【作者】 张晓辉；

【导师】 陈明；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 随着制造技术的发展,金属切削已呈现出高速高效、高加工要求和工件材料高性能等特点。为满足新形势下的加工需求,对刀具的性能也提出越来越苛刻的要求,目前刀具的发展方向为高精、高效、高可靠性和专用化。在工件材料性能和刀具技术日新月异的今天,切削加工工艺面临着前所未有的机遇和挑战,如何充分发挥机床和刀具的最大潜能,如何有效合理地选择切削参数已经成为制约切削技术发展的瓶颈。因此,新形势下的切削工艺数据比以往更具有较强的时效性,但切削过程中的力热本质是不变的,因此提出基于切削过程物理模型的参数优化问题研究。首先,分析了切削参数优化的三个基本要素:优化变量、目标函数和约束条件。优化变量是指切削用量:切削速度和进给量,任何形式的切削参数优化最终都是以切削用量为其自变量的;目标函数则主要指表面质量、切除率和刀具寿命,以适应不同的加工要求;约束条件主要是指切削过程中的力约束、热约束和振动约束三方面,这样才能使刀具在约束许可的范围内进行高效切削。本文将针对几种典型的工况分别从三个方面展开对参数优化问题的研究:力热约束、智能方法和颤振稳定性。切削力和切削热是反映金属切削本质最基本的物理量,同时也是难加工材料切削的突出特征。首先分析总结了斜角切削中切削力和切削热的形成。通过JC本构模型分析了金属在第一变形区内高温高应变率条件下的Mises流动应力特性;分析了刀刃钝圆所承受的应力特点及其计算方法,考虑了铣削交变应力对刀刃强度的影响,指出了每齿进给量的优化应满足刀刃的疲劳强度;为降低工件的加工硬化和刀具的高温磨损,以第二变形区的切削温度作为热约束条件,提出以材料的再结晶温度和刀具/涂层的扩散或氧化温度作为约束条件,将切削速度限制在一可行域内;另外,考查了表面粗糙度、机床功率和刀具寿命对参数优化的影响,指出参数优化的结果应是一个包含多种次优方案在内的具有一定选择范围的切削用量域,而非某个特定值。基于上述方法,以钛合金为代表的典型难加工材料为例对铣削切削速度和每齿进给量进行了优化。对于普通金属材料的加工,此时的切削力热特征不再突出,如何针对现有的切削数据进行多目标优化提出了采用神经模糊的方法。针对预拉伸铝合金铣削表面残余应力的预测优化进行了ANFIS建模,指出:当小样本用于网络训练时,可通过采用输入选择方法以降低输入数据的维数,从而提高预测效果。应用模糊综合评判方法对不同权重的多目标参数优化进行了探讨,通过采用不同的算子对多种方案进行不同的评判及排序,得出了在现有权重向量条件下的优化值,达到了预期的切削效果。对于弱刚性工艺系统如薄壁件加工或使用加长刀杆时,把机床、刀具、工件和夹具作为一个系统来考虑,需要对切削参数进行颤振稳定性校核。基于经典再生型切削颤振理论,首次提出了基于颤振稳定度的模糊化颤振理论。阐明了切削颤振稳定度的概念,它表明了切削系统自身保持其稳定性的能力和程度,指出切削系统从非稳定态到稳定态的过渡事实上是一个渐进的过程,即稳定度GOS属于[0,1]闭区间,提出了不同阶Lobe曲线由于曲线斜率的不同而应具有不同的过渡带宽度,并利用Sigmoid函数定义了各阶过渡带宽度的求解方法。由此,根据改进的模糊化稳定性Lobes图,以模具钢铣削为例进行了切削参数的稳定性校核。最后,针对具体的工程应用对刀具选用及切削数据库和基于物理模型的切削参数优化决策系统进行了基于Web的系统开发。这样,才能使之能够直接为生产实践服务。更多还原

【Abstract】 With the developing of modern manufacturing technology, high speed cutting, high efficiency cutting and high performance of work material have been the characteristics of metal cutting. In order to satisfy the situation, it puts forward rigorous demands for cutting performance of tool. So, the developing of tool are high precision, high efficiency, high reliability and specification. Thus, Cutting technology has faced much unprecedented opportunities and challenges nowdays. By now, cutting parameters optimization has been a bottleneck of cutting technology in order to exploit the maximal potentials of machine tool and cutting tool. Under this new situation, cutting parameters have shorter timeliness than ever before, but the essences of cutting process are invariable such as cutting force and cutting temperature. On the basis of this, parameter optimization based on physical models is performed here.Firstly, three essential elements of cutting parameters optimization have been analyzed: optimization variables, objective functions and constrain conditions. Optimization variables include cutting speed and feed rate. Objective functions refer to surface quality, material removal rate and tool life. Constraint conditions include forces, heat and vibration constraint. With the constraint conditions, cutting tool would be performed efficiency in a certain range of cutting parameters. In this dissertation, according to several typical working conditions the study of cutting parameters optimization would be expanded as three respects as follows: force and heat constraint, intelligent methods and chatter stability.Cutting forces and heat, the basic physical qualities in cutting process, is also the prominent features when difficult-to-cut material is machined. The formation of cutting forces and heat in oblique cutting is analyzed firstly. Then Mises flow stress in the primary deformation zone is studied by JC constitutive model. Stress characters and its computational methods on tool edge are studied. At the same time, the influence of alternate milling forces on cutting edge strength is discussed here. It indicates that the optimization of feed per tooth is depended on fatigue strength of tool edge. In order to reduce work hardening of workpiece and tool wear in high temperature, the cutting temperature in the secondary deformation zone is used as the thermal constraint. It indicates that cutting temperature is controlled by the range of recrystallized temperature of work material and service temperature of tool or coating. That is to say, cutting speed is limited by cutting temperature in a feasible zone. Besides, the impacts of surface quality, power consumption, and tool life to cutting parameters optimization are also studied. It shows that the result of cutting parameters optimization is not a specified value, but a range that includes several suboptimum solutions. Based on the above research, taking the difficult-to-cut material TC4 for example, the milling speed and feed per tooth are optimized in a certain range.As for common material, neuro-fuzzy optimization method is put forward based on multiple objectives optimization when cutting force and heat are not serious. Surface residual stress in pre-stretched aluminum milling is forecasted by an established ANFIS model. When small sample is used in ANFIS training, its forecasting effect can be improved by input selection in order to reduce the dimensions of input data. Besides, multiple objective functions are optimized by fuzzy synthetic evaluation based on different weight vectors. It shows that different sorting results can be obtained by use of different operators. An optimized result is obtained under the specified weight vector. Thus the corresponding cutting parameters can be solved by BP network with Bayesian regularization.When there are weak rigidity components in cutting process such as thin wall part, chatter stability verification to the whole system is absolutely necessary. The cutting system consists of machine tool, cutting tool, workpiece and chucks. According to conventional regenerative chatter theory, fuzzy chatter stability theory is put forward based on grade of stability (GOS). Cutting chatter stability grade represents the ability and grade of stability. In fact, the transition of cutting chatter from unstable to stable condition actually is a gradual process, that is to say, the grade of stability is in a range of a closed interval [0,1] not 0 or 1. Deeper studies on Lobes curves show that there should be different width of transition belt in different order Lobe curve because of the different Lobe slope. Thus, the method to calculate the transition belt width is defined according to Sigmoid function. Therefore, stability verification to milling parameters of die steel has been done based on the modified fuzzy stability Lobes.At last, according to specific engineering applications, a tool selection database and cutting parameters optimization decision-making system have been developed based on Web browser. In this way, it could service practical application directly.更多还原