table 2), the result is a very high temperature concentration in a narrow shearing

zone.

Page 19: Influence of High Cutting Speeds

11

This effect produces three main benefits:

• High temperatures of up to 1800°F in the shearing zone create a stress release

effect within the material /14/, /15/. The higher the speed, the more the

effect of stress release is apparent. The strain hardening effect caused by the

material deformation may even be neutralized. Because of the stress release

the material can withstand more shearing until the shearing strength is

exceeded and the material fractures.

• Due to the small deformation area, the springback of the parts is negligible

compared to blanking at lower shearing speeds. This phenomena results in

less return stroke load and therefore less tool wear /16/.

• Temperature related internal stresses and fractures are dramatically reduced

/17/.

These effects result in an improvement of the part edge quality by means of

decreasing the burr height and the rollover and increasing the shear zone. In

addition, less distortion is created than in blanks produced at low speeds /18/.

The heat transfer is characterized by the heat conduction within a material. A

characteristic value for the heat conduction is the heat conduction coefficient. The

following table provides a comparison for different materials:

Material Heat conduction coefficient [W/Km]

Steel (0.2 % C) 50

Steel (0.6 % C) 46

Copper 350...370

Aluminum (99.5%) 221

Brass 80...120

Table 2: Heat conduction coefficients for different materials /19/

Page 20: Influence of High Cutting Speeds

12

Table 2 shows that the heat conduction coefficient of copper and aluminum is

much higher than the one for steel. Therefore, the heat which is created by high

cutting velocities is also dissipating faster when cutting copper or aluminum.

This results in lower quality improvement for copper and aluminum when

blanking with high punch speeds.

Contrary to high speed blanking, the stress relief effects are negligible while

blanking at lower speeds. The edge quality of the blanked part is mainly affected

by the material properties and the tool geometry. Due to the stress profile and

the movement of the tools, the material strain hardens in the area close to the

cutting tool surface. Since this area can withstand higher stresses than the

material next to it, the rupture takes place in the direction of the maximum shear

stress within the unhardened material. The resulting stress profile created by the

force couple has two separate shear zones which grow towards each other from

opposite sides of the workpiece. In the zone between the two shear planes, the

stress builds up to the material’s tensile strength, causing it to rupture. This

results in an S-shaped edge on the blanked part /1/.

All these effects, seen at low speeds, result in blanked parts with a larger

deformation zone, more part deformation, a higher burr and a rough rupture

zone compared to high speed blanking /20/.

Ideal process conditions in high speed blanking are only achieved when the

strain hardening effect is reduced as much as possible by the stress relief effects.

This means that the optimum shearing speed has to be high enough that stress

relief occurs, but not too high in order to allow enough time for stress relieving,

which is a time dependent process.

Page 21: Influence of High Cutting Speeds

13

3. Equipment used

In the following chapters the press, tooling, instrumentation and data acquisition

system are described. Furthermore, a technique for measuring the burr height

and the materials used for the experiments will be introduced.

3.1 The Lourdes Press 100-OH

Figure 6: The Lourdes Press 100-OH

The experiments were conducted with a Lourdes Electro Activated Die Set with

the following specifications:

Page 22: Influence of High Cutting Speeds

14

Force (0.030” above bottom) 10 tons

Overall dimensions 10”x10”x19”

Maximum work area 4.5”x10”

Stroke length 0.5" to 1.5”

Open height 5.0”

Shut height 3.5”

Approx. weight 100 lbs

Approx. weight of untooled top plate 35 lbs

Table 3: Lourdes 100-OH press specifications (according to the manufacturer)

The Lourdes High Speed Press 100-OH uses high tool speed, rather than force or

pressure to perform work. It accelerates the tooling to speeds up to

approximately 12 ft/sec /17/.

Figure 7: Position of material strip in the press

The Lourdes Electromagnetic Press uses tractive Solenoids, comprised of a coil

structure, a ferro-magnetic flux path, and an Armature, to accelerate the motion

plate. The magnetic accelerator mounts directly to a precision die set (as shown

in Figure 8) /21/.

Page 23: Influence of High Cutting Speeds

15

The microprocessor control precisely energizes the accelerator causing the punch

to be rapidly accelerated towards the die. The control regulates the tool speed

and disconnects the driving forces just before the tool impacts the material. The

kinetic energy or momentum of the moving tool holder is converted to work as

the tooling impacts the material. Finally, any unused energy is absorbed by the

urethane stops and the tool holder plate is returned, aided by spring force, to the

initial position /17/.

AIR IN COOLING FAN

ARMATURE SPACERS

ARMATURE

GUARD (TRANSPARENTFOR CLARITY ONLY)

COIL ENCLOSURE

AIROUT

RETURN RATEADJUSTING

RETURNSPRING

POWER CABLE

TO CONTROL

AIROUT

URETHANERETURN STOP

STROKEADJUSTING

ARMATURESUPPORT

BALL BEARINGBUSHING

GUIDEPINBALL RETAINERADJUSTORURETHANESTOP

Figure 8: Schematic picture of the Lourdes Press 100 - OH

In order to minimize wear on the die set and tooling and to get the best blanking

results, three different press adjustments have to be made:

Page 24: Influence of High Cutting Speeds

16

1) Return Rate Adjustment

The return rate adjustment is made by two nuts, located on the top of each

Return Rate Spring Rod (Figure 8). This spring force only serves to return the

punch plate to the top of its stroke after the Die Set has been fired. It is not

intended for the use of material stripping. This return force has to be adjusted

depending on the upper die weight. In order to leave the maximum amount of

energy available for the actual application, the return rate has to be set to a

minimum.

2) Stroke Adjustment

This adjustment is located between the motion plate and top plate, and plays an

important part in developing the maximum force of the unit. The stroke length

has to be adjusted depending on the selected power level.

3) Armature Spacer Adjustment

The armature spacers (washers) located on top of the armature have to be

adjusted only if the tooling shut height differs from the press shut height. The

armature should sit flush with the top of the spring loaded T-bar that enters the

coil from the bottom side when the tooling is closed.

As soon as the adjustments described above have been made, the cutting speed

which is nesessary for each specific application has to be determined. For the

Lourdes 100 - OH press there are 9 power levels available. The cutting speed

varies between 2.5 (power level 2) and 12 ft/sec (power level 9), depending on

the blanked material.

The following graph shows the dependence of the cutting speed on the stroke

length for each power level. Shown are the settings for 0.5" (minimum stroke

length) and 1.5" (maximum stroke length). However, it is possible to set the

stroke length at any number in between these two extremes.

Page 25: Influence of High Cutting Speeds

17

0

3

6

9

12

15

1 2 3 4 5 6 7 8 9power level

velo

city

[ft/s

ec]

stroke length 1.5"stroke length 0.5"

Figure 9: Punch velocity versus the power levels of the press depending on the stroke

length. No cutting condition.

Figure 9 shows that up to power level 4 it is more efficient to set the stroke length

to 0.5" in order to reach the maximum punch velocity, whereas for power level 5

and higher, the maximum punch velocity can only be reached by setting the

stroke length to 1.5 ".

3.2 Experimental Setup

3.2.1 Punches and Dies

Usually the punch-die clearance is defined as a relative clearance per side in

percent of the material thickness (equation (2)) /17/.

cd d

td p=−

⋅2

100%

(2) c radial clearance [%]

dd diameter of the die

dp diameter of the punch

t material thickness

Page 26: Influence of High Cutting Speeds

18

The radial clearance is important, since it will affect the part edge quality,

distortion of the blanks, tool wear and production costs in general /18/.

According to previous investigations, increasing the punch-die clearance has the

following effects /3/, /6/, /10/, /18/, /22/:

• more rollover

• higher burr

• less shear and more rupture.

In general, small clearances (< 8%) create high strains on punch and die /6/.

Therefore, proper alignment of the punch and the die is necessary in order to

minimize tool wear. On the other hand, the part quality increases with

decreasing the punch-die clearance. To reduce strain, clearances higher than 8%

are preferred when using high strength steels /6/.

The tooling of the Lourdes Press consists of a punch, a die button and a polymer

stripper, which are shown in the following figure. All punches and die buttons

which were used for the experiments are made of M-2 high speed steel and are

mounted to the retainers by means of a ball lock (for fast punch and die change).

The polymer stripper is mounted directly to the punch and is used for stripping

the skeleton off the punch after blanking /23/.

Figure 10: Stripper, die button and punch

Page 27: Influence of High Cutting Speeds

19

In order to obtain different punch-die clearances a whole set of round punches

and die buttons was available. The following two tables show the resulting

clearances depending on the material thickness.

punch

diameter

material thickness [in]

[in] 0.016” 0.033” 0.041" 0.054” 0.488 38 18 14.5 11 0.491 28 14 11 8.5 0.494 19 9 7 5.5 0.496 13 6. 5 3.5 0.497 9 4.5 3.5 3 0.498 6 3 2.5 2 0.499 3 1.5 1.2 1

Table 4: Clearances in percent for different punch diameters and material thicknesses

(die button diameter: 0.500")

punch

diameter

material thickness [in]

[in] 0.033” 0.041" 0.054” 0.488 / / 24 0.491 / 28 21 0.494 30 24 19 0.496 27 22 17 0.497 26 21 16 0.498 24 20 15 0.499 23 18 14

Table 5: Clearances in percent for different punch diameters and material thicknesses

(die button diameter: 0.514")

3.2.2 Stock materials

Four different stock materials were used for conducting the experiments:

• Low carbon steel (0.0033" thickness),

• high strength steel (0.054" thickness),

• copper 110, annealed temper (0.016" thickness),

Page 28: Influence of High Cutting Speeds

20

• aluminum 2008 (0.041" thickness) and

• brass (0.031" thickness). Brass was only used for preliminary experiments.

