Creating a product through injection molding requires four steps. First, the mold cavity is filled with molten material. This can be metal, glass, or plastic. Next, the material is rapidly cooled, which causes it to harden. Methods of cooling and cooling times can vary depending on the material being used. Third, the mold opens, exposing the part to air and giving it a place to be ejected. Finally, pins eject the new product from the mold, and the mold closes again to receive more material.
Injection molding is very efficient for mass production. It can be fully automated which leads to high production rates with relatively little labor contribution. The molten material allows production of detailed and intricate parts. This means that the molds themselves must be carefully designed. Once a mold is ready, the products it creates don’t often need modification. Injection molds can also be repurposed to create new parts. Regardless of the part type, there is little waste during the injection process because much of the scrap being generated can be reprocessed.
Different materials can be combined to form one product through a process known as co-injection molding. This process usually involves two injection stages: first injecting the substrate material, then covering it with an over-mold of the second material. A common use of this process is to create materials with a high impact plastic core which increases a product’s overall strength.
Since high tooling costs can make injection molding untenable for the average independent designer, some alternatives have come to exist. These alternatives do not match injection molding efficiency for large projects but can be effective on a small scale. The first option is 3-D printing. There are many different types of 3-D printers which can handle a variety of materials. In certain contexts, 3-D printed materials may be more intricate than molded materials.
Another option is spin casting. Spin casting uses a rubber mold and centrifugal force to cast products into desired shapes. Rubber molds usually do not hold up as well as injection molds or 3-D printers, but their low cost can make them useful.
Recent advances in injection molding technology have allowed the process to be expanded into more industries than were possible in previous years. The number of materials that can be used with injection molding is expanding by more than 500 annually.
RFID tags can now be integrated into part production in multiple ways. Initially, the method for doing this was to mold products in parts then integrate RFID tags into the parts. In recent years, however, new heat resistant RFID tags have come to allow some products to be molded into one piece. This is a technological leap that would have been unthinkable in the early days of the development of injectable materials.
Printed Injection Mold Tools (PIMT) are now being used in combination with 3-D printed inserts to form the basis of an injection mold. 3-D printed inserts are made from materials that are not resistant to high heat, so they are not suitable for large production runs. Instead, PMIT technology has become particularly helpful during the prototyping phase and part testing.
Advancements in this technology will allow for the ability to print more durable inserts and increase the effectiveness of PIMT over time.
The technology involved in plastic injection molding is rapidly evolving which has provided a certain sense of security for the industry. We are excited to see the positive impact it will have on manufacturing plastic parts.
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