数控车床实用对刀方法与刀具补偿

通过对刀建立数控机床的工件坐标系是数控加工的重要内容,正确的对刀操作是数控加工精度的重要保证,也是实现数控机床高效率的基本要求.通过对对刀原理及机床坐标系的研究,针对FANUC-0i数控系统,对G50对刀、G54对刀和T指令对刀等多种不同的方法进行了较为深刻的分析,揭示了每种对刀方法与编程的联系.结合实例,对于合理设置...     

灵活运用工件坐标系实现零件的高效精确加工

数控车床加工零件时工件原点一般选择在工件右端面,但有时采用这种方案却很难实现零件的加工要求。结合一盘形端盖零件的加工,说明灵活运用工件坐标系能实现零件的高效、精确加工。     

整体叶盘加工原位测量系统的研制（英文）

针对五轴数控机床加工现场狭长空间的限制以及整体叶盘原位测量的需求,研制了一种悬臂式坐标测量机。设计并优化了密珠轴系的结构,分析了影响测量机测量精度的各项因素,并通过实验对测量机的测量精度进行了验证。结果显示,所设计的测量机结构能够满足测量指标的要求,可在机床加工原位对整体叶盘加工质量进行检测。所研制的测量机对于提高整体叶盘加工质量及发展大飞机生产都具有重要意义。     

考虑热误差的双转台机床工艺误差谱预测方法

五轴数控机床的几何误差和热误差是影响工件加工精度的两个重要因素,对这些误差因素进行分析可以有效提高薄壁件工件的加工精度。本文首先基于齐次坐标变换法,建立了双转台五轴数控机床的旋转轴几何误差模型;然后基于对标准球进行在机接触测量,辩识得出两旋转轴的12项几何误差,这些误差考虑了两旋转轴之间的相互影响和其热误差的影响;最后分析五轴数控机床加工空间的几何误差场,在该加工空间内几何误差从中心到外侧逐渐增加,当A轴旋转角度增加时,误差的最大值也随之增加。与其它位置误差辨识方法相比,本方法的测量精度符合加工要求,测量时间只需要30 min。     

Study on the influence of geometric errors in rotary axes on cubic-machining test considering the workpiece coordinate system

Evaluating the influence of geometric errors in rotary axes is a common method used by a five-axis machine tool for improving the machining accuracy. In conventional geometric error models, the table coordinate system is considered as the final workpiece coordinate system. In this study, an additional workpiece coordinate transformation was proposed to identify the influence of geometric error. First, a cubic machining test was conducted. Second, the necessity of workpiece coordinate transformation was analyzed, and a method for coordinate transformation was proposed. In addition, both machining simulation and an actual machining experiment of the cubic machining test were conducted to verify the efficiency of the proposed method. The results indicate that the workpiece coordinate transformation is an essential part of the geometric error model for accurately simulating the geometric error influence. The method for identifying the geometric error influence considering the workpiece coordinate transformation is applicable in manufacturing.     

多轴数控机床的在机测量方案创成及优化方法

多轴数控机床的在机测量会存在冗余运动自由度,由此导致一个测量任务会有多个与之对应的伺服运动方案,而确定最优的伺服运动方案,是保证在机测量性能的前提。针对这一问题,提出一种基于机床功能且面向测量任务的在机测量运动方案创成方法：采用多体系统理论及齐次坐标变换方法对被测对象的几何特征及数控机床的运动形式进行数学解析;建立以被测几何特征为自变量、以机床伺服运动为因变量的函数方程;求解该方程获得所有可能的测量运动方案。在此基础上,通过分析方程解的取值范围,验证所有测量运动方案的功能;考虑到数控机床的结构及伺服特性对测量精度的影响,提出了测量方案性能评价准则,并据此确定最优的测量方案。在某数控成形砂轮磨齿机上进行了齿形偏差的在机测量,试验结果验证了该方法的有效性和可行性。利用该方法确定的最优在机测量方案测量精度高、重复性好。     

