In order to the technological transformation of the automotive industry like electromobilityor autonomous driving and increasing requirements for CO2 emissions from vehicles on the political side, the manufacturers have to break new ground, this also applies to the foundry industry as a major supplier. Innovative casting components can further reduce vehicle weights and thus decrease emissions. In addition, thin-walled high pressure die casting components enable foundries to expand their product portfolio by making it possible to substitute existing plastic components as lighter, higher strength and functional integration parts by high pressure die casting.
The aim of this study was to show potentials for high pressure die casting components in new markets by reducing wall thicknesses. Stiffness losses and instability problems were avoided by an adapted structure. For effective lightweight construction, the mechanical properties of the material must be fully exploited and adapted to a structure suitable for the load. This can be ideally realised by the design freedom in the casting. In a product development process consisting of numerical topology optimization, strength calculation and manufacturing simulation, a seat armrest was completely new developed as a thin-walled high pressure die casting component. In order to exploit the lightweight construction potential of the process, wall thicknesses of less than 1 mm were considered for the construction.
The design space for topology optimization was developed based on anthropometric dimensions. With the topology optimization a maximum stiff structure should be found. In order to be able to manufacture this in die casting, manufacturing boundary conditions, such as a pull-out direction and minimum and maximum wall thicknesses, were specified. As there are no legal requirements for the withstanding loads of car armrests, load cases from the standards for furniture were used to define the load cases.
A full part topology optimization with the target wall thickness of 0.8 mm requires an enormous computing power, which was circumvented by a smart approach. Therefore, only the load paths were extracted from the design suggestion of the optimization by using a higher target wall thickness. During the reconstruction, the wall thicknesses were reduced compared to the design suggestion. With additional iteration loops from strength calculations and manual model adjustment, the wall thicknesses were further reduced. Thus, wall thicknesses of only 0.8 mm were achieved in the final model. This development method shows that wall thickness reduction, compared to other adjustments such as different rib designs and position or draft angles have a large influence on the weight without negatively affecting the stiffness.
Compared to a common armrest for commercial vehicles, made of fiber-reinforced plastic, PA 6 GF30 - polyamide with 30 % glass fibers, the potential of thin-wall high pressure die casting components becomes apparent. The new development made of the aluminum alloy AlSi10MnMg is 7 % lighter. In addition, the load capacity is more than doubled. An analysis of the armrest made of the magnesium alloy AZ91 reduces the weight by 38 % compared to the plastic version, with almost double load capacity. All necessary functions are included in this one casting part. The positive result in favor of the metals is due to the higher modulus of elasticity, which is decisive for the investigated load cases. The structure-mechanically optimized design reduces stress peaks and exhibits an intentional compliance.
A manufacturing simulation proves the manufacturability of the newly developed armrest made of high pressure die casting aluminum. One challenge in casting thin-walled components is the design of tempering channel system to ensure that the thin gates do not solidify too quickly to maintain the intensification phase for a longer time.
High pressure die casting components use the material properties efficiently due to the optimized wall thicknesses. The thin-walled design by using modern simulation tools enables a substitution of plastic parts and creates a weight advantage. Despite the weight reduction, the load capacity is increased and makes other applications in higher load environments possible. This shows the existing potential of structural-mechanically optimized components with wall thicknesses of less than 1 mm. As a result of wall thickness optimization foundries can open up new markets and extended their product portfolio.
