What Is Plastic Mold?
Plastic mold is an abbreviation for a combined mold used for compression molding, extrusion molding, injection, blow molding and low foam molding. The coordinated changes of mold convex and concave molds and auxiliary molding system can process a series of plastic parts of different shapes and different sizes.
Plastic molds are the mother of industry, and the release of new products will involve plastics.Plastic molds are tools that are matched with plastic molding machines in the plastic processing industry to give plastic products a complete configuration and precise dimensions. Due to the wide variety of plastics and processing methods, and the complex and simple structures of plastic molding machines and plastic products, the types and structures of plastic molds are also diverse.
A combined plastic mold for compression molding, extrusion molding, injection molding, blow molding and low-foaming molding. It mainly includes a cavity with a variable cavity composed of a concave mold combined substrate, a concave mold component and a concave mold combined card board The concave mold is a convex mold with a variable core composed of a convex mold combined base plate, a convex mold component, a convex mold combined card board, a cavity cut-off component and a side cut combined board.
Coordinated changes of mold convex, concave mold and auxiliary molding system. Series of plastic parts of different shapes and sizes can be processed. In the plastic processing industry, it is matched with plastic molding machines to give plastic products a complete configuration and precise size tools. Due to the wide variety of plastics and processing methods, and the complex and simple structures of plastic molding machines and plastic products, the types and structures of plastic molds are also diverse.
With the rapid development of the plastics industry and the continuous improvement of general and engineering plastics in terms of strength, the application range of plastic products is also expanding, and the amount of plastic products is also rising.
Plastic mold is a tool for producing plastic products. It is composed of several groups of parts, and there is a molding cavity in this combination. During injection molding, the mold is clamped on the injection molding machine, the molten plastic is injected into the molding cavity, cooled and shaped in the cavity, and then the upper and lower molds are separated, and the product is ejected from the cavity and out of the mold through the ejection system, and finally the mold is closed For the next injection, the entire injection molding process is carried out cyclically.
Generally, a plastic mold is composed of a movable mold and a fixed mold. The movable mold is installed on the movable template of the injection molding machine, and the fixed mold is installed on the fixed template of the injection molding machine. During injection molding, the movable mold and the fixed mold are closed to form a pouring system and a cavity. When the mold is opened, the movable mold and the fixed mold are separated to take out the plastic products.
Although the structure of the mold may vary widely due to the variety and performance of plastics, the shape and structure of plastic products, and the type of injection machine, the basic structure is the same. The mold is mainly composed of a pouring system, a temperature control system, forming parts and structural parts. Among them, the pouring system and molded parts are the parts that are in direct contact with the plastic and change with the plastic and the product. They are the most complex and the most variable parts in the plastic mold, requiring the highest processing finish and precision.
The gating system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, cold material cavity, runner and gate, etc. Molded parts refer to the various parts that make up the shape of the product, including movable molds, fixed molds and cavities, cores, molding rods, and vents.
my country’s plastic molds are driven by high technology and driven by the application requirements of pillar industries, forming a huge industrial chain, from the upstream raw and auxiliary materials industry and processing, testing equipment to downstream machinery, automobiles, motorcycles, home appliances, electronic communications , Construction and building materials and other major application industries, the development of plastic molds is full of vitality.
It mainly includes a concave mold with a variable cavity composed of a female mold combined substrate, a female mold component, and a female mold combined card board. A punch with a variable core composed of side-cut composite plates.
In order to improve the performance of plastics, various auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, colorants, etc., must be added to the polymer to become plastics with good performance.
1. Synthetic resin
Synthetic resin is the most important component of plastics, and its content in plastics is generally 40% to 100%. Because of the large content and the nature of the resin often determines the nature of the plastic, people often regard the resin as a synonym for plastic. For example, confuse polyvinyl chloride resin with polyvinyl chloride plastics, and phenolic resins with phenolic plastics. In fact, resin and plastic are two different concepts. Resin is an unprocessed raw polymer that is not only used to make plastics, but also a raw material for coatings, adhesives, and synthetic fibers. In addition to a very small part of plastics that contain 100% resin, most plastics need to add other substances in addition to the main component resin.
Fillers are also called fillers, which can improve the strength and heat resistance of plastics and reduce costs. For example, the addition of wood powder to the phenolic resin can greatly reduce the cost, making the phenolic plastic one of the cheapest plastics, and at the same time, it can significantly improve the mechanical strength. Fillers can be divided into two types: organic fillers and inorganic fillers, the former such as wood flour, rags, paper and various fabric fibers, and the latter such as glass fiber, diatomaceous earth, asbestos, carbon black and so on.
