Aluminium extrusion is an industrial forming process that is used to produce long profiles of a constant cross-section. This cross-section is shaped by the opening in a steel tool known as a die.
A huge advantage of designing with aluminium is that extrusions can be designed to form virtually any shape or size, some designs will be more challenging for an extruder and complexity will potentially increase the cost and slow down production speeds.
Knowing where and how to make minor tweaks and changes will yield significant benefits, not only in extrudability but also with manufacturing and production costs too.
It may seem obvious but understanding the function of your profile is key to it’s form and fit being successful in its end use.
When designing a profile for extrusion, it’s not just the overall look that needs to be considered, you also need to consider what you want the part to be able to do once produced.
Start with a list of 3 questions to ask yourself;
Once you have an understanding of the essential functions of your profile you will then need to consider the following;
There are three general categories that extruded profiles are categorised in: Solid, Semihollow & Hollow.
Solid profiles are typically the easiest to extrude as they are usually the least complex.
You can produce a variety of forms with a solid profile as long as it’s cross-section doesn’t have any voids.
A Semihollow profile is defined by it’s tongue ratio as it partially encloses a void. A semihollow profile will be defined mathematically by comparing the area of the partially enclosed void to the size of the gap (to the mathematical square of the gap size). If that ratio is larger than a pre-defined number, the shape is classified as semi-hollow; if the ratio is smaller, the shape is considered a solid.
Hollow profiles contain a void or maybe even multiple voids on a single profile.
This is the most basic description of these three categories, there are other factors which need to be taken into consideration when deciding whether your profile is one of the above shapes.
The less complex and easier to extrude a profile is, the more likely it will cost less than a profile that is complex and that will take longer to go through the extrusion process.
When it comes to designing profiles for extrusion, understanding the end use of the profile is essential. Dimensional tolerances are absolutely critical, especially if the profile is going to have mating components.
Tolerances will cover the characteristics of the profile such as the straightness, flatness, twist, thickness, angles, contours, corners and fillet radii.
It’s fairly easy to achieve standard dimensional tolerances but can be considerably difficult to achieve certain tolerances if the profile is more complex.
It is impossible to cover all of the standard dimensional tolerances that meet all situations which is why it’s recommended to talk to us about the tolerances that can be achieved first.
You can design a profile with dimensional tolerances that go beyond standard tolerances, these are called "special tolerances".
You will need to check with the us before going through the manufacturing process, special tolerances can be achieved but it's likely to end up being a more costly and timely process.
It's more cost effective if you can design your profile with a minimum requirement for special tolerances.
From a cost perspective, having a uniform wall thickness with a minimum aluminium thickness that meets the structural requirements is incredibly beneficial. It’s easier to extrude and costs less than a more complex profile.
Considerably uneven wall thicknesseses (especially if adjacent) can cause problems during the extrusion and cooling process which can lead to the profile not being able to hold its desired shape & also creates blend or witness lines which will become usually apparent after finish.
You should always avoid adjacent wall thicknesses that have a higher ratio than 2 -1 and use rounded corners to transition from walls which have different thicknesses. This is to help ease the flow of aluminium.
Factors that can determine minimal wall thickness;
Heat Generation – This is a key factor. When you push aluminium through a die, it produces heat. The larger the degree of forming, the more heat that is generated. When temperatures are high it can create problems on the extrusions surface in the form of pick ups and cracks.
Tolerances – Tolerances are affected by wall thicknesses, dimension size, location, profile type (solid or hollow) alloy used, cross section & the parts application. To get a better understanding on what tolerances should be used, contact us here.
Choice of Alloy – Your choice of alloy will determine the minimum achievable wall thickness. When an alloy has a high content of alloying elements, it’s harder to extrude than alloys with a lower content, thus requiring thicker walls.
Cross Section Complexity – Typically, it’s a lot easier to produce thin walls that are in simple sections as opposed to thicker walls in complex sections. Also, it’s worth considering that cavities are harder to fill in hollow sections with several channels. Speak to us for more information.
When designing your profile, It’s favourable to consider symmetry and constant wall thickness as it contributes to better flow characteristics.
Aluminium offers many options for surface finishing such as linishing finishing, satin finishing and buffing. Profiles can also be finished by clear or coloured anodising, powder coating & painting.
Knowing what finish your profile will require in the design phase can be important, often people overlook the dimensions a finish can add to your profile, although they can be very minor, it can lead to critical errors happening further down the line. Talk with us here to discuss what your finishing options and the dimensions it can add to your profile.
However, extrusion dies can be designed to orient the shape to protect the surface during the extrusion process, again, it’s worth talking to us about what finish you want to go for and what options you have available.
Your alloy choice depends on your profiles need and end use, there is a wide variety of alloys and tempers that are available which can be used to create your profile.
Understanding what strength your profile will need e.g. the weldability, forming characteristics, finish, machinability, corrosion resistance, etc. will be dependent on the alloy you choose to extrude your profile, some alloys are used more frequently than others.
Around 75% of alloys used are from the 6xxx-series, the most popular alloys are 6063, 6060 & 6082.
Increased profile complexity ultimately raises the overall cost as it can reduce production speed and cause other complications such as die failure and extended quality control. However, that doesn’t mean it isn’t possible to create a complex profile, these are just considerations to make before committing to the cost of your die being produced and your profile going through the manufacturing process.
Although there are many considerations to take into account, designing with aluminium gives you a lot of freedom with creativity and infinite opportunities of shapes and extrusions.
Find out if your profile is extrudable by getting a 3D printed prototype of it produced first. Not only does this eliminate potential design flaws, it’s also an opportunity to assess areas of the design and see if there are any tweaks or changes that can be made to reduce costs and make it easier to extrude.