Plastic molding metal mold related technology

1.1 Classification of heat treatment type and non-heat treatment type

Generally, the composition of molding resin and the number of die castings determine which mold material to choose. In other words, the amount of glass fiber (hereinafter called GF) within the resin and the number of die castings are important factors in choosing the mold material. According to the actual operation in the past, the number of die-casting can be divided into heat treatment type containing 35% GF as the dividing line, and heat treatment type above 500,000 (times) and no heat treatment type below 500,000 (times).

For example, if the resin containing 30% GF is used for molding below 300,000 times, under the condition of implementing N treatment for 30-32HRC pre-hardened steel, and if the resin containing 35% GF is used for molding 500,000 times, under the condition of implementing N treatment and PVD coating for 40HRC pre-hardened steel, the target die-casting number can be achieved even without using heat treatment type material. Of course, to contain 40%-50% GF resin for 700,000 times the die-casting molding mold, it must be the base material for high hardness heat treatment, and need to make N and PVD compound treatment, Japan Bujikoshi industrial company of many molds on such treatment.

1.2 Heat treatment conditions and mold quality

Heat treatment of the mold in the quenching, tempering deformation, therefore, in order to meet the quality requirements of heat treatment should be as fast as possible cooling, which is contradictory with the need to resist deformation as slow as possible between the cold, to meet both of these requirements is very difficult.

In addition to good cutting properties, the die material also needs to reduce the deformation of dimensions in the heat treatment process. Recently, cold forging die steel PD613 and HPM31 have been improved and developed into two materials, SLD-Magic and DCMX. Compared with JIS SKD11, the performance of these improved steels has been greatly improved. In the metal mold for plastic molding, because it is mainly for molding of refractory reinforced resin, it is necessary to consider the aging changes caused in molding in addition to its wear resistance and corrosion resistance.

Since the wear resistance is proportional to the hardness, a steel grade with a hardness of 60 HRC was used for the metal mold material. In addition, it should be noted that the material hard will become brittle, so for the possible breakage of the mold, should consider its ductility (also known as malleability), therefore, generally control the material hardness of 56-58HRC. and, when the need to consider corrosion resistance, in principle, the use of M (martensitic) system stainless steel. In the importance of corrosion resistance in the heat treatment, can not precipitate will reduce the corrosion resistance of carbide. Need to avoid tempering at temperatures above 450°C. However, in order to heat treatment after the implementation of N and coating treatment, high-temperature tempering and is the appropriate disposal.

In order to prevent aging changes, it is necessary to carry out low-temperature treatment, that is, tempering should be carried out at a temperature of 400 ℃ or less without precipitation carbide.

1.3 No heat treatment type mold material development

In the Japanese domestic plastic molding metal mold production, although facing the pressure of reducing costs, shortening delivery time and improving quality, but in the plastic mold using pre-hardened steel additional surface reforming conditions, even without heat treatment can meet the requirements of use. According to the survey, the number of non-heat treatment type molds that are converted from heat treatment type material to pre-hardened steel surface modification with hardness of 40HRC is increasing dramatically. It is expected that after a few years, the hardness of pre-hardened steel will be about 40HRC from the present to about 45HRC, so as to become a non-heat treatment type of mold material.

In the background of mold industry globalization, Japanese domestic mold enterprises in order to be able to survive, must take some countermeasures. Particular attention should be paid to the cost, delivery time and product quality and other important indicators, so as to be able to compete with overseas manufacturing of molds. The application of pre-hardened steel with a hardness of 40HRC with additional surface modification of non-heat treatment type material will be common. However, the use of such treatment is limited. Therefore, if the hardness of pre-hardened steel is hastily increased to about 45HRC, it may be difficult to meet the global demand for non-heat treatment type materials with hardness around 48HRC.

In order to achieve the set goal, steelmakers must organize the development of pre-hardened steels of the given hardness. The time to solve the problems of cutting and cutting of high hardness materials will influence the process of practical application of non-thermal treatment type pre-hardening steel.

2. Precision repair technology of metal mold with laser overlay welding

In the past, the overlay welding repair of the mold, generally used W-pole inert gas shielded arc welding (referred to as TIG welding). However, in recent years, due to pulsed laser overlay welding. However, in recent years, due to the introduction of the pulsed laser overlay welding machine, it is possible to repair the molds in a more delicate and precise way. In Japan, laser overlay welders were originally used for jewelry processing because of their precision handling. But now it has been widely used for repairing plastic, die-casting, stamping and other molds. Because of the mold parts, wear parts, defects and pinholes, etc. to 0.01mm within the precision of the overlay welding repair, so as an effective repair means, its market expansion, high demand, so that mold manufacturers and commissioned by the processing industry have introduced this technology and equipment.

2.1 Features of repair technology

Compared with the general TIG welding, laser overlay welding. Welding has a small welding heat input, no preheating and post-welding treatment, making it impossible to carry out the fine precision overlay welding. Welding is possible.

Since TIG welding is performed while melting the workpiece and the overlay material with the high heat of the torch, the overlay welding. Welding has the advantages of fast welding speed and high weld strength. However, because of its high heat input, the workpiece is prone to deformation, secondary edge gnawing and stress; and, because of the many burrs (flying edges), causing problems such as long machining and EDM processing time and rising costs. In addition, TIG welding is not suitable for fine parts (such as pin-like tips, groove-like bottom and sides, etc.).