More detailed information about these materials and their properties can be

found in the appendix A.

3.2.3 Sensors

In order to monitor the velocity profil over the stroke, the press was equipped

with a velocity transducer and a proximity sensor.

3.2.3.1 Analog Proximity Sensor

For monitoring the relative position of the punch an inductive proximity sensor

was used. The sensor (resolution: 0.0002", linearity: ± 4%, range: 1") was

mounted to the base plate and was detecting the motion plate (Figure 6). An

inductive proximity sensor consists of a coil and a ferrite core arrangement. The

oscillator creates a high frequency field, radiating from the coil in front of the

sensor, centered around the axis of the coil. The ferrite core bundles and directs

the electro-magnetic field to the front.

When a metal object (target) enters the high-frequency field, eddy currents are

induced in the surface of the target. This results in a decrease of energy in the

oscillator circuit and, consequently, a smaller amplitude of oscillation /24/. The

signal was further processed through an oscillator/demodulator, a signal

conditioner and an operational amplifier. For monitoring the relative position of

the slide, the probes were connected to a data acquisition board, which will be

described in chapter 3.2.4.

3.2.3.2 Linear velocity transducer

In addition to the proximity sensor, a linear velocity transducer was used in

order to monitor the velocity of the punch at different stages during the cutting

process. The velocity transducer consists of high coercive force permanent

Page 29: Influence of High Cutting Speeds

21

magnet cores which induce sizable DC voltage while moving concentrically

within shielded coils.

As shown in Figure 6, the shielded coil is mounted to the stationary chassis and

the permanent magnet core via a brass rod to the motion plate of the press. The

induced output voltage of the coil is directly proportional to the magnet's relative

velocity and field strength. For reducing the noise of the signal, an aluminum foil

shielding around the probes was used to improve the results. However, for

getting the most accurate results, one should operate in a magnetically shielded

enclosure /25/. The signal was also converted from high to low impedance by

means of an operational amplifier in order to stabilize the signal and avoid

compatibility problems with the data acquisition board.

3.2.4 Data Acquisition and Signal Analysis

The data acquisition PC was equipped with a National Instruments AT-MIO-

16F-5 data acquisition board in conjunction with the National Instruments

LabVIEW software used for real time monitoring of the sensor signals up to 200

kHz. A Labview program (the program code is shown in the appendix B) was

written for our specific application.

The program has the following features:

• It displays the velocity as well as the penetration of the punch in respect to

the time. One can read the correlating punch velocity for a given punch

position.

• It has an option to save the acquired data for further investigations/analysis

of the cutting speed.

Figure 11 shows the scheme of the discussed sensor wiring.

Page 30: Influence of High Cutting Speeds

22

linear velocitytransducer

voltagedivider

operationalamplifier

proximitysensor

oscillator/demodulator

signal conditioner

DAQ

BoardPC

Figure 11: Sensor wiring (schematically)

3.3 Techniques for evaluating the part edge

According to Lange there are basically four values, that should be considered

when evaluating the part edge of a blanked part (Figure 12) /4/:

• the burr height hb ,

• the percentage of shear with respect to the material thickness (called % shear),

• the percentage of rollover with respect to the material thickness (called

% rollover),

• the penetration depth tc .

Depending on the final use of the part, an ideal part edge has a minimum of

rollover and burr and at least 75 % shear.

3.3.1 Measuring the penetration depth, the shear zone and the rollover

The values for the penetration depth and the % rollover have been obtained from

the cross section of the slugs by using a microscope. To achieve the cross

sections, the slug first has to be sheared close to the centerline, then be mounted

in polymer, and finally be ground and polished in order to get a smooth surface.

For investigating the amount and the constancy of shear and rupture, the slug

has been microscoped from the side. Since the % shear value is not as constant as

the penetration depth or the % rollover for a certain clearance and cutting speed,

each slug has been measured at 4 different locations around the circumference.

Page 31: Influence of High Cutting Speeds

23

Pictures for different materials showing cross sections as well as side-views can

be found in chapter 5.3.

Figure 12: Microscope picture showing the cross section of a slug /4/

3.3.2 Technique for burr height measuring

A device for fast and reliable burr height measurements had to be developed.

Requirements for such a measuring device, a short overview about existing

methods and the final design are discussed in this chapter.

3.3.2.1 Definition of the burr height

Cross sections of the cutting edge show that the burrs may be either sharp-edged

or rounded. Due to different material properties the part may remain flat or

becomes domed during the blanking process. For that reason, the burr height is

defined as the difference between the highest point of the burr and the surface of the part

immediately adjacent to the burr.

tc

hb

se

cross section

with:

s material thickness

se edge draw-in/rollover

ss shear zone

sr rupture zone

hb burr height

tc penetration depth

% rollover = sse

% shear = sss

sr

ss s

Page 32: Influence of High Cutting Speeds

24

3.3.2.2 Requirements and design of the device

In order to measure the burr height in a precise and repeatable way, a new

device had to be developed. Since the burr is very small and soft, it is very

important that the burr is not damaged by the device while measuring. High

accuracy of the measurement tool guarantees repeatable results.

A literature review showed that there have been basically 3 different principles

of measuring the burr height:

• A device based on the principle of a caliper /26/,

• measuring the surface profile of the skeleton /22/,

• optical solutions /27/.

The advantages and disadvantages of these principles have already been

discussed in a previous report /28/. A technique based on the "caliper-method"

was chosen.

Figure 13: Burr height measurement device

1 2

1 micrometer head

2 reference tip

Page 33: Influence of High Cutting Speeds

25

Figure 13 shows a picture of the designed burr height measurement device,

which works as follows (Figure 14):

The head has to be moved down until the slug is clamped by the reference pin.

The pin clamps the part 0.1 mm (ca. 0.0039 in) beside the burr. After that, the

user turns the micrometer dial until the tip of the micrometer touches the burr.

The height of the burr can be read from the micrometer dial. The metal tip of the

micrometer and the plane table (with the part) are electrically isolated from each

other. A device which senses conductivity is connected across the micrometer

head and the table. As soon as the tip of the micrometer touches the burr, the

instrument indicates that the electrical circuit is closed. The main advantage of

this principle is a very small load on the burr during the measurement.

Figure 14: Method of working of the burr height measuring device

0.0039 in

reference pin

tip of micrometer

head

slug

flat surface

Page 34: Influence of High Cutting Speeds

26

Calibration of the device:

The device is calibrated by putting the reference pin directly on the plane table.

The micrometer is then lowered until it touches the table. The calibration value,

which has to be deducted from the measured burr height, is the value read on

the scale of the micrometer.

This device reduces the load on the burr to a minimum and has a resolution of

approximately 0.0003 inches. In contrast to other solutions, the device can also be

used to measure the skeleton.

Page 35: Influence of High Cutting Speeds

27

4. Experimental Procedure

Different experiments have been conducted in order to achieve the following

objectives:

1. Investigating the performance characteristics of the press.

2. Investigations of characteristics of the punch velocity during one stroke

(velocity investigations).

3. Determining the influence of high punch velocities in conjunction with

different punch-die clearances on the part edge quality depending on

different materials (part quality investigations).

Before performing any experiments with the press, preliminary work had to be

completed:

• Four different stock materials had to be chosen (chapter 3.2.2).

• The tooling had to be selected. Chapter 3.2.1 contains more detailed

information on the punches and dies. With the chosen punches and dies it is

possible to conduct experiments in a clearance range from 4% up to 24%.

• Punch-die alignment. The retainers had to be adjusted precisely.

In order to obtain repeatable results, the following points had to be taken into

account:

• Once the retainers were adjusted well, the adjustment was kept for all the

experiments. Only the punches and die buttons had to be changed for the

experiments with different punch-die clearances.

• During each measurement both channels (displacement and velocity) were

monitored continously through the stroke with a maximum sampling rate of

10,000 samples per second. This sampling rate was necessary so as not to lose

small signal peaks.

• All the experiments were conducted with sharp punches and die buttons.

Page 36: Influence of High Cutting Speeds

28

4.1 Investigation of press characteristics

First of all it is important to know in which velocity range the press is

performing. Therefore experiments using different power levels of the press have

been conducted under no cutting condition. The displacement as well as the

velocity of the punch have been monitored by means of a proximity sensor

(chapter 3.2.3.1) and a velocity transducer (chapter 3.2.3.2). Thus, a displacement-

time- and velocity-time-curve could be obtained (Figure 15). In addition, a

velocity-stroke-curve could be obtained by combining the information of these

two curves (Figure 16).

