[Below you will find information relating to typical extrusion manufacturing plants, Sapa RC Profiles in Belgium have specialties outside the general range usually available. For more information on the extremes of profile manufacture, please visit Sapa RC Profiles Belgium]
The aluminium extrusion process provides virtually unlimited opportunities to the product designer with the added benefit of low tooling costs and short lead times.
It is not just in new product design where aluminium extrusions are leading the way. In existing products, substitution of other materials and processes by aluminium extrusions can result in major cost savings through fewer components, reduced finishing, simplified assembly and improved supply chain logistics.
Clip-fits, screw-ports and circuit-board location grooves are just a few ways of reducing components and simplifying assembly at no additional cost.
Aluminium’s excellent corrosion resistance means that often no finishing is required. However, if additional corrosion resistance or aesthetics are important, there is a whole range of suitable finishing processes from polishing and brushing through to anodising and painting.
The anodising process offers unique benefits in terms of protection with almost no impact on the components eventual recyclability.
It can be that the low cost tooling, quick turnaround and the ability to produce a range of different length components from stock lengths can transform the supply chain. A leading supplier of electric motors shifted his production from aluminium castings. This not only revolutionised the production process but also resulted in increased strength, improved thermal conductivity and reduced risk for corrosion for the housings.
Different length motor housings can be produced from stock lengths, new designs can now go from the drawing board to production in 4 to 6 weeks at only a fraction of the tooling costs.
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.
The direct extrusion process can be clearly seen in the schematic diagram below. Cylindrical aluminium alloy billets of cast or extruded 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. This can be by water bath, water spray or forced-draught air, with the latter being particularly useful for thin section. 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.
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.
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.
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
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.
The smallest aluminium profiles have a minimum circumscribed circle of 5 mm and a minimum weight of 30 gr/m. Application fields of these tiny profiles : car luggage covers, sunroof and sunshade guides, automotive trims, shower cabins, interior furniture…
There are few extrusion specialists for these tiny profiles : one of them is Sapa in La Selva (Spain)
Large profiles have a diameter of 320 mm, 620×50 mm or 300 x 300 mm and a weight of 65 kg/m. Application fields of these large profiles : building constructions, containers, machines, sawing benches, heat exchangers, road signs, boat masts, energy transmission, renewable energy, trains, metro, ships, yachts, … Profiles in the larger shape range can sometimes be designed and extruded in thin wall thicknesses. There are few extrusion specialists for these large profiles : one of them is Sapa RC Profiles in Belgium.