Science and Technology of

Miniaturization of Subtractive and

Additive Manufacturing Process

Ramesh Singh

Machine Tools Lab

Department of Mechanical Engineering

Indian Institute of Technology Bombay

1

• Micromanufacturing: Motivation & Background

• Novel Subtractive Micromachining

– Ultra-high Speed Micromachining

– Laser Assisted Mechanical Micromachining

– Micro-Electrical Discharge Machining

• Additive Micromanufacturing

• Summary

2

3

Defense

Micro-mold Electronics

Biomedical

Why Scaling Down?

Ti Spinal

implants

Safe & arm parts

for Bofors shell

@IITB Micro-holes (~200 mm)

Hitachi microdrive

Restoration Jewelry

Jewelry pattern

@IITB

Laser clad SS Box

@ IITB

www.datron.com

Machined graphene

cantilevers @IITB 100 mm width

Traditional Micromachining

• Traditional methods for micromachining Lithography

Ablation

Etching

LIGA

• Limitations of traditional methods Simple shapes and low aspect ratios

Limited range of materials that

can be processed

Specialized equipment/environment Clean Rooms/Synchrotron

Scaling Down the Manufacturing Processes

• Subtractive processes

• Milling, drilling, turning, EDM

• Additive processes

• Laser based material deposition

• Can create 3-D free-form features in a wide range of

materials

Issues with Scaling

Fundamental science not well

understood at micro-scale

Technology Challenges

Micro-tool

Z stage

Spindle

Micro end mill

Dynamometer

Workpiece

6

Microscale Manufacturing Technologies

An enabler for global push towards miniaturization

Complements traditional micromachining

Subtractive and additive processes can be scaled down

Limited industrial ecosystem exists globally

Huge technology deficit: Science-enabled technology needed

Subtractive

Mechanical micromachining

Hybrid mechanical micromachining

Electrical discharge machining

Additive

Feature creation

Repair and restoration

Scaled Down

Manufacturing

Processes

As deposited Post micromachining

Subtractive Micromachining

• Microtools have orders of magnitude lower flexural stiffness

• Catastrophic tool failure rampant

– Especially high-strength difficult-to-machine materials

• To address this issue following approaches can be used

– Ultra-high rotational speeds (>100,000 rpm) required to reduce chip loads

and hence force

– Laser-induced thermal softening

– Micro-electrical discharge machining which does not use mechanical forces

7

f = 1 mm

I= 5x10-2 mm4

f = 100 mm

I= 5x10-6 mm4

Region of interest

> 100,000 rpm

Additive Micromanufacturing

8

Laser cladding based additive manufacturing or Laser Engineered Net

Shaping (LENS)

Localized heating and rapid fusion of material delivered via co-axial

nozzle

Relatively narrow dilution & HAZ

Direct Metal Laser Sintering Systems (DMLS)

Preplaced layer of material is melted via laser

Carried out in an inert nitrogen atmosphere

Challenges Microscale Manufacturing

Subtractive

• Technology issues

– Development of robust ultrahigh

speed micromachining center

– Hybrid Laser Assisted

Micromachining

– Development of novel micro-

EDM

• Scientific issues

– Dynamic instability

– Process modeling

Additive

• Technology issues

– Laser cladding head

– Material feeding system

– Free-form deposition

• Scientific issues

– Residual stress due to

metallo-thermomechanical

phenomenon

– Clad geometry due to

dynamic spreading

– Clad dilution due to diffusion

and mass transfer

9

10

Ultra-High Speed Machine Design

Issue

• Dynamic Instability

• Tool Stiffness

• High accuracy and Precision

• Versatility-milling /drilling

• Low cost

Solution

• High Damping granite structure

• Low chip load via high speed spindles

• Optimized structure & precise stages

• High torque spindle

• High precision Z-stage and low cost

x, y stage

11

Ultra-high Speed

Micromachining

center

12

Ultra-High Speed Micromachine Design Approach

0.00E+00

5.00E-07

1.00E-06

1.50E-06

12

3

Def

orm

atio

n(m

)

Model no.

Axial

Radial

0.00E+00

2.00E-08

4.00E-08

6.00E-08

8.00E-08

1.00E-07

12

34

Def

orm

atio

n(m

)

Configuration no.

