Original paper(Vol.45 No.7 pp.752)

Bending strength of ceramics ground by face grinding method

Sakaida Yoshihisa; Tanaka Keisuke; Tanaka Shigenori

Abstract:The surface of the bending specimens of silicon nitride was ground by the face grinding method. Face grinding was conducted with a cup-shaped diamond wheel whose mesh size was #200/230. The feed direction of face grinding was parallel and perpendicular to the longitudinal direction of the specimen. The surface roughness of the face-ground specimen was one-fifth of that of the surface-ground specimen, when a diamond wheel with the same mesh size was used for grinding. The residual stress state was compressive at the ground surface. The depth of the compressive residual stress zone was about 25 mm. The compressive residual stress took the maximum of about 1 Gpa which was slightly smaller than that of the surface-ground specimen. When compared with the lapped specimen, the face-ground specimens had higher bending strength in the directions both parallel and perpendicular to the feed direction, in contrast to the surface-ground specimens whose strength reduced by about 200 Mpa in the direction perpendicular to the grinding direction. The reasons for the increment of bending strength for the face-ground specimens were as follows:
(1)The main griding flaw induced by face griding was in the plane which was formed between the feed direction and the rotating direction of wheels, so that the grinding flaws were hardly remained in the face ground surface. (2)The compressive residual stress contributed directly to the increment of bending strength of the face-ground specimens, because the size of grinding flaws was smaller than the depth of the compressive residual stress zone.
It was concluded that the face grinding method was recommended for machining of ceramics, because of high efficient machining and a high quality of finished surfaces.

Key Words:ceramics, face grinding method, fracture strength, residual stress, grinding flaw, X-ray stress measurement