data:2014-12-26 19:16:32home stationviewed：2390
Precision injection molding machine
1, the comparison of fully hydraulic and fully electric
All electric injection molding machine is with the development of precision injection products and gradually into people's horizons. All electric injection molding machine, refers to adopt servo motor to replace the original hydraulic equipment, to complete the rotation of the screw, injection process, the process of injection molding machine. Mechanical principle of fully electric injection molding machine with the traditional hydraulic injection molding machine is basically the same, just in the control part adopts servo motor to replace the original hydraulic device, the injection device also includes the plasticizing and two parts. Plasticizing unit is composed of screw, barrel, nozzle, transmission part is composed of ball screw, servo motor, gear and clutch, etc. All electric injection molding machine clamping device has toggle and direct pressure type two kinds, with the traditional injection molding machine, it is also basically the same.
Through the understanding on the structure of electric injection molding machine, we can compare the electric injection molding machine with hydraulic injection machine on the performance of different. Due to the electric drive system of injection molding machine without the hydraulic oil, so it is possible that ruled out because of the hydraulic oil leakage characteristic parameters and hydraulic oil fluctuates according to temperature change caused by the process parameters. The precision of ball screw is higher, better repeatability, is conducive to the stability of the processing. Adopt servo motor control screw plasticization, its measuring accuracy is higher, also more stable, and more conducive to speed. Power direct transmission can also help to save energy. However, this kind of injection molding machine is driven by servo motor drives the ball screw injection screw, because of the large ball screw load, high speed rotation when worn, so general all electric injection molding machine injection rate is less than 500 mm/s, this is a weakness of fully electric injection molding machine.
Full hydraulic injection molding machine has many unique advantages in forming complex products, such as high precision mould, mould strength, etc. Its clamping device has a variety of structures, such as single cylinder liquid type, multi-cylinder liquid type, two board straight pressure type, a lot of more phyletic, the difference is big. Large single cylinder liquid injection machine, hydraulic oil easy to leak, booster slow, energy consumption is more. Multi-cylinder liquid type injection machine to a certain extent and improve these problems, the fuselage is shorter, the volume is small. Two plate straight pressure type injection molding machine to solve the above shortcomings, the journey is long, combining a model of high efficiency, the modulus and high accuracy, combining a model clamping deformation is little, mould replacement is convenient, but its control technology difficulty is big, hydraulic technology is also difficult to master.
Fully hydraulic and fully electric can say each has its characteristics. All electric injection molding machine in the process precision and service life as full hydraulic injection molding machine, and the fully hydraulic injection molding machine to ensure precision servo valve must be followed, which inevitably lead to improvements in cost. Now, people are actively developing electric - hydraulic precision injection molding machine, measurement plasticizing process driven by electric power to achieve energy saving effect; Hydraulic or electric - hydraulic composite clamping mechanism can effectively keep the processing accuracy and stability. Therefore, a combination of energy saving electric injection molding machine and hydraulic injection molding machine of high-performance electric - hydraulic precision injection molding machine has become a new trend of the development of precision injection today.
2, the micro injection moulding machine
The market demand to promote the development of micro precision injection molding machine. At present, the parts can be molded parts weighing 0.0003 g, wall thickness of 0.01 mm, size tolerance to + / - 0.005 mm. Therefore, forming these products puts forward higher requirements on injection molding machine. To melt and flow through a tiny nozzle, injection molding machine is required to provide higher injection pressure; In order to ensure material fills the cavity before cooling, insist on high injection speed. In addition, the precise injection quantity measurement and quick reaction capability are the requirements as set forth in micro injection molding machine, therefore, the accurate screw and cylinder design and precision injection control are required.
