Tight tolerance plastic injection molding produces parts that work together smoothly and contribute to an overall lower failure rate for the product.

In order for a product to work reliably and as intended, all of its parts must fit together smoothly. When designing parts to be manufactured via plastic injection molding, an important factor to consider is tolerance. Typically, parts should be produced with the best tolerance possible.

There are different ranges of acceptable tolerances; for example, a very tight tolerance is +/- 0.001”. Sometimes even a few thousandths of an inch can mean the difference between a part that fits and one that doesn’t. In these situations, the extra planning and attention to detail that goes into tight tolerance molding is well worth the effort.

It All Starts with Design

Calculating tolerances is done most successfully as a collaborative effort between the customer and the manufacturer during the design phase. The part designers and engineers develop an understanding of the part’s function and how to manufacture it within established parameters so it fits and functions correctly. Plastic injection molding experts also add their knowledge of influencing factors to the design process, advising in areas such as material selection and mold design.

Planning for a successful tight tolerance molding project may also include additional process controls and quality assurance testing or a higher-grade material with a lower shrinkage rate to produce more consistent results.

At Viking Plastics, we measure parts from a longer sample run (capability study run) to determine results, with statistical analysis of the data. If the part feature is small and the material is robust, we can capably hit tolerances even less than +/- 0.001”. We can engage all inputs into the injection molding process to deliver the best results.

Benefits of Tight Tolerance Molding

The additional attention to design, testing, quality control, and materials will result in several benefits:

1. Tight tolerance molding ensures the effective use of the part within its environment. Gears will mesh perfectly, shafts will fit into bearings, and threaded caps will fit securely.
2. Parts that work together smoothly mean an overall lower failure rate for the product. The customer will have an effective and reliable product at launch.
3. When tolerances are calculated well during the design phase, it can eliminate waste and save time and money. Parts won’t require extra machining processes post-molding in order to achieve fit. Production runs will not have to be repeated with overhauled processes. Moreover, tolerance done right will reduce the amount of rejected, useless product.
4. The level of consistency achieved with tight tolerances can make it feasible to convert some parts from metal to plastic, thereby reducing overall costs.

A good plastic injection molder can provide guidance in establishing the right tolerances, and can even tell you if your tolerances are too tight to be cost-effective.

For more information about tight tolerance molding, click here. You can also contact us to consult with the Viking Plastics team about the best tolerances for your project, or request a quote.