REVIEW OF DUCTILE MODE MACHINING OF GLASS

Presentation by

Denny J Ottarackal

Reg No:10002637

Under the Guidance of

Prof. Mathew J Joseph

Dept. of Mechanical Engineering

Amal Jyothi College of Engineering

1

Outline of Presentation

Introduction

● Background and Scope of Ductile Mode Machining of Glass

● Objectives and Methodology

Literature Survey

Ductile mode machining of Glass

● Basic concepts

● Experimental Setup

● Experimentation

Results and Discussion

References

2

Introduction

Background and Scope of Ductile Mode Machining of Glass

Glass - a brittle material.

Very difficult to machine material.

Functional material for optics and electronics.

Conventional grinding process causes surface damages.

For better surface finish glass must be machined in ductile mode.

3

Objectives and Methodology

Analysis of depth of cut, feed rate, tool wear and chip thickness.

Study of Side milling process.

Experimental study of ductile mode machining of glass by Ultraprecision vertical

spindle multipurpose machine tool.

To relate flank wear and machining time.

To study the relation between feed rate and surface roughness.

4

Literature Survey

Arif, Rahman and San stated about the relation between feed rate and brittle

fracture. They studied about the regimes in milling[1].

Venkatachalam, Li and Liange correlated stress intensity factor with ductile mode

machining[2].

Arif, Rahman and San described about the transition point of ductile-brittle

conversion[3].

5

Side Milling

In upmilling, deformed chip thickness increases

from zero to a max value with cutter rotation.

If the undeformed chip reaches a critical

value , brittle fracture will occur.

If the brittle fracture point is far from the level

of final machined surface and feed rate is low ,no

brittle fracture occurs.

6

Side milling process of glass (a)at low feed per edge(b)high feed per edge. Fig.1.

Plowing Effect

Minimum chip thickness effect in milling.

Chip thickness must be a certain minimum value for effective cutting.

If the chip thickness is below certain value , only plowing or elastic deformation

will occur.

Fracture propagation does not take place in particles of dimension smaller than,

dc = 10Eγ /Y2.

Here E is the modulus of elasticity, γ is the fracture energy and Y is the

yield stress of work-material.

7

Regimes in Milling

Three regimes in milling

● Plowing regime;

If the uncut chip thickness is less than what is

required for material removal.

● Ductile regime;

Ductile mode is achieved beyond plowing zone.

● Brittle regime;

If critical value of undeformed chip thickness reached at

some point beyond the ductile zone, brittle fracture occurs.

8

Different Regimes of Milling in Slot milling of Glass.Fig 2.

Experimental Setup

Ultraprecision vertical spindle multipurpose

machine tool is used (Fig 3).

Movement of Y-axis executed by table.

Movements in X and Z-axis by spindle motion.

Digital Tachometer for spindle speed measurement.

9

Vertical Spindle Multipurpose Machine ToolFig 3.

Cutting Tool

Super hard cemented microendmill was used.

Cutting edge radius of cutter was at submicron level.

Cutter with submicron edge radius is essential requirement for ductile mode machining of glass.

Workpiece

A rectangular piece of soda lime glass with the dimensions of

35×55×5 mm are used in the experiment.

Cutting was performed with cutter workpiece submerged in a pool of water serving as coolant.

Constant spindle speed of 3000rpm was used.

Each cutting was performed by new cutter.

10

Cutting Conditions

Cutting was performed with cutter workpiece submerged in a pool of water serving as

coolant(Fig 4).

Constant spindle speed of 3000rpm was used.

Each cutting was performed by new cutter.

Tool Wear

Two types

● Gradual wear of cutting edge

● Abrasion at the flank face

11

Cutting performed submerged in coolantFig 4

Experimentation

Axial depth of cut and feed rate varied

according to the Table 1.

After machining , the machined surface was

cleaned in acetone by applying ultrasonic

vibrations.

Machined surface was observd under optical

microscope for surface characterization.

12 Test no. Axial depth of cut(µm)

Feed rate(nm/rev)

1 0.2 40

2 0.2 80

3 0.2 120

4 0.2 160

5 0.4 40

6 0.4 80

7 0.4 100

8 0.4 120

9 0.4 140

10 0.4 160

11 0.6 40

12 0.6 80

Cutting conditions(spindle rpm = 3000).Table 1.

Results and Discussion

Too low feed rate cause powing and high

feed rate cause brittle fracture.

Ductile mode machining obtained at moderate

feed rate.

A high quality machined surface was obtained

at an axial depth of cut of 0.4µm and

feed rate of 80 nm/rev,shown in fig 5 and brittle

mode surface is shown in fig 6.

Surface machined in ductile mode. Fig 5.

Surface machined in brittle mode. Fig 6.

13

Results and Discussion

Flank wear occours at a slow rate at the beginning

as shown in Table 2, because of characteristics of

coating material of the cutter.

Relation between surface roughness and feed rate is

shown in Table 3.

14

Machining time(min)

Flank wear(µm)

3 4

7 5

10 15

14 29

17 39

22 52

25 65

Relation between machining time and flank wear.Table 2.

Feed rate(nm/rev)

Surface roughness(nm)

40 50

80 30

120 38

140 70

160 240

Variation of surface roughness with feed rate.Table 3.

Results and Discussion At low feed rate, the average value of surface roughness is slightly higher

due to powing effect.

At medium feed rate surface roughness is low due to ductile mode machining.

At high feed rate surface roughness is very high due to brittle mode machining.

Critical feed rate is between 120 and 140 nm/rev, corresponding chip thickness is between 60 and 70nm.

This undeformed chip thickness is less than theoretical value(45nm).Due to thermal softening effect.

AFM images of Ductile mode with powing effect, Ductile and Brittle surfaces is shown in

Fig 5, Fig 6 and Fig 7.

Fig 5 Fig 6 Fig 7

15

Conclusion

Feed rate and Depth of cut – critical factors in ductile mode machining of glass.

Tool wear has to be considerd for better surface finish.

Should be an optimum value of chip thickness for ductile mode machining.

Feed rate affects ductile-brittle transition.

Optimum value of feed rate for better surface roughness.

Energy for crack propogation is larger than that of plastic deformation.

Crack propogation is compressed in ductile mode machining.

16

References

•[1] Muhammad Arif., Mustafizur Rahman., Wong Yoke San.,`Ultraprecision ductile mode machining of glass by micromilling process’, Manufacturing Processes,Volume 13, Issue 1,2011.

•[2] Siva Venkatachalama., Xiaoping Li b., Steven Y. Liangc.,` Predictive modeling of transition undeformed chip thickness in ductile-regime micro-machining of single crystal brittle materials’, materials processing technology 2 0 9, 3306–3319( 2009 ). 

•[3] Muhammad Arif., Mustafizur Rahman., Wong Yoke San.,` Analytical model to determine the critical feed per edge for ductile–brittle transition in milling process of brittle materials’, Machine Tools & Manufacture, 51 170–181(2011).

 

17

Thank you...