Plastic molds are tools that are matched with plastic molding machines in plastic processing industry to give plastic products a complete configuration and precise dimensions. Due to wide variety of plastics and processing methods, complex and simple structures of plastic molding machines and plastic products, types and structures of plastic molds are also diverse.
So what is process of making plastic molds? Let's take a look together!

 

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, 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 can process series of plastic parts of different shapes and different sizes. In plastic processing industry, it is matched with plastic molding machines to give plastic products a complete configuration and precise size tools. Due to wide variety of plastics and processing methods, complex and simple structures of plastic molding machines and plastic products, types and structures of plastic molds are also diverse.
With rapid development of plastics industry, continuous improvement of general and engineering plastics in terms of strength, application range of plastic products is also expanding, and 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, mold is clamped on injection molding machine, molten plastic is injected into molding cavity, cooled and shaped in cavity, then upper and lower molds are separated, product is ejected from cavity and out of mold through ejection system, finally mold is closed. For 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. Movable mold is installed on movable mold plate of injection molding machine, fixed mold is installed on fixed mold plate of injection molding machine. During injection molding, movable mold and fixed mold are closed to form a pouring system and cavity. When mold is opened, movable mold and fixed mold are separated to take out plastic products.
Although structure of mold may vary widely due to variety and performance of plastics, shape and structure of plastic products, type of injection machine, basic structure is same. Mold is mainly composed of a pouring system, a temperature control system, forming parts and structural parts. Among them, pouring system and molded parts are parts that are in direct contact with plastic and change with plastic and product. They are the most complicated and the most variable parts in plastic mold, require the highest processing finish and precision.
Gating system refers to part of runner before plastic enters cavity from nozzle, including main runner, cold material cavity, runner and gate, etc. Molded parts refer to various parts that make up shape of product, including movable molds, fixed molds and cavities, cores, molding rods, and vents.
Driven by high technology and application of pillar industries, my country’s plastic molds have formed a huge industrial chain, from upstream raw and auxiliary materials industry, processing and testing equipment to downstream machinery, automobiles, motorcycles, home appliances, electronic communications, building materials and other major application industries, development of plastic molds is full of vitality.

 

According to different molding methods, 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.

It is mainly a molding mold that is most commonly used in production of thermoplastic products. Corresponding processing equipment for plastic injection molds is a plastic injection molding machine. Plastic is first heated and melted in heating cylinder at the bottom of injection machine, then driven by screw or plunger of injection machine, it enters mold cavity through injection machine nozzle and casting system of mold, plastic is cooled and hardened to form, and product is demolded.
Its structure is usually composed of molding parts, pouring system, guide parts, push-out mechanism, temperature adjustment system, exhaust system, support parts and other parts. Manufacturing materials usually use plastic mold steel modules, and commonly used materials are mainly carbon structural steel, carbon tool steel, alloy tool steel, high-speed steel, etc.
Injection molding processing method is usually only suitable for production of thermoplastic products. Plastic products produced by 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 production of plastic products.

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 characteristics of plastic, compression molding method heats mold to molding temperature (generally 103°—108°), then puts measured compression powder into mold cavity and feeding chamber, closes mold. Plastic becomes soft and viscous under action of high heat and high pressure. After a certain period of time, it is solidified and shaped into desired product shape.
Difference between injection molding and compression molding is that there is a separate feeding chamber. Mold is closed before molding. Plastic is preheated in feeding chamber and is in a viscous flow state. It is adjusted and squeezed into 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. .
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. Material used in manufacture of compression moulds is basically same as that of injection moulds.

 

A type of mold used to mold and produce continuous-shaped plastic products, also called extrusion molding heads, is widely used in processing of pipes, rods, monofilaments, plates, films, wire and cable coatings, profiled materials, etc. Corresponding production equipment is a plastic extruder. Principle is that solid plastic is melted and plasticized under conditions of heating and screw of extruder to rotate and pressurize, a continuous plastic product with same cross-section and shape of die is made through a die of a specific shape.
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 parts that need to be wear-resistant. Extrusion process is usually only suitable for production of thermoplastic products, its structure is obviously different from injection molds and compression molds.

