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Structure and material of plastic mold
2021-08-20
Structural parts:
1. Composition
The structure of blow molds, casting molds and thermoforming molds is relatively simple.
Compression molds, injection molds, and transfer molds are more complicated in structure, and there are many parts that make up this type of mold.
The basic parts are:
①Molding parts, including concave molds, convex molds, and various molding cores, are parts of the inner and outer surfaces or upper and lower end faces, side holes, undercuts and threads of the molded product.
②Support fixed parts, including mold base plate, fixed plate, support plate, cushion block, etc., to fix the mold or support pressure.
③Guiding parts, including guide posts and guide sleeves, are used to determine the relative position of the movement of the mold or ejection mechanism.
④ Core-pulling parts, including diagonal pins, sliders, etc., are used to pull out the movable core when the mold is opened to demold the product.
⑤Push out parts, including push rod, push tube, push block, push piece plate, push piece ring, push rod fixing plate, push plate, etc., to demold the product. Standard mold bases are commonly used for injection molds. This mold base is a complete set of basic parts that have been standardized and serialized in structure, form, and size. The mold cavity can be processed by itself according to the shape of the product. The use of standard mold bases is beneficial to shorten the molding cycle.
2. The role of common mold base parts
Fixed mold base plate (panel): Fix the front mold on the injection molding machine.
Runner plate (nozzle plate): Remove the waste handle when opening the mold to make it fall off automatically (three-plate mold).
Fixed mold plate (A plate): the front mold part of the molded product.
Movable mold fixing plate (B plate): the back mold part of the molded product.
Cushion: Mould foot, its function is to make the top plate have enough space for movement.
Push plate: When opening the mold, push out the product from the mold by pushing out parts such as ejector rods, top blocks, and inclined tops.
Movable mold base plate (bottom plate): Fix the back mold on the injection molding machine.
Guide post and guide sleeve: play the role of guiding and positioning, assisting the opening of the front and rear molds, and the basic positioning of the mold.
Support column (support head): Improve the strength of the B plate, effectively avoiding the deformation of the B plate caused by long-term production.
Top plate guide column (Zhong Tuo Division): guide and position the push plate to ensure smooth ejection.
Material requirements:
The working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150°C-200°C. In addition to being subjected to a certain pressure, they also have to withstand temperature. According to the different use conditions 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 50-60HRC, and the heat-treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. When the mold is working, due to the filling and flow of the plastic, it has to withstand greater compressive stress and friction. It is required that the mold maintain the accuracy of the shape and the stability of the 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 beneficial to improve its wear resistance.
2. Excellent machinability
In addition to EMD processing, most plastic molding molds require certain cutting processing and fitter repairs. In order to extend the service life of cutting tools, improve cutting performance, and reduce surface roughness, the hardness of the steel used for plastic molds must be appropriate.
3. Good polishing performance
For high-quality plastic products, the surface roughness of the cavity is required to be small. For example, the surface roughness value of the injection mold cavity is required to be less than Ra0.1～0.25, and the optical surface requires Ra<0.01nm, and the cavity must be polished to reduce the surface roughness value. For this reason, the selected steel requires less material impurities, fine and uniform structure, no fiber directionality, and no pitting or orange peel defects during polishing.
4. Good thermal stability
The shape of the parts of the plastic injection mold is often complicated and difficult to process after quenching. Therefore, it should be selected as much as possible with good thermal stability. When the mold is formed by heat treatment, the linear expansion coefficient is small, the heat treatment deformation is small, and the dimensional change caused by the temperature difference The rate is small, the metallographic structure and the mold size are stable, and the processing can be reduced or no longer needed to ensure the mold size accuracy and surface roughness requirements.
45 and 50 grades of carbon steel have certain strength and wear resistance, and are mostly used as mold base materials after quenching and tempering. High-carbon tool steel and low-alloy tool steel have higher strength and wear resistance after heat treatment, and are mostly used for forming parts. However, high-carbon tool steel is only suitable for manufacturing small-sized and simple shaped parts due to its large heat treatment deformation.
With the development of the plastics industry, the complexity and precision of plastic products have become more and more demanding, and higher requirements have been placed on mold materials. For the manufacture of complex, precise and corrosion-resistant plastic molds, pre-hardened steel (such as PMS), corrosion-resistant steel (such as PCR) and low-carbon maraging steel (such as 18Ni-250) can be used, all of which have good Cutting processing, heat treatment and polishing performance and high strength.
1. Composition
The structure of blow molds, casting molds and thermoforming molds is relatively simple.
