Injection Molding
Injection molding uses molds that are usually made of steel or aluminum and serve as special tools. The mold consists of many components, but can be divided into two halves. Each half is fixed on the injection molding machine, and the back half can be moved so that the mold can be opened and closed along the mold parting line. The two main components of the mold are the mold core and the mold cavity. When the mold is closed, the space between the mold core and the mold cavity forms the mold cavity, which is filled with molten plastic to produce the desired part. Sometimes multiple cavity molds are used, where the two halves of the mold create more than one identical part cavity.
Mold base body
The mold core and cavity are each mounted on the mold base and then connected to the plates on the injection molding machine. The front half of the mold base includes a support plate to which the mold cavity is attached, the runner bushing through which material flows from the nozzle, and a locating ring to align the mold base with the nozzle. The rear half of the mold base contains the ejector system to which the mold core is attached and a support plate. When the clamping unit separates the mold halves, the ejector rod activates the ejector system. The ejector rod pushes the ejector plate in the ejector box forward, which pushes the ejector pins into the die part. Ejector pins push the solidified part out of the open mold cavity.
Mold channels
Several channels are integrated into the mold design to allow the molten plastic to flow into the mold cavities. First, the molten plastic enters the mold through the spruce. Other channels, known as sewer channels, carry molten plastic from the channel to all the spaces to be filled. At the end of each runner, molten plastic enters the cavity through a gate that diverts the flow. The molten plastic solidified in these channels is adhered to the part and must be separated after the part comes out of the mold. However, sometimes hot runner systems are used that heat the ducts independently so that the material inside can be melted and separated from the part. Another type of channel placed in the mold is the cooling channels. These channels allow water to flow through the mold walls adjacent to the cavity and cool the molten plastic.
Mold design
In addition to sewer drains and doors, there are many other aspects to consider when designing moldings. First, the mold must be designed to allow molten plastic to flow easily into all cavities. Equally important is the removal of the solidified part from the mold, so a demoulding angle must be provided to the mold walls. Mold design must also take into account complex features of the part, such as undercuts or teeth that require additional molding. Most of these devices slide from the side of the mold into the mold cavity and are therefore called sliders or side sliders. The most common type of side door is a side hub, which can be used to create an external undercut. Other devices are inserted into the end of the die along the parting direction, such as inner core lifters that can create an inner undercut. To create threads in the part, a screwdriver is needed that can be removed from the mold after the threads are formed.