 

It is a kind of mold used to form plastic container hollow products (such as beverage bottles, daily chemical products and other packaging containers). According to process principle, forms of blow molding mainly include extrusion blow molding hollow molding, injection blow molding hollow molding, injection stretch blow molding hollow molding(commonly known as "injection stretch blow"), multilayer blow molding hollow molding, sheet blow molding hollow molding, etc.
Corresponding equipment for blow molding of hollow products is usually called a plastic blow molding machine. Blow molding is only suitable for production of thermoplastic products. Structure of blow mold is relatively simple, materials used are mostly made of carbon.

 

It is a kind of mold that uses plastic plates and sheets as raw materials to form some simpler plastic products. Principle is to use vacuum method or compressed air molding method to fix plastic plates and sheets on concave or convex mold. Under condition of heating and softening, it deforms and sticks to cavity of mold to obtain desired molded product, which is mainly used in production of some daily necessities, food, and toy packaging products.
Since pressure of blister mold is low during molding, mold material is mostly made of cast aluminum or non-metallic materials, and structure is relatively simple.

 

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.
Principle is that expandable polystyrene can be molded by steam in 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. Materials used to make this kind of mold are cast aluminum, stainless steel, bronze and so on.

Mold design and manufacturing are closely related to plastic processing. Success or failure of plastic processing depends largely on effect of mold design and mold manufacturing quality, and design of plastic molds is based on correct design of plastic products.
Structural elements to be considered in design of plastic molds are:
01 Parting surface is contact surface where concave mold and convex mold cooperate with each other when mold is closed. 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.
02 Structural parts, namely sliders, inclined tops, straight top blocks, etc. of complex molds. Design of structural parts is very critical, which is related to life of mold, processing cycle, cost, product quality, etc. Therefore, design of core structure of complex molds requires a higher comprehensive ability of designer, pursuit of a simpler, more durable, and more economical design plan is as much as possible.
03 Mold precision, namely avoiding jams, precise positioning, guide posts, positioning pins, etc. Positioning system is related to appearance quality of product, mold quality and life. According to different mold structure, different positioning methods are selected. Positioning accuracy control mainly depends on processing. Inner mold positioning is mainly considered by designer to design a more reasonable and easy-to-adjust positioning method.
04 Gating system, that is, feed channel from nozzle of injection molding machine to cavity, includes main runner, runner, gate and cold cavities. In particular, selection of gate position should be conducive to molten plastic filling cavity in a good flow state. Solid runner and gate cold material attached to product are easy to eject from mold and be removed when mold is opened (except for hot runner mold).
Plastic shrinkage and various factors that affect dimensional accuracy of products, such as mold manufacturing and assembly errors, mold wear, etc. In addition, when designing compression molds and injection molds, matching of process and structural parameters of molding machine should also be considered. Computer-aided design technology has been widely used in plastic mold design.

Punch pin, punch, guide post, guide sleeve, ejector pin, thimble, cylinder, steel ball sleeve, independent guide post, slider, date stamp, inclined top slider, sprue sleeve, positioning block, guide position fixing block, guide post auxiliary device (positioning post), guide post assembly, etc.

Structure of blow molds, casting molds and thermoforming molds is relatively simple.
Compression molds, injection molds, and transfer molds are more complicated in structure, there are many parts that make up this type of mold.
Basic parts are:
①Molding parts, including concave molds, convex molds, and various molding cores, are parts of inner and outer surfaces or upper and lower end faces, side holes, undercuts and threads of molded product.
②Support fixed parts, including mold base plate, fixed plate, support plate, cushion block, etc., to fix mold or support pressure.
③Guiding parts, including guide posts and guide sleeves, are used to determine relative position of movement of mold or ejection mechanism.
④ Core-pulling parts, including diagonal pins, sliders, etc., are used to pull out movable core when mold is opened to demold product.
⑤Push out parts, including push rod, push tube, push block, push plate, push ring, push rod fixing plate, push plate, etc., to demold 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. Mold cavity can be processed by itself according to shape of product. Use of standard mold bases is beneficial to shorten molding cycle.

