Extrusion Design Guide

The whole manufacturing and production process starts with the design. It is here that the extrusion takes shape and features are built in to reduce weight, simplify assembly, add functionality and minimise finishing costs. Here we take advantage of the unique benefits of aluminium, in combination with the extrusion process, to make a cost-effective product with optimal functionality and an attractive appearance.

Extrusion design tips – Jump to:

  1. Wall thickness
  2. Uniform wall thickness
  3. Exceptions
  4. Soft lines
  5. Solid profiles if possible
  6. Fewer cavities in hollow profiles
  7. Profiles with deep channels
  8. Heat sinks
  9. Decorate

Wall thickness

When deciding how thick the walls of a profile should be, strength and optimum cost-efficiency are two of the main considerations.

Profiles with a uniform wall thickness are the simplest to produce. However, where necessary, wall thickness within a profile can easily be varied. For example, a profile’s bending strength can be increased by concentrating weight/thickness away from the centre of gravity.

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Cost-efficient production

To optimise cost-efficiency, a profile’s design should always be as production-friendly as possible. To achieve this, the profile should:
– have a uniform wall thickness
– have simple, soft lines and radiused corners
– be symmetrical
– have a small circumscribing circle
– not have deep, narrow channels

Recommended wall thickness – guidelines

Amongst the factors having an effect on wall thickness are extrusion force and speed, the choice of alloy, the shape of the profile, desired surface finish and tolerance specifications.

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Uniform wall thickness

It is often acceptable to have a large range of wall thicknesses within a single profile. However, a profile with uniform wall thickness is easier to extrude (below right).

In the drawing below you can see in the left hand profile that the internal and external walls have different dimensions. It is an advantage if the internal and external walls are of the same thickness (below right). This decreases die stress and improves productivity.

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Exceptions

It is of course perfectly acceptable for a profile to have walls of different thicknesses. For example, for strength reasons, it may be best to concentrate weight/thickness away from the centre of gravity.

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Soft lines

The extrusion process cannot achieve razor-sharp corners without additional fabrication. Corners should be rounded. A radius of 0.5 – 1mm is often sufficient.

A design may demand sharp internal angles, e.g. a profile to enclose a box shape. This is easily solved by incorporating a hollow moulding.

As far as possible sharp tips should be avoided. The tip can easily become wavy and uneven. Tips should therefore also be rounded.

Following extrusion, a profile with large variations in wall thickness cools unevenly. This gives rise to a visible structural unevenness that is particularly marked after anodising. Always use soft lines.

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Solid profiles if possible

Solid profiles reduce die costs and are often easier to produce.

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Fewer cavities in hollow profiles

This hollow profile is extremely complex to produce.

By replacing the hollow profile above with two telescoping profiles, the product is considerably easier to produce.

Is it essential for this profile to have two cavities? In many cases, reducing the number of cavities in a hollow profile makes it easier to extrude. This increases die stability.

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Profiles with deep channels

For profiles with pockets or channels, there is a basic rule that the width to height ratio should be approximately 1:3. This ensures that the strength of the die is not jeopardised.

By using large radii at the opening of the channel, and a full radius at the bottom, the ratio can be increased to 1:4.

NB! Where channel width is under 2 mm, or where a profile’s design is complex, permissible channel depth must be determined on a case-by-case basis.

It may be possible to increase radii and opening dimensions without compromising functionality. Here, a holder has to enclose a slide. Redesigning the holder on the left gives a more extrusion-friendly profile and improved functionality.

A profile cab be extruded “open” and then rolled into shape.

The solution below shows a narrow, deep channel and an extrusion-friendly profile.

Reduced channel depth using a step. The step is removed during rolling.

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Heat sinks

The use of cooling fins on profiles greatly increases the heat dissipating area. This can be further increased by giving the fins a wavy surface. Where there is forced air-cooling longitudinally along the profile, it is better to leave the fins smooth. This helps to avoid the problem of eddy formation. An undulating surface increases the heat dissipation area of fins, as shown in the close up image below.

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Decorate

Decoration has several advantages:
– Design
– Masking of imperfections
– Protection against damage during handling and machining.

A decorative pattern can make a plain aluminium surface more attractive.
The consistent use of a pattern on all a product’s component profiles can help make it uniquely identifiable. There are endless possibilities for creating unique designs.

A joint can be elegantly hidden by making it part of a fluted design.

Masking of imperfections
Where a profile has, for example, arms and screw ports, there may be process induced shadowing (heat zones) opposite such features. Using decoration the heat zones can be completely masked.

Protection against damage
Well designed decoration can also protect profiles from handling and machining damage.

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