Thesis proved semi-automated spot welding tip dressing cell technology would provide a return on investment in a year's time. While maintaining spot welding shear strength and hardness values within acceptable range.

1. © Copyright 2015 David Palmer
Industrial Partner: SKD Automotive
Liaison: Ian Cross
Supervisor: Prof. T. North
By: Tom Broumas and David Palmer
University of Toronto
Faculty of Applied Science and Engineering
SPOT WELD TIP DRESSING
© Copyright 2015 David Palmer

2. Resistance Welding at SKD
 High production in stamping and welding
 Canadian, American and Mexican based plants
 Largest clients are:
Ford
General Motors
Daimler Chrysler
Honda
Mitsubishi
© Copyright 2015 David Palmer

3. Inefficient Comparison
 Robotic Mig Welder
 Arc Welder
 Spot Welding Cell
 Some cells can produce
5,000 to 10,000 welds per
pair of electrode tips
 Resistance Spot Welding
Cell can only produce
1200 welds per pair
© Copyright 2015 David Palmer

4. Improving Tip Life
 Interest in investment
of Spot Weld Tip
Dressing Equipment
 Retails for $3000
 Must be profitable and
economical
 Return on investment
in one year
© Copyright 2015 David Palmer

5. Jeep Liberty
© Copyright 2015 David Palmer

6. Tail Light Assembly
© Copyright 2015 David Palmer

7. Objectives
Test and compare:
 Hardness strength of the copper tips
 Shear strength of the welded joints
 The performance of the cells with and
without the tip dressing equipment
 Cost saving analysis
 Improve the tip life
© Copyright 2015 David Palmer

8. Resistance Spot Welding
Advantages of
Spot Welding
 Quick and Efficient
 Cost and Energy
 Pressure Instead of
Flux
 Easy Automation
 Adequate in Welding
Thin Sheets
© Copyright 2015 David Palmer

9. Copper Tips
SKD currently uses Copper as their tip electrode because they are:
Relatively cheap
Good welding quality
Good electrical conductivity
It will not easily stick to the metal panels being welded
© Copyright 2015 David Palmer

10. The Welding Process
 Preweld Interval
 Clamping
 Pressure = 900lbs
 Preheat
 Weld Interval
 Upslope
 Heat Time
(Impulse)
 Cool Time
 Post weld Interval
 Down slope
 Quench/Temper
 Hold
© Copyright 2015 David Palmer

11. Possible Benefits of Tip Dressing
 Maintain Original Geometry
 Reduce Downtime
 Reduce/Eliminate Steppers
 Less Overall Wear and Tear
 Extend Tip Life
© Copyright 2015 David Palmer

12.  Hardness Test  Shear Test
Testing Procedures
© Copyright 2015 David Palmer

13. Standardized Shear Test
 Must limit re-orientation of sample
 Concentrate stress on weld, not metal
 Ensure sample symmetry
© Copyright 2015 David Palmer

14. Teardown Test
 Performed by operators at SKD using a
jackhammer
 The nugget diameter > 4.1mm
© Copyright 2015 David Palmer

15. © Copyright 2015 David Palmer
Results and Discussion
© Copyright 2015 David Palmer

16. First Test – Regular Operation
 To develop a method and procedure for
testing weld samples
 To identify any trends that might exist
 To observe the extent of degradation of the
copper tips
 To establish a standard which can be used
as reference for future
© Copyright 2015 David Palmer

17. Stepper Chart (Part 1)
Stepper Current Plot for Different Welding Experiments
50
55
60
65
70
75
0 200 400 600 800 1000 1200
Number of Welds
%AppliedCurrent(A)
Running to 200 Parts
© Copyright 2015 David Palmer

18. © Copyright 2015 David Palmer
Max Load in Shear vs. Part
Number Graphs
(for regular operation)
© Copyright 2015 David Palmer

19. Normal Operation
Weld #6 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Normal Operation
Weld #5 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Normal Operation
Weld #1 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Normal Operation
Weld #4 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Normal Operation
Weld #3 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Normal Operation
Weld #2 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
1 2 52 53 100 150 200
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Weld
#3
Weld
#4
Weld
#5
Weld
#2
Weld
#6
Weld
#1
© Copyright 2015 David Palmer

20. Weld Designations
© Copyright 2015 David Palmer

21. Hardness Graph (Part 1)
Hardness Chart for Copper Tips Under Different Testing
Conditions
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
RockwellBHardness
Average Values 80.1 60.3
Unused 200 parts produced
© Copyright 2015 David Palmer

22. Optical Photomicrographs (Part 1)
Unused
After 200
parts
@ 12 M@ 6 M
@ 6 M @ 12 M
© Copyright 2015 David Palmer

23. Second Test – Extending Tip Life
 To examine whether the operation can
produced more than 200 parts per pair of
copper tips
 To observe the behavior of the copper tips
with this additional stress
 To study if weld quality will diminish
significantly
 (Note): After production of part #213, weld
quality was discovered to decrease. To
compensate, current was increase by 1%
manually (160 amps)© Copyright 2015 David Palmer

