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Common Obstacles of Capacitive Discharge Stud Welding

Recently, we spoke about the fast and effective process of Capacitive Discharge (CD) stud welding.  And though there are many benefits to using this method, like most things, it is not meant to be utilized with every application.  Read on to learn more about the potential obstacles of CD welding.

Arc Timing Pitfalls: Positioning, Texture and Chemistry

One of the major difficulties with CD welding is the affect it has on arc timing, which is controlled by the ignition tip length.  A shorter tip, in turn, equals a shorter weld time.  Too short of a weld time can lead to an insufficient amount of metal melted to have complete fusion.  Other factors affect this as well, such as the texture or chemistry of the metal.

·       Positioning

What does this have to do with positioning? Many customers like to locate the weld stud with a center punch mark.  This center punch mark forms a small, localized valley in the sheet metal.  While this is a successful way to locate the stud, it adversely affects the welding.  The ignition tip can “sit down” in this valley, effectively making the tip length shorter.  If a standard tip is about .03 inches long and the center punch mark is .015 inches deep, you have effectively shortened the arc time by 50%.  With the ignition tip length so critical to consistent weld performance, it is bad practice to use center punch marks for CD welding.

·       Smooth, Clean Surfaces Are Necessary

Due to the rapid speed of CD stud welding, the amount of arcing time spent melting metal is significantly less.  If the surface is rough (think structural steel) the arcing time will probably not be sufficient to melt all the high points, allowing a high quality weld.  Additionally, if the surface has contamination like rust, mill scale, oil or paint, the short arc time will not be adequate to burn those contaminates away, resulting in a weld failure again.

·       Difficult to Penetrate: Medium & High Carbon, High Tensile & Hard Materials

Again, we find ourselves dealing with necessity of a sufficient arc time.  Because medium and high carbon steels are more difficult to penetrate, the short arc time makes this an almost impossible application. And with the same going for high tensile and hard materials, it is better to use drawn arc stud welding in these situations.

Plating

To put it simply, CD stud welding works great on plating… as long as the plating is capable of being welded. Unfortunately, this means that CD welding is a poor choice for zinc-plated materials, such as sheet steel or zinc plated parts.

Size

If you find that you need a larger fastener for strength requirements (above 3/8 inches) then CD welding is not the way to turn.  Certainly in specialized applications, CD welding can go above 3/8, but for all practical purposes, CD stud welding maxes out at 3/8 Inches.  The CD process maxes out a 3/8 because the energy required becomes very large very quick.

Again, like most things in life, one size fits all is simply not the answer.  Different approaches, techniques and applications will be used in various scenarios.  For many situations (See previous blog) capacitive discharge stud welding is the ideal technique.  Yet, one must be aware of the limitations of this… or any process… to guarantee success.  At Image Industries, it is our job to know the time and place for such applications, and we look forward to helping you with your next job.