©2008 Mate Precision Tooling1
Basic Punching Theory
©2008 Mate Precision Tooling
• Die clearance too small
• Poor or no maintenance on the tool
• Turret alignment requires adjustment
The ‘BIG 3’ ProblemsThe ‘BIG 3’ Problems
©2008 Mate Precision Tooling
Punching a hole Die Clearance Punch Tonnage Choosing the right tool Correct tool maintenance …
Basic Hole Punching Theory
©2008 Mate Precision Tooling
Punching CyclePunching CycleImpact Penetration
Fracture (@ 30% t) Stripping
Material Punch
Die
Slug to go approx. 3 mm into die for slug free dies
Roll-over
Burnish zone
Fracture
Punch force diagram
©2008 Mate Precision Tooling
Cross Section of a Quality Hole
Cross Section of a Quality Hole
Burr height graphsSlug
©2008 Mate Precision Tooling
• Die clearance too smallDie clearance too small• Poor or no maintenance on the tool
• Turret alignment requires adjustment
The ‘BIG 3’ ProblemsThe ‘BIG 3’ Problems
©2008 Mate Precision Tooling
Proper vs. Tight ClearanceProper vs. Tight Clearance
©2008 Mate Precision Tooling
Proper vs. Tight ClearanceProper vs. Tight Clearance
Extra energy does not disappear,
but is converted into heat !!
- Punching forces are balanced, - Maximum piece part quality and tool life
Fracture lines meet
Fracture lines do not meet
- Secondary shear cracks, - Extra energy required,- Higher tool wear (dies wear quicker)
©2008 Mate Precision Tooling
Large Burr, not compressed and can be removed easily
More Rollover & Less Burnish zone
Excessive ClearanceExcessive Clearance
Tool lasts longer !
©2008 Mate Precision Tooling
Proper Die ClearanceProper Die ClearanceMaterial Type
Shear Strength Material
Thickness Piercing Total
Die Clearance % Blanking Total Die
Clearance %
Aluminum 22 –25 kp/mm²
Less 2.5mm
2.5mm to 5.0mm
Greater than 5.0mm
15% 20% 25%
15% 15% 20%
Mild Steel 40 kp/mm²
Less than 3.0mm
3.0mm to 6.0mm
Greater than 6.0mm
20% 25% 30%
15% 20% 20%
Stainless Steel 60 kp/mm²
Less than 1.5mm
1.5mm to 2.8mm
2.8mm to 4.0mm
Greater than 4.0mm
20% 25% 30% 35%
15% 20% 20% 25%
Note: 1) In general: shear strength determines clearance (10% is already good for low shear strength aluminium)
2) Minimum die clearance recommended : 0.08 mm
©2008 Mate Precision Tooling
Improper Die ClearanceImproper Die Clearance
©2008 Mate Precision Tooling12
Piercing
– The slug is scrap. The interior of the sheet is the product.
– Depending on the tool design, more than one hole can be punched at one time. Cluster tools for example.
– In piercing operations, the die clearance is calculated from the punch size.
Piercing vs. BlankingPiercing vs. Blanking
©2008 Mate Precision Tooling13
Blanking
– The punched item is of value. The slug is important.
– Special shapes are used mostly in blanking operations.
– Blanking operations calculate the die clearance from the desired blank dimensions.
Piercing vs. BlankingPiercing vs. Blanking
©2008 Mate Precision Tooling14
Punching TechniquesPunching Techniques
Blanking
– When the slug becomes the “good” or the “saved part”
©2008 Mate Precision Tooling15
Punching TechniquesPunching TechniquesBlanking rather than punching can save time, tool life and sheet usage
©2008 Mate Precision Tooling
Ordering Punches and DiesOrdering Punches and Dies
Piercing a Hole
Punch Size =
Desired Hole Size
Die Size =
Punch Size +
Total Clearance
Blanking a Part
Die Size =
Desired Blank Size
(no Slug Free dies !)