On the contrary, laser overlay welding . Welding is pulsed laser spot irradiation, which has minimal thermal impact on the workpiece and does not cause damage such as deformation or secondary galling of the workpiece. It is possible to use the attached microscope to confirm the weld. The laser welding operation can be performed while checking the weld area with the attached microscope. Moreover, the distance between the focus of the microscope and the laser focus can be continuously adjusted so that the weld. The weld area can be irradiated accurately. Of course, laser welding has the disadvantage of slow welding speed compared to TIG welding for a large number of overlays. However, laser welding is very accurate and can reduce the time and cost of subsequent finishing, and can be used to weld narrow grooves, the bottom of holes, internal corners and other small parts. Therefore, laser welding can be considered the best technology for repairing metal molds for plastic molding.

Along with plastic molding, die-casting, stamping and other mold repair and design changes, in addition to transformation and correction, there are mechanical parts, precision parts of the overlay welding. Welding, TIG and other repair of welding defects (such as secondary galling, pinholes, etc.), and overlay welding between various metals. Welding, etc.

2.2 Overlay welding method and use

Considering both the overlay welding. The laser pulse width, frequency, and beam diameter (focal point diameter) are adjusted by considering the material and shape of the welded part, thus setting the optimal overlay. Welding conditions. Since the microscope focus and laser focus distance are continuously adjusted, it is easy to set the conditions. First, to prevent poor fusion of the repair area, only the laser irradiates the weld area without using a wire. After that, the tip of the wire is inserted and a small amount of molten weld is applied, and then a normal weld is applied until a weld layer without pinholes or other welding defects is formed.

3. Rapid prototyping process

　　3.1 Outline of rapid prototyping

　　The so-called rapid prototyping is to process the three-dimensional shape of a solid object with a thin layer stack to realize the physical shape by stacking the main shape.
　　Specifically, the development of metal powder laser sintering technology and precision cutting composite processing technology has been carried out with the goal of making metal molds with high precision, ultra-short lead time, and mass production.
　　The basic principles of this technology are.
　　1) First, a three-dimensional computer-aided design is used to define the final shape of the three-dimensional part shape.
　　(2) Secondly, the processing of the contour shape of the equally spaced cut sheet is calculated from this 3D shape data in order to obtain the sheet data.
　　(3) Based on the sheet data, the actual powder material is sintered into a thin sheet using a CO2 laser on one side, and is joined with the lower layer that has been terminated, and the surface of the profile is cut and finished after repeated sintering by the laser.
　　4) Curing the material and cutting the sheet data repeatedly superimposed until the physical part with the same shape as the part defined on the computer.

3.2 Realization of rapid prototyping technology for injection molding metal molds

In this metal light molding method, it is possible to realize a single process processing that is not possible in the original mold processing, so you can expect ultra-short lead time and low-cost metal mold making. In the process method, the internal structure can be freely formed and a three-dimensional temperature control circuit can be formed, so it is expected to improve the precision of injection molding and shorten the molding cycle, and other innovations in highly functional metal mold technology and molding technology.

The Fe powder material used in this technology is mainly composed of alloy steel powder. The mold developed by using the mixture of Ni powder and Cu powder is also free of microcracks, and the maximum bending strength and hardness are the same as that of S50C, the steel used for metal molds in general. The surface dimensional accuracy of the machined specimen is ±0.03mm, and the surface finish is 20μmR2.

The adoption of this technology with water pipes inside the gate bushings shortens the cooling time, makes the injection molding process highly cyclical and resists the rise of the metal mold temperature, thus avoiding molding accidents and improving the mold life.

3.3 New technology related to plastic molding molds

Japan transferred the production of cheap metal molds for plastic molding to China and Korea. And there are some problems with the molds produced in China, mainly the poor appearance of molded plastic products, because of the inadequate research on the design of plastic thermal decomposition gas extraction and extraction mechanism in the molds. And, if the use of cheap materials and recycling materials, affected by its impurities, the occurrence of more thermal decomposition gas, but also easy to cause bad appearance of the product.

Some people use metal light molding composite processing machine, but it is recommended to use the dual channel method, which results in shortening the plastic injection molding cycle. Since the thermal decomposition gas and negative pressure are attracted from the metal gap by using the local low-density layer, the filling of resin is promoted, and under the condition of spraying high-pressure air after molding, the thermal decomposition gas is prompted to be discharged, and the impurities blocking the orifice are removed in the low-density layer, thus contributing to the improvement of product quality.

EOS suggested the direct molding technology of metal. Ecoparts Switzerland has carried out the technology development of repairing broken metal mold by DMLS, so that the damaged mold can be repaired effectively. It can reduce the cost and save the time compared with integral manufacturing.

Ultra-high strength martensitic aging treatment steel tensile strength of 1900MPa, hardness of 55HRC, the industry has recently been trying to apply it to die-casting metal molds and injection molding mold liner parts.

Sintermask has developed a laminated molding method for high-speed molten thermoplastic resin using a 10kW infrared lamp to generate section shape masks. Its maximum molding size is 300mm x 200mm x 800mm; it can be molded at a rate of 100μm thick per layer and 700mm per hour as long as it is a polyamide material; if a batch of individual shaped parts as large as a thumb is made at a time, 3,000 can be manufactured, achieving a productivity of less than 10 seconds each.