A 30 KVA welder probably is large enough for this butt welding job. You noticed in your trials that at lower forces results were poor. This was an indicator that force is the variable that should be addressed first. There are two forces in butt welding. One is the force to press/forge the two parts together. The other is the clamping force holding the parts to prevent them from slipping in the clamps. Ironically the clamping force is normally double (or greater) the force pushing the butt ends together. The clamps should have a slight knurl to prevent slipping. Confirm that the part does not slip during butt welding.
Stainless steel wire can be butt welded. As with all weld schedules one schedule does not fit all. The schedule shown works for a specific product and machine and can be used as a guide. Your material could be a different grade of stainless or different gauge either of which would require adjustment of the final settings. That being a given remember that one always starts a new set up on low power settings and works up to what is expected to be the end result to prevent damage to equipment and safety.
Reference Schedule for 300 Series (austenitic) Stainless Steel
Initial Die – 3/16”
Final Die – 3/32”
Weld Time – 20 cycles
Weld Force -- 225 lbs
Weld Current -- 1450 amps
Clamp Force on wire – 2750 lbs
In butt welding the steel rods must be clamped under force to be brought together. These clamps must conduct current into the rod to create the butt weld joint during the welding process. In most cases this material is Class 3 copper. This is a good conductor and has good mechanical wear and strength properties. The steel flash or bulge created during the butt weld must be removed. It can be done by hand with nippers or can be built into the machine cycle.
In the photo below trimming is done automatically in the butt weld sequence. The electrode on the side used for trimming the flash has a tool steel facing to do the metal cutting and Class 3 for current during the butt weld. This tool steel is frequently H13. Sometimes stainless steel has been used. After the butt weld the stationary Class 3 electrode side continues to clamp the rod and the movable tool steel faced side comes forward and trims the excess material. Then the product indexes and prepares for the next butt weld.
Yes, 12 mm (0.472 inches) Cadmium Copper rod can be butt welded. However safety must be considered with this material. OSHA regulations and cadmium's listing as a carcinogen have restricted the manufacture of this material in many parts of the world including North America.
In previous decades it was manufactured as rod and wire and was butt welded successfully. It was butt welded to make longer lengths in the various mills for drawing into wire coils. Any use of this material that could generate cadmium fumes in the work environment might need to be engineered properly to protect the personnel and the environment.
Butt welders are being used in industry to join copper alloy rods of this size in industry every day. Any butt welder manufacturer can develop a machine and process that would be suitable to butt weld this material provided that your OSHA/Safety laws permit its manufacture.
Flash and butt welding both use the work piece as the electrode. They both use a clamp to hold the parts and apply force. This clamp carries current so it must conduct current and dissipate heat. This makes copper alloys a first choice. In many cases the Group A copper alloys will be used for this application. If mechanical wear is an issue Class 3 might replace Class 2.
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