-9

-6

-3

0

3

6

9

12

0 0.005 0.01 0.015 0.02 0.025

time [sec]

punc

h ve

loci

ty [f

t\sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stop blocks

BDC

Figure 15: Velocity/displacement-time curve for no cutting condition at power level 5 of

the press

These first experiments under no cutting condition gave a rough idea, which

punch velocity could theoretically be reached at the 9 power levels of the press.

In addition, several influences on the performance of the press (like the

Page 37: Influence of High Cutting Speeds

29

adjustment of the return springs or the stroke length) have been examined. For

determining the minimum and maximum cutting velocity the different materials

were blanked. For each material five measurements were made, then the average

value was taken.

4.2 Velocity investigations

The main goal of these investigations was to obtain characteristic displacement-

time, velocity-time and the resulting velocity-stroke curves, as shown in Figure

16. The two curves in respect to the time (Figure 15) are important for roughly

calculating the cutting force (chapter 5.2) later on. They are also used to show

when blanking starts, when blanking is completed and when the polymer stop

blocks are reached.

0

2

4

6

8

10

-1 -0.5 0 0.5displacement [in]

punc

h ve

loci

ty [f

t/sec

]

stop blocks

Figure 16: Velocity-stroke curve for no cutting condition. Power level 5.

Page 38: Influence of High Cutting Speeds

30

In order to check the accuracy of the velocity transducer a monitored

displacement-time-curve was derived at particular points and the results were

compared. The measured and calculated velocity were corresponding with a

variation of ± 5%.

4.3 Part quality investigations

The following four characteristic values for evaluating the part edge quality were

measured and are shown in 4 different graphs for each material (chapter 5.3):

• burr height (measured with the burr height measurement device, chapter

3.3.2),

• % shear (expressed as a percentage of the material thickness, measured by

using the side view, that can be seen under a microscope),

• % rollover (expressed as a percentage of the material thickness, measured at

the cross-sections of the parts which were mounted in epoxy),

• % penetration (expressed as a percentage of the material thickness, measured

at the cross-sections of the parts which were mounted in epoxy),

The values mentioned above are shown on the y-axis whereas the x-axis shows

the punch-die clearance. Separate curves are shown for different cutting

velocities.

Before conducting the experiments to get the actual graphs that are shown in

chapter 5.3, preliminary experiments (using 3 different cutting speeds, 2 different

clearances and 6 different materials) have been conducted in order to find out

which materials, cutting speeds and clearances are the most promising to

investigate further.

Page 39: Influence of High Cutting Speeds

31

5. Experimental Results

5.1 Press characteristics and preliminary results

Figure 17 shows the highest cutting speed that could be reached for the different

stock materials. It can be seen that there is almost no influence of the clearance on

the cutting speed. The shown values represent the average of five measurements.

For each of the four materials the highest cutting speed is approximately 12

ft/sec.

10

10.5

11

11.5

12

12.5

0 5 10 15 20 25clearance[%]

cutti

ng s

peed

[ft/s

ec]

low carbon steelAl 2008110 Copperhigh strength steel

Figure 17:Maximum cutting speed for different punch-die clearances and stock materials

The following table shows the average value of the cutting speed that could be

reached at different power levels for each material. The measurements were

made with ideal stroke length.

Page 40: Influence of High Cutting Speeds

32

materials

low carbon

steel

high strength

steel

aluminum copper

power level 2 4.5 ft/sec 6 ft/sec (PL 3) 4.5 ft/sec 3 ft/sec

power level 5 9 ft/sec 8.5 ft/sec 9 ft/sec 9 ft/sec

power level 9 12 ft/sec 12 ft/sec 12 ft/sec 12 ft/sec

Table 6: Cutting speeds at different power levels of the press for different materials

The lowest cutting speed that could be reached with this press is about 4 ft/sec.

This is already regarded as high speed. In order to obtain curves at low cutting

speeds, additional experiments were conducted manually. This means that the

tooled plate of the press was moved down by means of an extension arm,

resulting in approximately 0.5 ft/sec.

As mentioned in chapter 4, the punch-die alignment was a very important issue

before conducting the experiments. The retainers for the punch and for the die-

button had to be adjusted in order to minimize wear on these tools and to

achieve a uniform part edge around the circumference. The retainer adjustment

was then checked by punching low carbon steel (14 % clearance, punch velocity:

4 ft/sec) and measuring the burr height and percentage of shear at four different

locations around the circumference of the slug. The results of these experiments

are shown in Figure 18. The burr height varied within a range of 3/10,000 of an

inch, the percentage of shear within a range of 5 %. Both values are regarded as

acceptable.

Page 41: Influence of High Cutting Speeds

33

0

0.0005

0.001

0.0015

0.002

0.0025

1 2 3 4

locations around the part

burr

hei

ght (

in)

0

10

20

30

40

50

% s

hear

burr height% shear

1

2

3

4

slug feeding direction

Figure 18: Uniformity of part edge (low carbon steel, 14% clearance, 4 ft/sec)

5.2 Velocity investigations

Since the velocity-time, displacement-time and velocity-stroke curves look

similar for the different materials, only the curves for low carbon steel are shown

and discussed in this chapter. The according graphs for the other stock materials

can be found in appendix C.

Page 42: Influence of High Cutting Speeds

34

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

time [sec]

punc

h ve

loci

ty [f

t\sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stripper

start blanking

blanking completed

Figure 19: Velocity/displacement-time curve. Material: low carbon steel. Power level 3,

stroke length 0.5"

Figure 19 and Figure 20 show the velocity and displacement of the punch versus

time for low carbon steel. The following points could be observed:

• The polymer stripper touches the material.

• The punch hits the sheet and blanking starts. This also causes vibrations due

to which the curve is oscillating afterwards.

• Blanking is completed, the punch "enters" the die button.

• The polymer stop blocks are reached. They are compressed and absorb the

remaining energy.

The bottom dead center (BDC) is reached. The moving direction of the punch is

inverted which results in zero velocity.

Page 43: Influence of High Cutting Speeds

35

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

time [sec]

punc

h ve

loci

ty [f

t\sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stripper

start blanking

blanking completed

BDC

stop blocks

Figure 20: Velocity/displacement-time curve. Material: low carbon steel. Power level 9,

stroke length 1.5"

Until blanking starts the punch velocity is constantly increasing. Compressing

the urethane stripper does not result in a velocity decrease. However , if the

maximum velocity is only 4 ft/sec, the blanking force is high enough to result in

a velocity decrease. As soon as the material fractures the velocity curve starts

oscillating due to the energy release of all structural components of the press

(also known as "snap-through" effect).

The following graphs show the punch velocity over the stroke. These curves

were used for calculating the forces that are shown in Table 7. Whereas Figure 21

shows a velocity decrease, Figure 22 shows an almost constant velocity during

blanking.

Page 44: Influence of High Cutting Speeds

36

0

1

2

3

4

5

6

-0.05 -0.025 0 0.025 0.05displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vst vm

vd

Figure 21: Punch velocity versus displacement. Material: low carbon steel. Power

level 3, stroke length 0.5"

In Figure 21 and Figure 22 the following abbreviations are used:

vSt = punch velocity when the stripper touches the material.

vm = punch touches the material (blanking starts).

vd = blanking completed.

vs = polymer stop blocks are reached.

Page 45: Influence of High Cutting Speeds

37

0

2

4

6

8

10

12

14

-0.05 0 0.05 0.1 0.15 0.2displacement [in]

punc

h ve

loci

ty [f

t\sec

] vmvst vd

vs

Figure 22: Punch velocity versus displacement. Material: low carbon steel. Power

level 9, stroke length 1.5"

The cutting force when blanking with low strain rates and cutting velocities can

be calculated by using the shear resistance of the blanked material and the tool

geometries /4/, /29/. A table including the shear resistance of the different

materials is shown in the appendix A.

F d tc s= ⋅ ⋅ ⋅π σ ( 3 ) with:

Fc = blanking force

σs = shear resistance

d = disk diameter

t = sheet thickness

Page 46: Influence of High Cutting Speeds

38

On the other hand, it is possible to calculate approximately the blanking force by

using the change of speed during the cutting operation. The force is calculated by

using the following equation:

F m a m dvdt

= ⋅ = ⋅ ( 4 ) with:

F = cutting force

a = acceleration

m = weight of the moving mass

If the time range of the deceleration is very short, the equation can be simplified

to:

F m vt

m v vt t

= ⋅ = ⋅−−

∆∆

1 2

1 2

( 5 )

The following table shows cutting forces calculated with the two different

equations described above for the four stock materials:

material thickness

[ in ]

cutting force, calculated

with equation (5) at

4 ft/sec

cutting force, calculated

according to equation (3)

low carbon steel 0.032 10.7 kN 334 kN/in 8.1 kN 253 kN/in

high strength steel 0.054 30.1 kN 557 kN/in 17.5 kN 324 kN/in

Al 2008 0.041 5.1 kN 124 kN/in 5.0 kN 122 kN/in

110 Copper 0.016 1.8 111 kN/in 3.2 kN 290 kN/in

Table 7: Cutting force for different materials

Page 47: Influence of High Cutting Speeds

39

In order to compare the forces of the different material thickness' which were

blanked, the actual forces have been divided by the material thickness.

