【作者】 陈传海；

【导师】 杨兆军；

【作者基本信息】 吉林大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 数控机床是装备制造业实现现代化的基本装备，是具有高科技含量的工作母机，能否研发功能先进、精度高和质量可靠的数控机床，反映了一个国家制造业水平的高低。国产数控机床与国外欧、美、日等发达国家制造的数控机床相比，功能和精度水平逐渐接近，但在可靠性方面尚有较大的差距，致使国内中高端机床及其关键功能部件市场、尤其高端数控机床产品市场长期大量被国外品牌占领。可靠性水平低已成为制约我国机床行业发展的瓶颈，因此提高国产数控机床及其关键功能部件的可靠性水势在必行。进行数控机床和关键功能部件可靠性设计是提高数控机床可靠性水平的主要途径之一，目前采用的主要是基于故障分析的可靠性综合设计，概率设计是机床可靠性设计的必然趋势，而机床载荷谱是可靠性概率设计的客观依据。目前各机床及功能部件制造企业的载荷信息积累严重不足，无法编制科学、合理的数控机床载荷谱。因此为使机床产品具有一定的设计阈值，往往依靠经验来选择相应的安全系数。然而，机床载荷和零件强度不是恒定值，而是随机变量，利用安全系数法设计的机床对可靠性而言缺少客观依据，所以设计出的机床缺乏可靠性保证。上世纪90年代，吉林工业大学针对当时的数控车床产品开展了一些载荷谱技术的研究，但载荷谱编制过程并没有考虑机床快速移动和切削过程中机床自身重力、摩擦力及惯性力的作用、刀具磨钝对切削力的影响等，导致载荷谱的建立方法不完善；同时，随着机械、控制、液压和测量传感技术的发展，机床与上世纪90年代产品相比结构更加简化，功能更加完善。当今机床多采用伺服电机驱动丝杠进给，传动链更短；采用交流或直流控制单元驱动主轴旋转，摒弃了采用多级齿轮副变速的复杂结构，且实现了主轴的无级变速；同时，为了实现精密切削，机床刚度也有了很大的提高。机床结构的改变导致载荷的传递规律也发生了变化；同时近年来随着切削工艺的改进，机床的使用工况与90年代相比也有很大不同，因此原有载荷谱已不能反映当今机床产品的实际工作情况。针对上述情况，本文结合国家科技重大专项课题“高速/精密数控机床可靠性设计与性能试验技术”和“数控机床可靠性考核试验方法的研究”的研究工作，对数控机床进行了故障机理分析，研究了数控机床载荷的传递规律、刀具磨钝量与机床切削力的映射关系，并研究了数控机床的载荷谱编制方法，最终形成了一套适用于数控机床的载荷谱编制方法，论文的主要研究工作如下：（1）论述了国内外数控机床的发展、数控机床可靠性技术、载荷谱技术的研究现状及其研究进展。对数控机床可靠性建模、故障分析、可靠性设计和试验技术进行了综述和分析，归纳了数控机床可靠性技术研究的状况和主要动态，分析了现阶段我国数控机床可靠性技术研究存在的问题。通过分析和研究我国数控机床可靠性技术的研究现状，总结凝练了数控机床可靠性研究的主要技术路线。论述了机械产品载荷谱技术的研究现状和载荷谱的编制流程，指出了数控机床载荷谱编制方法的不足，为此提出了考虑机床快速移动过程重力、摩擦力及惯性力等载荷，切削过程重力、摩擦力等载荷和刀具磨钝对切削力影响的载荷谱编制方法。（2）开展了数控机床现场可靠性试验，并收集了大量的故障信息。采取功能独立、功能共享和行业共识的原则，划分了数控机床子系统。基于此，利用主次分析方法对现场可靠性试验获得的故障信息进行了分析，得到了数控机床故障的频发部位。针对在故障危害度分析时没有考虑故障模式频率比、故障影响概率、故障率和难以定量表示故障影响概率的精确值的权重导致分析结果与实际不符的问题，本文提出采用数据包络分析方法为故障模式频率比、故障影响概率、故障率的权重客观赋予值、用三角隶属度函数表示对故障影响概率的评判值的求取危害度的方法。利用该方法对故障模式进行了分析，得到了影响数控机床可靠性的关键部位。最后，对关键子系统进行了故障机理分析：元器件、零部件和轴承损坏主要是载荷交变或冲击作用使其产生疲劳损伤或断裂；松动主要是载荷冲击和振动作用使其发生联接松动或引线松动；渗漏主要是摩擦和热应力使密封圈产生裂纹和磨损。通过故障机理分析可知，大部分故障是由于载荷作用造成的，因此提出对机床载荷传递规律及载荷谱技术进行研究。（3）分析了数控车床和加工中心的组成和结构。在此基础上，开展了机床切削载荷传递规律的研究。研究了数控车床在快速移动、车削、钻孔过程中载荷（切削力和切削扭矩）的传递规律，得到了车床主轴轴承、丝杠、导轨的受力模型和主轴电机、丝杠电机的扭矩模型；研究了加工中心在快速移动、立铣削、面铣削、钻孔过程中载荷（切削力和扭矩）的传递规律，得到了加工中心主轴轴承、丝杠、导轨的受力模型和主轴电机、丝杠电机的扭矩模型。（4）分析了数控机床切削载荷信息的获取方法，制定了载荷信息的收集流程，基于该流程，进行了数控机床现场载荷试验，并收集了大量的载荷信息。对机床切削力的演化规律进行了论述和分析，机床切削力除了受切削工艺参数影响外，还受刀具磨钝因素的影响。基于此，利用正交试验方法设计了切削力与刀具磨钝映射关系的试验方案。在数控车床和加工中心上搭建了切削力试验系统，并开展了试验研究。利用多元线性回归方法求出了考虑刀具磨钝影响的切削力经验公式，建立了刀具磨损量和切削力之间的映射关系。（5）论述了机械产品载荷谱的编制方法。在此基础上，根据数控机床的工作特点，对机床产品载荷谱的编制方法进行了研究，数控机床载荷谱编制的关键是切削载荷数据的获取、载荷循环的计数以及载荷分布模型的优选。以机床切削长度与进给量的比值作为载荷循环次数，机床切削力（或扭矩）与机床设计的最大切削力（或扭矩）的比值为相对切削载荷，相对切削载荷对应的循环次数与总循环次数比值为相对循环次数。以数控车床为对象，对数控机床载荷谱的编制进行了案例说明。分别利用威布尔、对数正态、伽玛和贝塔分布分别对数据进行了拟合。针对载荷数据服从多个分布的情况，提出以多种误差信息融合为评价因素，采用数据包络分析方法优选出了载荷的分布模型。通过本文的研究，提出了一套适用于数控机床载荷谱的编制方法，为后续进行数控机床多维、多层次载荷谱的编制和可靠性设计提供了方法和依据。更多还原

【Abstract】 NC machine tools are the basic device to modern manufacturing industry, which are themanufacturers with the high-technology. Whether the advanced functional machine tools thathave the high machining precision and reliability are developed reflects the level ofmanufacturing industry of one country. Comparing to NC machine tools made by Europeancountries, Japan, America, etc, Chinese ones have relatively low level of reliability, and stillit is a huge gap. The markets for high and mid-grade machine tools productions and keyfunctional parts, especially high-end NC machine tools, are secured by foreign brands in along period. Market share for NC machine tools made by china is low, high and mid-grademachine