Top 10 Injection Molding Defects and How to Fix Them

Injection Molding Defects and How to Fix Them

The manufacturing process is never easy. A number of unique defects normally occur and this practice is so common among different industries and processes, including injection molding and high volume injection molding. The combination of art and science is required for making injection molded prototypes. High level of concentration is required to prevent the small mistakes occurring during the molding process. Technical expertise is demanded to minimize the risk factors of defects. The defects can cause a big cost from the companies. And to be prevented from such situations there are companies which further involve the injection molding services for the high-quality products. The injection molding services also serve at giving the highly competent design.

Injection Molding Defects and How to Fix Them

Injection Molding Defects and How to Fix Them

Following are the major defects that may usually occur during the injection molding process:

Flow Lines:

These are the streak or lines commonly of toned color. The defects in the flow lines are major because of varying speed that causes the plastic to be solidified at different speeds. The flow of plastic also changes its direction.

Fixation: Bring the speed and pressure of the plastic to an optimal level to fill the cavities properly. Increase the temperature of the plastic so that it should get solidified early. Try to avoid the change in direction, round the corners.

Sink Marks:

The shrinkage on the inner portion of the injection mold causes the formation of depressed marks on the outer thicker wall. It is caused when the plastic has less cooling time and the plastic does have not been purely cold in the mold.

Fixation: Decreased molding temperature and increased holding time will prevent the sink marks. The thickness of the outer wall should be reduced as a cautionary measure.

Vacuum Voids:

They are the pockets of air trapped whether within or near the surface of the injection molded prototype. Uneven solidification is the major cause of the formation of voids.

Fixation: Move towards the less viscous plastic which ensures that less gas is trapped and the air is escaped. You can further increase the holding time and pressure.

Surface Delamination:

Due to the contaminated material, thin layers may appear on the surface which makes the coating over the part. They are usually peeled off. The cause of the delaminated surface is that the contaminant is the fault present in the plastic and they both cannot bond together.

Fixation: Pre-dries the plastic before molding and increase the temperature of the mold. You may smooth out the corners to avoid sudden changes.

Weld Lines:

A weld line appears at the point where molten plastics meet each other. The plastics are coming from the different directions. Partial solidification of molten plastic causes this condition.

Fixation: Raise the temperature of the mold with increased injection speed. Make use of the single source flow.

Short Shot:

In this condition, the molded plastic somehow does not occupy the overall cavity. This final product appears incomplete. This may occur because of the already occupied space by the air bubbles.

Fixation: The plastic should have the high flowing feature so that it should reach the cavities properly. Increase the temperature of the mold to further increase the flowability of plastic.


A deformation present due to the uneven shrinkage in different parts of the mold. This condition is present when the cooling of the plastic is not done uniformly.

Fixation: Focus on the cooling time, so that the cooling should be done sufficiently. Also, make use of the plastic material which has fewer chances to shrink or deform.

Burn Marks:

The rust color which appears on the surface of the mold indicates the burn marks. Excessive heating is the causative factor for such marks.

Fixation: Reduction in the injection speed and temperature of mold


The molten plastic fails to stick to the surface of the mold. Because of the low melting temperature and increased viscosity of plastic.

Fixation: Ensure the contact between molten plastic and mold by optimizing the gate design.


Flash is the defect that occurs when the molten plastic escapes from the mold cavity. This may be because of the decreased forced applied in joining them together.

Fixation: Make sure that the mold is properly cleared and provide enough force for clamping.

Related posts


7 + 17 =


1 × 1 =