Fixed mold base plate (panel): Fix front mold on injection molding machine.
Runner plate (nozzle plate): Remove waste handle when opening mold to make it fall off automatically (three-plate mold).
Fixed mold plate (A plate): front mold part of molded product.
Movable mold fixing plate (B board): back mold part of molded product.
Cushion: Mould foot, its function is to make top plate have enough space for movement.
Push plate: When opening mold, push product out of mold by pushing out parts such as ejector rods, top blocks, and inclined tops.
Movable mold base plate (bottom plate): Fix back mold on injection molding machine.
Guide post and guide sleeve: play role of guiding and positioning, assisting opening of front and rear molds, and basic positioning of molds.
Support column (support head): Improve strength of B board, effectively avoiding deformation of B board due to long-term production.
Top plate guide column: guide and position the push plate to ensure smooth ejection.

Working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150℃-200℃. In addition to being subjected to a certain pressure, they also have to withstand temperature. According to different use conditions and processing methods of plastic molding molds, basic performance requirements of steel for plastic molds are roughly summarized as follows:

Hardness of plastic mold is usually below 50-60HRC, heat-treated mold should have sufficient surface hardness to ensure that mold has sufficient rigidity.
When mold is working, due to filling and flow of plastic, it has to withstand greater compressive stress and friction. Mold is required to maintain accuracy of shape and stability of dimensional accuracy to ensure that mold has a sufficient service life.
Wear resistance of mold depends on chemical composition and heat treatment hardness of steel, so increasing hardness of mold is beneficial to improve its wear resistance.

In addition to EMD processing, most plastic molding molds require certain cutting processing and fitter repairs. In order to extend service life of cutting tools, improve cutting performance, and reduce surface roughness, hardness of steel used for plastic molds must be appropriate.

High-quality plastic products require small roughness on the surface of cavity. For example, surface roughness value of injection mold cavity is required to be less than Ra0.1～0.25, optical surface requires Ra<0.01nm, and cavity must be polished to reduce surface roughness value. For this reason, selected steel requires less material impurities, fine and uniform structure, no fiber directionality, and no pitting or orange peel defects during polishing.

Shape of parts of plastic injection molds is often complicated and difficult to process after quenching. Therefore, it is necessary to select those with good thermal stability as much as possible. When mold is formed by heat treatment, linear expansion coefficient is small, heat treatment deformation is small, dimensional change rate caused by temperature difference is small, metallographic structure and mold size are stable, processing can be reduced or no longer needed to ensure mold size accuracy and surface roughness requirements.
45 and 50 grades of carbon steel have certain strength and wear resistance, 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 development of plastics industry, complexity and precision of plastic products are becoming more and more demanding, and higher requirements are placed on mold materials. For 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 better cutting, heat treatment, polishing performance and higher 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 selecting materials with same structure. Under special conditions, one side can be plated or nitrided, so that the two sides have different surface structures.

Due to development of plastics and plastic molding industry, quality requirements for plastic molds are getting higher and higher, so failure of plastic molds and their influencing factors have become an important research topic. Main working parts of plastic molds are molding parts, such as punches, concave molds, etc., which form cavity of plastic mold to form various surfaces of plastic part and directly contact plastic, withstand effects of pressure, temperature, friction and corrosion.

General mold manufacturing includes mold design, material selection, heat treatment, machining, debugging and installation. According to investigation, among factors of mold failure, material and heat treatment used in mold are main factors that affect service life. From perspective of total quality management, factors that affect service life of mold cannot be measured as sum of polynomials, but should be product of multiple factors. In this way, pros and cons of mold materials and heat treatment are particularly important in the entire mold manufacturing process.
From analysis of common phenomenon of mold failure, plastic molds can cause wear failure, local deformation failure and fracture failure during service process. Important failure modes of plastic molds can be divided into wear failure, local plastic deformation failure and fracture failure.

 

With rapid development of manufacturing industry, plastic molds are an indispensable tool in plastic molding processing, their proportion in the total mold output is increasing year by year. With development and continuous production of high-performance plastics, types of plastic products are increasing day by day, their uses continue to expand, product are becoming more sophisticated, large-scale, and more complex. Molding production is developing at a high speed, working conditions of mold are becoming more and more complicated.

