Development of an aluminium filled epoxy insert using perfactory rapid prototyping technique and electroless nickel plating for low volume plastic injection moulding

摘要

In this research, a rapid tool for low volume production plastic injection moulding is designed, developed, and tested on an injection moulding machine. The tool is designed as a cavity insert of injection mould for plastic parts by an indirect rapid tooling approach. The plastic part is modelled in a CAD system and then built using a Perfactory rapid prototyping (RP) technique. Then a layer of nickel-phosphorous alloy is deposited on the prototype by electroless plating. This nickel plated RP model is then used as a casting pattern. A cavity insert, which is produced by using aluminium filled epoxy resin with the nickel plated casting pattern, is fabricated in a mouldbase for injection moulding. Experimental testing on the cavity insert using an injection moulding machine show that the tool is producing quality parts without any noticeable deterioration of the surface. The number of shots completed using the cavity insert is more than 600.Applying electroless nickel plating on the casting pattern made of rapid prototyping material was successful. It was found that pre-treatment processes are crucial. In addition, the rapid prototyping material cannot be plated with nickel without palladium activation and stannous sensitising. Results show that the deposited layer is uniform and composed of both nickel and phosphorous. The surface properties of the nickel and phosphorous deposit enhance the plated layer performance due to their low surface roughness and high lubrication characteristics. Moreover, the nickel-phosphorous layer also improves the surface hardness of the cavity insert since it is left on the cavity after the removal of the casting pattern. The cavity insert was installed on an industrial injection moulding machine for trials. Results show that the cavity insert performs well with Polyethylene at 170˚C at an injection pressure in the range of 80 ~ 100 bar. There are no signs of wear and tear on the cavity insert up to 620 shots. However, when the injection pressure is over 120 bar, cracks start developing in the cavity insert followed by catastrophic fracture. This research has shown that manufacturing an indirect rapid tooling using electroless nickel plating for low volume production of plastic injection mouldings is feasible for Perfactory produced RP models. The cavity insert can be fabricated using commonly available low cost materials within 48 hours.