Often resistance welding operators report that their setup is exactly the same except that now the welds are different. They don’t realize that a seemingly irrelevant adjustment to the geometry of the welding setup can change the spring constant of the linkages applying electrode force to the part. While a change in the spring constant of the machine setup causes no change to the static applied electrode force, it can cause significant changes to the dynamically varying forces occurring while the weld is taking place. At WeldComputer, we are always looking for ways to measure parameters that can impact welding performance.
The Cambridge Dictionary defines spring constant as “the force needed to stretch or press a spring, divided by the distance that the spring gets longer or shorter.” Resistance welding machine designs may not include springs, however, this calculation can quantify how the ram travel changes as different electrode forces are applied.
For example, if the electrodes shift their position so that the ram has to extend further, to bring the tips together, the spring constant will change. This changes the behavior of the dynamically varying forces applied by the electrodes against the part, which in turn can cause unintended changes to the welds being produced.
Hooke’s law states that the applied force F equals a constant k, times the change in length x, or F = kx.
By using Force and Displacement monitoring, it’s possible to incorporate measurement of the welding machine’s spring constant as part of the standard setup procedure for a resistance welding job.
To calculate, follow these steps:
- Lower the ram on the part and measure its position. Let’s call the force F1 and the position x1.
- Increase the force setting and measure the change in position of the ram. Let’s call this force F2 and the new position x2.
- Now, k = F/x = (F2-F1)/(x2-x1).
Recording this parameter for the welding setup is an action WeldComputer recommends as another step to take the guesswork out of resistance welding by applying science to the process. This procedure can also be automated, allowing the measurement to be performed by all welding operations in a matter of seconds.