 | WHAT IS RESISTANCE WELDING? |
| WHAT IS CONSTANT CURRENT? |
| WHAT IS STEPPER FUNCTION? |
| WHAT ARE LOW FORCE SQUEEZE AND FORGE? |
It is a technique used for joining metals. In this process, an electrical current flow through two pieces of metal, and a heat dissipation is created between the pieces up to fuse them. Different types of resistance welding exists depending on the type of piece to be welded and how the current is applied on the pieces:
| Spot welding |
| Projection welding |
| Butt welding |
| Seam welding |
The needed current for the welding is generated from the machine using one of the following tecnology:
| AC - single phase supply, alternate current output. |
| DC - three phase supply, rectified secondary to obtain direct current |
| MF - mediun frequency direct current, three phase supply, direct current output |
| CD - capacitor discharge |
Whit a constant current control unit it is possible to directly set the current value to be used for carrying out the welding process. During the welding process the control unit measures the welding current value, and, on the basis of a correcting mathematical algorithm, it maintains the set current.
This operating mode, besides simplifying the programming, enables to keep the desired welding current even in case of variations of factors such as: mains voltage, welding circuit impedance, status of the welding tools, superficial status of the materials in progress.
The stepper function enables to compensate the electrodes wear affecting the welds quality. When the electrode diameter is enlarged, the contact section area between the electrode and the workpiece is equally increased and, as a consequence, the current density (Ampere/mm2) decreases. If the current is maintained at a fixed value throughout the whole electrode life, it will be noticed that the last spots are of a lower quality in comparison with the first ones. The stepper function is used in order to overcome this problem. It gradually increases the current adjustment during the welding process in comparison with the electrodes diameter enlargement: this enables to maintain a constant current density.
Usually resistance welders are equipped with a simple pneumatic circuit providing a single force on electrodes.
Some welders are equipped with pneumatic circuit allowing the electrodes to approach the piece to be welded with a lower force. This avoid damages on the piece. It is useful in projection welding.
Other welders are equipped with a more complex pneumatic circuit allowing also to increase the electrode force during or after the welding. This function is called FORGE. It is used mainly in projection welding and high quality alluminium spot welding.
