FIELD

Embodiments described herein relate to an apparatus and method for extruding wide profiles, in particular wide sheets of metal or alloy material for use in various industries, e.g. the transportation industry.

BACKGROUND

Lightweight materials, such as aluminium and magnesium alloys, are in high demand for their use in modern transportation industries as construction components, especially in the automobile and aerospace industries in metal sheet or plate form.

An existing method for producing metal sheet or plate from a metal stock is rolling, which may employ multiple rolling passes with intermediate heating. Rolling techniques can be used to produce wide metal sheet for use in the automobile industry, such as aluminium alloy sheets with a width of 2200 mm or more, however, the multiple passes and heating often required in these rolling processes in order to make the sheet or plate wide enough make them energy intensive and therefore costly. For magnesium alloy, the cost is higher than for aluminium since the hexagonal close packed (HCP) crystal structure of magnesium is hard to deform by rolling. To overcome these drawbacks, a new manufacturing technique with fewer processing steps and reduced cost is desired.

Extrusion processes offer an alternative to rolling for producing metal sheet or plate and can also be used to manufacture straight lengths of a chosen complex-shaped cross-section. In contrast to rolling, extrusion is a one-step process and therefore requires no intermediate heating.

An existing extrusion method for producing metal sheet or plate involves extruding a thin curved profile (e.g. in a U-shape or W-shape) and then flattening the profile to produce a large flat sheet. Such a process may, for example, be that described in US2681734. The extrusion ratio to produce a wide sheet or plate via such extrusion methods from, e.g. cylindrical metal billets, would be very large and this results in large extrusion forces and pressures. Flattening the curved profile into a flat sheet or plate entails multiple rolling resulting in added costs and possible inconsistencies in mechanical properties across the sheet or plate where initially curved regions have been flattened. In practice, this kind of extrusion process is used to make sheet or plate extrusions with a width of up to around 1500 mm.

Another existing extrusion method for producing wide metal sheet or plate is called expanding extrusion which involves extruding a cylindrical billet through a rectangular orifice and allowing the extrudate to expand sideways before it is forced through a thinner slightly shorter rectangular die to form a thin sheet. Large extrusion forces are required for expanding extrusion due to the friction at the workpiece-tool contact surfaces. Also, edge quality of the sheet or plate is hard to control since if the extrudate material does not fill the expanding die well, extruded edges will have saw-tooth features. This would then require further downstream processing. Additionally, in practice, expanding extrusion can only produce profiles with a width less than 1.5 times the diameter of an extrusion container, because if the size of the expanding die is too large, it is difficult for the material in the die to flow to the positions far away from the centre of the die. Further, the rectangular section and profile dies would be expensive to build and maintain. In practice, this kind of extrusion process is usually used to make sheet or plate extrusions with a maximum width of up to around 800mm.

In general, the smallness in cross-sectional area of sheet or plate (its maximum width and minimum thickness) extruded from cylindrical billet is limited by the associated high extrusion ratio and hence high load and pressure required to produce it within an extruder. There is a need for new extrusion apparatus and methods obtaining the benefits of extrusion and capable of producing wide metal sheet or plate in an efficient and cost-effective way, e.g. a sheet wide enough for use in the automotive industry (2200 mm or wider).

The present disclosure seeks to alleviate, at least to a certain degree, the problems and/or address at least to a certain extent, the difficulties associated with the prior art.

SUMMARY

Aspects and features of the invention are set out in the appended claims.

According to one aspect of the present disclosure, there is provided an apparatus for extruding a material, the apparatus comprising: a block which includes two or more extrusion containers composed of heat resisting material, said containers being arranged to receive billets of the material; a die set arranged downstream of the block including the two or more extrusion containers; and one or more rams, wherein the one or more rams are aligned with the axes of the extrusion containers and are arranged to push the billets of material through the extrusion containers into the die set; wherein the die set includes an upper die including two or more extrusion channels for extruding material from each of said extrusion containers, and a lower die incorporating a welding chamber, wherein two or more extruded billets from each of said extrusion channels are welded together and passed out through the exit of the die set.

According to another aspect of the present invention there is provided a method of extruding a sheet of material using the apparatus as set out above, the method comprising: pre-heating two or more billets of material; transferring the pre-heated billets of material to the two or more extrusion containers; pushing the billets through the containers using the rams, such that the material is forced through the extrusion channels in the upper die; welding the extruded material in the welding chamber; and passing the welded material out through the exit of the die set.

