On the injection molding technology of the hottest

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With the development of international interconnection, a large number of it digital products have entered our lives. According to statistics, the total volume of DVD-R in the global market in 2005 was 1.7 billion, and it is expected to reach 3.5 billion in 2006, and will continue to grow at a rate of 2.5 ~ 3 times in the future. As far as China is concerned, the market consumption potential is huge. In recent years, a large number of VCD, DVD, PC and other related equipment have entered the market, which has also driven the market demand for optical discs. Compared with the markets in Europe and the United States, China's potential demand is still quite huge

optical disc is also called optical memory. The master plate is made of high-strength polycarbonate with high temperature resistance and is processed on an ultra precision injection molding machine with an ultra precision mold with a mirror precision of 20 ~ 30 nm. On the motherboard, there are countless signal recording grooves, which are pressed by the mold under the strong clamping force of the injection molding machine. The grooves also vary according to the disc format. Among them, the width of CD and VCD signal recording grooves is 0.56 μ m, the depth is 0.11 μ m, and the row spacing is 1.5 μ m; The width of the signal recording groove of DVD is 0.28 μ m, the depth is 0.11 μ m, and the line spacing is 0.75 μ M. Apply organic plastic on the prefabricated groove of CDR (one-time recording read-only disc). After the ablation of the laser signal of the recording laser head, the signal will be permanently retained on the disc, and the signal can be picked up after reading. The signal groove of CDRw (rewritable and recordable optical disc) is relatively shallow, only 40 ~ 50 nm, in which memory alloys AG, in, Sb, Te, etc. are sprayed and deposited. The difference in the beauty of laser reflection profile of the alloy in crystalline and amorphous states is used to erase, record and read signals

it is precisely because 3. The basic requirement of the filler is that the depth of the signal groove of the optical disc is at the nanometer level. The requirements for the accuracy of the mold and the injection molding equipment are particularly high. In the international market, the injection molding machines of the CD production line are mainly produced by Krauss Maffei of Germany, nestal of Switzerland, Sumitomo of Japan and toolex of Sweden. In particular, nestal of Switzerland and Sumitomo of Japan are the most famous companies, representing the highest level of injection molding machines

technical problems

optical disk injection molding machine is composed of mold locking device, injection device, cooling system, hydraulic system and computer control system. The outer diameter of the disc master is divided into 80 mm and 120 mm, but the thickness is less than 1.2 mm, which means that the process and channel ratio (the ratio of process depth to channel thickness) of the molten material of the master material in the mold cavity are very large. Therefore, the product quality of plastic melt is not easy to be uniform in the filling process. Moreover, the master disc is a circular disc, and the main sprue is located in the center of the disc. After the injected plastic melt enters the mold cavity, it must advance rapidly and evenly along the direction of 360 degrees around the circumference, and flow to the edge of the circumference in an orderly radial direction. If the local flow rate is too fast in the process, channeling or auxiliary flow will cause local melt molecular orientation and form internal stress; If the speed of the master plate is uneven during the cooling process, local residual stress will also be formed; If the mold locking templates are not parallel, not only the quality of the master plate will be unstable, but also the mold may be damaged. Therefore, in view of the characteristics of optical disc products, such as high precision, good stability, high production efficiency, high cleanliness and good optical performance, the requirements for the injection molding machine mainly include the following points:

◆ the overall operation of the system is stable and reliable, the opening and closing of the mold is fast and stable, the starting and stopping positioning accuracy of the template is high, the parallelism error of the template is small, and the clamping force is accurate and stable

◆ plasticizing system has high efficiency, fast speed, good quality and accurate measurement

◆ high injection pressure, fast injection speed, multi-stage adjustable. The pressure holding conversion point is accurate, the pressure holding pressure is stable, and multi-stage adjustable

◆ accurate temperature control

◆ the whole machine is low noise, clean and free of oil stain

comparative analysis of solutions

from the information of the China International optical storage equipment exhibition and academic exchange meeting, which ended in Shanghai in early September, at present, the international CD production lines mostly use full hydraulic or full electric injection molding machines, and in recent years, electric hydraulic composite injection molding machines have also been used

now compare the advantages and disadvantages of full hydraulic injection molding machine and full electric injection molding machine

I. mold closing part

CD injection molding requires fast and stable mold closing action, fast and accurate pressure conversion, and high requirements for template parallelism and starting and stopping position accuracy

although the full hydraulic injection molding machine has the compressibility problem of hydraulic oil, the pressure is equal everywhere when the hydraulic pressure is static, so the force on the template and mold is quite uniform

all electric injection molding machines generally use servo motors to replace the original oil cylinders to push the elbow rod to open and close the mold. Therefore, the problems existing in the original elbow bar structure continue to exist, such as high machining accuracy requirements, easy wear, difficult mold adjustment, etc. Due to the use of servo motor, the elbow bar can stop at different angles, which is conducive to the change of clamping force and compression molding. Moreover, since there is no influence of oil pressure inertia, the noise is relatively low and the control accuracy is high. But all this is based on the premise that the elbow rod and ball screw are not worn, the manufacturing and assembly accuracy is high, and the mold installation plane is parallel. Generally, after using the all electric injection molding machine for about a year, there will be troubles caused by the wear of elbow rod and ball screw. At this time, not only the precision of the machine will be reduced, but also an additional radial force will appear on the ball screw, which will accelerate the wear, further reduce the precision rapidly, and bring problems such as reduced efficiency and increased noise. In addition, if the elbow rod starts to be injected before it is fully supported, the powerful mold expanding force of high-pressure molten plastic on the mold will act on the ball screw and the spindle of the servo motor. When this force is large enough, it may cause damage to the ball screw and the servo motor

