Forming method and characteristics of coiled spring in small coil diameter and with high rectangular ratio in winding wire cross section

Abstract

This paper presents a new forming method of a coiled spring which is used as a forceps manipulator of a surgical robot. Joint parts of forceps manipulator are required to be “easy to bend and strong to twist”. This demand is fulfilled by using coiled springs with high rectangular ratio in winding wire cross section. However, the coiled springs are conventionally expensive as they are fabricated by machining. This study proposed a new and inexpensive forming method for fabrication of the coiled spring with high rectangular ratio in the wire cross section. In this method, the coiled spring with circular shape in the winding wire cross section is compressed in the coil axial direction by upsetting, and then the rectangle ratio of the wire becomes high. The coiled spring with a high rectangular ratio of 3 was obtained by the proposed method. In addition, a numerical analysis and an experiment were conducted for evaluation of the formed coiled springs in terms of tensile, torsional, and bending characteristics. The formed coiled springs were easy to bend and strong to twist from results. Moreover, the elastic limit of the formed coiled springs improved due to work hardening by upsetting.