Weld Stud Integrity

[InfoDrain]

I propose to use a 4-40 UNC weld stud as a replacement for a length of studding in a tapped hole. Although the weld stud principle is well documented, I haven't yet found a definitive answer to this question:
Is it only the fused pip of the stud which provides the strength or does the welded area extend across the whole face of the stud? I suspect the former is true and that the weld witness seen around the periphery of the stud face is not actually adherent and doesn't add to the strength of the joint.

Any ideas please? Many Thanks.

Jim

 

[sayee1]

The welded area extends over the entire surface of the stud and the spill over is similar to "flash" in forging, is flash the correct terminology. That is why the ferrule used in case of bigger sized studs to ensure that most of the molten metal contained in the required area and less of wastage as flash. This entire weld metal except for the flash is responsible for the strength!!! Interested in knowing the reason for your question though.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[InfoDrain]

Thank you for your response. I should point out that because my skills are not in welding but in electro-mechanical assemblies, I have to rely on others to confirm or otherwise that my design schemes are practical. I have 'browsed the web' for info and found a good deal of data on the subject but, as I mentioned, no actual clarification of my question.

Although we have CD stud welding equipment 'in house', the design engineer who introduced it is long gone. From the point of view of a practical engineer I can easily relate to the weld pip being melted and fusing in the 2 - 5 ms that I believe the discharge lasts, but it is much less obvious to me that in such a short time period the whole of the stud face and opposing surface will have time to melt to take part in the welding process.

I am expecting some sample weld studs to arrive sometime. When they do we will be able to perform pull tests and section the weld to see for ourselves what is going on.

Thanks again.

 

[sayee1]

The time for the discharge is in ms as you rightly noted, but the discharge is normally from a bank of capacitors. The arc in this case is produced by a rapid discharge of stored electrical energy with pressure applied during or immediately following the electrical discharge. The high A current and low voltage discharge takes place as soon as the stud tip touches the base plate. The current creates an arc which melts the entire face of the stud and a similar area of the work. The stud is then driven at high velocity into the molten pool.
In another version of stud welding, the power source used is same as that for SMAW welding,requires a ceramic ferrule to concentrate the arc and prevent air influx and contain the molten metal. The former method is normally used as it can be used for bigger diameter studs too with relative ease, whereas the latter version known as Arc Stud welding can be used only for small to medium diameter studs.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[InfoDrain]

Thanks again for your help.

You have given me much more confidence that using a weld stud will provide the best solution to my design problem.

Regards

Jim

 

[intimidator3]

The response to your question on stud welding integrity from Sayeeprasadr is absolutly correct.The "spill over" is what we call the collar.It has no structural value to the weld.We use a ceramic ferrule for the stated reasons,as we use studs at least 19mm dia. The welded area of the stud does extend over the entire area of the stud.
According to our inspector for the New York State D.O.T. and Nyc Dept.of Bridges, the standards for a design rated stud are "the stud must be able to be bent at a minimum of 45 deg.to plate surface without failure". This is usually done by hydraulic force, although it can be done by a hammer with a bit more effort.Those same standards also require 10% of the studs be tested.
As for stud welding being practical,if all procedures are followed,and the above mentioned testing is done,stud welding is a very cost effective way to go.

 

[InfoDrain]

Thanks for your comments. I'm looking forward to getting underway with weld trials. The stud is a non-standard size so we have to get them made to our drawing.

Thanks again everyone who responded.

Jim