tools productions and key functional parts mainly depend on import. The majorreason in the low market share is the relative lower reliability level of machine tools, and thisrestrains the development of machine tools industry in our country. Therefore, it is necessaryto improve the reliability of domestic machine tools and key functional parts.To carry out the reliability design for machine tools and key functional parts is onemain way to improve the reliability of machine tools, and load spectra are the foundation ofreliability design. However, there is no scientific and accurate load spectra because of thatdata are deficient in many companies, so workers always design production by choosingsafety factors based on their experience, and productions designed by this method may betoo larger. However, NC machine tools cutting load and strength of materials are notconstant, they are random variables. And those machine tools designed by experientialmethod doesn’t have the high inherent reliability and it make machine tools low level ofreliability and congenital defect. In the last century90’s, Jilin Technique Institute developeda serials of research on load spectrua for NC machine tools, but the method of these did notconsider the load influence to machine tools spectra during dry run, and the machiningcutters wear influence to machining load, which leaded the load spectra that built was notcompleted. Meanwhile, with the development of control, mechanics and sensing technology,machine tools have been improved a lot, especially the structure of machine tools have beenmore simplified comparing to productions made in last century. Feed system is driven byservo motor, so the chain of transmission becomes more shorter and AC or DC control unitmakes spindle rotation contiuously variable, so it abandoned the former step-by-step variable speed transmission. As well as, stiffness of machine tools improves a lot in order to realizehigh precision. The changes of structure of machine tools make machining load transfer lawsdifference to the former machine tools and the machine tools’ working conditions alteredmuch as well. Hence, load spectra cannot be applied to the reliability design of machinetools anymore now. To sum up, according to the project of “the Technology of Reliabilitydesign and Performance Testing for High speed/Precision NC machine tools” and project of“Research on Reliability Testing of NC machine tools”, which projects are founded byNational science and technology major special projects, failures analysis for machine toolsare analyzed, then obtained that the reliability design is the main reason that cause machinetools fail from that study. Research on machining load tranfer laws, the cutting loadinfluence by machining cutter wear and the establishing method of load spectra have beenconducted. The detailed work are as follows:(1) The development of machine tools, the technolgy of reliablity for machine tools andload spectra are analyzed, emphasizing the state and the hot research spots of reliability ofmachine tools in China. In this part, the reliability modelling method of machine tools,failure analysis technology, reliability design and tests are reviewed and analyzed. The maindynamic states of reliability technology study are summarized, the existing problems areproposed. The technology roadmap of machine tools reliability is presented.