Plasticizers can increase the plasticity and flexibility of plastics, reduce brittleness, and make plastics easier to process and shape. Plasticizers are generally high-boiling organic compounds that are miscible with resin, non-toxic, odorless, and stable to light and heat. The most commonly used are phthalate esters. For example, in the production of polyvinyl chloride plastics, if more plasticizers are added, soft polyvinyl chloride plastics can be obtained; if no or less plasticizers are added (amount <10%), rigid polyvinyl chloride plastics can be obtained .
In order to prevent the synthetic resin from being decomposed and damaged by light and heat during processing and use, and to prolong its service life, stabilizers should be added to the plastic. Commonly used are stearate, epoxy resin and so on.
5. Coloring agent
The colorant can make the plastic have various bright and beautiful colors. Commonly used organic dyes and inorganic pigments as colorants.
The role of the lubricant is to prevent the plastic from sticking to the metal mold during molding, and to make the surface of the plastic smooth and beautiful. Commonly used lubricants include stearic acid and its calcium and magnesium salts. In addition to the above additives, flame retardants, foaming agents, antistatic agents, etc. can also be added to the plastic.
According to the different molding methods, the types of plastic processing molds corresponding to different process requirements can be divided, mainly including injection molding molds, extrusion molding molds, blister molding molds, high-foamed polystyrene molding molds, etc.
1. Plastic injection (plastic) mold
It is mainly a molding mold that is most commonly used in the production of thermoplastic products. The corresponding processing equipment for plastic injection molds is a plastic injection molding machine. The plastic is first heated and melted in the heating cylinder at the bottom of the injection machine, and then melted in the screw of the injection machine. Or driven by the plunger, it enters the mold cavity through the nozzle of the injection machine and the pouring system of the mold, the plastic is cooled and hardened to form, and the product is demolded. Its structure is usually composed of molding parts, pouring system, guide parts, push-out mechanism, temperature control system, exhaust system, support parts and other parts.
Manufacturing materials usually use plastic mold steel modules, and the commonly used materials are mainly carbon structural steel, carbon tool steel, alloy tool steel, high-speed steel, etc. The injection molding processing method is usually only suitable for the production of thermoplastic products. The plastic products produced by the injection molding process are very wide. From daily necessities to various complex machinery, electrical appliances, and transportation parts, they are all molded by injection molds. It is the most widely used processing method in the production of plastic products.
2. Plastic compression mould
It includes two structural mold types: compression molding and injection molding. They are a type of molds mainly used to form thermosetting plastics, and their corresponding equipment is a pressure forming machine. According to the characteristics of the plastic, the compression molding method heats the mold to the molding temperature (generally 103°—108°), then puts the measured compression powder into the mold cavity and the feeding chamber, and closes the mold. The plastic is under high heat and high pressure. It is a softened viscous flow, solidified and shaped into the desired product shape after a certain period of time.
The difference between injection molding and compression molding is that there is a separate feeding chamber. The mold is closed before molding. The plastic is preheated in the feeding chamber and is in a viscous flow state. It is adjusted and squeezed into the mold cavity under pressure to harden and form. Compression molds are also used to form some special thermoplastics, such as hard-to-melt thermoplastics (such as polyvinyl fluoride) blanks (cold forming), resin lenses with high optical performance, slightly foamed nitrocellulose car steering wheels, etc. .
The compression mold is mainly composed of a cavity, a feeding cavity, a guiding mechanism, an ejecting part, a heating system, etc. Injection molds are widely used for packaging electrical components. The material used in the manufacture of compression molds is basically the same as that of injection molds.
3. Plastic extrusion mould
A type of mold used to mold and produce continuous-shaped plastic products, also called extrusion molding heads, is widely used in the processing of pipes, rods, monofilaments, plates, films, wire and cable coatings, profiled materials, etc.
The corresponding production equipment is a plastic extruder. The principle is that the solid plastic is melted and plasticized under the conditions of heating and the screw of the extruder to rotate and pressurize, and the cross-section is the same as the shape of the die through a specific shape of the die. Continuous plastic products.
Its manufacturing materials mainly include carbon structural steel, alloy tools, etc. Some extrusion dies will also be inlaid with wear-resistant materials such as diamond on the parts that need to be wear-resistant. The extrusion process is usually only suitable for the production of thermoplastic products, and its structure is obviously different from injection molds and compression molds.
4. Plastic blow mould
It is a kind of mold used to form plastic container hollow products (such as beverage bottles, daily chemical products and other packaging containers). The forms of blow molding are mainly extrusion blow molding hollow molding and injection blow molding hollow molding according to the process principle. , Injection stretch blow molding hollow molding (commonly known as “injection stretch blow”), multilayer blow molding hollow molding, sheet blow molding hollow molding, etc.
