Printer bottom shell hot runner injection mould
The printer bottom shell product is shown in Figure 1. The maximum size of the product is 381.91 mm x 287.33 mm x 99.25 mm, the average thickness of the plastic part is 2.00 mm, the material of the plastic part is HIPS, the shrinkage rate is 1.005, and the quality of the plastic part is 507.40 grams. The technical requirements for plastic parts are that there must be no defects such as peaks, dissatisfaction with injection molding, flow lines, pores, warpage deformation, silver lines, cold materials, jet lines, etc.
The bottom case of the printer is the bottom case of a certain Japanese printer. It can be seen from Figure 1 that the structure of the plastic part is a complex shell, the movable and fixed molds have many bone positions and column positions, etc., the size is relatively large, and the mold is a large mold. See the attached file for the product drawing of the plastic part and the 3D drawing of the mold. In addition to marking product dimensions and tolerances, the product drawings of plastic parts also mark detailed technical requirements. In addition, there are surface etching and matting areas, and surface polishing areas.
For large molds, the difficulty of mold design lies in ensuring the dimensional tolerances and technical requirements of the plastic parts, while the injection molding process is stable, the pouring system is reasonably designed, the ejection process is stable, the plastic parts are not deformed, and the injection cycle meets the requirements of the mold design specification. Any small mistake will cause a lot of losses, because the cost of trial molds for large molds is high.
The mold design cavity ranking is 1 out 1. There are 7 slide cores on the four sides of the plastic part, and the two large slides are designed on the side of the mold. Among them, the slider 7 and the slider 9 are limited by their positions, and the slider is used to drive the slider to change the core pulling direction.
The size of the plastic parts is large, and the design of the gating system is also very difficult. The design of the position and quantity of the gate is the key. When the bone position and structure of large plastic parts are complex, the plastic process is longer, and the balance of the gating system is very important. Too many gates or unreasonable gate positions will cause excessive injection pressure, large plastic deformation, waste of plastic raw materials, and prolong the injection cycle and cause economic losses. If the gate is too small, it will also cause filling difficulties.
In the early mold design, the gating system completely relied on the experience of the mold designer to solve the problem. Due to the rapid development of computer technology, mold design has changed from traditional empirical design to computer-aided design, auxiliary programming and processing. The most important of these is the simulation of the filling and flow of the plastic melt in the runner and cavity based on the rheology of the polymer. The mold flow analysis software provides convenient conditions for the correct determination of the gating system. In the product development department of large companies, a department specializing in mold flow analysis has been established. For example, the mold flow analysis engineer in the product research and development department of Canon, Japan, specializes in mold flow analysis of plastic parts to provide technical support for product design.
The establishment of specialized departments and fixed mold flow analysts facilitates the accumulation of big data and also facilitates the determination of a reasonable injection molding cycle, creating conditions for lean production. Through the application of mold flow analysis software, the bottom shell of the printer needs to be designed with 3 gates, as shown in Figure 2 of the mold design. The YUDO hot runner system is used to feed the glue.
Due to the hot runner system, the mold base is a non-standard mold base 7085. In order to improve the positioning accuracy, the four corners of the mold base are designed with tiger mouths. The tiger mouths of the A plate are protruding, and the tiger mouths of the B plate are recessed. The angle of the tiger mouth is 5゜～10゜. For large molds, fixed and movable molds need to design positioning pins separately. The positioning pins of the movable mold are ø25, and the positioning pins of the fixed mold are ø40. The fixed mold uses guide posts instead, mainly for hot runner molds with multi-layer templates. The temperature difference and thermal expansion of each template are different, which will generate greater stress, and a large-diameter positioning pin is required to protect the hot nozzle from force. And to prevent the hot nozzle from being damaged when the mold is installed. On the operating side of the mold base, two oblique positioning blocks are designed.
For a complicated case mold such as a printer bottom case mold, the design of the front and rear mold cores is also critical. Before mold design, review the plastic parts. For the changes in the edge shape of the plastic parts, carefully analyze the direction of the parting surface to determine the parting surface. Carefully check the demoulding angle of the plastic parts, and confirm with the customer in time if there is any doubt. In the Japanese product drawing, the draft angle is called hook matching. To determine the draft angle and the step difference, you must get the customer's confirmation. Generally, a special meeting is held to study the specific issues of mold opening.
The length and width of the front and rear mold cores are both 370×500. For mold cores with a length and width of more than 200, there are certain difficulties when lowering the frame. Because the size exceeds the processing range of a general surface grinder, the size of the fine frame and the dimensional accuracy of the mold core are both It is difficult to guarantee. In this case, the mold core needs to be positioned at a reference angle and compressed with a compression block. The specific method is to take the base angle of the mold base as the base, make a 3 ゜ slope on the two frame edges far away from the base angle, and use the squeezing block to compress the mold core. The detailed block diagram of the B board is shown in Figure 4. For the situation of more movable mold bones, the exhaust of the mold during injection molding is very important. Therefore, in order to ensure the surface quality of the plastic part, the fixed mold only partially divides the insert. The movable mold cores are all broken up to make inserts. When designing the mold, it is necessary to determine a few large pieces according to the structure of the plastic part, and then divide the small inserts. When determining the large insert, it needs to be combined with the design of the cooling water, and the direct water is designed as much as possible to ensure the cooling efficiency. For corners of closed deep cavity that cannot be cooled, beryllium copper inserts need to be designed to dissipate heat.
ABIS MOLD TECHNOLOGY CO.,LTD
Daisy Wang (Sales Engineering)
M: +86-150 1652 6799
E: daisy@abismold.com
A: Building B#,YingKeli Industrial Part, LongDong Community, LongGang District, Shenzhen, China 518116
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