July 14, 2022

Injection Molding Basics (Advantages and Disadvantages)

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Injection molding is one of the most important processing methods to produce plastic parts. Plastic injection molding techniques have been used and developed for a long time. Look around you, the case of your laptop, the case of intelligent cell phone, water filters, food containers, wash machines and quite a few components in your car… yes, we are living in a world that are full with plastic parts, most of the common plastic parts are made by injection molding. This article will show you the basics of plastic injection molding advantages and disadvantages.
Plastic injection molding basics
Injection Molding Basic Process
Feeding raw material from the hopper into the barrel, the plunger start to push, the plastic raw materials are pushed into a heating zone and then through the bypass shuttle, the molten plastic through the nozzle into the injection mold cavity, then water or oil run through the designed cooling system to cool down the injection mold to get a plastic article.

Plastic Injection Molding Advantages

1) High efficiency
Plastic injection molding is high efficiency production method, it takes very short time to supply custom plastic parts to the market, the injection molded parts come out of the mold by every few seconds, usually the injection molding operation runs all night and day once the mold is set up.

2) Cost effective
Automatic production of injection molding is possible, which means the operation is cost effective to manufacture custom plastic parts, in a full automatic injection molding factory, you only see a few workers there to ensure the machine runs smoothly.

3) Multiple materials molded at the same time
The benefit of co-injection molding is you can produce plastic part with more than one plastic material at the same time.

4) Wide range of plastic material can be used
Thanks to the development of chemical industry, more and more types of plastic materials can be used, and the performance and characteristics are more diverse, some of the materials with high strength can take place of steel in application, such as POM, some of the materials are soft, like PP, TPE. All of them can be benefited by injection molding to produce custom plastic parts.

5) Low scrap losses
Utilizing hot runner, plastic injection molding production can maintain very low scrap losses. Basically, in a stable production situation, the scrap loss is zero.

6) In Mold Decoration
In Mold Decoration technology allows the decoration to be molded together with the plastic parts, it means you don’t need to do secondary process after molding.

7) High tolerances are repeatable
Usually precision injection mold are built with steel cutting tolerance 0.005 mm, injection molded parts tolerance can reach 0.01 mm. This tight precision can be repeatable during injection molding cycles by cycles.

Although injection molding has a bunch of advantages, there are also some basic disadvantages need to be taken into consideration when you planning to molding plastics.

Plastic Injection Molding Disadvantages

1) High initial tooling cost
Plastic injection molding can’t work without a tooling, actually quality of the plastic parts rely heavily on the quality of tooling, tool making is a technical and labor intense job, a high quality tool could cost you a lot.

2) Expensive equipment investment
The injection molding equipment is very expensive, it could take a molder 2-3 years to cover the investment. When you ask an injection molding factory to produce your custom plastic parts, you need to know about the basics of their machines, different brand of machine cost differently and the performance of the machines are different accordingly, also machine with different capacity (usually by ton) cost differently as well, machine cost is one of the main cost of the injection molding.

3) Plastic parts must be designed with injection molding consideration
All the plastic parts designed to do injection molding must follow the basic rules of injection molding. Under cuts are allowed but part designers are required to minimize it as much as possible because it increase the complexity of injection molding and it’s cost, some other considerations like sharp edges, uneven wall thickness etc should be avoid as much as possible; most of the plastic parts are asked to make a draft angle for better de-molding. So usually a qualified part designer would know some basic knowledge of mold making and injection molding, so they know how to avoid injection molding problems during plastic part design.

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