Key points of online switch injection mold design
Time：2020-12-08 10:57:11 / Popularity： / Source：
Figure 1 Online switch product map
It can be ground from Figure 1, plastic part has a simple shape, does not require a side parting and core pulling mechanism, and mold structure is simple. Choice of plastic parts material is PC + ABS, which makes use of good weather resistance, rigidity, strength and dimensional stability of plastic alloy, it can prevent product from shrinking, warping. Product appearance is good, and it can process precision parts.Plastic alloy not only has excellent heat and weather resistance, dimensional stability and impact resistance of PC resin, but also has excellent processing fluidity of ABS resin. Therefore, it can maintain its excellent performance and good injection moldability when applied to thin-walled and complex-shaped products.
PC and ABS can be simply mixed and used, but effect is not good when two materials are directly mixed and injected. Blending of PC and ABS generally needs to be carried out in a screw extruder. In order to obtain a good mixing effect, a twin screw can be used in blending mode. Second-stage blending can obtain a very good blending effect, but material should reduce secondary high temperature expansion, which can consume a lot of energy, it is easy to degrade material and reduce performance.
First, PC and BAS resin are dried, then mixed with other modifiers in proportion, added to co-rotating twin-screw extruder, melted and extruded at a certain temperature and substitution, then cooled and pelletized to obtain milky white PC/ABS alloy particles.
Figure 2 shows relationship between PC/ABS ratio and impact strength, heat distortion temperature and fluidity. It can be seen from figure that PC content exceeds, strength of PC/ABS alloy increases; PC content exceeds, heat deformation temperature of PC/ABS alloy increases; PC content changes, PC/ABS alloy has worse fluidity. Therefore, when designing product, it is necessary to select a suitable PC/ABS alloy material ratio according to performance of plastic part.
Figure 2 Relationship between PC + ABS performance material ratio
Size of online switch mold design is 3, size of plastic part is small, and cavity layout is 4 cavity. See attached file for 3D drawing of product and mold. Gating system is designed as a side gate. Parting surface of plastic part fluctuates. In this case, selection of parting surface needs to be analyzed section by section using 3D software to ensure a reasonable draft angle. Connect results of each segment analysis smoothly or reasonably to make parting surface smooth and facilitate processing. For high and low parting surface, front and rear mold cores often have complex rubbing surfaces, angle of rubbing surface is smaller than angle of precision positioning block to ensure precise mold clamping. Therefore, effect of zero-degree positioning block is very good.Structure of plastic product is simple, and ejector is ejected by a ejector pin. Cooling of mold adopts independent cooling circuits for front and rear molds. For this small mold, a simple cooling circuit can solve injection problem.
Figure 3 Online switch mold diagram
Essentials of Injection Mold Design for Jingyi Box Cover
Product diagram of Jingyi box cover is shown in Figure 1. Maximum size of product is 197.00 mm * 197.00 mm * 15.70 mm, average thickness of plastic part is 3.00mm, plastic part material is ABS, shrinkage rate is 1.006, and weight of plastic part is 147.20 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.
Figure 1 Product picture of Jingyi box cover
As can be seen from Figure 1, plastic part is shaped as a square flat shell with a relatively simple shape. There are multiple protruding bone positions on inner side and four sides of inner side, which need to be designed with inclined roof. There is a stop on the edge of plastic part to match lower shell of precision instrument box. Appearance requirements of plastic parts are high, there should be no gate marks and ejection marks on the top and side. According to requirements of plastic parts, flip chip molds need to be designed. Flip die is a die with ejector system installed on the side of fixed die. Generally, it is ejected by an oil cylinder, but it can also be ejected by components such as a pull plate or a button. Use occasions are generally cover and shell products, surface requirements are relatively high and no gate marks are allowed. Structure diagram of Jingyi box cover mold is shown in Figure 2.Size of plastic part is large, and mold design cavity rank is 1 cavity. Mold base is a non-standard mold base 5050. In order to ensure mold clamping accuracy, 0 degree positioning blocks are designed on all four sides of mold base; four corners of front and rear mold cores are designed to position tiger's mouth, and compression block is used for fixing. Since ejector mechanism and gating system of flip chip are both designed on fixed mold side, it is necessary to pay attention to position of gating system and ejector components not to interfere in design; on the other hand, for flip chip mold, location and quantity of its gates need to be evaluated. Try not to design a three-plate mold with a thin nozzle as much as possible, because it is difficult to take out runner condensate under surrounding lifter and thimble. Therefore, in most cases, flip chip molds use hot runner injection methods. This set of mold uses INCOE's single hot nozzle DFQ18150-STT, and gate position is in the center of plastic part. This kind of hot nozzle is a needle valve nozzle. After injection is completed, needle valve is closed, and there is only a circular mark on final plastic part, which will not affect appearance of plastic part. Needle valve hot nozzle is shown in Figure 4.
Thickness of plastic part is 3mm, and material is thick. Therefore, in order to shorten injection cycle and avoid deformation of plastic part, an adequate cooling system must be designed. In order to prevent heat of fixed mold from being transferred to injection molding machine, a heat shield is designed on fixed mold base plate. Front and rear mold water transportation diagrams are shown in Figure 3. Fixed mold water transportation adopts direct water transportation, movable mold is designed to be both through water transportation and pond water transportation.
Plastic parts are ejected by inclined jacking and cylinder ejection. All inclined roofs are driven by T-slots, and inclined roof guide blocks are designed on the template. Mold opening adopts pull plate to pull mold. It is necessary to note that dimensions of four pull plates must be same, positions of pull screws must be consistent to avoid stress on a single pull plate and affect accuracy of mold.
Figure 2 Mold diagram of Jingyi box cover
Figure 3 Front and rear mold water transportation and inclined top view
Figure 4 Figure of needle valve hot nozzle
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