snelsons ltd, aluminium extrusions
extrusions homeextrusion processcontact

Aluminium Extrusion Process

Aluminium Extrusion

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 . consideration at this point is given to intended polished surfaces

Direct Extrusion

The direct extrusion process can be clearly seen in the schematic diagram below. Cylindrical aluminium alloy billets of cast manufacture are heated to between 450º and 500º before being loaded into a container and the billet squeezed through a die orifce using ram pressures of up to 680MPa. The die is supported by a series of back dies and bolsters so that the main press load is transferred to a front platen

On leaving the die the temperature of the section is more than 500ºC and with heat treatable alloys the quenching, or solution heat treatment, takes place in the production line. The approximate temperature drop during the transverse of the quench box 250ºC. To avoid distortion care has to be exercised in handling sections with extreme aspect ratios and large cariations in thickness.

After extrusion the section is guided down the table by a puller on to a slatted moving belt. Modern Pullers are based on linear motor systems and operate on tables up to 40 metres long. On completion of an extruded length, the section is sheared at the press end and lifted from the slatted table by eccentric pivoted arms. It is then transferred by a walking beam or multi-belt transfer table to the stretcher bay where it is given a controlled stretch to straighten and remove minor miss-alignments. The section is then taken and cut to ordered lengths on high speed tungsten carbide tipped saws. operating tolerances at the press on the cut length are ± 6mm


If the material is required in the solution heat treated condition (T4) it is released at this stage. If the full strength aged material (T6) is required, it is given a precipitation treatment before release. In the case of the T5 temper, there is limited cooling at the press exit and the material goes directly to precipitation treatment.

Indirect Extrusion

In the traditional direct method of extrusion, as described above, the die is stationary and the press ram applies pressure on to the billet. In the indirect method, the ram carries the die and applies pressure on to the stationary billet, in the opposite direction of extrusion. There can be variation to this basic concept, but in every case the billet remains stationary in relation to the container, there by keeping friction loss to a bare minimum

Types of Extruded Shapes
There are basically two main types of extruded shapes or profiles;
Solid extrusions without cavities – e.g. round bar
Hollow extrusions with cavities – e.g. round tube

extrusions 2

Nearly, if not all, commercial extrusion plants use a cylindrical feedstock, (aluminium billet) that is pushed through the centre of a cylindrical container. This imposes certain size restrictions and is often expressed in terms of the diameter of the circumscribing circle, (DCC). This is a measure of the extrusion’s overall size in cross-section and has a bearing on the material thickness and tolerances.
Below are the measurement limits within which most extrusion plants can supply aluminium extrusions based on the DCC.Types of

Extruded Shapes
There are basically two main types of extruded shapes or profiles;
Solid extrusions without cavities – e.g. round bar
Hollow extrusions with cavities – e.g. round tube