Extrusion is a very useful technique that allows precision tooling and a relatively simple process to make long and consistent sections of complex metal profiles. These can range from simple round bar as small as a few millimeters diameter up to complex hollow profiles of half a meter or more in maximum width.
Advantages of extrusion in manufacture
Using extruded sections in a design offers a range of significant design and product wins that make this a go-to process in a broad spectrum of applications;
- Cost-effectiveness which results from minimal waste due to precise control over material flow – and die costs are relatively low, when amortized over moderate scale production runs.
- Design flexibility, as a consequence of the ability to create intricate and complex net-shape cross-sections that are much harder to achieve with any other method. These can typically result in very high strength to weight ratios..
- High production rates are relatively easy to attain with a wide supplier base open to access.
- Faster tooling and setup compared to many other manufacturing processes, delivering shorter lead times.
- Strength and durability are high, as the process typically enhances the mechanical properties of extruded metals and can affect some plastics similarly.
- Consistent properties result along the entire length of the extrusion, if conditions are held constant.
- Extrusion is applicable to a variety of materials, including metals (e.g., Aluminum, Copper), many but not all plastics, and some composites.
- High dimensional accuracy and tight tolerances are typical, requiring little or no follow-on processing to deliver high quality and finished net-shapes with great surface finish.
- The ability to incorporate complex functional features (e.g., screw points, channels, tubes, slots, hinges, motion limiters) directly into the design reduces assembly, part counts and secondary operations.
These two parts illustrate good design in two functionally identical extrusions that differ in details. The double wall diagonals in the second part show a good use of the strengths of the process to produce a stiffer design with the same amount of material and some increased tooling complexity.
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DFM principles
There are a variety of basic guidelines, following which will result in easier manufacture of better quality extruded sections and better products. Close adherence to basic rules rarely imposes significant design limitations, but to fully exploit the capabilities of extrusion and deliver consistent, high quality outcomes does require some care in design for manufacture.
Materials and process selection
Choose materials that are specified for extrusion – the process does not suit all grades and material types. Select metal alloys, plastics and composites based on desired mechanical properties, corrosion resistance, and application specific details.
Select the extrusion supplier/machine size in principle while designing, in order to optimize process use in your extrusions.
Simplicity and symmetry
Keep cross-sectional profiles simple, where possible, to reduce tooling complexity/lead time, operational reliability and cost. Simplicity is not only about feature presence or complexity – feature rich extrusions can still be considered simple.
Use symmetric profiles to minimize uneven material flow and transverse imbalances in cooling/contraction during and immediately after extrusion.
As far as possible try to maintain uniform wall thickness to prevent warping and ensure consistent quality. Where variations in wall thickness are necessary, consider coring and aim to constrain the differential stresses and make them transverse-uniform. Aim to design with walls of uniform thickness to avoid weak points and material waste by allowing unnecessary weight in sections that are not working hard.
Design hollow sections with straightforward, easy-to-manufacture shapes. Complex internal sections result in particularly weakened tooling areas and higher wear.
Integrate features such as screw ports, channels, and slots directly into the extrusion design to minimize secondary machining operations. It is important to fully exploit the capabilities of the production process in order to deliver value.
Design with weight reduction in mind, utilizing only sufficient material to achieve the required level of structural integrity and strength. Thinner sections extrude more reliably,down to the general process limit that your supplier can help you understand. Less material means lower cost. Since extrusion is often priced by the tonne, less material in the section results in longer lengths of product for the same price.
Consider material flow from billet to profile
Use rounded corners instead of sharp edges. This enables smoother material flow and reduces stress concentrations that can otherwise lead to local and generalized distortion.
Small radii can result in material tearing in internal corners, potentially destroying the integrity of the product. Larger radii reduce tool wear by easing the flow of material from the billet to the final profile with less harsh transitions.
Realistic tolerances and finishes
Specify tolerances that are more easily achievable through the extrusion process. This avoids the need for slower extrusion and reduces the need for support/straightening operations after extrusion.
Don’t over specify surface quality, as this can influence production rate and tooling cost.
Indicate required surface finishes based on the application (e.g., anodizing, painting) to guide the tooling development, extrusion process and post-processing.
Use the process optimally
Consider the design in terms of the final application of the extruded part, to ensure compliance with functional requirements and manufacturability. Where funcion and manufacturing issues appear to clash, it is often wise to go back to first principles in the design of the extrusion, to understand the options better and to avoid the constraints that early design stages may have imposed.
Design with production volume in mind, ensuring the extrusion process is scalable for high-volume production if needed. It is common to prototype with lighter tooling and re-tool for volume once the production issues in the design have been refined. Multiple tools can allow quick ramping of productivity, where scaling is a challenge.
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Conclusion
The careful application of DFM in extrusion processes significantly enhances the efficiency, quality, and cost-effectiveness of product development. By integrating DFM principles, you can optimize material utilization, reduce waste, and achieve complex geometries that meet specific functional requirements.
This approach lowers tooling costs, speeds up production and ensures consistency and precision in the final products. The versatility of extrusion allows for the use of various materials, including metals and plastics, making it suitable for a huge diversity of applications, from wire making to complex heat exchanger production, from window/door frames to street furniture manufacture.
The ability to incorporate complex functions and multiple features directly into extruded parts minimizes the need for secondary operations and additional assembly stages, streamlining manufacturing. Overall, DFM in extrusion can enable designers to innovate, make sustainable products, and improve competitiveness, making it a valuable tool in the designers arsenal.