Tool Life Prediction and Avoidance of Cutting Tool Breakage in CNC System

刀具切削刃的脆性失效，如崩刃、断裂和疲劳裂纹，可能对刀具、工件和机床造成实质性损坏。人们从分析预报、监测技术和自适应控制方法等多个角度对这一问题进行了广泛的研究。然而，至今还没有一种有效的防止脆性破坏的方法。因此，出于安全原因，切削条件不可避免地被限制在低于最佳值的低估水平，这必然导致生产性能差。这是在对比逐渐类型的故障，即磨损的切削刀具，这已经克服了一些成功地通过各种methods.In这项研究中，提出了一种新的方法，在中断车削脆性故障占主导地位的自适应控制，并进行有效的切削，通过优化的切削条件内确定的时间变化的安全限制的基础上，由于脆性故障的刀具寿命的分析。本文首先提出了自适应控制系统的概念，然后描述了基于断裂力学的切削刃脆性破坏的分析预测，并讨论了为避免脆性破坏而进行的自适应控制实验，在使用碳化钨刀具的普通碳钢工件的断续CNC（计算机数控）车削过程中进行了自适应控制实验。结果表明，在大多数切削条件下都能避免脆性破坏，而且通过自适应控制系统，切削时间大大缩短。还讨论了脆性或磨损型失效可能占主导地位的区域。建议的系统被发现更有效的使用时，与较大的进给速度，在较低的切削速度，并增加重切削比。

Brittle failure of the cutting edge of a tool, such as chipping, fracturing and fatigue cracking, may cause substantial damage to the tool, the workpiece and the machine tool. Extensive efforts have been focused on solving this problem from various points of view including the analytical forecast, monitoring technique and the adaptive control approach. However, an effective method preventing brittle failure has not yet been developed. Therefore, cutting conditions have inevitably been restricted for safety reasons to an underestimated level below the optimum value, and this has necessarily resulted in poor production performances. This is in contrast to gradual type failure, i.e. wear of cutting tool, which have been overcome somewhat successfully by various methods.In this study, a new approach is proposed for adaptive control in interrupted turning where brittle failure predominates, and efficient cutting is performed by optimizing the cutting conditions within time-varying safe-limit determined on the basis of an analysis of the tool life due to brittle failure. This paper first proposes a concept for the adaptive control system, then describes an analytical prediction based on fracture mechanics of the brittle failure of the cutting edge, and discuss adaptive control experiments conducted to avoid brittle failure.The adaptive control experiments are conducted during an interrupted CNC (Computer Numerical Control) turning operation on a plain carbon steel workmaterial using a tungsten carbide tool. It is found that brittle failure avoiance is accomplished in most cutting conditions employed, furthermore quite significant reduction in cutting time is achieved through the adaptive control system. The region where either brittle or wear-type failure can become predominant is also discussed. The proposed system is found more effective when used with larger feed rates, at lower cutting speeds, and with increased rel-cut ratios.