The corresponding equipment for blow molding of hollow products is usually called a plastic blow molding machine. Blow molding is only suitable for the production of thermoplastic products. The structure of the blow mold is relatively simple, and the materials used are mostly made of carbon.
5. Plastic blister mold
It is a kind of mold that uses plastic plates and sheets as raw materials to form some simpler plastic products. Its principle is to use the vacuum method or compressed air molding method to make the plastic plates and sheets fixed on the concave mold or the convex mold. Under the condition of heating and softening, it is deformed and pasted on the cavity of the mold to obtain the desired molded product, which is mainly used in the production of some daily necessities, food, and toy packaging products. The blister mold is made of cast aluminum or non-metallic materials because of the low pressure during molding, and the structure is relatively simple.
6. High-expansion polystyrene molding die
It is a mold for using expandable polystyrene (beads composed of polystyrene and foaming agent) raw materials to form various desired shapes of foam packaging materials.
The principle is that the expandable polystyrene can be steam-formed in the mold, including two types of simple manual operation molds and hydraulic straight-through foam plastic molds, which are mainly used to produce industrial packaging products. The materials used to make this kind of molds are cast aluminum, stainless steel, bronze and so on.
Mold design and manufacturing are closely related to plastic processing. The success or failure of plastic processing depends largely on the effect of mold design and mold manufacturing quality, and the design of plastic molds is based on the correct design of plastic products.
The structural elements to be considered in the design of plastic molds are:
① Parting surface,
That is, when the mold is closed, the contact surface where the concave mold and the convex mold cooperate with each other. The selection of its location and form is affected by factors such as product shape and appearance, wall thickness, molding method, post-processing technology, mold type and structure, demolding method, and molding machine structure.
That is, the slider, inclined top, and straight top block of complex molds. The design of structural parts is very critical, and it is related to the life of the mold, processing cycle, cost, product quality, etc. Therefore, the design of the core structure of a complex mold requires a higher comprehensive ability of the designer, and the pursuit of simpler, more durable, and more economical is as much as possible. Design.
That is, avoiding jams, precise positioning, guide posts, positioning pins, etc. The positioning system is related to the appearance quality of the product, mold quality and life. According to the different mold structure, different positioning methods are selected. The positioning accuracy control mainly depends on processing. The internal mold positioning is mainly considered by the designer to design a more reasonable and easy-to-adjustable positioning Way.
That is, the feed channel from the nozzle of the injection molding machine to the cavity, including the main runner, the runner, the gate and the cold material cavity. In particular, the selection of the gate position should be conducive to the molten plastic filling the cavity in a good flow state. The solid runner and gate cold material attached to the product are easy to eject from the mold and be removed when the mold is opened. Except for road model).
③The shrinkage rate of plastics and various factors affecting the dimensional accuracy of products
Such as mold manufacturing and assembly errors, mold wear, etc. In addition, when designing compression molds and injection molds, the matching of the process and structural parameters of the molding machine should also be considered. Computer-aided design technology has been widely used in plastic mold design
The various tools and products used in our daily production and life, ranging from the base of the machine tool, the body shell, to a small screw, button and the shell of various household appliances, are all closely related to the mold. The shape of the mold determines the appearance of these products, and the processing quality and precision of the mold also determines the quality of these products. Because of the different materials, appearance, specifications and uses of various products, molds are divided into non-plastic molds such as casting molds, forging molds, die-casting molds, and stamping molds, as well as plastic molds.
In recent years, with the rapid development of the plastics industry and the continuous improvement in strength and precision of general and engineering plastics, the application range of plastic products is also expanding, such as: household appliances, instrumentation, construction equipment, automobile industry, In many fields such as household hardware, the proportion of plastic products is increasing rapidly. A reasonably designed plastic part can often replace multiple traditional metal parts. The trend of plasticization of industrial products and daily-use products is on the rise.
The general definition of mold: In industrial production, various presses and special tools installed on the press are used to make metal or non-metallic materials into parts or products of the required shape through pressure. Such special tools are collectively called molds.
Description of the injection molding process: A mold is a tool for producing plastic products. It is composed of several groups of parts, and there is a molding cavity in this combination. During injection molding, the mold is clamped on the injection molding machine, the molten plastic is injected into the molding cavity, cooled and shaped in the cavity, and then the upper and lower molds are separated, and the product is ejected from the cavity and out of the mold through the ejection system, and finally the mold is closed For the next injection, the entire injection molding process is carried out cyclically.
A. Injection molding mold-TV shell, keyboard buttons, electronic products, computer peripheral plastic products, toys, housewares (most commonly used)
B. Blow mold-beverage bottle
C. Compression molding mold-bakelite switch, scientific porcelain dishes
D. Transfer molding mold-integrated circuit products
E. Extrusion mould-glue pipe, plastic bag
F. Thermoforming mold-transparent molded packaging shell
G. Rotary forming mold-soft doll toy
According to the different types of gating system, the molds can be divided into three categories:
(1) Large nozzle mold: The runner and gate are on the parting line and are demolded together with the product when the mold is opened. The design is the simplest, easy to process, and low cost, so more people use the large nozzle system to work.
