To meet increasingly strict government requirements regarding CO2 emissions, the automotive industry has been working for many years to reduce fuel consumption of newly manufactured vehicles by reducing their weight. New materials, designs, and manufacturing methods have made possible lighter parts and components.
Press hardening of sheet steel has been vital to the progress made so far. As this technology continues to improve, other materials and material combinations have been developed, such as high-strength aluminum. While considerably lighter than steel, this material has entailed high costs and presented some forming challenges.
In 2013 AP&T began to investigate the development of a new process for hot forming of complexly designed parts made of high-strength aluminum. During the following three-year period, the company worked with customers, universities, and suppliers on testing the material, production processes, and equipment. The result in 2016 was an initial prototype line and a number of prototype components that showed potential for future use.
In 2017 AP&T inaugurated its first full-scale production line for hot forming of high-strength aluminum—including hot forming, W-tempering, and warm forming—at its Ulricehamn, Sweden, test center. The first of its kind in the world, the line offered new possibilities for producing lightweight car body components. Autobody weight could potentially be reduced by up to 40 percent when conventional sheet steel was replaced with high-strength aluminum, which can be made significantly thinner while retaining strength.
Today the company offers a scalable system to original equipment manufacturers and tier suppliers. The production line includes:
The scalability makes the new technology suitable for large and small manufacturing volumes, and production capacity can be increased relatively easily.
High-strength aluminum’s formability allows its use in the production of single-piece, hot-formed parts as alternatives to parts comprising several different components joined together. This reduces the number of operations in the manufacturing process, resulting in simpler handling and logistics, fewer tools, and better material usage, and thus lower production costs per unit.
One of the challenges in streamlining production was to lower the time for the artificial aging process.
In hot forming of aluminum, the conventional approach to harden the material is to heat it to its solution heat-treatment temperature and form and cool it in the tool. To obtain the desired mechanical properties, the material then needs to be artificially aged by heating it again to a certain temperature for a specific amount of time. However, this can take several hours, and the material is hardened before the component is assembled to a car body, which could result in difficulties during joining operations.
To reduce cycle time, AP&T executes a pre-aging process after forming and quenching the part to prepare the material for the subsequent paint-baking process, which imparts final hardening, after car body assembly. This pre-aging step, which takes 5 to 30 minutes, leads to very ductile material behavior during the final assembly of the component in the car body shop and results in good joinability. The company developed this pre-aging sequence in collaboration with Hydro Aluminium, which developed an aluminum alloy (AA6XX) tailored for this process.
High standards are put on tools used in sheet forming to ensure that body parts meet the required tolerances and to prevent cracking. AP&T has combined tool coatings and lubricants to help optimize the tribological behavior between the tool surface and high-strength aluminum blanks.
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For effective finite element method (FEM) simulation in sheet forming, the company has analyzed the mechanical properties of various grades of high-strength aluminum. It also has validated its simulation capabilities using different test geometries to ensure effective interaction among FEM simulation, tool design, and tool manufacturing.
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