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Assessment of Mechanical Fastening Techniques for Dissimilar Metals Joining in Car Bodies

Project Code: 30185

Objectives

  • Perform a critical assessment of all available means of mechanically joining steel and aluminium for automotive structures
  • Investigate what range of materials (strength and gauge) can be joined with each technique to help determine its range of applicability
  • Benchmark the performance of each technique against critical automotive production requirements
  • Provide wider production economics data including the cost of equipment, cost of consumables, weight of each joint and time to produce each joint 

Project Outline

TWI will perform a benchmarking study on the full range of mechanical fastening technologies for steel to aluminium joining. Each technique will be tested against critical performance criteria:

A first level assessment will be performed looking at the following for each technique:

  • What grades and gauges of steel and aluminium can be joined
  • How well do the processes work in combination with structural adhesives
  • How sensitive are the joints to loosening or deformation as a result of differential thermal expansion of steel and aluminium in a typical automotive paint baking cycle
  • What are the relative joint strengths in tensile shear and cross tension

 

The following areas have been identified as requiring solutions:

  • Lack of reliable NDT techniques available for nearly all mechanical fastener types
  • Production rates of fastening techniques are considered too slow (and costly) in most cases
  • Single sided joining processes desired
  • The size and weight of many fasteners is considered too great
  • Post-crash repair techniques are not available for all fasteners
  • The perfect fastener solution is not yet available on the market

 

Relevant Industry Sectors

Industry Need

The automotive sector is reducing vehicle weight to achieve present and future performance and emission targets. Many car companies see a multi-materials strategy as the best way to achieve weight savings, with a hybrid structure of steel and aluminium being the goal of most automotive producers.

In recent years the automotive sector has seen significant technology development in the area of mechanical fastening for the joining of similar and dissimilar materials. Today a modern automobile can contain; self-pierced rivets (SPR), clinched joints, blind rivets, blind rivet studs and bolts, flow drill screws, high speed joints, friction rivets (Ejot-weld), resistance element welds, solid punch rivets. Although many possible techniques now exist for dissimilar materials joining, each has advantages and disadvantages in terms of joint strength, production speed, cost, weight and range of materials that can be joined. At present much confusion exists regarding when and where each technique should be used.

For more information please email:


contactus@twi.co.uk