Future development and technical innovation of micro injection molding machine

With the development of science and technology, the products are developing towards miniaturization, which leads to the MEMS technology needed by the industry in the new century In 2002, the world created 45 billion US dollars of output value in this field Its main products play an important role in photoelectric communication, image transmission, biochemical medicine, information storage, precision machinery and other application fields In order to produce micro components with practical value, many new manufacturing technologies have emerged, including photolithography, electroforming and demoulding Technology (Liga), UV etching technology (UV), EDM, microinjection molding, precision grinding and precision cutting Among them, micro injection molding technology has become one of the research hotspots of manufacturing technology in the world because it is easy to achieve the advantages of low-cost large-scale production of precision micro structure parts The quality of the finished product is calculated in milligram, and the micro injection molding simultaneous interpreting the finished product's geometry size is a new advanced manufacturing technology Compared with the conventional and conventional injection molding technology, the micro injection molding technology has different requirements for molding materials, molding technology and molding equipment, etc in the end of 1980s Many existing and mature injection molding technologies and theories are not suitable for microinjection molding technology, so it is necessary to systematically and thoroughly study and discuss the technical characteristics of microinjection molding technology in theory and practice At the beginning of the development of micro injection molding technology, there was no special injection molding machine for manufacturing micro parts In production practice, the traditional medium and large-scale injection molding machines are usually used to cooperate with the design of multi-mode cavity mold to realize the preparation of parts, which not only requires a high balance design of the flow channel of the mold, but also makes the molding quality of parts difficult to control Therefore, special injection molding machine is needed to meet the requirements of miniaturization and high precision of parts Compared with traditional injection molding technology, micro injection molding technology has many special requirements for production equipment, which are mainly shown in the following aspects: (1) High injection rate: the quality and volume of micro injection molding parts are small, and the injection process is required to be completed in a short time to prevent the parts from under injection due to the solidification of molten materials, so the injection rate is required to be high during molding The injection speed of the traditional hydraulic driven injection molding machine is 200 mm / s, and that of the electric servo motor driven injection molding machine is 600 mm / s however, the injection speed of the polymer melt is usually required to meet the requirements of the micro injection molding process The viscosity of the polymer melt was reduced at high injection rate by using the shear thinning principle of polymer melt above 800 mm / s, so that it could fill the micro cavity smoothly (2) Precision injection quantity measurement: the quality of micro injection molding parts is only measured in milligrams, so the micro injection molding machine needs to have a control unit to precisely measure the injection in the process of one-time injection, its quality control accuracy is required to reach milligram level, and the screw stroke accuracy is required to reach micron level The traditional injection molding machine usually adopts the linear reciprocating screw injection structure, the injection control quantity error is relatively large, which can not meet the micro control requirements of micro injection molding, and has a great impact on the molding quality of parts (3) Rapid reaction ability: the injection volume is very small in the process of micro injection molding, and the movement stroke of the screw / plunger of the corresponding injection equipment is also very small Therefore, the driving unit of the micro injection molding machine must have a very fast reaction speed, so as to ensure that the equipment can achieve the required injection pressure in an instant 2 classification of microinjection molding machines In view of the application limitations of traditional injection molding machines in the field of microinjection molding, in the 1990s, some companies in Europe, Japan and the United States cooperated with scientific research institutions to develop various types of special microinjection molding machines (usually the clamping force is less than 15t =, at present, the main foreign equipment suppliers include Nissei, Dr boy, Battenfeld, MCP, Babyplast, Gaoqiao, etc The main functions of micro injection molding machine usually include three parts: plasticization, measurement and injection, which can be classified by the driving mode of each part or by the mechanism design of each part According to the driving mode, it can be divided into hydraulic / pneumatic driving, all electric driving and electro-hydraulic composite driving The rotary / reciprocating motion of plasticizing unit and injection unit is driven by hydraulic / pneumatic system, which has the advantages of high injection pressure and speed, meeting the requirements of micro injection molding process, and poor control accuracy All electric drive means that all units of the equipment are driven by servo motor, which has the advantages of high control accuracy, fast response speed and small environmental pollution; the disadvantage is that the output thrust of servo motor is limited, and the injection pressure and speed that can be achieved are not high The electro-hydraulic compound drive is the combination of the high injection pressure and injection speed of the hydraulic drive with the control and rapid response of the all electric drive, as the driving source of the system According to the mechanism design classification of plasticizing and injection unit, it can be divided into screw type, plunger type, screw plunger mixed type and other special forms 2.1 the plasticization, measurement and injection of screw micro injection molding machine are all completed by a group of screws, and the rotation and reciprocating motion of each unit are all on one axis, so the structure is simple and easy to control However, due to the check ring structure of the front end of the screw, the control accuracy of the equipment to the primary injection quantity is poor The representative models of this kind of microinjection molding machine are boy12a of Dr boy company of Germany, hm7-denkey of nisin Resin Industry Co., Ltd., jmw-015s-5t of Shuyan industry and EC5 of Toshiba 2.2 plunger type Micro injection molding machine includes single plunger type and plunger plunger type The single plunger type pushes the granular or powdery plastic forward, flows around a torpedo shaped