Resistance spot welding (RSW) is widely used for joining sheet metal components. It operates with three process parameters: current, force, and time. However, a good weld can only be made within a certain range of parameter combinations. Below the lower limit, no weld can be made. Above the upper limit, there will be expulsions. This working range is the process window (weldability lobe).
To ensure the best weld quality and production stability, it is crucial to select optimal parameters in the middle of the process window or slightly adjusted for other considerations such as electrode life etc. So, the key to optimization of resistance spot welding is to find the process window.

How to Find the Process Window?
The traditional way to find the process window is by trial and error with numerous weld tests for every sheet combination. This is highly costly and time consuming. With the latest developments in numerical simulations, it can be done much faster and more effectively with optimization by digital twins.
Trial & Error by Weld Tests
After preparing all materials, electrodes, and welding machine, numerous weld tests can be performed with varied settings of current, force and time. The process window can then be determined by measuring the resulted weld nugget sizes and marking the parameter combinations with good welds without expulsion. However, due to limited time and resources, it is nearly impossible to do this for every sheet combination. In reality, many companies are running welding production with compromised parameters, leading to increased maintenance costs with poor welds and expulsions.

Optimization by Digital Twins
Using advanced simulation functions of SORPAS® along with a few approval weld tests, it is now possible to optimize spot welding much faster and more effectively with digital twins:
- Predict weld nugget sizes and expulsion limits.
- Generate weldability lobes and process windows.
- Get optimal welding parameters with weld planning.
- Excel batch optimizations for mass production


