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

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.

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)?

What material, how was it welded?

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

Regards

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.

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

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?

• https://files.engineering.com/getfile.aspx?folder=c4cbbb4d-faf6-4c9a-b567-3

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

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

Quote (dogbural)

M6x20 stud on zinc plated steel

There's your problem.

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

Need to remove the zinc befor stud welding.

Why don't you look at ASME IX?

Regards

Quote (R6155)

Why don't you look at ASME IX?

Because not everything is a boiler or a pressure vessel.

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.

@ 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

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.

Here is a link and a lead
https://pubs.aws.org/p/930/whc209-arc-stud-welding

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.

ANSI/AWS C5.4-93 Recommended Practices for Stud Welding
Sample at the AWS store

See Also AWS D1.1 section on developing WPS for stud welding

and
thread178-415358: Stud Welding

Removing the zinc plating prior to welding both defeats the purpose of having zinc plating and is labor intensive. Perhaps there is a stud that can be welded through the zinc plating. I suggest trying silicon bronze studs. You may need to use a flux.

https://www.tescosteel.com/silicon-bronze-weld-stu...

I have had good luck torch brazing silicon bronze on zinc plated steel.

Welding zinc is deadly poisonous

A problem that is easily mitigated with ventilation.

I don’t know that I would say deadly poisonous, but it certainly isn’t good to breath. Most people who experience excessive zinc inhalation from welding describe it as a flu-like symptom, which is usually abated by a glass of milk or two.

It may become deadly after long term, high exposure rates.

The devil is in the details; she also wears prada.

I know of welders that passed from breathing in fumes.

https://www.metalfinishingsltd.co.uk/articles/weld...

thanks guys, I will have discussion with our eng team.

supplier just confirmed that the parts are plated after weld.

Stud is made of copper.

Supplier advised that the possible reason for the broken stud is due to the stud being slanted during welding process.
Every round of torque testing/ tightening process, the force that applied at the slanted stud eventually damaged the welding condition.

There are two challenges for their current method.
One is the binding between the stud and plate; As it’s manually weld, there might be inconsistency of the welding condition.
Second is the slanted stud during welding process. Although 100% visual inspection on the studs, if the studs insignificantly slanted, it will be challenge to detect.

To be more detailed, currently supplier verify the stud/weld condition by tightening the nut at the stud with specific range of torque.
Do you think the bending method would be more beneficial, like advised earlier.
https://www.youtube.com/watch?v=cwE5YPy4ztE&t=...

Op
Do they have a weld schedule, (wps)
Was there documentation of the weld inspected and verified with an inspector.
The welds that Crack have lack of penetration
It's been a while were the settings of the machine recorded.
The work Holding sufficient to maintain squareness to the machine.

The studs don't look like copper. If they are, then they are plated over the copper. What is the plating? Consider a copper plated steel stud to weld to steel.

The weld has incomplete fusion - it looks contaminated.

It's common for steel studs to be copper plated, many welding rods and wires are copper plated as well. The coating prevents corrosion and burns off during the welding process. Copper itself cannot be welded directly to steal. There are copper alloys that can be welded directly to steel. These will usually have quite a bit of nickel in them.

What type of stud welding equipment is being used? Are these actual studs or are they more like a projection weld in that there is a small nub that acts as a stand off? There are several variations and each has its own particularities. Consistent results require consistent welding parameters and consistent base metal preparation.

Best regards - Al