The present invention uses multiple small containers to replace the single conventional large container, which can hugely decrease the effective extrusion ratio for wide extrusion and therefore the load requirement and cost are decreased, compared with the conventional single container extrusion. Load requirement in the present invention is decreased significantly with the increase of the number of the small containers. The process enables manufacture, with a low applied force, of a wide, metal material that could be used in the automobile industry and other industries, (for example, a width of more than 2200 mm). The apparatus and method of the present invention applies primarily to processing aluminium and magnesium alloy material, but in certain circumstances, it could also be used to manufacture other metal materials such as steel and titanium alloys, and the shape of extrusion could be complex and of wide profile, especially useful for aircraft, train, bus, truck and construction applications.

Other optional and preferred features of the apparatus and method of the present invention are set out below in the detailed description and follow in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic example of an apparatus according to the present invention comprising an extruder with multiple close-spaced containers in a block arranged to produce wide sheet material; Figure 2 shows a schematic example of two units according to the present invention arranged sideways, each comprising multiple containers;

Figures 3a and 3b show schematic representations of block configurations according to the present invention;

Figure 4 is a graph showing the comparison of the applied force requirement between an apparatus according to the present invention and a conventional extruder when extruding a sheet of AA6061 material with a width, w = 700 mm, and a thickness, t = 5 mm;

Figure 5 shows schematically the die set as used in an example of the present invention; and Figure 6 shows schematically an exploded view of the dies set as used in an example of the present invention.

DETAILED DESCRIPTION

The present invention processes raw material in the form of cylindrical billets which could be acquired by casting or other alloy agglomerating processes. The number of billets is the same as the number of extrusion containers within the apparatus. Prior to insertion into the apparatus of the present invention, the billets are heated in preparation for extrusion. For aluminium alloys, for example, the preheating might be in the range of 400-580°C depending on the alloy. This would generally be around the solution heat treatment temperature. The heated billets are then placed into each one of the containers within the apparatus and simultaneously pushed by hydraulic system through the extrusion die set and formed into wide sheets/components. The container block and the die set can be used in cold state or hot state using internal and/or external heating.

Wide components which are not very thin could be formed directly by extrusion. To form very thin wide metal sheet, the hot extruded wide sheet can be hot rolled, to further reduce thickness and quenched for subsequent cold forming, if required. The hot rolled and quenched sheets could be further cold rolled for surface refinement and finally cut to size and shape. Alternatively, according to the production requirement, the quenched material could be cold or hot stamped to form contoured panel components.

An example of an apparatus according to the present invention to produce wide sheets/components by extrusion is shown in Figure 1. The extrusion unit is designed as a block with multiple, close-spaced containers made of heat-resisting material. Each billet 2 of raw material is pushed by a ram 1 through the containers in block 3 into a die set 4. The multiple billets are extruded through the first part of die set 4 and then welded in the second part of die set 4 and pushed out to extrude the billets into a wide sheet or component 5. The welding chamber design and strength check of die set 4 is similar to conventional porthole die. The exit of die set 4 could be at any angle, 0 to 90° to the plane of the container axes, in order to increase the level of deformation strain within the extruded product. To further reduce extruded thickness in order to produce wide sheet, the extrusion may be transferred to rolling stands 6 for further thickness reduction.

The containers may be manufactured as cylindrical circular holes through the block, and the strength of the container is guaranteed by dispersing the internal stress generated by extrusion throughout the block 3. The axes of the containers are parallel and can be in one plane or in different planes depending on whether the extruded product is to be a flat sheet or have another final product shape. If the final product is not to be a flat sheet then it may be that the axes of the containers are in different planes, but the axes would still be parallel to each other. The arrangement of block 3 can be changed according to different cross-section and size of the product. Figure 1 shows the situation that the axes of the containers are parallel and in one plane, but this could be varied depending on the required characteristics of the product.

Figure 1 show only one extrusion unit, but multiple extrusion units also can be used for higher productivity. Referring to figure 2, extrusion units 7 and 9 work simultaneously in opposite directions, to push billets into the common die set 8. This technique can have a higher production efficiency compared with single extrusion unit. More extrusion units (more than two) can be assembled around the common die set to further raise the productivity by allowing a higher rate of extrusion through the multiple extrusion units. The number of containers in each block is sufficient to enable the correct width of product to be formed.