Micro injection moulding machine is a new direction in the development of injection molding equipment, created the fine a new way of structural components and system research, its advantage is to be able to achieve high accuracy, high precision parts mass production and low cost. For micro injection molding machine screw, the plasticizing, measurement and injections are performed by a set screw, so the structure is simple, easy to control. The shortage is due to screw the front non-return ring structure, makes the equipment for a injection quantity control accuracy is poorer, and increase the risk of material degradation in the injection cylinder, affecting the quality of parts forming stability. For plunger decay injection moulding machine, although its high control accuracy of injection quantity is screw type, but the small amount of plasticizing and mixing performance is poor, the quality of material plastication than screw is poor, is not conducive to high surface quality and the optical properties of molding parts. And screw plunger mixed decay injection moulding machine is integrated the advantages of the plunger and screw to screw as plasticizing unit, plunger as measurement and injection unit, the control precision of the micro injection molding and parts molding quality are improved obviously, but usually its structure is relatively complex, control and maintain a plunger type and screw type.
Micro injection molding machine of different principle has different performance indicators, suitable for different requirements of micro structure parts. So according to the fine structure of the specific parts of the cost, size and quality and so on various aspects factor comprehensive consider to choose configure appropriate micro injection moulding machine. As the electromechanical integration technology, the continuous development of computer network technology and other related technology, for the development of the micro injection moulding machine provides many new ideas and new direction. Look from the current research state of micro injection moulding machine, the future for a period of time the development trend of micro injection molding is probably reflected in the following aspects: the development of high precision, high sensitivity, low cost and high thrust driving devices and methods; Explore new way of material plasticizing, solve the problems are caused by the existing way of plasticizing, reach the purpose of clean and efficient plasticizing injection material; To further improve the micro injection molding process of the new material research and development is suitable for various molding materials of micro injection molding machine; Micro injection molding machine of high precision, high efficiency product testing unit to explore, for the micro injection molding machine to provide reliable performance test and evaluation standard; Intelligent and networked research the development and application of micro injection moulding machine, make the micro injection molding machine with the help of computer and network to realize multiple on-line control and remote control of production.
Micro injection moulding machine research and development history is not long, but it is a great potential for development of technology, to carry out the research of this field can not only promote the development of the traditional injection molding technology, but also can promote the fine microstructure products manufacturing and application. As countries for micro-electro-mechanical systems (MEMS) and fine development of CAD/CAE/CAM products continue to strengthen, fine microstructure products market will continue to grow, the demand for precision micro injection moulding machine will increase year by year, micro injection moulding machine will certainly play an increasingly important role in the field of advanced manufacturing.
Precision injection mold design
In precision injection molding, the mold is one of the keys to guarantee the quality of products meets the requirements. Precision injection mold must conform to the requirements for the dimension precision of products, at the same time, the mold design must be reasonable, otherwise will directly affect the shrinkage of plastic products. Due to the mold cavity dimension is obtained by the estimate of the size of plastic products and shrinkage rate, therefore, the properties of plastic raw materials, product shape and size, gate location and distance, injection pressure, cavity pressure, melt temperature, mold temperature, the type and dosage of additives, and so on are the problems of what should be considered in the mold design. Precision injection mold design, therefore, in addition to mold issue to consider, consider the following: adopting proper mold tolerance; Prevent molding shrinkage ratio error; To prevent plastic deformation; Prevent demoulding deformation; Make the mould manufacturing to minimize error.
In injection molding, often difficult to infer the shrinkage rate of completely accurate, so the experience is very important. Generally speaking, in the fixed mold, the notch size to big, lobe to the small size. So in the design, the size of the concave part of shrinkage rate is chosen to smaller, convex to choose a larger size, the former supporting core to choose smaller shrinkage and shear core to choose.
In order to keep under the injection pressure and clamping force of precision mold, mold structure design of mold parts must be considered when the feasibility of grinding, grinding and polishing processing. Despite the cavity and core manufacturing has reached the requirement of high precision, but also with the shrinkage expected, however, due to the migration time molding center, the molding of products inside and outside the related dimensions are difficult to meet the design requirements. In order to keep moving precision mould in the size of the parting surface, the mold must be equipped with conical positioning pin or wedge blocks, etc., in order to ensure accuracy.