(2) Fine nozzle mold: runners and gates are not on the parting line, generally directly on the product, so it is necessary to design an additional set of nozzle parting lines, the design is more complicated, and the processing is more difficult. Generally, the selection depends on the product requirements. Fine nozzle system.
(3) Hot runner mold: The structure of this type of mold is roughly the same as that of the nozzle. The biggest difference is that the runner is in one or more hot runner plates and hot nozzles with constant temperature. There is no cold material demoulding, runner and pouring. The port is directly on the product, so the runner does not need to be demolded. This system is also called a nozzleless system, which can save raw materials, and is suitable for situations where raw materials are more expensive and products require higher requirements. Design and processing are difficult, and mold costs are higher.
The hot runner system, also known as the hot runner system, is mainly composed of a hot sprue sleeve, a hot runner plate, and a temperature control electric box. Our common hot runner system has two forms: single-point hot gate and multi-point hot gate. The single-point hot gate uses a single hot sprue sleeve to directly inject the molten plastic into the cavity. It is suitable for plastic molds with a single cavity and single gate; the multi-point hot gate branches the molten material to each The sub-heat sprue sleeve then enters the cavity. It is suitable for single cavity multi-point feeding or multi-cavity molds.
◆Advantages of hot runner system
(1) No nozzle material, no need for post-processing, so that the entire molding process is fully automated, saving working time and improving work efficiency.
(2) The pressure loss is small. The temperature of the hot runner is equal to the nozzle temperature of the injection molding machine, which avoids the surface condensation of the raw materials in the runner, and the injection pressure loss is small.
(3) The repeated use of the nozzle material will degrade the performance of the plastic, and the use of the hot runner system without the nozzle material can reduce the loss of raw materials, thereby reducing the cost of the product. The temperature and pressure in the cavity are uniform, the stress of the plastic part is small, and the density is uniform. Under a small injection pressure and a short molding time, a better product can be injected than the general injection molding system. For transparent parts, thin parts, large plastic parts or high-demand plastic parts, it can show its advantages, and can produce larger products with smaller models.
(4) The hot nozzle adopts standardized and serialized design, equipped with various nozzle heads to choose from, and has good interchangeability. The uniquely designed and processed electric heating ring can achieve uniform heating temperature and long service life. The hot runner system is equipped with hot runner plates, thermostats, etc., with exquisite design, diverse types, convenient use, and stable and reliable quality.
◆The shortcomings of hot runner system application
(1) The closing height of the overall mold is increased, and the overall height of the mold is increased due to the addition of hot runner plates, etc.
(2) The heat radiation is difficult to control. The biggest problem of the hot runner is the heat loss of the runner, which is a major issue that needs to be solved.
(3) There is thermal expansion, thermal expansion and contraction are issues that we must consider when designing.
(4) The cost of mold manufacturing increases, and the price of standard parts of the hot runner system is higher, which affects the popularization of hot runner molds.
1. Don’t just focus on product design and ignore plastic mold manufacturing.
When developing products or trial production of new products, some users often only focus on product research and development at the initial stage, and ignore communication with plastic mold manufacturers. After the product design plan is initially determined, there are two benefits to contact with the mold manufacturer in advance:
1. It can ensure that the designed product has a good forming process, and the finalized design will not be modified because the parts are difficult to process.
2. The mold maker can make design preparations in advance to prevent ill-consideration in a hurry and affect the construction period.
3. To produce high-quality plastic molds, only the close cooperation between the supply and demand sides can ultimately reduce costs and shorten the cycle.
2. Don’t just look at the price, but consider the quality, cycle, and service in an all-round way.
1. There are many types of molds, which can be roughly divided into ten categories. According to different requirements of parts materials, physical and chemical properties, mechanical strength, dimensional accuracy, surface finish, service life, economy, etc., different types of mold forming are selected.
2. Molds with high precision requirements need to be processed by high-precision CNC machine tools, and mold materials and forming processes have strict requirements, and CAD / CAE / CAM mold technology must be used for design and analysis.
3. Due to the special requirements of some parts during molding, the mold also needs advanced technology such as hot runner, gas-assisted molding, and nitrogen cylinder.
4. The manufacturer shall have CNC, EDM, wire cutting machine tools and CNC copy milling equipment, high-precision grinders, high-precision three-coordinate measuring instruments, computer design and related software.