Punch Size =
Die Size – Total Clearance
©2008 Mate Precision Tooling
Required Punch Tonnage (tons) =
hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²) 1000
Some important shear factors shear factors (): Aluminium 22 -25kp/mm2
Mild Steel 40 kp/mm2
Stainless Steel 60 kp/mm2
Tonnage calculationTonnage calculation
Cluster tools :Cluster tools : multiply by number of punchesTonnage reduction by ‘step’-punching: step = ½ material thickness
F (tons) = P x t x S / 1000
Note Note : : try not to exceed 80% of punch press capacity
©2008 Mate Precision Tooling18
Material shear factors ( ) :
Aluminum = 22-25 kp/mm2
Mild steel = 40 kp / mm2
Stainless steel = 60 kp /mm2
Tonnage calculationTonnage calculation
18
©2008 Mate Precision Tooling
Formula:Formula: Tonnage =
hole perimeter (mm) * material thickness (mm) * shear factor (kpmm²) 1000
Ø 30mm hole
3mm stainless steel
Material shear factors ( ) :
Aluminum = 22-25 kp/mm2
Mild steel = 40 kp / mm2
Stainless steel = 60 kp /mm2
Example: Ø 30mm hole in 3mm stainless steel
Tonnage = (30 x 3.14) x 3 x 60 = 16,96 t 1000
Tonnage calculationTonnage calculation
©2008 Mate Precision Tooling
Required Tonnage + Stripping Force must be Tonnage to be within Machine Capacity !
Keep in mind : Stripping springs !Keep in mind : Stripping springs !
©2008 Mate Precision Tooling
Perim
ete
r Calcu
latio
ns
Calculate diagonals to
determine station size
Calculate perimeters for
tonnage calculations
A = Diagonal Dimension
(Station Size)
L = Hole Perimeter
©2008 Mate Precision Tooling
Calculator program for Clearance / Tonnage / Station Size
©2008 Mate Precision Tooling
Use of Shear on PunchesUse of Shear on Punches• Shear typically 1.5 – 2 mm• Max up to 80% of machine
capacity• Shear punches need sharp
edges (sharpen frequently)
• Best shear is rooftop; use min. 75-80% of length; can be used at high tonnage
• Concave shear: inverts stresses, good alternative for nibbling; max 15 Ton
• One-way: good blanking shear
• Four-way: very good on squares; hard to regrind
• Trumpf ‘Whisper’ very good, but hard to regrind
• Cup shear on rounds (Tr)
©2008 Mate Precision Tooling
Punch Shear ExamplesPunch Shear Examples
One-way & Whisper Cup
Concave RooftopFour-Way
©2008 Mate Precision Tooling
Tonnage reduction
Noise reduction
Slug control
Reduced shock loads on the machine
Flatter sheets
Improved stripping
Increased tool life
Advantages of ShearAdvantages of Shear
©2008 Mate Precision Tooling
Treated PunchesTreated Punches
Please note! Nitrated punches not recommended for diameter or width less than 6 mm !!
©2008 Mate Precision Tooling
Treatment vs. Coating Treatment vs. Coating Nitride Treatment
Nitriding is a heat treatment feature for HSS punches. Punches are more wear resistant, but also more brittle (esp. during stripping).Recommended for materials that cause galling, such as stainless steel, galvanized steel, or aluminum, but not if the material is too thick, as stripping might cause chipping. Can also be used for mild steel, will increase tool life (up to 4x).Also recommended for punching abrasive materials such as fiberglass.It is not recommended for punches smaller than 6mm in diameter or width, as punch is too brittle and may chip off.
Maxima® Coating
Maxima is a hard, wear-resistant, multilayer Zirconium Titanium Nitride (ZrTiN) coating,It puts a hard surface on the punch, adds wear resistance and ‘lubricates’ the process.The coating acts as a barrier between the punch and the sheet metal being punched. Its exceptional lubricity, reduces the friction that occurs during the stripping portion of the punching cycle, thus especially recommended in thicker material.Less friction means less heat build up, less galling and longer tool life. Also recommended upon high use of the punch, or as a problem solver.
Maxima Coating is more expensive than Nitride Treatment.
©2008 Mate Precision Tooling
Treatment vs. Coating Treatment vs. Coating
©2008 Mate Precision Tooling
Mate Slug Free® DieMate Slug Free® DieSlug Free® Die Components
1. Punch
2. Stripper
3. Material
4. Slug Free® Die
5. Slug
6. Grind Life
7. Entry -- Constricting Taper 0.5°
8. Pressure Point (at specific depth (*))
9. Exit -- Relief Taper 5.0°
Hole/Slug Geometry
A. Rollover
B. Burnish
C. Fracture
D. Burr
(*) depth = 1.5 mm + 0.7 * thickness (max = 3.0 mm)
©2008 Mate Precision Tooling
Material held securely by stripper before punch makes contact
Penetration begins and metal deforms into the entry taper
Material begins to fracture at stress points
Slug fractures away from sheet
Pressure point constricts slug
Punch stroke bottoms out as slug squeezes past pressure point
Punch retracts and slug is free to fall down and away through exit taper
Punch
Stripper
Material
Slug Free® Die
Slug Free® Die DetailSlug Free® Die Detail
©2008 Mate Precision Tooling
Uniform Clearance DiesUniform Clearance Dies
-No corner burrs with Constant Clearance in shaped die corners
-Stress relief in die corners
©2008 Mate Precision Tooling
Uniform Clearance DiesUniform Clearance Dies
Corner burrs when non-uniform clearance dies are used
©2008 Mate Precision Tooling
Slug Free Light ®Slug Free Light ®
Optional Die Land to prevent slug-pulling in problem materials or extremely thin material.
