How Accurate Is Injection Molding?

Plastic Injection Molding is widely known for its ability to produce large quantities of identical, highly consistent parts. But how accurate is injection molding? In industries such as automotive, medical, and electronics, even small dimensional errors can lead to performance issues and product failure. Therefore, it is important to understand the accuracy of this process.

This blog takes a deep dive into injection molding accuracy, factors that affect accuracy, and how to ensure parts meet tight dimensional tolerances.

How accurate is plastic injection molding?

Most plastic injection molding processes can achieve dimensional tolerances of ±0.005 inches (±0.127 mm) or better. In high-precision applications such as the medical device and electronic connector industries, tolerances as low as ±0.001 inches (±0.025 mm) can be achieved using specialized equipment and materials.

However, not every part or project requires extremely tight tolerances. For many consumer products and packaging applications, a tolerance of ±0.010 inches (±0.25 mm) may be sufficient.

Major Factors Affecting Injection Molding Accuracy

Several factors can affect the dimensional accuracy of plastic molded parts. Understanding these factors will help you design more effectively and communicate better with your injection molding supplier.

1. Material Selection

Plastics shrink at different rates as they cool. For example, nylon typically shrinks more than ABS or polycarbonate. Mold design must account for shrinkage, which can range from 0.5% to more than 2% depending on the resin type.

2. Mold Design and Processing Accuracy

High-precision injection molding begins with high-precision mold design. The mold cavity must be carefully CNC machined. Mold design defects and processing errors can cause part warping, burrs, uneven wall thickness, etc., reducing part accuracy.

3. Part Shape

Simple shapes can be molded with higher accuracy than complex shapes. Parts with thin walls, sharp angles, or long runners are more prone to warping and dents. Dimensional stability can be improved by using uniform wall thickness and avoiding undercuts.

4. Process Control

Even the best molds can produce parts with lower accuracy if the molding process is not strictly controlled. The main variables are:

• Injection pressure
• Cooling time
• Mold temperature
• Clamp force

How to Ensure Dimensional Accuracy

If your application requires high-precision parts, you can take the following steps:

• Work with an experienced plastic injection molding manufacturer with a track record of tight tolerance production.
• Request a design for manufacturability (DFM) analysis to identify features that may affect accuracy.
• Use 3D measurement tools and first article inspection (FAI) to verify sample parts.
• Clearly specify tolerances and communicate critical to quality (CTQ) on 2D drawings.

Final Thoughts

So, how accurate is injection molding? In the hands of a skilled manufacturer, plastic injection molding can produce parts with exceptional precision, repeatability, and reliability. By understanding the factors that influence accuracy—and by collaborating closely with your supplier—you can ensure your molded parts meet even the most demanding specifications.