A comparison of the numbers shown in Table 7 shows that there is no reliable

accordance between the forces calculated in different ways. Therefore, it is not

advisable to calculate the force derived from a measured velocity. If one wants to

know the cutting force, the experimental setup should be equipped with a force

measurement device.

In addition to the force, the required energy for blanking was investigated. There

are two different ways to approach this problem. Since the cutting force

calculated with equation (3) and the entry depth of the punch before fracturing

begins are known, it is possible to calculate the energy as follows:

E F lc c f= ⋅ ( 6 ) with:

Fc=cutting force

lf=entry depth until fracture

The entry depth before fracturing begins is approximately the experimentally

observed length of the shear zone (see also % shear curves). On the other hand,

the cutting velocity and the energy used for blanking are related through the

following equation:

E mv=12

2 ( 7 ) with:

E = energy [J]

m = weight of the moving mass [kg]

v = velocity of the moving mass [m/s]

Page 48: Influence of High Cutting Speeds

40

Since the two distinct points, start of blanking and blanking completed, are

known, the cutting energy can be calculated as the energy difference between

these two points:

E E E m v vc = − = −1 2 12

221

2( ) ( 8 )

The weight of the tooled plate of the press is 40 lbs. This leads to the following

calculation for the two curves shown:

Ec represents the energy used for blanking with a speed of 4 ft/sec (using

equation (8)):

E ft lb ft Jc 4 150 6 32

2sec sec.

= ≈

In contrast to this equation, it is not possible to calculate the energy needed for

blanking with 12 ft/sec. The velocity is staying almost constant during the

blanking operation, Figure 22. This means that the energy required for cutting is

very small compared to the available energy of the moving mass (compare with

Table 8).

Energy available for cutting at 4 ft/sec in [ J ]: 14

Energy available for cutting at 12 ft/sec in [ J ]: 121

Energy used for cutting (at 4 ft/sec) in [ J ]: 6

Table 8: Energy level at different cutting speeds

Page 49: Influence of High Cutting Speeds

41

material thickness

[ in ]

entry

depth until

fracture

[in]

cutting

velocity

[ ft/sec ]

cutting

energy

according to

(6) in [ J ]

cutting

energy

according to

(8) in [ J ]

low carbon steel 0.032 0.0128 4 2.64 6.3

high strength steel 0.054 0.0162 5 7.21 19.5

Al 2008 0.041 0.0144 4 1.82 8.2

110 Copper 0.016 0.0112 2.5 0.92 1

Table 9: Cutting energy for the stock materials

Table 9 shows approximate energy numbers for cutting the four different stock

materials. It shows that the thinner and softer materials require less energy for

cutting. But also in this case it could be observed that the energy derived from

the cutting velocity does not correlate very well with the calculated numbers.

This shows that the fastest and most reliable way to get information about

blanking force and energy is by implementing a load sensor in the experimental

setup. This will be done in the next phase of the project.

5.3 Part quality investigations

It should be mentioned that the discussion of the results is divided based on the

blanked materials. The part edge quality is evaluated for the different parameter

settings and the four stock materials (see also appendix A). After drawing

conclusions regarding the process conditions for each material, the results of the

different materials are compared.

Page 50: Influence of High Cutting Speeds

42

5.3.1 Experiments with low carbon steel

The results of the experiments conducted with low carbon steel are shown in the

next four graphs. In addition, seven cross-sections and side views are shown.

0

1

2

3

4

5

6

0 5 10 15 20 25punch-die clearance [%]

burr

hei

ght [

0.00

1 in

]

12 ft/sec9 ft/sec4 ft/sec0.5 ft/sec

Figure 23: Burr height versus punch-die clearance (low carbon steel)

Figure 23 shows the burr height versus the punch-die clearance for different

cutting speeds. The following characteristics were observed:

• The burr of the slugs blanked with 0.5 ft/sec is constantly increasing with an

increasing clearance. Table 10, pictures 1, 7 and 11 confirm that.

• For velocities above 4 ft/sec the burr height is almost constant at 0.0013" up to

14 % clearance. Increasing the clearance further results in a linear burr height

growth.

• When blanking with low cutting speeds of 0.5 ft/sec and a small clearance the

burr is about 0.0035", which is about three times as much as when blanking

with high speed.

Page 51: Influence of High Cutting Speeds

43

This graph shows that in the commonly used clearance range between 5 and 10%

the burr height is less than half as large when blanking at cutting speeds above 4

ft/sec compared to low speed blanking.

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

12 ft/sec9 ft/sec4 ft/sec0.5 ft/sec

Figure 24: % shear versus punch-die clearance (low carbon steel)

Figure 24 shows the influence of the cutting speed on the formation of the shear

zone. The following characteristics were observed:

• Increasing the cutting speed above 4 ft/sec has no influence on the amount of

shear.

• The punch-die clearance has a major influence on the percentage of shear. For

all cutting speeds there is a large difference in the percentage of shear

between 4% clearance and 14 % (compare Table 10, Table 11: pictures 2 and 8

or pictures 6 and 10). Increasing the clearance further has only a minor

influence on the amount of shear.

Page 52: Influence of High Cutting Speeds

44

• The influence of high velocities on the percentage of shear is not as distinct as

the clearance influence. However, the percentage of shear is about 5-20 %

higher for parts blanked with high speeds compared to parts blanked with

low speeds (see also Table 11, pictures 8 and 10).

Although there is an increase in the percentage of shear when using high speeds,

it is not enough to compensate the decrease of % shear which is caused by an

increasing clearance. This means that for getting a part edge of 75% shear, one

still has to go with a relatively small clearance of about 5 to 8%.

The next graph (Figure 25) shows the % rollover in respect to the punch-die

clearance for cutting speeds of 0.5 ft/sec (low speed) and 12 ft/sec (high speed).

The following characteristics can be seen:

• Up to 15% clearance, the % rollover of the slugs is constantly increasing for all

cutting velocities (see Table 10, Table 11: picture 1 and 7 and pictures 5 and 9).

For a further clearance increase the rollover stays constant.

• At a clearance of 15%, the % rollover is about 3 times as big as at 4%

clearance.

• Using high cutting speeds results in a decrease of % rollover (compare Table

10: pictures 1, 3 and 5). For 4 % clearance, the % rollover is more than twice as

big at low speeds than at high speeds.

Page 53: Influence of High Cutting Speeds

45

0

5

10

15

20

25

30

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

0.5 ft/sec12 ft/sec

Figure 25: % rollover versus punch-die clearance (low carbon steel)

It is obvious that the selected clearance has the main influences on the plastic

deformation of the part which results in the rollover zone. However, for a given

clearance the % rollover can be always reduced by blanking with high speeds.

Figure 26 shows the % penetration in respect to the punch-die clearance for high

and low cutting speeds:

• For both velocities the curves show a constant increase of % penetration with

an increasing punch-die clearance (Table 10, Table 11, Table 12: pictures 5, 9

and 13).

• High cutting speeds result in less penetration depth, whatever clearance is

selected (Table 10: pictures 1, 3, 5). At small clearances, around 4% to 50%

reduction could be seen.

Page 54: Influence of High Cutting Speeds

46

Since the edge of the slugs should be as straight as possible for most applications,

it is important that the penetration depth is as small as possible. With a low

cutting speed it is not possible to produce parts with a % penetration smaller

than 8%, even if the clearance is very small. By using high cutting speeds,

however, it is possible to reach a % penetration as low as 4% (Table 10, picture 5).

0

5

10

15

20

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

0.5 ft/sec

12 ft/sec

Figure 26: % penetration versus punch-die clearance (low carbon steel)

Page 55: Influence of High Cutting Speeds

47

Cross-section side view

Clearance: 4 %.

Characteristic part

edge for 0.5 ft/sec

punch velocity.

Clearance: 3%.

Characteristic part

edge for 4 ft/sec

and 9 ft/sec punch

velocities.

Clearance: 3 %.

Characteristic part

edge for 12 ft/sec

punch velocity

Table 10: Cross section and side view for low carbon steel. Clearance: 3/4%.

1 2

3 4

5 6

Page 56: Influence of High Cutting Speeds

48

Cross-section side view

Clearance: 15 %

Characteristic

part edge for 0.5

ft/sec punch

velocity.

clearance: 14 %

Characteristic

part edge for 4

ft/sec, 9 ft/sec

and 12 ft/sec

punch velocites.

Table 11: Cross-section and side view for low carbon steel. Clearance: 15%.

7 8

9 10

Page 57: Influence of High Cutting Speeds

49

Cross-section side view

Clearance: 21 %

Characteristic

part edge for 0.5

ft/sec punch

velocity

clearance: 24 %

Characteristic

part edge for 4

ft/sec, 9 ft/sec

and 12 ft/sec

punch velocities.

Table 12: Cross-section and side view for low carbon steel. Clearance: 21/24%.

11 12

13 14

Page 58: Influence of High Cutting Speeds

50

5.3.2 Experiments with high strength steel

In this chapter the results of the experiments conducted with high strength steel

are discussed. In particular, the influences of clearance and cutting speed on the

formation of the different zones of the part edge are discussed.

