In injection plastic injection molding services, each cavity in a mold must have a small opening known as a gate, which allows hot plastic to enter the cavity before passing through and around the internal features of the mold until it is completely filled with plastic. Once the part has been ejected from the mold, the sprue, runner, or small lump of plastic that has remained attached to the gate must be removed, which is usually done by hand, which presents a significant challenge. Depending on the style of gate, the type of plastic used, and the geometry of the part, this can leave a slight vestige—also known as a witness mark—on the surface of the gate.
Attempt to pick up any plastic injection molded part and you'll notice that most gates leave a trace that is barely noticeable—assuming the mold was designed properly, which is the case. In the first instance, gates can and should be placed in areas that are not aesthetically pleasing whenever possible. When a gate must be placed in an unattractive location, or when the raw material necessitates a gate that is larger than average in size (glass-filled resins, for example), steps can be taken to reduce the unsightly factor.
Moldplasticinjection uses three different styles of gates in its plastic injection Plastic Injection Mold Services operations, and this design tip provides guidance on how to use these gates to produce aesthetically pleasing and cost-effective molded parts in the shortest amount of time.
The most common type of gate is the tab gate
The tab gate is the most commonly used (and largest) type of gate available. Look at an untrimmed part and you will see the gate as a tapered rectangle protruding from the part's outer surface. As much as possible, it's placed where the part is thickest, and it's always placed at the parting line, making it relatively easy to trim and having the least impact on both the appearance and functionality of the part.