Coinjection, gas assist migrate to metal

Gas-assist and multiple-material molding are among the hottest value-adding developments to hit injection molding in years. Investigations are under way in Europe to determine if the materials cost savings and productivity-boosting benefits brought by these processes to plastics molding can also be extended to PIM. Speakers at the 2nd European Symposium on PIM brought attendees up to date. 

Research scientists from the School of Industrial & Manufacturing Science, Cranfield University (Cranfield, U.K.), authored a presentation on their work using a Moldflow FEA software package designed for synthetics coinjection to simulate coinjection MIM. They found that they were able to predict the thickness and thickness distribution of the thin skin layers around green cores with a surprising degree of accuracy. 

Actually, when compared to the results of a plastic coinjection analysis, their data correlations for a MIM part with a thin 316L stainless steel skin over a carbonyl-iron core were more accurate. They think this is because of the better data quality used to measure the feedstocks. Only the single-point property data in the FEA software database was used for the synthetics. 

Gas Results 
Equally exciting news came from molding R&D center IKV (Aachen, Germany) regarding its successful experiments in GAPIM, or gas-assist PIM. Short- and full-shot tests involved aluminum-oxide ceramic powder, a 66-ton Arburg running a materials-saving hot runner tool, and various Clariant binders. 

The IKV reports that gas injection delay time has the greatest influence on wall thickness distribution, more than feedstock composition or any other parameter. Also, it was reported that gas assist provides considerable savings in debinding time in larger parts traditionally molded with thicker walls. And, as in thermoplastics injection molding, GAPIM was shown to provide a greater degree of design-integration freedom. Complex-geometry CIM parts were molded that are capable of piping aggressive fluids, or piping fluids at extremely high temperatures and pressures through channels formed by the gas. 

MuCell is also making inroads into metal. To learn more see the April 2001 issue of IMM. A copy of the presentation given by Martin Koch et al is available from the EPMA; Shrewsbury, U.K.; +44 (1743) 248 899; fax +44 (1743) 362 968; e-mail [email protected]; www.epma.com.