Stud welding involves the same basic principles and metallurgical aspects as any other type of arc welding procedure — a controlled electric arc is used to melt the end of a stud or electrode and a portion of the base metal to form a bond. The stud is plunged automatically into the molten metal and a high quality fusion weld is made where the weld is stronger than the stud itself. A variety of metals can be used in stud welding, however, the more common types include mild steel, stainless steel and aluminum.
Dependent upon the type of application, studs may be fed into the welding gun automatically or manually. In either case, a simple squeeze of the trigger produces a positive attachment in a split second. Stud weld fasteners may be most any size, shape or type and there are literally hundreds of types available. However, the stud material must be weldable and one end of the stud must be designed for welding. While conventional DC welding machines may be used, special power units designed specifically for high-strength fastening are recommended.
There are three primary types of stud welding processes – electric arc, capacitor discharge and gas arc or short cycle. Nelson has perfected a fourth type, Stored-Arc®, or drawn arc capacitor discharge, which combines the best features of the first two processes to complete a far superior and more cost-effective stud welding process.
Electric Arc welding is the most common process and is utilized whenever metal is fabricated. The best bond forms when the base plate is heavy enough to support the full strength of the welded fasteners, but is sometimes used with lighter gauge materials. Using a stud welding gun, the stud is welded to the base plate using a ceramic ferrule to hold the molten metal in place until the bond is formed. This results in a dense, strong weld that will develop the full strength of the fastener and the base plate. Welding currents range from 250 to 3,000 amps and the weld cycles range from 0.1 to 1.5 seconds, depending upon the diameter of the fastener and the materials being joined.
Capacitor Discharge stud welding incorporates a power source utilizing energy stored in a bank of capacitors and solid state controls permitting quick weld fusion in two to three thousands of a second. Studs used in this process are engineered with a small projection or tip, which presents a high resistance to the stored energy and rapidly disintegrates creating an arc that melts the end of the stud and a portion of the base metal. The capacitor discharge process limits the heat generated and has a low penetration level so that studs can be welded to extremely thin and/or coated materials. Used specifically for light gauge applications. No ferrule or flux is required with this process. Hand, semi-automatic and automatic feed systems can be utilized through 5/16” diameters of carbon, stainless, aluminum and brass materials.
Drawn Arc Capacitor Discharge or Stored-Arc® is a Nelson patented process that utilizes a combination of electric arc and capacitor discharge stud welding processes resulting in high speed stud welding with higher quality at a lower cost than can be achieved by either of the individual processes. This approach gives more precise control over the welding operation by controlling the elapsed time of current flow independent of the geometry of the welding end of a stud. In effect, time and current controls are transferred from the geometry and design of the stud shape to the welding equipment itself.
Short Cycle and Gas Arc processes both offer ferrule-less stud welding. The short cycle process uses studs that do not have flux loads and have blunt weld ends and flange diameters slightly larger than the studs’ diameter to facilitate auto feeding and assure weld strength. Short cycle systems are typically mounted on robots in automotive plants requiring high productivity, but can also be used for low volume hand gun applications. The gas arc process utilizes gas shielding in place of ceramic ferrules to protect the weld metal and arc. Gas can be used to weld mild steel, stainless and aluminum studs up to 3/8" diameter. The process is used extensively to weld studs to aluminum pots and pans for securing handles and legs.
Nelson’s engineering professionals will work with you to determine the type of welding process that best meets your application’s design criteria. In addition to numerous stud types, Nelson also offers a full line of fasteners and stud welding equipment to perform all of the processes described above.