The selection of mold materials is a relatively important issue in mold design and manufacturing, which directly affects a series of issues such as the service life of the mold, the manufacturing process of the mold, the molding quality of the plastic parts, the processing cost and the use cost of the mold.

Because of this, scholars at home and abroad have developed new mold steels with good processing and service performance and small heat treatment deformation, such as pre-hardened steel, new quenched and tempered steel and maraging steel. In addition, in order to improve the life of the mold, many researches and engineering practices have been done on the surface strengthening treatment of molded parts, and good results have been achieved. So far, the above-mentioned research and development work is still going on in depth, and the results obtained are being vigorously promoted.

The working conditions of plastic molds generally need to work at 150~200°C, in addition to being affected by a certain pressure, there is also the influence of temperature. According to the different conditions of use and processing methods of plastic molding molds, the basic performance requirements of steel for plastic molds are roughly summarized as follows:

(1) Sufficient surface hardness and wear resistance

The hardness of the plastic mold is usually below 50~60 HRC, and the heat-treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. Due to the filling and flow of plastic, the mold is subjected to large compressive stress and friction during work, which requires the mold to maintain the stability of shape accuracy and dimensional accuracy to ensure that the mold has a sufficient service life. The wear resistance of the mold depends on the chemical composition and heat treatment hardness of the steel, so increasing the hardness of the mold is conducive to improving its wear resistance.

(2) Good machinability

It is necessary to choose a steel grade that is easy to cut and can obtain high-precision parts after processing. For this reason, medium carbon steel and medium carbon alloy steel are the most commonly used, which is especially important for large molds. For parts that require EDM, the burn hardened layer of this steel type is also required to be thin.

(3) Excellent polishing performance

High-quality plastic products require a small roughness value on the surface of the cavity. Therefore, most of the working surfaces of injection molded parts need to be polished to a mirror surface, Ra≤0.05μm, and the hardness of the steel should be 35~40 HRC. A hard surface will increase the difficulty of polishing, and will also increase the production cost. For this reason, the selected steel requires less material impurities, uniform and dense microstructure, no fiber directionality, and no pitting or orange peel-like defects during polishing.

(4) Good thermal stability

The shape of plastic injection molded parts is often complex and difficult to process after quenching. Therefore, materials with good thermal stability should be selected as much as possible, so that the molded parts have a small linear expansion coefficient after heat treatment, small heat treatment deformation, and dimensional changes caused by temperature differences. The rate is small, the metallographic structure and mold size are stable, and processing can be reduced or no longer required to ensure the mold dimensional accuracy and surface roughness requirements.

(5) Good wear resistance and fatigue resistance

The cavity of the injection mold is not only washed by the high-pressure plastic melt, but also subjected to the temperature stress of alternating cold and heat. General high-carbon alloy steel can obtain high hardness through heat treatment, but its toughness is poor, and it is easy to form surface cracks, so it is not suitable for use. The selected steel type should enable the injection mold to reduce the number of polishing and repairing molds, maintain the dimensional accuracy of the cavity for a long time, and reach the service life of mass production.

(6) Corrosion resistance

For some plastic varieties, such as polyvinyl chloride and flame-retardant plastics, it is necessary to consider the selection of steel types with corrosion resistance.

In addition, the prevention of scratches and gluing must also be considered when selecting materials. If there is relative movement between the two surfaces, try to avoid choosing materials with the same structure. In special cases, one side can be plated or nitrided to make the two sides have different surface structure.

Goodwill Precision Machinery was established in 2004. Its main products involve industrial automation, aerospace, marine engineering equipment, unmanned driving, semiconductors, new energy, medical treatment, communications, automobiles, optics, lighting, and other fields. Customers provide high-quality precision parts

Goodwill Precision Machinery Co., Ltd. is a company specializing in precision parts custom processing. Goodwill Precision Machinery started with precision machining, but not limited to precision machining. Goodwill Precision Machinery has more than 18 years of precision parts manufacturing and equipment OEM/ODM With experience, we have continued to OEM/ODM many equipment for many equipment companies at home and abroad, many of which are high-end automation equipment for the world's top 500 companies, involving industries such as agriculture, new energy, automobiles, semiconductors, and medical industries. Cooperative customers of many domestic semiconductor equipment manufacturers, we have a wide range of processing services, such as CNC turning, milling, optical grinding machines, sheet metal, slow wire, drilling and surface treatment, etc., based on an average annual experience of more than 20 years The national technical management team and high-end imported hardware equipment group, as well as the strict German and Japanese quality management system are escorted, and are continuously trusted and praised by customers. If you are looking for precision machining or equipment OEM, ODM manufacturers. We provide the most cost-effective solutions. If you want to know more about CNC precision machining, or need customized parts, you can visit the website of Dongguan Zhaoheng Machinery Co., Ltd. to contact us!