Which aspects should be considered for dimensional control of injection molds and products?

----With the rapid development of the mold industry in recent years, the application scope of new technologies and new processes has been continuously expanded and improved, and there has been a qualitative change from traditional experience accumulation to the application of software development.

----The wide application of CAD, CAM and CAE has opened up the rising space for the geometric size control technology of our molds and mold products. Due to the great difference in the market demand of molds and mold products, there are many kinds of changes in shape, size, materials, structure and other aspects, and high requirements, we have met many problems and difficulties in the production process of molds and products. How to effectively control the geometry of the mold and the product is also very important.

----There are different control technologies and methods for different types of molds and products. Today I will talk about my experience in the control of the molding dimensions of injection molded products. When talking about injection molded products, we must talk about injection molds. Generally speaking, I start from the following aspects.


1.There are different control technologies and methods for different types of molds and products. Today I will talk about my experience in the control of the molding dimensions of injection molded products. When talking about injection molded products, we must talk about injection molds. Generally speaking, I start from the following aspects.

2.The shrinkage, flow mark, draft angle, weld line and crack of injection molded product are fully considered.

3.Under the premise of not affecting the function and pattern of the injection molded product, the mold processing method should be simplified as much as possible.

4.The selection of parting line need to be appropriate due to it will affect the mold processing, cosmetic surface..etc.

5.To choose the appropriate ejection type, how to adopt the ejector pin, stripper plate, ejection sleeve should be also took into consideration. Furthermore, it also need to consider whether the position of the ejector pin and stripper plate is appropriate.

6.Whether the use of demoulding mechanism is suitable, flexible and reliable, and without stuck phenomenon.

7.What method of temperature control is more suitable for plastic products, what kind of structural circulation system is used for heat transfer oil, warm water and coolant, and whether the size, quantity and position of coolant holes are appropriate.

8.It’s necessary to evaluate if the gate type, the size of the runner and gate location are appropriate.

9.Take the heat treatment in deformation into consideration, also judge if the selective of standard mold components is suitable.

10.Whether the injection volume, injection pressure and clamp force of the injection molding machine are sufficient, whether the nozzle R and the aperture of sprue bush is matched properly.

These aspects of comprehensive analysis preparation, from the initial stage of the product should be strictly controlled.



Although comprehensive and sufficient consideration and arrangements have been made in the design stage, many problems and difficulties will still arise in actual production. We should try our best to comply with the original design intent in production and find more effective, economical and reasonable process means in actual processing.

1.Select economically suitable machine tools for 2D and 3D machining schemes.
2.To avoid the product deformation and the fluctuation of shrinkage, to guarantee the mold machining precision, it can also take into consideration for the use of fixture for helpful production.
3.To avoid the product deformation and the fluctuation of shrinkage, to guarantee the mold machining precision, it can also take into consideration for the use of fixture for helpful production.
A: The mold manufacturing error is about 1/3
B: The error caused by mold wear is 1/6
C: The error caused by the unbalanced shrinkage of the formed part is about 1/3
D: The error caused by the inconsistency between the predetermined shrinkage rate and the actual shrinkage rate is about 1/6

The total error =A+B+C+D, so it can be seen that the mold manufacturing tolerance should be less than 1/3 of the dimensional tolerance of the formed part, otherwise the mold is difficult to ensure the geometric size of the formed part.


After plastic forming, fluctuation of geometric dimensions is a common and frequently occurring phenomenon:

1.Material temperature and mold temperature control

Different grades of plastic have different temperature requirements. On the one hand, there will have different situations in the use of poor plastic flow and more than two kinds of mixed materials, so it should be controlled in the best flow value range.
On the other hand, it is more complicated to control mold temperature. There are certain cooling system requirements in geometry, size and wall thickness ratio of different forming parts,  because mold temperature largely controls the cooling time.
Therefore, in order to shorten the injection cycle and improve production efficiency, it need to keep the mold in the permissible low temperature state, change the mold temperature, then the shrinkage rate will also change.
Keep the mold temperature stable will also keep its dimensional accuracy stable, which can prevent the deformation, poor luster, cooling spots and other defects of the formed parts. It is also can keep the physical properties of plastic in the best state. Besides, we need a debugging process, especially on the multi-cavity mold forming parts.

2.Pressure and exhaust adjustment control

When debugging the mold, you should make sure that the injection pressure is appropriate and the clamping force is matched. In the mold cavity and core, the air in the gap and the gas generated by the plastic must be discharged from the mold through the exhaust groove. Otherwise, it can occur insufficient filling and result in weld marks or burns. Sometimes these molding defects appear in the same part.

When there are thick walls around the thin-walled part of the formed part, on the one hand, if the mold temperature is too low, insufficient filling will occur, and on the other hand, if the mold temperature is too high, burning will occur. In addition, welding marks will usually appear at the burned part at the same time. In this case, the exhaust groove is often ignored and is generally in a small state.

Therefore, as long as there is no burr, and the exhaust boss of the vent groove be opened as deep as possible, and the rear part of the boss should be opened with a larger size so that the gas behind the boss can be quickly discharged from the mold. If there is a special need, open the exhaust groove on the ejector pin. Similarly, one is to keep without waste edges, and the other is to maintain fast gas discharge.

3.Supplementary shaping control for injection molded parts size

As the shape and size of some plastic molded parts are different, after demoulding, based on the changes of mold temperature and pressure drop, it’s easy to lead the plastic molded parts deformed.
In this case, it can use the fixture to bring the size into spec. This action need to be carry out immediately after the injection molding.