The Ultimate Guide to Draft Mark: Everything You Need to Know

What is Draft Mark?

Draft mark is a ripple-like surface defect that occurs on injection molded plastic parts. It is caused by the air that is trapped in the mold cavity when the molten plastic is injected. As the plastic cools and solidifies, the trapped air expands and creates a void in the part. This void then collapses, causing the surface of the part to ripple.

Draft mark can be a cosmetic issue, but it can also affect the structural integrity of the part. In some cases, draft mark can weaken the part and make it more susceptible to failure.

Causes of Draft Mark

There are several factors that can contribute to draft mark, including:

• Insufficient draft angle
• Trapped air in the mold cavity
• High injection pressure
• Slow cooling rate
• Improper mold design

How to Prevent Draft Mark

There are several things that can be done to prevent draft mark, including:

• Use a sufficient draft angle. The draft angle is the angle of the sidewalls of the mold cavity. A draft angle of 2 degrees or more is typically sufficient to prevent draft mark.
• Vent the mold cavity. Vents are small channels that allow air to escape from the mold cavity. Vents should be placed in areas where air is likely to be trapped.
• Use a lower injection pressure. A lower injection pressure will help to prevent air from being trapped in the mold cavity.
• Increase the cooling rate. A faster cooling rate will help to prevent the trapped air from expanding and creating a void in the part.
• Optimize the mold design. The mold design should be optimized to minimize the amount of air that is trapped in the mold cavity.

Conclusion

Draft mark is a common problem that can affect the appearance and structural integrity of injection molded plastic parts. By understanding the causes of draft mark and taking steps to prevent it, you can improve the quality of your parts and reduce the risk of failure.

Draft Mark