When creating a part for injection molding, an important step is to consider where you will put the “parting line” in the design of the mold. The parting line indicates the direction of the line of draw for the mold, or the point where you can separate the two halves of the mold to release the part without damage. Usually, the parting line is down the middle of the part, but this varies due to part geometry. The parting line determines the direction to draft features for easy removal from the mold.

The final goal of mold design is to make a mold as simple as you can. Sometimes, however, to accommodate part features, the mold will need extra elements included to ensure the part can be removed without damage. These extra elements include cam actions and lifters, in addition to the cooling elements needed to control temperature as the molten material solidifies. Of course, all of these mold elements and features add to the cost of developing a mold.

To select where to put the parting line, decide which side of the mold is the A side and which is the B side. The A side is usually the side where the show surface of the part will be. When opening the mold, the part will stay on the B side and be removed from that part of the mold, either easily due to the design, or with the use of cam actions or ejectors.

Cooling elements for the mold are usually on the B side of the mold. Most materials shrink a bit as they cool in the mold, which can be used to advantage when designing the mold and ensuring the part stays on one side of the mold when opening.

If you know you will be using injection molding to make a design, sometimes a CAD program will suggest optimal placement, or you can always consult with the injection molding provider about the best placement for the parting line.