用于加工中心的在线工件自动测量系统

介绍一种可用于加工中心的在线工件自动测量系统的构成及功能。该系统采用新型触发式传感器 ,可使刀具刀尖自身作为测头测试工件加工尺寸。该系统可用于工件的装夹找正 ,也可对工件进行自动在线测量 ,并能根据测量结果对加工误差进行补偿以提高加工精度     

The effect of welding atmosphere on the pitting corrosion of AISI 304L resistance spot welds

In industry, many taper shafts are designed with tolerances of a few microns. To cut them in finish turning, paths of the tool in virtual machining should be accurately generated beforehand. For this purpose, the dimension errors and surface roughness of the virtually cut workpiece should be predicted. Unfortunately, the current tool path generation methods cannot accurately calculate the errors and the roughness, resulting in the taper errors larger than the part tolerance. Our research formulates equations of the effective turning edge to accurately calculate the dimension errors and the surface roughness, and then proposes a new approach to CNC programming for high-precision CNC turning. It lays a theoretical foundation of modeling parts in virtual turning and can generate tool paths to machine taper parts with high accuracy.     

Integration of cutting force control and chatter suppression control into automatic cutting feed adjustment system design

Abstract

This study designed an automatic cutting feed adjustment system for computer numerical control (CNC) turning machine tools, which integrate the operational characteristics of cutting force control and chatter suppression control to shorten the machining time and maintain the quality of workpieces. The setting of appropriate machining conditions (such as cutting feed, spindle speed and depth of cut) to consider both machining quality and efficiency often causes difficulties for machine tool operators. Therefore, this study uses cutting force control to design an automatic cutting feed adjustment method for cutting tools, and then, the chatter suppression control design is used to modify the cutting force command to suppress cutting chatter. The experimental results of the CNC turning machine tool show that the use of the cutting force control to adjust the cutting feed can shorten the machining time; however, the cutting chatter results in larger surface waviness on the workpiece surface. When the cutting force command is properly modified by actuating the chatter suppression control, the workpiece shows better surface roughness with prolonged machining time. Therefore, the cutting tests demonstrate that the proposed system is feasible for satisfying the machining requirements of the manufacturing processes of mechanical parts for high speed and high accuracy.     

Development of a finite element analysis tool for fixture design integrity verification and optimisation

Machining fixtures are used to locate and constrain a workpiece during a machining operation. To ensure that the workpiece is manufactured according to specified dimensions and tolerances, it must be appropriately located and clamped. Minimising workpiece and fixture tooling deflections due to clamping and cutting forces in machining is critical to machining accuracy. An ideal fixture design maximises locating accuracy and workpiece stability, while minimising displacements.The purpose of this research is to develop a method for modelling workpiece boundary conditions and applied loads during a machining process, analyse modular fixture tool contact area deformation and optimise support locations, using finite element analysis (FEA). The workpiece boundary conditions are defined by locators and clamps. The locators are placed in a 3-2-1 fixture configuration, constraining all degrees of freedom of the workpiece and are modelled using linear spring-gap elements. The clamps are modelled as point loads. The workpiece is loaded to model cutting forces during drilling and milling machining operations. Fixture design integrity is verified. ANSYS parametric design language code is used to develop an algorithm to automatically optimise fixture support and clamp locations, and clamping forces, to minimise workpiece deformation, subsequently increasing machining accuracy. By implementing FEA in a computer-aided-fixture-design environment, unnecessary and uneconomical “trial and error” experimentation on the shop floor is eliminated.     

Compatibility of tolerancing

Tolerances are assigned to a mechanical engineering design either on the basis of functional and/or manufacturing requirements (toleranced dimensions, geometrical tolerances) or on the basis of the general categories—fine, medium, coarse—of the international standards or the designer's knowledge and experience (untoleranced dimensions). Conventional dimensions of the currently applicable dimensioning rules and implicit dimensions, including those attributed to geometrical tolerances, thus create four groups of tolerances which may or may not be compatible. In addition, any tolerance compromise, however tedious and difficult, not achieved systematically may well lead to accuracies which cannot be produced by the available machine tools. In the paper, a systematic approach to the above problems is presented. A methodology is demonstrated for the verification of the tolerance compatibility and for the assignment of compatible, producible and cost optimum tolerances.     

