The quality of the finished product is measured in milligrams. The micro-injection molding technology of the finished product geometry measured in micrometers began in the late 1980s. It is an emerging advanced manufacturing technology, compared with traditional and conventional injection molding technology. It has different requirements for molding materials, molding processes and molding equipment. Many existing and mature injection molding techniques and theories are not suitable for micro-injection molding technology. The technical characteristics of the micro-injection molding process must be systematically and thoroughly studied and discussed in theory and practice.
Special requirements for micro-injection molding machines At the beginning of the development of micro-injection molding technology, there was no special injection molding machine for the manufacture of micro-parts. In the actual production, the traditional medium and large injection molding machine is usually used together with the multi-cavity mold design to realize the part preparation. This not only has high requirements on the flow path balance design of the mold, but also the molding quality of the parts is difficult to control. Therefore, special injection molding machines are 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, mainly in the following aspects:
(1) High injection rate: The quality and volume of the micro-injection molded parts are small, and the injection process is required to be completed in a short time to prevent the solidification of the molten material and cause the parts to be underfilled. Therefore, the injection speed is required to be high during molding. The conventional hydraulically driven injection molding machine has an injection speed of 200 mm/s, and the electric servo motor-driven injection molding machine has an injection speed of 600 mm/s. The micro-injection molding process usually requires a polymer melt injection speed of 800 mm/s. In the above, the viscosity of the melt is reduced at a high injection speed by using the principle of shear thinning of the polymer melt, so that the micro-standard cavity is smoothly filled.
(2) Precision injection volume measurement: The quality of micro-injection molded parts is only measured in milligrams. Therefore, the micro-injection molding machine needs to have a control unit for one injection in the precision metering injection process. The quality control precision is required to reach milligram level, and the screw stroke precision is required. Up to the micron level. The traditional injection molding machine usually adopts a linear reciprocating screw injection structure, and the injection control amount error is relatively large, which cannot meet the micro-control requirements of micro-injection molding, and has a great influence on the molding quality of the parts.
(3) Rapid reaction capability: the injection volume during the micro-injection molding process is quite small, and the movement stroke of the screw/plunger of the corresponding injection device is also relatively small, so the drive unit of the micro-injection molding machine is required to have a relatively fast reaction speed, thereby Ensure that the device can reach the required injection pressure in an instant.
The classification of 2 micro-injection molding machines is limited to the application limitations of traditional injection molding machines in the field of micro-injection molding. In the 1990s, some companies in Europe, Japan and the United States cooperated with scientific research institutions to develop various types of special micro-injection molding. Machine (usually clamping force <15t=, currently major foreign equipment suppliers include Nissei, Dr.Boy, Battenfeld, MCP, Babyplast, Takahashi, etc. The main functions of micro injection molding machines usually include plasticization, metering and injection. It can be classified by the driving method of each part, or it can be classified by the mechanism of each part.
Classified by drive mode, it can be divided into hydraulic/pneumatic drive, all-electric drive and electro-hydraulic hybrid drive. The hydraulic/pneumatic drive, ie the rotation/reciprocation of the plasticizing unit and the injection unit, is driven by the hydraulic/pneumatic system. The advantage is that the injection pressure and injection speed can be achieved, which can meet the requirements of the micro-injection molding process; The control accuracy is poor. All-electric drive means that all units of the equipment are driven by servo motor. The advantages are high control precision, fast response and low environmental pollution. The disadvantage is that the output thrust of the servo motor is limited, and the injection pressure and speed can be achieved. The electro-hydraulic hybrid drive combines the high injection pressure of the hydraulic drive, the injection speed with the precise control and rapid response of the all-electrical drive as the source of the system.
According to the design of the plasticizing and injection unit, it can be divided into screw type, plunger type, screw plunger type and other special forms.
2.1 The plasticization, metering and injection of the screw type micro-injection molding machine are all completed by a set of screws. The rotation and reciprocating motion of each unit are on one axis, and the structure is simple and easy to control. However, due to the true anti-reverse ring structure before the screw, the accuracy of the control of the injection amount of the device is poor. Representative models of such micro-injection molding machines include BOY12a of Dr. BOY, Germany, HM7-DENKEY of Nissei Resin Industry Co., Ltd., JMW-015S-5T of Shuyan Industry, and EC5 of Toshiba.
2.2 Plunger micro-injection molding machine includes two types: single plunger type and plunger-plunger type. The single plunger type pushes the granular or powder plastic forward, and passes through a torpedo-shaped split shuttle. The function of the cavity and the diverting shuttle is to disperse the plastic on the inner surface of the tube to make the plastic easier to plasticize. The plunger-plunger type is a plasticizing and metering injection function of the two sets of plungers. This type of micro-injection molding machine usually has a small amount of plasticization, the quality of plasticization is not high, and the mixing performance is also poor. Representative models include Babyplast6/10 from Cronoplast in Spain, Rabbit2/3 from MCP in the UK and Sesame from Medical Murray in the US.
2.3 Screw plunger hybrid micro-injection molding machine uses screw as plasticizing unit to complete mixing and plasticizing. The small-diameter plunger is matched with servo motor and controller as micro-injection unit to complete precision metering and injection. The micro-injection molding machine According to the plasticizing metering mechanism design, it can be divided into two types: two-stage metering type and three-stage metering type.
(1) Two-stage metering type: The plasticizing screw first plasticizes the plastic and carries out coarse metering, and then sends it to the injection chamber, and then carries out precision metering and injection by a small-diameter plunger. Representative models of such micro-injection molding machines are 12/90HSP of MCP Company of the United Kingdom, TR18S3a of Sodick Company of Japan, au3E of Nissei Resin Co., Ltd. and EPOCHSHOT7 of Tianrui Company.
