New technology for injection molds

- Oct 07, 2019-

Modern industrial requirements for injection molded parts require not only high precision, but also excellent internal quality. In order to meet this requirement, it is necessary to develop new technologies for injection molding. Currently, in the southern coastal areas, the injection molds imported from abroad are being gradually promoted. New technology has played a big role in improving the quality of injection molded parts.

The clamping force of the commonly used injection machine is proportional to the area of the mounting die table. The closing height of the injection mold with a large tonnage clamping force can also be large. When forming some large flat plastic parts, often Although the projected area of the plastic part is large, the required clamping force is small.

In order to make full use of the clamping force of the injection machine, a laminated mold should be used. This new technology is to design the mold into a two-layer cavity, and the plastic parts are removed from the two parting surfaces during demolding. In a two-layer cavity, the height of the mold does not exceed the allowable closing height of the injection machine. The feed port of the mold must be extended to the sprue plate in the middle of the mold to feed the cavities on both sides, thus forming a complete single-layer injection mold on both sides of the sprue plate located in the middle of the mold. . This laminated mold has two parting faces and two ejector systems. An interlocking mechanism should be arranged between the movable mold of the laminated mold, the intermediate runner plate and the fixed mold, and the rack gear interlocking mechanism can be used. When the mold is opened, the intermediate runner plate is retracted with the moving mold to open the first one. The parting surface, when the moving mold moves to a certain position, the intermediate runner plate stops moving, and the mold is continued to retreat, and the second parting surface is opened. There are also toggle joint interlocking mechanisms and hydraulic cylinder interlocking mechanisms. The mold can also simultaneously form a matching plastic part in a pair of molds to ensure a precise fit.

The injection molding process generally first closes the mold, melts the cavity, cools the shrinkage, and maintains the pressure. If the mold is first formed by injection molding, the mold is first closed, the first closed mold does not completely close the moving and fixed molds, but a certain compression gap is retained, and then the molten material is injected into the cavity. This new technology mold must be in the core. Part of the step is set. Although the mold is not closed, it can ensure that the melt will not leak. After the injection is completed, the second closed mold is performed by a special closed mold piston. During the process of closing the mold, the melt in the cavity is simultaneously compressed. After the plastic is solidified, the dedicated closed-die piston must undo the pressure on the mold, and then mold and eject the plastic part. This is the injection molding and compression mold that is being promoted and utilized in the South. The mold compresses the melt in the cavity, reduces the influence of the molecular orientation on the injection, improves the reproducibility of the plastic, and reduces the required injection pressure by not using the pressure-preserving feed. At the same time, the residual stress of the plastic can be reduced, and the warpage deformation of the plastic after cooling can be reduced. This mold can be used to form high-precision plastic parts such as plastic optical lenses, laser discs and artificial kidney dialysis filters, as well as thin-walled plastic parts that are difficult to form.

In the production, many plastic parts are formed on the metal base plate after forming. For example, many plastic components are installed on the metal base plate of the tape recorder and the television set. Nowadays, some manufacturers in the south have developed an assembly injection molding process in which a metal base plate is directly placed in a mold to form all the plastic parts at a time, which not only saves a lot of manpower, but also improves assembly quality. This process is completed by a fully automatic injection molding device consisting of an injection machine with a turntable, an automatic alignment device for metal components, a chuck for mounting metal components, a sprue take-out chuck, a plastic chuck, and a turntable device. It consists of plastic and sprue waste collection boxes. During operation, the metal component box continuously supplies the metal component to the automatic arrangement device of the metal component. After the metal component is inserted into the metal base plate, the metal component is confirmed by the inspection device, and the metal component is inserted by the indexing device with 90 arms. The metal bottom plate is placed in the lower mold on one side of the rotary table, after which the rotary table is rotated by 180°, so that the lower mold that has been placed in the metal bottom plate enters the forming position of the injection machine, and the injection molded lower mold is turned to Just put the lower mold position of the metal bottom plate. At this time, the injection machine enters the closed mold and the injection molding process, and the lower mold is transferred from the forming position, and the metal bottom plate and the sprue waste after the injection molding are taken out from the rotating position, and the metal bottom plate into which the metal member is inserted is placed. After the two actions are completed, the rotary table moves to the next work cycle. It can be seen from the above work process that in the assembly and injection molding, it is necessary to match one upper mold and two identical lower molds (down to page 78), sample materials, quality assurance engineering drawings, various equipments, tool places, etc. Condition and quantity, then calculate the cost and production capacity of the new production line based on this result, and take into account various factors that may affect quality in the production process, and make mistake-proof design work in advance; in terms of equipment and tools, design according to actual conditions. Simple and accurate tools and small equipment are put into use. At the same time, PLC control, NC machinery, simple robots, etc. are used as much as possible in the level of automation; and there is a real-time online technician guarantee system to promote the continuous improvement of production and management. The target crime rate of “0, in the library” is nearly the same.

In the coil manufacturing department where the author is located, the previous processes are relatively scattered. For example, the preparation process, the hardening process, and the packaging process are independent. In the past two years, through the continuous design and development, some small-scale, but highly automated small-sized ones are used. The equipment concentrates the production of the entire product in one production line, which reduces the waste of the moving distance, reduces the cost of the equipment, and improves the quality and production efficiency of the product. For example, a simple welding machine made of a stepping motor unit, a small automatic oven replaces a large-scale hardening furnace, and a small packaging machine made of PLC is used. Although these small equipments are inexpensive, the degree of automation is high and the effect is very obvious.

It can be seen from the above introduction that lean manufacturing has three main characteristics in the manufacturing site: it emphasizes the role of “people”, and the company takes employees as the center and implements the working mode of self-governing groups to maximize the creativity of each individual.

It is to simplify the organization and product development process, that is, to minimize non-production costs and management levels, and to delegate responsibility and rights to the “self-governing group” as much as possible, so that the production organization form is changed from a hierarchical division of work to a distributed network.

It adopts more advanced numerical control manufacturing unit and process concentration form to complete the whole process of production and processing of the whole workpiece in one manufacturing unit. Through continuous improvement, we strive to achieve no-defective, waste, and no inventory, and achieve the goal of “perfect perfection”.

(Continued from page 76). Therefore, the mold must have a good fit precision, and within the range of the positioning accuracy of the rotary table, and the mold can automatically guide the mold to close. Since plastic is a viscoelastic body, if it only relies on shrinkage to bond it to the metal plate, the relaxation will affect the firmness of the bond after a period of time. Therefore, the metal base plate should be grooved, embossed or stepped to improve the bonding. The degree of firmness. When designing such a mold, it should be ensured that the formed plastic stays on the lower mold, otherwise the ejection mechanism should be designed in the upper mold. Since this forming process can greatly reduce assembly man-hours and in-stock plastic parts, it is a high value-added forming process. This forming process is particularly suitable for the manufacture of plastic parts that are complex, delicate or tiny and difficult to assemble. The latest plastic molding processes and molds. Shanghai: Shanghai Science and Technology Press,