Tolerances in Plastic Extrusions Lesson 101
What is a tolerance? Simply speaking, it is the amount or measure of room given from the dimensional ideal. Often, the dimensions of a product will fluctuate, which allows for tolerances to be determined at +/- measurements. Tolerances are essential in manufacturing processes because they allow room for variability in the part’s dimensions (thickness, length, and width of parts can all be affected). Why do we bring this up? As a master in plastic extrusions, we frequently find that tolerances are not properly understood throughout industries. Let us provide you with a quick overview of tolerances, specifically in plastic extrusions.
First, it is important to determine the manufacturing process being used. For example, the plastic industry has a wide variety of fabrication processes, which each carry different tolerances. It is also essential to know that tolerances for plastic extrusions differ widely from those of metal extrusions. Since metals harden quickly, they typically hold tighter tolerances than extrusions made of plastic materials. When it comes to plastic extrusions, tolerances are usually based upon the raw materials used, the complexity of the part, and the tooling that is made to produce the part. Generally, tolerances are held the tightest when they are cooled—some materials cool more efficiently, so these materials, such as PVC, hold tolerances much better. Others, however, hold onto heat, so it is more difficult to have tighter tolerances (one such example is polypropylene). Another important factor to pull heat out of the part and hold our shapes during the cooling process is the calibration. Less sophisticated calibrators do not hold the shape of the extrusions well. It is recommended to use well-designed tooling, then, so that the extrusions are calibrated and streamlined at the highest level (and the tolerances will be tighter, too!). In terms of part complexity, think of it this way: if a part has many inside pockets and hollows, the tolerances will be larger than those that do not. The reason for this is simple—it is more difficult to then cool the inner dimensions of the part, which results then in bigger tolerances. In clearer terms, tolerances are directly related to how efficiently manufacturers can take heat out of the part.
Hopefully, we have made sense out of tolerances in plastic extrusions. See the below chart for our standard tolerances, and visit our website for more plastic extrusion information.