Plastic Injection Molding

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INTRODUCTION Plastic Injection moulding is a manufacturing technology for producing identical parts from a mould. It is the one of the most commercially significant plastic processing method of all as it allows highly automated production with high precision. The process involves the melting of plastic pellets and injecting it at high pressure into cooled steel mould to form desirable shape. Insert moulding is a variant based on this process, in which plastic is moulded over a component with different properties, forming a product with unique visual or ergonomic appeal in one single manufacturing procedure. The process is not limited to two material components, repeated injection process can be performed until the desirable properties have been achieved with the required number of layers. HISTORY Plastic industry has a relatively short history compared to other materials, the industry did not emerge until the 1930s and did not take off until the World War II (Elias, 2003). Manufacturing of plastic parts with heat-meltable plastic was made available followed by the invention of injection moulding machine in the 1930s (Harper, 2006). The origin of this invention can be traced back in the 1872, when the Hyatt brothers invented the ‘packing machine’ that moulds camphor-plasticised cellulose nitrate. The machine was later improved which led to the the version that are commonly used today. The growing importance of added value manufacturing has urge the demand of multi-material moulding in a low-cost and efficient manner. As a consequence, many variants have been developed based on this modern industrial process despite of its young history, as shown in Fig.1. FIg.1 Variations of multi-material injection moulding process In... ... middle of paper ... ...response to specific material feeds through the use of moving slides or inserts, as shown in Fig. 2. The main advantage of this method is the ability to complete the process without having to open the mould or transfer the pre-form to another location for sequential shots of injection. Also, it provides stronger bond between materials as the time between the injection of the two materials can be optimised accordingly, despite the cooling rate might affect the cycle time. However, depend on the number of component in the structure, tooling cost could be relative expensive as high level of intricacy is required to activate all slides and openings. Throughout analysis on the economical implication should be made when considering. Fig.2 Moving slide/insert opens and closes for injection in core back moulding (source: Goodship, 2002) ROTATING TOOL INJECTION

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