Achieve Tighter Injection Molding Tolerances 

Technological advancements across many sophisticated industries have increased the requirements for plastic components. In many cases, parts need to be smaller, further increasing the need for precise measurements and dimensions. Manufacturers serving these markets must adhere to tight injection molding tolerances to provide the high-quality parts and components necessary.

When discussing tight tolerances, it’s important to remember that the exact definition and dimensions can differ according to the specific injection molder. In general terms, however, tight tolerance is recognized as being within +/- 0.002 inches of specification, with very tight tolerance within +/- 0.001 inches.

There are a number of different factors that impact the ability of injection molding manufacturers to reach and achieve tight tolerances on finished parts. These include the level of complexity in the design in the part itself, the material chosen, the types of manufacturing processes used, and the utilization (or lack) of automation and robots to perform repeatable, precision actions.

Let’s dive in.

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Considerations for Injection Molding Tolerances

In the long run, consistency achieving tight injection molding tolerances results in saving time and money.

Parts with proper tolerances will fit as they should, whether that is snapping or sliding into place, or as part of an assembly. Not every part or application will require tight tolerance and finding the tolerance level that is a best fit for your application is important.

Tight tolerances are typically required for complex or critical parts, particularly those used in high-risk applications — for the medical and transportation sectors for example. Achieving the proper injection molding tolerances, consistently means maximizing the resources used to produce the parts and other benefits, such as:

  • Improved part performance and reduced part failure
  • Fewer rejections
  • Fewer mating problems during assembly

Accounting for tight tolerances means considering the impact of four key components during the injection molding process.

Design Phase

When designing any part, including a plus and minus tolerance for every dimension is critical because, without a tolerance, the manufacturer won’t understand the importance of that dimension. For tight tolerance dimensions, providing a plus and minus tolerance should be a given. With that said, tolerances should be as large as possible while allowing the fit and functionality of the part to be maintained.

Mold Flow Analysis

Conducting mold flow simulation during the design phase will help ensure tight tolerances can be met. The team can evaluate the problems in part geometry that may require special mold features. During the evaluation, the team may decide that certain features, such as gates, gate locations, weld line locations, runners, and so on, must be changed to produce a part that meets your tolerance requirements.


Automation plays a critical role in achieving the desired tolerance for an injection molding project. Robots ensure consistency during many steps in the process, eliminating potential human error that could impact finished projects that have exact requirements. From machine tending to CAD-assisted post-mold machining, and even complete turnkey molding automation, robotics should be incorporated into the production process for any injection molder looking to adhere to the tightest tolerances possible.

Material Choice

The resin picked to produce the part will also impact tolerance. The shrinkage rates vary between plastic materials (amorphous generally demonstrating less shrinkage than crystalline) and so the tolerances they can hold also vary. A higher shrink rate usually means that keeping a tolerance is less repeatable. Finding the material that has the qualities you need and can hold the tolerances you need may require a trade-off between which is most important. An experienced injection molder can help you find the right balance.

Need a Turnkey Tending System? We do that: Learn more about our 6-axis robots that allow for consistent part removal, degating, and outgoing placement 24/7.

Tackle Tough Injection Molding Tolerances with Noble Plastics

For more than 20 years Noble Plastics embraced and pioneered the use of technology to refine, improve, and optimize the production process for our customers’ plastic parts.

With capabilities second to none, we’re equipped to help businesses across many industries adhere to the injection molding tolerances needed for their specific requirements. With machine tonnage ranging from 35 to 940 tons, we give you options — from small-run prototypes up to production runs of more than a million pieces. Our combination of precision molding, available post-mold machining, and consistent automated handling are key when producing tightly toleranced parts.

  • We have more than 15 years of experience as an ITAR-registered supplier to Department of Defense Prime contractors.
  • Our engineers use virtual molding software to manage expectations by simulating the injection molding processes during manufacturing.
  • Our advanced metrology tools quickly inspect parts, including those with complicated GD&T specifications.
  • We’re at the forefront of robotic automation systems, including a new distribution partnership.

Connect with Noble Plastics to learn how we can help you achieve tight injection molding tolerances and further remove the mystery from manufacturing.


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