| The first part of this study dealt with tool wear of Carbide and Polycrystalline Diamond (PCD) inserts for machining Graphite/Epoxy (Gr/Ep) composite materials. Two different cutting modes, continuous and interrupted, were applied for carbide inserts under dry cutting conditions. In the interrupted cutting mode, a wave form of flank wear was observed with one third peak-to-peak value of one-ply thickness. In the continuous cutting mode, severe nose wear and rounding of cutting edge wear was observed due to the high temperature around the nose region, which accumulated heat on the cutting edge. Heat generation was found to influence the carbide life both under continuous cutting and interrupted cutting modes.; The flank wear of PCD inserts was below 100 {dollar}mu{dollar}m for 60 minutes of cutting time, whereas that of carbide inserts exceeded 300 {dollar}mu{dollar}m within 5 seconds of cutting time. Therefore, it was found that PCD inserts have excellent tool life when compared to carbide inserts. Based on these experiments, flank wear models were constructed to predict tool life for given cutting conditions.; The second part of this study dealt with orthogonal cutting characteristics of machining unidirectional and laminate Gr/Ep and unidirectional model Carbon Fiber Reinforced Plastic (CFRP) composites. Chip formation, cutting force, and surface morphology were considered as cutting characteristics. Powder-like chips for Gr/Ep composites and ribbon-like chips in small depths of cut for CFRP composites were observed. Chip formation was found to be dependent on fiber orientation. Four common fiber orientations, 0{dollar}spcirc,{dollar} 45{dollar}spcirc,{dollar} 90{dollar}spcirc,{dollar} and {dollar}-45spcirc,{dollar} had different cutting mechanisms of chip formation. Bending, peel fast fracture, and fracture perpendicular to the fiber direction were the general cutting mechanisms for the 0{dollar}spcirc{dollar} fiber orientations when machining unidirectional and laminate composites. Cutting and shearing along the fiber direction were found for the 45{dollar}spcirc{dollar} fiber orientations when machining unidirectional and laminate composites. Little bending of the end of the 90{dollar}spcirc{dollar} ply, as if a positive ply, accompanied cutting when machining laminates. Shearing with in-depth damage, fiber pullout, debonding fibers, and interlaminar cracks, were dominant for the {dollar}-45spcirc{dollar} ply when machining laminates.; Fluctuation of the cutting force for the 0{dollar}spcirc{dollar} fiber orientation and laminate composites was also evident for chip formation mechanisms for the 0{dollar}spcirc{dollar} and {dollar}-45spcirc{dollar} plies. Cutting force prediction models were constructed for principal and thrust cutting directions. Surface quality was found to be dependent on the fiber orientations. Matrix smearing was dominant on positive fiber orientations, but bare fibers with scarp and cusps are usually found in the 0{dollar}spcirc{dollar} fiber orientation. Average surface roughness (R{dollar}sb{lcub}rm a{rcub}){dollar} and maximum height roughness (R{dollar}sb{lcub}rm y{rcub}){dollar} were not adequate for indicating surface quality of laminates because of different material removal mechanisms compared to isotropic materials. |