Blips 0,05mm deep are cut into the die wall to allow the slug to expand into the slots. Blips act as mechanical locks to trap the slug.
Especially for bigger diameters and thin material (max. 1,5 mm).
Material Type Recommended Material Maximum
Stainless Steel 0.80mm
Mild Steel 1.00mm
Aluminum 1.20mm
©2008 Mate Precision Tooling
Standard Back-taperStandard Back-taper
1/8 degree per side(1/4 degree TOTAL)
Punch Size
©2008 Mate Precision Tooling
Heavy Duty Back-taperHeavy Duty Back-taper
1 degree per side(2 degrees TOTAL)
Punch Size
Recommended when punching force over 18 tons and/or thickness above 4 mm
©2008 Mate Precision Tooling
Punching Thick Material (>4mm)Punching Thick Material (>4mm)
When ordering tools:
• HD tool configuration (Rooftop punch with extra Backtaper)
• Clearance of 25-30% of Material Thickness
• 0.5mm radius on all punch corners
• Punch to material thickness ratio of 1 minimum
When punching:
• Lubricate the sheet / punch / guide
• Run Machine on slow cycle
• Inspect tools frequently for wear / Use sharp Punches & Dies
©2008 Mate Precision Tooling
Punching Thick Material (>4mm)Punching Thick Material (>4mm)
Common Poblems / Solutions
•Stripping problemsHD configuration – Lubrication – Coating on
punch – Use bigger station – Gas canister
•Excessive tonnage / High tool wear / High vibrationsMake sure tonnage calculation is correct – Use Lubrication – Sharp tools – HD
configuration – Maxima coating – Shear on punch – Correct die clearance – Pre-pierce holes – Bridge hitting
•Work piece distortion/stretchingChange punch pattern (bridge hitting) – Slow
down machine – Use Fully Guided – Sharpen tools
©2008 Mate Precision Tooling
Slitting TipSlitting TipBridge HittingBridge Hitting
As consecutive nibbling may cause unbalanced forces,apply bridge hitting to avoid side loading during slitting
operations:
©2008 Mate Precision Tooling
Large Holes Without ExceedingPress Tonnage
Large Holes Without ExceedingPress Tonnage
The customer wants to pierce a 50.0mm dia. hole in thick mild steel.He does not want to buy a special shape radius tool, but wants to use standard tooling.
Tool 1 Use one Square 10mm and pre-pierce along the 50mm periphery 8 holes with equal pitch.
Tool 2 Finalize the hole with a 50mm flat punch
8 hits 10mm sq..
Final Hit 50mm round
©2008 Mate Precision Tooling
Punching Thin Material (<1mm)Punching Thin Material (<1mm)
When ordering tools:
You may require
• Ultra Light canisters
• Light shear on punches
• Fully Guided guide/stripper solution
• Urethane stripper pads
• Slug Free Light dies
When punching:
• Run Machine on slower cycle
• Inspect tools frequently for wear
• Use sharp punches & dies
©2008 Mate Precision Tooling
Punching Thin Material (<1mm)Punching Thin Material (<1mm)
Common Poblems / Solutions
•Sheet markingUrethane stripper pads – Ultra Light
•Slug pullingMaximize die penetration – Demagnetise tools –
Slug Free Light – Correct die clearance – Slug ejectors – Shear on punch
•High tool wear due to small clearanceMaintain turret alignment
•Work piece distortion/stretchingChange punch pattern – Slow down machine – Sharpen tools – Use Fully Guided
©2008 Mate Precision Tooling
Punching non-metallic materialPunching non-metallic material
Use concave shear punches
Use Maxima or Nitride punches
Reduce die clearance with 5 %
Use sharp punches and dies
Run the machine on a slower cycle
Lubricate hard plastics if possible
Use urethane pads if marking occurs
Support thin material if needed
©2008 Mate Precision Tooling
‘Shaving’ – Make Straight Walled Holes Without Drilling
‘Shaving’ – Make Straight Walled Holes Without Drilling
Finished hole size is the starting point.
Punch #1 = finished hole size – clearance (20%)Die #1 = finished hole size + 0.1 mm
Punch #2 = finished hole size (full mat’l contact : Maxima !)Die #2 = die #1
.