shunting shuttle, and injects it into the mold cavity through the nozzle The shunting shuttle's function is to disperse the plastic on the inner surface of the tube, making the plastic more tolerant and easy to plasticize; while the plunger plunger type is to complete the plasticizing and metering injection functions respectively by two groups of plungers This type of micro injection molding machine usually has small plasticizing amount, low plasticizing quality and poor mixing performance Its representative models are Babyplast 6 / 10 of cronoplast in Spain, RABBIT2 / 3 of MCP in the UK and sesame of medical Murray in the US 2.3 the screw plunger hybrid micro injection molding machine takes the screw as the plasticizing unit to complete the mixing and plasticizing, and takes the small diameter plunger with the servo motor and controller as the micro injection unit to complete the precise measurement and injection The micro injection molding machine can be divided into two sections of measurement type and three sections of measurement type according to the design of plasticizing measurement mechanism (1) Two stage metering type: the plasticizing screw first plasticizes the plastic and carries out rough metering, then sends it to the injection chamber, and then carries out precise metering and injection by the small diameter plunger The representative models of this kind of micro injection molding machine include 12 / 90hsp of MCP company in the United Kingdom, tr18s 3a of Sodick company in Japan, au3e of nisin resin Co., Ltd and epoch shot 7 of Tanrui company (2) Three stage metering type: after the plasticizing screw plasticizes the plastic and carries out rough metering, it is sent to the metering chamber of * stage, after metering by the metering plunger of * stage, the injection is sent to the metering chamber of the second stage, and then the injection is carried out after precise metering by the metering plunger of the second stage The representative models of the micro injection molding machine are microsystem50 of Battenfeld company and fx25 improved by ferromatic Milacron company of Germany and IKv Research Institute of Aachen University 2.4 the injection machine of Ettlinger company in Germany has a coaxial screw / plunger compound injection unit, which can produce 0.1 -For 5.0g plastic parts, the outstanding feature of this type of mechanism is to adopt direct injection molding The hot runner system is integrated into the injection machine through the needle nozzle with special structure design, which enables the micro injection molding process to adopt the runner free mold, saves materials and shortens the molding cycle The development trend of micro injection molding machine micro injection molding machine is a new direction of the development of injection molding equipment It has created a new way of manufacturing micro structural parts and systems Its outstanding advantage is that it can achieve high-precision, high-precision parts in large quantities and low-cost production For screw micro injection molding machine, its plasticization, measurement and injection are all completed by a group of screws, so the structure is simple and easy to control The disadvantage is that because of the check ring structure of the front end of the screw, the control accuracy of the equipment to the primary injection quantity is poor, and the probability of material degradation in the injection barrel is increased, which affects the stability of the part forming quality For the plunger microinjection molding machine, although the control accuracy of the injection quantity is higher than that of the screw type, its plasticizing quantity is small, the mixing performance is poor, and the plasticizing quality of the material is worse than that of the screw type, which is not conducive to the forming of parts with high requirements for surface quality and optical characteristics The screw plunger hybrid microinjection molding machine combines the advantages of the plunger type and the screw type With the screw as the plasticizing unit and the plunger as the metering and injection unit, the control accuracy and the molding quality of the parts of microinjection molding are significantly improved, but its structure is usually more complex, and the control and maintenance are more complicated than the plunger type and the screw type The above micro injection molding machines with different principles have different performance indexes, which are suitable for the requirements of different micro structure parts Therefore, the appropriate micro injection molding machine should be selected according to the cost, size and quality of specific micro structure parts However, because microinjection molding technology is a new technology field, many basic theories are not perfect, and microinjection molding technology is not mature enough, which needs further exploration and research At the same time, with the continuous development of electromechanical integration technology, computer network technology and other related technologies, many new ideas and new directions are provided for the development of micro injection molding machine Therefore, the further development of micro injection molding machine still faces many challenges, mainly in the following aspects: (1) Driving mode: at present, most microinjection molding machines use high frequency and high torque servo motor and high-precision mechanical transmission device to realize the precision measurement and high-speed and high-pressure injection required by microinjection molding technology However, due to the use of mechanical transmission device, there are transmission gap error and accumulated mechanical deformation error, which affect the precision control and speed of the equipment Quick reactivity At present, only medical Murray company in the United States and Fanuc company in Japan have adopted this driving mode (2) plasticizing method: the plasticizing units of micro injection molding machine are screw type or plunger type Because the plasticizing effect of plunger type is not good, it has not become the mainstream of current development Although the plasticizing effect of screw type is good, there are still problems such as difficult processing of small-size screw, limited service life and long plasticizing time Therefore, new environmentally friendly plasticizing methods need to be further explored, such as ultrasonic plasticizing, microwave plasticizing and laser plasticizing At present, IKv research center in Germany has studied the ultrasonic plasticizing method of injection molding machine and made gratifying progress (3) Injection materials: most microinjection molding machines take polymer as the injection object, and the molding scope covered by microinjection molding technology includes not only polymer but also powder feeding Due to the great difference between powder feed and polymer melt in material properties and process requirements, with the increasing maturity of micro powder injection molding technology, the research of special micro injection molding machine for powder feed needs further study (4) Product performance test