Plastic injection molding is a technique for manufacturing plastic in which molten plastic is injected into a mold at a high pressure and allowed to cool before it is removed from the mold. Plastic injection is the most common method of plastic manufacturing and can be used with a variety of plastics including nylon, polyethylene, polyvinyl chloride and styrene.
The machines that perform plastic injection are called presses and hold the mold closed while they are filled. Plastic injection molds require pressure ranging from under five tons to more than 6,000. The plastic molds are relatively expensive to make and usually only economical for production runs in the thousands of units.
The most expensive and longest-lasting plastic molds are made from some type of hardened steel. Aluminum molds are much cheaper and are economical for hundreds of thousands of runs while copper-beryllium molds are most often used for molds that generate a great deal of heat.
Three points to consider when using plastic injection molds are:
- Hot runner plastic molds have advantages over cold runner molds.
- Manufacturers offer test runs so you can get the bugs out of your plastic injection molding process.
- Not all manufacturers are equipped to handle odd-shaped projects.
Action Steps
The best contacts and resources to help you get it done
Choose between cold runner plastic molds and hot runner molds
A cold runner mold initially injects the plastic into a runner system where it is redirected to the individual cavities and has a lower start-up cost. Hot runner plastic injection molds inject the plastic directly into the cavities and therefore requires less handling.
I recommend: Find a plastic molding company such as
BMJ Molding that performs both types of plastic molding for a less biased comparison of the two techniques.
LongMold Technology Co., Ltd. specializes in making runners for both types of plastic molds.
Sample different plastic injection processes to find the best one for your part
Many full-service plastic mold manufacturers offer mold tryouts and limited production runs. This allows you to find defects in your molding process before tooling up for full-scale production.
I recommend: Get a full range of production runs for plastic injection molding at
Dynamic. Get consultation on the plastic molding process from concept to finished product at
ACM Molders.
Use a company experienced in plastic part design for unusual parts
Some types of plastic parts do not lend themselves to the plastic molding process and may require special expertise in designing the part.
I recommend: Get a quote from
Plastic Mold Designs, a company that specializes in molding plastic parts that are not well-designed for injection molding.
Tech Molded Plastics also has substantial experience with difficult projects in plastic molding.
Tips & Tactics
Helpful advice for making the most of this Guide
- Fill new plastic molds slowly to 99% capacity. Apply a holding pressure until gate freeze-off has occurred and increase the pressure until the parts no longer have sinks. Produce a setting sheet to repeat the desired results.
The official source of Plastic Injection Molds is
the Plastic Injection Molds page at Business.com
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