Junying Die Casting Company
Methods to Eliminate Cracks of Injection Molding Products
May 11, 2017
Teresa
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The crack problem of plastic products is very common to be seen in the injection molding process, so what can we do to solve the problem?
First, the cause of cracks in plastic products
1. Residual stress caused by molding conditions(molds with too much packing).
2. Residual stress occurred in demoulding.
3. Stress concentration caused by the shape of the product.
4. Error caused by the thermal expansion of the same insert.
5. Deterioration of the material.
Second, the relevant knowledge
1. Preheating the metal inserts can ease the residual stress during molding. Following the same principle, using annealing after molding instead of insert heating is also a method.
2. The measure of decreasing injection pressure is the most effective method in molding conditions.
3. If the knockout pin is balanced, you can add more force in the demoulding process.
Third, solutions to cracks of injection molding products
1. Immediately: to improve the barrel temperature, reduce the injection pressure and the demould speed.
2. Short-term: to improve the smooth finish of the mold cavity.
3. Long-term: to have the draft angle just great enough, knockout pin of balanced distribution, products design without acute angles as well as almost no differences among the products' thickness.
Fourth, differences of materials
1. We need to pay attention to polycarbonate (PC) PVC materials which easily adheres to the mold chrome layer, forming an inverted cone at the corner especially.
2. Polycarbonates (PC) can easily cause cracks in the mold insert part. In this case, we had better add the glass fiber to the material.
First, the cause of cracks in plastic products
1. Residual stress caused by molding conditions(molds with too much packing).
2. Residual stress occurred in demoulding.
3. Stress concentration caused by the shape of the product.
4. Error caused by the thermal expansion of the same insert.
5. Deterioration of the material.
Second, the relevant knowledge
1. Preheating the metal inserts can ease the residual stress during molding. Following the same principle, using annealing after molding instead of insert heating is also a method.
2. The measure of decreasing injection pressure is the most effective method in molding conditions.
3. If the knockout pin is balanced, you can add more force in the demoulding process.
Third, solutions to cracks of injection molding products
1. Immediately: to improve the barrel temperature, reduce the injection pressure and the demould speed.
2. Short-term: to improve the smooth finish of the mold cavity.
3. Long-term: to have the draft angle just great enough, knockout pin of balanced distribution, products design without acute angles as well as almost no differences among the products' thickness.
Fourth, differences of materials
1. We need to pay attention to polycarbonate (PC) PVC materials which easily adheres to the mold chrome layer, forming an inverted cone at the corner especially.
2. Polycarbonates (PC) can easily cause cracks in the mold insert part. In this case, we had better add the glass fiber to the material.
