Limited natural resources and international statutory requirements increase the demand on highly efficient machinery and transportation means. New energy-saving mobility concepts require design optimization through downsizing of components. Component downsizing can be performed either by structural optimization or by substituting heavy materials with light-weight ones providing high strength to density ratios.
In the automotive industry the light-weight alloys aluminum and magnesium are preferred, with aluminum as the major alloy partner. Special interest lays on the specific properties of aluminum, namely good strength to density ratio, high strength up to 500 MPa, reliable corrosion resistance and relatively high Young’s Modulus. Due to these properties, aluminum alloys are gaining more and more importance in applications such as drive line, suspension and chassis components.
To jump on this technology train, the PWK division of MacLean-Fogg Component Solutions formed a single ball joint from aluminum (patent pending) by a cold extrusion process based on a comparable SBJ steel part.
Experimentation
By changing the material of the cold forging process from steel to aluminum several parameters were taken into account:
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Select aluminum alloys
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Bar stock from direct or indirect extrusion process
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Raw part geometry: flat cylindrical or cylindrical with concave cavities
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Heat treatment condition: untreated, soft-annealed, or quenched and artificially aged
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Several lubrication variables
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Surface condition of the forming tools: polishing direction, surface quality
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Heat treatment after cold forging: quenched and artificially aged, meeting minimum hardness requirements
The process sequence was similar to the serial production of the steel part, but with a significant difference that a heat treatment (quenched and artificially aged) must be carried out to achieve the required tensile strength.
Experimental results
During the tests the heat treatment condition of the raw parts showed an enormous influence on formability. Forging quenched and aged raw parts lead to insufficient form filling, internal and surface damage. Using untreated raw parts formability increased but complete form filling could not be achieved. Only the soft-annealed raw parts showed sufficient formability and were therefore used for further testing.
Another important parameter was lubrication. Only one type of lubrication system led to flawless samples. The other lubrication systems that were considered failed due to the occurrence of cracks.
Using the optimum test parameters that were defined, flawless SBJs could be produced. They were examined by our laboratory which analyzed dimensional accuracy, heat treatment condition and mechanical properties.
In microscopy, typical grain orientation with grain refinement was detected, which leads to higher fatigue strength compared to machined or casted samples. Furthermore, the influence of the bar stock extrusion process can be identified by longitudinal stretched grain structure.
With the know-how that was gained, we were able to deliver flawless SBJs to our customer for further testing, machining operations and to implement the part into the assembly.
PWK achieved positive feedback from the customer considering part quality and mechanical properties. Recently, our further research and development has been concentrating on additional applications.
Expect more expert content from our linkage and suspension engineering team in this experts section coming soon!
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