Laser Assisted Machining - IIT Kanpur

Chapter 3

Laser Assisted Machining

Dr. J. Ramkumar1 and Gaganpreet Singh2

1Professor and 2Research Student

Department of Mechanical Engineering

Micromanufacturing Lab, I.I.T. Kanpur


Introduction

• Advance material such as Aluminum alloy, Titanium alloy, Hastelloy etc. are difficult to machine using conventional machining

• Localized heating of such material can be used for relatively easy machining

• Localized heating of material during machining is known as thermally assisted machining (TAM)

• TAM soften the workpeice which reduces the yield strength, hardness and strain hardening

• TAM leads to change of deformation behavior form brittle to ductile

2/2/2019 2Micromanufacturing Lab, I.I.T. Kanpur

Variation of Tensile strength with Temperature[1]

• In 1970 laser was used for the first time for TAM which is known as Laser Assisted Machining (LAM)

• Laser beam offers a local, rapid and controllable heat source to the work

• Control over the various laser parameters such as spot size, energy, and speed makes it the first choice for TAM

Introduction Cont…..


http://www.nitttrchd.ac.in/sitenew1/app_sc/ppts/laser/Laser%20Material%20Processing.pdf

http://cuttingedgeconversation.blogspot.com/2013/03/top-performance-grades-get-laser-assist.html

E2

E1

hʋ

hʋ

hʋ

light

byamplificationstimulated emission

of radiation

(Electromagnetic

radiations)

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Population inversion

Stimulated emission

Amplification

Initially Number of electron

in E1 i.e. N1 > Number of

electron in E2 i.e. N2, At some

point N2 > N1 which is called

population inversion

E3 = Higher energy state, (10-8 sec)

E2 = Meta stable state 3x 10-3 milli sec

E1 = Ground energy state

These electrons losses very less energy

(thermal energy)

𝑵𝟐 = 𝑵𝟏𝒆𝒙𝒑[−(𝑬𝟐 − 𝑬𝟏)/𝒌𝑻]Boltzmann equationT and k are the absolute temperature

and Boltzmann constant

1

3

2

External energy source or pumping

Gain/Amplification medium

Fu

ll mirro

r

Pa

rtial

Stimulated emission, population inversion,

amplification, monochromaticity.



XeCl (308nm),

KrF (249nm)

Neutral or

atomic

gas

Ion laser

Gas laser Solid State/Glass Liquid/Dye Semiconductors/diode

Excimer Molecular InGaAs(980nm), AlGaAsP

(630-680nm), AlGaAs (780-

880nm)

Rhodamine 6G (570-640nm),

Coumarin 102 (460-515),

Stilbene (403-428nm)

Nd: YAG(1,064

nm), Ruby

(694nm)

CO2

(10,600nm)

Argon (Ar+) (488,

514.5nm), krypton (Kr+)

(520-676nm)

HeNe (632.8nm),

Cu (510.6,

578.2nm), Au

(628nm)

Laser

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Types of Lasers

• Easy beam transfer• Shorter wavelength• Energy efficiency• High laser output

per power supply


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Laser Assisted Machining Processes

Laser-Assisted Turning

Laser-Assisted Milling/Grinding

Laser-Assisted Jet ECM

Laser-Assisted Waterjet Machining


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• Laser is used to heat material before machining using turning tool

• Simple to intergrate with turning process as the tool is stationary

• Both single beam and multibeam laser beam are used for LAM

• There are different ways in which single laser beam can be integrate with turning process such as:

a) Normal to workpeiceb) Normal to chamfered surface• For better machining,temperature

distribution at the cutting edge should be uniform

• Turning tool should not be heated while machining


Rashid et. al (2013)[2]

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+Normal to workpeice

Normal to Chamfer

East to integrate Difficult to integrate

Machined surface will not be heated

Effect of heat on machined surface

Heat is not enough for high depth of cut

Heat can reach upto more depth of cut

Less reduction in cutting forces

More reductionincutting forces

Normal to ChamferedNormal to Workpeice

Multibeam LAM



https://www.industrial-lasers.com/articles/print/volume-26/issue-1/features/laser-assisted-machining.htmlKiswanto et. al(2014)[3]

https://www.industrial-lasers.com/articles/print/volume-26/issue-1/features/laser-assisted-machining.html

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• Laser-Assisted milling/Grinding is a type of thermally-assisted machining process in which a workpieceis locally softened by a laser heat source before machining.

• It is difficult to integrate laser with milling as compare to turning

• Laser assisted milling can be achieved by two ways

1. Separate arrangement of laser unit

2. Integration of laser in spindle itself

3. Using deflection mirror


Lee et al. (2016)[4]

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Lee et al. (2016)[4]

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• High power laser is required to cover the machining area

• Green machining process, because it saves energy by reducing the cutting force

• Easy to use in single direction machining

• For machining complex 2D or 3D parts require more axis of machine motions.

• It becomes difficult to control the heat source and cutting tool simultaneously.

