【作者】 陈明；

【导师】 张仕进；

【作者基本信息】 上海大学 ， 机械制造及其自动化， 2024， 博士

【摘要】 作为当今世界上唯一一种冷态高能束加工技术,磨料水射流因其独特优势在高性能材料加工方面展现出巨大潜力,但由于误差超差及误差无法预测等问题不得不依赖大量试切工作,导致其无法应用于关键领域复杂构件的规模生产。针对该问题,本文从理论角度对射流流形进行精确描述,结合实验数据建立了精确的射流流形三维时变模型,将其作为表征真实流形的虚拟刀具,通过虚拟切割结果提前预测实际切割过程中可能出现的误差形状及误差大小,并提出了误差最小化的射流空间姿态调控机制。主要包括以下内容:(1)针对磨料水射流从微观角度单颗磨料颗粒冲蚀机理到宏观角度切缝误差特征形成过程演变逻辑不明的问题,开展了磨料水射流材料去除过程及加工误差形成机理研究。首先,系统分析了磨料水射流加工原理,基于基础理论探讨了磨料能量分布规律。其次,通过深入分析切割前沿形貌变化对磨料颗粒多次非完全弹性碰撞过程的影响规律阐述了材料去除过程的理论观点,并通过射流切割透明材料时的明光及暗光拍摄实验进行了验证。最后,分析了射流基本加工误差形成机理和复杂路径轨迹下的组合空间误差类型,为后续物理建模和实体建模奠定理论基础。(2)针对射流流形单一特征经验模型适用范围窄且依赖大量切割实验的问题,开展了射流流形主要特征的机理建模和实验建模研究。首先,基于流形特征分析和一定假设条件,通过理论推导得到射流平面基础流形机理模型,并在此基础上引入空间碰撞角度,通过理论推导得到射流空间三维流形机理模型。其次,引入高速摄像技术及特征提取方法采集了射流切割透明材料过程中大量动态变化的流形特征实验数据,分别建立了平面流形的滞后量偏差修正系数经验公式和空间流形的方位角度偏差修正系数经验公式。最后,通过结合两者形成数理耦合驱动的平面基础流形及空间三维流形特征数学模型,并用实验数据进行了模型性能评估验证了其准确性和实用性。(3)针对材料内部切缝误差特征采集困难且二维特征描述流形三维实体不够准确的问题,开展了基于特定实验方法的流形实体建模研究。首先,通过分离速度实验与数值方法结合,获取不同材料的可加工性数值,将射流流形模型拓展到不同材料上。其次,通过整/拼块实验方法保留切缝形貌特征,对于不同实验样块采集修正机理模型所需不同维度的流形特征数据。最后,通过对拼块样块形貌三维点云数据的分割处理,得到不同切缝深度的流形截面轮廓特征并建立了更加精确的射流流形三维时变模型。(4)针对射流误差无法预测且误差补偿依赖大量试切的问题,开展了磨料水射流切割过程仿真和调整射流空间姿态机制的研究。首先,提出软刀子数控加工仿真机制,基于射流流形三维时变模型、刀具更新机制和布尔运算实现磨料水射流虚拟切割过程及仿真原型系统。其次,对比实际切割过程和虚拟切割过程及结果,提出误差最小化的射流空间姿态调控机制。最后,在各类极端工况下针对性地提出补偿策略并进行了应用验证。通过上述内容及相关研究成果,本文从理论角度推导得到了磨料水射流切割过程中射流流形前沿曲线的机理模型,结合经验模型建立了数理耦合驱动的流形前沿曲线数学模型,通过实验采集流形特征建立对应射流流形物理实体的精确三维模型。基于射流流形三维模型和软刀子数控加工仿真机制实现了磨料水射流虚拟切割过程,进一步通过射流空间姿态调控机制实现复杂结构件的磨料水射流精密加工,从而免去传统解决方案中大量的反复试切和切割实验消耗,为磨料水射流应用于航空航天等关键领域零部件规模加工扫清障碍。更多还原