second, the injection part

the optical disc is a thin-walled product, and the depth of the information groove on the optical disc is nano precision. In order to ensure the accuracy of the duplicate signal, the injection process is required to be carried out under the conditions of high speed and high pressure, and the speed and pressure of the injection and pressure maintaining process are adjustable in multiple sections, and the pressure maintaining conversion point is accurate. Otherwise, after the disc is manufactured, there may be signal loss, incomplete signal, disc warpage, crazing and other defects. At the same time, in order to ensure that the cycle cycle of the whole machine is as short as possible, the plasticizing speed of the barrel screw is required to be very high, and the plasticizing amount is required to be very accurate. The plasticizing speed and back pressure are also multi-level adjustable to meet the good plasticizing effect in the case of high speed. Therefore, a special screw is used, which is also conducive to ensuring that bubbles, black spots, impurities and other defects will not appear in the molding process

at present, the structure of the injection part of the full hydraulic injection molding machine is generally divided into two types: double cylinder injection and single cylinder injection. The double cylinder injection device has the advantages of short axial length and simple connection between injection cylinder, screw and oil motor. However, this structure has a large injection load and is difficult to be accurately controlled. Single cylinder one-line injection device is conducive to precision control, but the structure is more complex, and the manufacturing accuracy requirements are relatively high

in the fully electric injection molding machine, the injection system generally has two structures, one is the belt drive structure, and the other is the direct drive of the motor. Obviously, the accuracy will be affected after adding belt drive. Although the structure of belt drive is relatively simple, the motor speed is required to be low, the torque is large, and its overload protection ability is weak. However, when using servo motor to control the screw rotation during plasticization, the accuracy of plasticization measurement will be relatively high, the speed will be relatively stable, and stepless speed regulation can be achieved. During injection, the servo motor drives the ball screw to drive the screw for injection. The control accuracy is also very high, and the response is also very sensitive, which is conducive to multi-stage injection adjustment. However, due to the high load, high speed and frequent start and stop of the ball screw, the wear is also relatively large. The starting speed of the servo motor during injection is faster than that of the general hydraulic type, but if the hydraulic system is equipped with an accumulator, it will start faster than the servo motor. Similarly, if the accumulator is used for rapid injection, its speed can also be faster than the injection speed of the servo motor. Of course, the control of injection pressure and speed with servo motor is relatively accurate, but when entering the pressure maintaining, because the servo motor cannot provide large torque in the state of shutdown, it can only rotate intermittently and supplement pressure by measuring the pressure of the material in front of the screw. In this way, on the one hand, the continuous start and stop of the ball screw under the impact force will accelerate the wear, on the other hand, the frequent start and stop of the motor will lead to heating, increased energy consumption, and unstable pressure

generally speaking, all electric injection molding machine and all hydraulic injection molding machine have their own advantages and disadvantages, and the injection molding machine made by combining the two is not satisfactory. Therefore, the international high-precision injection molding machine is still developing in the direction of full electric and full hydraulic. The following will be compared and discussed from 10 aspects:

1) energy saving

all electric injection molding machine has certain advantages over all hydraulic injection molding machine in energy saving, but it is not as high as the energy-saving efficiency advertised by some manufacturers. Because the biggest energy consumption of the injection molding machine is in the heating process, injection process and plasticization process, the action of the hydraulic injection molding machine is carried out in sequence, while the electric injection molding machine must be started frequently; Moreover, the effect of reducing wind resistance while saving energy and light weight varies greatly in the production of different products. If we use all electric production of thin-walled products, we may not save so much energy. Moreover, the energy saving of many manufacturers is compared with the single cylinder hydraulic type. If compared with the full hydraulic type or elbow bar type of other structures, the energy saving effect is not so obvious. At the same time, if the full hydraulic injection molding machine adopts the multi pump and variable pump hydraulic system, applies the frequency converter to control the motor speed, and adopts the load reaction injection system, its energy-saving effect can also be comparable with that of the full electric type

2) in terms of noise reduction

a slogan of the all electric injection molding machine is tranquility. For this point, if the elbow rod and ball screw are not worn and the assembly accuracy is high, this is indeed the case. However, once there is wear or the assembly accuracy is not high, there will be great vibration and noise in the process of injection and mold opening, and once it happens, all these will accelerate its further deterioration

3) accuracy

although the full hydraulic type has problems such as the compressibility of hydraulic oil, the pressure is equal everywhere when the hydraulic pressure is static, so the accuracy of using two plate hydraulic clamping mechanism is very high. If the servo valve control is used in the injection and plasticizing system, its control accuracy will also be very high. Due to the wear problem of elbow bar and ball screw, the mechanical accuracy and wear will inevitably affect the product quality, so its mold locking accuracy is still not as high as that of the full hydraulic type. This aspect has also been verified in the processing of optical discs. The all electric type can only produce DVD5, VCD, CD, etc., and it is difficult to use the electric injection molding machine for processing above DVD9 and CD-R, DVD-R, DVD-RW, etc. Not only that, the accuracy of all electric type will continue to decline with the increase of service time

4) in terms of price and cost, the price of all electric type is higher than that of all hydraulic type

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