stud weld - continuous breakage 1

[dogbural]

Hi,
I have a plate with studs welded. Some of the studs ended up breakage while applying torque.
Looking at the broken face, would it be any possible cause for this failure?
Supplier also checked the parts by applying the torque. In their end, the parts are all conforming. But sometimes, we faced such failure.

 

[desertfox]

Hi dogbural

First question are the studs breaking off the part they are welded too or just on the threaded part?
The picture looks to me as though failure is in the the threaded portion of the stud but not 100%, if I am right then I would say the threads are failing from being over tightened however you have supplied no information about what torque value you are using and or the tightening procedure. Can you give us any more information please?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dogbural]

Hi desertfox

Actually it broke off at the welded point.
They checked it with a torque of 5 while we apply 4.5nm.
What would be the possible reason? Contamination on welded surface? Or just poor welding?

It does not happen all the time but happens time to time.

 

[kingnero]

AT first sight, incorrect weld settings. Looks like not enough fusion all around the surface of the stud.
Contaminants could certainly be part of the reason, but I suspect insufficient capacitor discharge as main culprit.
Also, do you have a good spring value (the force that pushes the stud to the surface)?

 

[david339933]

What material, how was it welded?

 

[r6155]

Any photo before breaking up?, dimensions ? , sketch? ...?

Regards

 

[3DDave]

A typical acceptance test for a weld stud is to hammer it to 90 degrees and not come loose.

There is something severely wrong with the weld process, probably failure to clean the surface or some plating?

Tough to tell from a picture of only one part of the problem.

 

[desertfox]

Hi dogbural

So what do the manufacturer’s state the maximum torque for that stud is and what is the stud size?
So if it failed at the welded interface then that clearly suggests a problem with the welding/welding process, clarify what you mean by they test at 5 but you torque to 4.5Nm?



“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dogbural]

Hi all,

M6x20 stud on zinc plated steel grade 250 (thickness 2mm).

Supplier apply 5.71Nm according to ISO 898/1, while we apply 4Nm.

3DDave mentioned hammering to 90 degree as a typical test. Do you think this is better than checking with a torque?

now supplier propose a self-clinching. would it be a good idea?

 

[3DDave]

Acceptance of the process by bending, not of the final product. It might be tough on 2mm plate with a stud 3X of diameter over that thickness.

Those studs look like the welds were incomplete - again, what does the plate look like?

ISO 898/1 does not appear to apply to weld studs. Possibly ISO 14555:2017 Welding — Arc stud welding of metallic materials

 

[desertfox]

Hi dogbural

Yes if you can adapt your process self clinching would be good.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[MintJulep]

M6x20 stud on zinc plated steel

There's your problem.

Zinc causes all sorts of problems when welding, including porosity and susceptibility to cracking.

 

[weldstan]

Need to remove the zinc befor stud welding.

 

[r6155]

Why don't you look at ASME IX?

Regards

 

[MintJulep]

Why don't you look at ASME IX?

Because not everything is a boiler or a pressure vessel.

 

[3DDave]

ASME IX does seem like overkill, but there don't seem to be other ASME standards for arc discharge stud welds. $700 seems rather steep; however ISO 14555 isn't particularly cheap at about $225. If this is a life-critical item then sure, money is no object.

If the zinc can be removed cheaply, the weld studs are faster and cheaper and should be less prone to other production problems than self-clinching, but there's room in the world for both. Self clinching preserves the most zinc, but needs good control of hole diameter and depends far more on the strength of the plate. Welding requires uniform power and uniform pressure and uniform cleaning of the surface to get uniform results.

 

[r6155]

@ MintJulep

As an example, ASME IX also applies to:

AWS Dl 4.1 Specification for Welding of Industrial and Mill Cranes and Other Material Handling Equipment:

AWS D1.1 Structural Welding Code-Steel

Regards

 

[mfgenggear]

Op
As others have stated zinc had to be remove before welding. All oxide has to be removed before welding. Weld schedule just like any other weld is required. Testing by the specifications is a must.
I can't quote any specs it's been to long.
But sure others will. Start with AWS, Google stud welding specs. Do more research.
Stud welding has been used for decades with no problems. If the welds Crack start a failure analysis. Eliminate what it is not.

 

[mfgenggear]

Here is a link and a lead

https://pubs.aws.org/p/930/whc209-arc-stud-welding

 

[mfgenggear]

OP
99% of weld failures are from improper
Removing plate, oxides and lack of improper cleaning. Secondly there is a time period that after weld prep.
Must weld before oxide reforms.
So welding should start asap after prep.
Weld schedule of machine settings.
Based on the material. And full penetration. While I commend 3d Dave
Which is true. I would also torque the stud till failure. To prove it will hold
The actual prevailing and final torque.
Thus proving the required shear and or ultimate tensile.