A revolutionary new process for feeding molten metal into casts will cut the cost of making metal parts. The manufacture of metal parts has changed little over generations. Die-casting sees molten metal fed through runners into moulds made in the shape of the component. High Pressure Die-Casting (HPDC) is used to make a wide range of metal products, such as plumbing fixtures and parts for vehicles and machines. A new technology developed by CSIRO - Commenwealth Scientific and Industrial Research Organisation- however, promises to deliver major improvements to an age-old die-casting process, making HPDC cheaper and improving the quality of the end product.
Casting costs cut
The new process, Advanced Thixotropic Metallurgy (ATM), takes a new approach to HPDC by using a revolutionary feed system for forcing metal into the dies. It is particularly suited to aluminium and magnesium alloys. ATM is about 10 per cent cheaper to operate than conventional HPDC and does not require major investment in new equipment. ATM has the potential to give Australian manufacturers a competitive edge against imports by producing higher quality products. Lyndon Joss, managing director of Melbourne-based Excel Pacific Diecasting, says this is critical for local manufacturers. "Adopting best-practice die casting methods is crucial to the survival of die casting manufacturing in Australia. Using processes our grandfathers used and saying 'that’ll be all right' does not work anymore," Joss said.
A new feed approach
Conventional HPDC involves molten metal being forced into a cavity through small tunnels, or runners. During this process, air can be trapped within the melt. This trapped air appears as porosity in the finished part and can be detrimental to its quality. To exclude the worst of the affected metal and reduce porosity of the part, cavities usually have substantial overflow zones. Conventional feed systems can also contain pre-solidified grains that continue to grow while being forced into castings. Particularly large grains can seriously affect casting properties. Dr Rob O’Donnell, project manager for ATM, says the feed system in the ATM process involves a radical redesign of the runners. This makes for a more uniform product with reduced porosity, and at a lower unit price than traditional casting. The process has been in low-volume production since 2002. More than 15 manufacturers are now trialling the technology, and most are reporting immediate improvements.
ATM advantages
ATM has several advantages over traditional HPDC, including: reduced rejection rates reduced production time, which lowers labour and machine costs reduced wear on machines negligible overflow zones, reducing metal use and waste more uniform distribution of nucleation sites, leading to a more uniform product reduced energy costs, as less metal needs to be melted for casting, and dies do not need to be preheated to as high a temperature. According to Dr O’Donnell, in a part that normally costs one dollar, a die-caster can now save between 10 and 20 cents. Low porosity also enables the end product to be heat-treated, which is impossible with conventional HPDC products. Heat treatments can significantly increase the metal’s pliability and can more than double product strength. "We love that part. We have the opportunity to manipulate the microstructure so that, where strength is critical, lighter parts can be designed to perform the same task," Dr O’Donnell explained. "We are now introducing this development to component designers and showing them what can be done. It could mean thinner or lighter road wheels, for example."
