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Auxiliary Analysis of Mould Defects – Shrinkage Marks and Sealing
Injection moulding is widely used in the production of plastic products in various industrial and commercial applications. Commonly used materials such as ABS, PP, PA, PE and PC, are all thermoplastics, which are mouldable and mainly used in injection moulding processes. Injection moulding is a complex process, involving the injection of plastic material at high pressure into a mould to shape a desired product. Many injection moulding parts, including those constructed from thermoplastics, are made to tight tolerances; therefore it is important to identify any mould defects as soon as possible and take measures to rectify them. Under such circumstances, this paper discusses the auxiliary analysis of two common injection moulding defects – shrinkage marks and sealing.
Shrinkage, where plastic material in the form of a linear mark is pinched on at or near the surface of a moulded component, is one of the common defects of injection moulding. It usually occurs between two parts that form an interlocking seam and is mostly attributed to the differential shrinkage of the plastic in the package. A defect analysis revealed that most shrinkage marks occur when the mould temperature is too low, the mould temperature is not constant during injection, or the injection pressure is too high. Shrinkage marks can also occur if the plastic material is unsuitable for injection moulding, or if the injection flow is distorted.
The sealing of injection-moulded components occurs when the melted plastic flows into tiny cracks or gaps between two parts that are intended to be held in place. It is caused by improper venting of the mould, insufficient injection pressure, low mould temperature, or improper gate design. For sealing defects, the problem is more complex and requires more efforts to find solutions. It is generally necessary to disassemble and rework the part with the correct gate position and size, to reduce the mould temperature, and to increase the injection pressure and time.
In conclusion, the most effective way to reduce shrinkage marks and sealing defects in injection moulding is to ensure high accuracy injection moulds and quality assurance. This includes temperature control and regular cleaning and maintenance of the mould, followed by rigorous testing of the moulded parts to identify any potential defects. Adhering to these simple prescriptions and involving good communication channels between the moulding machines and the manufacturing process can improve product quality and reduce the costs of moulding processes.