Plastic melt flows in mold cavity under a certain pressure, solidified plastic part comes out of mold, which will cause friction on molding surface of mold and cause wear. Root cause of plastic mold wear failure is friction between mold and material. However, specific form of wear and wear process are related to many factors, such as pressure, temperature, material deformation speed and lubrication condition of mold during working process.
When materials and heat treatment used in plastic mold are unreasonable, surface hardness of plastic mold cavity is low, and wear resistance is poor. Performance is: size of cavity surface is out of tolerance due to wear and deformation; roughness value becomes higher due to roughening, surface quality deteriorates.
Especially when solid materials are used to enter plastic mold cavity, it will aggravate wear of cavity surface. In addition, when 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 plastic mold cavity, resulting in failure.
If there is abrasion damage at the same time as wear, plating layer or other protective layer on the surface of cavity is destroyed, which will promote corrosion process. Cross action of the two types of damage accelerates corrosion-wear failure.

Pressure and heat on the surface of 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. Material used in plastic mold has insufficient strength and toughness, and low deformation resistance; another reason for plastic deformation failure is that hardened layer on the surface of mold cavity is too thin, deformation resistance is insufficient, or working temperature is higher than tempering temperature, which causes phase change and softening, which causes mold to fail early.

Main cause of fracture is structural stress, thermal stress or insufficient tempering caused by structure and temperature difference. At service temperature, retained austenite is transformed into martensite, causing local volume expansion and structural stress generated inside mold.
Working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150℃-200℃. In addition to being subjected to a certain pressure, they also have to withstand temperature. There are multiple failure modes for same mold, multiple damages may occur even on same mold. From failure modes of plastic molds, it is very important to select plastic mold materials and heat treatment reasonably, because they are directly related to service life of mold. Therefore, steel for plastic molds should meet following requirements:

With advent of high-speed molding machinery, plastic products run faster. Since molding temperature is between 200-350℃, if plastic fluidity is not good and forming speed is fast, surface temperature of mould part will exceed 400℃ in a very short time. In order to ensure precision and small deformation of mold during use, mold steel should have high heat resistance.

With expansion of use of plastic products, it is often necessary to add inorganic materials such as glass fiber to plastic to enhance plasticity. Due to addition of additives, fluidity of plastic is greatly reduced, leading to wear of mold, so mold is required to have good wear resistance.

For most plastic molding molds, in addition to EDM, certain cutting processing and fitter repairs are required. In order to prolong service life of cutting tool, work hardening is small during cutting process. In order to avoid mold deformation and affect accuracy, it is hoped that residual stress of processing can be controlled to a minimum.

Shapes of parts of plastic injection molds are often complicated and difficult to process after quenching. Therefore, materials with good thermal stability should be selected as far as possible.

Surface of cavity is smooth, molding surface is required to be polished into a mirror surface, surface roughness is lower than Ra0.4μm to ensure appearance of plastic molded part and facilitate demolding.

In mold failure accidents, accidents caused by heat treatment are generally 52.3%, so that heat treatment occupies an important position in the entire mold manufacturing process. Quality of heat treatment process has a greater impact on quality of mold. Generally require small heat treatment deformation, wide quenching temperature range, low overheating sensitivity, especially greater hardenability and hardenability, etc.

During forming process, corrosive gases may be released and heated to decompose corrosive gases, such as HC1, HF, etc., which corrode mold, sometimes rust and damage mold at mouth of air flow passage. Therefore, mold steel is required to have good corrosion resistance.

General plastic molds are often 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 higher requirements for dimensional accuracy and surface quality of plastic cavities, a series of new mold steels have recently been developed.

Carburized plastic mold steel is mainly used for cold extrusion molding of plastic molds with complex cavities. This type of steel has a low carbon content and often adds element Cr, while adding appropriate amounts of Ni, Mo and v to improve hardenability and carburizing ability. In order to facilitate cold extrusion forming, this kind of steel must have high plasticity and low deformation resistance in annealed state, annealing hardness is ≤100HBS. Carburizing, quenching and tempering treatment are carried out after cold extrusion forming, and surface hardness can reach 58---62HRC.
This type of steel has special steel grades abroad, such as 8416 in Sweden, P2 and P4 in 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 service life of mold is improved. Elements cr, Ni, Mo, and V in steel increase hardness and wear resistance of carburized layer, strength and toughness of core.

