The use of aluminum molds for not only low volume/short run projects but also high volume production has been in the news lately. Synventive has many years of experience producing hot runner systems specifically for use in aluminum molds. This experience has led us to develop a set of guidelines for producing a hot runner for maximum performance in an aluminum mold.
Aluminum can offer many benefits to moldmakers and molders. Its soft nature makes it much easier to machine, it allows faster time to market than conventional steel molds, and offers shorter cooling times, resulting in reduced cycle times, increased molding productivity and better part-to-part consistency. Plastic flows longer distances with less injection pressure than is necessary with steel molds, resulting in faster fill times; and finished parts typically have minimal warp and better dimensional stability. Finally, aluminum provides significant weight reduction over steel, for when crane capacity is an issue. If your application fits, overall mold cost for aluminum can be significantly less than steel.
Synventive has developed many hot runner systems for use in aluminum molds over the years. Experience has shown that our systems can be successfully used in aluminum molds as long as a few minimal design changes are incorporated. These include:
-Thermal isolation of the hot runner from the mold is critical given aluminum’s high thermal conductivity (aluminum has 4-5 times higher thermal conductivity than P-20 steel). Cooling water line locations must be carefully designed into the aluminum tool block.
-Hardened steel inserts, sleeves, bushings or pads must be used at all hot runner-to-tool contact areas. This is necessary for thermal isolation and to prevent wear and/or damage to the base aluminum tool block.
-All inserts must be properly engineered to support the loads of thermal expansion and preload of hot runner components, and to transfer that load to the base aluminum block
-All inserts must be tightly fitted to provide sufficient thermal transfer in critical areas (i.e., nozzle tip diameters)
As in any hot runner application, communication is critical. It is important that Synventive be informed at the earliest stages of the project that an aluminum tool is being used. Communication between Synventive, the moldmaker, molder and material supplier will help ensure a successful application.