Weldment

[Anonymous]

I have an example of a lifting lug assy consisting of the lug and a reinforcement pad.The lug will be welded to the pad and then the whole assy welded to a larger fabricated assy.

The question is ! if i convert this into a weldment precisely what does this mean, does it mean that the two parts are fused together as perhaps as if it was a casting.

Until i create a weldment  then i cannot use the weld tools ,is this correct.

If i create a weldment, then show some welds and perform some analysis to see how the assy reacts with a force about the lug hole with a constraint around the perimeter of the pad, this should tell me if the welds are strong enough.

This approach raises the question of whether its the lug to pad welds which are being analysed or the fusion between the lug and pad (welment) or even both?

Confused ?

[Roelof.Feijen]

Hi @Anonymous,

The question is ! if i convert this into a weldment precisely what does this mean, does it mean that the two parts are fused together as perhaps as if it was a casting.

No. You will still have two parts and a BOM.

Until i create a weldment  then i cannot use the weld tools ,is this correct.

Yes, this is correct.

This approach raises the question of whether its the lug to pad welds which are being analysed or the fusion between the lug and pad (weldment) or even both?

It is very hard to validate welds in an analysis. Ask yourself if you want to validate weld or determine the weld size.

There is a good presentation on Autodesk University "A Job Weld Done”: Getting to the bottom of modeling welds in FEA… Debunking common perceptions." http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2015/nastran-in-cad/im11105#chapter=0

[blair · Accepted solution]

To add to this, within Inventor, a Weldment becomes a "fixed/inseperable" assembly. You can't use the "Flexible" option or demote items within the weldment to other assembles.

As posted, the best way to test welding, is to test the welders. This means having them weld test coupons which are sent for destructive testing or to X-Ray welds or Mag-Particle test. Nothing beats pulling random items and performing destructive testing if costs allow.

FEA analysis will only tell you if a perfect weld will fail or pass, it won't tell you anything about the actual weld. Are you dealing with a "Cold-Lap" weld with no penetration (only the fillet portion) or does the weld have proper penetration with mixing of the parent and filler materials at the weld root.

[Anonymous]

Thanks Blair
I would presume that because this is a pressure vessel part, the welders also being coded that proper penetration would be achieved,
The design of lifting lugs has always been a contentious issue and it's also a case of whether the people doing the lift use the proper
equipment i.e. shackles etc. This is a good reason to create a proper lifting procedure showing the various pieces of equipment required.
Of course again its whether its followed or not , one could argue that the responsibility ends with the design of the lifting lug, once In the field
it's up to the riggers to do their part properly.
As they say " you can lead a horse to water but you can't make it drink".
Regards

[Anonymous]

Thanks Roelof

I will have a  look at the link.

In the past this would have been a calculation carried out by hand using the weld throat thickness, yield strength of the weld material and total run of weld.

To some degree any FEA complicates the process what with singularities etc, it really is the interpretation of the results which is the hardest part.

Regards

Martin