Integral foam parts are defined as castings having a cellular core and an integral solid skin with the transition from the skin to the core being gradual. In this work the so-called High Pressure Integral Foam Moulding (HP-IFM) process for the production of light metal integral foam parts is presented. The process is an adaptation of the established high pressure integral foam moulding processes used for the production of net-shaped polymer integral foam parts.Net-shaped polymer integral foam parts are commonly produced very economically by injection moulding in a onestep process. Many process variations have been developed for the production of polymer integral foam parts. Generally, they are distinguished in low pressure and high pressure injection moulding processes. [1] In both process variations a mixture of melt and blowing agent is injected into the part cavity. In the low pressure processes the cavity is deliberately not filled completely, complete filling is achieved by the expansion of the blowing agent. In the high pressure process variations the part is -as in standard injection mouldingfilled completely. Subsequently the cavity is expanded allowing the formation of foam. A low pressure (LP-IFM) and a high pressure (HP-IFM) integral foam moulding process for the production of light metal (magnesium and aluminium) integral foam parts in an analogous way have been developed. [2,3] The HP-IFM process allows the production of netshaped aluminium integral foam parts which can -due to the local expansion of the mould -contain only a locally foamed core. In the following, the process technology and the influence of the process parameters on the resulting foam structure will be discussed. High Pressure Integral Foam Moulding TechnologyThe high pressure integral foam moulding (HP-IFM) process is an adaptation of the high pressure processes used in polymer processing. The high pressure injection moulding processes consists of three steps: [1,4] admixing of the blowing agent to the melt, filling of the mould cavity and foaming of the part through mould expansion. The development of an equivalent process for light metal processing has to find appropriate technological solutions for each of these steps. Thereby the similarities between polymer and metal processing can be exploited, for the differences new technical solutions have to be developed. The most important differences between polymers and light metals are the lower viscosity, the higher thermal conductivity and the higher processing temperatures of metal melts. The high thermal conductivity and therefore much higher cooling and solidification rates of the metal melt is the most challenging difference. Compared to polymers, the time available for foam formation is one to two orders of magnitude lower. Due to the higher process (mould and melt) temperatures and the different melt chemistry (light metals instead of polymers) other blowing agents have to be used and admixing of the blowing agents is different.The equivalent equipment to a polymer injection mo...
Integral foam moulding (IFM) is an economical way to produce castings with integrated cellular structure, i.e. a solid skin and a foamed core. IFM has been known for polymers for more than four decades and is well established in industrial production. Polymer integral foam parts are accepted as a material system with own properties which simplifies designs, reduces production costs and weight, and increases stiffness and overall strength. On the other hand, integral foam moulding for metals is a new field of research. The development of metal based integral foam moulding processes at WTM moves along analogous paths as that of polymers by transferring and adapting successful moulding technologies for polymer integral foam to metals. Two moulding techniques for metal integral foam are presented, a low and a high pressure process. In the low pressure process, the molten metal charged with blowing agent is injected into a permanent steel mould without completely filling it. In this case, the mould gets eventually filled by foam expansion.In the high pressure process foaming is initiated by expansion of the mould cavity after it has been filled completely with the mixture of the metal melt and the blowing agent. The moulded parts are characterized with respect to their cellular structure, density profile and pore size distribution. Mechanical properties such as stiffness and damping behaviour are discussed.
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