Multiphysics Simulation: Holistic Analysis of Complex Manufacturing Processes

What is a Multiphysics Simulation?

A multiphysics simulation is a computer-based method that combines several physical disciplines – such as electrical, thermal, and mechanics – to realistically analyze complex interactions. Especially in processes like resistance welding, it provides valuable insights that go beyond traditional calculations. Analytical methods are often insufficient, particularly when physical domains influence each other. Multiphysics simulation opens up new possibilities in this area, enabling a deeper understanding of processes, well-founded optimization, and more efficient product development.

CADFEM has developed a simulation-based model that visualizes key effects such as current flows, heat distribution, and mechanical forces. This allows processes to be improved in a targeted manner – for example, by optimizing cooling rates to prevent seam embrittlement.

How Do Electrical, Thermal, and Mechanical Factors Influence Each Other in Technical Processes?

When electrical current flows through a component, Joule losses occur, causing the component to heat up. Suboptimal contact properties make it particularly difficult for current to flow at the point of contact between two components. As a result, the losses and thus the heating are greatest at the contact point, leading to thermal expansion there. This expansion, in turn, affects the contact and thus the current and ultimately the heating. This completes the feedback loop. Especially in high-temperature processes, considering mutual influences is essential.

What Role Does Multiphysics Simulation Play in Resistance Welding?

An example of these “high-temperature processes” is resistance welding. In this process, so much heat is generated through the application of electrical energy that metals, which are solid at room temperature, reach the phase transition range, melt, and thereby form a material bond between the joining partners.

If that weren’t complex enough, this method is used to join two geometries made of different materials. Such requirements are typical in resistance spot welding. Fortunately, these complex processes can be designed and analyzed using user-friendly simulation models.

The electrical current required for heating is transmitted via copper electrodes to the first joining partner, flows from there through the mechanically pressed contact into the second joining partner, and from there either into a second electrode or the applied grounding cable. The goal is to heat the contact point between the two joining partners so that the weld seam can withstand the mechanical forces it will face later.

Why Is Targeted Cooling During Welding Just as Important as Heating?

While a lot of heat needs to be transferred between the components to be joined, the temperature at the transitions to the electrodes must remain as low as possible in order to avoid parasitic welds. This not only means heating, but also cooling!

Between welds, the electrodes can release the absorbed heat energy back into the environment. However, this takes time and reduces productivity. Simulation models provide insight into the global temperature behavior at any location and time, and illustrate, for example, the temperatures of the electrodes via virtual measuring points to derive insights about possible cycle times.

Time history of the maximum electrode temperature across six welding cycles. | © CADFEM Germany GmbH

The temperature progression at the weld point is also of interest. The model allows for the evaluation of the local temperature distribution inside the material, especially after reaching the maximum temperature. As the name suggests, spot welding processes are concentrated on a point and thus a small area. Since the surrounding metallic mass quickly draws the provided heat away from the weld point, this self-quenching can lead to embrittlement of the weld. This reduces the quality of the seam.

Influence of Electrode Temperature History on Weld Quality and Process Performance

To examine this issue in more detail, CADFEM developed a multiphysics coupled simulation model that considers the effects of electricity, heat, mechanics, time progression, and cycle rates in combination.

Temperature and deformation distribution in the cross section of the weld spot. | © CADFEM Germany GmbH

 From the temperature progression over multiple welds, it can be deduced that the temperature history of the electrodes influences the temperature at the weld point, the thermally induced strain there, and the resulting changes in electrical and thermal conductivities. This, in turn, affects the welding performance.

In addition to understanding this relationship, further data can be obtained regarding its extent. How much heat is conducted from the electrodes into the joining partners, and what effect does this have on the required heating time? These insights enable the implementation of targeted corrective measures. 

Multiphysical Analysis for Better Welding Results

Multiphysics simulations provide comprehensive insight into the location and magnitude of physical result variables such as electrical current densities, heat generation rates, contact pressures, and component temperatures – all while considering nonlinear material data, structural deformations, and time-dependent influences.

The simulation results ultimately provide answers to critical questions: Why am I melting too much material? What must I do to melt the correct area? In addition to the “mandatory” task of eliminating undesirable effects, the simulation model can also be used for “optional” tasks in the form of process improvements. This includes questions such as: Can geometric changes to the electrodes influence the temperature behavior? Should the surrounding material be preheated to reduce embrittlement? What alternative processes could there be? How does the process behave with other materials?

The analysis of “what-if” scenarios offers enormous potential for deeper understanding and the development of improved processes.