Carbon content of this type of steel is 0.3% -0.55%, 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 pre-hardened delivery hardness is 35_40 HRC, and it has good machinability. It can be used directly without heat treatment after processing. Adding Ni solid solution strengthening and increasing toughness, adding Mn and S to form free-cutting phase MnS; adding Cr, Mo, and V to increase hardenability of steel. 8Cr2S steel is sufficient for free-cutting precision 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, hardness is 28-32HRC, mechanical processing, and then 4800C aging. During aging, Ni3Mo, Ni3Ti and other intermetallic compounds are folded out to make hardness reach 48-52 HRC. Steel has high strength and toughness, small dimensional changes during aging, good weld repair performance, but steel is expensive and not very popular in China.

Plastic products made of polyvinyl chloride (Pvc) and ABS plus flame-resistant resin will decompose and generate corrosive gas during forming process, which will corrode mold. Therefore, plastic mold steel is required to have good corrosion resistance. Corrosion-resistant plastic mold steels commonly used abroad include martensitic stainless steel and precipitation hardening stainless steel. Foreign ones include STVAX (4Crl3) and A SSAB-8407 of Sweden ASSAB.

Various tools and products used in our daily production and life, ranging from base of machine tool and body shell, as small as a embryo head screw, button and shell of various household appliances, are all closely related to mold. Shape of mold determines appearance of these products, processing quality and precision of mold also determines quality of these products. Because of 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.

1. Such as: household appliances, instrumentation, construction equipment, automobile industry, daily hardware and other fields, proportion of plastic products is increasing rapidly. A reasonably designed plastic part can often replace multiple traditional metal parts. Trend of plasticization of industrial products and daily-use products is on the rise.
2. 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 required shape through pressure. These special tools are collectively called molds .
3. Description of injection molding process: A mold is a tool for producing plastic products.
4. General classification of molds: can be divided into plastic molds and non-plastic molds:
⑴Non-plastic molds include: casting molds, forging molds, stamping molds, die-casting molds, etc.
A. Casting mold-faucet, pig iron platform
B. Forging die-car body
C. Stamping die-computer panel
D. Die casting mold-super alloy, cylinder block
⑵Plastic molds are divided into different production processes and products:
A. Injection molding mold-TV shell, keyboard buttons (the most common application)
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. Rotational mould-soft rubber doll toy
◆ Injection molding is the most commonly used method in plastic processing. This method is suitable for all thermoplastics and some thermosetting plastics. Number of plastic products produced is beyond reach of other molding methods. As one of main tools of injection molding processing, injection mold is in terms of quality accuracy, manufacturing cycle and injection molding process. Level of production efficiency, etc. directly affects quality, output, cost and product update of products, also determines ability and speed of enterprises to respond in market competition.
◆Injection mold is composed of several steel plates with various parts, and is basically divided into:
A Forming device (concave mold, convex mold)
B Positioning device (guide post, guide sleeve)
C Fixing device (I-shaped board, code mold pit)
D Cooling system (water hole)
E Constant temperature system (heating tube, heating wire)
F Runner system (chill nozzle hole, runner groove, runner hole)
G ejection system (thimble, ejector)
According to different types of gating system, molds can be divided into three categories:
⑴ Large nozzle mold: Runner and gate are on parting line, product is demolded together with product when mold is opened. Design is the simplest, easy to process, and low cost, so more people use large nozzle system to work.
⑵ Fine nozzle mold: runner and gate are not on parting line, generally directly on product, so it is necessary to design an additional set of nozzle parting lines, design is more complicated, and processing is more difficult. Generally, fine nozzle system should be selected according to product requirements.
⑶ Hot runner mold: Structure of this type of mold is roughly same as that of nozzle. The biggest difference is that runner is located in one or more hot runner plates and hot nozzles with constant temperature. There is no cold material demoulding, runner and gate are directly on product, so runner does not need to be demolded. This system is also called a nozzleless system, which can save raw materials, is suitable for situations where raw materials are more expensive, products are required to be high, design and processing are difficult, and mold costs are high.
Hot runner system, also known as 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. Single-point hot gate uses a single hot sprue sleeve to directly inject molten plastic into cavity. It is suitable for plastic molds with a single cavity and single gate; multi-point hot gate is to branch molten material into each sub-heat gate sleeve through hot runner plate, then enter cavity. It is suitable for single-cavity multi-point feeding or multi-cavity molds.

