Characteristics, requirements and design considerations of plastic molds/injection molds

Characteristics of injection molds／Precautions for mold design

The characteristics of thermoplastic injection molding molds are determined by the characteristics of plastic raw materials. There are two main points:

• The flow characteristics of plastic melt when filling the mold during injection molding.
• Shrinkage behavior of molten plastic in cavity when it cools and solidifies.

These two points determine the particularity and design points of the injection mold.

Since the plastic melt is a viscoelastic body, the viscosity of the melt flow will change with the shear stress and shear rate. During the flow process, the macromolecules are more likely to be oriented along the direction of the melt flow; after the mold cavity is filled The melt of the mold is partially compressed during the pressure holding stage; the shrinkage of the plastic during the cooling and solidification process is very complex, and the plastic shrinkage rate is different in each part and direction in the mold cavity. , The same brand of plastic resin has different formulas during processing, and the flow characteristics and shrinkage rates of its filling cavity will also be different.

Basic requirements and precautions for mold design

Reasonable selection of mold structure

According to the drawings and technical requirements of the plastic parts, research and select the appropriate molding methods and equipment, combine the mechanical processing capabilities of the factory, put forward the mold structure plan, and fully solicit the opinions of relevant parties, conduct analysis and discussion, so as to make the designed mold Reasonable structure, reliable quality and convenient operation. If necessary, according to the mold design and processing needs, put forward the requirements for modifying the drawings of plastic parts, and change the structure or type of the product to achieve the expected goals of both parties.

Correctly sizing mold-formed parts

Molded parts are a direct factor in determining the shape, size and surface quality of the product, which is very relevant here, so special attention is required. When calculating the size of molded parts, the average shrinkage method can generally be used. However, for products with high precision and need to control the mold repair allowance, the increase or decrease can be calculated according to the tolerance zone method to meet the quality requirements of mass production; for large precision products, it is better to use the analogy method to compare and calculate. The shrinkage rate of the measured plastic product geometry in different directions is calculated to compensate for the influence of some factors that are difficult to consider in theory.

Design molds to be easy to manufacture

When designing a mold, try to make the designed mold easy to manufacture, so that the cost can be cheap, especially for those more complex molded parts, whether to use general machining methods or special processing methods must be considered; if using special processing methods, how to assemble after processing. Similar problems should be considered and solved when designing molds. At the same time, it is also necessary to consider the direction of mold repair after mold trial and leave enough mold repair allowance.

Fully consider the design features of plastic parts and minimize post-processing

Try to use the mold forming concept to produce products that meet the design characteristics of plastic parts, including some design concepts such as holes, grooves, convexness, and concave parts, reduce the size of gates and overflows, reduce complex unnecessary designs, and avoid unnecessary post-processing. However, the feasibility and economy of mold design and manufacturing should be considered together to prevent one-sided thinking from causing more overhead or difficulty.

The designed mold should be efficient, safe and reliable

This requirement involves many aspects of mold design, such as runner system, filling system, etc., which need to achieve fast filling, high and safe mold opening and closing rate, mold temperature control system that meets expectations, flexible and lightweight demolding mechanism, high degree of automation and so on.

Mold parts should be wear-resistant and durable, in line with the product life cycle

The durability of the mold parts affects the service life of the entire mold. Therefore, when designing this type of parts, not only the necessary requirements for its materials, processing methods, heat treatment, etc., but also the selection of steel, it is necessary to consider the opening and closing friction of the mold structure. , the hardness of the steel needs to be adjusted, and the inclined pin guide posts such as push-pull rods are also easy to be stuck, bent, broken, etc., so the failures account for most of the mold failures. To this end, we should also consider how to easily adjust and replace but pay attention to whether the life of the parts is compatible with the mold.

The mold structure should be adapted to the molding characteristics of the plastic

When designing a mold, fully understand the molding characteristics of the plastic material used, so as to meet the actual requirements of its products as much as possible, and also an important measure to obtain better quality products.

The characteristics, requirements and design considerations of plastic molds/injection molding molds require comprehensive consideration. From product design to mold steel, from mold disassembly to the processing methods of each process, all of them affect the actual mass production of molds. Service life, Production cycle, maintenance and maintenance costs, the biggest key is the development cost of the initial mold. If you have mold opening and production needs, you can contact us, and let Yeh Her Yow make the most complete multiple considerations for you from a professional standpoint.