Plastic injection molding is the most commonly used manufacturing process for the production of small, medium, and large-sized plastic parts. The process utilizes an injection molding machine, raw plastic material, and a mold. The plastic is melted to molten heat in the machine and then injected into the mold, where it cools and solidifies into the final part.
Plastic parts are incorporated into products found in almost every industry, including automotive, medical, small engine, plumbing, industrial, agriculture, and more. Using the latest plastic injection molding technologies and production processes, manufacturers can produce ultra-high qualities of plastic parts with the highest level of precision and speed.
Like many manufacturing processes, plastic injection molding has evolved greatly over the last 20 years. Once driven by time and pressure, essential elements of molding are now position, peak pressure, and process repeatability. According to a feature in Plastics Today, scientific molding expert John Bozzelli, and Rosti partner RJG, were major pioneers in the development of decoupled and data-driven or “scientific molding.”
Plastic injection as an “art” gave way to plastics processing as a science of repeatability, standardization, and part success.
An injection molding machine is made up of a material hopper, barrel, an injection ram/rotating screw, heating device, moveable pattern, ejectors, and mold inside the mold cavity. Generally, machines work in a horizontal manner.
The function of the clamping unit is opening and closing a die, and the ejection of parts. There are two types of clamping methods - a toggle type shown and the straight-hydraulic type, which allows a mold to directly open and close with a hydraulic cylinder.
The hopper is located at one end of the barrel, and the hydraulic rotating screw runs by electric motor. The screw is rotated to melt plastic introduced from the hopper. After the required amount of molten plastic is accumulated, the injection process is started. On the other side of the barrel, a mold is attached.
While molten plastic is flowing in the mold, the injection molding machine controls the speed of the screw (or the injection speed). It also controls pressure as plastic fills the cavities. Speed control and pressure control is set where screw position and injection pressure reaches a certain value.
Molds for plastic injection consist of high-strength metal components that have been machined to operate in two halves. The molten plastic flows into a mold through a sprue and fills cavities by way of runners and gates. Then, the mold is opened after the cooling process and the ejector rod of the injection molding machine pushes the ejector plate of the mold to eject moldings.
The composition of an injection mold is significant in order to function properly during the injection molding process. Although molds typically have two halves, a cavity side and a core side, there are often dozens of precision features that make up each half.
Almost all of the machined mold components that function to manufacture a custom-molded part are machined to tolerances of less than +/- 0.001″ or 0.025mm, one-third of the thickness of a piece of copy paper.
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