Injection molding economic importance

Due to the low cost of thermoforming molds we can economically make short runs of specialty or niche market products, for which an injection mold would be prohibitively expensive. This is especially important for large moldings, such as whirlpool tubs and large panels for recreational vehicles, for which injection molds and presses would be astronomically expensive. 

Injection molding allows the rapid, economical production of small to large parts. It provides close tolerances and the same machine can be used to mold many different articles. Parts can be molded combining the polymer with other polymers and with any number of additives. Further, it can be nm so that various parts can be easily married as part of an entire or combined-parts production assembly of an article. The ability to easily modify the operating conditions of the injection-molding machine is important because of the variety of articles that may be needed, variety of material employed to produce the same (general) article, variety of materials to produce different injection-molded articles, and the variability of supposedly the same polymer material from batch to batch. 

It is important that the product designer is always aware that the goal is not only to arrive at a product design that will function as stipulated but also that it can be made in the most economical way. In general, virtually every shape can be injection molded successfully. The question is, then, how can such shape be designed without the need for extraordinary measures when building the mold and when running the mold ... 

This method, like extrusion, requires a molten polymer. The equipment is schematically illustrated in Fig. 3.5a. In this method, polymer granules are fed into a hopper and a screw transports the polymer through a barrel where the polymer is heated to make it flow, and the polymer melt is forced through a nozzle into a closed mold. The mold is cooled after it is filled, and the molded part ejected, and the equipment readied for the next shot. Injection molding is thus a semi-continuous batch process and is usually used for large-scale production, where high throughput and reproducibility are important. The process is economical. The method is commonly used for thermoplastics. E.g. PLA, PGA and copolymers. Some... 

The position of the gate as well as the type of gate is very important for the mold design and the economic efficiency of the injection molding production. An overview is shown in Figure 1.29. 

The fact that thermoplastic resins of the above type may be adapted for use in the economical injection molding processes ves them a practical advantage over the thermosetting resins w hich will undoubtedly- play an important role in their future development. Their transparent, colorless nature gives them potential value as non- hatterable substitute for glass, indicating uses similar to those of the better known vinyl esters and ac-lylates. 

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