Because plastic melt are sticky projectile, the melt flow when the viscosity with the shear stress, shear rate, the flow in the process of production along the flow direction orientation, the cavity is filled, the melt was part of the compression, cooling and solidification process of the plastic shrinkage is very complex, each part of the mold cavity, the direction of plastic shrinkage rate is different, different species, there were significant differences in brand of plastic shrinkage rate, the same brand of resin or plastic in the processing, on the basis of different formula, the molding of liquidity and shrinkage rate is different.
Based on the above characteristics, the injection mold design should fully understand the characteristics of the processed plastic raw materials, so that the designed injection mold reasonable use, and effectively use the characteristics of the plastic in the design process.
Therefore, the following issues need to be considered in the injection mold design process:
1. In-depth analysis of the structure and technical requirements of plastic parts.
Plastic parts structure determines the complexity of the structure of injection mold, plastic parts of the technical requirements (such as dimensional accuracy and surface roughness) determines the difficulty of the injection mold making and molding process, so for to do not meet the special requirements of plastic injection molding, such as unreasonable structure shape, all should put forward the improved design scheme of injection molded parts, otherwise it will increase the injection mold design and manufacturing and the difficulty of the injection molding process.
2. Familiar with the technical specifications of injection molding machine.The technical specification of injection molding machine restricts the size of injection mold and the range of injection products that can be molded.
3. Understand the processing performance and process performance of plastics.Line including the plastic melt flow, melt flow can achieve greater distance than: analysis of the flow channel and flow resistance in all parts of the cavity, the cavity within the original air discharge, plastic crystallization may occur in the injection mold, orientation and cause of stress, plastic cooling contraction and compensation, plastic injection mold temperature requirements, etc..
4, considering the design and manufacture of injection mold, mainly solve the following problems.
A. The injection mold structure should be selected reasonably.According to the drawings and technical requirements of plastic parts, research and select the appropriate molding method and equipment, combined with the factory's mechanical processing capacity, put forward the injection mold structure plan, fully solicit the opinions of the relevant parties, analysis and discussion, in order to design a reasonable injection mold structure, reliable quality, easy to operate.When necessary, according to the needs of injection mold design and processing, put forward the requirements of modifying plastic parts drawings, but only after the consent of the user can be implemented.
B, the size of injection molding parts should be calculated correctly.Molding parts are the direct factor to determine the shape, size and surface quality of plastic parts.The average shrinkage method is generally used to calculate the size of parts.For the plastic parts with high precision and need to control the mold repair allowance, it can be calculated according to the tolerance zone method. For the large precision plastic parts, it is possible to use the analogy method to calculate the shrinkage rate of the measured plastic geometric shape in different directions, so as to make up for the influence of some factors that are difficult to be considered in theory.
C. The designed injection mold shall be easy to manufacture.When designing injection mold, try to make it easy and cheap to manufacture.Especially for those more complex molding parts, must consider whether to use the general machining method or the use of special processing methods.
If the use of special processing method, then how to assemble after processing, similar problems in the design of injection mold need to consider and solve, but also should consider the mold after the trial mold repair, to leave enough mold repair margin.
D. The designed injection mold shall be efficient, safe and reliable.
This requirement involves many aspects of injection mold design, such as pouring system to fill, closed module, temperature adjustment xirong good effect, demoulding mechanism flexible and reliable.
E, the parts of injection mold shall be wear-resistant and durable.
The durability of injection mold parts affect the entire life of the injection mold, so in the design of this kind of parts should not only deal with its material, processing methods, heat treatment and other necessary requirements, such as push rod pin column is easy to get stuck, bending, broken, so the fault caused by the injection mold fault of the majority.
For this reason, we should also consider how to adjust and replace conveniently, but we should pay attention to the life of the parts and the injection mold.
F. The structure of injection mold should adapt to the molding characteristics of plastics.
In the design of injection mold, should fully understand the characteristics of the plastic used and try to meet the requirements, which is also an important measure to obtain high quality plastic parts.