• To reduce the need for separate motional stages laser can be integrated with work spindle


Tian et al. (2008)[5]

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Laser-Assisted Jet Electrochemical Machining

• Laser is employed to improve the precision of machining

• Low power laser beam is used to activate the outer surface layer of material

• Laser assist the ECM process by directing the electrochemical energy

• Thermal energy enhances the kinetics of ECM reactions, which enables the localization of dissolution to a specific area

• Laser-workpeice and laser- electrolyte interaction causes a higher MRR in axial direction instead of lateral direction

• This improves the dimensional precision of material


De Silva et al.(2011)[6]

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• Advantage of • Electrolyte conductivity increase which

increase the current density1. Easier initiator of ECM reaction2. Diffusion intensified the transportation3. Improve process productivity4. Reduce stray machining

• Disadvantages1. Induce HAZ and thermal stresses in

material2. Intensified gas agitation3. Causes electrolyte boiling

Laser-Assisted Jet Electrochemical Machining


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• LAWM is developed to minimize the thermal damages during laser machining

• In this process, instead of melting and vaporizing the material laser is used to soften the material, which is removed by the expulsion of a high pressure waterjet

• This process requires less thermal energy input which is helpful for high speed movement of laser

• Less thermal energy input also reduces the thermal damage

• Waterjet not only removes the soften material but also takes the heat away from the substrates


Tangwarodomnukun et al.(2012)[7]

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• Laser and waterjet moves simultaneously while machining

• Laser interacts with the material from outside of waterjetperimeter, water thickness is almost 10% of jet diameter

• Waterjet diameter depends upon the impact angle

• Laser power, impact angle and waterjet pressure controls the grove width and depth in this process

• Machining of materials using this process incurs almost zero HAZ


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Characteristics of laser- assisted machining of hard-to-machine materials

• Titanium Alloys

• Nickel-Based Super Alloys

• Ceramics

• Composites


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Titanium Alloy• Properties: High strength-to weight ratio, strong wear and corrosion resistances, high

creep, ability to retain high strength at high temperature• Difficult to cut: Low elastic modulus , low thermal conductivity and high chemical

affinity• Carbide tools are commonly used to machine Titanium alloys • These tools experience flank wear , crater wear, high cutting temperature, short tool life

and high vibration• LAM is used to reduce cutting forces in machining of Titanium tool• Reduction in cutting forces is controlled by the cutting speed, depth of cut, laser power,

position and incident angle of laser beam• Optimum temperaure for machining Ti-6Al-4V alloy is 250℃• Laser power is optimized to achieve this temperature• LAM improves formability of material, which enables shear deformation at the primary

shear zone• LAM produces smoother surfaces with less grain pullout and smaller depth of the

deformation zone.• It also reduces the compressive residual stress at the surface which may lower the

fatigue resistance


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Nickel-based Super Alloy• Properties: Retain strength and toughness under high pressure

• Difficult-to-machine: Rapid work hardening, flank wear and notching wear

• LAM causes thermal softening which lowers the cutting forces in conventional machining.

• Location of laser beam plays an important role in tool wear reduction

• Experimental studies shows that there is great reduction in notch wear if the laser beam is incident to chamfer shoulder

• In laser-asisted milling of Inconel 718, positing of laser on the edge of the workpeicefor longer time reduce tool edge chipping

• LAM using ceramic tool can achieve roughness of .5µm and residual stress of 260 MPa

• LAM also induces compressive residual stress which improve the fatigue resistance


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Ceramics• Properties: High temperature strength, low density, thermal and chemical stability

and good wear resistance

• Difficult-to-machine: High hardness and brittleness

• LAM modify the deformation behavior of ceramic by changes its property from brittle to ductile

• Reduces the yield strength to a value below the fracture strength

• In LAM of ceramics material removal is achieved through the combination of brittle fracture and plastic deformation due to thermal softening of glassy phase material

• The cutting forces and specific energy decreases with increase in laser power

• Roughness of machined surface in ceramics depends upon the size and distribution of ceramic grains

• LAM can reduces the edge chipping if the material is preheated between brittle transition temperature and global softening temperature


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Composites• These materials are Inhomogeneous and anisotropic in nature as a combination of

reinforcement fibers with matrix metals

• Properties: Hardness and wear resistance

• Difficult-to-machine: Excessive tool wear, poor surface finish due to delamination

• Laser preheating, softens the reinforcement and leads to reduction in cutting forces

• In LAM soft metal matrix is squeezed out from the machined surface while reinforcement is pushed in from the machined surface

• It leads to higher concentration of reinforcement on the which improves surface roughness

• Compressive residual stresses are found to be three times greater than conventional machining


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Case Study: Laser-assisted Grinding of ceramics• Ceramic: Si3N4 and Al2O3

• Properties of Si3N4 and Al2O3 : High temperature stability, corrosion resistance, toughness

• Application: Bearing, teeth implants, cutting tools

• Conventional Grinding tool: Diamond

• Disadvantages of Diamond grinding tool:

1) Costly Process

2) Low MRR

3) High diamond wheel wear rate

• To reduce the above mentioned disadvantages diode laser is integrated with grinding machine


