Formability and Dimensional Accuracy Enhancement with Controlled Tool Rotational Speed in Stretch Forming Process.

We present a new stretch forming method for axisymmetric sheet metal parts production. A test bench is designed, fabricated, and mounted on a drilling machine. The blank is fixed rigidly around its periphery in the apparatus, and the forming tool is mounted on the machine spindle. Thus, the control of tool rotational speed, feed rate, and vertical motion from the upper sheet surface becomes possible. Experimental tests are then conducted to form a reference shape. Rotational speed, feed rate, lubrication effect on the final thickness distribution, and geometric profiles are studied. A new multi-pass forming method is also developed and verified. The feed rate decrease, within the range of 0.11–0.18 mm/rev, reduces the sheet thinning, while its increase improves the dimensional accuracy. The rotational speed increase, within the range of 112–710 rpm, reduces the thickness, while its decrease enhances the geometrical accuracy. Mineral oil seems to be more effective than greases, so the thickness drop is reduced and the dimensional accuracy is improved. The use of the multi-pass strategy avoids the sheet cracking at great forming depth. The decrease in step size, within the range of 0.3–1 mm, reduces the thickness minima, while good dimensional accuracy can be obtained in the range of 0.5–1 mm. [ABSTRACT FROM AUTHOR]