As the third largest plastic producer in the world, more than a million Americans work in plastic manufacturing in the United States.
When it comes to the manufacture of parts for machines and for mass produced items, there are many methods which can be used to make it happen including reaction injection molding, structural foam molding and polyurethane injection molding or plastic injection molding.
Here’s what you need to know about different types of molding:
Structural foam molding is a process where inert gas is added to a melted polymer. The melted polymer is then injected into an injection molding tool. As the molding tool cools, a skin forms against the mold and the action produced through foaming creates a honeycomb structure that reduces shrinkage once molding is finished.
With structural foam molding, the parts produced in this method are significantly lighter and there are many other advantages to using this process:
- Strength: The honeycomb structure produced during this molding process gives parts an increased strength and good stiffness-to-weight and strength-to-weight ratios.
- Impact resistance: The honeycomb structure produced in the structural foam molding process also gives parts increased impact resistance, so they won’t break easily.
- Low stress: The process of structural foam molding cuts down on stress and warpage on parts, ensuring that they will last for a considerable amount of time.
- A good substitute: The parts produced by structural foam molding can replace many different types of materials including wood, fiberglass and concrete due to the increased strength and impact resistance.
- Good use of aluminum: Since structural molding is a low pressure process, aluminum works well for creating molds and there is a better heat transfer as well.
Another way of manufacturing parts is done through plastic injection molding. Plastics injection molding sees the injection of molten materials into a mold and can be done with many materials. The process of die-casting for example involves using this process with molten metal. Materials are put into a heated barrel, travel through valve gating and are then forced into a mold cavity, which eventually cools and hardens.
During the molding process, some of the most important tools available are hot runner systems. Hot runner systems are assemblies of heated parts used in injection molds that inject hot (or molten) plastic into a mold cavity.
For the molding process, hot runner systems offer plenty of advantages:
- Hot runner systems require a small amount of time to run.
- They start very easily and there are fewer instance of under-filled parts.
- The design flexibility of hot runner systems allow the gates of a part to be located easily by a hot runner nozzle.
Reaction injection molding (RIM) also involves plastics, but this process sees two liquids mixed and injected into a mold where they chemically react. Advantages to using plastic injection molding include:
- Details: In this process, injection molds are subjected to high pressure, which makes injected plastic press harder into a mold. By doing this, manufacturers can get creative in their design and add details for specific parts. In addition, the plastic can be formed into complex shapes to go along with detail, so parts manufacturing by injection molding can be as simple or as complex as needed.
- Strength: By adding fillers to injection molds, the density of plastic used in manufacturing is reduced and the fillers also add strength to the part once it’s been molded. For lines of work that require long-lasting, strong parts, injection molding gives them a strength not offered through other molding processes.
- Versatility: Another advantage of injection molding for manufacturing is that various types of plastic can be used at the same time. With co-injection molding, companies don’t have to stick to just one type of plastic.
- Efficiency: Once molds for a specific part have been designed and everything has been programmed, the molding process is relatively quick, which means a single mold can yield more parts on average. This makes injection molding highly efficient and very cost effective.
There are advantages to each of the different types of molding when it comes to parts manufacturing. Knowing the differences and benefits of each will help a company find the process that works best for them.