Servo-controlled drive three-stage metering: plasticizing screw plasticizes the plastic and carries out coarse metering, then feeds it into the first section of the metering chamber, after being metered by the first section of the metering plunger, the injection is sent to the second section of the metering chamber, and then The second section of the metering plunger is precisely metered and then injected. Representative models of this type of micro-injection molding machine include the Microsystem 50 from Battenfeld and the FX25 from the IKV Institute of the University of Aachen in Germany.
4 Other special forms The injection machine from Ettlinger GmbH has a coaxial screw/plunger compound injection unit that can produce 0.1-5.0g plastic parts. The outstanding features of this type of mechanism are direct injection molding and special structure design. The needle nozzle integrates the hot runner system into the injection machine, enabling the micro injection molding process to use a runnerless mold, saving material and shortening the molding cycle.
3 Micro Injection Molding Machine Development Trend Micro injection molding machine is a new direction in the development of injection molding equipment, creating a new way of research on micro-structure parts and system manufacturing. Its outstanding advantage is the ability to realize high-precision, high-precision parts in large quantities. Low cost production. For the screw type micro injection molding machine, plasticization, metering and injection are all completed by a set of screws, so the structure is simple and easy to control. The disadvantage is that due to the true anti-reverse ring structure before the screw, the precision of the control of the injection amount of the device is poor, and the probability of degradation of the material in the injection cylinder is increased, which affects the stability of the molding quality of the part. For the plunger type micro-injection molding machine, although the precision of the injection amount is higher than that of the screw type, the plasticizing amount is small, the mixing performance is poor, and the plasticizing quality of the material is worse than that of the screw type, which is disadvantageous to the molding surface quality and optics. Parts with higher characteristics. The screw plunger hybrid micro-injection 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, so that the control precision of the micro-injection molding and the molding quality of the parts are both There is a significant improvement, but usually its structure is more complicated, and the control and maintenance are more complicated than the plunger type and the screw type.
The various micro-injection molding machines of the above various principles have different performance indexes and are suitable for the requirements of different microstructure parts. Therefore, it is necessary to comprehensively consider the appropriate micro-injection molding machine according to various factors such as the cost, size and quality of the micro-structured parts. However, since micro-injection molding technology is an emerging technology field, many basic theories are still not perfect, and the micro-injection molding process is not mature enough, and further exploration and research are needed. At the same time, with the continuous development of related technologies such as mechatronics technology and computer network technology, many new ideas and new directions are provided for the development of micro-injection molding machines. Therefore, the further development of micro-injection molding machines still faces many challenges, mainly in the following aspects:
(1) Drive mode: At present, most micro-injection molding machines use high-frequency and high-torque servo motors with high-precision mechanical transmission devices to achieve precision metering and high-speed high-pressure injection required by micro-injection molding technology, but this method is adopted. Mechanical transmission devices, there are transmission gap errors and mechanical cumulative deformation errors, affecting the precise control and rapid response of the equipment. The use of linear motor drives has the problem of less thrust and higher cost. Currently, only MedicalMurray of the United States and FaNUC of Japan have adopted this type of drive.
(2) Plasticizing method: the plasticizing unit of the micro injection molding machine adopts screw type or plunger type. Due to the poor plasticizing effect of the plunger type, it has not become the mainstream of current development, and the screw type has better plasticizing effect. However, there are still problems such as difficulty in processing small-sized screws, limited service life and long plasticizing time. Therefore, new environmentally friendly and efficient plasticization methods have yet to be further explored, such as ultrasonic plasticization, microwave plasticization and laser plasticization. At present, the German IKV Research Center has carried out research on the ultrasonic plasticizing method of injection molding machines and has made gratifying progress.
(3) Injection materials: Most micro-injection molding machines use polymers as injection targets, and the micro-injection molding technology covers molding ranges including not only polymers but also powder feeds. Due to the large difference in material properties and process requirements between powder feed and polymer melt, with the increasing maturity of micro-powder injection molding technology, the research on special micro-injection molding machine for powder feeding needs further progress. .
(4) Product performance test: The micro-injection molding products are small in size, and few suitable test instruments can fully and correctly test the molding performance of the product, and the test efficiency is also low. The performance of the molded product is an important evaluation index for the performance and stability of the molding machine. Therefore, perfecting the function of the product performance detecting module in the micro injection molding machine is also one of the main challenges in the development of the micro injection molding machine.
(5) Intelligent equipment: The current micro-injection molding machine mainly plays the role of product production. With the development of computer and mechatronics, the micro-injection molding machine not only has to complete the task of product production, but also designs the product through computer. Effective integration of computer simulation analysis, production management and customer service systems for intelligent production manipulation.
(6) Networking: With the development of computer network technology, the micro injection molding machine will develop a control system and detection system with network communication capabilities to make production management and control network. The micro-injection molding expert system can operate the micro-injection molding machine online, monitor and automatically adjust the molding process parameters of the molded parts, improve the molding precision and stability of the parts, and effectively reduce the technical dependence of the operators, which is beneficial to multi-production and marketing. The control of the outlets.
4 Conclusions and exhibitions The development of micro-injection molding machines is based on the development of electromechanical technology and injection molding technology, driven by the demand for micro-injection molding products. From the current research status of micro-injection molding machines, the research and development trend of micro-injection molding in the future may be reflected in the following aspects:
(1) Further research on the driving method of equipment to develop high-precision, high-sensitivity, high-thrust, low-cost driving equipment and methods;
(2) Exploring new plasticizing methods of materials, solving many problems brought by the existing plasticizing methods, and achieving the purpose of tidy and high-efficiency plasticizing injection materials;
(3) Further improve the microinjection of new materials into
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