OPTIMIZATION OF CUTTING EDGE GEOMETRY OF DRILLS IN DRILLING DIFFICULT TO CUT MATERIALS

1.对于具有人工控制刀屑接触长度的大负前角刀具或具有自然刀屑接触长度的刀具的切削，给出了变形模式近似于粘性不连续线的切削模型。两种切削模型均能较好地解释主前刀面含死金属切屑形成过程的过渡。即使在切削液供应充足的低摩擦条件下，前刀面上的死金属也不会消失。2.对于三前刀面切削，即倒角刀面和二次前刀面，在人为控制刀-屑接触长度的条件下，建立了考虑沿着切削刃的平动速度的三维斜切削模型。用快速止动装置进行了冻结切屑形成的实验，发现在50°倾角范围内，死金属继续存在。3.根据用能量法测得的平头前刀面钻削切削力等数据，用有限元法计算了切削温度。在钻削不锈钢SUS 304（JIS）时，长节距切屑的形成，在主切削刃的外缘和内缘处会出现高温区。4.用高速钢或烧结硬质合金钻头钻削不锈钢SUS 304（JIS）时，通过试验发现，要获得较长的刀具寿命，最佳条件是倒角部分的前角（一次前角）; -15 〜 -30°，二次前角面投影长度; 0.3〜 0.7倍进给速度（高速钢）、0.15〜0.3倍进给速度（烧结碳化物）和总投影刀屑接触长度;约1.4倍进给速度。

1.FOR CUTTING WITH LARGE NEGATIVE RAKE ANGLE TOOLS HAVING ARTIFICIALLY CONTROLLED TOOL-CHIP CONTACT LENGTH OR WITH THAT TOOLS HAVING NATURAL TOOL-CHIP CONTACT LENGTH, CUTTING MODELS IN WHICH THE MODE OF DEFORMATION IS APPROXIMATED WITH THE VELOCITY DISCONTINUITY LINES ARE DEVELOPED. THE CUTTING MODELS ARE ABLE TO EXPLAIN THE TRANSITION OF CHIP FORMATION PROCESS INVOLVING DEAD METAL ON THE PRIMARY RAKE FACE IN TWO MODELS. THE DEAD METAL ON THE RAKE FACE DOES NOT DISAPPEARED EVEN IN LOW FRICTIONAL CONDITION WHERE CUTTING FLUID IS SUPPLIED SUFFICIENTLY. IT IS FOUND THAT PREDICTED RESULTS ARE IN GOOD AGREEMENT WITH EXPERIMENTAL RESULTS.2.FOR CUTTING WITH TOOLS HAVING THREE RAKE SURFACES, THAT IS, CHAMFERED EDGE AND SECONDARY RAKE FACE WITH ARTIFICIALLY CONTROLLED TOOL-CHIP CONTACT LENGTH, THREE-DIMENSIONAL OBLIQUE CUTTING MODEL CONSIDERING TRANSLATIONAL VELOCTY ALONG THE CUTTING EDGE IS DEVELOPED. EXPERIMENTS USING QUICK STOPPING DEVICE TO FREEZE THE CHIP FORMATION WERE MADE, AND IT IS FOUND THAT THE DEAD METAL CONTINUES TO EXIST IN THE RANGE OF 50° OF INCLINATION ANGLE.3.BASED UPON THE DATA SUCH AS CUTTING FORCES OBTAINED THROUGH ENERGY METOD FOR DRILLING WITH FLAT RAKE FACE DRILL, CUTTING TEMPERATURE IS CALCULATED USING FINITE ELEMENT METHOD. FOR LONG-PITCH CHIP FORMATION IN DRILLING STAINLESS STEEL SUS304(JIS), HIGH TEMPERATURE REGIONS APPEAR IN OUTER PORTION CORRESPONDING TO MARGIN AND INNER PORTION OF THE MAIN CUTTING EDGE.4.FOR DRILLING STAINLESS STEEL SUS304(JIS) WITH DRILLS OF HIGH SPEED STEEL OR SINTERED CARBIDE, IT IS FOUND FROM EXPERIMENT TO GIVE LONG TOOL LIFE THAT THE ADEQUATE CONDITION IS RAKE ANGLE OF CHAMFERED PORTION (PRIMARY RAKE ANGLE) ; -15 〜 -30°, PROJECTED LENGTH OF SECONDARY RAKE FACE ; 0.3〜O.7 TIMES FEED RATE(HIGH SPEED STEEL), 0.15〜0.3 TIMES FEED RATE(SINTERED CARBIDE) AND TOTAL PROJECTED TOOL-CHIP CONTACT LENGTH ; ABOUT 1.4 TIMES FEED RATE.