The present invention relates to a structural member made out of an extrudeable material, in particular aluminium or an aluminium alloy. Further the invention relates to a method and a tool for producing such a structural member and the use of same. The method involves a combined extrusion and pressing operation. More particularly, the method involves producing structural members by hot impact extrusion. In accordance with the method, it is possible to produce hollow section profiles having an integrated flange at one end. Flanged structural members can be applied in the automotive industry, such as front-/rear longitudinal side members as well as crashboxes in vehicles.

US patent 5,893,436 discloses a one piece aluminium pressure tube with rod guide for shock absorbers. The pressure tube is made in one piece comprising a hollow section provided with an inwards directed flange at one end where the flange comprises a centrally extending bore serving as rod guide. The manufacturing process is not disclo- sed. One way of making such components could be to start from one-piece extrusion of the hollow section while machining the press rest to the desired shape.

Manufacture of structural members in aluminium incorporating flanges may involve extrusion of the hollow section while the flange which is cast is welded on the hollow section. This way of manufacturing members involves several different production steps and result in expensive components.

In accordance with the present invention it is now possible to produce components such as flanged structural members in one integrated pressing process. The pressing of the profile sections gives improved mechanical and metallurgical properties comparable to extruded sections, however, there is no extrusion weld and deviations in wall thickness are significantly smaller due to higher stability of the mandrel. The end of the pressing cycle can be compared with a forging operation, providing stable and. favourable

mechanical and metallurgical properties compared to casting. The grain structure in the transition from flange to profile section follows the direction of material flow in the process, thus representing an optimum for most loads. The one piece design enables reduced weight compared to assembled components.

In the following the invention will be further described by figures and examples where : Fig. 1 shows a structural member comprising a hollow section and a flange, Fig. 2a shows a upper and a lower tool part to be driven by a press and a blank, where the press is in production mode, Fig. 2b shows the same as in Fig. 2a, where the the press operation is terminated and the upper and lower tool parts have been separated, Fig. 3 shows a lay-out diagram of a hot impact extrusion facility Fig. 4 shows in part the left side of Fig. 2a, where the lower tool part includes a pusher.

Figure 1 discloses a structural member 1 comprising a hollow section 2 and a flange 3 at one end. The flange may comprise a mounting hole 4. The member is preferably made out of an aluminium alloy, for instance 6000 or 7000 or other alloys with similar extrude- ability. The member is produced in the press operation as shown in Figure 2a.

In Figure 2a, the blank stock 23 is provided as a plate that may be produced by extrusion and further comprises a hole which describes the inner contour of the hollow section.

The hole may be formed by a punching operation. The blank stock is heated up to about solution temperature before the press operation. The blank stock is then placed in the lower tool part 21 which comprises a cup 22 with a hole 24 describing the outer contour 25 of the hollow section 2. As the upper tool part 20 is lowered, the mandrel 26 protru- des through the hole in the blank 23. As the upper tool 20 is moving further downwards, the blank stock 23 is subjected to pressure, and the material is forced to flow through the gap 27 between the upper tool mandrel 26 and the lower tool hole 24. The upper tool further comprises a radial extending surface 28 which co-operates with the radial exten- ding surface of the cup 22. Between these two surfaces the flange of the-member is

formed. These surfaces may be contoured and provided with recesses or projections, to produce the final or semi-final net shape of the flange. Such details may for instance comprise a mounting hole 4, as shown in Figure 1.

In Figure 2b, the press operation is terminated and the upper and lower tool parts 20,21 have been separated, and the structural member 1 is given a net shape with flange 3 and hollow section 2. It should be understood that the tool parts may comprise means for forcing out the member following the pressing operation, see Fig. 4 which discloses in part the left side of Fig. 2a. Such means may comprise one or more pushers arranged in appropriate surfaces of the tool parts. For instance may valve-shaped pushers 50 be arranged in the lower tool part 21, in the radial surface 22 thereof, to force out the member after pressing. In the Figure, the upper tool part is indicated at 20. This kind of pushers may comprise a valve 51 and a seat 52 arrangement similar to that of combustion engines, which will ensure a good sealing capability at high pressures. The stem of the pusher 50 may be driven by appropriate means, to ensure an operation co-ordinated with the press cycle.

Features can be integrated in the flange, by giving the tool halves a negative shape of the desired flange geometry, see Figure 1 where the flange comprises a mounting hole 4. In the member, the grain structure in the profile (hollow) section will be similar to that of extruded profiles. The grain structure in the flange will be similar to that of forging.

The mechanical properties will be similar to that of extruded profiles of similar alloys. In the Figure there is shown a hollow section with an integrated, open flange. Alternatively the flange could be closed, i. e. the flange close the hollow section at the flanged end. A closed flange can be provided by arranging a standing mandrel in the lower tool part, while the upper tool part constitutes of a planar surface facing the blank. Further, the blank should not be provided with a hole in this situation (not shown).

Further, in accordance with the invention it is possible to produce hollow sections having variations in wall thickness in the profile lenght. This is possible, e. g. by introducing a step in the mandrel (tapered mandrel), which establishes a larger gap between the mandrel and lower tool part at the beginning of the press cycle. As the step enters the

hole of the blank, and protrudes into the hole of the lower tool, the gap is reduced (not shown).

Both tool and blank stock must be heated, see Figure 3 which discloses a lay-out diagram of a hot impact extrusion facility. The process starts by stamping the hole through the blank in the first press 100. Then the blank is heated in a furnace 101 and placed into the hot impact extrusion tool/press 102. After quenching in a quench 103, the flash is stamped off in press 104, followed by machining in a milling machine 105 and finally washing in washing machine 106. Indexes A-F represent robots or manipulators for producing a member in accordance with an automatised process. The actual pressing in the hot impact extrusion press lasts for a few seconds only, this reducing the total cycle time. The process requires lubrication of blank stock and/or tooling. The method applies relatively low pressures due to the applied heat extrusion process.

Several further applications in automotive structures are possible. In principle all T-joints will feature increased load capacity if the joint is supported by a flange on one of the components, caused by increased interface surface thus making possible longer weld or mechanical fastening. Application also sensible where tolerances must be compensa- ted in cross direction, e. g. front end module adjustments on front longitudinals. Further examples are cross-members in cabin floor, suspension support elements, etc. Applicati- ons are also possible in suspension components. Although the previous mentioned appli- cations are related to automotive components, it should be understood that structural members in accordance with the invention may have other fields of use for instance aviation, construction and all other fields of use where such members may have a compe- titive advantage.

The applicability of the member is proved for longitudinals through FE analysis and crash tests, crash boxes will feature similar functions as folding crashboxes assembled from hollow section profile (or sheet) and plate.