1. Capacitor Discharge Welding
Percussion Welding
Magnetic Force (AC)
Stud Welding
The stud welding process is a process used to weld studs onto a workpiece in order to attach that workpiece to some other structure using the stud. It is commonly used for attaching fascia to buildings or for attaching automotive or appliance body panels or trim, etc..

2. Stud Welding Learning Activities View Slides; Lesson Objectives
Read Notes,
Listen to lecture
Do on-line workbook
Lesson Objectives
When you finish this lesson you will understand:
The three methods of stud welding
Typical Applications of this process
Keywords
Stud Welding, Capacitor Discharge, Initial Contact Method, Initial Gap Method, Drawn Arc Method

3. Variations of Capacitor Discharge Stud Welding
Initial Contact Method
Initial Gap Method
There are a couple of variations in the stud welding process. They all have some sort of a stud, either threaded or not, but vary in the application of the stud to the workpiece. These variations include the “initial contact method” the “initial gap method” and the “drawn arc method” as illustrated here. In the initial contact method, there is usually a nib on the end of the stud which is brought into contact with the workpiece before the weld contactors are closed and before and current flows. When the contactors are closed, all the current from the capactors discharge through the nib, melting it and providing heat while the stud is rammed into the part, the liquid fluxing the interface and the weld made. In the initial gap method, the stud is separated from the workpiece by a short distance, the contactor is closed but no current flows because of the gap. Then the stud is rammed into the workpiece. At the moment of contact of the nib, current flows, melting occurs and the weld is made. The drawn arc process is a little different. Usually the drawn arc studs do not have a nib on the end, but rather have a somewhat rounded or conical shape, and they tend to be of the larger diameter. The studs are initially in contact with the workpiece, the contactor is closed and the stud is drawn back from the workpiece to start an arc. The the motion is revered and the stud is rammed into the workpiece making the weld. The drawn arc process takes a little more control but the current is larger so large studs, up to 1 inch diameter, can be welded.
Drawn Arc Method
AWS Welding Handbook

4. Initial Contact Method
is used only with portable quipment, principally for welding mild steel studs. Equipment simplicity makes it ideal for welding mild steel insulation pins to galvanized duct work.
Initial Gap Method
is used with portable and fixed equipment for welding mild
steel, stainless steel, and aluminum. Generally, it is superior to both the drawn arc and initial contact methods for welding dissimilar metals and aluminum. Inert gas is not needed for welding aluminum.
Above is a description of the most often used applications and materials with each of the methods.
Drawn Arc Method
is ideally suited for high speed production applications involving automatic feed systems with either portable equipment or fixed position. Inert gas is required for aluminum.
AWS Welding Handbook

5. Typical Parameters For the Three Variations Peak Welding Currents
Vary from
,000 amps
Here is the weld current vs. time (in milliseconds) curves for each of the processes. The initial contact and initial gap methods generally have higher current peaks but shorter time of current flow than does the drawn arc method. The peak weld currents can reach 600 to 0ver 20,000 amps.
Drawn Arc has lower
peak current - longer time
AWS Welding Handbook

6. This is a table from the Welding Handbook with typical materials that can be stud welded. Notice the wide variety of materials listed.
AWS Welding Handbook

7. A good stud weld looks like that presented in A
A good stud weld looks like that presented in A. There is some liquid metal squeezed out to effect the fluxing action. A poor weld with power too high shows excessive splashing, while a poor low power weld show no melting at all. Any tangential load on this stud would probably cause a weld centerline failure.
AWS Welding Handbook

8. This is as an example of the stud before welding with the nib clearly showing. After welding the nib and part of the base melt and the weld metal squeezes out at the bond line.
Metals Handbook, ASM, 1983

9. to facilitate arc start Most often used, easily machined
Flange
Used for Drawn
Arc. Slightly pointed
to facilitate arc start
Most often
used, easily
machined
Used for critical
applications and
nonflanged Aluminum
Here are a few examples of stud shapes and the applications in which they are used.
Metals Handbook, ASM, 1983

10. Here is an example of a initial gap stud welding gun
Here is an example of a initial gap stud welding gun. The stud is places into the brass collate at the end. The three feet help position and stabilize the gun for application of the stud.
AWS Welding Handbook

11. This is the hook-up arrangement with the gun, power supply and workpiece.
Metals Handbook, ASM, 1983

12. Here is an example of a drawn arc stud welding arrangement attached to an automated device.
AWS Welding Handbook

13. The are a number of ways to apply the accelerated force to the stud
The are a number of ways to apply the accelerated force to the stud. In this case the gun is spring loaded which activates upon trigger application.
Spring Loaded Hand Gun
Metals Handbook, ASM, 1983

14. Gravity Drop In this case, gravity drop mechanism applies the force.
Metals Handbook, ASM, 1983

15. Automated Initial Gap Machines often have a detergent spray
With Detergent Spray
Weld spatter is often a concern with stud welding and it has been found that the application of some detergent to the weldment before welding helps reduce the spatter.
Without Detergent Spray
Automated Initial Gap Machines often have a detergent spray
between gap before welding to reduce weld spatter.
Metals Handbook, ASM, 1983