Weld process optimizations

< Problem > Need numerous weld tests with real materials to find out the process window, which is time-consuming and highly costly.

< Solution > Predict process windows with Weld Growth Curves and Weldability Lobes by numerical simulations and optimizations.

< Principle > To achieve welding process windows as large as possible to ensure good quality welds without expulsion/splash/spatter.

What is a process window?

Process window (or weld lobe) show the parameter ranges for acceptable weld size

A process window represents the ranges of weld parameters, such as current, time, and force that will produce good quality welds.

Since the weld nugget by resistance welding is hidden between the sheets, it is difficult to verify the quality of welds by visual examination. Thus, finding the process window and using the right parameters is very important to maintain good weld quality.

Methods to find process windows

Due to the limitation of time and cost, many companies are running welding production with un-optimized parameters. They usually determine the parameters by trial-and-error tests, which can cause frequent production maintenance problems such as expulsions or poor welds.

It is necessary to find the process window for determining the right welding parameters.

A traditional way to find the process window is by repeating numerous physical weld tests with possible combinations of different weld parameters. There are ISO standards about the testing procedures for determining the weldability lobes and weld growth curves. This method is time-consuming and highly costly. When the availability of test materials and welding machines is limited, it is difficult to accomplish all tests and find the right parameters in time.

A faster and more cost-effective way to find the process window is by simulations with SORPAS®. After running a set of simulations, SORPAS® determines the process window. It has been used by many companies worldwide through many years to predict process windows and maintain good weld quality, especially for spot welding of all grades of steel sheets and aluminum alloys.

Find process windows by SORPAS®

In SORPAS, there are several automated functions to predict the welding process windows

1) Weld growth curve

The weld growth curve represents the range of weld current that will produce acceptable welds. Since it only predicts the range of weld current, it is recommended for users who have enough knowledge about the reasonable values of weld force and time.

2) Weldability lobe

The weldability lobe represents the ranges of weld current and time or weld current and force that will produce acceptable welds. This is a more systematic way to determine the process window for a given weld combination. It gives an overview of more complete process possibilities.

Which parameters to choose?

To keep good weld quality, it is important to choose parameters inside the process window.

Even though all parameters inside the process window may produce acceptable welds, it is preferred to choose the weld parameters close to the splash limit. This is because there are always some dynamic disturbs during the production such as electrode degradation which could reduce the weld nugget sizes. Therefore the parameters close to the splash limit can be a safe choice for a more stable welding production and consistent weld quality.

The prediction of splash limit is one of the key strengths of SORPAS®. It is also essential for the advanced function of Weld Planning by SORPAS® 2D.welding to predict individually the optimal welding parameters for spot welding of different material and thickness combinations.