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Solutions to Common Molding Defects of Injection molding

Solutions to Common Molding Defects of Injection molding


The degradation is caused by the raw material being damaged. Long chain molecules that form plastics will decompose under the action of excessive heat or excessive shear stress. During the decomposition of molecules, the volatile gas will speed up the degradation process, which will cause the de-coloring of the raw material. The decomposition of large amount of molecules will finally break the content of the raw material and cause negative influence on the mechanical properties.

There are two main causes for lamination. The first one is that when two different kinds of raw materials mixed together incorrectly. The two raw materials will be transported into the barrel at the same time under the pressure. However, when the mold cannot be melted together when it is cooled, just as different layers are forcibly pressed together to form products.

The decomposition could lead to many results. The extent and severity of the problem vary, too. In the most serious case, it may cause complete discoloration of the product and poor mechanical properties. Local degradation will only cause dark stripes or spots.

Sink Marks: Sink marks occur when the cooling of the plastic is uneven, resulting in depressions or sinkage on the surface of the part. To mitigate sink marks, the following solutions can be implemented:

Increase the injection pressure or packing pressure to ensure proper filling and packing of the mold.

Optimize the cooling system design to improve uniform cooling of the part.

Increase the mold temperature to enhance material flow and reduce cooling rate.

Warping: Warping is the deformation or twisting of the part due to non-uniform cooling or stress within the material. To address warping, the following solutions can be employed:

Adjust the mold design to incorporate uniform wall thickness and adequate draft angles.

Optimize the cooling system to ensure even cooling and reduce thermal gradients.

Use materials with lower shrinkage rates or incorporate additives to minimize warping.

Flash: Flash is excess material that escapes from the mold cavity and forms thin, unwanted edges or fins. To eliminate flash, the following solutions can be considered:

Increase the clamping force to prevent mold separation during injection.

Optimize the mold design, ensuring proper alignment of mold components and tight seals.

Adjust process parameters, such as injection speed and pressure, to minimize material leakage.

Short Shots: Short shots occur when the mold does not completely fill with plastic material, resulting in incomplete parts. To overcome short shots, the following solutions can be applied:

Read more: https://www.djmolding.com/solutions-to-common-molding-defects-of-injection-molding/

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