WELDING FIXTURES 1

[imaz]

Hi everyone. I am new here in this company and I one of my duties is making fixtures for fabrication. We mainly use hot rolled and high strength steel in all our parts that are used to make the final welded part.Our fixtures are mainly tack fixtures. However we have to compare our final welded parts to the engineering designed ones. After we weld the parts they are send to CMM in QC, that issues a rejection or accepted parts report. If accepted the fixture is welded and send to production. If rejected we have to try to make some adjustement to the fixture and redo the whole process again.I have a problem with the existing process and QC does not agree with me.
I want the tacked parts to be accepted so we can have a reference for adjustments. What do you guys think? Any other suggestion is welcome. Anyone out there make fixture under different procedue?

Thank you guys.

MT
Manufacturing eng.

 

[CWIC]

The final welded parts will provide more info than a tack welded part. The welded part will have experienced some degree of dimensional shrinkage as the welds have cooled. This will be apparent if you measured a welded and tack-welded part in the CMM.

If there are substantial dimensional variations from 2 parts welded in the same fixture, then I would approach the reviewing welding sequence and welding parameters - provided the fixture has a history of producing accepatble weldments. If 2 (or more) welders are are joining sub-assemblies in the same manner using the same heat input, the parts should be identical.

Having worked in an aerospace environment myself, most weldments are fabricated in fixtures which have been inspected and re-inspected about every 6-12 months depending on the part. Many fixtures also had a set-up procedure and welding sequence documentation. This is to ensure repeatability.

Only a few large fixtures required disassembly and pretensioning of the parts to be welded to counter weld shrinkage. Even these (through inspection & trial & error) had the adjusment required factored in to maintain the repeatability. The parts came out the same regardless of who performed the welding. We often worked to tolerances of 0.030&quot; or less. These included very small parts (<6&quot; in length) and parts that were relativley large (wing spars for a military transport plane).

 

[imaz]

Hi again. I just want to add that we inspect the welded parts and then make correction to the fixtures.Any distortion to the parts used is hard to predict.I was thinking that the tacked parts,ounce inspected by QC, will give us some information to the deviation due to distortion.Our tolerances are +/-0.030&quot;.


We usually recheck our fixtures for every x-parts welded.

Thank you again.

MT