数控机床主动力系统载荷能量损耗系数的计算获取方法

机床量大面广,能量消耗巨大并且能量效率低、能量效率规律复杂,因此机床能量效率的研究和应用正在全球迅速兴起。机床主动力系统载荷能量损耗,是机床最复杂的部分,一般占到机床切削能量的10%~20%,其具体多少决定于载荷损耗系数。针对机床主动力系统载荷损耗系数在线获取非常困难,以及现有获取方法存在切削仪器昂贵、测量过程复杂以及许多机床无法安装等不足,提出一种根据数控机床主动力系统载荷能量损耗数学模型而建立的载荷损耗系数计算获取方法。上述数学模型由三部分组成:基于主电动机的变频器额定功率、额定功率损耗和散热器额定功率等基础参数的变频器功率损耗近似计算模型;基于主电动机额定功率、基频、空载功率和基频下的效率等基础参数的主电动机功率损耗模型;基于机床机械传动系统中每种传动副的数量和载荷效率等基础参数的机械传动系统载荷损耗模型。实际计算时只需获取基础参数和测量机床主动力系统空载功率,便可计算出机床主动力系统的载荷能量损耗系数。基于上述计算方法,计算获取了数控加工中心PL700主动力系统的载荷能量损耗系数。实验结果证实了该方法的准确性和实用性。该方法可广泛用于数控机床的切削功率获取、数控机床能量效率评价和工件能量效率预测及优化等研究和应用中,具有多方面的应用前景。     

机床固有能量效率的内涵及其评价方法

机床能量效率的评价是机床能效优化研究的基础。现有评价方法主要集中在机床加工过程的能量效率评价,对支持高能效机床设计的机床自身能量效率评价研究还存在不足和问题。为此,提出表征机床自身能量效率的机床固有能量效率新概念;它是机床加工能力范围内的未来可能的所有加工过程的综合平均能量效率。分析了机床固有能量效率的内涵,提出了机床固有能量效率的有效描述法即虚拟工件法;建立由固有比能效率、固有能量利用率两个综合评价指标和待机功率、当量启动能耗、当量空载功率、当量附加载荷损耗系数四个单项指标构成的机床固有能量效率评价指标体系;基于虚拟工件法,进行上述机床固有能量效率综合评价指标的获取方法研究,实现了机床固有能量效率评价。应用案例研究验证了所提方法的可行性和实用性。该方法可为高能效机床的设计、新制造系统的设计与组建以及高能耗设备改造提供支持,从而提升机床使用生命周期全过程的综合能量效率。     

机床机电主传动系统服役过程能量效率获取方法

制造系统能效评估及其机床能效评价研究正在国际上迅速兴起,生产现场的机床服役过程(Machine tools’ service process,MTSP)能量效率的方便获取是其关键问题之一。为此,对MTSP中机电主传动系统(Electro-mechanical main driving system,EMDS)能量效率获取方法进行研究。在分析机床能量效率内涵的基础上,基于MTSP中EMDS的时段能量模型,建立基于输入功率检测的和基于输出功率获取的两类4种EMDS能量效率模型;提出对应的能量效率模型中基础数据和基础系数特别是机床载荷损耗系数的获取方法;形成MTSP中EMDS能量效率获取方法。应用该方法,只需现场检测EMDS输入功率,就可获得MTSP中EMDS的现场能量效率。应用案例表明,应用本方法不仅能实现MTSP能量效率现场获取,而且误差较小;可用于机床及制造系统的能效评价、能效监控和能效优化研究中,具有较广阔的应用前景。     

三轴数控铣床切削力引起的误差综合运动学建模

使用齐次坐标变换的方法建立了三轴数控铣床的切削力误差综合数学模型.首先基于三轴数控铣床的结构分析对切削力误差元素进行识别,然后在机床各运动部件上建立一系列坐标系并推导出各相邻坐标系间的齐次坐标变换矩阵,最后根据切削加工中刀具切削点与工件正被切削点在基坐标系中的坐标值相同列出等式,推导出切削力误差综合模型.该模型包含30个对机床加工精度影响较大的切削力误差元素,适用于计算误差补偿时的补偿量.     