0

1

2

3

4

5

6

7

0 5 10 15 20 25punch-die clearance [%]

burr

hei

ght [

0.00

1 in

]

12 ft/sec8.5 ft/sec6 ft/sec0.5 ft/sec

Figure 27: Burr height versus punch-die clearance (high strength steel)

Figure 27 shows the burr height versus the punch-die clearance for different

cutting speeds. The following characteristics were observed:

• The major changes in the burr height are taking place between 3% and 6%

clearance. The smallest burr is obtained at 6% clearance. A further increase of

the clearance has only a minor effect on the formation of the burr.

• The cutting speed has an influence on the formation of the burr. The largest

burr height decrease is seen between 0.5 and 6 ft/sec cutting speed.

Increasing the cutting speed further than 8.5 ft/sec does not give any

improvement concerning the burr.

Page 59: Influence of High Cutting Speeds

51

The previous graph shows that at the commonly used clearance of 6% the burr

height is reduced by 70% when blanking at high speeds.

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

12 ft/sec8.5 ft/sec6 ft/sec0.5 ft/sec

Figure 28: % shear versus punch-die clearance (high strength steel)

The effect of the punch-die clearance and the cutting speed on the % shear is

shown in Figure 28:

• Increasing the cutting speed above 6 ft/sec has no remarkable effect on the

amount of shear (see also Table 14: pictures 8 and 10).

• There is a large influence of the punch-die clearance on the % shear when

using clearances smaller than 14%. Larger clearances have only a minor

influence on the amount of shear (compare Table 13: picture 4 and Table 14:

picture 10).

• An increase of the percentage of shear when using higher cutting speeds can

only be noted at clearances smaller than 14%.

Page 60: Influence of High Cutting Speeds

52

0

10

20

30

40

50

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

0.5 ft/sec12 ft/sec

Figure 29: % rollover versus punch-die clearance (high strength steel)

Figure 29 shows the % rollover in dependance of the punch-die clearance and the

cutting speed. The following characteristics were observed:

• In general, the % rollover of the slugs is linearly increasing with increasing

clearance for all cutting speeds (see also Table 13: pictures 1, 7 and 11).

• For small clearances the % rollover can be reduced by 50% when blanking

with high speeds (compare Table 13: pictures 1 and 3).

• For getting less than 10% rollover one has to blank with high speeds and

small clearances.

The next graph shows the % penetration in respect to the punch-die clearance for

cutting speeds of 0.5 ft/sec and 12 ft/sec. The following characteristics can be

seen:

Page 61: Influence of High Cutting Speeds

53

• Independent of the cutting speed, the % penetration is constantly increasing

with an increasing punch-die clearance (compare Table 13: pictures 1, 7 and

11).

• High cutting speeds result in less penetration. To get a straight part edge with

less than 10% penetration one has to go with high speeds and small

clearances (see also Table 13: pictures 1 and 3).

0

5

10

15

20

25

30

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

0.5 ft/sec

12 ft/sec

Figure 30: % penetration versus punch-die clearance (high strength steel)

Page 62: Influence of High Cutting Speeds

54

Cross-section side view

Clearance: 4 %.

Characteristic part

edge for 0.5 ft/sec

punch velocity.

Clearance: 3%.

Characteristic part

edge for 6 ft/sec,

8.5 ft/sec and 12

ft/sec punch

velocities.

Clearance: 3 %

Characteristic part

edge for 12 ft/sec

punch velocity.

Ca. 100% shear!

Table 13: Cross-section and side view for high strength steel. Clearance: 3%.

1 2

3 4

5 6

Page 63: Influence of High Cutting Speeds

55

Cross-section side view

Clearance: 14 %

Characteristic

part edge for 0.5

ft/sec and 6

ft/sec punch

velocity.

clearance: 14 %

Characteristic

part edge for 8.5

ft/sec and 12

ft/sec punch

velocities.

Table 14: Cross-section and side view for high strength steel. Clearance: 14%.

7 8

9 10

Page 64: Influence of High Cutting Speeds

56

Cross-section side view

Clearance: 20 %

Characteristic

part edge for 0.5

ft/sec punch

velocity

clearance: 24 %

Characteristic

part edge for 6

ft/sec, 8.5 ft/sec

and 12 ft/sec

punch velocities.

Table 15: Cross-section and side view for high strength steel. Clearance: 20/24%.

11 12

13 14

Page 65: Influence of High Cutting Speeds

57

5.3.3 Experiments with aluminum

The results of the experiments conducted with aluminum are shown in the next

four graphs. As in the previous chapters, cross-sections and side views are

discussed as well.

Figure 31 shows the burr height versus the punch-die clearance for different

cutting velocities. The following characteristics were observed:

• The major influence on the formation of the burr is the punch-die clearance.

High speed has no effect on the formation of the burr.

• For all cutting speeds there is an optimum clearance of about 7%, where the

burr is smallest.

• For clearances smaller or bigger than 7% the burr is constantly increasing

regardless of the cutting speed.

0

0.5

1

1.5

0 5 10 15 20 25punch-die-clearance [%]

burr

hei

ght [

0.00

1 in

]

12 ft/sec9 ft/sec4 ft/sec0.5 ft/sec

Figure 31: Burr height versus punch-die clearance (aluminum)

Page 66: Influence of High Cutting Speeds

58

The next figure shows the percentage of shear versus the punch-die clearance.

The following characteristics can be seen:

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

12 ft/sec9 ft/sec4 ft/sec0.5 ft/sec

Figure 32: % shear versus punch-die clearance (aluminum)

• The bigger the punch-die clearance gets, the less % shear occurs. The

percentage of shear doubles by decreasing the clearance from 21% to 5% (see

also Table 16, Table 17, Table 18: pictures 2, 6 and 10).

• The cutting speed has almost no influence on the percentage of shear

(compare Table 10: pictures 2 and 4).

Page 67: Influence of High Cutting Speeds

59

0

10

20

30

40

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

0.5 ft/sec12 ft/sec

Figure 33: % rollover versus punch-die clearance (aluminum)

Figure 33 shows the % rollover versus the punch-die clearance for high and low

speed. It could be observed that:

• Up to clearances of 15% neither the clearance nor the cutting speed is

influencing the % rollover (see also Table 16, Table 17: pictures 1, 3, 5 and 7).

• Only at clearances around 20% can the plastic deformation be decreased by

choosing high cutting speed.

The next figure shows the influence of the punch-die clearance and the cutting

speed on the % penetration. The following characteristics can be seen:

• Since the material fractures earlier when blanking with large clearances also

more penetration is observed.

• Like with the rollover, high cutting speeds show the biggest improvement in

combination with large clearances (Table 18: pictures 9 and 11).

Page 68: Influence of High Cutting Speeds

60

0

5

10

15

20

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

0.5 ft/sec

12 ft/sec

Figure 34: % penetration versus punch-die clearance (aluminum)

Page 69: Influence of High Cutting Speeds

61

Cross-section side view

Clearance: 5 %.

Characteristic part

edge for 0.5 ft/sec

punch velocity.

Clearance: 5%.

Characteristic part

edge for 4 ft/sec,

9 ft/sec and 12

ft/sec punch

velocities.

Table 16: Cross-section and side view for aluminum. Clearance: 5%.

1 2

3 4

Page 70: Influence of High Cutting Speeds

62

Cross-section side view

Clearance: 15 %

Characteristic

part edge for 0.5

ft/sec punch

velocity.

clearance: 15 %

Characteristic

part edge for 4

ft/sec, 9 ft/sec

and 12 ft/sec

punch velocities.

Table 17: Cross-section and side view for aluminum. Clearance: 15%.

7 6

7 8

5

Page 71: Influence of High Cutting Speeds

63

Cross-section side view

Clearance: 21 %

Characteristic

part edge for 0.5

ft/sec punch

velocity

clearance: 21 %

Characteristic

part edge for 4

ft/sec, 9 ft/sec

and 12 ft/sec

punch velocities.

Table 18: Cross-section and side view for aluminum. Clearance: 21%.

9 10

11 12

Page 72: Influence of High Cutting Speeds

64

5.3.4 Experiments with copper

The softest material used in the experiments was copper. It also has the highest

heat conduction coefficient in comparison to the other investigated materials.

The results of the experiments conducted with copper are shown in the following

graphs, side views and cross-sections.

There is no graph showing the burr height versus the punch-die clearance,

because the burrs of the blanked parts were too small to be measured with the

measurement device described in chapter 3.3.2.2. Since the resolution of that

device is 0.0003", it can be noted that the burr of the copper slugs (no matter

which clearance or cutting velocity) was always less than 0.0003".

In comparison to the other materials, the copper slugs were domed. This made

the mounting in epoxy as well as all other measurements more complicated, and

is also the reason for the inclined shear zone (see part cross sections).

Figure 35 shows the percentage of shear versus the punch-die clearance. The

following characteristics were observed:

• Increasing the punch-die clearance results in a decrease of % shear. Between 6

and 19 % clearance this decrease is as much as 25% (see also Table 19 and

Table 21: pictures 4 and 12).

• Increasing the cutting speed up to 12 ft/sec results in an increase of %shear of

approximately 15% (Table 19: pictures 2 and 4).

