5 key points to the stability of injection molding

5 key points to the stability of injection molding
To meet the product expectation, adjusting the settings of the injection machine properly is very important in the beginning. For example, if you see water ripples, color difference or cracks on the injection molded product, if the problem is not found immediately, or if we don't know how to adjust the machine, it may add a lot of expenses to repeated try-out, a large number of defective parts, and the cost of modifying molds. Do you know under what circumstances there will be these defective products? When these defective products appear, which settings of the machine or mold can you adjust first? In this article, we have sorted out 5 key points, allowing you to accurately inject the finished product to reduce the defect rate. See the sharing as following, 


Injection plasticizing temperature

The temperature of the plastic during injection is a relatively large factor that affects the plastic injection. After the plastic melts, there will be a processing temperature range. For example, the processing temperature range of the main injection component of Lego toys, ABS, is 190-235℃, in this temperature range ABS can be injected normally, but the temperature within the range has an impact on the injection molding process. The higher the temperature of the injected plastic, the smoother (the thinner) the plastic will flow, which means that when ABS is at 235℃, the flow will be smoother and faster than 190℃. In addition, studies have also pointed out that the higher the temperature of the injected plastic, the lower the shrinkage rate of the plastic after cooling. This means that the deformation rate of ABS after cooling at 235℃ will be much lower than that of 190℃. So if circumstances permit, we usually recommend using high-temperature plastic injection. Regarding the temperature of the injection plastic, it should be noted that too high temperature will cause the finished product to be stuck on the mold or the injection port, while too low temperature will cause the product to be injected insufficiently and incompletely. Common conditions include water wave lines and bonding lines. Such problems are often caused by too low temperature.

Mold temperature

The flowing 235℃ liquid ABS plastic will solidify and harden as soon as it encounters a lower temperature 30℃ mold, which causes the later plastic to bypass the solidified plastic before it can enter the mold. The thicker it is, the width of the runner will become smaller and smaller, and it will become more difficult to inject. If the temperature is too low, problems such as incomplete injection of the finished product and uneven structure will cause the finished product to break. Therefore, during the injection molding process, we recommend using the mold temperature is increased to avoid a large temperature difference between the plastic and the mold; in addition, studies have shown that increasing the temperature of the mold can make the finished product more practical, more resistant to fracture, and higher plasticity. It can be seen that the mold temperature is also the key to the stability of injection molding.

Injection speed

The moment the plastic is injected into the mold, the plastic will begin to solidify and form, which will affect the function of the injection molded product. Therefore, the injection speed of the plastic is usually required not to be too slow, but not too fast. When producing thinner products, it is recommended that the injection speed is fast enough. If it is too slow, the finished product will be deformed, or there will be problems such as bonding lines or flow lines on the product. In severe cases, it may even cause incomplete injection and deformation; but The injection speed should not be too fast, otherwise it will easily leave injection lines (jet lines) or burn marks on the appearance of the product. Therefore, the injection speed setting is recommended to be adjusted based on the cross-sectional area covered by the front end of the melt flow to fill up faster and without defects.

Injection pressure

The injection pressure has a certain relationship with the injection speed. If the injection speed is to be faster, the injection pressure must be adjusted higher. What else will the injection pressure affect? Under the premise of the same volume, sometimes the shape of the product is too long, too wide, or the shape is special, and the injection pressure has to be adjusted, so that the injection can be molded. Too high injection pressure will often cause the finished product to stick and deform; If the pressure is too low, there will be defects such as incomplete injection and ripple lines. If you want more stable injection molding, you must also consider the injection pressure!

Gate and runner

The runner refers to the distance from the injection molding machine to the mold, and the gate refers to the opening of the runner connected to the mold. When the plastic leaves the injection machine, the first touch is the runner and then injected into the mold through the gate. After a period of injection molding, a layer of plastic will be attached to the gate and runner. If the radius of the gate is too small, this layer of plastic will block the injection port and affect the injection; the radius is too large, too much plastic will be attached to the runner, because the attached plastic is not a part of the product and cannot be recycled. In addition to increasing the production cost, the more serious problem is that the quality of the finished product is unstable.

Mold venting

In the injection molding stage, the plastic will quickly enter the mold from the injection molding machine. If the air in the mold is not completely discharged from the vent, when the plastic fills the mold quickly, it will be compressed to air, and the high temperature of the plastic and mold also heat the air. This hot air will make the finished product of injection molding become scorched, and the quality of the finished product will be incomplete or even shrink. Well exhaust is one of the keys to the stability of injection molding.


The above 5 keys are common factors that affect the quality of the finished product during injection. There are problems with the injection molded product, which may involve many reasons and possibilities. It is not possible to determine the problem with only one key. It is recommended to record and review each time. In addition to these points, the injection molding machine itself may also be the key to the quality of injection. In order to produce a perfect product, you must first have a high-precision injection molding machine. We are a professional injection molding machine integration company. We have rich manufacturing experience and won many awards. We are committed to injection molding development and integration technology. Please contact us if you need any information.
〈Extended reading: How to choose the injection machine? 8 key points let you choose the right injection molding machine!
〈Extended reading: What are injection molding machines? What are the types?
(This article is owned by EdeX, please indicate the source for reprinting the text and pictures.)