‌Common‌ ‌Injection‌ ‌Molding‌ ‌Defects

Injection Molding is an efficient production method when high volumes of identical parts are needed. However, it also requires a high degree of technical expertise to master. With so many different variables in play, small, seemingly minor mistakes in early phases of product development can lead to major problems — and even compromise product integrity — down the line.

Defects can reduce the speed and cost-efficiency of the entire product development process, and can potentially shorten product life spans if left unchecked. Injection molding issues and defects can be caused by a host of reasons, including poor design, production process mistakes, quality control failures, and more. As such, it’s important to take a proactive approach to risk mitigation throughout the product development process so as to reduce the chances of potential injection Molding Defects.

Here are a few of the most common defects that may occur in plastic injection molding

1. Flow Lines
Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. These are caused by the shot of molten plastic moving at different speeds throughout the injection mold, which ultimately causes the resin to solidify at different rates. This is often a sign that injection speed and/or pressure are too low.

2. Sink Marks
Sink marks appear as depressions, dents, or craters in thick sections of a part. Thicker sections take longer to cool, which can have the often unanticipated side effect of the inner portions of the part shrinking and contracting at a much different rate than the outer sections.

3. Surface Delamination
What is delamination? Delamination is a condition that causes a part’s surface to separate into thin layers. These layers, which appear like coatings that can be peeled off, are caused by the presence of contaminants in the material that do not bond with the plastic, creating localized faults. An over-dependence on mold release agents can also cause delamination.

4. Weld Lines
Also called knit lines, these defects mark where two flows of molten resin came together as they moved through the mold geometry. This happens around any part of the geometry that has a hole. As the plastic flows and wraps around each side of a hole, the two flows of plastic meet. If the temperature of the flow isn’t just right, the two flows won’t properly bond together and will instead cause a visible weld line. This reduces the overall strength and durability of the component.

5. Short Shots
“Short shots” refer to instances in which the resin doesn’t entirely fill the mold cavity, resulting in incomplete and unusable parts.

6. Warping
Injection molding warping refers to unintended twists or bends caused by uneven internal shrinkage during the cooling process. Warping defects in injection molding are generally the result of non-uniform or inconsistent mold cooling, which creates stresses within the material.

7. Jetting
Jetting defects in injection molding are another potential result of an uneven solidification process. Jetting occurs when an initial jet of resin enters the mold and has enough time to begin setting before the cavity fills. This creates visible, squiggly flow patterns on the piece’s surface and decreases the strength of the part.

Injection molding can be a highly efficient manufacturing method for producing highly repeatable plastic parts, but, as with many processes, producing high quality end-parts requires a high level of attention to detail and a proactive approach to risk management. Everyone involved in the product development process — from the initial design and proof-of-concept stages all the way to fulfillment — needs to do their due diligence to ensure products meet the highest quality standards and avoid these common plastic injection molding issues.

Choosing a manufacturing partner like Xiamen ABBYLEE, who is well-versed in common defects in injection molding and their troubleshooting, can mean the difference between high-quality parts — produced on-time and within budget — and those marked with weld lines, jet, flash, sink marks, and other defects. In addition to being an experienced on-demand manufacturing shop, we also provide design consulting and optimization services that ensure we’re able to help every team create functional, elegant, high-performance parts as efficiently as possible. Contact us today to learn more about our injection molding services.