5. Generally, large-scale stamping dies (such as automobile covering parts dies) should consider whether the machine tool has an edge holding mechanism, even edge lubricant, multi-station progressive, etc. In addition to stamping tonnage, the number of punches, feeding devices, machine tools and mold protection devices must also be considered.
6. The manufacturing methods and processes of the above-mentioned molds are not available and mastered by every enterprise. When choosing a cooperating manufacturer, you must understand its processing capabilities, not only on the hardware and equipment, but also on the management level, processing experience, and technical strength.
7. For the same set of molds, the quotations of different manufacturers sometimes differ greatly. You should not pay more than the cost of the mold, nor should it be less than the cost of the mold. Mold manufacturers, like you, must make reasonable profits in their business. Ordering a set of molds with a much lower quotation would be the beginning of the trouble. Users must proceed from their own requirements and comprehensively measure.
Third, avoid multi-head collaboration, try to make plastic molds and product processing through one-stop.
1. With qualified molds (qualified test pieces), it may not be possible to produce batches of qualified products. This is mainly related to the selection of the part processing machine tool, the forming process (forming temperature, forming time, etc.) and the technical quality of the operator.
2. With a good mold, there must be a good forming process, it is best to cooperate in one-stop, and try to avoid multi-head cooperation. If the conditions are not met, it is necessary to choose one party to be fully responsible, and it must be clearly stated when signing the contract.
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 fixing plate (A plate):
The front mold part of the molded product.
Movable mold fixed plate (B plate):
The back mold part of the molded product.
The mold foot, its function is to make the top plate have enough space for movement.
When the mold is opened, the product is pushed out of the mold by pushing out parts such as ejector pins, top blocks, and inclined tops.
Movable mold seat plate (bottom plate):
Fix the back mold on the injection molding machine.
Guide post and guide sleeve:
Play the role of guiding and positioning, assist the front and rear mold opening, and mold and basic positioning.
Support column (support head):
Improve the strength of the B board, effectively avoiding the deformation of the B board caused by long-term production.
Roof guide column (Zhong Tuo Division):
Guide positioning push plate to ensure smooth ejection.
The basic performance requirements of plastic mold steel:
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. The mold is required to 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 far 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.
First, effectively manage product data management, process data management, and drawing document management:
Carrying out effective mold product data management, process data management, drawing document management, can ensure the comprehensiveness of the file, the consistency of the drawing version; so that the drawing can be effectively shared and effectively inquired and used.
A complete file management computer database can be established, and the design drawings accumulated by the design department, scattered, previously scattered and isolated information can be organized and used to prevent 2d, 3d confusion due to design drawings, original, design changes, and maintenance versions Confusion, 3D model and 2D drawing data inconsistency, 2D drawing design is not standardized and chaotic, which causes problems that are not easy to be discovered and corrected in time, causing molds to be modified and reworked, or even obsolete, increasing mold manufacturing costs and lengthening mold manufacturing The production cycle affects the delivery time.
Second, maintain the consistency and integrity of plastic mold drawings, processing technology, and physical data: through effective, meticulous, and strict testing methods, ensure the consistency and integrity of mold drawings, processing technology, and physical data sex.
Third, the design and manufacturing cost of each set of plastic molds must be summarized in time:
By effectively controlling the issuance of work subpoenas in the workshop, effectively managing the scrapping of tools; through accurate mold structure design, efficient mold parts processing and accurate parts detection, it will effectively reduce molds caused by design changes and maintenance. Additional cost, so as to obtain the actual cost of each set of molds, and effectively control mold quality.
Fourth, overall planning:
The planning, design, processing technology, workshop production situation, human resources and other information are organically organized and integrated for overall planning, so as to effectively coordinate planning and production, which can effectively ensure the quality of plastic molds and deliver on time.
Fifth, develop a complete and practical plastic mold production management system:
Develop a complete mold production management system to realize the computer information management system of product data management, process data management, plan management, and schedule management of the mold production management process, including plastic mold production plan formulation, mold design, process formulation, and workshop Task assignment, product inspection, warehouse management, etc., enable mold manufacturing and related auxiliary information to achieve comprehensive tracking management from planning to completion and delivery.
1. Working conditions of plastic molds
Due to the development of the plastics and plastic molding industry, the quality requirements for plastic molds are becoming higher and higher, so the failure of plastic molds and their influencing factors have become an important research topic. The main working parts of plastic molds are molding parts, such as punches, concave molds, etc., which form the cavity of the plastic mold to form various surfaces of plastic parts and directly contact the plastic, and withstand pressure, temperature, friction and corrosion, etc. effect.
