The present invention relates to a method and a joint for joining structural elements of a plastic defor able material, e.g. aluminium, with one of the structural elements having a male portion for insertion to engagement in a female portion of the other structural element.

The invention was especially developed for joining extruded aluminium profiles, but it may obviously be used generally for joining structural elements which are made from a plastic deformable material. Even though the invention finds special application for extruded profiles, the invention may also be used for profiles which are not extruded. The invention may be used for joining structural elements, e.g. for building scaffolding, banisters, framework, trusswork, etc.

Structures like scaffolding of aluminium with welded joints have proved to have a tendency to crack due to fatigue when used for some length of time. Welded connections will often be undesirable from an aesthetic point of view, and welding operations being time consuming they are also undesirable as regards costs.

It is an object of the invention to avoid welded connections of structural elements and to replace such connections by joints which are not subjected to fatigue, are aesthetically attractive and permit the joining operation proper to be performed rapidly.

According to the invention this is achieved by a method of the above mentioned kind, accordning to which joining occurs by the aid of a punching press means, and which is charac¬ terized by the fact that the female portion is partly cut through into discrete areas to form partly cut out recessed

members, said recessed members concurrently being upset .and pressed with a wedging effect towards at least one reaction surface on the male portion.

Thus a joint of the above mentioned kind is provided, which is characterized by the fact that one of the structural elements has at least one engaging surface and at least one reaction surface, and that the second structural element has at least one engaging surface for engagement with the engaging surface of the first structural element, and at least one recessed member for wedging cooperation with the reaction surface(s) said elements being locked in a clamped state.

Further features of the invention will appear from the dependent claims.

Other and further objects, features, and advantages will appear from the following disclosure of an embodiment of the invention which is preferred at present .and is described to Illustrate the invention without being limiting, and given with reference to the appended drawings, in which:

Figure 1 shows the finished joint according to the invention for joining structural elements;

Figure 2 shows both structural elements according to Figure 1 before one is inserted into the other;

Figure 3 is a sectional view through one of the struc¬ tural elements, in which some critical angles are marked;

Figure 4 is a sectional view through the joined struc¬ tural elements with a diagrammatically shown punch press means;

Figure 5 shows structural elements with a shape that differs from the shape shown in Figures 1-4; and

Figure 6 shows the structural elements according to Figure 5 in a finished joint.

With reference to Figure 1, two different structural elements 5, 10 are shown, which are connected to form a finished joint 1. The basis of joint 1 is that one structural element 5 has a male portion 8 which is intended for insertion into a female portion 9 in the second structural element 10, as will appear from Figure 2. The structural element 10 has an engaging surface 3 which is intended for abutment against engaging surface 6 of the other structural element 5. Before the final joining of structural elements 5 and 10 it is necessary to ensure that engaging surfaces 3, 6 are in tight mutual abutment. As shown in Figure 2, the structural element 5 may in the shown embodiment consist of a cut-off length of an elongated extruded profile. In this manner the male portion 8 may obtain its desired shape in a simple manner and without secondary treatment. Thus grooves formed by surfaces 7 and 2 are, shaped immediately during continuous extrusion. In order to save weight and material, the male portion 8 may be formed with one or a plurality of voids 11. The structural element 10 may be an extruded standard profile, e.g. having a rectangular or square cross section and a suitable thickness. A square profile may be provided with rounded off internal and external corners. The internal corners may be recessed hollow keys. It should be understood that the cross sectional shape of male portion 8 perpendicular to the section of profile is complementary with the internal shape of structural element 10.

Figure 3 is a sectional view of a structural element 5, 1. e. Its section of profile. The longitudinal axis of the profile is designated A. In the intersection line of reaction surface 7 and surface 2 a normal N Is orthogonal on axis A. The angle α between surface 2 and the normal N may advantage¬ ously be in the range of 45° - 80°, and is preferably approximately 70°. Angle β between the reaction surface 7 and the normal N may advantageously be in the range of 5° - 45°, preferably it is approximately 20°.

Figure 4 shows a sectional view of the joined structural elements 5, 10 when inserted into a punch press means 15 comprising die block means 16, which are movable towards and away from structural elements 5, 10. Cutting and stamping punching tools 14 are mounted on the surface of blocks 16 facing the structural elements 5, 10. When the structural elements 5, 10 are correctly positioned in the press 15 the cutting and punching tools 14 are aligned with grooves formed by surfaces 2, 7 on the male portion 8. At the first contact with the female portion 9 of the structural element 10 the cutting and punching tools 14 will cut into and through the thickness of the profile and upset the cut out flaps or pressed-in portions 4 down into the groove which is defined by the surfaces 2 and 7. The flaps 4 which are cut out in the female portion 9 may be pressed into engagement with the inclined surface 2 on the male portion 8, although this Is not a critical condition. At the same time the front face 12 of flap 4 will press towards the inclined reaction surface 7 on the male portion 8 which will provide a wedging effect between the structural elements 5, 10 which will cause the engaging surfaces 3 and 6, respectively to be further pressed against each other. In this manner a firm and stable connection is achieved between the structural elements 5 and 10. This connection or joint 1 will resist high compression forces in particular through the engaging surfaces 3 and 6, and simultaneously resist high tensile forces through the cooperating reaction surfaces 7 and 12.

Figures 5 and 6 show another embodiment of the joint according to the invention. Parts corresponding to the embodiment of Figures 1-4 are designated by the same reference numerals which are, however, marked. As will appear from Figure 5, the method and the joint for connecting structural elements of a plastic deformable material are used to join profiles of a substantially circular cross section. The structural element 5' has a male portion 8'

which is intended for insertion into the female portion 9' of the other structural element 10'. The structural element 5' is inserted into the structural element 10' to provide contact between the engaging surfaces 3' and 6' on respective structural elements. Upon insertion the structural elements 5', 10' are, as mentioned above, conveyed to a press (not shown) for punching out recessed members 4' and upsetting the same, preferably Into contact with the surfaces 2' on the male portion 8' and to provide wedging cooperation between the reactions surfaces 7' and 12'. After joining the joint will be rigid as regards buckling due to the guiding of the male portion 8' inside the female portion 9'. The joint 1' will be able to resist both high compression forces and tensile forces.

It will appear from the above disclosure that the joint may be used to connect structural elements of variously shaped profiles, and it may be used for ordinary longitudinal extension, as indicated in Figures 5 and 6. Furthermore, it should be understood that any suitable cross sectional shape of the profile is possible, e.g. be triangular, square, hexagonal, or generally polygonal, elliptical, oval, or desired shape in addition to the shown rectangular and circular cross sectional shapes.

As mentioned, the invention was in particular developed for structural elements of aluminium, but it may, obviously be used with other materials which are plastic deformable, e.g. steel, copper, brass, and various alloys. It may also be used with materials of plastic, if desired with a subsequent hot- sealing operation.

It should also be understood that the number of recessed members may be from one, but is preferably two, or more. The longitudinal extent and width of the recessed members may obviously be adapted to the application of the structural members. If the structural members 5, 10 or joint 1 will be

subjected substantially to compression forces, the number of recessed members may be few, optionally said members may have a relatively small width. If the joint 1 is to be subjected substantially to tensile forces the number of recessed members 4 may be more, but the percentage of cut through area should not be higher than half of the total cross sectional area.