PREDICTION OF TOOL LIFE IN MACHINING WITH RESTRICTED CONTACT TOOLS

A semi-empirical method is described for predicting tool life in orthogonal machining with restricted contact tools. The method uses a well established machining theory to predict cutting forces, tool-chip contact length and cutting temperatures for the corresponding plane face tool i.e. tool having the same cutting edge geometry but no restricted contact. These predicted parameters and a set of empirical relations are then used to calculate the cutting temperatures and tool life for the restricted contact tool. A comparison has been made between predicted and experimental results obtained from the literature and from tests carried out by the authors.     

SURFACE FINISH AND TOOL WEAR CHARACTERIZATION IN HARD TURNING USING A MATHEMATICAL CUTTING TOOL REPRESENTATION

The development of a general 3D model for a corner-radiused, chamfered, edge-honed cutting worn tool is elaborated. The surface of the cutting tool was constructed using one angular scalar specifying location on the corner radius and leading/trailing edges and another non-dimensional scalar for specifying location on the relief, edge-hone, chamfer and tool-top. Then, for given geometric parameters and cutting conditions, the angular extremities of contact on the corner radius and leading/trailing edges was obtained and validated. The kinematic surface finish on the workpiece surface including the Brammertz and sideflow effects was then simulated in typical hard turning. The model was expanded to allow wiper edges and flank wear. A simplified crater wear model was adopted for continuous hard turning to allow virtual cross-sectioning. Accurate estimation of flank and crater wear volume was also enabled. The model results for the fresh tool agreed with well-known trends from 2D modeling. Preliminary results indicate that there exists a geometric basis for higher R_a and R_t for a worn tool. The Brammertz effect simulation, though not in agreement with the data of Knuefermann (2003 Knuefermann , M.M.W. ( 2003 ) Machining surfaces of optical quality by hard turning, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, UK . [Google Scholar]) corroborated the modification proposed therein.     

IN-PROCESS TOOL CONDITION MONITORING USING ACOUSTIC EMISSION SENSOR IN MICROENDMILLING

Recently researchers and manufacturers have shown keen interest in fabricating micro-components through tool based mechanical micromachining processes namely micromilling, microdrilling, microturning, etc. In this scenario, microendmilling is used in the manufacture of micro-molds, micro-dies, micro-channel, micro-gear, etc. The major issue in microendmilling process is the unpredictable life of the micro-tool and its premature failure during operations. Therefore in this work, an attempt has been made to monitor the tool condition (in-process) using acoustic emission (AE) sensor in microendmilling of different materials such as aluminum, copper and steel alloys. From this study, it is observed that there is a strong relationship between the tool wear (flank wear) and acoustic emission (AE_RMS) signals, surface roughness (R_a) as well as chip morphology. In order to understand the mechanism of tool wear, SEM and EDAX analyses were carried out on the microendmill after machining. Scanning Electron Microscope (SEM) and energy dispersive X-ray spectroscopy (EDAX) analyses indicated occurrence of the tool wear mechanism such as adhesion and plastic deformation in all three materials. Coating delamination is also observed while machining steel alloy. This work provides significant and new knowledge on the usage of AE sensor in monitoring the tool condition and understanding the tool wear mechanism in microendmilling of different materials.     

用红外热像技术在线评定原油加热炉管剩余寿命

通过对原油加热炉管表面温度场的连续红外热像检测,快速、准确地在线测量了炉管工作温度,结合炉管运行史数据,利用拉森-米勒和腐蚀损伤的剩余寿命估算模型。对加热炉炉管的工作状态进行了在线评估和诊断,提供了判断炉管检修与更换的科学依据。具有广泛的工程实用性。     

随机载荷下焊接结构疲劳寿命的一种有效计算方法

随机载荷下的疲劳寿命估算方法通常涉及两个方面,循环计数和损伤累积。本文研究了一种用于随机载荷下焊接构件疲劳寿命预测的有效计算方法。按照这种方法,只要求已知应力历程的功率谱密度和常规疲劳试验数据,就可以对承受随机载荷的焊接构件作出疲劳寿命计算。利用结构系统的复频响应函数,可以由已知的输入功率谱求出结构响应的谱密度。这就使得结构设计者即使在设计阶段不知道结构承受的应力历程,而只知道结构系统的输入,也同样可以对所设计的结构作出疲劳寿命预测。本文所述方法被用于某超重型矿用汽车车架的疲劳寿命计算,计算结果与实际情况基本吻合。     

基于小裂纹扩展的耐久性分析和经济寿命预测方法

综述基于小裂纹扩展的耐久性分析和经济寿命预测方法.该方法将小裂纹扩展的△Keff理论与耐久性设计、分析的概念相结合,用于建立结构的损伤度变化曲线和预测结构的经济寿命.由于采用小裂纹理论,该方法不依赖载荷谱,而且能很好地考虑结构的实际形状、载荷谱以及三维小裂纹的实际状况对经济寿命的定量影响,从而克服现有耐久性分析方法的不足.同时,当上述因素改变时无需重新进行结构模拟试件的耐久性试验,因而在结构初步设计阶段的耐久性分析更能体现它的优越性.     

高低周复合载荷作用下微动疲劳寿命预测研究

对高低周复合载荷作用下微动疲劳寿命预测方法进行了研究。首先，进行了高低周复合载荷作用下的桥式试件和榫联接试件的微动疲劳试验。其次，对微动疲劳中的力学参数进行分析，提出了将力学参数分为应力状态参数和微动摩擦参数两类。用边界元法对试件接触表面的参数进行分析。最后，基于数值分析和试验结果，建立了合金钢在高低周复合载荷作用和受钛合金微动作用时的微动疲劳寿命预测公式，并将其应用于榫联接试件的寿命计算，结果令     

Tool life prediction using Bayesian updating. Part 1: Milling tool life model using a discrete grid method

According to the Taylor tool life equation, tool life reduces with increasing cutting speed following a power law. Additional factors can also be added, such as the feed rate, in Taylor-type models. Although these models are posed as deterministic equations, there is inherent uncertainty in the empirical constants and tool life is generally considered a stochastic process. In this work, Bayesian inference is applied to estimate model constants for both milling and turning operations while considering uncertainty.     

Tool life prediction using Bayesian updating. Part 2: Turning tool life using a Markov Chain Monte Carlo approach

According to the Taylor tool life equation, tool life reduces with increasing cutting speed following a power law. Additional factors can also be added, such as the feed rate, in Taylor-type models. Although these models are posed as deterministic equations, there is inherent uncertainty in the empirical constants and tool life is generally considered a stochastic process. In this work, Bayesian inference is applied to estimate model constants for both milling and turning operations while considering uncertainty.