Compression molds, injection molds, and transfer molds are more complicated in structure, and there are many parts that make up this type of mold.
The basic parts are:
①Molding parts, including concave molds, convex molds, and various molding cores, are parts of the inner and outer surfaces or upper and lower end faces, side holes, undercuts and threads of the molded product.
②Support fixed parts, including mold base plate, fixed plate, support plate, cushion block, etc., to fix the mold or support pressure.
③Guiding parts, including guide posts and guide sleeves, are used to determine the relative position of the movement of the mold or ejection mechanism.
④ Core-pulling parts, including diagonal pins, sliders, etc., are used to pull out the movable core when the mold is opened to demold the product.
⑤Push out parts, including push rod, push tube, push block, push piece plate, push piece ring, push rod fixing plate, push plate, etc., to demold the product. Standard mold bases are commonly used for injection molds. This mold base is a complete set of basic parts that have been standardized and serialized in structure, form, and size. The mold cavity can be processed by itself according to the shape of the product. The use of standard mold bases is beneficial to shorten the molding cycle.
2. The role of common mold base parts
Fixed mold base plate (panel): Fix the front mold on the injection molding machine.
Runner plate (nozzle plate): Remove the waste handle when opening the mold to make it fall off automatically (three-plate mold).
Fixed mold plate (A plate): the front mold part of the molded product.
Movable mold fixing plate (B plate): the back mold part of the molded product.
Cushion: Mould foot, its function is to make the top plate have enough space for movement.
Push plate: When opening the mold, push out the product from the mold by pushing out parts such as ejector rods, top blocks, and inclined tops.
Movable mold base plate (bottom plate): Fix the back mold on the injection molding machine.
Guide post and guide sleeve: play the role of guiding and positioning, assisting the opening of the front and rear molds, and the basic positioning of the mold.
Support column (support head): Improve the strength of the B plate, effectively avoiding the deformation of the B plate caused by long-term production.
Top plate guide column (Zhong Tuo Division): guide and position the push plate to ensure smooth ejection.
Material requirements:
The working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150°C-200°C. In addition to being subjected to a certain pressure, they also have to withstand temperature. According to the different use conditions 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 50-60HRC, and the heat-treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. When the mold is working, due to the filling and flow of the plastic, it has to withstand greater compressive stress and friction. It is required that the mold maintain the accuracy of the shape and the stability of the 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 beneficial to improve its wear resistance.
2. Excellent machinability
In addition to EMD processing, most plastic molding molds require certain cutting processing and fitter repairs. In order to extend the service life of cutting tools, improve cutting performance, and reduce surface roughness, the hardness of the steel used for plastic molds must be appropriate.
3. Good polishing performance
For high-quality plastic products, the surface roughness of the cavity is required to be small. For example, the surface roughness value of the injection mold cavity is required to be less than Ra0.1～0.25, and the optical surface requires Ra<0.01nm, and the cavity must be polished to reduce the surface roughness value. For this reason, the selected steel requires less material impurities, fine and uniform structure, no fiber directionality, and no pitting or orange peel defects during polishing.
4. Good thermal stability
The shape of the parts of the plastic injection mold is often complicated and difficult to process after quenching. Therefore, it should be selected as much as possible with good thermal stability. When the mold is formed by heat treatment, the linear expansion coefficient is small, the heat treatment deformation is small, and the dimensional change caused by the temperature difference The rate is small, the metallographic structure and the mold size are stable, and the processing can be reduced or no longer needed to ensure the mold size accuracy and surface roughness requirements.
45 and 50 grades of carbon steel have certain strength and wear resistance, and are mostly used as mold base materials after quenching and tempering. High-carbon tool steel and low-alloy tool steel have higher strength and wear resistance after heat treatment, and are mostly used for forming parts. However, high-carbon tool steel is only suitable for manufacturing small-sized and simple shaped parts due to its large heat treatment deformation.
With the development of the plastics industry, the complexity and precision of plastic products have become more and more demanding, and higher requirements have been placed on mold materials. For the manufacture of complex, precise and corrosion-resistant plastic molds, pre-hardened steel (such as PMS), corrosion-resistant steel (such as PCR) and low-carbon maraging steel (such as 18Ni-250) can be used, all of which have good Cutting processing, heat treatment and polishing performance and high strength.
In addition, when selecting materials, you must also consider preventing scratches and bonding. If there is relative movement between the two surfaces, try to avoid choosing materials with the same structure. Under special conditions, one side can be plated or nitrided to make the two sides have different The surface structure.
