Tailor Welded Blanking goes digital

The need for the ever more efficient use of energy and resources remains a major challenge that can only be overcome by way of innovative solutions. Digital methods offer rapid, cost efficient and resource-saving approaches. Especially for more demanding production chains, such as the manufacture of car body components from tailor-welded blanks, it is expedient to simulate the product design or process design digitally and holistically before actual production so as to eliminate tool adjustments and unnecessary trials. This can be achieved by using a so-called digital twin for the existing or fictional process chain by linking numerical simulations that map the individual process steps.

On the course to climate-neutral vehicles, emissions from the development and production phase of vehicles and components are becoming increasingly significant due to the lower emissions resulting during the use phase. Consequently, it is important to recognize and exploit the savings potentials in these phases. The future potential of digital methods is particularly evident in scenarios involving complex components that require sophisticated development and process design, allowing process-overarching interactions to be detected and exploited in a resource-saving manner.
The adaptation of the process chain for Tailor Welded Blanks (TWBs) when using new materials is a salient example.

With the help of finite element simulation, a large number of simulations of experiments can be carried out realistically without having to use actual materials or tools. As a rule, this approach is taken in optimizing individual manufacturing steps, such as welding or forming. These individual simulations must be linked in order to find use in production chains, which also allows interactions and influencing factors on other processes to be evaluated. Initially, the individual models are validated for an explicit parameter set on real components. Subsequently, the simulations are linked by way of a digital platform developed in-house. This allows parameters to be varied within certain process windows and enables the testing of different strategies. In the case of energy- and material-intensive design processes such as tailor-welded blanking, this approach yields tremendous savings compared to conventional methods by reducing the number of physical tests.
Moreover, a large number of tests can be carried out semi-automatically within a very short period of time, allowing the welding process to be optimized in terms of forming. Welding parameters optimized for the forming process are achieved as the final result. The main focus here is on forming as a controlling variable: this result determines the further requirements for the welding strategy.

Parameters influencing the forming result can be divided into three categories.

• Independent material properties (rolling direction of the blank)
• Welding properties (position, width and strength of the weld seam and the shape of the heat-affected zone)
• Direct forming parameters (blank holder force, tribology and tool geometry as well as weld seam recesses)

The evaluation of the targeted change in parameters is based on the defined target values. Thanks to this evaluation recommendations for the welding process can be derived.
In this way complicated relationships can be investigated, such as the relationship between welding speed and the tendency to crack during forming. This is achieved by changing one parameter within the welding simulation, whereby all other parameters remain constant and the result of the welding simulation is transferred to the forming simulation in connection with adjusted parameters.

In most cases, the simulation software was developed for specific applications, meaning that the results of one welding simulation software cannot be readily used as input for the other in carrying out the forming simulation. In order to be able to transfer the results of the thermal welding simulation as an input variable to the mechanical forming simulation, new components were developed for an in-house digital data management platform enabling the linking of the two simulations.
Consequently, an intermediate step is required in which the geometry is simplified in order to transfer the welding simuation to the forming simulation.
By way of analyzing and transforming the results of the welding simulation, a geometry that can be read in for the forming simulation can be generated. This geometry consists of several zones to which different thicknesses and material cards can be assigned. A so-called digital twin – a digital image of the component – is created for the simulation.

[Translate to Englisch:]

Das Durchlaufen der Strecke im digitalen Zwilling umfasst die folgenden Punkte.

1. Upload der Ergebnisse der Schweißsimulation auf die Plattform

2. Generierung einer 2D Außenkontur als Datei
Aus den Lageinformationen der verschweißten Komponenten wird eine 2D Außenkontur abgeleitet. Die Geometrien der Schweißnaht und Wärmeeinflusszone werden über Schmelzbad (maximal erreichte Temperatur) und Beginn des Anstiegs des Martensitgehalts gegenüber dem Grundwerkstoff markiert.

3. Download des Inputs für die Umformsimulation
Der Umformer kann die so generierte Datei herunterladen. Er führt anschließend die Umformsimulation in seiner Software und seinen Parametern durch.
Die Anpassung der Schweißsimulation schließt den Loop.
Die Schweißsimulation stellt ihr Ergebnis mittels dreidimensionaler Volumenelemente dar. Mithilfe der digitalen Plattform wird eine vereinfachte zweidimensionale Darstellung erzeugt, die Informationen über die Lage der Schweißnaht und Wärmeeinflusszone enthält und dadurch in Schalenelementen modelliert werden kann. Diese Daten werden für die Umformsimulation genutzt und das Ergebnis wieder in die digitale Plattform eingespeist. Die Parameter der besten Simulationsergebnisse werden hervorgehoben, und helfen bei der Planung neuer Schweißsimulationen.

Den kompletten Artikel finden Sie im Magazin „Stahl + Eisen“, Ausgabe 10 vom Oktober 2023, S. 43 ff.