Understanding the structure and cutting mechanism of shaver blades: A case study on articular cartilage

Mechanical shaver blades have been used in minimally invasive knee arthroscopy surgery for nearly 50 years, however, the tooth structure and cutting mechanism of shaver blades were less reported. This paper designed several shaver blades (triangular tooth/TT, circular tooth/CT and convex arc tooth/CAT), defined the cutting edges and angles of the original shaver (OS) and proposed a newly designed shaver (NDS) with a positive secondary rake angle to optimize cutting performance. The cutting process and theoretical model of the OS and NDS were analysed from 2D and 3D perspectives. A comparative experimental analysis of cutting performance, including cutting force, surface roughness, and groove geometries, was carried out to verify the influence of tooth structures and secondary rake angle. The results showed that the tooth of the OS has three different cutting edges, among which the secondary cutting edge sited at the tube section contributes to the puncturing process, and the primary cutting edge located on the outer wall of the tube participates in the oblique cutting process and finally removes the soft tissue. The cutting process of the secondary cutting edge of NDS has been changed from puncturing to oblique cutting, therefore, only the oblique cutting exists throughout the shaving process. This makes the shape and quantity of the chips of OS and NDS different, which has been verified by experiment. The cutting performance of CT was superior to that of TT and CAT, highlighting the importance of tooth roots in the cutting process. Positive secondary rake angle significantly improved the cutting performance of CAT, but not that of TT with a small profile angle (30°) and CT, which means both the puncturing and oblique cutting play important roles. Not all the positive secondary rake angle was helpful to the cutting process and 30° and 45° were suggested.