Max def

def_x

def_y

def_z

(a) Spindle tip deformation (b) Max deformation in machine tool

Design

approach

Static Structural Design

Modal and Dynamic analysis

Error Budgeting

One of the most precise machines to be designed and built in India @

IITB Can create sub-micron features on hard materials

High damping granite structure

X-Y stages with DC brushless servomotor with submicron resolution.

Pneumatically counterbalanced linear motor stage z stage: 5 nm resolution/±50 nm

accuracy

Spindle with ceramic bearing, maximum rpm 150,000, torque and power 5.6 N-cm and

800 W respectively

Commercialization in India and Israel is underway

Micromachining center

Critical

mode

Z-axis FRF

Static deflection

Scientific Challenges

• Low stiffness and high rotational speeds render the process

unstable under dynamic force variation

• Dynamic instability driven tool failure is a major impediment

13

Single DOF Dynamic Stability Model

Equation of dynamic motion

Tangential cutting force

Radial cutting force Micromilling end mill modelling

14

(V is velocity and ft is chip load)

Critical depth of cut

Prediction fails

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

30000 40000 50000 60000 70000 80000 90000 100000

Aver

age

pow

er s

pect

ral d

ensi

ty (m

m n

m2 )

Speed (rev/min)

Chatter

Stable

Chatter onset

Experimental validation: • Force dynamometer did not have the band width

• Noise in displacement and acoustic sensor

• Finally powers spectral analysis of surface topography was used

Singh et al, 2015

Probable explanation of the observation

– The spindle system damping reduces at ultra-high speeds

– Misalignment effects are amplified at ultra-high speeds

Unstable

3-D Feature Creation

100 micron channel grid on SS 316 steel

16

3-D Feature Creation

Spiral channel ball end mill (400 micron)

Spiral channel with flat end mill ( tool 100 micron) Micro-hole 100 microns

Machined micro-channel

17

Laser Assisted Mechanical

Micromachining (LAMM)

• Limitations of mechanical micromachining – Range of materials

– Tool flexural strength/machine-tool system stiffness

– Slow process

• Hybrid laser assisted mechanical micromachining (LAMM) – Integrates thermal softening with mechanical micro-cutting

– Thermal softening of workpiece results in low cutting forces

– Overcomes limitations of machine-tool system stiffness, flexural strength and low MRR

18

Laser Assisted Micromachining

L aser C ollimator Assembly

C utting T ool and Workpiece

L aser C ollimator Assembly

C utting T ool and Workpiece

m-Milling Turning

19 Thin-walled structure

Sinusoidal surface

20

Reverse micro-EDM

• Fabrication of high aspect ratio micro-electrode arrays

via spark erosion between a cathode and anode

21 6x6 array 4x4 array

30 mm- 2 mm

Measured Contact angle on Reverse Micro EDM pattern is to around 1120

Reverse EDM of Ti6Al4V for Textured Surfaces

22

23

24

Metallo-thermomechanical

effect:

Residual stress affects the

service life

Differential thermal expansion &

contraction

Volume dilation

Transformation induced plasticity

Inter granular strain due to 2nd

phase particles

Thermo-viscous effect:

Spreading affects final

clad geometry &

shape

Issues with Laser Cladding

Thermo-capillary effect:

Dilution

DamageAssessment

Tensile residual stress in clad is detrimental

Preliminary Experimental Setup

25

Z-stage

X-stage

Y-stage

Powder delivery systemLaser controller

Fiber Laser System

Fiber delivery

collimator

Beam shaper

Co-axial powder delivery nozzle

Focusing lens

Additive prototypes of SS 304

made in Machine Tools Lab, IITB

Algorithm for Moving Heat Source Modeling &

Metallo-thermomechanical Analysis in Abaqus

Read nodal temperature

(NT) at material point

Transformed

Initial melt pool

Tanner’s Law

Clad geometry

Contact angle

Start of

increment

Define the co-ordinates of the

starting point and the moving heat

source using DFLUX

AC1 ≤ NT ≤ AC3 ??

