Injection molding functional areas

The past introduction of TP materials into the area of printed circuit substrates has led to a broader type of application for the circuits. The products can be injection molded and the circuit applied to a molded part which will have a molded-in connector structure used to interconnect the device to the rest of the system. By combining the connector and substrate functions, it is possible to make very compact printed circuit units. 

Figure I-l represents the organizational structure of a medium-sized to large injection molding company, i.e. a company of more than 50 but fewer than 500 employees. The organizational structure determines the way, in which the individual departments or functional sections are assigned hierarchiaUy in relation to eaeh other. Two main areas are highlighted ...

The purpose of injection molding is to produce polymer end products with high efficiency and to shape the products with complicated forms. Scientific molding is an important initial practice to make proper short shot. To start up with any mold, short shot is to be made for the safety of the machine and mold. Therefore, fimctional areas such as barrel and heating zones are important for their individual functions. 

Molded plastics parts in many ways seem analogous to castings since the mold can be any shape. There are a number of limitations on the part because of the fact that the mold is filled with plastics material and it represents, in addition to the form for the product, the flow path for the plastics material. One factor that is affected is the wall thickness of the part. The viscous melts produced by many plastics require that a minimum wall thickness be used based on the ability to fill the mold rather than on the function of the part. For example, rarely is any injection molded part of any size designed with a wall thickness less than 0.025 to 0.030 inch. This is particularly true if the part has a fairly large surface area because the plastics will not flow to properly fill the part. In addition, as will be seen in Chapter 10, flow conditions can severely affect the properties of the material. 

To broaden the area of TPO applications to the low modulus side offering plastics with elastomeric properties, compounds with both a thermoplastic PP matrix and vulcanized domains of ethylene butylene rubber (EBR) have been introduced. These offer a route to mbber-hke materials that can easily be produced through injection molding. As a special feature, these thermoplastic elastomers (TPE) can be sequentially co-injected with normal TPO to give parts with specific functional zones. 

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