Instructions for selection of injection moulded parts and materials

Time:2019-05-17 08:31:54 / Popularity: / Source:

Injection molds are a tool for producing plastic molded products and a tool for giving plastic molded products complete structure and precise dimensions. Plastic injection molding is a processing method used in mass production of complex parts with certain shapes. Specifically, plastic melted by heat is injected into cavity by high pressure of plastic injection molding machine, and after solidification by cooling, a molded article is obtained.

1. Injection moulded parts refer to injection moulded parts that are in direct contact with plastic to form products, such as cavities, cores, sliders, inserts, inclined tops, side draws, etc. .
2. Material of injection moulded parts is directly related to quality and life of mold. It determines appearance and internal quality of plastic molded products. It must be very cautious. Generally, it should be based on contract provisions and customer requirements, according to requirements and characteristics of products and molds.
3. Selection principle of materials for injection moulded parts is: according to type of plastics to be formed, shape and dimensional accuracy of products, appearance quality and use requirements of products, production batch size, etc., taking into account cutting, polishing, welding, etching, etc. of materials, deformation and wear resistance of materials, while considering economics, mold manufacturing conditions, processing methods to select different types of steel.
4. For molds for forming transparent plastic molded products, cavity and core should be made of high-grade imported steel with high mirror polishing performance, such as 718 (P20+Ni), NAK80 (P21), S136 (420), H13. Steel, etc. In which 718 and NAK80 are pre-hardened, no further heat treatment is required; S136 and H13 steels are all annealed, hardness is generally HB160-200, vacuum quenching and tempering are required after roughing. Hardness of S136 is generally HRC40-50, and hardness of H13 steel is generally HRC45-55. (can be determined according to specific grade).
5. For molds with high appearance quality requirements, long-life and high-volume production, materials of injection moulded parts are as follows:
a, Cavity needs to use high-grade imported steel with high mirror polishing performance, such as 718 (P20+Ni), NAK80 (P21), etc., all in pre-hard state, no need to heat treatment.
b. Core can be selected from medium and low grade imported P20 or P20+Ni steel, such as 618, 738, 2738, 638, 318, etc., all of which are pre-hardened; for molds with small production batches, domestic plastic injection molding steel or imported high-quality carbon steel such as S50C and S55C can also be used.
6. For mold with middle appearance quality requirements of product, material of injection moulded parts is selected as follows:
a, small, precision mold cavity and core can be selected from mid-range imported P20 or P20 + Ni steel.
b. Large and medium-sized molds, plastic forming have no special requirements for steel. Cavity can be selected from medium and low grade imported P20 or P20+Ni steel; core can be imported with low grade P20 steel or imported high quality carbon steel S50C, S55C, etc. Domestic plastic injection molding steel can also be used.
c. For cortical-patterned cavities, P2 + Ni 2738 (738) grade should be avoided when eroding pears.
7. For internal structural parts without appearance quality requirements, molding materials have no special requirements for steel, and injection moulded parts are selected as follows:
a. For large and medium-sized molds, cavity can be selected from low-grade imported P20 or P20+Ni steel. It can also be imported with high-quality carbon steel S55C, S50C or domestic P20 or P20+Ni plastic injection molding steel; core can be made of imported or domestic high quality carbon steel.
b. For small molds, if output is high and structure is more complicated, cavity can be selected from low-grade imported P20 or P20+Ni steel and domestic P20 or P20+Ni plastic injection molding steel. Core can be made of domestic plastic injection molding steel.
c. For small molds with simple structure and low output, cavity core can be made of domestic plastic injection molding steel or high quality carbon steel.
8. For plastic forming corrosive plastics such as fluorine and chlorine, or various types of molds with added flame retardant plastics, if requirements of products are high, imported corrosion-resistant steel may be used. If requirements of products is middle, domestic corrosion resistant steel may be selected.
9. For molds with strong friction and impact plastics for steel, such as molds for injecting nylon with glass fiber materials, it is necessary to use imported or domestic H13 steels with high wear resistance, high heat tensile strength and high toughness.
10. Molded inserts are generally made of same material as parts to be inlaid. For parts where mold is difficult to cool or where cooling effect is high, insert material should be made of beryllium bronze or alloyed aluminum.
11. Principles for selecting materials for moving parts involved in mold are as follows:
a, Transparent parts should use high-grade imported steel with good polishing properties, such as 718, NAK80 and so on.
b. Non-transparent parts, generally use medium-grade imported steel with high hardness and strength, such as 618, 738, 2738, 638, 318, etc. Surface is nitrided, depth of nitride layer is 0.15-0.2mm, and hardness is HV700 -900.
c. If mold requirements are low, low-grade imported steel or domestic steel may also be used. Hardness of nitriding treatment is generally HV600-800.

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