Molding Variations

These are just a few examples of the enormous range of products made by injection molding. The next section will cover variations to the injection molding process. Some of these variations are so innovative they make possible unique products that would otherwise be enormously expensive or practically impossible to produce. 

Even though it is possible to produce a seemingly countless number of products using conventional injection molding techniques, variations to this process open up even more opportunities. This section will cover some of the injection molding variations that are used to improve the properties, increase the production efficiency, and expand the usefulness of injection molded products. 

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Otto Bayer produced PUs in the 1940 s by reacting diisocyanates, such as tolyl diisocyanate, with dihydric alcohols, such as ethylene glycol. In another experiment he added a diisocyanate to cure synthetic rubber (SR) containing hydroxyl groups. The rubber was cured (vulcanized), but it stuck to the mold. Variations of products from these two experiments are now used as two-component adhesives for bonding footwear and automotive plastic parts. 

Although most injection molding processes are covered by the conventional process description discussed earlier in this chapter, there are several important molding variations including ... 

This approach may be necessary where operating conditions require stringent load-bearing capabilities without resorting to overdesign and thus unnecessary costs. Such as analysis produces maximum accuracy and would, therefore, be suitable for finite element analysis (FEA) on complex parts (Chapter 19). However, the one difficulty with this method is that the core modulus and the as-molded variations in skin thicknesses cannot be accurately measured. 

Stamp molding n. A compression-molding variation in which the mold is closed so suddenly that the plastic is impacted rather than pressed, as in forging. 

Tensile bars were molded. Variation in process conditions was eliminated by using the same injection molding process based on a two stage velocity - position transfer process. Tensile bars were then aged for 140 days at 60°C in the ovens. Each tensile bar was then tensile tested to determine the changes in ultimate elongation in comparison to time aged. 

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