(2) The method of reliability data collection is drawn up,then the field reliabilitytestings are carried out and lots of failure data were collected. Based on the principles offunctional independences, functional shares and the conventions, the machine tools aredivided into several subsystems. Then the subsystems with high frequent failures areobtained by eareto diagram method. The criticality effect factors don’t take into accout whenFMECA and it is difficult to give a quantify for those factors, so the analysis result is notreasonable. To overcome this issue, the triangle-shape mbership functions are used toperform the fuzzy evaluation of researchers, the weight of factos are determined byfuzzy-DEA method. Based on this, a new criticality evaluating method is executed and thekey subsystems which have main effect on reliabiltiy are got. And then failure mechanism isanalyzed briefly.(3) The performance and structures of abundant NC machine tools are investigated,based on this, the load transfer laws during dry running, turning and drilling of NC machinetools are studied, then the laws of force and torque transfer are obtained and models of forceand torque are developed. The force models include force of axis bearing, force of leadscrew and pressure of guide rails. The torque models include torque of spindle motor and screw motor. Similarly, the load trasfer laws of machining center are obtained.(4) The load data collections of machine tools is determined. Based on this process thefield load tests were conducted, then the lots of load information were collected. Withstudying and analyzing on laws of machining force, the cutting force is also influenced bywear of tools. Then, the experiment of machining force affected by wear of tools wereperformed using the orthogonal experiment method. Finally, the experiential formulation ofmachining force are got by adopting multiple linear regression model.(5) The development of load spectra of machine tools are studied. According tofunctional performance of NC machine tools, the methods of establishing load spectrum arestudied. The key is to obtain data of machining load, accounting of circulation of machiningload and selecting of load model. Take the ratio of feeding length to the feed speed ascirculation amount, and the ratio of machining force or torque to the maximum machiningforce and torque as the relative load. On the basis of this, the relative load is the variable of xaxis and the relative circulation is the variable of y axis. After that, the data are fitted tolognormal distribution, Weibull distribution and the distribution of Beta and gamma. Finally,the best model is determined by data envelopment analysis.This study summarized the reliability characteristic of machine tools and gave the studydynamic spots. As shown there, the new FMECA considered the critically effects weightswas proposed and it would be a great complements to FMECA. Moreover, empirical formulaconsidered the wear of cutters was developed and then the load spectra establishing methodwas presented based on the new load transfer laws. Through this study, it would provide anestablishing load spectra method and a foundation for reliability design.更多还原