Page 73: Influence of High Cutting Speeds

65

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

12 ft/sec9 ft/sec4 ft/sec0.5 ft/sec

Figure 35: % shear versus punch-die clearance (copper)

The influence of the cutting speed and the punch-die clearance on the % rollover

is shown in the next figure. In particular, it can be observed that

• the clearance has the main effect on the % rollover. Like with most other

materials, the larger the clearance the larger the % rollover (compare Table 19

and Table 21: pictures 3 and 11).

• Also, with this material it was observed that the high cutting speeds only

show improvement when combined with large clearances.

Page 74: Influence of High Cutting Speeds

66

0

10

20

30

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

0.5 ft/sec12 ft/sec

Figure 36: % rollover versus punch-die clearance (copper)

Figure 37 shows the % penetration versus the punch-die clearance depending on

the cutting speed. The following characteristics can be observed:

• There is no obvious influence of high cutting speeds on the formation of the

% penetration.

• The penetration of the material fracture is only influenced by the clearance up

to 13%.

Page 75: Influence of High Cutting Speeds

67

0

5

10

15

20

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

0.5 ft/sec

12 ft/sec

Figure 37: % penetration versus punch-die clearance (copper)

Page 76: Influence of High Cutting Speeds

68

Cross-section side view

Clearance: 6 %.

Characteristic part

edge for 0.5 ft/sec

punch velocity.

Clearance: 6%.

Characteristic part

edge for 4 ft/sec,

9 ft/sec and 12

ft/sec punch

velocities.

Table 19: Cross-section and side view for copper. Clearance: 6%.

1 2

3 4

Page 77: Influence of High Cutting Speeds

69

Cross-section side view

Clearance: 13 %

Characteristic

part edge for 0.5

ft/sec punch

velocity.

clearance: 13 %

Characteristic

part edge for 12

ft/sec punch

velocity.

Table 20: Cross-section and side view for copper. Clearance: 13%.

7 6

7 8

5

Page 78: Influence of High Cutting Speeds

70

Cross-section side view

Clearance: 19 %

Characteristic

part edge for 0.5

ft/sec punch

velocity

clearance: 19 %

Characteristic

part edge for 4

ft/sec, 9 ft/sec

and 12 ft/sec

punch velocities.

Table 21: Cross-section and side view for copper. Clearance: 19%.

9 10

11 12

Page 79: Influence of High Cutting Speeds

71

5.3.5 Material comparison

After discussing the influence of different parameters on the formation of the

part edge for every material, the different materials will be compared between

each other in this chapter.

0

1

2

3

4

0 5 10 15 20 25punch-die clearance [%]

burr

hei

ght [

0.00

1 in

]

low carbon steelhigh strength steelAl 2008Copper 110

Figure 38: Burr height versus punch-die clearance, 0.5 ft/sec

0

1

2

3

4

0 5 10 15 20 25punch-die clearance [%]

burr

hei

ght [

0.00

1 in

]

low carbon steelhigh strength steelAl 2008Copper 110

Figure 39: Burr height versus punch-die clearance, 12 ft/sec

Page 80: Influence of High Cutting Speeds

72

Figure 38 and Figure 39 show the burr height versus the punch-die clearance for

low and high cutting speeds. The following conclusions could be drawn:

• At low cutting speeds, low carbon steel shows by far the highest burr.

• For copper, aluminum, and high strength steel the punch-die clearance has

the main influence on the formation of the burr. Only for low carbon steel is

the burr height decreased when blanking with high speeds.

• The two softest materials used in the experiments, copper and aluminum,

show the smallest burr, regardless of speed.

Another important value for the quality of the blanked part is the percentage of

shear, Figure 40 and Figure 41. The following characteristics were observed:

• For all materials the major influence on the percentage of shear is the

clearance.

• The only material which shows a shear zone increase due to high cutting

velocities is copper. When blanking with small clearances and high speeds a

shear zone of up to 95% could be reached.

• Regardless of speed, low carbon steel can be made to fracture after 80% of

shearing only when blanking with small clearances.

Page 81: Influence of High Cutting Speeds

73

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

low carbon steelhigh strength steelAl 2008Copper 110

Figure 40: % shear versus punch-die clearance, 0.5 ft/sec

0

20

40

60

80

100

0 5 10 15 20 25punch-die clearance [%]

% s

hear

low carbon steelhigh strength steelAl 2008Copper 110

Figure 41: % shear versus punch-die clearance, 12 ft/sec

Page 82: Influence of High Cutting Speeds

74

The next two figures show the percentage of rollover versus the punch-die

clearance for low and high cutting speeds, Figure 42 and Figure 43. The

following characteristics can be seen:

• In the commonly used clearance range of between 5 and 15%, there is an

obvious decrease of the % rollover by increasing the cutting velocity only for

high strength steel. The other materials show no velocity influence.

• When blanking low carbon steel with small clearances (< 5%) and high

cutting velocities, the plastic deformation could be decreased.

• The influence of high cutting speeds is more distinct when blanking with

more than 15% clearance.

Figure 44 and Figure 45 show the percentage of penetration versus the punch-die

clearance. It could be observed that:

• High strength steel shows the highest percentage of penetration.

• As expected, for all materials the % penetration is increasing with an

increasing punch-die clearance. That means that the clearance has a major

influence on the % penetration.

• For aluminum and high strength steel, increasing the cutting speed results in

a decrease of % penetration for all clearances.

• For low carbon steel and copper, a higher cutting speed results in less %

penetration for clearances smaller than 6%.

Page 83: Influence of High Cutting Speeds

75

0

10

20

30

40

50

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

low carbon steelhigh strength steelAl 2008Copper 110

Figure 42: % rollover versus punch-die clearance, 0.5 ft/sec

0

10

20

30

40

50

0 5 10 15 20 25punch-die clearance [%]

% ro

llove

r

low carbon steelhigh strength steelAl 2008Copper 110

Figure 43: % rollover versus punch-die clearance, 12 ft/sec

Page 84: Influence of High Cutting Speeds

76

0

5

10

15

20

25

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

low carbon steelhigh strength steelAl 2008Copper 110

Figure 44: % penetration versus punch-die clearance, 0.5 ft/sec

0

5

10

15

20

25

0 5 10 15 20 25punch-die clearance [%]

% p

enet

ratio

n

low carbon steelhigh strength steelAl 2008Copper 110

Figure 45: % penetration versus punch-die clearance, 12 ft/sec

Page 85: Influence of High Cutting Speeds

77

Overall, it can be noted that a positive influence of high cutting speeds on the

quality of the part edge is more obvious (especially concerning the burr height

and the percentage of rollover) for low carbon and high strength steels. Benefits

for aluminum and copper could be only observed for a few parameter

combinations. This agrees with the theory described in chapter 2.6: most of the

positive effects of high cutting speeds are temperature related. Copper and

aluminum have much higher heat conduction coefficients than steel. That means

that the heat produced by the increased cutting velocity is dissipating relatively

quick compared to steel. Thus, the benefits of high cutting speeds are not as large

for copper and aluminum as for steel. However, the punch-die clearance has the

major influence on the formation of the part edge, independent of which material

is blanked and which cutting speed is used.

Page 86: Influence of High Cutting Speeds

78

6. FEM simulations with DEFORM 2D

6.1 The Finite Element Code DEFORM 2D

For simulating the blanking process a modified version of the FEM-code

DEFORM 2D (Version 4.1.5) was used. DEFORM includes three parts:

• The pre-processor,

• the simulation engine and

• the post-processor.

These parts will be described in the following /30/.

6.1.1 Pre-processor

The pre-processor consists of:

• An input module for introducing the model geometry and the process

conditions,

• an automatic mesh generation program, which creates a mesh taking various

process parameters into consideration (die and workpiece geometry, strain,

strain-rate and temperature),

• an interpolation module for interpolating the deformation history of the old

distorted mesh into the newly generated mesh.

These three tasks, called automatic remeshing, make it possible to perform a

continous simulation without any intervention by the user, even if several

remeshing steps are required. The automatic remeshing capability reduces the

total calculation time of the FE analysis. All the data generated in the pre-

processor is saved in a data base.

6.1.2 Simulation engine

This program provides different choices in the analysis mode:

Page 87: Influence of High Cutting Speeds

79

• Isothermal, non-isothermal or heat transfer,

• rigid, plastic, elastic, elasto-plastic, porous object type.

As mentioned before, the simulation results are stored in a binary format and are

accessed by the post-processor.

6.1.3 Post-processor

The post-processor displays the simulation results in graphical or

alphanumerical form. The graphic presentation includes the mesh, contour plots

(line or continous tone in colors) of strain, strain rate, temperature, velocity

vectors and load-stroke curves. Two other important capabilities are 'point

tracking' (provides deformation histories of selected points in the workpiece

throughout the deformation) and 'flownet' (allows the user to observe the

deformation of the circles or rectangles defined on the underdeformed

workpiece).

6.2 Simulations of the high speed blanking process

6.2.1 Simulation settings

Four simulations have been performed for low carbon steel. The geometry of the

tooling was designed and meshed on CAEDS and then imported into DEFORM

2D via an universal file. The simulations were performed using standard units.

