Grinding the sharp tip in thin NiTi and stainless steel wires

This paper investigates the grinding process to generate the sharp tip of thin nickel titanium (NiTi) and stainless steel (SS) wires, which are commonly used in medical device applications. The large deflection of thin wires and variation of forces during grinding a 15 degrees bevel angle tip are studied experimentally using the cubic boron nitride (CBN) and silicon carbide (SiC) wheels, respectively. During grinding, as the wire length gradually decreases and the stiffness increases, the wire deflection generally reaches a peak value and then gradually decreases. The results show that CBN grinding has a lower (about 1/3 - 1/2) grinding force and smaller (about 1/4 - 1/3) wire deflection than that of the SiC. Compared to SS wire, the NiTi exhibits a larger grinding force and wire deflection, lower surface roughness, and the breakage of wire at the collet chucking location using the SiC wheel due to the high stress induced phase transformation and brittle fracture. The grinding forces and wire tip deflection have large effects on the contact length and grinding time. A model based on the measured grinding forces as the input is developed to estimate the wire deflection and grinding time. This model is validated with experimental measurements and the effects of burr formation and NiTi phase transformation on grinding time are discussed. (c) 2012 Elsevier Ltd. All rights reserved.