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How to make a plastic mould?

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What is the plastic mould making process?Here’s some details.

The manufacture of injection moulds includes five major steps.

1.Process analysis of plastic products

Before the mould design, the designer should fully analyses and study whether the plastic products are in line with the principles of injection moulding processing, which requires careful consultation with the designer of the products and has reached a consensus. The necessary discussion includes the geometric shape, dimensional accuracy and appearance requirements of the product. And then try to avoid unnecessary complications in the manufacture of the mould.

2.Mould structure design

For a set of high quality moulds, not only need good processing equipment and skilled mould manufacturing workers, but another very important factor is to have a good mould design. Especially for complex moulds, more than 80% of the mould quality depends on the mould design. An excellent mould design is the one that makes the processing cost lower, the machining easier and the processing leadtime shorter, subject to customer’s requirement.

Follow the below to improve the mould design.

1) Study every detail in each mould design and understand the purpose of each part in the mould.

2) Refer to previous similar cases when in the design. To learn the status in tooling and molding.

3) Learn more about the working process of the injection machine, to understand the relationship between mould and injection.

4) Study the machining processes in site, to understand the features and limitations of each process.

5) Review the results of mold trials every time, and to improve the mould design.

6) Try to adopt the previous more successful mould structure in the design.

7) Learn more about the effects of the gate.

8) Study special mould structures and learn about the latest mould technology.

3.Determine the mold material and choose standard parts

Regarding to the selection of mould materials, not only the product accuracy and quality should be considered, but also the correct choice of machining and heat treatment capacities. In addition, in order to shorten the manufacturing cycle time, should use the standard components if possible.

4.Mould components machining and mould assembly

In addition to giving the best structure and reasonable tolerance during the design, the accuracy of the mold is very important for component machining and mold assembly. Therefore, the choice of machining accuracy and machining method plays an absolutely dominant role in mold manufacturing.

The dimensional tolerance of the injection product comes from the below.

1) The tolerance caused by mould manufacture is around 1/3.

2) The tolerance caused by the wear and tear of mould is around 1/6.

3) The tolerance caused by the uneven shrinkage of the molded part is around 1/3.

4) The tolerance caused by the inconsistency between the intended shrinkage and the actual shrinkage is around 1/6.

Total tolerance = (1)+(2)+(3)+(4)

Therefore, in order to reduce the tolerance while in mould manufacturing, the first step should be to improve the machining accuracy. With the use of CNC machine tools, this problem has been well controlled. In addition, in order to prevent the tolerance caused by mould wear and deformation, quenching treatment shall be adopted for the key parts such as the cavity and core when processing the mould with high precision and large product output.

In order to save materials and facilitate processing and heat treatment in medium and large-scale molds, the mosaic structure should be used as much as possible in mold design.

5.Mould trial

It is only 70% ~ 80% of the whole manufacturing process from mould design to assembly. The mould trial is to verify the tolerance which caused by the inconsistency between the predetermined shrinkage and the actual shrinkage, to verify the mold-releasing and the cooling effect.

Mould trial is an indispensable step to check whether the mould is qualified and select the best molding process.


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