Abstract
By the actual use of the Stiefel-Mannesmann piercer, the authors studied the effects of piercer plug contours designed in various ways upon the piercing phenomena from the practical points of view. The variations of piercer plug contours were, with the other factors kept constant, made upon two theoretical sections, namely reducing section and reeling section respectively. The results obtained were summarized as follows:
As we changed the plug contour in reducing section from the stumpy shape (Q type) into the acute shape (O type),
(1) The dimension of tubes became larger, with a slight increase of diameter and wall-thickness, while the elongation decreasad with the increased twist of tube surfaces.
(2) While the kM/sec. remained unchanged, the kM rose sensitively.
(3) The axial moving speed of tubes increased. The authors actually discovered from the recent test that the adoption of O type instead of Q type resulted in increase of the speed equal to that obtained by expansion of the roll inclined angle by approximately three degrees.
(4) As regards the variations of strain rate in the course of piercing operation, the peak-load considerably rose and the position of the peak moved towards the outlet side owing to the unreasonable deformation in the latter half of piercing operation.
(5) Both inside and outside defects of tubes tended to be formed.
When plugs of no reeling section were used, the wall-thicknesses of tubes tended to assume undulating shapes with the aggravation of non-uniformity. As outside diameter of tubes became lessened also, the elongation rate fell. The twists of tube surfaces decreased with a slight effect on the whole. the kM/sec, kW and axial moving speed fell. The highest strain rate in the course of piercing operation somewhat decreased and the distribution phase became sharp. Sensitive effects were seen upon the formation of inside defects of tubes. Especially defects tended to be formed when round billets were of inferior quality. Almost no effect upon outside defects was observed, but the defects still tended to increase.
