There are several variables in the machine set up that can affect the weld. These are secondary voltage, flashing rate, flash time, current and upset distance and force. The effects of these variables are related to how they cause the parts to be over heated or to cool or forged too little or too much. If the material is too plastic or not enough different observations and results will occur.
Flash and butt welding both use the work piece as the electrode. They both use a clamp to hold the parts and apply force. The entire cross section of the work piece is welded. It is in the timing and application of force and current that they differ.
Flash welding uses similar clamps but the parts are placed close to each other before force is applied. Current initiates with the intent of creating an arc which generates large amounts of metal flash. This flashing action both cleans and heats the mating faces of the parts. Then force is applied and Joule H= I2rt heating begins. Power is turned off. Part cools and force is removed.
In general flash welding does not require part preparation. The two mating surfaces do not need to be cleaned. The arcing will remove the surface contaminants. The surfaces do not have to be flat to mate up well. In fact a rough cut creates arc initiation sites. If anything one might cut the material on purpose to create a rough surface or even a sloped surface. A sloped surface will concentrate the arc at the point which touches first. It will burn away quickly until the whole surface is arcing. It is the arcing action which cleans and brings the part up to the desired conditions needed for good joining.
Flash welding is designed to begin the process with an electrical arc struck between the two parts to be welded. This arc will create an excessive amount of heat on the two mating surfaces where it makes contact. The result is molten material forms at the point of impact. This molten material frequently is expelled out of the joint as flash. It is hot and dangerous and shielding should be used for personal safety. This same flash can accumulate on the machine, the part and surrounding areas. Clean up will be required to maintain good safe housekeeping. Minimize magnetic materials in the area if welding to reduce steel slag accumulation.
This flash is good for the process and is necessary because it is both heating and cleaning the faying surfaces in preparation for making a good joint.
Yes, non-cast wheel rims are made by flash welding. The work acts as the electrode and the entire cross section is welded. The parts are clamped and brought close together. Force is not applied and the current begins. The intent is to strike an arc between the two surfaces. This resultant arc heats and by removing the surface material in the flash cleans the mating surfaces and prepares them for bonding. At the proper time force is applied and the arc current is removed. The surfaces come together and the heating may continue with standard Joules Law heat H= I2rt heating at the joint. The metal upsets and a joint is formed. The current is turned off and cooling begins. When cooled, force is removed and the part joint is complete and ready for slag/flash removal.
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