Plastic Injection Mold Design and Process Tips

Plastic Injection Molding (Written as “Moulding” in British Form of English) has established a significant place in the manufacturing industry, mostly as plastic has emerged as the fastest growing construction material in use today. Plastic Injection mold design is a complicated part of Injection molding process and needs to be understood well in order to gain maximum benefits from Plastic, as properly designed plastic parts are fast replacing their metallic and wooden counterparts in almost all industrial and domestic machinery components. Not only have they successfully replaced huge car parts, such as panels, bumpers and dashboards, but also fine precision components such as the camera lens assemblies, including the clear lens itself, and numerous minute watch parts.

Modern Engineering plastics such as the Liquid Crystal Polymer (LCP), Polybutylene Terephthalate (PBT),
Polyphenylene Sulfide (PPS), have replaced metallic components in automobile industry due to their excellent strength and mechanical properties, while offering evident reductions in cost and weights of machinery. With cycle times as low as 5 seconds with both thermoplastics and thermosets, injection molding has broken the barriers of costs and time limits in modern engineering. Metallic parts manufactured by conventional machining or casting processes, took around a few hours of labor and machining to obtain the finished product of similar levels.
The above discussion leaves no doubt in our mind as to why plastic injection molding is emerging as a clear process of choice over other manufacturing and machining operations. On this site, we will be discussing about very important details related to the process and design aspects of injection mold design. Plastic Injection Molding Process: Plastic in the molten form is injected or forced by pressure into a die, known as mold, and held in the mold at a high pressure until the plastic solidifies. For reducing the time required to cool the plastic, cooling channels are provided. Water is circulated through these channels at a decided temperature, which is defined by the plastic resin being used, and the molding machine’s toggle unit provides the pressure needed to carry out the operation without any opening of mold halves.

The mold is split into two halves (Core and Cavity or Fixed half or movable half), sometimes more (Sliders and Angular ejectors or lifters), depending on the shape of component to be molded. This splitting provides a means of ejection of parts from mold after complete injection cycle and also facilitates in the easy machining and replication of shape of part. The More complex a part is, the more parting lines are needed to successfully eject it without damaging the part or the mold. If it has opening or bosses perpendicular to the opening direction of cavity and core, then we need to make use of sliders or angular ejectors (also called as lifters).
A mold designer has to be conversant with a number of important aspects about mold tooling and plastic resins. He needs to be able to clearly distinguish the type of resins or plastic material to use for a specific application and function. He needs to know which materials or alloys to use for making the core and cavity of the mold and which ones to use in the manufacturing of the other mold plates and standard parts such as ejector plates, ejector pins, sprue bush, knockout rods, support pins etc. Further, he needs to have basic understanding of injection molding machines, process, injection conditions and parameters, part design related aspects such as sink marks and weld lines. It usually takes years of experience to become a complete mold designer. Due to constant developments in both, the engineering plastic resins and mold materials, he needs to keep himself updated with the latest trends and make use of them while actually designing the molds.
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