AC1: Austenization start

temperature of substrate

AC3: Austenization end

temperature of substrate

NT: Nodal temperature

NT > Vaporization

temperature (powder) ??

Melting temperature (substrate) ≤ NT ≤

Vaporization temperature (powder) ??

Yes/vaporized

No

Yes/molten

AC3 < NT < Melting

temperature (substrate) ??

No

No Yes

HAZ

Strain due to

differential thermal

expansion &

contraction (Clad)

refT

refT

th

ij

TTT

TTTT

00

_

ijm

TF

ij F 044.03

1

Volume dilation

strain

(Transformed)

ijm

mTP

TP

ij SF

FK

213

Transformation

plasticity strain

(Clad)

_Total strain, , , , ,

Stress-strain relationship,

el p th TP TF

ij ij ij ij ij ij

p th

ij ijkl ij ij ij

f

C

Ashby & Esterling, 1984

Ramesh & Melkote, 2008

End increment

Residual Stress Evolution

27

Direction of residual stress measurement

Contour of residual stress along normal direction

28

Thermal analysis

Nodal temperature

s

mmm tmRR

m

13

law) s(Tanner’droplet

of radius Calculate

13

0

13

ifs ttt

Update clad height

HR L

0

0

Approximate initial sessile

drop radius (Tanner, 1979)

2R

H

metalmolten of viscosityDynamic

tensionSurface

droplet oflength sticCharacteri

height drop Initial

volumemetalMolten

0

m

L

H

Spreading Model for Prediction of Clad

Geometry

Calculate solidification time from

temperature gradient

Calculate initial melt

pool dimension

Paul et al., 2015

Summary & Future Work

29

• Science-enabled technology development for

micromanufacturing

– 5 axis micromachining

– Robotic free-form deposition system

• Commercialization of technologies with existing Industry

linkages

• Creation of a viable micromanufacturing ecosystem in

India to bolster “Make in India” theme

Acknowledgements

• Students

– Santanu Paul

– Kundan Singh

– Rinku Mittal

– Bhaskar Bharti

– Pratik Mahambre

– Kumar Keshav

– Prakash Kattire

• Collaborators: Wenyi Yan (Monash); R. Balasubramniam (BARC);

V. Kartik (IITB); Rajkumar Singh ( Bharat Forge); Baidyanthan

and Srinivisan Iyer (Interface Design Associates); Sunil Taneja

(Axis Microtools)

30

Publications

In Area (2014-2015) 1. Kattire P., Paul S., Singh R., Yan, Wenyi, Singh R. K., “Experimental characterization of laser

cladding of CPM 9V on H13 tool steel for die repair applications” accepted to Journal of Manufacturing Processes

2. Singh, K., Kartik, V. and Singh, R, “Modeling Dynamic Stability in High-speed Micromilling of Ti-6Al-4V via Velocity and Chip Load Dependent Cutting Coefficients” International Journal of Machine Tools and Manufacture, 96(2015), pp. 56–66

3. Gupta, I., Ashraf, K., Paul, S. and Singh, R., "Characterization and Modeling of micro-scale pre-placed powder cladding via fiber laser," ASME Journal of Manufacturing Science and Engineering, 137 (3) (2015), 031019-031032.

4. Singh, K., Singh, R, and Kartik, V. “Comparative Study of Chatter Detection Methods for High-Speed Micromilling of Ti6Al4V,” Procedia Manufacturing (2015) pp. 593-606

5. Paul. S., Ashraf, K., and Singh, R., “Residual Stress Modeling of Powder Injection Laser Surface Cladding for Die Repair Applications,” ASME MSEC Conference, Detroit, 2014

More than 25 publications in micromachining and laser processing Books and Book Chapters

• Singh, R., and Srivastava, A., “Engineering Applications of Lasers,” Manuscript under preparation to be published by CRC press (In progress)

• Singh, R., and Melkote, S. N., “Laser Assisted Mechanical Micromachining,” Smart Devices and Machines for Advanced Manufacturing, co-edited by Dr. Lihui Wang and Dr. Jeff Xi, Springer-Verlag, London, 2008

• Paul S., Singh R., Yan W., “Finite element simulation of laser cladding for tool steel repair”, Lasers based Manufacturing, Springer 2015

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