The input parameters of the different components of the simulation are shown in

the following tables:

Page 88: Influence of High Cutting Speeds

80

Component

Sheet Punch

Object type rigid-plastic rigid

Number of elements ~4500 ~200

Material properties AISI 1015 none

Temperature at beginning 68 F 68 F

Thermal conductivity [Btu/sec/in/F] 5.082 E-4 3.74 E-4

Heat capacity [Btu/in3/F] 0.03106 0.03106

Emissivity 0.25 0.45

Table 22: Input data of the low carbon steel sheet and the punch

Component

Die button Blank Holder

Object type rigid rigid

Number of elements ~230 ~40

Material properties none none

Temperature at beginning 68 F 68 F

Thermal conductivity [Btu/sec/in/F] 3.74 E-4 3.74 E-4

Heat capacity [Btu/in3/F] 0.03106 0.03106

Emissivity 0.45 0.45

Table 23: Input data of the die button and the blank holder

The simulations were performed with the following settings:

• Material: low carbon steel. Properties from AISI 1015 were taken, because

they are very close to the properties of the low carbon steel that was actually

used. The sheet thickness was 0.033".

Page 89: Influence of High Cutting Speeds

81

• Clearances: 5% and 18% (punch diameters: 0.488 in and 0.497 in; die button:

0.500 in),

• punch velocities: 0.5 and 12 ft/sec,

• non isothermal status,

• axisymmetric problem: though only one half of the geometry was simulated.

The inter object relationship was defined with a constant friction coefficient of

µ=0.05 for all contacts between tool and sheet. This value is typically used for

cold forming. The interface heat transfer coefficient was 0.3397 E-2

Btu/sec/in2/F.

Furthermore, the following restrictions apply:

• One has to be careful when interpreting the results of the simulations: high

speed blanking deals with high strains and high strain rates (ε ≈ 500% and

& /ε ≈ 10000 s ). Since there are only data for low strains (~70%) and low strain

rates (90/s) available, DEFORM extrapolates the values for higher strains and

strain rates. This is a very critical point concerning the simulation results,

because the accuracy of the simulation is influenced by the material flow-

stress curve.

• The non isothermal simulation mode was used. In this mode the program

was not able (softwarewise) to fracture the material. Therefore conclusions

can only be drawn about the plastic deformation at the beginning of blanking

resulting in rollover. This shows that we are still in the beginning stage of

simulating the high speed blanking process.

6.2.2 Simulation results

The pictures shown in the appendix D show results of the simulations for

different stages of the process. Each picture contains of three figures:

Page 90: Influence of High Cutting Speeds

82

• A load versus time curve,

• the workpiece, the die button and the punch,

• a magnification of the area where the actual shearing takes place.

Simulations with a punch-die clearance of 18%:

Figure D-1 through D-5 show the simulated shearing process for low speed (0.5

ft/sec). Two intermediate steps are shown in addition to step1 (starting position,

figure D-1) and step 102 (shearing completed, figure D-5). Like in the

experiments, only the slug (left part of the sheared sheet in the pictures) was of

interest. As mentioned earlier, in this stage of the simulation software, only the

formation of the rollover could be observed. For 18% clearance and low as well

as high speed it is around 20 %. That means the simulations do not show an

influence of the high speeds on the formation of the rollover.

Simulations with a punch-die clearance of 5%:

The same characteristics as with 18% clearance were also seen with a punch-die

clearance of 5%: Increasing the cutting speed does not result in a decrease of the

rollover.

According to the simulations, the punch-die clearance is the main influence on

the formation of the rollover.

6.2.3 Comparison of the experimental and simulated results

Experimental and simulated results exist only for low carbon steel at clearances

of 5 and 18% and for low and high cutting speeds. Table 24 shows the percentage

of rollover for the different cases.

Page 91: Influence of High Cutting Speeds

83

5% clearance 18% clearance

low speed high speed low speed high speed

experiment 12% 7% 26% 22%

simulation 12% 13% 21% 21%

Table 24: Comparison of the experimental and simulated results (low carbon steel)

Although the simulation results do not show the influence of high cutting speed,

the experimental and simulation results show a good correlation. Only for small

clearance and high speeds do the results not correlate.

It will be important in the future to be able to simulate the fracture as well and

accrue information about the burr height , % shear and penetration depth. These

values are necessary to predict the quality of the part edge by means of

simulations.

A more in depth comparison between simulations and experiments will be

possible as soon as the FEM program is able to handle high strains and strain

rates for the fracture simulation. This study will provide a large database for

fine-tuning the FEM simulation.

Page 92: Influence of High Cutting Speeds

84

7. Summary and conclusions

This report discusses the influences of several parameters on the part edge

quality of blanked parts. Different experiments as well as blanking simulations

have been conducted in order to investigate the characteristics of the velocity-

stroke curve and to determine the influence of high punch velocities in

conjunction with different punch-die clearances on the part edge quality. Four

different materials: low carbon steel, high strength steel, aluminum and copper

have been blanked with punch-die clearances between 4% and 24%. All the

experiments were conducted with a Lourdes impact press which reaches cutting

speeds of up to12 ft/sec.

The displacement-time, velocity-time, and velocity-stroke curves were monitored

by means of a velocity and proximity sensor. This setup provided the velocity

when blanking starts and the velocity decrease during blanking. It was shown

that a velocity decrease due to blanking is only measurable for low cutting

speeds of around 4 ft/sec. The kinetic energy at high speeds is much higher than

the energy required for blanking. That results in an almost constant punch speed

while blanking. Blanking force and energy were determined based on the

velocity changes measured at low cutting speeds. The numbers matched only in

part with the numbers calculated from the shear strength of the different

materials. If one wants to know the exact cutting force the experimental setup

should be equipped with a force measurement device.

When evaluating the part edge quality of the blanked parts, all the different

zones were taken into consideration (burr height, shear, rupture/penetration

depth, and rollover). The results of the part quality investigations show that the

positive influence of high cutting speeds on the quality of the part edge is more

obvious for low carbon and high strength steels. Benefits for aluminum and

Page 93: Influence of High Cutting Speeds

85

copper could only be observed for a few parameter combinations. This agrees

with the theory that most of the positive effects of high cutting speeds are

temperature related. Since copper and aluminum have much higher heat

conduction coefficients than steel, the heat generated by the increased cutting

velocity dissipates relatively fast. The temperatures in the shear band are not as

high as when blanking steel materials. Therefore, the benefits of high cutting

speeds are not as large for copper and aluminum as for steel. However, the

punch-die clearance has the major influence on the formation of the part edge,

regardless which material is blanked or which cutting speed is used.

Blanking simulations were performed for low carbon steel at different cutting

velocities and punch-die clearances. At the current stage of the development of

the simulation program, only the plastic deformation and shearing of the

material could be simulated. The experimental and simulation results show a

good correlation concerning the investigated zones of the part edge. However,

simulating small clearances when blanking with high velocities will need

additional investigations. For predicting the part quality by means of simulations

it will be necessary to simulate the whole process. Thus, a more in depth

comparison between simulations and experiments will be possible as soon as the

FEM program is able to handle high strains and strain rates for the fracture

simulation.

In the future it will be of particular interest to obtain more knowledge about the

effects of the high cutting velocities on tool wear. In conjunction, it will be

interesting to investigate the influence of lubricants and the running mode of the

press (either single or continous operation) on the tool wear. Also, it would be

desirable to obtain additional information about the high speed effects on the

part edge. Therefore, investigations concerning the microstructure of the part

edge as well as temperature measurements during blanking could be helpful. As

Page 94: Influence of High Cutting Speeds

86

shown in previous investigations, further part edge quality improvements can be

achieved by increasing the cutting speed to 40 ft/sec /1/.

Page 95: Influence of High Cutting Speeds

87

8. List of references

/1/ Svahn, O. Superfast blanking prevents defects

Pressworking

Industry Quaterly, Volume 8, No.4, 1993

/2/ Smith, D.A. Die Design Handbook,

Society of Manufacturing Engineers,

Dearborn, Michigan, 1990

/3/ Lascoe, O.D., Handbook of Fabrication Processes

ASM International, 1988

/4/ Lange, K. Blanking and Piercing

Handbook of Metal Forming

The McGraw-Hill Book Company, 1985

/5/ Smith, D. A. Fundamentals of Pressworking

Society of Manufacturing Engineers

Dearborn, Michigan, 1994

/6/ Schüssler, M. Hochgeschwindigkeitsscherschneiden im

geschlossenem Schnitt zur Verbesserung der

Teilequalität

Dissertation, University of Darmstadt, 1990

/7/ Breitling, J. Investigations of different loading conditions

Wallace, D. in a high speed mechanical press

Page 96: Influence of High Cutting Speeds

88

Journal of Materials Processing Technology,

Volume PRO 059/1-2, pp. 18-23

/8/ Dannenmann Umdruck zur Vorlesung Schneiden

University of Stuttgart, Germany, 1992

/9/ Lange, K. Umformtechnik

Band3: Blechbearbeitung

Berlin, Heidelberg, New York, 1990

/10/ Neumann, C.-P. Die Schneidbarkeit von Elektroblech und ihre

Prüfung unter besonderer Berücksichtigung von

Blechwerkstoff und Schneidspalt

Dissertation, University of Hannover, Germany, 1979

/11/ Schenk, H. Schneidspaltoptimierung fuer Elektrobleche

Prölss, E. Fertigung 4/77, Germany, 1977

/12/ Kühne, H.-J. Der Schneidvorgang selbst und die Stempel-

geometrie als Ursache für

Maßungenauigkeiten und Spannungen beim

Scherschneiden von Elektroblechen

Magazin Trennen Rohre Profile, 1991

/13/ Huml, P. Der Einfluß der hohen Geschwindigkeit auf das

Schneiden von Metallen

Institute of metal forming, Stockholm

Annals of the CIRP, Volume 23/1/1974

Page 97: Influence of High Cutting Speeds

89

/14/ Davies, R. Developments in High Speed Metalforming

Austin, E.R. The Machine Publishing Company Ltd

BN1 4 NH, Brighton, Sussex, 1970

/15/ Turkovich, B.F. On a class of Thermo-Mechanical Process during

rapid Plastic Deformation (with special reference to

metal cutting)

Annals of the CIRP, Volume 21/1/1972

/16/ Tobias, S.A. Hochgeschwindigkeitsumformen

Das Petro-Forge-Umformsysytem

Fertigung 1/1971

/17/ N.N. Brute Force vs. High Tool Speed

Bulletin, Lourdes Systems, Inc.

