A joint project is underway to develop a robust laser welding process for ship building. Led by Laser Zentrum Hannover (LZH), the ‘Laser Welding of Steel to Aluminium for Applications in Shipbuilding’ (LaSAAS) project aims to construct hybrid steel-aluminium structures to reduce weight in parts like ship hulls.
Ship hulls are already made of steel and aluminium superstructures, which has the advantage of weighing less as well as lowering the ship’s centre of gravity for improved stability. However, at the moment, the different metals are joined using an adapter piece. This is done with explosive cladding, a complicated and cost intensive joining technology. The scientists and industrial partners of the LaSAAS project want to replace this adapter piece.
Precitec, Scansonic MI, and Trumpf Laser- und Systemtechnik are working together with LZH to develop a laser processing head with weld penetration depth control. Using this, the LZH will develop a laser welding process under lab conditions that will later be tested in cooperation with German laser company, Laser On Demand. Afterwards, the process will be transferred to actual applications with the semi-finished product manufacturers Druckguss Service Deutschland and Hilbig as well as the shipyards Fr. Lürssen Werft and Meyer Werft. In addition, the Fraunhofer Institute for Structural Durability and System Reliability (LBF) will examine the fatigue behaviour of the seams, especially under the influence of salt water.
Generally, when thermally welding steel to aluminium, brittle intermetallic phases occur, meaning the seams can prematurely fail under stress. However, the weld seam characteristics can be optimised based on the mix ratio of the metals respective to the weld penetration depth. The project partners plan on controlling the weld penetration depth by analysing the spectral process emissions and short coherence interferometry.
If successful, the process would be suitable for other industries assembling large metal pieces, such as train coach or commercial vehicle construction.
LaSAAS is funded by the German Federal Ministry for Economics and Energy (BMWi), and supervised by the Forschungszentrum Jülich (PTJ).