Hot form quench process improves alloy sheet component formability

Materials World magazine
,
25 Mar 2019

Understand a patent relating to a method of operating a press at two speeds during sheet metal forming.

Age-hardenable aluminium alloy (Al-alloy) sheet components that are typically cold formed, following heat treatment and quenching, often exhibit poor formability. While hot stamping improves this, it may also adversely affect the microstructural and mechanical properties of the alloy. Post-forming heat treatment can restore these, however, it can also result in distortion of the formed components.

Impression Technologies Ltd, in Coventry, UK, was founded in January 2013 as a portal between Imperial College London’s faculty of engineering and the automotive industry. It developed the hot form quench (HFQ) process, which provides excellent formability of and high-strength retention in complex-shaped components made from lightweight Al-alloys. For the first time, this process enabled components such as the 6XXX Al-alloy-based A-Pillars for the Aston Martin DB11 to be manufactured using a single draw procedure.

In the HFQ process, an Al-alloy blank is solution heat treated (~525°C for AA6082) and rapidly transferred to a set of cold dies, which are immediately closed to form a shaped component, and the shaped component is held in the cold dies during cooling. To minimise heat loss, closure of the die press involves a fast descent mode whereby they are quickly brought into contact with, or adjacent to, the sheet blank. Hydraulics are engaged and the press operated in a fast pressing mode. The forming of complex-shaped components to a high standard was only thought to be possible using hydraulically powered high-speed presses, because previous logic required fast pressing to be performed throughout the entire stroke, where a faster overall speed would result in better draw-in of material and material thickness distribution.

Recently, Impression Technologies Ltd was granted UK patent GB 2530709, titled Method to operate a press at two speeds for metal sheet forming. This process lowers the energy expended during forming, thereby reducing manufacturing costs while retaining the capability to form complex-shaped components.

Considering the improved malleability of the sheet blank immediately after solution heat treatment, the inventors realised the minimal pressing force provided by the fast descent mode as the die falls under the action of gravity could be used to form the component.

The pictured diagram, taken from GB 2530709, shows the modified ram displacement profile of the present invention. Optionally, formation of the component is initiated by closing the die press at a first speed using a non-powered or a low-powered high-speed stroke. Contrary to this, the fast descent mode (1) is not disengaged once contact with the sheet blank is made.

Instead, it is used to partially form the component and ends at a
pre-determined displacement (2), close to the absolute bottom position of the press. Subsequent forming of the component is then completed by closing the die press, using a powered stroke at a second and relatively slower speed. The press is operated in standard mode (3) using hydraulic power or otherwise, until the dies are fully closed around the sheet blank. This enables finer details of the component, such as sharp edges, to be precisely formed.

This patented process shows that the initial fast descent mode, as a conventional method of lowering the tool, can be used as a non-powered high-speed stroke that can form complex components from sheet metal blanks at elevated temperatures. Ram displacement requiring power is significantly reduced to the later stage of forming, and slower speeds are needed for finalising the component, making
this an energy-efficient process. Also, conventional presses without high-speed closure capabilities for fast pressing can be easily
modified to perform this method without expensive re-fitting or entirely new systems.

*Dr Tahsin Ali Kassam is a part-qualified patent attorney at The IP Asset Partnership Ltd.


Read the full patent here: bit.ly/2SSpSCe