tailieunhanh - Handbook of Advanced Ceramics Machining Episode 4

Tham khảo tài liệu 'handbook of advanced ceramics machining episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 76 Handbook of Advanced Ceramics Machining FIGURE Specific grinding energy versus undeformed chip thickness Norton 400 grit diamond wheel . energy for material removal by brittle fracture. That portion of the grinding energy associated with brittle fracture can be estimated as the product of the surface area generated by fracture and the material s fracture energy per unit area 51 . For simplicity the particles removed by grinding can be assumed small cubes of dimension bf. In this case the total surface area produced per unit volume of material removed af is equal to the total surface area of a cube divided by its volume 6b 6 af n3h b bf 3 25 Mechanisms for Grinding of Ceramics 77 FIGURE Specific grinding energy versus undeformed chip thickness Norton 180 grit diamond wheel . Approximating the fracture surface energy as half the critical energy release rate Gc Gc Kc2 E for crack formation two surfaces the specific energy due to fracture becomes Uf GA 3Gc j af V The smallest particles removed by grinding are approximately 1 mm in size although many are much larger. For HPSN Gc 80 J m2. Using these values for bf and Gc leads to a specific fracture energy Uf J mm3 which is only a negligible portion of the extrapolated minimum grinding energy for 78 Handbook of Advanced Ceramics Machining HPSN. This same argument would also apply to all the other workpiece materials as listed in Table with the possible exception of RBSN. Therefore most of the grinding energy must be expended by ductile flow even though material removal is mainly by brittle fracture. Plowed Surface Area Analysis SEM observations reveal characteristic grooves and a heavily deformed layer on the ground surface. The generation of this deformed surface layer is apparently related to plowing by numerous abrasive points passing through the grinding zone thereby leading to surfaces with multiple overlapping scratches and grooves. Therefore it might also be worthwhile to analyze