To analyze the mechanical changes after CMT based WAAM on SS316L as a Single-walled and Multi-Walled.

1. Supervised by: Nitesh Kumar Sharma
Dr. S .Jerome 112116041
Assistant Prof. MME MME (2016-2020)
Analysis of Single-walled and Multi-walled
SS 316L Sample Manufactured using CMT
based WAAM

2. Wire Arc Additive Manufacturing (WAAM)
▪ This is emerging welding technology that promises to reduce part cost by reducing
material wastage.
▪ Layer by layer deposition with high deposition rate,
▪ Automatic process with the help of Robotics depending on the welding
▪ Faster Welding process compare to conventional welding
▪ High materials utilization.
▪ Producing both simple shapes and complex contours
▪ Various materials like TI, Al, Ni alloy, and Steel easily fabricated.

3. Cold Metal Transfer(CMT)
▪ The CMT machine detects a short circuit which sends a signal that
retracts the welding filler material, giving the weld time to cool before
each drop is placed
▪ It has an excellent quality on welded beads, extremely stable arc, lower
heat input
▪ Wire is fed through the system that is controlled by a computer, the
computer adjusts things such as wire feed, welding speed,
and amps going through the wire.
▪ Very little slag and spatter, resulting in a cleaner finish weld.

4. Materials and Methods
Dimensions
▪ Base Plate(SS316L) : 250 mm ×100 mm × 10 mm
▪ Single -walled : 90 mm ×10 mm × 50mm
▪ Multi-walled : 90mm ×30mm ×50mm

5. Experiment Conditions
Process parameters
▪ Substrate : SS316L
▪ Filler wire: SS316L (0.8 mm diameter)
▪ Shielding Gas : 97.5% Ar+ 2.5% CO
▪ Starting Current : 120 A, Voltage : 15.6V
▪ Finishing Current : 70A , Voltage : 14.1V
▪ Torch Speed : 300mm/min
▪ Arc Length : 10mm
▪ Different number of beads in different layer

6. Experiment Conditions
▪ single-pass and multi-layer forming tests, and a single variable was
considered in each part of the experiment. Influence of the welding
current, welding speed, and interlayer cooling time.
▪ Formed part appearance, and the microstructures and mechanical
properties were investigated.
▪ Through parameter adjustment, the effects of gradual and transient
currents between the bottom layers were studied.
▪ Surfacing welding, sanders were used to grind out the oxide , small part
of spatter generating during welding.
▪ To avoid large error, the most central stable part near the vertical wall
body was selected, and transverse and longitudinal sections with 10 mm
width were cut to prepare microstructure and hardness samples

7. Results and Discussion
Microstructural Analysis of Single-Walled Sample
Single walled (A)Base Materials (B) First layer and BM (C) Columnar and Equiaxed (D) Austenite Dendrites
All at 100X (Delta ferrite&austenite)

8. Results and Discussion
Microstructural Analysis of Single-Walled Sample
▪Microstructures of single walled in which transverse cross-sections
were studied and metallographic images reveals that the austenite
and delta ferrite.
▪The cross-section center was composed of a large number of coarse
columnar grains that grew upward in the main axis direction.
▪These features were mainly due to the different heat dissipation
conditions that the inner grains dissipated heat through the
interlayers and grew upward and perpendicular to the interlayer re-
melting line.
▪Black spots are Tiny Oxide due to insufficient cleaning during the
welding

9. Results and Discussion
Microstructural Analysis of Multi-Walled Sample
Multi-walled sample (A) Base Metal (B)Near BM, finer grains (C) Mixture of coarser and finer grains

10. Results and Discussion
Microstructural Analysis of Multi -Walled Sample
▪ Mixture of coarser and finer grains
▪ Near the Base Materials having finer grains.

11. Results and Discussion
Microhardness Analysis of Single-walled
Load :500g Indentor: Diamond Dwell Time: 20 s
Distance from Base Metal (in mm) Vickers Hardness Number ( In VHN )
0 204.8
2 194.7
4 198
6 180.1
8 187.4
10 196.4
12 193.6
14 186.2
16 193.9
18 185.5

12. Results and Discussion
Microhardness Analysis of Single walled
▪ The hardness values of the middle layers were relatively stable in the range of 193.6 -
196.4 HV, because the heat input and heat dissipation achieved equilibrium.
▪ The average hardness at the bottom was in the range of 191.93 HV, which is slightly
large.
▪ The average hardness at the top was 189.7 HV, which is slightly small. This result was
mainly obtained because the heat accumulation affected the microhardness of the
deposited samples. At room temperature, the bottoms of the samples close to the
substrate could dissipate heat through the substrate during solidification and cooling.
▪ In addition, as several layers were deposited continuously above the bottom, the
bottom sustained several transient thermal cycles with different heat amplitudes.
Therefore, the bottom hardness was also slightly higher than that of the upper part. In
this test Diamond Inventor were used.

13. Results and Discussion
Ferrite Number Analysis
▪ Ferrite number is the amount of retained delta ferrite into the weldments
of austenitic stainless steel, which may support mechanical and corrosion
properties. It is measured by Ferritoscope.
▪ A correct ferrite measurement helped to avoid both solidification cracking
and corrosion in stainless steel.
▪ From the below table of ferrite number, it is can be stated that Multi-walled
sample are having slightly higher amount of ferrite contents than Single-
walled due to high heat input and solidification.
▪ There was a little more amount of ferrite content in the vertical sample in
case of Single -walled. Same with the case of Multi-walled sample in which
vertical direction of sample is having more amount of ferrite contents

14. Results and Discussion
Ferrite Number Analysis
Sample Ferrite Number
Single –Walled Sample 1 2.654
Sample 2 3.3153
Multi- Walled Sample 1 3.557
Sample 2 3.8875

15. Conclusions
▪ Hardness is mainly determined by the heat effect. As the high cooling rate and
latter layers’ heat effect acted on the bottom part, the bottom hardness was
slightly higher than those of the middle and upper parts of the deposited
samples.
▪ We observed that Multi-Walled samples have higher hardness than Single-
Walled Sample due to high value of heat input
▪ The average hardness value for the single -walled was approximately 192.06
HV and 207 HV respectively
▪ Microstructure of the single walled consists of Delta ferrite, Austenite phase
and Dendritic Austenite was observed in columnar and equiaxed grains.
▪ Finer grains were observed in Multi-walled sample having mixture of finer
and coarser grain.
▪ Observed higher ferrite content in Multi-walled sample than Single-walled.

16. References
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17. THANK YOU