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Fourier law• In grinding laser heating is used to achieve temperature between 850-950℃• In laser, due to conduction temperature decreases from the laser heating target surface to

the machining region• Temperature at the machined region can be approximated using Fourier’s law• Fourier's law: Rate of heat transfer per unit area Fq is proportional to the thermal

conductivity (κ) and the temperature gradient in the direction of normal to an isothermal surface

• 𝐹𝑞 = −κ∆𝑇

• This equation can be used for steady state heat transfer, but for nonsteady-state heat conduction can be described as

• ∆2𝑇 =ρ𝑐

κ

𝜕𝑇

𝜕𝑡−

𝐴𝑣𝐼(𝑥,𝑦,𝑧,𝑡)

κ

• where Av is the fraction of the radiation energy absorbed to per unit volume of the workpeice, and I is the Gaussian distribution of intensity


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Experiments


Yang et al.(2009)[8]

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Experiments• Machine: MUGK7120X5• RPM of spindle: 60000• Diameter of wheel: 3mm• Grit size: 70-80µm• Thickness of Diamond layer: .3mm• Length of Diamond layer: 15 mm• Laser Power for Si3N4 : 45 W• Laser Power for Al2O3 : 70 W• Wavelength of laser: 808nm• Absorption rate: 75%• Spindle speed: 5000-15000

rev/min• Feed rate: 8-20mm/min• Cutting depth: 1-5 µm


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Results and Discussions: Grove DepthSi3N4

Al2O3

• Grove depth is maximum in LAM

• Grove depth increase because of thermal expansion of workpeice

• Tool also expands due to thermal expansion which affects the dimensional accuracy

• Air cooling along with laser heating countered the elongation effect which provides better dimensional accuracy


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Results and Discussions: Grinding Force

Conventional Grinding of Al2O3 Laser assisted Grinding of Al2O3

• Laser assisted grinding of Al2O3 requires less force for grinding operation

• This happens because laser lower the strength of the material

• Lower strength material is easy to remove which decrease the forces required

• Further grinding force increases air cooled laser assisted grinding is used


Chang et al.(2007)[9]

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Results and Discussions: Roughness

Conventional LAM

• Laser assisted grinding of Al2O3

produce better surface finish• Conventionally produced cutting

region is rough and vibration occurs because of the material’s naturally high cutting resistance

• Cutting region produced by LAM is smooth and straight, which is attributable to the plastic flow of the material.

Micromanufacturing Lab, I.I.T. KanpurChang et al.(2007)[9]

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Conclusion• LAM is one of the well researched hybrid machining process

• Reduced cutting forces and improved surface finish and surface integrity have been proved for various difficult-to-machine materials

• However all these benefits have been explored in laboratory environment

• For industrial implementation further research for the following points has to be taken care:

1. Development of multiscale and multiphysics modeling

2. Optimization of processing parameters

3. Development of low-cost and flexible LAM add-on device

4. Integration of controller of LAM device into traditional CNC machine controller


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References1. Garcí, Virginia, Iban Arriola, Oscar Gonzalo, and Josu Leunda. "Mechanisms involved in the improvement of Inconel 718 machinability

by laser assisted machining (LAM)." International journal of machine tools and manufacture 74 (2013): 19-28.2. Rashid, RA Rahman, M. J. Bermingham, S. Sun, G. Wang, and M. S. Dargusch. "The response of the high strength Ti–10V–2Fe–3Al beta

titanium alloy to laser assisted cutting." Precision Engineering 37, no. 2 (2013): 461-472.3. Kiswanto, G., D. L. Zariatin, and T. J. Ko. "The effect of spindle speed, feed-rate and machining time to the surface roughness and burr

formation of Aluminum Alloy 1100 in micro-milling operation." Journal of Manufacturing Processes 16, no. 4 (2014): 435-450.4. Lee, Choon-Man, Dong-Hyeon Kim, Jong-Tae Baek, and Eun-Jung Kim. "Laser assisted milling device: A review." International Journal of

Precision Engineering and Manufacturing-Green Technology 3, no. 2 (2016): 199-208.5. Tian, Yinggang, Benxin Wu, Mark Anderson, and Yung C. Shin. "Laser-assisted milling of silicon nitride ceramics and Inconel

718." Journal of manufacturing science and engineering 130, no. 3 (2008): 031013.6. De Silva, A. K. M., P. T. Pajak, J. A. McGeough, and D. K. Harrison. "Thermal effects in laser assisted jet electrochemical machining." CIRP

Annals-Manufacturing Technology 60, no. 1 (2011): 243-246.7. Tangwarodomnukun, V., J. Wang, C. Z. Huang, and H. T. Zhu. "An investigation of hybrid laser–waterjet ablation of silicon

substrates." International Journal of Machine Tools and Manufacture 56 (2012): 39-49.8. Yang, Budong. "Experimental and numerical investigation of laser assisted milling of silicon nitride ceramics." PhD diss., Kansas State

University, 2009.9. Chang, Chih-Wei, and Chun-Pao Kuo. "An investigation of laser-assisted machining of Al2O3 ceramics planing." International Journal of

Machine Tools and Manufacture 47, no. 3-4 (2007): 452-461.

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Thank you


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Laser Assisted Machining - IIT Kanpur