Alumide tooling for limited production plastic injection moulding

Abstract

Existing techniques for the production of conventional steel tooling for plastic injection moulding are expensive and time consuming. The result is that many new products often do not advance beyond the prototype stage. This thesis describes an investigation into the possibility of using laser-sintered Alumide® (an aluminium-filled polyamide material) in a novel approach as an alternative process for producing rapid tooling inserts for the injection moulding process. Alumide® material properties and process parameters, such as heat capacity, accuracy and surface roughness, required for injection moulding applications, were examined. To reduce internal stresses during the manufacturing process of Alumide® inserts, which could result in warpage, the inserts need to be shelled. For shelled inserts to withstand the injection pressures occurring during an injection moulding cycle, they need to be backfilled. A suitable backfilling material as well as a suitable wall thickness for the shelled Alumide® inserts was determined. Injection moulding trials conducted with Alumide® inserts showed that conformal cooling channels inside the inserts have an influence on the cooling of the inserts. During the trials, cooling channels underneath the cavities of the Alumide® inserts collapsed due to injection pressures of the molten polymer. To prevent cooling channels from collapsing during an injection moulding cycle, a suitable distance between the cavity surface and a cooling channel was ascertained. To determine the durability of Alumide® inserts for the injection moulding process, a geometrical product was developed and Alumide® inserts were manufactured for injection moulding trials. Two hundred geometrical parts were manufactured from Alumide® inserts using Polypropylene (PP) and Acrylonitrile-Butadiene-Styrene (ABS) with minimal wear on the inserts. Injection moulding trials conducted with Polycarbonate (PC) and Polyamide 6 (PA 6) resulted in significant wear during the first few injection moulding cycles. From these trials, it was concluded that polymer materials with process parameters similar to PP and ABS can be used with Alumide® inserts for the injection moulding process. A limited production run for an electrical enclosure was conducted with Alumide® inserts. Two sets of inserts were manufactured and injection mould trials with PP and ABS were conducted. Two hundred parts were manufactured from each set of inserts using PP and ABS, without significant wear to the inserts. Production with the ABS material was continued and 2500 parts were manufactured from the Alumide® inserts with deformation occurring to the fixed side insert (cavity) and minimal wear to the moving side insert (punch). A manufacturing cost and time comparison between Alumide® inserts, tool steel and aluminium inserts (manufactured through conventional manufacturing techniques), additive manufactured inserts (through the Direct Metal Laser Sintering (DMLS) and PolyJet processes) and parts manufactured directly from additive manufacturing processes (rapid manufacturing), were conducted. From the comparisons, it was evident that Alumide® inserts are the most cost-effective manufacturing process to produce limited run plastic injection moulded parts.