⑴No nozzle material, no need for post-processing, so that the entire molding process is fully automated, saving working time and improving work efficiency.
⑵Pressure loss is small. Temperature of hot runner is equal to nozzle temperature of injection molding machine, which avoids surface condensation of raw materials in runner, injection pressure loss is small.
⑶ Repeated use of nozzle materials will degrade performance of plastics, use of hot runner systems without nozzle materials can reduce loss of raw materials, thereby reducing product costs. Temperature and pressure in cavity are uniform, stress of plastic part is small, and density is uniform. Under a small injection pressure and a short molding time, injection molding produces a better product than 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.
⑷Hot nozzle adopts standardized and serialized design, equipped with various nozzle heads to choose from, and has good interchangeability. Uniquely designed and processed electric heating ring can achieve uniform heating temperature and long service life. Hot runner system is equipped with hot runner plates, thermostats, etc., with exquisite design, diverse types, convenient use, stable and reliable quality.

⑴Closing height of the overall mold is increased, and the overall height of mold has increased due to addition of hot runner plates, etc.
⑵Heat radiation is difficult to control. The biggest problem of hot runner is heat loss of runner, which is a major issue that needs to be solved.
⑶ There is thermal expansion, thermal expansion and contraction are issues that we must consider when designing.
⑷Cost of mold manufacturing has increased, price of standard parts of hot runner system is higher, which affects popularization of hot runner molds.

PTC’s EMX, Siemens’NX Mold Wizard, CimatronE, Topsoild, Delcam Moldmaker, Missler’s Topsolid Mold, Think3’s Mold Design, Manusoft’s IMOLD, R&B’s MoldWorks, Solidworks, Pro-e, UG (the latter three are mainly product design, but mold design integration can be done), etc.

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.

 

General process of plastic mold polishing is as follows:

Diamond polishing paste is mainly used for fine polishing. If polishing cloth wheel is mixed with diamond abrasive powder or abrasive paste for polishing, usual polishing order is 9μm (#1800) ~ 6μm (#3000) ~ 3μm (#8000). 9μm diamond abrasive paste and polishing cloth wheel can be used to remove hair-like wear marks left by #1200 and #1500 sandpaper. Then use sticky felt and diamond paste for polishing, order is 1μm (#14000) ~ 1/2μm (#60000) ~ 1/4μm (#100000). Polishing process with an accuracy requirement of 1μm or more (including 1μm) can be carried out in a clean polishing room in mold processing workshop. For more precise polishing, an absolutely clean space is necessary. Dust, smoke, dandruff and saliva can all scrap high-precision polished surface obtained after several hours of work.

Surface after milling, electric spark, grinding, etc. can be polished by using a rotating surface polisher or ultrasonic grinder with a speed of 35 000-40 000 rpm. Commonly used method is to remove white electric spark layer by using wheels with a diameter of Φ3mm and WA # 400. Then there is manual whetstone grinding, strips of whetstone are added with kerosene as a lubricant or coolant. 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.

Semi-precision polishing mainly uses sandpaper and kerosene. 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 mirror surface.

Mechanical polishing is a polishing method that relies on cutting and plastic deformation of material surface to remove polished convex parts to obtain a smooth surface. Generally, oil stone sticks, wool wheels, sandpaper, etc. are used, and manual operation is main method. Special parts such as surface of rotating body can be used. Using auxiliary tools such as turntables, ultra-precision polishing can be used for those with high surface quality requirements. Ultra-precision polishing is use of special abrasive tools, which are pressed against processed surface of workpiece in a polishing fluid containing abrasives for high-speed rotation. Using this technology, 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 surface microscopic convex part of material in chemical medium dissolve preferentially than concave part, so as to obtain a smooth surface. 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. Core problem of chemical polishing is preparation of polishing liquid. Surface roughness obtained by chemical polishing is generally several 10 μm.

