Plastic molds are specialized tools used in plastic production and processing to provide detailed configurations and precise specifications for plastic products. Due to the diverse types and production methods of plastics, as well as the varying structures of plastic molding machines and plastic products, the types and structures of plastic molds are also diverse.
The working standards of plastic molds are different from those of cold stamping molds. Generally, they must be operated at temperatures between 150 ° C and 200 ° C. In addition to being subjected to certain working pressures, they also have to bear temperature hazards. Based on the application standards and production processing methods of plastic molding molds, the basic characteristics of steel used in plastic molds are summarized as follows:
1. Adequate surface strength and wear resistance
The strength of plastic molds is generally below 50-60HRC. Molds that have undergone heat treatment must have sufficient surface strength to ensure sufficient bending stiffness. In mold work, due to the addition and fluidity of plastic, it is necessary to bear significant compressive stress and sliding friction. It is required to maintain the precision of the mold's appearance and the reliability of its specification precision to ensure that the mold has sufficient service life. The wear resistance of the mold depends on the composition and heat treatment strength of the stainless steel plate, so improving the strength of the mold is beneficial for enhancing its wear resistance.
2. High quality drilling process performance
Most plastic molding molds require certain drilling production and milling mechanical and electrical maintenance in addition to EMD production and processing. To increase the service life of cutting tools, improve machinability, and reduce surface roughness, the hardness of steel used for plastic molds must be moderate.
3. Excellent polishing and polishing characteristics
High quality plastic products require a small surface roughness value on the concave mold surface. For example, the surface roughness value of the concave mold of an injection mold is specified to be lower than the Ra 0.1-0.25 level, while the electronic optical surface is specified to be Ra< 0.01nm, the concave mold needs to be polished to reduce the surface roughness value. Therefore, the stainless steel plate used requires minimal raw material residue, uniform mechanism, no chemical fiber specificity, and no black spots or orange peel like defects during polishing.
4. Excellent heat resistance
The appearance of parts in plastic injection molds is usually very complex, and cannot be produced or processed after heat treatment. Therefore, it is advisable to use parts with excellent heat resistance as much as possible. When the mold is formed and produced and processed after heat treatment, due to the small coefficient of thermal expansion, small heat treatment deformation, and temperature differences, the specification elasticity coefficient is small. The alloy composition and mold specifications are stable, and production processing can be reduced or will not be carried out again, which can ensure the precision of mold specifications and the specified surface roughness.
5. 50 type alloy steel has certain compressive strength and wear resistance, and is often used as raw material for mold after heat treatment. High carbon steel alloy steel and low-carbon tool steel have high compressive strength and wear resistance after heat treatment, and are often used for forming parts. However, high carbon steel alloy steel is only suitable for producing small and simple shaped parts due to its large heat treatment deformation.
With the development trend of plastic industry production, the diversity and precision of plastic products are becoming increasingly high, and higher regulations are also clearly proposed for mold raw materials. For the production of complex, refined, and corrosion-resistant plastic molds, pre soft steel (such as PMS), corrosion-resistant steel (such as PCR), and low-carbon environmentally friendly austenitic aging steel (such as 18Ni-250) can be selected, all of which have good drilling, production processing, heat treatment, polishing and high toughness.
In addition, when selecting raw materials, it is also necessary to consider avoiding scratches and plywood. If there is a relative velocity between the two surfaces, try to reduce the selection of raw materials with the same organizational structure. In unique cases, one side can be coated or nitrided to give the two sides a different surface structure. Raw material selection:
1. Working standards for plastic molds
Due to the development trend of plastic and plastic molding industry production, the quality standards for plastic molds are becoming increasingly high. Therefore, the problem of ineffective plastic molds and their influencing factors have become a key research topic. The key components of plastic molds are formed parts, such as convex molds, cavities, etc. They form the concave molds of plastic molds to form various surfaces of plastic products and immediately touch the plastic, bearing the effects of working pressure, temperature, friction, and erosion.
2. The root cause of ineffective plastic mold raw materials
In general mold production and manufacturing, it includes the entire process of mold design scheme, use of raw materials, heat treatment, mechanical processing and manufacturing, adjustment and installation, etc. According to research, among the factors that make molds ineffective, the raw materials and heat treatment used in the molds are the key factors that endanger their service life. From the perspective of comprehensive quality control, the various factors that endanger the service life of molds cannot be considered as the sum of algebraic equations, but should be multiplied by multiple factors. In this way, the quality of mold raw materials and heat treatment appears to be particularly critical throughout the entire mold production and manufacturing process.
From the analysis of the common existence of ineffective molds, plastic molds can cause wear failure, reversible deformation failure, and fracture failure throughout their service life. The key ineffective ways of plastic molds can be divided into wear failure, partial plastic deformation failure, and fracture failure.
3. With the rapid development trend of the processing and manufacturing industry, plastic molds are a specialized tool that cannot be lacking in plastic molding production and processing. Their proportion in the total mold production is gradually increasing. With the development trend of high-performance plastics and continuous production and manufacturing, the types of plastic products are increasing, and their main uses are constantly developing. Products are moving towards precision, import substitution, and complex development. The trend of high-speed development in molding production and manufacturing has led to increasingly complex standards in the work of molds.
4. New plastic mold steel
Generally, plastic molds are produced using quenched 45 steel or quenched and tempered steel after heat treatment. Plastic molds with high strength requirements are manufactured using steel such as CrWMn or Crl2MoV. For plastic molds with high operating temperatures, hot work mold steel with high ductility can be selected. In order to better consider the higher requirements for precision and surface quality of plastic molds, a series of new mold steels have been developed recently.