The present invention relates to a method of joining profiled members into structural units, and more specifically to an improved snap type connection method, applied members and the resulting structural units provided by such method.

The so-called snap connection principle has been known and applied for several decades now to build larger structural units like panels, side boards etc. DE 1140330 discloses one embodiment of such structural unit based on a resilient interlocking of abutting complementary shaped edges of connected members by means of projecting tabs and engaging recessing grooves, respectively. Additionally, a loose fit locking bar is inserted extending transversely inwardly between the frictionally engaged resilient tabs to secure the connection against unlocking.

However, in the case of exposure to larger loads or forces it is often necessary and customary to apply some further connection principle like e.g. screwing/bolting, (spot) welding or gluing. Different drawbacks are connected to the use of such connecting methods like local material weakening due to perforating and temporary heating of members, or in the case of gluing there are rather strict requirements to clean surfaces and considerable drying/curing time is involved. Generally, these methods are characterized as complex and time-consuming, something which influence negatively the cost of joining.

It is therefore a principal object of the present invention to provide a new method of joining profiled members avoiding the above difficulties resulting in simple and strong connections based solely on mutual interlocking engagement of the members.

This and other objects are achieved by provision of suitable special profiled members and a new method of joining as it appears from the characterizing parts of the attached patent claims.

The invention will now be described in details in connection with preferred embodiment(s) referring to the accompanying drawings, Figs. 1-5, where

Fig. 1 shows schematically in a cross-sectional view a configuration of abutting edge regions of two profiled members to be joined,

Fig. 2 illustrates schematically the first step of the joining process,

Fig. 3 illustrates the subsequent joining step and the resulting connection between the profiled members,

Fig. 4 shows in enlarged cross-sectional view details of a joint area, and

Fig. 5 shows a structural unit comprising a plurality of joined members.

Referring to Fig. 1, the basic profiled members 1,2 are shown in a transversal cross-section as elongated hollow shapes extruded of light metal material, e.g. aluminium or Al-alloy, having central portions 10,20 reinforced by transversal partition walls 13,23 and longitudinally extending edge portions 14,24 being mutually complementary shaped to ensure an interlocking connec¬ tion between the members when abutted and forced into an engagement. The edge portion 14 of the first member 1 is provided with two parallel longitudinally extending ribs 15 terminating slightly convergating walls 11,12 defining the central portion 10 of the member 1. The ribs 15 are configurated as lateral undercut recesses 17 in the shape walls 11,12 and ^' adjacent outwardly protruding tabs 18.

The edge portion 24 of the second member 2 orientated in facing relation to the edge portion 14 of the first member is provided with locking tabs 25 transversely projecting into a slot 26 defined by a transverse wall 27 connecting the substantially parallel walls 21,22 of the central portion 20.

The ribs 15 are further integrally connected to each other by a transversely extending web 16 being co-extruded with its length larger than the perpendicular distance between the ribs and shown in the figure as a V-configurated transverse web having reduced wall thickness compared to the wall thickness of the edge portion and ribs.

The reasons for providing the first member 1 with slightly convergating walls 11,12 will be apparent from Fig. 2 illustrat¬ ing the first step of the joining process. As a result of extensive investigations it has been found out that in order to ensure a strong connection between the mebers care must be taken to avoid/minimize the creation of any substantial friction between the respective edge portions during the joining opera¬ tion. Consequently, according to the present invention the

convergating walls 11,12 allow an interference-free insertion of the ribs 15 into the slot 26 of the second member 2. A deforma¬ tion tool shown as an expansion tool 3 comprising a mandrel 31 activated by an expanding member 32 is accomodated in a holder 33 adapted to and inserted into the cavity of the first member. This arrangement allows to use the first member itself as a dolley in the following deformation of the transverse V-configurated web 16 as illustrated in Fig. 3.

The expanding member 32, e.g. a hydraulically or pneumatically operated hose, is expanded into firm contact with the surrounding walls of the holder 33 exhibiting pressure on the mandrel 31 and thus causing a gradual deformation (flattening) of the web 16 under the successive vertical movement of the mandrel 31 towards the web. At the maximum predetermina ed extension (stroke) of the mandrel 31 the web 16 is forced to bypass the perpendicular distance between the ribs 15, the ribs being pressed apart until a firm wedgelike engagement is achieved between the end portions 14,24 being complementary shaped and dimensioned to accomodate their respective tabs and recesses.

As shown in an enlarged cross-sectional view of the joint area in Fig. 4 this particular way of deforming the web 16, applying the first structural member 1 as a dolley, results in a very lenient joining method. No significant friction forces causing distortion (deformation) of the lateral walls of the slot 26 and consequent¬ ly weakening of the joint are created between the surfaces of the joined edge portions 14,24 of the structural members until a wedge frictional locking is achieved at maximum extension of the deformed web 16.

The web 16 is further optionally provided at its opposite lateral edges with longitudinally extending grooves 19 to ensure a complete control of the deformation process. The resulting

superior strong joint is thus not primarily based on the inherent resilient back pressure from the ribs 15, but on the locking pressure exhibited by the permanently deformed web 16. Measure¬ ments of stretch strength conducted on the load bearing structure resulting from joining of profile members according to the above method show that the actual burst (rupture) occurs outside of the joints.

Such bearing structure unit embodied as a floor structure 5, e.g. for a vehicle, is shown in Fig. 5. A plurality of profile members 1,2 being connected and interlocked according to the above described principle extend e.g. between two side profile members having a cross-sectional configuration adapted to the purpose/- function of the actual structural unit (not shown in the Figure) .

The above described deformation tool is advantageously applied as handling means for the structural members, something which simplifies significantly the assembling of the members.

The scope of the present invention is not limited to the ilus- trated and described specific embodiments. Modifications may be made to the invention without departing from its spirit. Thus, e.g. the transverse web could have an arcuated configuration instead of the shown folded V-like shape and the elongated basic profile member can be provided with a central portion constituted by a single wall instead of the shown hollow shapes. Rolling means, instead of the shown mandrel 31, can also be used as deformation tool 3.