The objective of the research is to study the machinability of 3D printed materials and provide fundamental insight into the material removal mechanism. Specifically, this study aims to investigate how the porosity in 3D printed materials can affect its machinability in terms of cutting force, surface quality, and tool wear. It is believed that machining response during the subtractive cycle of the process could be used to provide feedback on printing quality for the upcoming addictive cycle to improve the quality of the parts. This could be achieved by the machinability studies of 3D printed parts with varying degrees of defects such as porosity to obtain a one-to-one correlation between the machining response, e.g., cutting forces and vibrations, and the defect concentration e,g, porosity. The present study is limited to the most extensively used Titanium alloy-6Al-4V which is 3D printed by the Selective Laser Sintering process. Micro-end milling is used as the machining process to conduct the machining experiments.

1. Machinability Study Of 3D printed Ti-6Al-4V
IIT Bombay
Sajjad Ahmad

2. Content
 Background and Motivation
 Link Slide
 Literature Review
 Research Gap
 Research Objectives and Scope
 Preliminary Experiment
 Effect of porosity on machinability of 3D printed Ti-6Al-4V
 Conclusions
 Broader application of the research
 Recommendations and Future Work
Machinability Study of 3D printed Ti-6Al-4V 2

3. Background and Motivation
Engine Block (Curtesy : Fitnik ) Prosthetics (Curtesy : Imaginarium India Pvt Ltd)
Fuel Nozzle (Curtesy : GE) Turbine Runner blades (Curtesy : GE)
Machinability Study of 3D printed Ti-6Al-4V 3
3D Printed Parts

4. Background and Motivation
Titanium Applications
Machinability Study of 3D printed Ti-6Al-4V 4
Oil and Gas Industry
Curtesy : NeoNickel
Chemical Industry
Curtesy : CSIR
Marine Industry
Implants
SR-71 Blackbird
Curtasy:USAF
Turbine Blades
Curtesy: www.azon.com
Spoiler actuator
Curtesy : www.ato.ru
Curtesy : FDA
Curtesy : www,perrymanco.com
Curtesy : www.pngtree.com
Curtesy : FDA

5. Near-net shape-Impeller
(Curtesy: GEFERTEC)
Porosity
Poor surface finish
(Curtesy: NASA)
Background and Motivation
Melt ball formation
(Curtesy: Sames et.al)
Delamination
(Curtesy: Sames et.al)
Machinability Study of 3D printed Ti-6Al-4V 5
Defects

6. Background and Motivation
Milling Grinding Hybrid Manufacturing
HIP
• Milling
• Grinding
• Hybrid Manufacturing
• Hybrid Manufacturing
• Hot Isostatic Pressing (HIP)
To address
Dimensional inaccuracy
Surface quality
Porosity
Lack of fusion
Machinability Study of 3D printed Ti-6Al-4V 6
Post-Processing

7. Background and Motivation
• Cause : Incomplete filling near
perimeter
• Remedy : Increase flow at the point
of intersection
Sub-perimeter voids
FusedDepositionModeling
• Cause : Inconsistent material flow
• Remedy : Use better gripping
rollers
• Cause : Incorrect road width
selection
• Remedy : Select closest width with
increased final flow
Inter-road voids & road thickness
variation defects
Core voids
Curtesy : Bland et. al
SEM shows porosity and particles which
are not fused (Curtesy : Bland et.al)
20µm
• Causes : Entrapement of gas during
solidification process and improper fusion
of particles which leads to gap between the
particles
• Remedies : Adjust scan speed, laser power,
Double scanning each layer
Porosity
SelectiveLaserSintering
Machinability Study of 3D printed Ti-6Al-4V 7
Porosity Causes

8. Link slide
3D printed part Poor surface finish
Material defects
Dimensional inaccuracy
Machining
is required
Discontinuity of internal microstructure
Uneven stiffness distribution
Anisotropy
Fluctuating cutting forces
Process instabilities
Inferior machined surfaces
Rapid tool wear
Effect
Good Surface quality
Minimize Tool wear
NeedStudy effect of porosity
on machining response
Achieve
Other
application
In-situ prediction and control of
porosity in Hybrid manufacturing
Machinability Study of 3D printed Ti-6Al-4V 8

9. Literature Review – Machining porous material
Porous Stainless steel
Porous stainless steel microstructure (Curtesy : Liu, Z et.al)
No. Cutting Speed
(m/min)
Axial depth of cut
(µm)
Feed/ tooth
(mm/tooth)
1 50 10 0.25
2 75 20 0.5
3 100 30 0.75
4 125 40 1.0
Main results
Tool wear
Surface topography
• It was observed that less burrs are formed at higher speed as
compared to the machining at lower speed
• The burr formation was minimum at the cutting speed of 75
m/min
• As the axial depth of cut increases than more burrs are formed
and are elongated
Effect of cutting parameters on cutting forces
• As the cutting speed and axial depth of cut increases than the
cutting forces first increases than decreases, but the cutting
force increases with the increase in feed rate
• diffusion wear
• micro-cracks
• Oxidation
• adhesive wear
Machinability Study of 3D printed Ti-6Al-4V 9

