A STUDY OF CHIP FORMATION AND CUTTING FORCES IN DRILLING OPERATION

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1. A CUTTING MODEL TAKING ACCOUNT OF THE VARIATION OF WORKING NORMAL RAKE ANGLE, CUTTING VELOCITY AND OTHERS ALONG THE CHISEL EDGE IS DEVELOPED FOR THE CASE THAT THE CHISEL EDGE PORTION IS THINNED TO BE A UNIFORM TOOL-CHIP CONTACT LENGTH. THE MODEL INCLUDING SEVEN VARIABLES WITH RESPECT TO THE GEOMETRY OF DEFORMATION ZONE AND VELOCITIES REPRESENTS THAT THE WHOLE CHIP PRODUCED BY THE CHISEL EDGE IS TO BE A HELICAL ONE.2. A MODEL OF OBLIQUE CUTTING, IN WHICH BOUNDARY OF THE CHIP AND WORKPIECE IS CONSTRUCTED BY TWO CIRCULAR ARCS AND TRANSLATIONAL VELOCITY IS CONSIDERED FOR EXPLAINING THE DIRECTION OF CHIP FLOW, IS DEVELOPED FOR PREDICTING THE CHIP FORMATION SUCH AS UP-CURL OF THE CHIP AND CUTTING FORCES. BY SPECIFYING VALUES OF THE MEAN FRICTIONAL STRESS, FRICTION ANGLE ON THE TOOL FACE AND OF TOOL-CHIP CONTACT LENGTH, ONE SITUATION HAVING A RADIUS OF UP-CURL OF THE CHIP IS DETERMINED AS THE SITUATION TO BE REALIZED BY MINIMIZING THE RATE OF ENERGY CONSUMPTION.3. A CUTTING MODEL INVOLVING UP AND SIDE-CURL OF THE CHIP AND THE VARIATION OF CUTTING VELOCITY ALONG THE CUTTING EDGE IS ALSO DEVELOPED. IN THE MODEL IT IS ASSUMED THAT THE WHOLE CHIP FORMATION PROCESS CAN BE TREATED AS A COMBINATION OF ELEMENTAL OBLIQUE CUTTING ALONG THE CUTTING EDGE. CALCULATED VALUES OF SIDECURL OF THE CHIP CHANGE WITH THE DIFFERENCE OF CUTTING VELOCITY ALONG THE CUTTING EDGE FROM INFINITY IN OBLIQUE CUTTING TO THREE OR FOUR TIMES WIDTH OF CUT.4. CONDITIONS OF GEOMETRIC SIMILARITY BETWEEN DRILLS OF VARIOUS DIAMETERS ARE ESTABLISHED. FROM THESE AND BY CONSIDERING THE VARIATION OF SPECIFIC CUTTING FORCES CHANGING WITH RAKE ANGLES AND THE CONDITION OF TOOL-CHIP CONTACT ON THE TOOL FACE, THE EQUATIONS FOR TORQUE AND THRUST ARE DERIVED.