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Injection Molding is a manufacturing process for producing parts in large volume. It is most typically used in mass-production processes where the same part
is being created thousands or even millions of times in succession.
Why Use Injection Molding:
The principal advantage of injection molding is the ability to scale production en masse. Once the initial costs have been paid the price per unit during injection
molded manufacturing is extremely low. The price also tends to drop drastically as more parts are produced.
Injection Molding produces low scrap rates relative to traditional manufacturing processes like CNC machining which cut away substantial percentages of an original plastic block or sheet. This however can be a negative relative to additive manufacturing processes like 3D printing that have even lower scrap rates.
Two of the major disadvantages to injection molding are the high tooling costs and large required lead times. Tooling is almost a project in and of itself and only one
phase of the entire injection molding process. Before you can produce an injection molded part you first have to design and prototype a part (probably via CNC or 3D printing),then you have to design and prototype a mold tool that can produce replicas of the part in volume. Lastly, and typically after extensive testing in both of the aforementioned stages，you get to injection mold a part. As you can imagine, all of the iteration required to get the tool correct prior to mass production requires both time and money.
It is rare that you would prototype an injection molding tool. It does happen though, especially for parts that will be made in a multi-cavity tool. For example, let's say we were going to injection mold a new shampoo bottle cap. That cap would likely have threads to attach it to the bottle, a living hinge, a snap closure, and potentially some overmolding too.
A company may choose to make a single cavity tool of that part to make sure all of the features will mold as desired. Upon approval, they will make a new tool, that is capable of
molding, for example, 16 caps at a time. They do the single cavity tool first so if there are any issues, they don't have to pay and wait for it to be fixed 16 times for each cavity.
Injection molding is a great technology for finished production on a massive scale. It is also useful for finalized prototypes that are used for consumer and/or product testing. Prior to this late stage in production, however, 3D printing is much more affordable and flexible for products in the early stages of design.