1.Molded parts refer to mold parts that directly contact plastic and form products,such as cavities,cores,silders inserts,inclined tops,side drawers,etc.
2.The material of the molded parts is directly related to the quality and life of the mold,and determines the appearance and internal quality of the molded plastic products.It must be very careful.Generally,on the basis of contract regulations and customer requirements,according to the requirements of products and molds and feature selection.
3.The selection principle of molding parts materials is: according to the type of plastic to be molded,the shape of the product,dimensional accuracy,the appearance quality of the product and the use requirements,the size of the production batch,etc.,taking into account the cutting,polishing,welding,etching,deformation,etc. of the material.Various properties such as wear resistance,and at the same time consider the economy and the manufacturing conditions and processing methods of the mold,so as to select different types of steel.
4.For the mold 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 type),NAK80(P21 type),S136(420 type),H13 type steel,etc.,among which 718 and NAK80 are in the pre-hardened state and do not need to be heat treated again;S136 and H13 steels are in the annealed state,the hardness is generally HB160-200,rough machining after that,vacuum quenching and tempering are required.The hardness of S136 is generally HRC40-50,and the hardness of H13 steel is generally HRC45-55(which can be determined according to the specific grade).
5.For molds with high requirements on product appearance quality,long life and mass production,the materials for forming parts are selected as follows:
1)The cavity should be made of high-grade imported steel with high mirror polishing performance,such as 718(P20+Ni type),NAK80(P21 type),etc.,which are all pre-hardened and do not need to be heat treated.
2)The core can be made of low-grade imported P20 or P20+Ni steel,such as 618,738,2738,638,318,etc.,which are all pre-hardened;for molds with small production batches,domestic plastic mold steel can also be used or imported high-quality carbon steel such as S50C and S55C.
6.For molds with general product appearance quality requirements,the materials for forming parts are selected as follows:
1)Small and precision mold cavity plastic have no special requirements for steel,and the cavity can be selected from mid-grade imported P20 or P20+Ni steel.
2)For large and medium-sized molds,the plastics to formed have no special requirements for steel.The cavity can be selected from imported P20 or P20+Ni steel of low grade;the core can be selected from low-grade imported P20 steel or imported high-quality carbon steel S50C,S55C,etc.Use domestic plastic mold steel.
3)For the cavity of the etched skin pattern,when the pear ground pattern is etched,the 2738(738) grade of P20+Ni should be avoided.
7.For internal structural parts without appearance quality requirements and molds that have no special requirements for steel materials,the selection of materials for forming parts is as follows:
1)For large and medium-sized molds,low-grade imported P20 or P20+Ni steel can be used for the cavity,or imported high-quality carbon steel S55C,S50C or domestic P20 or P20+Ni plastic mold steel;the core can be imported or domestic high-quality carbon steel.
2)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 cavity,or domestic P20 or P20+Ni plastic mold steel can be used;domestic plastic molds can be used for the core steel.
3)For small molds with simple structure and low output,the cavity core can be made of domestic plastic mold steel or high-quality carbon steel.
8.For molding fluorine,chlorine and other corrosive plastics and various types of flame retardant plastics molds,if the product requirements are higher,imported corrosion-resistant steel can be used,and domestic corrosion-resistant steel is generally required.
9.For molds that have strong friction and impact on steel,such as molds used to inject nylon+glass fiber materials,imported or domestic H13 types with the advantages of high wear resistance,high thermal tensile strength and high toughness should be selected stee.
10.Forming inserts are generally made of the same material as the part being inserted.For the part of the mold that is difficult to cool or the part that requires a high cooling effect,the insert material should be beryllium bronze or alloy aluminum.
11.The principle of material selection for the moving parts involved in molding in the mold is as follows:
1)Transparent parts should be made of high-grade imported steel with good polishing properties,such as 718,NAK80,etc.
2)For non-transparent parts,generally medium-grade importe steel with high hardness and strength should be selected,such as 618,738,2738,638,318,etc.,the surface is nitride,the depth of the nitride layer is 0.15-0.2mm,and the hardness is HV700-900.
3)If the mold requirements are low,low-grade imported steel or domestic steel can also be used,and the hardness of nitriding treatment is generally HV600-800.
Material selection of non-molding injection mold parts
1.The mold base material refers to the mold base standard.The formwork generally adopts imported S50C or domestic SM45,requiring HB160-200,uniform hardness,small internal stress,and not easy to deform.The material of the guide post is GGra15 or SUJ2,and the hardness is HRC56-62.The guide sleeve,push plate guide sleeve and reset rod can be made of Ggr15 or SUJ2 with a hardness of HRC56-62;T8A and T10A can also be used with a hardness of HRC52-56.
2.General structural parts in the mold,such as ejector positioning ring,column,ejector limit block,limit tie rod,lock module,etc.,have no special requirements for hardness and wear resistance,domestic SM45 steel can be selected,normalized state,Hardness HB160-200,no need for heat treatment.
3.Sprue sleeves,wedge blocks,wear-resistant blocks,slider pressure plates and other parts in the mold that require high hardness,strength and wear resistance should use carbon tool steel or high-quality carbon tool steel,such as T8A,T10A etc.These steels are required to be quenched to improve their hardness and wear resistance.
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