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Laser Joining Technologies for Dissimilar Material Combinations (JODIS)

Final Report Summary - JODIS (Laser Joining Technologies for Dissimilar Material Combinations)

The topic of this project was the up-scaling of the laser joining technology for material thicknesses up to 5 mm, focussing on the material combination steel/aluminum. Joint geometries like butt- and T-joints were evaluated, targeting on the potential of assemblies made of dissimilar material combinations.

As the implementation of expensive laser welding equipment would not be economically affordable for small ship yards, suppliers specialized in laser welding would have to enable them by transfer of know how.

The goal of this project was the strengthening of the competitiveness of small European ship yards and their suppliers by the implementation of advanced laser joining technology for dissimilar material combinations.

Thereby the main project objective was defined as the development of a laser based joining technology applicable in SMEs to produce aluminum/steel dissimilar material joints in butt- and T-joint configuration within a material thickness range from 3-5 mm.

To realise this goal the following subdividing goals were defined:
- General development of a joining technology for butt and T-joints.
- Characterisation and optimisation of the mechanical properties of the joints by metallurgical optimization of the seam area.
- Implementation of the technology at the project partners.
- Proof of the technological applicability by production of prototypes defined by the SME.
- Defining guidelines for standardization for joining dissimilar material combinations.

The main results were achieved on the fields of process development, design studies and joining of demonstrators. The detailed results of the process development were the following:
- T-joints of aluminium with steel could be joined up to thicknesses of 5 mm by the laser/cold wire joining process.
- The joint strength of the laser welded T-joints achieved 149 MPa for 3 mm thick plates and 139 MPa for 5 mm thick plates.
- The joining of 3 mm plates in butt joint configuration by the laser MIG hybrid process was successfully performed applying the statistical test planning.
- The maximum achieved joint strength of the butt joints was 140 MPa; it was established that high wetting lengths on the steel sheet side and low intermetallic phase layer thicknesses lead to higher joint strengths.
- For 5 mm Al/St butt joints no appropriate joining technology could be evaluated due to too high energy inputs which cause distortion and an increased intermetallic phase formation.
- The CMT process demonstrated benefits in terms of heat input. Thus, the production of aluminum-steel butt and T-joints up to 3 mm sheet thickness was realized by a double sided joining process. For joining of thicker materials, the penetration depth of the CMT process was insufficient.

Concerning design studies, joining of demonstrators and technology transfer, the following main results were achieved:
- The laser MIG hybrid joining technology for 3 mm butt joints was transferred from BIAS to BLS for the production of 1 m Al/St transition joints.
- Further 1 m long Al/St segments of 3 mm thickness were joined in butt joint configuration at Stealcom by the double-sided CMT process.
- The segments joined at BLS and Stealcom were shipped to Aluship, where by conventional welding processes door-demonstrators were assembled.
- The design for the demonstrators was defined by the constructors SMST and Newcruise. Whereas Newcruise designed a concept for side doors on yacht decks, SMST designed an aluminum-steel beam for jet-ski cranes.
- The Al/St transition joints for the crane beam demonstrator were laser or CMT joined at UT and Stealcom. The assembling of the demonstrators took place at WEKA and JJWelding.