Plastic case injection mloding
I. Introduction
Figure 1 shows the housing parts and materials for the thermosetting resin, low price, high temperature resistance, burn resistance, high pressure, anti-aging and surface gloss, etc., the original use of compression molding, but the molding cycle is long, low productivity, mold easily damaged, forming unstable quality, so to injection molding.
Shell part 1
Although the use of injection molding has many advantages, but there are still many problems to be solved, especially thermosetting plastics injection molding fiber orientation appears to make products that exist within the internal stress, can cause Warpage or cracking, so to consider a different processing techniques, namely injection compression process. Injection compression molding and compression molding combines the advantages of injection molding, when the injection molding of thermosetting plastics , the application of compression molding injection molding plastic parts can significantly reduce the undesirable in fiber orientation. Thermosetting
plastic injection molding scrap rate is high, generally about 15% to 25%, because each injection will produce a certain amount of gating system can not be recycled condensate material, especially for small products, multi-cavity injection mold , which issue is particularly prominent, scrap rate can reach 50%. To solve this problem, and now the new injection technology, based on the compression, then normal flow technology used in forming processes. Second, the general flow of thermosetting plastic injection-compression process and
mold design injection-compression process using injection molding with thermosetting resin shell mass-produced product in three production stages: injection, compression and ejection. Figure 2 shows the feeding room with a shared two-cavity
mold structure, then the mold is not fully closed mode. Relatively simple mold structure, forming a small amount of plastic parts flash, together with the top of the plastic parts. Sprue bushing is designed to function with normal flow.
Figure 2 2 cavity cold runner injection compression mold structure
1 cut side 2. flash chamber 3 cavity 4 splitter 5. sprue bush 6 cooling channel 7 insulation gap 8 flash chamber 9 cavity 10 pressure sensors 11. drum heater 12. overflow trough 13. insulation board 14. putter 15. supporting column
Forming material is composed of multiple components from the reaction of the injection compression works as follows: still left in the mold is closed to 6 ~ 8mm compression space, the expansion of the molding material into the mold cavity of a certain size (ie shared storage material cavity) in order to overcome the initial resistance of the material flow. Completely closed mold, the molding compound in compression cavity, the material will completely fill the mold cavity, the material component of each cross-linking or curing. This way to ensure the production of molded plastic parts no warpage, no stress.1, the injection phase of the molding material is assigned to the two cavities with corresponding recesses of the cone with the shunt 4 implementation, the injection period, the shunt sprue bushing 5 against the discharge port. After the injection, molding compounds, divided into two roughly equal parts of the material remain in the mold parting surface is located at the common feeding chamber (see Figure 3).
Figure 3 share the feeding room
2 cavity around the flash chamber 8 cavity around the flash chamber 14. putting
2, the suppression of phase with the mold completely closed, molding compounds are pressed into the cavity 3 and the cavity 9, the mold temperature (about 180 ℃) under the action of curing. Molded plastic parts produced in the compression phase of the fiber orientation and in a closed mold to produce the fiber orientation of injection molding were significantly reduced. In the suppression period, the shunt inserted into the sprue bushing 4 5, plugged in the parting surface of the sprue bushing 5. Standard jacketed sprue bushing with a cooling channel 6, because the role of the cooling channel, the sprue bushing in the molding material to keep the temperature at 90 ~ 100 ℃, so the molding material curing does not occur (ie, normal flow channel system). As the mold is heated, out-side shunt only hotter, forming curing compound where, and therefore the material flow in the form of loss is limited to shunt a small amount of material at the groove 4, thereby reducing the loss of material flow. Sprue bushing and mold in the insulation by the insulation gap between the 7 guarantee. In the compression phase, forming compounds will flow through the mold cavity surface and the formation of a prominent flash. 3, mold and exhaust molded plastic parts based on the geometry and the type of molding compounds, plastic parts of the mold must be set to different stripping slope, usually take 1 ° ~ 3 °. In the plastic mold, due to relatively high temperatures (such as 170 ℃), the contraction of thermoset plastic parts is very small, the results do not necessarily stay in the plastic mold on the same side. During production in order to avoid this problem, ensure the plastic parts are always the same side of the ejection from the mold, the mold has taken the following measures. To ensure the ejection, the molded plastic parts with smooth flash separation, in the mold cavity 3 around the flash chamber 2 is set in the mold cavity 9 cavity around the set, flash 8, as shown in Figure 3 with the overflow common feed chamber cavity material placed in the mold parting surface dynamic simulation side. In order to make injection-compression, the mold must have a cutting edge, located in the sub-surface near the edge of a cut determines the size of common feeding chamber, cut side profile and the details of the gap shown in Figure 4. Give different surface overflow trough 12 different radius (0.8 ~ 2.4mm) increased the overflow trough rigidity, and to many in the overflow trough behind the putter can easily fly out of the top edge. The role of design is a small groove 17: When the mold opens, the flash can stay in the dynamic simulation side.
Figure 4 cut edges (Figure 2 X enlarged) 12. Overflow trough 17. Groove
Typically, the thermosetting plastic in the mold is not fully cured, more brittle, so when the plastic mold, putting a sufficient number should be set to avoid damage to plastic parts. As in the cross-linked thermoset plastic when precipitation hardening a large number of volatile gases, in addition to putting up the role of stripping, but also from the exhaust effect. Exhaust groove depth of about 0.01 ~ 0.03mm, and the need for highly polished, in order to form flash easily removed after the ejection. Third, the mold structure die by electric heating, cross-linking reaction requires heat to get from the mold. Thermosetting plastics melt and the mold cavity once the surface contact, the melt viscosity can flow from a small gap, that the melt viscosity becomes low enough to penetrate the very narrow gap, and the formation flying side, so the mold must be assembled very closely, while the mold cavity must also be able to fully exhaust. These relatively contradictory requirements, can not completely eliminate the flash of reason, so the mold should be designed to have very good rigidity, in order to avoid deflation and deformation caused by the formation of flash, and use the pressure sensor 10 to measure and monitor pressure .The choice of materials for die life expectancy is extremely important, and thermoset injection compression molding the part surface temperature is usually (165 ± 5) ℃, the heater higher ambient temperature, so the use of heat-resistant material is better. Thermosetting plastic using injection compression process, the mold temperature is higher than the melt temperature, melt into the mold and the die wall after contact with the temperature increased, viscosity decreased, so a higher flow rate. And contain hard filler in high-speed melt erosion, abrasion cavity mold runner and serious, and should therefore be high-strength and wear-resistant material, easy to wear and tear on the mold parts designed to be easy to replace, insert, forming by the hardened steel inserts. Fourth, the heating and insulation from the cartridge heater 11 heating the mold, testing found mold heating capacity depends on the required size of the mold, according to the quality of the mold, to 30 ~ 40W per kilogram. Deputy dies of the whole, through the control loop is divided into six high-power cylindrical heater 11 heating, the heating capacity can evenly throughout the mold. Each ring comes with a heated thermocouple, and use this six thermocouple control the mold temperature, thermocouple placed between the heating element and molding parts, tooling and machinery with the insulation board 13 template isolation to prevent heat losses and the resulting temperature. V. Conclusion fiber orientation, remove the flash and flow channel material losses in the thermosetting plastics processing cost of the main problems affecting the use of these methods can reduce these costs. Well-designed shunt device, shared storage material system allows access to each mold cavity of molding compounds can be more precise measurement.Injection compression molding and compression molding combines the advantages of injection molding, using this technology can produce a particularly good-quality plastic parts, high efficiency, easy to automate the production environment is good.