三轴数控铣床切削力引起的误差综合运动学建模

使用齐次坐标变换的方法建立了三轴数控铣床的切削力误差综合数学模型。首先基于三轴数控铣床的结构分析对切削力误差元素进行识别,然后在机床各运动部件上建立一系列坐标系并推导出各相邻坐标系间的齐次坐标变换矩阵,最后根据切削加工中刀具切削点与工件正被切削点在基坐标系中的坐标值相同列出等式,推导出切削力误差综合模型。该模型包含30个对机床加工精度影响较大的切削力误差元素,适用于计算误差补偿时的补偿量。
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基于铣削力精确建模的工件表面让刀误差预测分析

航空航天制造业结构件的高速铣削加工中,在切削力作用下由整体铣削刀具挠度变形所引起的工件表面让刀误差,严重制约零件的加工精度和效率。针对这一问题,通过建立铣削力精确预测模型,结合刀具刚度特点,对工件让刀误差进行预测分析。将切削速度和刀具前角对切削力的影响规律引入二维直角单位切削力预测模型,并通过试验进行相关系数标定。借助等效前角将直角切削力预测系数应用到斜角切削力的预测,通过矢量叠加构建整体刀具三维切削力模型。分析刀具挠度变形对铣削层厚度及铣削接触中心角范围影响规律。基于离散化的刀具模型和切削力模型,建立铣削载荷条件下刀具等效直径悬臂梁模型弯曲变形计算方法。构建以刀具变形对铣削过程影响作用规律为反馈的刚性工件表面让刀误差及切削力柔性预测模型,通过整体铣刀铣削试验验证所建立理论模型的预测精度。     

切削功耗变化视角下的刀具磨损监测方法

刀具磨损监测是机械加工领域关注的重点问题,基于机床功率变化的刀具磨损监测方法是当前主流的监测方法。对于微铣削加工而言,由于材料切削功率占机床总功率的比例极小,运用传统方法难以监测到机床功率在加工过程中因刀具磨损产生的变化。针对微铣刀具在加工过程中的磨损问题,本论文以切削功耗为基础提出了一种刀具磨损监测方法：文章从切削力做功的角度出发对材料切削功耗进行了建模,结合材料去除体积提出了单位功模型;在切削参数固定的条件下,从切向剪切力系数和切向犁切力系数两个方面分析了刀具磨损对单位功的影响;以小直径硬质合金立铣刀铣削铝合金7075为例开展了多次刀具磨损实验,并在实验过程中监测了单位功的变化趋势,通过将单位功的变化趋势与刀具磨损进行关联,验证了本文方法的可行性,证明了该方法可用于微铣削过程中的刀具磨损监测。     

车削过程中工件的振动力学建模与分析

针对车削过程中工件受轴向移动三维切削力的动态作用,建立车削轴的振动力学模型,其中考虑被加工轴的直径和质量变化的影响。用Matlab软件对振动模型的运动方程进行数值求解,得到在不同车削条件下直径和质量随时间变化的轴的振动响应。计算结果表明,车削加工中工件直径和质量变化对工件的振动响应影响较大,载荷移动速度影响工件的振动幅度,该模型更符合实际车削轴加工过程的情况。     

机床主轴和轴承的设计

除了刨床、牛头刨床和拉床外,其他切削机床切削过程中的工件和刀具的相对运动,都是由工件或工具的旋转运动或工件和刀具二者的旋转运动而得到的。工件表面光洁度、几何精度以及尺寸的准确性都和设计上如何解决回转运动有联带关系。换言之,机床的工作精度和工件轴、刀具轴以及和它们的支承有重大的关系。 人们要求这些机械另件,在各种不同的作业要下,如低限和高限的转速,工件重量的大小负荷,工件和切削力的不平衡等等──都不致失去精度。此外它们应具有高度的回转精度和振动的阻尼作用,这种振动是由运动链和切削过程所引起的。 满足这些要求…     

基于约束与尺寸混合驱动的虚拟数控机床技术

提出了一种虚拟数控机床设计方法。该方法首先建立虚拟数控机床模型,在机床运动部件中的主动与从动件之间建立约束关系,采用组件矩阵变换技术对主动部件的位姿矩阵进行变换,驱动部件运动;再利用WAVE技术在刀具与工件之间建立链接,实现切割运算,去除工件材料;最后采用插补技术对加工路径进行计算,得到各个运动轴的进给量,用它驱动机床运动轴运动,模拟加工过程。将虚拟数控机床技术运用于整体叶轮叶片电解加工,利用该技术建立了五坐标数控机床模型,并用它完成叶片加工过程模拟、运动干涉检查、加工自动编程等工作,有效地提高了工作效率与加工自动化程度。     

Three-dimensional tool radius compensation for multi-axis peripheral milling

Few function about 3D tool radius compensation is applied to generating executable motion control commands in the existing computer numerical control (CNC) systems. Once the tool radius is changed, especially in the case of tool size changing with tool wear in machining, a new NC program has to be recreated. A generic 3D tool radius compensation method for multi-axis peripheral milling in CNC systems is presented. The offset path is calculated by offsetting the tool path along the direction of the offset vector with a given distance. The offset vector is perpendicular to both the tangent vector of the tool path and the orientation vector of the tool axis relative to the workpiece. The orientation vector equations of the tool axis relative to the workpiece are obtained through homogeneous coordinate transformation matrix and forward kinematics of generalized kinematics model of multi-axis machine tools. To avoid cutting into the corner formed by the two adjacent tool paths, the coordinates of offset path at the intersection point have been calculated according to the transition type that is determined by the angle between the two tool path tangent vectors at the corner. Through the verification by the solid cutting simulation software VERICUTwith different tool radiuses on a table-tilting type five-axis machine tool, and by the real machining experiment of machining a soup spoon on a five-axis machine tool with the developed CNC system, the effectiveness of the proposed 3D tool radius compensation method is confirmed. The proposed compensation method can be suitable for all kinds of threeto five-axis machine tools as a general form.     

