Teach you how to remove dents from automotive interior plastic parts
1. Causes of dents
1-1 The thickness of each part of the product is different
1-2 automotive interior plastic parts lack internal pressure
1-3 Insufficient cooling of automotive interior plastic parts
1-4 Deformation due to insufficient cooling time
2. Associated knowledge
2-1 In the process of producing products, dents occur more frequently among the bad phenomena. The plastic injected into automotive interior plastic parts shrinks in volume during cooling. The early cooling part, that is, the surface hardens first, and bubbles will be generated inside. The so-called A dent, that is, a part that cools slowly creates a conspicuous concave surface in the direction in which the bubble shrinks.
2-2 Materials with high shrinkage are also prone to dents. When changing the molding conditions to eliminate dents, the setting conditions should be set in the direction of less shrinkage. That is, the mold temperature and barrel temperature decrease, and the injection pressure increases, but it should be noted that residual internal stress may be caused by this.
2-3 Because the dent is better to be inconspicuous if it does not affect the appearance, it is deliberately processed on the automotive interior plastic parts to look like corrosion, such as grain, grain, etc. If the molding material is HIPS, it is also effective to lower the finish by lowering the mold temperature. However, once a dent occurs in these methods, it is difficult to repair the polished product.
Three, the solution
3-1 Immediate: increase the injection pressure, prolong the injection pressure holding time, reduce the temperature of the barrel and the temperature of the automotive interior plastic parts, and force cooling in the place where the dent is generated.
3-2 Short term: fill in the flow edge where the dent is created (Fig. A). When there is a narrow place in the material where the dent is generated, make this part thick (Fig. B).
3-3 Long-term: The difference in thickness of design products should be completely avoided. Reinforcing ribs that are prone to dents, the narrow and long shape should be as short as possible
4. Differences in materials
4-1 Materials with high molding shrinkage have large dents. For example, PE, PP, even if there is only a little reinforcing rib, will produce dents.
5-1 When the temperature is lowered to the point where dents do not occur, if there is still pressure on the material in the cavity, it should be considered that dents will not occur. The pressure of the material in the automotive interior plastic parts, the static pressure, is not constant no matter where. The pressure near the gate is high. If the material has a wide-open side, the pressure difference between the gate and the part far from the gate is very small compared with the overall pressure due to the transmission of pressure to all corners, so that no concave will occur. It is possible to obtain a product with no residual internal stress. When some materials flow into difficult places, there is high pressure in this place, and the pressure in other places decreases, which will cause dents. The residual high pressure in this part means that the internal stress of the product is also large. In the ideal state, the temperature of the material rises with the temperature of the automotive interior plastic parts, the fluidity of the material is better, and the injection also becomes bottom in the static pressure state.
5-2 When changing the molding conditions, the combination of temperature, pressure, and time should be prepared in advance, and the results can be known early by proceeding in sequence. First of all, after a long time, it is easy to know every small change in pressure. It should be noted that: the results obtained when the temperature changes should be produced after the temperature drops after the injection material.