How to choose the correct steel for injection mold

The core of the injection mold is the mold core, the quality of the mold core is directly related to the quality of the mold and the quality of the plastic parts, how to control the quality of the mold core, we must start from the raw materials, that is to say, the steel of the injection mold must be selected , The material of the mold core is related to the service life of the mold and the appearance and texture of the plastic parts. What factors should be considered in the selection of mold steel materials? Mainly from the mold process and work requirements to consider.





The mold meets the process performance requirements


Satisfying the process performance is mainly judged from the following aspects: product appearance requirements, for example, we often make mirror products and require mold polishing, while ordinary steel cannot meet the high gloss requirements, there will be material lines or insufficient luminosity. We usually choose NAK80; there are also some engineering material injection molds, whose injection plastic material is relatively hard, and the requirements for the hardness of the mold material are relatively high. We need to use higher hardness steel or quenching treatment to increase the hardness of the material. The manufacture of molds generally goes through several processes such as forging, cutting, and heat treatment. In this case, S136H or S136, SKD61 quenching is generally used. For some molds with special structures, such as the glue position is too deep or too thin, or it is difficult to remove the mold, beryllium copper will be used instead of mold steel, and its heat transfer speed is fast. When the plastic solution is injected into the mold cavity, the beryllium copper part can be The temperature rises quickly, the cavity is filled and the temperature can be cooled quickly. Secondly, beryllium copper has self-lubricating effect, and the product is easy to release from the mold.





Selection of steel for forming parts


1. For transparent plastic products, the following options are required:


(1) If the requirements of the product are very high, high light transmittance or mirror effect is required, and the molding plastic is ABS, PS, PMMA, PC, etc., it is advisable to choose high-end imported ones
P20 series, this series includes 718H(ASSAB), S136ESR(ASSAB),
S136H (ASSAB), etc. Among them, 718H (ASSAB) is in the pre-hardened state, and generally no heat treatment is required, and S136ESR (ASSAB) is in the annealed state, and the hardness is generally
HB160-230, vacuum quenching is required after rough machining, the hardness is generally HRC50±2


(2) If the product requirements are not very high, and the molding materials are PP, ABS, PS, etc., mid-range imported P20,
2738 (import), etc.


2. For non-transparent products with high appearance requirements, there are the following options:


(1) Small, precise molds and the plastics used have strong impact on steel, so high-grade imported P20 should be selected
series, such as: 718H(ASSAB), S136ESR(ASSAB), S136H(ASSAB), etc.


(2) For medium and large plastic products, the molding material has no special requirements on steel. The appearance surface of this type of mold can be selected from the mid-range imported P20 series, such as: 2738 (imported), etc. Formed non-appearance parts can choose low-grade imported P20 series or domestic P20 series.


(3) For other molds with simple structure, low output and no high appearance requirements. Domestic P20 should be selected
series. Such as: 718H (Shanghai Iron and Steel Plant No. 5), forging 718 (Baosteel
/ Fugang), forgings P20 (Baosteel / Fugang)


3. The requirements for the products are not high, and the materials used have no special requirements for steel. This type of mold has the following options:


(1) For large-scale products, the low-end and medium-grade imported P20 series are selected for the exterior components, which can also be selected upon approval by the customer
718 (domestic) steel material, imported high-quality medium carbon steel, such as S55C, S50C, etc.





(2) For small products, the output is higher and the structure is more complicated, and the low-grade imported P20 can be used for the forming components
series.



(3) For other molds with simple structure, low output and no high appearance requirements, P20 (
Domestic B30PH).


4. The following options are available for the active parts involved in molding:


(1) Transparent parts should be selected from high-end imported P20 series with good polishing properties, such as
718H(ASSAB), S136H(ASSAB), 2738(import)
Wait



(2) For non-transparent parts, medium and high-grade imported P20 series with high hardness and strength should generally be selected, and the surface should be hardened by ion nitriding, such as: inclined roof adopts
2738 (imported), the depth of the nitrided layer is 0.15-0.2mm, and the hardness is HV700
.



(3) For the cores that participate in the molding, it is best to choose the medium and high-end imported P20 series with high hardness and strength, and those with low requirements can be used
P20 (domestic B30PH) instead.


5. Selection of materials for special applications:


(1), for forming PVC and electroplating
ABS and other plastic molds that are corrosive to steel, if the product requirements are high, you can choose imported corrosion-resistant steel, such as S136ESR (ASSAB), S136H (ASSAB), etc. It is generally required to choose domestic corrosion-resistant steel.





(2) For the part of the mold that is difficult to cool or requires a high cooling effect, beryllium copper alloy should be used. (MM40
)



(3) The material of the product is PP+ glass fiber or the hard mold specified by the customer should be selected
8407.


(4) Ventilable steel can be selected if the trapped gas position of the product cannot be exhausted by other methods.