Referring to figure 3(a), a schematic representation of a first configuration of the block according to an embodiment of the present invention is shown. In this configuration, the individual containers comprise separate cylinders. The block of the extrusion unit consists of several parallel close-spaced cylinders 11 which are enclosed, located and supported under load, by upper and lower bolsters 10. The containers 11 are made of hot extrusion tool material, and the bolsters could be made of cheaper material such as cast iron or steel, as they do not suffer from wear. The bolsters 10 can be held by squeezing them together over the cylinders 11 using hydraulic pressure or other means. Referring to figure 3(b), another configuration of the block according to an embodiment of the present invention is shown. In this configuration the extrusion container chambers are machined into a single hot work tool steel block, 12. The block is reinforced against extrusion pressure by being clamped between two bolsters 13 made of cheaper material.

Referring to figures 5 and 6, further detail of the die set 4 as shown in figure 1 is given. As shown in figure 6, for sheet extrusion, the die set usually includes two parts, which are the deflector (also considered as upper die) and the lower die. The welding chamber is a critical area located in lower die, where multiple billets are forced to be welded together. It has huge influence on metal flow and weld quality. In the embodiment of figure 1, a die set 4 as shown in figure 5 would be used with the billet 2 of raw material being forced through the containers of the block 3 into the upper die of die set 4 and extruded out through the upper die into the welding chamber where the extruded billets are welded together and extruded out through the exit of the die set. In the embodiment of figure 3 with multiple extrusion units there would be an upper die associated with each of the blocks, each leading to a common welding chamber in the lower die and, in operation, each block would simultaneously push through the billets into the welding chamber resulting in a faster overall production rate.

Referring to figure 4, there is shown a comparison of the present invention with a conventional wide extrusion apparatus. The apparatus and method of the present invention substantially extends the width range of the product which can be produced due to reduced extrusion force for producing a wide product when compared with a conventional single container extrusion product. The effect of the number of containers n, on the force required for operating an extruder according to the present invention (F _nd ) and the force required for conventional large container (F _D ) is shown in figure 4, when extruding AA6061 sheet material with a width (w) of 700 mm and thickness (/) of 5 mm. This is a simplified calculation to show the difference between the apparatus of the present invention and a conventional apparatus and the actual forces and dimensions of the product may differ slightly, but this shows the effect of the present invention. The diameter sum of all containers for the apparatus of the present invention is assumed to equal to the extrudate width, i.e., w = D = n d, where d and D are the container diameter for each container in the apparatus of the present invention with n multiple small containers and the conventional extruder with a single large container, respectively. As shown in figure 4, when using two small containers, the force required for the apparatus of the present invention is halved compared with the conventional design, i.e. F _nd = 6 x 10 ⁵ kN. When using five small containers, the force required for the proposed design is less than a fifth that for the conventional design, i.e. F„ _d = 2 x 10 ⁵ kN, and it keeps decreasing with increasing number of small containers.

The number of containers within the block is determined by the maximum extrusion force and the possible minimum size of extrusion container, which is related to the instability of the extruders, the amount of materials to be extruded, the length of cylinders, etc. The equipment space also has limitation on the number of containers. The number of containers cannot increase infinitely since there is a minimum size of each container. For the same extrusion product, more containers can decrease extrusion force but mean the size of container needs to be smaller. If the size of container is too small, then the corresponding extrusion stem feeding in to the welding chamber will be too thin to handle the extrusion force and the quality of extrusion welding could be affected due to low welding pressures.

An additional process of hot rolling-quenching and cold rolling could be performed after extrusion to further reduce thickness and/or to acquire a smoother surface finish, if required. These would be using conventional rolling and quenching techniques and are not described in further detail here. Alternatively, or in addition, in order to produce specific 3-D profiles, after hot rolling and quenching, cold or hot stamping, Hot Form Quenching (HFQ) could be utilised. Again, this would be done in a conventional manner and is not described in further detail here.

As will be clear from looking at the figures, and in particular by looking at figures 3 and 4, the apparatus of the present invention is very flexible in that it is straightforward to change the number of containers within the block, whether in the form of a single block or as individual containers enclosed by upper and lower bolsters. It is therefore simple to extrude metal or alloy material of a range of widths, from small (for example 100mm wide) up to large wide sheets (for example, up to 5000mm wide or even wider). Similarly, a range of thicknesses of extruded sheet can be produced by the apparatus and method of the present invention, for example from thin sheets of 1mm thickness or less up to thick plate type shapes of 25mm or more can be produced.

While cylindrical containers and billets are preferred, the present invention could also use containers and billets of different shapes, for example triangular, cuboid, pentagonal, hexagonal, heptagonal, octagonal or star shaped. Such shapes are less preferred as they have higher tooling and manufacturing costs and have a shorter lifetime as the non-uniform stress concentration weakens the container more quickly than for a cylindrical container.