并联机床数控加工碰撞干涉检验算法研究

由于并联机床与通用数控机床在结构上差别较大 ,因此在开发与其配套的CAD/CAM系统时 ,考虑到并联机床的结构特点 ,针对哈尔滨工业大学研制的并联机床BJ -30的结构形式 ,提出了并联机床的数控加工碰撞干涉检验算法。该算法较好地解决了刀具过切、少切 ,以及动平台与工件、刀具夹具与工件的碰撞等数控加工中较难解决的问题。仿真结果证明了该算法具有运算速度快、检验效率高等优点     

机床相对激振试验分析

介绍通过相对激振试验测定机床切削点刀具和工件两侧绝对动柔度、并分析查明机床结构动刚度较低部位的原理、方法与实例。     

数控机床出现低速爬行的原因及其设计对策

机床出现爬行时,将严重影响加工工件表面质量、表面粗糙度及定位精度,甚至还会影响机床零件的使用寿命,缩短刀具的使用寿命。机床导轨爬行严重时,可导致机床丧失加工能力。主要分析了数控机床爬行的原因及其对策。     

曲面加工中走刀路线优化

针对刀具不同走刀路线对工件加工精度影响的问题,应用成组技术对曲面进行分析,并阐述了曲面加工时常用的插补方法.分析不同走刀路线对工件精度及加工效率的影响,优化二维与三维曲面加工,正确选择刀具走刀路线的方法,以更好地达到工件的加工精度及其他技术要求.     

Automatic selection of cutter orientation for preventing the collision problem on a five-axis machining

The rotation joints of a five-axis machine tool can offer freedom and appropriate rotation to prevent interference problem between workpiece and the cutter. However, to a five-axis machine tool, it is quite difficult to determine the collision-free cutter orientation. Over this problem, a two-stage cutting tool collision check method is proposed to prevent the collision problem during the cutting process on a five-axis machine tool. The proposed method is capable of determining the collision free ball-end cutter orientation automatically. The first stage is to obtain the tilting and collision-free angle range in the plane that is normal to the tool path obtained. Next, a checking cone generated from this collision-free tool axis range is used for the second collision check. The collision region is formed by the intersection of the neighboring surfaces. This implies a collision-free yaw angle range. The final cutting tool orientation is determined automatically by referring the original spindle axis and the least angular variation from the spindle axis. Finally, the implementation issue is discussed with example.     

A manufacturing model of helical groove on rotary burr and a universal post processing method

A systematic machining theory and precision method to determine cutter location in a grinding system is presented for rotary burr. First, the helical cutting edge on various kinds of revolving surfaces is built. Then, based on the geometry model of the helical cutting edge, the smooth spiral rake surface with constant normal rake angle and flank surface can been formed during the one-pass grinding process by this method. No interference between the grinding wheel and workpiece happens by the wheel special rotation. The method has the characteristic of detaching the grinding wheel path solution from specified machining conditions. The grinding wheel path is suitable for different NC machine tools through post processing. Meanwhile, a mechanism kinematic model of the NC machine tool is built, and a generalized algorithm for post-processing of multi-axis NC machine tools is presented. This model is applied to arbitrary configuration of NC machine tool, and the motion value for each axis will be generated by the inputting structure and motion parameters of the machine tool. The model, together with the machining method mentioned in this paper, make the calculation and generation of the grinding wheel path simpler and universal. At last, the validity of the method given in the paper is identified by an example of grinding.     

A study of deformation of the machined workpiece and tool under different low cutting velocities with an elastic cutting tool

To understand the effects of cutting velocity, tool elastic deformation generated by high normal stresses during metal cutting processing and artificial tool flank wear on the cutting process, an iterative mathematical model for calculating the tool–workpiece contact problem was developed in this paper under the assumption of elastic cutting tools. In this model, the finite element method is used to simulate cutting of mild steel by the P20 cutting tool with constant artifical tool flank wear under the condition of three different cutting velocities. The results obtained in the simulation were found to match the experimental data reported by related studies. The simulation results also indicate that the thrust and the cutting forces are functions of cutting velocity. Besides, both the normal stress on the tool rake face and the residual stress of machined workpiece generally decrease with increase in cutting velocity. According to the findings in this study, though the residual stress of the machined workpiece decreases as the cutting velocity increases, its value is still higher than that in ordinary conditions due both to the influence of tool flank wear and tool elastic deformation. Also, the phenomenon of curvature at the workpiece end easily occurs.