2. Analysis of failure causes of plastic mold materials
Generally, mold manufacturing includes mold design, material selection, heat treatment, machining, debugging and installation. According to the investigation, among the factors of mold failure, the material and heat treatment used in the mold are the main factors affecting the service life. From the perspective of total quality management, the factors that affect the service life of the mold cannot be measured as the sum of polynomials, but should be the product of multiple factors. In this way, the advantages and disadvantages of mold materials and heat treatment appear special throughout the mold manufacturing process. important.
From the analysis of the common phenomenon of mold failure, plastic molds can cause wear failure, local deformation failure and fracture failure during the service process. The important failure modes of plastic molds can be divided into wear failure, local plastic deformation failure and fracture failure.
3. Plastic mold steel performance requirements.
With the rapid development of the manufacturing industry, plastic molds are indispensable tools in plastic molding processing, and their proportion in the total mold output is increasing year by year. With the development and continuous production of high-performance plastics, The types of plastic products are increasing day by day, and their uses continue to expand. Products are becoming more sophisticated, large-scale, and more complex. The molding production is developing at a high speed, and the working conditions of the mold are becoming more and more complicated.
1) Wear and corrosion of cavity surface
The plastic melt flows in the mold cavity under a certain pressure, and the solidified plastic part comes out of the mold, which will cause friction on the molding surface of the mold and cause wear. The root cause of plastic mold wear and failure is the friction between the mold and the material. However, the specific form of wear and the wear process are related to many factors, such as the pressure, temperature, material deformation speed and lubrication condition of the mold during the working process.
When the materials and heat treatment used in the plastic mold are unreasonable, the surface hardness of the plastic mold cavity is low, and the wear resistance is poor, which is expressed as: the size of the cavity surface is out of tolerance due to wear and deformation; the roughness value becomes higher due to napping , The surface quality deteriorates. Especially when solid materials are used to enter the plastic mold cavity, it will aggravate the wear of the cavity surface. In addition, when the plastic is processed, components such as chlorine and fluorine are heated to decompose corrosive gases HC1 and HF, which cause corrosion and wear on the surface of the plastic mold cavity, resulting in failure. If there is abrasion damage at the same time as the wear, the plating layer or other protective layer on the surface of the cavity is destroyed, which will promote the corrosion process. The cross action of the two types of damage accelerates corrosion-wear failure.
2) Plastic deformation failure
Pressure and heat on the surface of the plastic mold cavity can cause plastic deformation failure, especially when small molds are working on large-tonnage equipment, they are more likely to produce overload plastic deformation. The material used in the plastic mold has insufficient strength and toughness, and low deformation resistance; another reason for plastic deformation failure is that the hardened layer on the surface of the mold cavity is too thin, the deformation resistance is insufficient, or the working temperature is higher than the tempering temperature, which causes phase change and softening. , And make the mold fail early.
The main cause of fracture is structural stress, thermal stress or insufficient tempering due to the structure and temperature difference. At the service temperature, the retained austenite is transformed into martensite, causing local volume expansion, and the structure generated inside the mold Caused by stress.
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 must also be subjected to temperature effects. There are multiple failure modes for the same mold, and multiple damages may occur even on the same mold.
From the failure mode of the plastic mold, it is very important to select plastic mold materials and heat treatment reasonably, because they are directly related to the service life of the mold. Therefore, steel for plastic molds should meet the following requirements:
1) Heat resistance
With the advent of high-speed molding machinery, plastic products run faster. Since the molding temperature is between 200-350℃, if the plastic fluidity is not good and the molding speed is fast, the surface temperature of the mold part will exceed 400℃ in a very short time. In order to ensure the precision and small deformation of the mold during use, the mold steel should have high heat resistance.
2) Sufficient wear resistance
With the expansion of the use of plastic products, it is often necessary to add inorganic materials such as glass fiber to plastics to enhance plasticity. Due to the addition of additives, the fluidity of the plastic is greatly reduced, resulting in mold wear, so it is required to have good Abrasion resistance.
3) Excellent machinability
Most plastic molding molds require certain cutting processing and fitter repairs in addition to EDM. In order to prolong the service life of the cutting tool, the work hardening is small during the cutting process. In order to avoid mold deformation and affect accuracy, it is hoped that the residual stress of machining can be controlled to a minimum.
4) Good thermal stability
The shape of the parts of the plastic injection mold is often complicated and difficult to process after quenching. Therefore, materials with good thermal stability should be selected as far as possible.
5) Mirror processing performance
The surface of the cavity is smooth, and the molding surface is required to be polished into a mirror surface, and the surface roughness is lower than Ra0.4μm to ensure the appearance of the plastic molded part and facilitate demolding.
6) Heat treatment performance
In mold failure accidents, the accident caused by heat treatment is generally 52.3%, so that heat treatment occupies an important position in the entire mold manufacturing process, and the quality of the heat treatment process has a greater impact on the quality of the mold. Generally require small heat treatment deformation, wide quenching temperature range, low overheating sensitivity, especially greater hardenability and hardenability, etc.