10. Literature Review – Machining porous material
Titanium Foam
Main results
• Porosity increases the mean cutting force decreases but
there is large oscillations in the values around the mean
force
• The correlation between porosity and cutting forces is
noti100%
• Material removal can also occur due to micro particle
breakout/separation, inthat case, cutting forces
deviate from their regular pattern of variation
Curtesy : Wei et.al
Machinability Study of 3D printed Ti-6Al-4V 10
Curtesy : Wei et.al

11. Research Gap
• Machining of 3D printed material with different level of porosity remains unexplored in
terms of cutting force signature, machined surface morphology and tool wear.
• Porosity is not characterized
Machinability Study of 3D printed Ti-6Al-4V 11
• Cutting mechanics and tool wear is not analyzed deeply

12. Research Objectives and Scope
Micro End Mill
Objective
How ? Porosity affect machinability
of 3D printed part
In terms of • Cutting force
• Surface quality
• Tool wear
Application Machining response can be
used as feed back mechanism
For that
One-to-one correlation
Scope
Material
Tool
3D printed Ti-6Al-4V by SLS
WC Micro End Mill (500µm)
1,2&3-3D printed Ti-6Al-4V;4-Conventional Ti-6Al-4V
1 2 3 4
Machinability Study of 3D printed Ti-6Al-4V 12

13. Preliminary Experiment
Parameters
Feed/flute
(μm)
Speed
(rpm)
Depth of cut
(μm)
0.0625 25000 50
0.125 25000 50
0.25 25000 50
0.5 25000 50
1 25000 50
2 25000 50
Conventional Ti-6Al-4V
Four fluted End Mill
Experimental
Methodology
Material
Tool
Conventional Ti-6Al-4V
WC Micro End Mill (500µm)
Machinability Study of 3D printed Ti-6Al-4V 13

14. Preliminary Experiment
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
MeanForce(N)
Feed/flute (μm)
Exp 1
Exp 2
0
0.5
1
1.5
2
2.5
3
MeanForce(N)
Feed/flute (μm)
Exp 1
Exp 2
Force in cutting direction Force in feed direction
0
0.2
0.4
0.6
0.8
1
1.2
1.4
AverageRoughness(μm)
Feed/flute (μm)
Ra value for
Exp1
Ra value for
Exp2
Ra value of slots
Conclusions
• At feed of 0.5 µm the forces are within limits i.e. it is not too
low nor is too high
• Surface quality is comparatively good at 0.5 µm
Results
Machinability Study of 3D printed Ti-6Al-4V 14

15. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Experimental Material
• EOSINT M 280 machine with 200W ytterbium (Yb) fiber
laser
• EOS Titanium Ti64ipowder
• Straight lines rotated by 700 are used for melting each layers
• Samples are cubical having 20mm sides
• Once the samples were built they were removed from the
build plate without any post processing heat treatment so as
to study the samples in as-built condition EDS of (a) 3D printed (b) Conventional
sample
1 2 3 4
1,2&3-3D printed Ti-6Al-4V;4-Conventional Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 15
(a)
(b)

16. Effect of porosity on machinability of 3D printed Ti-6Al-4V
SEM image of End Mill
Tool specification
• Two flute WC End Mill
• Edge Radius : 1-3µm
• Tool diameter : 500µm
• Shank diameter : 3mm
• Helix angle : 300
Cutting Edge
Tool Diameter
Rack Angle
Tool specification
SEM image of micro End Mill
Machinability Study of 3D printed Ti-6Al-4V 16

17. Workpiece
Micro End Mill
Spindle
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Experimental setup
Dynamometer
3 axis CNC machine
• Four trials are done on each block with a new tool for
each trial of length 20mm
• The real time orthogonal cutting force data are captured
for each trial
• After machining the images of the blocks are taken
from Alicona Optical Profilometer and
Stereomicroscope to calculate the average roughness
and the area porosity respectively
• Further the SEM of tools after experiments are done to
determine the tool wear.
Experimental Design
Speed
(rpm)
Feed/tooth
(μm)
Depth of cut
(μm)
Porosity
(%)
25000 0.5 50 0,20,50,70, 80
Machinability Study of 3D printed Ti-6Al-4V 17

18. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Porosity =
Number of black pixles
Total Number of pixles
Area Porosity Measurement
(a) Cropped images from the block
(b) Converted cropped images to binary images
(b)(a)
Material Void
Slot Area Porosity Measurement
Porosity Measurement
X 100
Machinability Study of 3D printed Ti-6Al-4V 18

19. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Characterization of porosity
20% 50% 70% 80%
Machinability Study of 3D printed Ti-6Al-4V 19
Problem faced while identifying pores centroid
• For 20% and 50% there were no significant problem
• For 70% and 80% there are interconnected pores so
separating them was a challenge

20. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Characterization of porosity
Image from Stereomicroscope Median filter and Binarization
Connection of the centroidsCentroid of the pores (red dots)
80%
Machinability Study of 3D printed Ti-6Al-4V 20

21. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Characterization of porosity
Centroids of the pores are shown in red dots
18% 53%
61% 72%
18% 53%
61% 72%
Machinability Study of 3D printed Ti-6Al-4V 21

22. Effect of porosity on machinability of 3D printed Ti-6Al-4V
Characterization of porosity
P1= Area porosity
P2= Number of pores
P3= Average distance between the pores
Pc= Porosity coefficient
Pc =
1000 ∗ P1
P2 ∗ P3
Porosity coefficient
18% 53%
61% 72%
Machinability Study of 3D printed Ti-6Al-4V 22

23. Results and Discussion
Effect of porosity on machinability of 3D printed Ti-6Al-4V
20% 50%
70%
80%
Force signature of conventional material
70%
Cutting Force Analysis
Machinability Study of 3D printed Ti-6Al-4V 23

24. Results and Discussion
Cutting Force Analysis
Effect of porosity on machinability of 3D printed Ti-6Al-4V
70%Machinability Study of 3D printed Ti-6Al-4V 24

25. Correlation of cutting forces and area porosity
Cutting force thresholding
No of flutes of tool = 2
Tool rpm = 25000
Acquisition frequency = 10kHz
Cutting frequency =
No. of flutes ∗ tool rpm
60
= 833.33
Number of data to draw the envelop(np) =
Acquisition frequency
Cutting frequency
=
10000
833.33
= 12
np= 500
np= 12
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 25

26. Cutting force thresholding
The mean forces are calculated taking a
window of size of tool diameter i.e. 500μm.
Mean of the peak and the valley force data
points are taken to calculate the difference of
the peak and valley forces
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 26
Correlation of cutting forces and area porosity

27. Difference of mean of peak-valley forces
Method
Correlation
coefficient
Force Thresholding 0.872
Difference of P-V 0.897
Cutting force thresholding
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 27
Correlation of cutting forces and area porosity

28. Frequency Analysis
0% 20% 80%
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Rotational
Cutting
Rotational
Cutting Cutting
Rotational
Machinability Study of 3D printed Ti-6Al-4V 28

29. Tool Wear
Cutting edge
Chipped out
SEM of the tool (a) before and (b) after experiment with continuous material
Weared Cutting Edge(a) (b)
SEM of the tool (a) before and (b) after experiment with 3D printed material
(a) (b) Weared Cutting edge
Chipped end surface
Broken cutting edge
Cutting Edges
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 29

30. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0% 20% 50% 70% 80%
AverageRoughness(µm) Porosity
Average Roughness Measurement
Conventional Ti-6Al-4V
3D printed Ti-6Al-4V
Effect of porosity on machinability of 3D printed Ti-6Al-4V
Machinability Study of 3D printed Ti-6Al-4V 30

31. Conclusions
Surface Analysis
-0.1
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
0% 20% 50% 70% 80%
AverageRoughness(µm)
Porosity
Cutting Forces
Machinability Study of 3D printed Ti-6Al-4V 31

32. Conclusions
Tool Wear
ChippingEdge wear
Broken cutting edge
Flank wear
Method
Correlation
coefficient
Force Thresholding 0.872
Difference of P-V 0.897
Cutting force and Porosity correlation
Machinability Study of 3D printed Ti-6Al-4V 32

33. Broader Application of the Research
Porosity Monitoring
In-situ
1. In-line monitoring
2. On-line monitoring
Ex-situ
1. At-line monitoring
2. Off-line monitoring
A schema of metrological approaches in 3D printing (Tofail et.al)
Machinability Study of 3D printed Ti-6Al-4V 33

34. Recommendations and Future Work
1. Aquatics analysis may help in determining the porous and non-porous region and also variation in porosity.
2. Altering the machining parameters such as feed, speed and depth of cut can further give some highlight on the
effect of porosity on the machining response in terms of cutting forces, surface roughness, vibration and tool
wear.
3. A detailed analysis of the machining frequency with time is required for detecting any tool wear or some other
phenomenon coming into play.
4. The effect of cutting fluid on tool wear is needed to be studied.
Machinability Study of 3D printed Ti-6Al-4V 34