and 6 it should be noted that the joining procedure not necessarily open the die cavity as much as shown in fig9 and could be finalized before the deformed material in the joint touches the support elements 203 experiments have shown that an efficient clamping of the sheet formed members as close as possible to the centre of the joint will contribute to greater strength of the joint therefore the form of the support elements according to the invention is very advantageous in order to minimise the sliding of the material over the surface 210 this surface could be treated to give enhanced friction fig1 a d show in different views the embodiment according to fig7 a d additionally provided with channels 212 for compressed air in the body of the tool part 201 fig1 c and 10d show advantageous positions of the outlets 213 from the channels fig1 a d show in different views said spring element separately this element has been described in detail in relation to fig4 a d fig1 a f show an embodiment according to which the movable die elements 208 u2032 have been provided with an end stop in the form of a vertical heel formed element 215 at the rear end of the elements the heel element 215 could reach along the full width of the element 208 u2032 or part of the width as can be seen especially in fig1 b the heel element is co operating with a corresponding recess 214 in the tool part body 201 u2032 the fig1 a c show the die anvil combination in.