©2008 Mate Precision Tooling
Preventing Slug PullingPreventing Slug PullingUse Slug Free® Dies
Eliminate Magnetism In Tools
Lightly Dull Recently Sharpened Tools (with oil stone)
Decrease Die Clearance
Maximize Die Penetration
Use Shear on Punches
Use Urethane Slug Ejectors (need replacement !)
©2008 Mate Precision Tooling
Overcoming Stripping ProblemsOvercoming Stripping Problems
Use Sharp Punches & Dies
Lubricate Sheets
Remove Galling
Check Stripping Springs For Fatigue
Use Additional Back-Taper on Punches
Increase Die Clearance
Use HD Tool Configurations
With Spring Tooling Use Larger Station
©2008 Mate Precision Tooling
GallingGallingGalling is an adhesion to the punch tip by the metal being punched, caused by pressure and heat.
The best technique for removing galling is to rub it off with a fine stone. The rubbing should be done parallel to the direction of the punching motion. This will polish the surface that contacts the material, decreasing any chance of future galling. Do not sandblast, belt sand or use other harsh abrasive methods. These create a coarse surface finish to which material adheres more easily.
©2008 Mate Precision Tooling
Reduce GallingReduce GallingUse sharp Punches & Dies
Lubricate Work Piece
Adjust Machine Hit Rate (Slower)
Use ABS If Available (Tool Lubrication)
Increase Die Clearance
Use Maxima or Nitride Treated Punch
©2008 Mate Precision Tooling
Small Diameter or Narrow Holes
Small Diameter or Narrow Holes
When punching small diameter or narrow holes, maintain the following ratio of punch size (minimum) to material thickness:
Material
Aluminum
Mild Steel
Stainless Steel
Punch to Material Ratio
0.75 to 1
1 to 1
2 to 1
©2008 Mate Precision Tooling
Material
Aluminum
Mild Steel
Stainless Steel
Punch to Material Ratio
0.75 to 1 (Fully Guided 0.5 to 1)
1 to 1 (Fully Guided 0.75 to 1)
2 to 1 (Fully Guided 1 to 1)
Small Diameter or Narrow Holes
Small Diameter or Narrow Holes
With Fully Guided
©2008 Mate Precision Tooling
Minimum Spacing Between Holes and Forms
Minimum Spacing Between Holes and Forms
Minimum = 2 x Material Thickness between holes
Minimum = 2 1/2 x Material Thickness to sheet edgeTo
p v
iew
of
sh
ee
t
To avoid hole distortion:
©2008 Mate Precision Tooling
Minimum Spacing Between Holes and Forms
Minimum Spacing Between Holes and Forms
Spacing between forms
Minimum = 2 1/2 x Material Thickness to sheet edge
©2008 Mate Precision Tooling
NibblingNibblingNibbling
– Minimum feed rate is equal to material thickness.
©2008 Mate Precision Tooling
NibblingNibbling
Nibbling is not always recommended …
©2008 Mate Precision Tooling54
Excessive NibblingExcessive Nibbling
Nibbling patterns can be done with much less hits with a banana tool or multi-radius tool (with tool rotation)
©2008 Mate Precision Tooling
Punching Tip Punching Tip Combating WarpageCombating Warpage
To avoid sheet warpage when punching multiple holes,
punch every other hole first, then come back
©2008 Mate Precision Tooling
In order to reduce noise , vibrations and tonnage on cluster tools it is recommended to shorten 50 % of the cluster punches with about 50 – 60% of the sheet – thickness.
Example:
Cluster of 16 x square 10mm
Perforating in 1mm mild steel
Insert Punch length 37mm
Shorten 8 Punches to length 36,5mm ( Balanced Shortening)
Cluster ToolsCluster Tools
©2008 Mate Precision Tooling
Blanking --
When the slug
becomes the
“good” or the
“saved part”
Blanking OperationsBlanking Operations
©2008 Mate Precision Tooling
Blanking OperationsBlanking Operations
•Blanking rather than punching can save time, tool life and sheet usage …
•Special shapes can be done with a combination of standard tooling
©2008 Mate Precision Tooling
Blanking OperationsBlanking Operations
Extremely sharp punches and dies
Reduce die clearance by 5%
Determine which blank dimensions & tolerances are critical
Notify tooling provider that tooling required will be used for blanking
Use non-slug free or straight taper dies
Punches should be flat faced or with slight one-way shear
Frequently inspect tools for wear
Note: Be aware of the changing of burr side when piercing and blanking is combined.
