This cross section of steel is large and would probably not be a candidate for spot welding. Butt or flash welding would be a better choice. I am not aware of any chart available in the marketplace to offer power requirements or suggested schedules by cross section for this type of material.
If your facility has equipment in house or you can rent time somewhere, trial and error would be my suggestion. Always start trials at low power settings and work up to higher power levels for safety sake. When you begin to get some sort of welding hone in slowly to good results and record all welding conditions.
Copper, aluminum and steel wire and rod are frequently butt welded in industry in order to form large coils for drawing down from large gage diameters to smaller gages. This reduces handling and costs.
STEEL ROD BEING BUTT WELDED
The question is where can one find a butt weld schedule for this process? AWS C1.1 “Recommended Practices for Resistance Welding” lists one schedule. It is for Aluminum 1.6 mm Thick (0.063”). There is nothing readily available for rod or wire.
To solve this issue one must turn to trial and error.
To do this a controlled experiment will be set up with the parts on the butt welder to be used.
The first step is to Get the machine ready for operation. Maintenance may need to be performed on the equipment. Definitely the equipment condition needs to be evaluated. This evaluation can be performed by following the steps outlined in AWS J1.2 “Guide To Installation and Maintenance of Resistance Welding Machines”.
When the machine is ready to operate then it is time to prepare samples for testing.
Prepare Samples *
Clean up the Butt Welder
Prepare tooling – Clean up and align properly
Make sure tool will grip the part properly
Set transformer tap, control/power supply to lowest settings
Adjust force – clamping force should be at least twice the forging force
Forging force will depend upon material being welded and its diameter?? and your machine capability.
Try a dry run without power??
Did the part slip? More clamping?
Too much forging force?
At lowest power/ON run the first sample - What happened?
No weld ?
Adjust time or power or tap up modestly, try again
What Happened? No Weld
Repeat till a satisfactory butt weld is achieved.
THIS IS TRIAL AND ERROR – The secret to every successful process
SCHEMATIC OF A BUTT WELD
With a good weld schedule that works record all of the variables on the weld schedule sheet take a photo of the set up and start production.
Reference: AWS C1.1 - Recommended Practices for Resistance Welding
AWS J1.2 - Guide to Installation and Maintenance of Resistance Welding Machines
RWMA – Resistance Welding Manual 4th Edition
*Important many machine set up steps were not have been listed here. This was meant to demonstrate the sample testing starting at low power settings and adjusting up to higher satisfactory levels.
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.
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