Basic principle of electrolytic polishing is same as that of chemical polishing, that is, by selectively dissolving tiny protrusions on the surface of material to make surface smooth. Compared with chemical polishing, it can eliminate influence of cathode reaction, and effect is better. Electrochemical polishing process is divided into two steps: (1) Macroscopic leveling. Dissolved products diffuse into electrolyte, geometric roughness of material surface decreases, Ra>1μm. ⑵ Small light leveling. Anode polarization, surface brightness is improved, Ra<1μm.

Put workpiece in abrasive suspension and put it together in ultrasonic field, relying on oscillation effect of ultrasonic, so that abrasive is ground and polished on the surface of workpiece. Ultrasonic machining has a small macro force and will not cause deformation of 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 solution, so that dissolved products on the surface of workpiece are separated, corrosion or electrolyte near surface is uniform; cavitation effect of ultrasonic in liquid can also inhibit corrosion process and facilitate surface brightening.

Fluid polishing relies on high-speed flowing liquid and abrasive particles carried by it to wash surface of workpiece to achieve 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 liquid medium carrying abrasive particles flow back and forth across surface of workpiece at high speed. Medium is mainly made of special compounds (polymer-like substances) with good flowability under lower pressure and mixed with abrasives. Abrasives can be made of silicon carbide powder.

Magnetic abrasive polishing is to use magnetic abrasives to form abrasive brushes under action of a magnetic field to grind workpiece. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. Using suitable abrasives, surface roughness can reach Ra0.1μm. Mechanical polishing is based on this method: polishing mentioned in processing of plastic molds is very different from surface polishing required in other industries. Strictly speaking, polishing of 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. 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 geometric accuracy of parts due to methods such as electrolytic polishing and fluid polishing. However, surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods are not up to requirements, so mirror surface processing of precision molds is still mainly mechanical polishing.

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 paste. Choice of polishing procedure depends on the surface condition after pre-processing, such as machining, EDM, grinding, and so on.

China's annual plastic mold output value reached 53.4 billion yuan? Do you believe it? Due to rapid development of Chinese economy, requirements for plastic mold industry are becoming more and more stringent, which provides a huge impetus for the development of plastic mold industry. According to accurate statistics, China's annual plastic mold output value reached 53.4 billion yuan, which is an existing fact.
With rapid development of automobile manufacturing industry and IT manufacturing industry, domestic mold industry has achieved rapid development. It is understood that proportion of plastic molds in mold industry in my country can reach 30%. It is expected that in the future mold market, proportion of plastic molds in the total molds will gradually increase, development speed will be faster than other molds.
It is reported that mold industry has grown rapidly at a rate of 20% per year since 2000, which has promoted improvement of mold grades. Sophisticated mold manufacturing equipment has provided a guarantee for improvement of mold technology.
Analysis believes that, since precision, large, complex, and long-life molds account for majority of imported molds, from perspective of reducing imports and increasing localization rate, market share of such high-end molds will gradually increase. Rapid development of construction industry has made various profile extrusion molds and PVC plastic pipe joint molds become a new economic growth point in mold market. Rapid development of highways also puts forward higher requirements for automobile tires. Therefore, development of radial rubber tire molds, especially active molds, will also be higher than the overall average; replacing wood with plastic and metal with plastic makes demand for plastic molds in automobile and motorcycle industries huge; household appliance industry will have a great development during "Twelfth Five-Year Plan" period, especially demand for plastic molds for parts such as refrigerators, air conditioners, and microwave ovens.
At the same time, pace of structural adjustment of plastic mold industry is accelerating, number and capabilities of market-oriented professional plastic mold manufacturers are also growing rapidly. According to analysis of production, sales, market conditions, industry structure, products, import and export of plastic mold manufacturing industry, with reference to development trend of plastic mold related industries, predict future development direction of China's plastic mold manufacturing industry and how much development potential my country's plastic mold manufacturing industry has. These all need to be verified.