/18/ Jana, S. Effect of punch clearance in the High-Speed Blanking

Ong, N.S. of thick metals using an accelerator designed for a

mechanical press

Journal of Mechanical Working Technology

/19/ Beitz, W. Dubbel, Taschenbuch für den Maschinenbau

Küttner, K.-H. 17. Auflage, Springer Verlag, Heidelberg, 1990

/20/ Hippenstiel, H.-R. Elektrodynamische Hochgeschwindigkeitspresse

Röttger, R. Werkstatt und Betrieb, S. 683-687, Nr. 110, Germany

1977

Page 98: Influence of High Cutting Speeds

90

/21/ N.N. Operating Instructions for Lourdes Electro Activated

die sets overhead units

Lourdes Systems Inc.

/22/ Cammann, J. H. Untersuchungen zur Verschleißminderung an

Scherschneidwerkzeugen der Blechbearbeitung

durch Einsatz geeigneter Werkstoffe und

Beschichtungen, Dissertation

University of Darmstadt, Germany, 1986

/23/ N.N. Pivot Basic Series, catalog 1000,

Pivot Punch Corporation, New York 1993

/24/ N.N. Sensors catalog

Turck Inc., 1992

/25/ N.N. Linear velocity transducer, Series 100

Transtek Inc., Bulletin S012-0028

/26/ Borchert, P. Einflüsse der Werkzeuggeometrie und der Maschine

beim Schneiden von kaltgewalztem Elektroblech

Dissertation, University of Hannover, Germany, 1976

/27/ Seidenberg, H. Presseneinwirkungen auf Werkzeugverschleiß und

Grathöhe beim Schneiden von Feinblech

im geschlossenen Schnitt

Dissertation, University Hannover, Germany, 1965

Page 99: Influence of High Cutting Speeds

91

/28/ Pfeiffer, B. Investigations of the performance of in-die sensors for

high speed blanking

ERC Report, Columbus, 1996

/29/ N.N. Aida Press Handbook

Third Edition, Aida Engineering, Ltd., 1992

/30/ Wolff, Christian Metal flow simulations for flashless-forging of a cross

grooved inner-race

ERC Report NSM-B-95-25, Columbus, 1995

Page 100: Influence of High Cutting Speeds

1

APPENDIX A Material low carbon

steel

high strength

steel

Al 2011 110 Copper

Thickness 0.033” 0.054” 0.041" 0.016"

Grade/heat treat. EDDQ 50-XF T3 annealed temper

Chemical composition (wt %)

C 0.003 0.07 Mn 0.1 0.39 P 0.006 0.006 S 0.007 0.004 Si 0.01 0.063 Cu 0.01 0.02 5.5 99.90 Ni 0.02 0.01 Cr 0.02 0.02 Mo 0.01 0.01 V 0.002 0.004 Sn 0.003 0.005 Al 0.049 0.058 Ti 0.056 Cb 0.001 0.01 N 0.004 0.005 B 0 0.0001

Ca 0.0004 0.004 Bi 0 0 0.4 Pb 0 0 0.4 O 0 0 0 0.04 Sb 0.0052 0.001

Tensile Properties

Yield [ksi] 20.55 n/a 43 10-53

UTS [ksi] 40.98 n/a 55 32-66

Shear resistance σs

[kgf/mm2]

~25 ~32 ~12 ~20

Table A-25: Material properties of the stock materials used

A - 1

Page 101: Influence of High Cutting Speeds

1

APPENDIX B

Figure B - 1: Labview program code

B - 1

Page 102: Influence of High Cutting Speeds

1

APPENDIX C

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

time [sec]

punc

h ve

loci

ty [f

t\sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stripper

start blanking blanking

completed

Figure C - 1: Velocity/displacement-time curve. Material: high strength steel. Power

level 3, stroke length 0.5"

0

1

2

3

4

5

6

-0.05 -0.025 0 0.025 0.05 0.075displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vmvst

vd

Figure C - 2: Punch velocity versus displacement. Material: high strength steel. Power

level 3, stroke length 0.5"

C - 1

Page 103: Influence of High Cutting Speeds

2

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

time [sec]

punc

h ve

loci

ty [f

t/sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

start blanking

blanking completed

stop blocks

BDC

Figure C - 3: Velocity/displacement-time curve. Material: high strength steel. Power

level 9, stroke length 1.5"

0

2

4

6

8

10

12

14

-0.05 0 0.05 0.1 0.15 0.2displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vst vmvd vs

Figure C - 4: Punch velocity versus displacement. Material: high strength steel. Power

level 9, stroke length 1.5"

C - 2

Page 104: Influence of High Cutting Speeds

3

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

time [sec]

punc

h ve

loci

ty [f

t/sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stripper

start blankingblanking completed

Figure C - 5: Velocity/displacement-time curve. Material: aluminum 2008. Power

level 2, stroke length 0.5"

0

1

2

3

4

-0.05 -0.025 0 0.025 0.05 0.075displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vst vm

vd

Figure C - 6: Punch velocity versus displacement. Material: aluminum 2008. Power

level 2, stroke length 0.5"

C - 3

Page 105: Influence of High Cutting Speeds

4

-9

-6

-3

0

3

6

9

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

time [sec]

punc

h ve

loci

ty [f

t/sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

stripper

start blanking

blanking completed

stop blocks

BDC

Figure C - 7: Velocity/displacement-time curve. Material: aluminum 2008. Power

level 9, stroke length 1.5"

0

2

4

6

8

10

12

-0.05 0 0.05 0.1 0.15 0.2displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vst vdvm

vs

Figure C - 8: Punch velocity versus displacement. Material: aluminum 2008. Power

level 9, stroke length 1.5"

C - 4

Page 106: Influence of High Cutting Speeds

5

-9

-6

-3

0

3

6

9

12

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

time [sec]

punc

h ve

loci

ty [f

t/sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

blanking completed

stripper

start blanking

BDC

Figure C - 9: Velocity/displacement-time curve. Material: copper 110. Power level 2,

stroke length 0.5"

0

1

2

3

4

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vst vmvd

Figure C - 10: Punch velocity versus displacement. Material: copper 110. Power level 2,

stroke length 0.5"

C - 5

Page 107: Influence of High Cutting Speeds

6

-9

-6

-3

0

3

6

9

12

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

time [sec]

punc

h ve

loci

ty [f

t/sec

]

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

disp

lace

men

t [in

]

velocitydisplacement

start blanking

blanking completed

BDC

stop blocks

Figure C - 11: Velocity/displacement-time curve. Material: copper 110. Power level 9,

stroke length 1.5"

0

3

6

9

12

-0.5 0 0.5 1 1.5displacement [in]

punc

h ve

loci

ty [f

t/sec

]

vmvst vd vs

Figure C - 12: Punch velocity versus displacement. Material: copper 110. Power level 9,

stroke length 1.5"

C - 6

Page 108: Influence of High Cutting Speeds

1

APPENDIX D

Figure D - 1: Simulation model, Step 1 of 102, 18% clearance, 0.5 ft/sec

D - 1

Page 109: Influence of High Cutting Speeds

2

Figure D - 2: Simulation model, Step 40 of 102, 18% clearance, 0.5 ft/sec

D - 2

Page 110: Influence of High Cutting Speeds

3

Figure D - 3: Simulation model, Step 80 of 102, 18% clearance, 0.5 ft/sec

D - 3

Page 111: Influence of High Cutting Speeds

4

Figure D - 4: Simulation model, Step 102 of 102, 18% clearance, 0.5 ft/sec

D - 4

Page 112: Influence of High Cutting Speeds

5

Figure D - 5: Simulation model, Step 105 of 105, 5% clearance, 0.5 ft/sec

D - 5

Page 113: Influence of High Cutting Speeds

6

Figure D - 6: Simulation model, Step 110 of 183, 5% clearance, 12 ft/sec

D - 6

Page 114: Influence of High Cutting Speeds

1

Figure D - 7: Simulation model, Step 56 of 56, 18% clearance, 12 ft/sec

D - 7