24. Stepper Chart (Part 2)
Stepper Current Plot for Different Welding Experiments
50
55
60
65
70
75
0 200 400 600 800 1000 1200 1400 1600 1800
Number of Welds
%AppliedCurrent(A)
Running to 200 Parts
Running to 300 Parts
© Copyright 2015 David Palmer

25. © Copyright 2015 David Palmer
Max Load in Shear vs. Part
Number Graphs
(for extending tip life)
© Copyright 2015 David Palmer

26. Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #1 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
5.0
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #2 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #3 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #4 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #5 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
5.0
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
Without Copper Tip Dressing
Weld #6 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
215 221 225 254 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Weld
#1
Weld
#2
Weld
#3
Weld
#6
Weld
#5
Weld
#4
© Copyright 2015 David Palmer

27. Hardness Graph (Part 2)
Hardness Chart for Copper Tips Under Different Testing
Conditions
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
RockwellBHardness
Average Values 80.1 60.3 50.0
Unused 200 parts produced 300 parts produced
© Copyright 2015 David Palmer

28. Optical Photomicrographs (Part 2)
8 mm
After 300 Parts
@ 12 X M @ 25 X M
© Copyright 2015 David Palmer

29. Optical Photomicrographs (Part 2)
After 300 Parts
Side-view of Copper Tip @ 12 X M
© Copyright 2015 David Palmer

30. Final Test – Application of Tip
Dressing
 To observe how tip dressing alters the
surface properties of the copper tips
 To compare the difference in down time of
changing tips vs. tip dressing
 To study if tip dressing improves the quality
of the welds
 (Note): Due to the difficult demand in setting
up a tip dresser on an operational robot, SKD
preferred to use on-site equipment for this
experiment (a manual tip dresser was applied
to the copper tips).
© Copyright 2015 David Palmer

31. Stepper Chart (Part 3)
Stepper Current Plot for Different Welding Experiments
50
55
60
65
70
75
0 200 400 600 800 1000 1200 1400 1600 1800
Number of Welds
%AppliedCurrent(A)
Running to 200 Parts
Running to 300 Parts
Running to 200 Parts,
Apply Tip Dressing, Run
Addtional 100 Parts
© Copyright 2015 David Palmer

32. © Copyright 2015 David Palmer
Max Load in Shear vs. Part
Number Graphs
(for application of tip dressing)

33. Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #1 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #2 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #3 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #4 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #5 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Production Past 200 Tail Light Assemblies
With Copper Tip Dressing
Weld #6 Shear Strength vs. Production Number
2.0
2.5
3.0
3.5
4.0
4.5
206 225 250 275 299
Tail Light Assembly Production Number
WeldMaxLoad(kN)
Weld
#1
Weld
#2
Weld
#3
Weld
#4
Weld
#6
Weld
#5
© Copyright 2015 David Palmer

34. Hardness Graph (Part 3)
Hardness Chart for Copper Tips Under Different Testing
Conditions
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
RockwellBHardness
Average Values 80.1 60.3 50.0 73.0 69.9
Unused
200 parts
produced
300 parts
produced
200 parts
produced, with
300 parts
produced, with
© Copyright 2015 David Palmer

35. Optical Photomicrographs (Part 3)
Dressed
6.5 mm
7 mm
@ 12 X M
@ 12 X M
@ 25 X M
@ 25 X M
After 100
additional
parts
© Copyright 2015 David Palmer

36. Optical Photomicrographs (Part 3)
 Left side appears
similar to tip that
produced 200 parts
 Right side
appears similar to
tip thatproduced 300 parts
© Copyright 2015 David Palmer

37. $$
$
$$
$
© Copyright 2015 David Palmer

38. Cost Savings Analysis
 Regular Operation (9 tip changes per day)
 total cost of replacing tips per year
= $6570.00
 money lost due to down time per year
= $3285.00
 Total cost per year
= $9855.00
© Copyright 2015 David Palmer

39. Cost Savings Analysis (cont’d)
 Minimal Tip Dressing (3 tip changes per day)
 total cost of replacing tips per year = $2190.00
 money lost due to down time per year = $1168.00
 Total cost per year = $3358.00
 Maximum Tip Dressing (2 tip changes per day)
 total cost of replacing tips per year = $1490.00
 money lost due to down time per year = $ 815.17
 Total cost per year = $2305.17
© Copyright 2015 David Palmer

40. Conclusion
 Tip dressing is a viable way of improving the
spot welding process
 More cost-effective and efficient, without the
need of extra energy
 Automated processes are preferred over
manual dressers (eliminates human error)
 SKD can save an estimated $6500 to $7500 per
year
© Copyright 2015 David Palmer

41. Acknowledgements
Ian Cross
Prof. W. Curlook
John Callaway
Farnoush Heidarzahoh
John Di Bello
Prof. Tom North
Mike King
© Copyright 2015 David Palmer