6 Injection Molds defects and How to Prevent Them

A common industrial process known as “injection moulding” uses molten material to create a desired shape by injecting it into a mold cavity. While injection moulding is generally a reliable process, it can be subject to defects that can compromise the quality of the finished product. Let us take a look at some common injection mold defects and explore some of the underlying causes and potential solutions that might help injection molds manufacturer.

Flashing

Flashing occurs when excess material escapes from the mold cavity and creates a thin layer around the part. Flashing is otherwise known as “spew” or “burrs”. This defect can be caused by several factors, including excessive injection pressure, a worn-out mold, or a poorly designed mold. The high temperature or the pressure of the molds can also cause flashing. 

To prevent flashing, it’s important to ensure that the mold is properly designed and maintained. To enhance material flow, injection molds manufacturer should adjust the temperature of the injection mold, the injection pressure, and the ventilation.

Sink marks

Sink marks are minute depressions or dips in a molded part’s otherwise flat and uniform surface. This can happen when a molded component’s inside shrinks, drawing material from the surface inward, and occurs when the material in the center of the part cools and contracts more quickly than the material at the edges. This may occur if the molds are not properly ventilated or if the injection pressure is too high.

It’s important to ensure that the mold is properly vented and that injection pressure is carefully controlled and increases the time taken for cooling to limit shrinkage. Following these steps will help injection molds manufacturer to prevent sink marks.

Warping

Warping is a deformation of the part that occurs when the material cools and contracts unevenly. Plastic and other materials can warp during the cooling process when unequal shrinkage places extra stress on different segments of the molded object, similar to how wood can warp when it dries unevenly. The completed part bends or twists as it cools because of the increased stress. This can be seen in a part that is supposed to lay flat but leaves a gap when placed on a flat surface. When the injection pressure is too high or the injection molds are not properly developed, this can occur.

Ensure that the mold is properly designed and that injection pressure is carefully controlled to prevent warping. In some cases, it may be necessary to add additional cooling to the mold to help prevent warping.

Burn marks

Burn marks are discolorations or black spots that occur on the surface of a part. The substance may overheat or an excessively high injection pressure may cause this. Burn marks on injection-molded items are typically caused by trapped air or by the resin heating up in the mold cavity during the injection. Burns are frequently caused by overheating due to excessive injection speeds or material heating.

To prevent burn marks, injection molds manufacturer should ensure that the material is properly heated and reduce the injection speed to allow the air trapped inside to escape.

Short shots

Short shots occur when the mold is not filled with material, resulting in a part that is incomplete or undersized. Short shots could show up as, for instance, missing prongs on a plastic fork or unfinished sections in plastic display shelves. Short shots are frequently categorized as a serious flaw that can impair the molded part’s ability to perform or appear. This can happen when the injection pressure is too low or when the material is not properly heated.

To prevent short shots, it’s important to ensure that the injection pressure is carefully controlled and that the material is properly heated.

Flow marks

Flow marks are streaks or lines that occur on the surface of a part. This can happen when the material cools too quickly or when the injection pressure is too high. Flow lines typically develop on thinner portions of the molded component and take the form of a wavy pattern that is usually somewhat different in color from the surrounding area. Flow markings normally do not affect the component’s integrity. However, if they are present in particular consumer goods, like high-end eyewear, they can be unflattering and possibly unacceptable.

To prevent flow marks, it’s important to ensure that the molds are properly designed and that injection pressure is carefully controlled. In some cases, it may be necessary to add additional cooling to the mold to help prevent flow marks.

At Best Precision, an injection molds manufacturer,  we take pride in our commitment to providing high-quality injection molds and plastic molds. Our goal is to help our customers avoid mold defects and achieve the best possible results for their production processes.

We are the top plastic molds manufacturer with manufacturing techniques to produce molds that are precise, reliable, and durable. We work closely with our clients to understand their unique needs and requirements, and we tailor our solutions to meet those needs. 

Our injection molds are designed to minimize the risk of defects such as warping, sink marks, and surface defects. We achieve this by using high-quality materials and precision machining processes, as well as conducting thorough testing and quality control measures.