Engineers consider several factors to ensure plastic components both perform properly and are produced efficiently.
These include the application environment, assembly processes, aesthetic requirements, critical tolerances and more. Fully understanding these issues also can lead to opportunities for cost savings or product enhancements.
In this post, we provide a brief look at considerations for the following:
- Material Selection
- Wall Thickness
- Sink Marks
- Hollow Sections
- Production Processes
During an initial assessment, the profile design, materials, tooling and processing needs are all evaluated. Additional attention is given to how the part will be installed or joined with mating components.
By weighing each of these variables, engineers can recommend the best package of solutions for your specific application and production timeframe.
Choosing the right plastic compound ensures you will meet performance demands without overpaying for materials.
Polymer blends can be developed to meet many needs. These include operating temperatures, UV resistance, coloration or opacity, flame resistance, rigidity and more.
The important thing to keep in mind is that every material has benefits and limitations.
Typically, the best course of action is to identify a material that will provide a balance of the properties desired for an application.
Why uniform wall thickness matters
Designing plastic profiles to have a uniform wall thickness can avoid problems in two key stages of the extrusion process.
First, the consistent flow of material through the die is critical to ensuring that an extrusion maintains its shape. Significant variances in wall thickness can cause material to flow unevenly and lead to distortions in the profile.
The second consideration is the even cooling of a part once it exits the die.
Thicker walls and interior supports will require additional time to decrease in temperature. Proper design will prevent bowing or twisting that can occur due to these differences in cooling rates.
Engineers can help you determine wall thickness requirements and limitations based on the complexity of the part and the chosen material.
Avoiding sharp corners
Sharp corners can create a weak point in extruded plastic profiles. The result is that when a part is subjected to impact or stress, cracking is more likely to occur.
To remedy this, the radii of corners should be as large as possible given the demands of the application. This improves the strength of the final product as well as the flow of the material during extrusion.
A good rule of thumb is to make the radii of outside corners at least 1 1/2 times the wall thickness, and the inside radii should be 1/4 times the wall thickness.
Because of differences in cooling rates, sink marks can occur where two perpendicular projections are joined. A greater variation in the thickness of these projections will increase the severity of this cosmetic defect. The appearance of sink marks can be minimized by reducing size variations or by adding a notch or other surface design.
While it is common to extrude plastic profiles with hollow sections, there are important limitations. Hollows within hollows or hollow sections that contain other design features should be avoided.
The interior of the part will cool at a slower rate, preventing these sections from maintaining their shape.
One way to achieve more favorable pricing is to determine which tolerance requirements are critical to part performance.
While it may be possible to meet precise specifications, achieving these tight tolerances can lead to an increase in tooling, material and production costs. This can be due to the need for higher-grade compounds, slower run times or additional processes such as offline cutting.
In some cases, material properties along with complex part designs may limit the ability to hold certain tolerances.
Understanding production options
Plastic parts can range from simple profiles to complex dual- and tri-durometer extrusions in which different materials are coextruded to enhance performance properties.
For example, rigid and flexible materials may be combined to create a part that installs easily while offering dynamic sealing or protective features.
Processes such as cutting, drilling and notching can often be performed efficiently in-line with product extrusion. More complex designs and assemblies can be achieved offline in specifically-designed work stations.
A plastic manufacturer’s production and tooling capabilities, market experience and organizational sophistication are among the factors that will play a role in delivering high-performing, cost-effective solutions.
Whether you’re starting a new project or looking for ways to improve production of an existing part, our engineers can help you evaluate solutions. Take a closer look at our custom plastic extrusion capabilities.
Download our Intro to Designing Extruded Plastic Profiles.