Selection standards for mold steel

source：宏森    data：2024-05-10

1、 Selection of Materials for Forming Components

1. Formed components refer to mold components that come into direct contact with plastic to form products, such as cavities, cores, sliders, inserts, inclined roofs, side pulls, etc.

The material of the formed components is directly related to the quality and service life of the mold, determining the appearance and internal quality of the plastic products formed. It must be carefully selected based on the requirements and characteristics of the product and mold, as stipulated in the contract and customer requirements.

The principle of selecting materials for formed parts is: based on the type of plastic formed, the shape and dimensional accuracy of the product, the appearance quality and usage requirements of the product, the production batch size, etc., taking into account the cutting, polishing, welding, etching, deformation, wear resistance and other properties of the material, while considering the economy and manufacturing conditions and processing methods of the mold, different types of steel are selected.

For molds for forming transparent plastic products, the cavity and core should be made of high-grade imported steel with high mirror polishing performance, such as 718 (P20+Ni class), NAK80 (P21 class), S136 (420 class), H13 class steel, etc. Among them, 718 and NAK80 are in a pre hard state and do not require further heat treatment; S136 and H13 steel are both in an annealed state, with a hardness of HB160-200. After rough machining, vacuum quenching and tempering treatment are required. The hardness of S136 is generally HRC40-50, while the hardness of H13 steel is generally HRC45-55 (which can be determined according to specific grades).

For molds with high requirements for appearance quality, long lifespan, and mass production of products, the selection of forming component materials is as follows:

a) The cavity needs to be made of high-end imported steel with high mirror polishing performance, such as 718 (P20+Ni class), NAK80 (P21 class), etc., which are in a pre hard state and do not require further heat treatment.

b) The core can be made of medium to low-grade imported P20 or P20+Ni steel, such as 618, 738, 2738, 638, 318, etc., all in a pre hardened state; For molds with small production batches, domestic plastic mold steel or imported high-quality carbon steel such as S50C and S55C can also be selected.

For molds with general requirements for product appearance quality, the material selection for their formed components is as follows:

a) Small and precision mold cavities and cores are made of medium grade imported P20 or P20+Ni steel.

b) Large and medium-sized molds, the plastic formed has no special requirements for steel, and the cavity can be made of medium and low-grade imported P20 or P20+Ni steel; The core can be made of low-grade imported P20 steel or imported high-quality carbon steel S50C, S55C, etc., or domestic plastic mold steel can be selected.

c) For cavities with etched skin patterns, efforts should be made to avoid using P20+Ni grade 2738 (738) when etching pear ground patterns.

For internal structural components without appearance quality requirements and molds with forming materials that do not have special requirements for steel, the selection of forming component materials is as follows:

a) For large and medium-sized molds, low-grade imported P20 or P20+Ni steel can be used for the mold cavity, as well as imported high-quality carbon steel S55C, S50C, or domestically produced P20 or P20+Ni plastic mold steel; The core can be made of imported or domestically produced high-quality carbon steel.

b) For small molds, if the output is high and the structure is complex, low-grade imported P20 or P20+Ni steel can be used for the mold cavity, or domestically produced P20 or P20+Ni plastic mold steel can be used; The core can be made of domestically produced plastic mold steel.

c) For small molds with simple structures and low production, domestic plastic mold steel or high-quality carbon steel can be selected for the cavity and core.

For molds that contain corrosive plastics such as fluorine and chlorine, as well as various types of plastics with added flame retardants, if the product requirements are high, imported corrosion-resistant steel can be selected, while domestically produced corrosion-resistant steel can be used for general requirements.

For molds that have strong friction and impact on steel, such as those used for injection of nylon+fiberglass materials, imported or domestic H13 steel with high wear resistance, high thermal tensile strength, and high toughness should be selected.

. 10 Forming inserts generally use the same material as the embedded parts. For parts of the mold that are difficult to cool or require higher cooling effects, the inlay material should be beryllium bronze or alloy aluminum.

The principles for selecting materials for active components involved in molding in molds are as follows:

a) Transparent parts should be made of high-quality imported steel with good polishing properties, such as 718, NAK80, etc.

b) Non transparent parts should generally be made of medium grade imported steel with high hardness and strength, such as 618, 738, 2738, 638, 318, etc. The surface should be nitrided with a nitriding layer depth of 0.15-0.2mm and a hardness of HV700-900.

c) If the mold requirements are low, low-grade imported steel or domestic steel can also be selected, and the nitriding treatment hardness is generally HV600-800.

2、 Material selection for non formed components

1. The material of the mold base shall refer to the mold base standard. Generally, imported S50C or domestically produced SM45 templates shall be selected, with HB160-200 requirements, uniform hardness, low internal stress, and not easy to deform. The guide pillar material is GCr15 or SUJ2, with a hardness of HRC56-62. The materials for the guide sleeve, push plate guide pillar, push plate guide sleeve, and reset rod can be GCr15 or SUJ2, with a hardness of HRC56-62; T8A and T10A can also be used, with a hardness of HRC52-56.

The general structural components in the mold, such as the ejection positioning ring, column, ejection limit block, limit pull rod, lock module, etc., do not have special requirements for hardness and wear resistance. Domestic SM45 steel, in normalized state, with a hardness of HB160-200, can be selected without further heat treatment.

Parts such as sprue sleeves, wedge blocks, wear-resistant blocks, and slider pressure plates in molds that require high hardness, strength, and wear resistance should be made of carbon tool steel or high-quality carbon tool steel, such as T8A, T10A, etc. This type of steel requires quenching treatment when used to improve its hardness and wear resistance