Extrusion Design Hints:
Extrusions give the designer a freedom to choose the cross-section most suited to his or her requirements which no other process offers. Most shapes can be extruded but there are limitations which must be considered. The most fundamental factors are as follows:

Complexity or Shape Factor
This is the FACTOR of the section and is a measure of the amount of surface that is generated per kilogram of metal extruded. The shape factor affects the production rate in the cost of manufacture and also the maintenance of the die. What appears complex to the designer may not necessarily appear so to the extruder. For example, the designer may consider a shape complex if it replaces an assembly or looks intricate. The extruder may find this same shape quite simple to extrude and price it accordingly. We therefore recommend that you contact our sales office at an early stage to ensure the best result for all parties.

Uniformity and Symmetry of Shape
The thinner the wall thickness the more susceptible the shape is to distortion during extrusion and damage during handling. Lack of shape symmetry has a greater distorting effect when wall thicknesses are low. Thick-thin reconditions create metal flow problems which may mark the surface, cause distortion or die breakage. When thick-thin conditions are necessary, the transition should be streamlined by a radius at the junction.

Design Hints

Instead of this:		Consider these:		Because:
				Transition is smoother at thick-thin junction.
				Less metal used, metal thickness more uniform.
				Thick-thin junction avoided.
				Better balanced symmetrical shape.
				Thin wall detail at end of a long flange avoided. General wall thickness balanced.
				Long frail die tongues causing a semi-hollow should be avoided. Long tongues are liable to die breakage.
				Long voids with narrow gaps cause die deflection giving shape distortion giving shape distortion problems.
				Due to flexing of opposing tongues the overall width is difficult to maintain and will vary from one end to the other..

Dimensions which can be measure across solid material are easier to produce to close tolerances than those which include a gap or an angle. When designing matching fits rely as much as possible on metal dimensions and keep points of contact to a minimum and at two places only. Do not try to make two sections together at three places. Also a section cannot be guaranteed to mate with two other sections fitted together.
Clip Fits:
Fits may be releasing	or permanent
Always give a good lead in, and ensure one section has long flanges as in a channel, to allow the necessary spring to effect engagement.
short legs do not allow any spring, causing the metal to be overstressed to effect a clip fit.	Suggested arrangement
Dovetail or Tee slide fits:
These fits are only recommended for lengths up to 600mm (max) as any slight variation in straightness, twist or flatness of the two parts will affect the fit. Relieve out parts as shown to reduce contact surfaces.
Extrusion design is less a matter of following rules than acquiring experience in automatically bypassing expensive features. While streamlining for production, a designer will often discover a simplification, a better assembly method	or a more balanced shape - in short, an improved design at a lower cost, with closer dimensional control and better surface finish.