MANUFACTURING TECHNOLOGY
Efficient heat treating of high strength, automotive aluminium fasteners
Tim Donofrio, product manager, CAN-ENG Furnaces International Ltd
Introduction The use of automotive aluminium fasteners is growing
as a result of new power train and magnesium component developments. Aluminium is favoured by automobile engineers due to its unique combination of strength, reduced weight, crash energy absorption, and corrosion resistance. The latest Ducker report confirms that aluminium content growth to be in the 4 to 5 pounds per vehicle per year range and will approach 300 pounds per vehicle worldwide by 2020. The introduction of automotive magnesium and aluminium
cast components presents challenges when considering the integration of conventional steel fastener products. These challenges include galvanic corrosion, thermal loading differences and clamp force losses. The use of aluminium fasteners overcome these challenges and are favoured over its steel predecessor.
Furnace design characteristics High strength aluminium fasteners require heat treatment to
provide the desired set of mechanical and corrosion properties necessary for an automotive application. Heat treatment processes typically require multiple heating and holding steps with intermediate cooling or quenching operations followed by artificial aging. The benefits of an continuous automated system for
aluminium fasteners are numerous. Typical design features associated with high volume steel fastener heat treatment systems have been integrated into continuous high volume aluminium fastener mesh belt heat treatment systems. These include:
• Individual part lot tracking. • Gentle handling techniques. • Elimination of part mixing potential. • Compact space saving designs.
High volume aluminium fastener heat treatment system
Loading The loading system consists of a bulk hopper and computerised
weigh feeding system. Software is used to control the feeder based on a load rate, cycle time and loss in weight program. Fastener features are integrated into the loading equipment, synthetic linings on slide chutes and vibratory feeders, eliminating catch points and well-designed chutes.
Solution heat treatment Mesh belt furnaces for aluminium fasteners are designed to
process small aluminium products up to 600°C. Fasteners are held at temperature to lock the alloys into solid solution resulting in uniform mechanical properties. High forced convective recirculation heating systems provide the temperature uniformity requirements of ±3°C.
Batch versus continuous heat treatment systems Given the increasing volumes in aluminium fastener
production, the quality and volume requirements that were well managed using conventional batch systems are no longer practical. Improved capacity and functional systems have been sought after to meet the aluminium fasteners demand. These new systems are more commonly processed using higher volume continuous belt heat treatment systems.
134 Fastener + Fixing Magazine • Issue 74 March 2012
“ Given the increasing volumes in aluminium fastener production, the quality and volume requirements that were well managed using conventional batch systems are no longer practical.”
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