Laser Assisted Micro Machining

Pratik S. Gandhi B.Tech. Production

111213021

Contents 1. Introduction2. LAMM (Micro & Macro Scale)3. LAMM on Ceramics4. Setup & Parameters5. Tool & w/p Contact Detection

6. Measured Responses7. Laser Assisted Micro Grinding8. Advantages & Disadvantages9. Discussions & Conclusion10. Area For Improvements

Introduction

• Need – Parts with Micro Level Features• Conventional Machining Process Imposes Limitations • Micromachining – Range of Materials & Variety of Sizes• Limitations – Low MRR, Tool Failure , Poor Feature Accuracy• Assistance – Cutting Fluids, Coating on Tools, Lubrications

Introduction (Contd.)

• LAMM – Assist for Localized Thermal Softening• Control – Power, Spot Size, Scan Speed• Approaches :- 1. Thermal Softening of Hard Metals 2. Thermal Cracking of Ceramics • Critical Distance between Tool & Laser Spot

LAMM (Micro & Macro Scale)

• Parameters – Wavelength,Efficiency, Mode of Operationa. Continuous Waveb. Pulse Wave• Common Lasers – CO2, Nd- YAG, Excimer Laser• Irradiation Mechanism for

Metal Removal

• Reduction of Cutting Forces, Rise in MRR• Deformation Mechanisms & Shear Zone Stresses• Optimize Variables to

Minimize Tool Wear• Excessive Heating –

Degradation of Microstructure & Mechanical Properties

Micro Scale Macro Scale

LAMM on Ceramics

• Ceramics – High Temp. Wear Resistance, Chemical Inertness, Good Strength-to-Weight Ratio• Brittle Fracture – Surface Micro Cracks• High Speed, Low Depth Multiple Cuts (Rough & Finishing)• Continuous Wave Laser – Induce & Propagate Thermal

Cracks• Local Tensile Stress – Crack Tip Development• Rapid Laser Heating followed by Cooling

Setup

• Ytterbium doped CW Infra – red Fiber Laser

• Electric Motor – Spindle Speed up to 80,000 rpm

• Machine – 3 Stacked Linear Motion stages and a Rotary stage

• Tool – Square End Mill, TiAlN coated Tungsten

Carbide

Setup (Contd.)

ATS – 125

• X, Y Translation

• 1 µm Accuracy

• 100 mm Travel

• 180 N Axial Force

• Speed – 30 to 34 m/min

AVS – 105

• Z Axis Lift Motion

• 5 mm Travel• 50 N Max

Force• Speed – 0.3

m/min

URS – 150cc

• Rotary Motion• DC Servo

Motor Driven• 360º Travel

Range• Speed - 80º/

Sec• Max Force –

300 N

Process Parameters

• Laser Power Desired Temp. Rise• Wavelength – 1.06 m , Peak Power – 35 W• Laser emission – 7 µm Dia Single Mode Fiber through a

Collimator• Spot Size – Adjusting Distances between Lenses of

different Focal Lengths• Positioning Error +/- 10 µm

Tool & w/p Contact Detection

• Accurate Tool Setting => Dimensional Accuracy 1. Laser based Detection 2. Use of Machine Vision (High Magnification Camera &

Direct Line of Sight)3. Electrical Signal Generation (Only for Conducting

Material)4. Acoustic Emission Sensor – RMS Value of Output

Voltage5. Spectral Content of Lateral Vibration of Milling

Spindle

Measured Responses • Resultant Force a. R = Fx + Fy + Fzb. 3 Axis Piezoelectric Dynamometer c. Specific Cutting Energy – Average over each Groove • Tool Wear a. Change in Corner Radius of Tool Tip b. LAMM => Less Rubbing & More Cutting at High Feed Rate

Measured Responses (Contd.)

• Groove GeometryIn absence of Laser – Groove Profile varies due to Tool Wear

• Burr Height – Lager in LAMM due to Higher Ductility of Softened w/p Material

• Heat Affected Zone – Tempered Region surrounds Laser Path

Laser Assisted Micro Grinding

• Laser Irradiation – Induce & Confine Thermal Cracks• Cutting speed – 200 m/min• Abrasive Grinding Pencil of Dia 0.8 mm • Thin Layer of Material after Scanning by Laser becomes

Amorphous• Constant Feed Rate

Advantages & Disadvantages

Advantages Disadvantages

Efficient Cutting of Hard Materials

Higher Feed Rate; Not Proper Pre- Heat

Short Manufacturing Time Excess Laser Power

lessen Material Hardness

Economic Production of Complex Features

High Temp at Tip causes Tool Wear

Longer Tool Life due to Less Cutting Forces

Feasible only up to Depth of cut of 3 mm

Discussion & Conclusions

• LAMM results in reduction in Tool Wear & Cutting Stresses• Resultant Forces decreased by nearly 60%• Rounding of Tool Corner is Significantly lower• Excessive Spot Size greater than Tool Dia increases Burr

Height• Slow Scan by Laser makes the Material Soft; Results in

increase in Surface Roughness • Though it is Efficient for Complex Features, it is useable

only for superficial cuts

Area for Improvements

• Optimization of Laser Parameters – Use of Simulation Softwares like ANSYS

• Tool Coatings & Cutting Edge Radius• Setup can be used for Heat treatment process like Laser

Hardening• Minimize Residual Thermally affected Zone• Accuracy of Groove depends on Tool feed, Temp of Zone and

Strength of Tool• Implementation on Commercial scale

THANK YOU!