T 1270/08 04-08-2009

Reasons for the Decision

1. The appeal is admissible.

2. Inventive step

2.1 The Board agrees with the undisputed view of the Opposition Division that document D5 represents the closest prior art. This document discloses a method according to the preamble of claim 1 of the patent in suit, namely (see Figs. 2 and 7) a method of manufacturing a composite body having a welded zone at which two members are joined by welding, comprising the steps of arranging said members edge-to-edge for welding so that said two members, where the welded zone is to be formed, have first surfaces (lower surfaces) and have second surfaces (upper surfaces) at the opposite side of said members from said first surfaces, said first surfaces being, as seen in cross-section across the zone to be welded, co-linear with each other across the zone to be welded; performing a friction stir welding process by inserting a friction stir welding probe (tool) into said members at said second surfaces (upper surfaces) thereof, so as to unite the two members by forming, in said friction stir welding process, a welding bead. D5 further discloses (see Fig. 7a) the features of the characterizing portion of claim 1 according to which said welding bead which is formed extends through said members from said second surfaces (upper surfaces) thereof to said first surfaces (lower surfaces) thereof, and said first surfaces (lower surfaces) provide a flat surface after the friction stir welding, as seen in cross-section across the welded zone; and in that said first surfaces (lower surfaces) provide in the welded composite body an exterior face of the body at the welded zone (this feature relates to the intended use of the composite body and the lower surfaces of the welded body shown in Fig. 7a of D5 are suitable for forming the exterior face of a - generally defined - composite body).

2.2 The subject-matter of claim 1 differs from the known friction stir welding method in that each said member has on said second surface thereof a raised portion acting as a material flow compensation portion at its edge at which the member is to be welded, said friction stir welding probe entering said raised portions so that a gap between the members is filled by flow of material.

2.3 In accordance with the wording of claim 1, these distinguishing features have the effect of filling the gap between the members. The distinguishing features moreover have the effect of reducing the formation of a sink at the weld bead, corresponding to the volume of lost material that has flowed down by the downward force exerted by the friction welding probe (see par. [0004] and [0024] of the patent in suit). Thus, as correctly stated by the opposition Division in the decision under appeal, the distinguishing features obviate the inconvenient deformation of the joint region due to the downward material flow.

Accordingly, the objective technical problem solved can be generally stated as improving weld formation.

2.4 The appellant referred to documents D1 and D4. The Board agrees with the appellant that these documents deal with friction welding processes. This in fact is also the view of the Opposition Division: although on page 3 of the decision it is stated that "D1 and D4 deal with friction heating", on page 4, where these documents are discussed in more detail, the term "welding" is mentioned in respect of both of them.

As correctly stated in the decision under appeal, neither D1 nor D4 disclose a friction stir welding process, i.e. a friction welding process in which a rotating tool (or probe) having a shoulder and a projecting pin is plunged into the joint line, whereby the friction heating produced by the rotating shoulder and pin heats and plasticizes the abutting joint faces, the plasticized material is crushed by the leading face of the pin profile and transported to the trailing face by a mechanical stirring and forging action imparted by the pin and its rotation. Consequently, a weld is formed as the tool moves away (see D5, page 42, "The Principle of Operation").

In particular, as can be seen from the figures, D1 refers to a friction joining method, in which a pin (a) upstanding from a lower plate (B') is put in correspondence of a hole (Aa) in an upper plate (b), the pin is heated by means of a rotating tool (c) and the material of the pin is forced to fill the hole (Figs. 3 and 5), thereby joining the two plates. Thus not only D1 does not relate to friction stir welding; it also does not relate to edge-to-edge welding.

As regards D4, it discloses a method of friction welding the ends of tubing or abutted portions of sheets or plates by friction welding (see Figs. 3 to 6 and col. 5, lines 38 to 44 and col. 6, lines 62 to 65). In the embodiment of Fig. 5, D4 discloses the use of a tool shown as a mandrel (87) which is positioned and moved so that the nose end (88) thereof is brought to bear against both pieces (12a, 12b) to be welded where they abut each other and rotated at high speed while compressively engaging the assembly to generate sufficient heat to cause melting of the material of both members adjacent the abutted interface (see col. 6, line 62 to col. 7, line 23). The tool is not plunged into the joint line and therefore the process according to the embodiment of Fig. 5 is not a friction stir welding process. Furthermore, D4 does not disclose the provision of raised portions acting as material flow compensation portions on the surfaces of the members to be welded together. It is true that Fig. 3 shows abutted tubing flared portions (77 and 79), but these are the portions to be welded together and moreover the weld does not extend (see Fig. 4) up to the internal surface of the abutted parts.

Therefore, neither D1 nor D4 include any indication that would suggest to the skilled person the claimed solution to the technical problem of improving weld formation in friction stir welding of members arranged edge-to-edge for welding.

2.5 In its statement of grounds of appeal the appellant also referred to documents D2 and D3, however only in respect of the dependent claims. As correctly stated by the Opposition Division, these documents are not relevant to the solution of the technical problem underlying the patent in suit because they do not disclose the provision of raised portions at the edges of members to be welded as the source of filling material. In fact, D2 and D3 go in a different direction because they teach that the filling material is obtained from one of the workpieces that are joined. D3 discloses (see Abb. 2) that the extremity of a partition wall (11) or (see Abb. 3) the extension of profiles (13) can provide material for filling a gap between two plates (9, 9) to be welded (see page 2, lines 101-118). A solution similar to that of D2 is shown in D3, where an additional T-profile is inserted between two plates to be welded (see the independent claim and figures).

2.6 It follows from the above, that the subject-matter of claim 1 and that of dependent claims 2 and 3 involves an inventive step (Article 56 EPC 1973).

3. Procedural issue

For the sake of completeness, the Board notes that the statement of grounds of appeal (page 2, first paragraph) includes, in addition to the arguments contesting the reasoning of the Opposition Division in the decision under appeal, a submission according to which the decision of the Opposition Division was identical to the provisional opinion set out in the communication dated 13 December 2007 and a thorough discussion of the issues could not take place during the oral proceedings before the Opposition Division. Although it is not clear whether with this submission the appellant intended to make an allegation that a substantial procedural violation had been made, the Board has considered this possibility. In the Board's view, if it was the appellant's intention to make such an allegation, then the allegation must be rejected as unfounded, because the appellant has neither indicated what facts and arguments that were clearly central to his case and which might speak against the decision taken have been completely disregarded in the decision under appeal (see e.g. T 763/04, point 4.1), nor indicated why a thorough discussion of the issues did not take place during the oral proceedings. In fact, it appears from the minutes of oral proceedings, that have not been contested by the appellant, that the opponent was given the possibility of discussing inventive step and in particular of explaining why D1 to D4 were relevant to inventive step when taken in combination with D5.