Plastic Machining VS Plastic Injection Molding: How to Choose

2022-04-15 14:49:03

When it comes to custom plastic parts, some customers may be confused and have no idea which way to choose. Before making a decision, let’s find out what they are.

Plastic injection molding is a manufacturing process where resin in a barrel is heated to a molten state, then shot into a mold to form a part in the shape of the mold. 

In precision plastic machining, a larger block of solid plastic is whittled down to the desired dimensions using advanced machinery. Commonly used machining methods include sawing, shearing, punching, turning, planing, drilling, grinding, polishing, threading, etc. In addition, plastics can also be laser cut, punched and welded.

Both manufacturing processes can achieve what you need, so how to decide between them?

1.The Quantity for Custom Plastic Parts

Despite plastic injection molded parts are less expensive than plastic machining, the injection molding requires mold cost, which varies from a few thousand dollars to a few hundred thousand, depending on different products and complexity. So it makes more sense to choose plastic machining if you only need several hundred or thousand. While if it is a project requiring hundreds of thousands, then injection molding is more suitable as it saves money for long term.

2.The Design for Custom Plastic Parts

For injection molding, if you decide to change product design after mold completion, there would be extra cost and lead time for mold modification. So be careful before each alteration. Or you can choose plastic machining, it is more flexible as you can change the design at any point.

3.The Lead Time for Custom Plastic Parts

Before making a decision, taking timing into account. Generally speaking, the injection molding requests longer period of time. Mold fabrication involves a lot of workload to do, this development process can last 45 days to 90 days or longer, depending on mold structure. While  plastic machining can machine within 7-10 days, or even shorter. 

4.The Precision for Custom Plastic Parts

Normally, the plastic is soft which may impact the product precision during manufacturing process. Taking plastic machining as an example, it can deform when machining. But it still has higher precision than injection molding. During injection molding process, the plastic will be heated then cooled to form the product, where plastic contracts with cold causing shrinkage. At Eternal, we can achieve precision within 0.03mm of specifications.

5.The Appearance of Custom Plastic Parts

Do you need your product to be perfect, especially for appearance which may influence the product sales? In that case, it’s preferable to choose plastic machining. For example, the gates of the mold create a slight flaw upon removal, as do the knockout pins used to remove the part, which leave small depressions. 

In conclusion, there are factors to consider when placing an order. The simplest way is to seek for professional advice from us. With over 20 years of experience on metal & plastic and a wealth of engineering knowledge, you can always discuss with our experts for any design or technical support. From low volume work to high volume production runs, we have the expertise and facilities to meet our customers contract manufacturing needs. 



If you have any questions about products, please contact us.