7) Corrosion resistance
During the forming process, corrosive gas may be released and heated to decompose corrosive gas, such as HC1, HF, etc., which corrode the mold, and sometimes the mold is rusted and damaged at the air flow passage mouth. Therefore, the mold steel is required to have good corrosion resistance.
4. New plastic mold steel
Generally, plastic molds are made of normalized 45 steel or 40Cr steel after quenching and tempering. Plastic molds with higher hardness requirements are made of steel such as CrWMn or Crl2MoV. For plastic molds with higher working temperature, hot work mold steel with high toughness can be selected. In order to meet the higher requirements for dimensional accuracy and surface quality of plastic cavities, a series of new mold steels have recently been developed.
1) Carburized plastic mold steel
Carburized plastic mold steel is mainly used for cold extrusion molding of plastic molds with complex cavities. This type of steel has low carbon content, often adding element Cr, and adding appropriate amounts of Ni, Mo and v at the same time to improve hardenability In order to facilitate cold extrusion forming, this kind of steel must have high plasticity and low deformation resistance in the annealed state, and the annealing hardness is ≤100HBS. Carburizing and quenching and tempering treatment are carried out after cold extrusion, and the surface hardness can reach 58—62HRC. There are special steel grades for this kind of steel abroad, such as 8416 in Sweden, P2 and P4 in the United States and so on. In China, 12CrNi3A and 12Cr2Ni4A steel, 20Cr2Ni4A are often used, which have good wear resistance, no collapse and surface spalling, and the life of the mold is improved. The elements cr, Ni, Mo, and V in the steel increase the hardness and wear resistance of the carburized layer and the strength and toughness of the core.
2) Pre-hardened plastic mold steel
The carbon content of this type of steel is 0.3% -0.55%, and the commonly used alloying elements are Cr, Ni, Mn, v and so on. In order to improve its machinability, elements such as s and ca are added. Several typical plastic mold steels Y55CrNiMn-MoVS (SMI) have been developed through research and introduction, which are S-containing free-cutting plastic mold steels developed in China. Its characteristic is that the pre-hardened delivery hardness is 35_40 HRC, which has better cutting performance. Processability, no heat treatment after processing, can be used directly. Adding Ni solid solution strengthening and increasing toughness, adding Mn and S to form a free-cutting phase MnS; adding Cr, Mo, V, increasing the hardenability of steel 8Cr2S steel is sufficient for free-cutting precision mold steel.
3) Age-hardening plastic mold steel
Maraging steel with low cobalt, no cobalt, and low nickel has been developed. MASI is a typical maraging steel. After 8150C solution treatment, the hardness is 28-32HRC, mechanical processing, and then 4800C aging, Ni3Mo, Ni3Ti and other intermetallic compounds are folded out during aging, so that the hardness can reach 48-52 HRC. Steel has high strength and toughness, small dimensional changes during aging, and good weld repair performance, but steel is expensive and not very popular in China.
4) Corrosion resistant plastic mold steel
Plastic products made of polyvinyl chloride (Pvc) and ABS plus flame-resistant resin are decomposed during the forming process.
Corrosive gas will corrode the mold. Therefore, plastic mold steel is required to have good corrosion resistance. There are two types of corrosion-resistant plastic mold steels commonly used abroad: martensitic stainless steel and precipitation hardening stainless steel. Foreign ones include STVAX (4Crl3) and A SSAB-8407 of the Swedish company ASSAB.
The basic procedure of plastic mold polishing In order to obtain high-quality polishing results, the most important thing is to have high-quality polishing tools and auxiliary products such as oilstone, sandpaper and diamond lapping paste.
The general process of plastic mold polishing is as follows:
1. Fine throwing
Diamond polishing paste is mainly used for fine polishing. If the polishing cloth wheel is mixed with diamond abrasive powder or abrasive paste for polishing, the usual polishing order is 9μm (#1800) ~ 6μm (#3000) ~ 3μm (#8000).
9μm diamond abrasive paste and polishing cloth wheel can be used to remove the hair-like wear marks left by #1200 and #1500 sandpaper. Then use sticky felt and diamond paste for polishing, the order is 1μm (#14000) ~ 1/2μm (#60000) ~ 1/4μm (#100000).
The polishing process with an accuracy requirement of 1μm or more (including 1μm) can be carried out in a clean polishing room in the mold processing workshop. For more precise polishing, an absolutely clean space is necessary. Dust, smoke, dandruff and saliva can all scrap the high-precision polished surface obtained after several hours of work.
