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How to Deal with Possible Problems with Parting Line

How to Deal with Possible Problems with Parting Line?

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The parting line in injection molding is also called the flashing line: the excess plastic flows out from the joint of the mold, leaving visible traces after cutting the overflowing edge, sometimes called the mold mark or the interface line, which also refers to the material flowing into the gap between the mold parts. A seam created on a plastic part or casting, or a seam under the main model from which the mold is made, to indicate where the mold is divided into two halves or parts.parting line


Often, the more complex the structure of the product, the more difficult the parting line in injection molding is to control, and it is easy to be difficult to tear, too brittle, and burst edges.

Next, let’s take a look at the factors that affect the parting line in injection molding, and we will know why some factories cannot control the parting line:

1. Mold traces

Generally, parting line marks on plastic parts depend on the precision of the mold. Under normal circumstances, due to the low processing accuracy, the mold is not well matched, and there are obvious mold line traces on the plastic parts, and even flash. For this reason, in addition to the high machining accuracy of the mold, it is also required to pay attention to the following three points when timing the mold:

1) The parting line should be located in an inconspicuous part of the plastic part

2) The parting line should be located on the part of the plastic part where it is easy to remove the flash

3) The parting line is best set on the plane


2. Design

The female mold and the male mold of mold must be closely matched to avoid the appearance of contour or stepped parting lines. If the parting line must be designed on the side wall of the part, the surface of the side wall of the part should be designed as shown in Figure 1 below, and the distance between the two sides is 0.254~0.381mm. Where possible, 0.254mm convex circles can be designed on the side walls, as shown in (Figure 2 below).design for the surface of the side wall  (Figure 1)


 (Figure 1)design for the surface of the side wall ( Figure 2)


(Figure 2)

Since the surface of the molded part needs to be trimmed, an arc edge with a radius of 0.381~0.794mm is designed at the parting line in injection molding, as shown in Figure 3 below. Set a distance, as shown in Figure 4 below, this distance is about 1.98~2.36mm, so it is easy to remove the flash. When designing the mold clamping, try to use the rounded parting line, because the circular parting line is easier to design than the straight or deformed parting line.circular arc edge

  (Figure 3)


side wall with groove(Figure 4)


3. Causes of burrs

There are two main reasons for the burrs of the clamping line. One is process control, which is often caused by overfilling, excessive injection pressure, or insufficient clamping force, and the other is mold. The solution is:

① Don’t fill up the material first, see if there is no burr, then extend the injection time, and then increase the pressure holding time;

②Increase the clamping force and lock the mold;

③ Repair the mold, weld the part with large burrs, and then grind and polish it to the specified size.

After reading these, do you want to control the clamping line of the product, it is not as difficult as it seems. Next, let’s take a look, at how does Zhongde control the bad parting line in injection molding?

1. There are problems with the clamping line, most of which are caused by improper mold design. We should check the mold the first time, such as if the front position is not sharp enough, the exhaust groove is defective, the upper and lower mold alignment deviation value, etc.

2. If there is no problem with the mold, then it is likely to be the processing of the product in the later stage, the unskilled hands are not skilled, and the product is difficult to process, etc., so some not-so-beautiful clamping lines will be produced. The impact on the product is great. For example, too many raw materials, uneven discharge, and partial shortage of materials will cause problems such as unsightly mold parting lines.

Products from polyurethane on the exhibition stand. Industry

Zhongde has a professional engineering team consisting of mold engineers, senior programmers, mold design engineers, and other professional technical personnel. In addition, Zhongde also has its own project management department to provide customers with more professional and efficient customized services. Communicate at all stages of a project, from design to production, to minimize costs and address your concerns. If you are still troubled by the parting line and need an injection molding service, welcome to consult Zhongde.

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