New industrial laser welding process tackles coating challenges

SPANISH AUTOMOTIVE component manufacturer Gestamp has developed an innovative, industrial-grade laser welding process which overcomes a significant production hurdle. 

Based on TRUMPF technology, the process addresses an area where conventional methods often struggle: quickly and flexibly joining large, coated structural components. "We rely on large structural components instead of many individual components in order to simplify industrial processes. This reduces complexity in final assembly, which means more cost-efficiency," said Miguel Ángel Ferrández, director of joining technology Tokyo and Bilbao at Gestamp.

Tackling material challenges

In automotive production, the fewer components a vehicle needs, the more efficiently it can be manufactured and assembled. Gestamp is pursuing this strategy with its Ges-Gigastamping family, large-format structural components using hot forming from high-strength steels. 

These parts offer significant advantages in terms of weight, stability, and crash safety, but place high demands on the joining process. "The challenge begins with the material," explained Ferrández. "We process press-hardened steels with an aluminum-silicon coating (AlSi). This protects the component from corrosion but makes welding rather difficult. It was therefore necessary to replace traditional welding processes with an industrial laser welding process that offers greater speed and flexibility."

Streamlining the laser welding process

Gestamp had already laid the groundwork with the development of the new G-Weld laser welding process. At the centre of this is a G-shaped overlap seam specially designed for overlapping blanks and assembly components after forming. The new welding process is more efficient, ensures more stable seams, and enables welding up to five times faster.

However, unlike spot welding, laser welding required the AISi coating to be removed before joining. This additional process step negated the time savings. Gestamp turned to the laser specialists at TRUMPF. "Our goal was to weld the components securely and efficiently without having to remove the coating in a previous process step," said Ferrández. "This was the only way we could streamline the process and improve component quality."

The challenge in laser welding coated components is that the two different materials do not bond homogeneously. During the melting process, intermetallic phases and alpha ferrite form, which are structural components that negatively affect the seam quality and the resulting structural mechanical properties of the component. "The key to the solution lies in laser beam shaping, and in Gestamp's case, in the multifocus optics option," said Marc Hummel, global business development manager, Mobility at TRUMPF. 

Multifocus makes the difference 

With the multifocus option, the laser beam is split into four individual beams, each with the same energy input. Each beam has a core beam and a ring beam. The latter ‘calms’ the melt pool with its additional energy and prevents spatter formation. The four individual beams mix the AlSi coating in a controlled and homogeneous manner in the melt pool, thus preventing the formation of intermetallic phases and alpha ferrite. The result: a stable seam with high strength and tensile hardness. "You can compare it to stirring dough," suggested Hummel. "The more stirrers that mix the dough, the more smoothly it mixes."

For Gestamp, the new process strategy brings a number of advantages. "Thanks to TRUMPF's laser beam shaping, we achieve significantly higher speeds and better seam quality during welding," said Ferrández. "In addition, we benefit from significantly better accessibility when it comes to difficult areas of large structural components without any loss of process speed. Finally, single-sided welding with the laser also gives us an advantage known as a ‘semi-visible surface’. The seam is no longer visible on the outside of the component."

The company has now internally validated the new laser welding process. "The close cooperation with TRUMPF was an important factor,” Ferrández affirmed. “Together, we developed a solution that has the potential to change the production of structural components."

For more information: 

www.trumpf.com

Tel: +44 1582 725335