Before mold design, designer should fully analyze and study whether plastic product conforms to principle of injection molding, needs to negotiate with product designer carefully, and a consensus has been reached. Including geometric shape, dimensional accuracy and appearance requirements of product, necessary discussions, try to avoid unnecessary complexity in mold manufacturing.

A set of high-quality molds requires not only good processing equipment and skilled mold manufacturing workers, but also a very important factor is to have a good mold design. Especially for complex molds, quality of mold design accounts for 80% of mold quality. An excellent mold design is: on the premise of meeting requirements of customers, processing cost is low, processing difficulty is small, and processing time is short.
To achieve this, it is necessary not only to fully digest customer's requirements, but also to understand injection molding machine, mold structure, processing technology and mold factory's own processing capabilities. Therefore, to improve level of mold design, following points should be achieved:
1. Understand every detail in design of each mold and understand purpose of each part in mold.
2. When designing, refer to previous similar designs, understand situation in its mold processing and product production, learn from experience and lessons.
3. Learn more about working process of injection molding machine to deepen relationship between mold and injection molding machine.
4. Enter factory to understand process of processed products, recognize characteristics and limitations of each process.
5. Understand results of mold trial and mold modification of mold designed by yourself, and learn lessons.
6. In design, try to use more successful mold structure before.
7. Learn more about impact of mold water on products.
8. Research some special mold structures and understand the latest mold technology.

 

In selection of mold materials, in addition to considering accuracy and quality of product, it is also necessary to combine actual processing and heat treatment capabilities of mold factory to give correct choice. In addition, in order to shorten manufacturing cycle, use existing standard parts as much as possible.

Except for the best structure and reasonable tolerance matching in design, accuracy of mold is very important for parts processing and mold assembly. Therefore, choice of processing accuracy and processing method occupies an absolute dominant position in mold manufacturing.
Dimensional error of molded products is mainly composed of following parts:
1. Manufacturing error of mold is about 1/3
2. Error caused by mold wear is about 1/6
3. Error caused by uneven shrinkage of molded parts is about 1/3
4. Error caused by inconsistency between scheduled contraction and actual contraction is about 1/6
Total error = (1) + (2) + (3) + (4)
Therefore, in order to reduce mold manufacturing errors, machining accuracy should be improved first. With use of CNC machine tools, this problem has been well controlled. In addition, in order to prevent errors caused by mold wear and deformation, when molds with high machining accuracy and large product output are required, key parts such as cavity and core should be quenched. In medium and large molds, in order to save materials, facilitate processing and heat treatment, mosaic structure should be adopted as much as possible in mold design.
In order to solve error caused by uneven shrinkage of molded part and inconsistency between predetermined shrinkage and actual shrinkage, 1/3 of product tolerance is generally selected during mold manufacturing as manufacturing tolerance of mold, purpose is to leave a larger adjustment room for subsequent molding process to solve errors caused by molding process.

A set of molds only completes 70% to 80% of entire manufacturing process from design to assembly. Error caused by inconsistency between predetermined shrinkage and actual shrinkage, whether demolding is smooth or not, how cooling effect is, especially influence of size, position, and shape of gate on accuracy and appearance of product, must be tested by mold trial. Therefore, mold trial is an indispensable step to check whether mold is qualified and select the best molding process.