How to Avoid Sink Marks and Voids in Injection Molding

When it comes to plastic injection molding, Avoid Sink Marks and voids is crucial to achieving the desired product. Sink marks, which are often caused by improper design or processing, can result in unsightly blemishes, making the final product unappealing to potential customers. In this blog, we will provide you with a complete guide to sink marks and how to avoid them. 

We will walk you through the causes of sink marks, discuss how to prevent them, and provide tips on maintaining proper mold temperature. Additionally, we will cover other common defects such as silver streaks and splay marks, warpage, and their solutions. With our detailed guide, you can be confident that your injection molding process will produce high-quality, blemish-free products every time.

What’s Sink Mark In Injection Molding?

A sink mark is a common defect that occurs on the surface of injection-molded parts, and it generally looks like a dimple or groove on thicker sections of the part. This issue is caused by variations in wall thickness – when the outer part cools quicker than the inner one, the molecules in the thicker section contract more, causing a dimple. 

To avoid sink marks, one needs to choose the material carefully – going for materials that don’t shrink much or adding fillers like glass fibers or talcum powder to the material mix can reduce the chances of sink marks appearing. Additionally, making sure that the part design has consistent wall thickness can help avoid sink marks. An experienced injection molding partner can help integrate additional measures and ensure that the final product is functional and void-free.

Sink Marks:

Sink marks are a common surface defect in injection molded parts. They appear as dimples or grooves on the surface of the part and are caused by variations in wall thickness. The thicker portions of the part cool at a slower rate, causing them to sink inwards when the thinner portions have already solidified. Thicker wall sections, such as those found at the bases of ribs and bosses, are more prone to sink marks.

In order to avoid sink marks, it’s important to control the injection pressure, cooling time, and wall thickness of the part. The cooling time can be increased to allow for more even cooling, or the wall thickness can be reduced in thicker sections to prevent uneven cooling. By following these guidelines, manufacturers can produce injection molded parts with fewer surface defects and greater consistency.

Avoid Excess Mold Temperature:

When it comes to injection molding, sink marks are often a common issue that many manufacturers face. Sink marks are caused by areas of a molded part cooling at different rates and can result in cosmetic defects. One way to avoid sink marks is to avoid excess mold temperature. 

A mold temperature of between 80-120℃ / 176-248℉ should be maintained to prevent sink marks. Setting too high a temperature can prevent the gate from sealing properly and on time. The recommended injection molding temperature for common plastic should also be adhered to. In addition, mold plumbing should be checked to ensure there are no water flow issues. By following these steps, excess mold temperature can be avoided, resulting in a quality product without sink marks.

How to Avoid Silver Streaks and Splay Marks in Plastic Injection Molding:

Sink marks are a common issue in injection molding that occur when there are variations in wall thickness. They appear as a dimple or grooves on the surface of thicker sections of molded parts. The root cause of sink marks is a difference in cooling time between the outer and interior portions of a plastic part.

Silver streaks and splay marks are also common defects in injection molding. Silver streaks appear as silver-colored lines on the surface of plastic parts, caused by moisture in the material. Splay marks appear as streaks or spots with a hazy appearance and are caused by gas or moisture in the material.

To avoid these defects, it is important to ensure that the mold is properly designed and that the plastic material is of high quality. Additionally, adjusting mold temperature, pressure, and fill speed can also help to prevent sink marks, silver streaks, and splay marks from occurring.

How to Avoid Warpage in your Plastic Production:

In injection molding, a sink mark is a depression or indentation that occurs on the surface of a molded product due to the unequal cooling of thick and thin portions of the plastic part. To avoid sink marks and warpage in plastic production, it is important to follow certain guidelines, such as selecting proper materials with lower shrinkage rates and higher flowability. 

Additionally, increasing the melt and mold temperatures and designing the mold to ensure proper venting of gas can greatly improve flowability and reduce the risk of warpage. Another tip is to use reinforced plastics or structural foam to reduce shrinkage defects. If these steps do not work, increasing the material feed or switching to a machine with higher material feed can also help. By implementing these strategies, manufacturers can minimize the risk of sink marks and warpage in injection molding.

Conclusion:

In conclusion, sink marks and voids in injection molding take a toll on not just the aesthetics but also the physical properties of the molded part. An experienced plastic injection molding professional knows how to design a mold that balances pressure, temperature, and cooling time to avoid sink marks and voids. Don’t compromise on the quality of your molded products. 

If you want to create high-quality plastic parts that are free from voids and sink marks, discuss your options with our engineers. Learn more about avoiding molding defects by reading our blog on other molding issues like silver streaks and splay marks, or warpage.