Nowadays, dieless and flexible sheet forming methods are gaining much interest in prototyping and low production. In this research, a new method is developed to change the cross-sectional area of metal tubes in a longitudinal direction without using special dies. This technique is based on the force applied by a rotary tool to the inside/outside surface wall of a tube. The forming tool is mounted on a CNC milling machine and moves spirally with a specific pitch. In order to study the effects of process parameters on the product quality, a full factorial design of experiments was designed and performed. The input parameters were the feeding depth, forming pitch and tool velocity. Three responses including roughness, minimum thickness and production time were precisely measured for this purpose. The results showed that surface quality and minimum thickness is reduced with increasing the forming pitch and feeding depth. Tool rotational velocity does not have a significant effect on the forming parameters except for production time. Using a multi-objective response optimization, forming pitch of 0.25 mm, feeding depth of 1.25 mm and velocity of 800 mm/min were found to be the best configuration. پرونده مقاله