【Abstract】 As the only cold high-energy beam machining technology in the world today,abrasive water jet(AWJ)has great potential in the machining of high-performance materials due to its unique advantages.However,such technology cannot be applied to the industrial production of complex components in key applications due to the overshoot and unpredictability of the error,which have to rely on a large number of trial cuts.To solve this problem,this dissertation provides a mathematical description method of the jet profile from a mechanistic point of view.An accurate three-dimensional(3D)time-varying model of jet profile is established in combination with experimental data.And it is used as a virtual tool to characterize the jet profile.The shape and size of the error that may occur in the actual cutting process can be predicted in advance through the virtual cutting process and results.Based on this,a jet spatial position and attitude control mechanism is proposed to reduce the shape error.The dissertation mainly includes the following contents:(ⅰ)Aiming at the problem of the unknown evolution logic from the erosion mechanism of single abrasive particle under the microscopic perspective to the formation process of kerf defect characteristics under the macroscopic perspective,the research is carried out on the material removal process of AWJ and the formation mechanism of kerf defects.Firstly,the principle of AWJ machining is systematically analyzed.And the energy distribution trend was explored based on the basic theory.Then,the theoretical viewpoint of the material removal process is elaborated through analysis of the influence of morphological changes at the cutting front on the multiple incomplete elastic collision process of abrasive particles.And it is verified by the bright light and dark light photography experiments when the AWJ cuts transparent materials.Finally,the basic shape error formation mechanism and the combined spatial shape error type under the complex trajectory are analyzed to lay the theoretical foundation for the subsequent physical modelling and solid modelling.(ⅱ)Aiming at the problem that the empirical model of the single feature of jet profile has a narrow scope of application and relies on a large number of cutting experiments,the research is carried out on mechanism modelling and experimental modelling of the main features of jet profile.Firstly,based on the analysis of the profile characteristics and certain assumptions,the basic jet profile mechanism model is obtained by theoretical derivation.Based on this model,the spatial collision angle is introduced,and the spatial jet profile mechanism model is obtained by theoretical derivation.Then,the high-speed camera technology and feature extraction method are introduced to collect a large amount of experimental data of the time-varying feature of the jet profile.The empirical formulas of jetlag deviation correction coefficients for basic jet profile and azimuthal angle deviation correction coefficients for spatial jet profile are established respectively.Finally,the mathematical models of basic jet profile and spatial jet profile characteristics driven by data-mechanism coupling are formed by combining the empirical and theoretical model.And the models’performance is evaluated with experimental data to verify its accuracy and practicality.(ⅲ)Aiming at the problem that it is difficult to collect the characteristics of kerf in the material and the 2D features are not accurate enough to describe the 3D entities of jet profiles,the research is carried out on the jet profiles modelling based on specific experimental methods.Firstly,the machinability numbers of different materials are obtained by combing separation speed experiments with numerical methods.In this way,the mathematical model is extended to different materials.Then,the kerf morphology is preserved by the whole/integrated block experimental method.And different dimensional characteristics of jet profile are collected for different experimental samples to modify the model.Finally,by segmenting the 3D point cloud data of the integrated block samples,the cross-sectional characteristics of the jet profile at different cutting depths are extracted to establish a more accurate 3D time-varying model of the jet profile.(ⅳ)Aiming at the problem that the shape error cannot be predicted and the error compensation relies on a large number of trial cuts,the research is carried out on the simulation of the AWJ cutting process and the mechanism of jet spatial position and attitude control.Firstly,a CNC machining simulation mechanism for soft knife is proposed.And the virtual cutting process and simulation prototype system are realized based on the 3D time-varying model of jet profile,tool updating mechanism and Boolean operation.Then,by comparing the actual cutting process and the virtual cutting process and the results of both,the jet spatial position and attitude control mechanism is proposed to minimize the shape error.Finally,the compensation strategy is proposed and verified under various extreme working conditions.Through the above research contents and results,the mechanism model of jet profile front curve in the cutting process is derived from the theoretical point of view in this dissertation.The mathematical model driven by data-mechanism coupling of the jet profile is established by combining with the empirical model.Through a small number of experiments,the characteristics of the jet profile can be corrected to establish an accurate 3D model corresponding to the physical entity of the jet profile.The virtual cutting process of AWJ is realized based on the 3D models and the CNC machining simulation mechanism for soft knife.And the AWJ precision machining of complex components is further realized by the jet spatial position and attitude control mechanism.And then the consumption of a large number of cutting experiments and trial cuts in the traditional solution can be eliminated.It paves the way for AWJ machining technology to be used for large-scale machining in critical areas such as the aerospace industry.更多还原