With dozens of manufacturers, hybrid materials, additives, and fillers available on the market, there are thousands of material options. This can be overwhelming. However, in reality, there are only a handful of materials that make up the bulk of the market. It&#;s easier to understand if you start with some core material characteristics.
Please visit our website for more information on this topic.
Plastics (in this context) are nothing more than groups of polymer chains. These are microscopic groups of repeating atoms (think of it like DNA). The composition of these polymer chains varies between different types of plastics. That variation has a significant impact on the properties of the plastic and your part. Two plastics could look the same but exhibit drastic differences in performance.
For the sake of design, we just want to understand the general characteristics of plastics. We will look at the major characteristics of plastics and some design considerations. There are two major categories of plastics; Thermosets and Thermoplastics.
Boss
Refers to the round protrusions on plastic parts and molds (#2 in Figure 1 below)
Cavity
Refers to the upper half of the injection mold usually the show surface of the finished product but is mainly concave
Core
Refers to the side of the tool where the plastic part is injected from; also known as the bottom half of the tool
Core Outs
Refers to the portion of a part that is gutted out in order to achieve uniform wall thickness. This portion of the part has no end use function other than lightening the part and reducing warp
Draft
Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. Generally all plastic components should be designed with draft where possible
Gate
Refers to where the plastic enters into the cavity of the mold. The two types of gates are as follows:
1. Automatically Trimmed Gates: Gates that incorporate features in the tool to break or shear the gate as the molding tool is opened to eject the part
2. Manually Trimmed Gates: Gates that require an operator to separate parts from runners during a secondary operation
Gibbs
Area of the custom injection mold that holds the slide down so the cam can actuate it
Hand Load
Aluminum or steel feature in a mold used to create undercuts in molded parts. They are manually removed from the mold during the part ejection process.
Heel
Refers to the portion of an automatic custom injection mold that keeps the slide in the forward position when the molding machine is closed on the mold
Horn Pin
Pin used to actuate the slide on an automatic injection mold
Line of Draw
The direction in which the two custom injection mold halves will separate from the plastic part allowing it to be ejected without any obstructions from metal creating undercuts
Ribs
Refers to thin bladed features on a part that are used for strengthening wall sections and bosses. Also, used to minimize warp (#3 in Figure 1 below)
Yihua Mould supply professional and honest service.
Runner
A channel cut into custom injection molds, in which plastic travels from the injection molding machine, through the sprue, through the runner and then through the gate ultimately filling the part
Shear
Refers to when plastic enters into the mold and the melt is maintained by friction produced by speed and pressure. Too much shear can cause the plastic material to burn, too little can cause the material to freeze off causing short shot
Short Shot
The result of a plastic part not filling completely, including some or all of the details
Shrink Rate
Refers to how much the plastic material will shrink after cooled. This % of shrink is added to the part before the mold is designed. Every plastic material has its own shrink rate ranging from .001 per inch to as much as .060 per inch. Although most fall in between .004" and .021"
Side Action
Term used for slides and/or hand pulls used in the injection mold build process
Sink Marks
Refers to areas of the molded part where it seems to be sunk in, due to un-uniformed wall sections, thick wall sections and rib/boss to thickness ratios being off
Slide
Area of the custom plastic injection molds that is used for creating undercuts. Required for automatic injection molds
Sprue
Channel that links the injection molding machine nozzle to the runner
Steel Safe
Refers to the amount of metal left on the mold in order to tweak in a dimension. For example, if you have an inside diameter that is supposed to be .500 you may leave the mold at .505 in case you get excessive shrink
Thin Wall Molding
The molding of plastic parts with wall thicknesses .005" to .060" thick
Undercuts
Refers to the portion of the designed component where a slide or hand pull is required to create holes, windows or clips that are not in the line of draw (#1 in Figure 1 below)
Vestige
Material protruding from the gate area after gate runner has been removed from the injection molded part. This vestige is usually trimmed by the molding machine operator
Wall Thickness
Refers to how thick the cross section of the plastic part is
Warp
Refers to area of a injection molded part that distorts during cooling or molding, causing undesired results in the finished product. Usually caused by un-uniform wall sections
Want more information on plastic injection mold design? Feel free to contact us.