Multi-material assemblies

“Find the winning combination”

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■  Assembly of two materials of the same type may seem to be a perfectly well understood field, but finding or not solutions to join different materials together (metallic materials and synthetic materials, for example) or assembling distinct grades from the same family can slow down an innovation project, or even stop it.

■  Experts have made the following forecast: multi-materials are overtaking “new” materials of the 1980s because the performances achieved or expected are high and a vast number of materials are available. Today, a vehicle has more than 14 types of grade of polymers, to which different metals (alloys of steel, aluminium and magnesium), glass, wood, ceramics or titanium are aggregated.

■  By combining, for example properties, costs qualities or the recyclability of different materials, the transport industry, the household goods, household electrical appliances, building, biomedical and sports and leisure sectors will replace classic structures with unique combinations that require multi-material assemblies.

■  To improve the characteristics of their products (reduce weight or better absorb shocks), to improve perceived quality (with noble surfaces, which are value-adding but expensive), or simply to confront the incredible diversity of materials that imposes more and more complex products (the bonnet of the Laguna II is made of steel, cast iron and aluminium), industrial players must assemble different, disparate and even incompatible materials successfully: they have to command multi-material assemblies.

■  Thus, assembly methods have had to be improved or invented, which continue to meet users' classic requirements: parts that stay in contact perfectly, resistance over time to effort without altering the materials’ characteristics or properties, and that also meet criteria of productivity, flexibility, recycling, reparability, etc.

■  Traditionally segmented into mechanical assemblies or those with filler material, the performances and specific characteristics of the main techniques influence the engineer’s choice. So, although screwing, clipping and stapling can be used to assemble practically all materials and are easily demountable, they make the weight of structures heavier, often require special tools and are sometimes difficult to robotise.

■  Self-piercing riveting is developing well and makes it possible to successfully assemble materials which until now were incompatible (aluminium and steel), but generates phenomena of electrical conduction that may cause corrosion.

■  Soldering, and its different derivatives (diffusion soldering, laser joining, etc.) are largely used to assemble materials of the same nature and are now being used to combine different materials; however, there are related cost or scheduling restrictions which sometimes remove them from the competition.

■  With braze welding and gluing, we have assembly techniques that, when used carefully or to complement another solution, can add secondary functionalities (water-resistance, vacuum filling, absorption, etc.).

■  By combining the systematic surveillance of R&D programmes with ongoing watch activities of concrete results and feedback, Innovation128 intends to help industrial players get the most from the wide choice of materials and to get rid of the technological blockages that hold them back.

■  In order to make the results obtained legible and to help industrial players in their choice of solutions, a table comparing the main identified assembly methods (segmented by material pairs) will be compiled and updated every six months. This technological watch is a veritable decision-making help tool.

Main themes

■  Mechanical assemblies

  • screwing, clipping, stapling, etc.
  • clinching, riveting (classic or self-piercing)
  • soldering (laser soldering, laser joining, diffusion soldering, friction soldering, etc.)
  • bracing
  • emerging technologies (magnetoforming, flow-turning, etc.)
  • characterisation and control

■  Assemblies with filler material

  • gluing
  • soldering, braze welding
  • emerging or substitution fill material
  • characterisation and control

■  Hybrid assembly processes

  • technologies associated with soldering
  • technologies associated with gluing
  • emerging processes
  • characterisation and control

■  Disassembly and recyclability

■  Feedback by market

  • automobile construction
  • aeronautics and ship construction
  • space & defence
  • packaging
  • household electrical appliances and household goods
  • building and infrastructures
  • sports & leisure
  • electronics and electrical engineering
  • biomedical
  • optical
  • textiles

■  Market data and trends

  • Europe
  • North America
  • Asia

■  Appendix: comparative table of possible processes