Common Injection Molding Defects

The Toolroom is committed to exceptional and flawless results with our award-winning plastic injection molds, rubber injection molds, machining custom tool design, rapid prototyping and more.

We are leaders in full-service mold manufacturing, and your choice of The Toolroom as your partner for complete injection molding services is a smart one. Even with the strictest quality control measures in place, defects are possible in injection molding, especially when choosing a company with less experience than The Toolroom.

Common defects encountered in injection molding can arise due to various factors such as material properties, mold design, processing parameters, and machine settings. Identifying and addressing these defects promptly is crucial for maintaining product quality and manufacturing efficiency.

Here’s a list of common defects along with their definitions:

Sink marks: Depressions or dents on the surface of the molded part caused by uneven cooling or shrinkage.
Flash: Excess material that extends from the molded part at the mold parting line, caused by the mold not closing properly or excessive injection pressure.
Weld lines (knit Lines): Weak areas where two or more molten flow fronts meet and solidify, resulting in a visible line on the part surface.
Short shots: Incomplete filling of the mold cavity, resulting in a part that does not fully form, usually caused by inadequate injection pressure, temperature, or time.
Burn marks (burning): Discoloration or blackening of the molded part due to excessive heat, often caused by overheating of the resin or prolonged residence time in the barrel.
Warpage: Deformation or bending of the molded part from its intended shape, caused by non-uniform cooling or excessive internal stresses.
Jetting: A defect where material flows too quickly through narrow sections of the mold, resulting in visible streaks or lines on the surface of the part.
Blistering: Formation of bubbles or raised areas on the surface of the part, typically caused by trapped air or moisture in the mold or resin.
Splay: Surface imperfections characterized by a streaky or veined appearance caused by moisture or volatile substances in the resin.
Flow lines: Lines or streaks on the surface of the part caused by variations in material flow rates during injection, resulting in uneven surface texture.
Mold filling imbalances: Non-uniform filling of the mold cavity, leading to variations in part dimensions or properties.
Jetting: Occurs when the molten plastic cannot fill the mold cavity quickly enough, resulting in a visible seam or lines on the surface of the part.
Sinks: Depressions or indentations on the surface of the part caused by shrinkage during cooling.
Overpacking: Excessive pressure applied during the packing phase, leading to distortion or deformation of the part.
Cold slugs: Solidified resin remnants that are not fully incorporated into the part, often caused by insufficient injection pressure or poor mold design.

Achieving a flawless manufactured part isn’t just about avoiding specific defects; it’s a holistic process that begins with meticulous planning and extends through to continuous monitoring. The Toolroom prioritizes quality along with efficiency and value for our clients. Our blueprint for defect-free injection molding is multifaceted.

Quality, US injection molding from The Toolroom means the right material selection and preparation
Materials form the very essence of your injection molded products. We utilize the highest-grade material that meet the specifications of the product. We are judicious in the use of fillers, colorants, and other additives, as they can affect the material’s flow and the integrity of the finished part. We ensure proper drying of your parts, as residual moisture can lead to splay, bubbles, and poor mechanical properties.

Meticulous mold design and maintenance
The mold translates a design into reality. Attention to design details and regular maintenance is crucial. The professionals at The Toolroom ensure your mold design supports proper material flow, even cooling, and easy part ejection. We properly vent the mold to prevents air traps and burning. We calibrate injection speed, as too fast and you risk burning, too slow and it leads to splay. We balance the fill pressure with the mold design is key for preventing warping and short shots. Proper temperature control during the process and uniform cooling are also vital to quality end products.

Trained team of experts
Our highly skilled operators are the guardians of your quality standards. Regular and thorough training keeps operators adept at spotting and preventing defects. We also have a solid record of process parameters and troubleshooting that can be referenced to understand and prevent recurring issues.

We want you to choose The Toolroom for your next injection molding project because of our extensive experience, a full array of capabilities, excellent reputation, and earnest commitment to quality. Our complete service mold manufacturing will save you resources so you can concentrate on your business. The Toolroom is the St. Louis area’s leading plastic injection molding service. For exceptional results, contact us today at (573) 437-4154.