Extrusion Tolerances and Why They Are Important

Strong, lightweight, and moldable, plastics improve the performance, convenience, and safety of thousands of products we use every day. Plastics that make up carpets, window trim, and exterior siding keep us comfortable, whereas components in portable electronic devices let us access the Internet or communicate with family and friends on the go. Plastics in sports helmets and bullet-proof vests keep wearers protected.

All of the plastic products above are produced at large quantities through the extrusion process. None of them, however, can function as intended when made repeatedly without standardized manufacturing quality conformance requirements like extrusion tolerances.

Preferred Plastics is dedicated to delivering extruded plastic parts and assemblies that fit, form, and function as envisioned on time and at a competitive price. We meet this benchmark by reviewing and communicating design, drawing, or specification requirements to our highly trained production and quality teams. Here’s an in-depth look at why extrusion tolerances benefit plastic product manufacturing.

What is Plastic Extrusion?

Plastics extrusion is a high-volume manufacturing process in which raw plastic is melted and formed into a continuous profile. Extrusion produces items such as piping and tubing, weather-stripping, fencing, deck railings, window frames, plastic films, thermoplastic coatings, and wire insulation, to name a few.

This process starts by feeding plastic materials – pellets, granules, flakes, or powders – from a hopper into the extruder barrel. The material is gradually melted by the mechanical energy generated from turning screws and heaters arranged along the barrel. The molten polymer is then forced into a die, which forms the polymer into a shape that hardens during cooling. Advantages of this process include:

• Fast
• Efficient
• Complex shapes can be produced with varying thickness, textures, and colors
• Low cost

Manufacturing Tolerances Explained

In high-volume manufacturing, ambiguity is not your friend. Nobody knows the importance, or the unimportance, of a dimension without a tolerance. Not only can a lack of tolerances lead to improper fitment, but they can also delay project schedules and increase total manufacturing costs.

Adding extrusion tolerances to your design, print, or specification can easily avoid this type of scenario, however. Tolerance is the difference between maximum and minimum limits. Typically, this is shown as upper and lower limits or an allowable amount above and below a nominal dimension.

When it comes to plastic extrusions, tolerances are usually based upon the raw materials used, the complexity of the part, and the tooling that produces the part. Other factors include the quality extrusion equipment used and customer requirements.

Generally, tolerances are held the tightest when they are cooled. Some materials cool more efficiently, so they hold tolerances better. Others, however, hold onto heat, making it increasingly difficult to maintain tight tolerances.

Thermoplastics vary in the degree of tolerance control that can be achieved with equivalent dies and fixtures. Rigid plastics hold closer tolerances than flexible materials, for example.

Another critical factor in pulling heat out of the part and holding our shapes during the cooling process is calibration. Less sophisticated calibrators do not hold the shape of the extrusions well.

Benefits of Extrusion Tolerances

You have a lot to gain when adding extrusion tolerances to your project documents. Parts with identified tolerances have a higher chance of fitting and functioning as desired.

Identifying extrusion tolerances can also curb costs. They allow room for variability in the part’s dimensions – such as thickness, length, and width – without impacting performance. When there are no tolerances at all or unnecessarily tight ones, parts become more expensive to produce. Valuable time is consumed, and delivery timelines may be missed.

Your Extruded Plastic Design Partner

The successful design of any profile extrusion depends on an array of factors. One way to take your design from idea to finished product is partnering with Preferred Plastics.

We’re an industry-leading extruder of thermoplastic resins, specializing in rigid, flexible, and co-extruded products for a wide range of markets throughout the world. Our team of experts can work with you to develop product design functionality and maximize processability, including extrusion tolerances and material selection.

It’s critical to understand the importance of extrusion tolerances and how they impact the production of extruded plastic parts. Give us a call to learn more about extrusion tolerances and other issues that can improve your design’s manufacturability and performance.