wall 25 it is this entrance angle 24 which presents the problem as can be plainly seen if the part is removed from the fixture and the flange trimmed flush with the outside wall 26 the structure may separate because of a void formed by the angle 24 the object of this invention is to make certain that this void does not occur fig2 shows a structure quite similar to that of fig1 except that the engaging upper and lower surface of the fixture 21a is shown relieved at 23 to increase pressure the surfaces are sloped inwardly and doubler material 27 is inserted between the inner surface of the two inside sheets 16 and 17 the location of the doubler or the slope is not critical however two things are critical i e there must be sufficient material to be upset forged to fill the noted void and sufficient forging pressure a single doubler may be used between the inner sheets as shown in fig2 or two doublers may be used one each between the inner and outer sheets as shown in fig5 in fact the two doublers as shown in fig5 is the preferred embodiment for the four sheet process because the inner sheets are welded together in a pre determined pattern to establish the webs 18 and it eases the task to place the doublers 27a between the inner and outer sheets also while the surfaces of the fixture 21 and 22 may be square to the vertical walls of the fixture if the surfaces are canted or the wedge tapered a force is created forcing the upset forged material into the cavity.