American Leopold Kiernicki et al developed a precision injection method of optical fiber ring. This method through the study of the improvement of mold, used in the process of forming a kind of adjustable core and receivers, accurately positioning mandrel and die out of line in the device. Mandrel were identified in molded ring inside the channel, and out of line in the ring forming small diameter longitudinal hole, the holes and internal channel connection, at the end of this molding ring is pinpointed the internal channels and holes. The invention has 2001 patents, including the United States are obtained.
German LindnerE. In view of the CD on various aspects to meet the requirements of high precision, such as plane, thickness, waveform and the surface quality, the structure of injection mold and conditions put forward certain requirements. Optical disks in a single cavity, and with a conical sprue and ring gate injection mold. Mold cavity tolerance unit must be within a few microns, the degree of surface polished to mirror finishing. Mould forming part of steel 1.2083, rockwell hardness of 50. Mold work under 60 ℃, cycle time is less than 4 s.
Japan HigashiY. People invented a kind of using laser assisted sintering and metal forming technology at a high speed. Using the technology to make injection mold can reduce cost, shorten production cycle, and manufacturing of the mold can be used to produce ultra precision plastic products more than 10000.
Mold technology is an important symbol of a country's industrial development. At present, precision injection molds have dominated the market remains as the United States, Japan, the Japan accounted for about 40% of the global market, the United States accounted for 20%. Precision of the domestic can produce precision mould within 5 microns can be said to be rare, not to mention the production precision in 1? 2 microns between mold. Therefore, China mold manufacturing from design, manufacturing to the management of the factory is still in its infancy, to reach the United States, Japan and even South Korea mold manufacturing level still has a long way to go, set up their own system of die and mould industry is a long way to go.
Precision injection molding technology.
1, the second molding technology
Current development after the first injection pressure is secondary molding the compressed mode used in injection molding plastic parts on board, the injection machine injection of billet, reuse compression modulus of compression molding. The molding method can guarantee that in the process of forming good contact between mold and plastic parts, uniform temperature and pressure distribution of the resin, eliminate internal stress, reduce the shrinkage of resin. The key technology of this process is the mould structure design and control of temperature and pressure. Shape of this method for some simple optical parts can have obvious effect, the internal stress distribution of homogeneous products, for more complex optical parts is powerless.
2, the injection compression molding
So-called injection compression molding in is when injected into cavity of the resin shrinkage due to cooling from the outside and a compulsory force makes the smaller the size of the cavity, so that the contraction of partly compensated molding method. Injection molding in general is indirectly controlled by control the movement of the precise screw cavity feeding speed and pressure, in order to ensure the quality of the finished product; Is through the cavity to the resin and injection compression molding pressure to improve the quality of directly. Is the resin filling part for the lens part on the pressure resulting from the optical axis direction compression, make uniform surface pressure, the volume of molding products determined by pressure and temperature of the resin, with the method of adjusting process conditions, release keep in low temperature stress, which can potentially reduce the shrinkage of the volume. Due to adopt the method of mechanical compression, so can under low pressure injection plastic and keep a long time in the mould molten state for the molecular orientation of reply, and does not require the holding pressure to compensate for shrinkage after injection, so that you can reduce or eliminate caused by pressure and forming the internal stress of resin molecular orientation, improve the uniformity of material, moulded and reduce the residual stress, refractive index and birefringence optical performance are greatly improved. In this way can already produce and glass precision optical parts, and the price is only 1/10 of the glass.
3, ultra precision molding
Using injection molding in, mold temperature is usually set below the heat deformation temperature of resin used. Therefore, melt to the mold cavity injection filling resin into solid, liquid mixture, temperature and pressure gradient. And adopt injection molding in, to prevent to produce "hole", is injected resin filling, need to maintain pressure "pressure" operation, the causes of resin orientation: from then on. Compression molding in injections, the mold resin after curing, makes every effort to make the inner cavity volume compression, finish high precision copying, but due to the curing of the resin, can not be implemented uniform pressure transmission. Therefore, injection molding and injection compression forming technology to make the thickness of the plastic lens with large diameter, the density and refractive index is not uniform, there are a lot of residual stress and birefringence, surface shape accuracy is not ideal In view of the defects of the precision molding method, based on the relationship between the temperature and pressure of the resin, can be used with ultra precision mould technology, the preparation of high precision plastic optical parts.
