1. Weld Types – Butt Joint with Backing

2. Butt Joint with Backing
A Butt Joint with Backing is the basis for many automotive structural sectioning welds.
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3. Butt Joint With Backing Example
Rail ready for welding.
Right and left rail section with plug holes and center insert.
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4. Butt Weld with Backing
You should now have an understanding of what a butt joint weld is and where it is used.
The next step is to tune the welder and perform a butt weld that will be evaluated visually and destructively.
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5. Butt Joint with Backing
Joins two pieces of closely butted metal with a backing piece.
Requires a Root gap of 3 metal thicknesses.
Too small of a root gap will limit penetration.
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6. Fit Up and Clamping Root Gap Two Top Pieces
Backing is out of the same metal
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7. Butt Joint with Backing
Set two coupons on top of the backing
Set the proper root gap
Mark 1” to 1.5” in the center
Secure coupons for weld
1” to 1.5”
Root Gap 3x metal thickness
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8. Gun Position
The proper gun to work piece for a butt joint with backing is 90 degrees to the surface. 90 90
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9. Tune the Welder
Make sure to “Tune the Welder” by making practice welds on the same material that will be used for the final weld.
Make the necessary voltage and wire speed adjustments and check for proper penetration before beginning the final weld.
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10. Lab Assignment Print off the Butt Weld “Task Performance Sheet”.
Set up and tune the welder.
Set up and mark the coupons for the weld.
Perform the Butt with Backing Weld.
Visually inspect the weld.
Destructively test the weld.
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11. Check for penetration on back of coupons
Visual Inspection
Length = 1” to 1.5”
Melt Through = 1/16” max.
Bead width = 3/16” to 3/8”
Height = 0” to 1/8”
Check for penetration on back of coupons
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12. Using I-Car’s WQT Gauge
I-Car has provided a gauge to help in visually inspecting welds for:
bead length
width
height
penetration
defects
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13. Using gauge to check:
Bead length
Bead Height
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14. Gauge also checks:
Weld Penetration
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15. Record The Results
After the visual inspection is complete record the results on the task performance sheet and have the instructor verify your results.
Now the destructive test will need to be performed.
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16. Destructive Weld Test Bend the top pieces toward each other.
Clamp in Vise.
Chisel off backing piece.
There should be continuous fusion on all three pieces.
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17. Notice the torn section – This is a sign of a good weld
Destructive Test
Notice the torn section – This is a sign of a good weld
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18. Final Weld
When the welds pass the visual and destructive test observe the final voltage and wire speed setting.
Record the destructive test results on the task performance sheet.
Complete your final weld series in the flat vertical and overhead position.
Turn these in for grading.
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19. References
Miller Electric Mfg. Co. Education
Lincoln Electric Co. Lincoln Welders
Inter Industry Conference on Automotive Collision Repair. I-CAR Online Training
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