30 June 2014
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Fasteners solve conductivity problem for lightweight bonded assemblies

Driven by the demand for lower emissions and increased fuel economy, lightweight vehicle assembly developments are creating challenges that in turn question traditional assembly techniques infrastructure.

Automotive OEMs are reducing vehicle weights by bonding advanced materials such as aluminium thin sheet. Whilst highly effective, this can create issues where electrical continuity through areas of the vehicle structure needs to be maintained but is broken by the wafer thin sheet of glue between the metal sheets.

The obvious solution has been simply: drive stainless steel fasteners through the sheets, not with a view to adding strength to the bond, but simply to reintroduce electrical pathways. However the prerequisite of a pilot hole for each fastener makes this short-term solution is time-heavy.

Shared group technology
In the UK, EJOT has overcome these issues by utilising fastening technology originally developed by the EJOT Group for its worldwide Building & Construction portfolio. Innovative twin thread geometry that displaces, rather than cuts the metal, was adapted and modified – making it possible to reduce debris whilst generating faster installation speeds. More significantly, the screw is manufactured with a pierce-point tip which eliminates the need for a pilot hole, thus significantly shortening installation time.

EJOT's research and development team then had to address the issue of corrosion resistance with research pointing to a figure of 720 hours salt-spray resistance. Normally zinc plated fasteners require a top coat such as an organic coating to increase the corrosion resistance and to help speed up installation. However adding an organic coat also drastically reduces conductivity by acting as an insulator. Collaboration between the company's Applitec testing laboratories near Leeds and its counterpart in Germany found that by adding Nickel to the Zinc plating provides excellent salt spray resistance, works well as a lubricant and successfully maintains electrical conductivity.

The resulting product has been named the E-connectivity fastener and is currently being trialled by several OEMs with an interest in light weight assembly processes. EJOT UK's Industrial Engineering team also believes that the new fastener presents a highly cost effective solution for standard thin sheet applications of up to 2mm thickness.

Readers can see the EJOT E-Connectivity fastener range by visiting the FAST Exhibition at the Williams Conference Centre on September 10th, 2014. Follow the links to register.

Paul Gay

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