ANALYSIS OF MECHANICS OF CHIP FORMATION WITH TOOLS HAVING LARGE NEGATIVE RAKE ANGLE AND OPTIMIZATION OF TOOL RAKE FACE GEOMETRY

1.在切削力减小的刀具和具有大负前倾角的倒角刃刀具的情况下，建立了以速度间断线近似TE变形模式的切削模型。将能量法应用于这些切割模型，预测结果与实验结果吻合较好。切屑模型能够解释切屑形成过程从涉及二次切屑到涉及前倾角和前刀面摩擦条件下的毛刺的转变。在模型预测数据的基础上，用有限元方法计算了切削温度。对于普通碳钢(JISS48C)，即使在高速切削条件下，前刀面的切削温度达到1000℃，二次切屑仍然存在。据此认为，二次切屑的消失取决于静平衡条件，而不取决于切削温度。在刀具具有三个前刀面，即二次前刀面上具有CAMFERED刃口和人工控制刀屑接触长度的情况下，建立了刀具的切割模型。研究发现，切屑的产生受一次、二次前角的组合以及倒角边表面摩擦条件的影响。利用减摩工具的实验数据，预测结果与实验结果吻合较好。对于S48C钢切削，发现较大的倒角刃口对粗大断口和切边具有一定的强度，但磨损量随着倒角刃口长度的增加而增加。在产生二次切屑的切削速度范围内，获得了良好的表面粗糙度，但一次前角为-60°时会产生抛光和毛刺。

1. IN TE CASE OF CUTTING WITH REDUCD CONTACT TOOLS AND WITH CHAMFERED EDGE TOOLS HAVING LARGE NEGATIVE RAKE ANGLE, CUTTING MODELS IN WHICH TE MODE OF DEFORMATION IS APPROXIMATED WITH THE VELOCITY DISCONTINUITY LINES ARE DEVELOPED. BY APPLYING ENERGY METHOD TO THESE CUTTING MODELS, PREDICTED RESULTS ARE IN GOOD AGREEMENT WITH EXPERIMENTAL RESULTS.2. THE CUTTING MODELS ARE ABLE TO EXPLAIN THE TRANSITION OF CHIP FORMATION PROCESS FROM INVOLVING SECONDARY CHIP TO INVOLVING BURRING WITH RAKE ANGLE AND FRICTIONAL CONDITION ON THE RAKE FACE. BASED UPON THE DATA PREDICTED FROM THE MODELS, CUTTING TEMPERAYURE IS CALCULATD USING FINITE ELEMENT METHOD. FOR PLAIN CARBON STEEL (JIS S48C), THE SECONDARY CHIP CONTINUES TO EXIST EVEN IN TE CONDITION WHERE THE CUTTING TEMPERATURE ALONG THE RAKE FACE REACHES 1000℃ AT HIGH CUTTING SPEEDS. ACCORDINGLY IT IS CONSIDERED THAT THE DISAPPEARANCE OF THE SECONDARY CHIP DEPENDS ON THE CONDITION OF STATIC EQUILIBRIUM, BUT DOES NOT ON THE CUTTING TEMPERATURE.3. IN THE CASE OF CUTTING WITH TOOLS HAVING THREE RAKE SURFACES, THAT IS, CAMFERED EDGE AND ARTIFICIALLY CONTROLLD TOOL-CHIP CONTACT LENGTH ON THE SECONDARY RAKE FACE, CUTTING MODELS ARE DEVELOPED. TEREFORE IT IS FOUNF THAT THE GENERATION OF THE SEONDARY CHIP IS INFLUENCED BY THE COMBINATION OF THE PRIMARY AND SECONDARY RAKE ANGLES AND FRICTIONAL CONDITION ON THE SURFACE OF CHAMFERED EDGE. USING THE EXPERIMENTAL DATA OF REDUCED CONTACT TOOLS, PREDICTED RESULTS ARE IN GOOD AGREEMENT WITH EXPERIMENTAL RESULTS.4. FOR CUTTING STEEL OF S48C, IT IS FOUND THAT LARGE CHAMFERED EDGE GIVES STRENGTH FOR GROSS FRACTURE AND EDGE CHIPPING, BUT WEAR-LAND WEAR INCREASES WITH THE LENGTH OF THE CHAMFERED EDGE. IN THE REGION OF THE CUTTING SPEEDS PRODUCING SECONDARY CHIPS, GOOD SURFACE ROUGHNESS IS OBTAINED, BUT A PRIMARY RAKE ANGLE OF -60°GIVES BURNISHING AND BURRING.