Design of needle valve hot runner injection mold for scanner bottom shell+3d

Scanner bottom shell products are shown in Figure 1. The maximum dimensions of the product are 450.60 mm x 410.38 mm x 63.60 mm; the average thickness of the plastic part is 2.50 mm, the material of the plastic part is PS HI, the shrinkage rate is 1.005, and the weight of the plastic part is 657.90 grams. The technical requirements for plastic parts are that there should be no defects such as peaking, injection dissatisfaction, flow lines, pores, warping deformation, silver streaks, cold material, and jetting lines, and meet ROSH environmental protection requirements.

  Figure 1 Scanner bottom shell product map
It can be seen from Figure 1 that the shape of the plastic part is a flat plastic part with a large size, and the corresponding mold is a large mold. The middle part of the plastic part is relatively flat, the glue position on the edge and several corners is complicated, the plastic flow is difficult, and it is difficult for the mold to eject from the edge and corners. It is necessary to prevent the deformation of the plastic part. There are side holes in the installation parts at both ends of the plastic part, and the slider core-pulling mechanism needs to be designed separately.
The edges and corners of plastic parts have many fine structures, and the flow of molten plastic is long. Therefore, the position and number of gates are the key points of mold design. The hot runner injection molding of thermoplastics adopts a heating method to the gating system of the mold to keep the plastic melt in a molten state at all times, thereby avoiding the generation of condensate in the gating system. The hot runner injection mold is equipped with an electric heater, which is equipped on the runner plate and nozzle, and is equipped with a temperature control system. The molten material is distributed to each gate through the runner plate, which can realize multi-point injection of large plastic parts, or multi-cavity molding in one mold. The driving cylinder of the needle valve is installed in the fixed plate of the fixed mold, and the pin of the valve needle passes through the runner plate. There are nozzles with gates or without gates, and the diameter of common gates is 2 ~ 8mm, and the maximum can reach ø20mm. Multiple needle-valve nozzles are suitable for time-sequential control injection, and the respective injection pressure-holding time can be arranged for each injection point nozzle, so as to control the injection and pressure-holding of each material stream, and can control the position of the fusion seam or eliminate the fusion seam. Therefore, the needle valve sub-nozzle has four advantages in the application of the hot runner system:
1) It can ensure that the pins are accurately controlled to close the gate during the solidification of plastic products; it can ensure that each nozzle has a consistent gate closing time after holding pressure; it can often reduce the injection cycle time; it also makes each injection of a mold with multiple cavities Points are counted the same.
2) There is no waste residue on the product, only the cylindrical mark left by the pin can meet the high-quality requirements of the product surface; there is no drooling and wire drawing at the gate.
3) It has a large gate channel, so it can be used for low shear resistance or shear sensitive plastic injection.
4) It is suitable for the injection of large plastic products, with a lower holding pressure, so that products with lower residual stress can be obtained.
Through mold flow analysis, this set of molds has determined 4 needle valve point gates, as shown in Figure 2.

  Figure 2 Schematic diagram of gate location

Figure 3 3D diagram of the rear mold core and parting surface
The plastic part is a large plastic part, and the mold is a large mold. Due to the needle valve hot runner system, the mold base is a non-standard mold base 7580. In addition to the ordinary three-level positioning, the four corners of the mold base are designed with tiger mouths, and the guide posts and guide sleeves are included in the tiger mouths. . According to the structural characteristics of the plastic part, the parting surface and the locking position of the entire tiger mouth as shown in Figure 3 are designed.

Figure 4 Layout of the full mosaic mosaic
 

   Figure 5 Design of inclined roof and its oil tank
 

Figure 6 Slider and its travel switch
For large and medium-sized moulds, the structure of the glue position is complex, and the all-inlaid structure is a mold design method that takes the manufacturing process of the mold core into consideration, shortens the mold manufacturing cycle, improves the manufacturing accuracy, and improves the injection molding process. For medium Above, large or extra-large injection molds, in order to shorten the processing cycle and facilitate processing, the design idea of the full inlay structure is to divide the entire mold core (usually mainly the rear mold core) into multiple inserts for simultaneous processing , which not only simplifies the processing time of inserts, but also saves a lot of mold steel. Therefore, the fully inlaid mosaic structure has been widely used in Japanese mold design. See Figure 4 for the layout of all inlaid mosaic parts in this set of molds.
When the size of the plastic product is more than 150*150, and there are many deep bones on the side of the moving model, it is the most common practice to use a fully inlaid structure on the moving model. The principle of the all-inlaid structure is that the split position of the insert should be conducive to reducing EDM, so that the parts can be processed by wire cutting or grinding machine as much as possible. Wire cutting or grinding machine processing has high dimensional accuracy and short processing time.
The starting point of the full mosaic structure is to divide the mold core into multiple inserts based on the mold processing technology. In large and medium-sized complex molds, such as mold cores and sliders of automobile molds, printers, air conditioners and large home appliance shell molds, etc. There are a large number of inserts in the parts. The irregularities of the inserts are caused by the complexity of the surface of the plastic parts and the slope of the mold release. There are also small inserts inside the parts, so how to divide them, the division of the full-set mosaic structure must fully consider the processing technology, and the main points of the division are as follows: Before dividing the full-set mosaic structure inserts, it is necessary to determine the processing standards of the inserts and the benchmark for all insert assembly. The benchmark of the mold core and the benchmark of the fine frame on the mold base coincide with each other. There are two kinds of benchmarks for opening the fine frame on the mold base, one is four-sided centering and processing based on the center, and the other is processing based on the reference angle. For the mold design of the full mosaic structure, the latter method is used for processing It has the advantage of high precision. When dividing inserts and determining benchmarks, avoid weak parts and do not damage the strength of the mold core.
Plastic parts are ejected using thimbles, cylinders and slanted jacks. There are many slanted jacks. In order to protect the slanted jacks, the oil tank is designed as shown in Figure 5.
The two sliders of the plastic part use inclined guide pillars to pull the core, and the stroke of the slider is controlled by a travel switch, as shown in Figure 6.