On the Catastrophic Shear Instability in High-Speed Machining of an AISI 4340 Steel
On the Catastrophic Shear Instability in High-Speed Machining of an AISI 4340 Steel
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DOI：
10.1115/1.3185807
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发表时间：
1982-05
期刊：
影响因子：
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通讯作者：
R. Komanduri;T. Schroeder;J. Hazra;B. Turkovich;D. G. Flom
中科院分区：
文献类型：
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作者：
R. Komanduri;T. Schroeder;J. Hazra;B. Turkovich;D. G. Flom
以高达2500 m/min（8000 SFPM）的各种速度加工AISI 4340钢（325 BHN）。切屑的纵向中段进行了解剖学检查，以描绘在不同速度下的切屑形成特性的差异。发现碎片在30至60 m/min（100至200 SFPM）下是连续的，但在低于该速度下是不连续的。在切削过程中的不稳定性，导致不同类型的周期性芯片的形成，观察切削速度超过60米/分钟（200 SFPM）。在切削速度高于275 m/min（800 SFPM）时，在切屑中观察到由相对较少变形的材料的大面积（段）分离的完全发展的灾难性剪切带，类似于加工钛合金时的情况。段之间的强烈剪切带似乎是在主剪切带中的段的局部强烈变形之后形成的。随着切削速度的增加，段之间的接触程度被发现迅速减少。在1000 m/min（3200 SFPM）及以上的速度下，由于片段之间的快速强烈的局部剪切，发现这些片段作为孤立片段完全分离，而不是作为长芯片保持完整。发现这种脱粘发生的速度取决于机械加工钢的冶金状态及其硬度。与加工钛合金的情况一样，切屑在工具面上滑动时的变形，即，当高速加工这种AISI 4340钢时，“二次剪切区”似乎可以忽略不计。基于对切屑的冶金学研究以及在高速下加工这种材料和在正常速度下加工钛合金的相似性，在主剪切区中的循环现象被确定为负责大规模不均匀性的不稳定性的来源，并提出了在高速下加工AISI 4340钢时切屑形成的机制。
An AISI 4340 Steel (325 BHN) was machined at various speeds up to 2500 m/min (8000 SFPM). Longitudinal midsections of the chips were examined metallurgically to delineate the differences in the chip formation characteristics at various speeds. Chips were found to be continuous at 30 to 60 m/min (100 to 200 SFPM) but discontinuous below this speed. Instabilities in the cutting process, leading to different types of cyclic chip formations, were observed at cutting speeds above 60 m/min (200 SFPM). Fully developed catastrophic shear bands separated by large areas (segments) of relatively less deformed material, similar to that when machining titanium alloys, were observed in the chips at cutting speeds above 275 m/min (800 SFPM). The intense shear bands between the segments appeared to have formed subsequent to the localized intense deformation of the segment in the primary shear zone. As the cutting speed increases, the extent of contact between the segments is found to decrease rapidly. At speeds of 1000 m/min (3200 SFPM) and above, due to rapid intense, localized shear between the segments, these segments were found to separate completely as isolated segments instead of being held intact as a long chip. The speed at which this decohesion occurs was found to depend upon the metallurgical state of the steel machined and its hardness. As in the case of machining titanium alloys, the deformation of the chip as it slides on the tool face, i.e., “secondary shear zone,” appeared to be negligible when machining this AISI 4340 steel at high speed. Based on the metallurgical study of the chip and the similarities of machining this material at high speed and that of titanium alloys at normal speed, a cyclic phenomenon in the primary shear zone is identified as the source of instability responsible for the large-scale heterogeneity and a mechanism of chip formation when machining AISI 4340 steel at high speed is proposed.