©2008 Mate Precision Tooling
Punch 3.0-5.0mm flat
1.5-3.0 degree one-way shear can be used
Blanking Punch Configuration
Blanking Punch Configuration
©1999 Mate Precision Tooling
Note: Shear punches give flatter workpieces
©2008 Mate Precision Tooling
• Die clearance too small
• Poor or no maintenance on the Poor or no maintenance on the tooltool
• Turret alignment requires adjustment
The ‘BIG 3’ ProblemsThe ‘BIG 3’ Problems
©2008 Mate Precision Tooling
Fracture betweenplate and s lug
Burr
Burr
Punch sectionw ith du ll edge
D ie sectionw ith du ll edge
S lug :
S heet :
S traight wall
S traight wall
Roll- over
Roll- over
Close-up of a burrClose-up of a burr
©2008 Mate Precision Tooling
R = 0.25mm
Sharpen when a
0.25 mm radius
forms on the punch or the die
Sharpen when a
0.25 mm radius
forms on the punch or the die
- When the cutting edge shines- When hole quality changes- When the sound of punching changes
Recognize dull toolsRecognize dull tools
When to Grind ?When to Grind ?
©2008 Mate Precision Tooling
Grind Life = SBR - (Stripper Thickness + Material Thickness + Die Penetration)
Stripper Land - Ultra A-B = 4 mm- Ultra C-D-E = 8 mm
Material Thickness
Die Penetration
Usable Grind Life
Punches have a bigger grind life in smaller thickness
Max.
ThicknessSBRUltra
A 3,8 18,9
B 6,4 18,9
C-D-E 6,4 25,5
Calculating grind lifeCalculating grind life
How much to Grind ?How much to Grind ?
©2008 Mate Precision Tooling
Improper Sharpening Proper SharpeningTotal HolesProduced
RadiusFormed
Total HolesProduced
RadiusFormed
100,000 0.25mm 100,000 0.25mm50,000 0.50mm 100,000 0.25mm25,000 0.75mm 100,000 0.25mm10,000 1.00mm 100,000 0.25mm
185,000Total Hits
1.0mmTotal Removed
400,000Total Hits
1.0mmTotal Removed
More than DOUBLE the tool life when sharpened frequently!
Importance of frequent grinding Importance of frequent grinding
How frequent to Grind ?How frequent to Grind ?
©2008 Mate Precision Tooling
Sharpen frequently Shear punches to be reground more often than flat punches
Use coolant
Correct wheel parameters
Demagnetize all tooling after regrinding
Break edges with oil stone
Sharpening Rules Sharpening Rules How to Grind ?How to Grind ?
©2008 Mate Precision Tooling
SharpeningSharpening
Excellent sharpening results
©2008 Mate Precision Tooling68
IMPORTANCE OF CORRECT MAINTENANCE : bad sharpening practices
IMPORTANCE OF CORRECT MAINTENANCE : bad sharpening practices
©2008 Mate Precision Tooling
Benefits of ProperTool MaintenanceBenefits of ProperTool Maintenance
Flatter sheets (Note: Shear punches give flatter sheets)
Cleaner holes
Less stress on tool and machine
Longer tool life
Maxima coating not affected
©2008 Mate Precision Tooling
Sharpen frequently
Use proper die clearance
Use proper shear configuration
Lubricate punch, guide and sheet
Inspect tool holders for wear
Use treated tools for special applications
Use radii on all sharp corners
Demagnetize all tooling after regrinding
Check turret alignment regularly
Maximizing Tool LifeMaximizing Tool Life
©2008 Mate Precision Tooling
• Die clearance too small
• Poor or no maintenance on the tool
• Turret alignment requires Turret alignment requires adjustmentadjustment
The ‘BIG 3’ ProblemsThe ‘BIG 3’ Problems
©2008 Mate Precision Tooling
Thick Turret Alignment ToolsMate PILOT Alignment System
Standard Alignment tool
©2008 Mate Precision Tooling
PILOT Alignment ToolPILOT Alignment Tool
©2008 Mate Precision Tooling
PILOT Alignment ToolPILOT Alignment Tool
©2008 Mate Precision Tooling
Mate PILOTMate PILOT
Indicator light color :
– Red – not aligned
– Yellow – aligned within 0.0012 (0.030)
– Green - aligned within 0.0003 (0.008)
©2008 Mate Precision Tooling
Loosen upper and lower tool holder retaining screws
Mate PILOTMate PILOT
©2008 Mate Precision Tooling
Station Alignment to machine
– alignment bar and dial-indicator
Mate PILOTMate PILOT
©2008 Mate Precision Tooling
Questions?Questions?
©2008 Mate Precision Tooling
Thank you !