Weld Types – Butt Joint with Backing

Butt Joint with Backing

A Butt Joint with Backing is the basis for many automotive structural sectioning welds.

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Butt Joint With Backing Example

Rail ready for welding.

Right and left rail section with plug holes and center

insert.

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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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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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Fit Up and Clamping Root Gap

Two Top Pieces

Backing is out of the same metal

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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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Gun Position

The proper gun to work piece for a butt joint with backing is 90 degrees to the surface.

9090

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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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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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Visual Inspection

Length = 1” to 1.5”

Bead width = 3/16” to 3/8”

Height = 0” to 1/8” Check for penetration on back of coupons

Melt Through = 1/16” max.

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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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Using gauge to check:

Bead length Bead Height

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Gauge also checks:

Weld Penetration

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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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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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Destructive Test

Notice the torn section – This is a sign of a good weld

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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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References Miller Electric Mfg. Co. Education.

http://www.millerwelds.com/education/library.html, 2006.

Lincoln Electric Co. Lincoln Welders. http://www.lincolnelectric.com/, 2006.

Inter Industry Conference on Automotive Collision Repair. I-CAR Online Training. http://www.i-car.com/, 2006.

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