Hot Forming of 7075 Aluminium Alloy Tubes to Produce Complex and Strong Components 2012-01-0539

Lightweight tubular products offering enhanced stiffness and strength have always been of major concern for transportation and recreational applications. Hence, industries have turned to complex-shaped tubes to increase product performance and reduce energy costs. High-performance aluminum alloys, like 7075 for instance, have good mechanical properties such as high strength, but low formability at ambient temperature.

Fortunately, hot tensile tests on 7075 samples have yielded an increase in formability with temperature. Therefore, testing has recently been launched at the Aluminum Technology Center to develop a new product application. More precisely, a 1,000-ton hydraulic press was equipped with +600°C heating plates and fitted with a bicycle handlebar mold. The plates provide 10 separate heating zones that can be adjusted independently. A thermo-mechanical model was also developed using LS-DYNA to determine tube temperatures around the heating zones. Hot tensile test results were also utilized to model tube behavior using an elastic viscoplastic temperature-dependent material constitutive law to predict tube wall stresses and strains.

The finite element model can predict tube temperatures and gas pressures relative to time. Hot-forming process parameters were rapidly adjusted to successfully produce perfect handlebars. Conclusions not only include successful application where high formability is required, but also lead to a significant decrease in forming loads and lower tooling and mechanical energy costs.