2. Rough toss
After milling, EDM, grinding, etc., the surface can be polished with a rotating surface polisher or ultrasonic grinder with a speed of 35 000-40 000 rpm. The commonly used method is to remove the white EDM layer with wheels with diameter Φ3mm and WA # 400. Then there is manual whetstone grinding, and the strips of whetstone are added with kerosene as a lubricant or coolant. The general order of use is #180 ~ #240 ~ #320 ~ #400 ~ #600 ~ #800 ~ #1000. Many mold manufacturers choose to start with #400 in order to save time.
3. Semi-precision throwing
Semi-precision polishing mainly uses sandpaper and kerosene. The number of sandpaper is: #400 ~ #600 ~ #800 ~ #1000 ~ #1200 ~ #1500. In fact, #1500 sandpaper only uses die steel suitable for hardening (above 52HRC), not pre-hardened steel, because it may cause burns on the surface of pre-hardened steel.
For fine polishing with abrasive paste, 8000 and 10000 will reach the mirror surface.
Mechanical polishing is a polishing method that relies on cutting and plastic deformation of the material surface to remove the polished convex parts to obtain a smooth surface. Generally, oil stone sticks, wool wheels, sandpaper, etc. are used, and manual operations are the main method. Special parts such as the surface of the rotating body can be used. Use the turntable and other auxiliary tools, and the ultra-precision polishing method can be used if the surface quality is high. Ultra-precision polishing is the use of special abrasive tools, which are pressed tightly on the processed surface of the workpiece in a polishing fluid containing abrasives for high-speed rotation. Using this technology, the surface roughness of Ra0.008μm can be achieved, which is the highest among various polishing methods. Optical lens molds often use this method.
Chemical polishing is to make the surface microscopic convex part of the material in the chemical medium dissolve preferentially than the concave part, so as to obtain a smooth surface. The main advantage of this method is that it does not require complex equipment, can polish workpieces with complex shapes, and can polish many workpieces at the same time, with high efficiency. The core problem of chemical polishing is the preparation of polishing liquid. The surface roughness obtained by chemical polishing is generally several 10 μm.
The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, by selectively dissolving tiny protrusions on the surface of the material to make the surface smooth. Compared with chemical polishing, the effect of cathode reaction can be eliminated, and the effect is better. The electrochemical polishing process is divided into two steps: (1) Macroscopic leveling The dissolved products diffuse into the electrolyte, and the geometric roughness of the material surface decreases, Ra>1μm. ⑵ Low-light leveling: Anode polarization, surface brightness is improved, Ra<1μm.
Put the workpiece in the abrasive suspension and put it together in the ultrasonic field, relying on the oscillation effect of the ultrasonic, so that the abrasive is ground and polished on the surface of the workpiece. Ultrasonic machining has a small macroscopic force and will not cause deformation of the workpiece, but it is difficult to manufacture and install tooling. Ultrasonic processing can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution, so that the dissolved products on the surface of the workpiece are separated, and the corrosion or electrolyte near the surface is uniform; the cavitation effect of ultrasonic in the liquid can also inhibit the corrosion process and facilitate surface brightening.
Fluid polishing relies on high-speed flowing liquid and abrasive particles carried by it to wash the surface of the workpiece to achieve the purpose of polishing. Commonly used methods are: abrasive jet processing, liquid jet processing, hydrodynamic grinding and so on. Hydrodynamic grinding is driven by hydraulic pressure to make the liquid medium carrying abrasive particles flow back and forth across the surface of the workpiece at high speed. The medium is mainly made of special compounds (polymer-like substances) with good flowability under lower pressure and mixed with abrasives. The abrasives can be made of silicon carbide powder.
Magnetic grinding and polishing
Magnetic abrasive polishing is to use magnetic abrasives to form abrasive brushes under the action of a magnetic field to grind the workpiece. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. Using suitable abrasives, the surface roughness can reach Ra0.1μm.
2 Mechanical polishing base
The polishing mentioned in the plastic mold processing by this method is very different from the surface polishing required in other industries. Strictly speaking, the polishing of the mold should be called mirror processing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy. Surface polishing generally only requires a bright surface. The standard of mirror surface processing is divided into four levels: AO=Ra0.008μm, A1=Ra0.016μm, A3=Ra0.032μm, A4=Ra0.063μm. It is difficult to precisely control the geometric accuracy of parts due to methods such as electrolytic polishing and fluid polishing. However, the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods are not up to the requirements, so the mirror processing of precision molds is still mainly mechanical polishing.
To obtain a high-quality polishing effect, the most important thing is to have high-quality polishing tools and auxiliary products such as whetstone, sandpaper and diamond lapping paste. The choice of polishing procedure depends on the surface condition after pre-processing, such as machining, EDM, grinding and so on.
Link to this article：What Is Plastic Mold?