Before the introduction of superfinishing moulding, it is necessary to study the plastic state in the heating process. Resin in the process of heating volume increasing, when more than glass transition temperature of the resin, the volume increase rate is bigger, and reduce the volume during cooling. Assume that resin at a certain temperature in the heating process T1, using volume with the same volume of the space with the resin mold filling resin, and then continue to heat close to the glass transition temperature of resin, at this point, no longer increases, the volume of the resin pressure increases, once more than glass transition temperature, pressure and increased dramatically. If from the cooling temperature, the plastic pressure will decrease, when temperature T1, plastic pressure equals the atmospheric pressure, the volume is equal to the cavity volume. If further temperature down to room temperature, the volume of the volume of resin and before heating are equal, but less than mould volume. This reversible phenomenon of the resin is when the temperature uniformity of the resin can be established. As mentioned earlier, in order to prevent shrinkage hole plastic optical parts, need to "pressure" or reduce the cavity volume, but the specific volume of resin is not constant. For the constant volume, need to high pressure injection filling molten resin, immediately the block within the cavity. In addition, as soon as possible to eliminate the temperature of the molten resin and the pressure in the cavity is not uniform as well as the orientation, mold temperature must be controlled in forming above the glass transition temperature of the resin. After injection of filling, while maintaining the temperature and pressure evenly distributed, at a constant volume will mold cooling to the thermal deformation temperature of the resin. Super-fine molding was studied by using the properties of plastic molding method.
Heat the mold to the glass transition temperature of the resin above a certain temperature, injecting molten resin into the cavity and sealed immediately. Injection pressure and the amount of resin filling pressure is equal to atmospheric pressure to set according to the initial resin. After sealing, will remain above the glass transition temperature, mould temperature ensures equal distribution of pressure and temperature of the resin. Then, at the same time of maintaining resin pressure and temperature uniformity, at a constant volume mold cooling to the thermal deformation temperature of the resin. Then, open mold molding plastic optical parts. The displayed is the ultra precision molding. In ultra precision molding process, mold temperature, molding in higher than usual, filling injection pressure is big, so it is difficult to use the general sliding mechanism. The molding in the use of special small metal ball seal resin. Before closing the small metal ball in the mold in the injection port. Injection molding machine filling molten resin, metal ball injected resin into the cavity side, set aside for the resin injection into the mold cavity. Molten resin high pressure cavity after, molding machine stop injection, at this time due to the pressure difference, secretion of resin and the metal ball into the injection port, thereby blocking resin. Before using the agency to keep the pressure for sealing pressure of more than 95%.
Done for the displayed, cooling, and increasing the pressure of the resin and equal to atmospheric pressure condition, the injection filling molten resin and control the mold temperature is the key. Therefore, even if is forming the shape of the plastic optical parts size is different, if keep resin pressure and temperature uniformity of the break time and cooling time enough, only change the filling conditions, can obtain high precision plastic optical parts. Its surface has a high precision molding products, shrinkage hole, bubble significantly reduced, birefringence decreased, the form deviation is reduced, can produce the ideal plastic optical parts.
With the increasing demand for plastic products in all walks of life and its requirements gradually improve, precision injection brighter prospects is self-evident. However, when we count precision injection, do not worry about the present situation of domestic precision injection molding industry, precision injection molding machine, precision injection molds and products design, our country is still in a dogfight, high-end lost, at the bottom end of the state. As a plastic practitioners, more want to see the rise of domestic related enterprises to grow. Of course, the law of the development of enterprise has its objective, with the improvement of China's economic strength, the progress of productivity, precision injection of domestic enterprises will start my own a piece of the sky.