Premachining Computer Numerical Control Contour Validation

The current procedure followed to manufacture a new part by computer numerical control (CNC) machining is to write the part program, machine a test part, and measure the test part for conformance to the required dimensions and tolerances. If the test part dimensions are incorrect, the part program is modified, and the process is repeated until a successful part is machined. In many applications, such as the aerospace industry, where material cost and machining time are high, this iterative process becomes economically unacceptable. Research has been conducted to test the feasibility of using the laser ball bar (LBB), a spatial coordinate measuring device, to measure dynamic continuous path contours of CNC part programs to micrometer accuracy before machining. In this way, a virtual test part can be measured and compared to the design drawings to validate the CNC part program. This reduces or eliminates the costly and time-consuming steps involved in the machining of physical test parts. This paper outlines the testing method and results acquired using one LBB to measure dynamic part paths employing sequential trilateration. A circular contour was measured using an encoder trigger for data capture. The radial error motions of the spindle used to generate the circular contour were also measured using a capacitance probe nest to verify the LBB results. Comparable error waveforms between the LBB and cap probe measurements verified the possibility of using the LBB to measure dynamic continuous path contours. Future work using three LBBs simultaneously is also outlined.     

数控车床对刀操作

提出了数控编程与加工之间存在的主要问题,分析数控系统建立工件坐标系的方法,说明数控机床对刀操作的过程与目的。对每一种方法都给出了输入数据的计算式,总结其中的要点,比较方法之间的联系与不同。分析了工件坐标系与机床坐标系之间联系方法,并进行了实际验证。     

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.     

Computer-aided geometrical dimensioning and tolerancing for process-operation planning and quality control

This paper describes an extension of a model which determines an optimum set of dimensions and tolerances for machining processes at minimum manufacturing cost. This optimisation minimizes the cost of scrap, which is a function of manufacturing tolerances, as the objective function. Requirements of design sizes, geometrical tolerances (including both form and position) and machining allowances are expressed mathematically as constraints for the optimisation. A computerised trace method has been extended to determine the relationships between geometrical tolerances and associated relevant manufacturing dimensions and tolerances. In addition to the manufacturing cost, the model takes into account manufacturing sequence, distribution of manufacturing dimensions, process capabilities, tolerances, design sizes, geometrical tolerances, machining allowances and optimum scrap level. The resulting computerized interactive system can be used not only in process planning, but also in quality control.     

冷挤压刀具在高精度细长孔加工中的应用

机械加工中往往会遇到细长孔加工,细长孔加工相当困难,特别是对于尺寸精度和几何公差要求高以及表面粗糙度值较小的细长孔加工;因此,使用传统车削和研磨加工的难度就更为突显。为了有效地解决这一加工难题,设计了一款冷挤压刀具,通过冷挤压加工,使工件达到了精度要求,同时,工件表面发生了金相变形,使强度和硬度均优于工件原金相组织结构,在提高产品使用寿命的同时也提高了生产效率。     

典型车加工零件的工艺分析与数控加工

通过对批量典型车加工零件的精度和形位公差要求进行分析,制定出合理的加工工艺及采用合适的夹具,用CNC车床加工出符合图纸要求的工件.     

数控加工中行程保护区域的应用

机床大小的选择所选用数控机床的加工范围应能满足零件的需要.数控机床的主参数及尺寸参数应满足加工需要.如最大圆弧直径,备坐标方面的行程距离,工作台面的尺寸等是否满足安放工件和夹具的需要及加工要求.行程开关在实际生产工作中,通常是被预先安装在特定的位置,这样生产机械的运动部件按照事先预计的行动路线运行,部件上模块撞击行程开...     

四轴数控螺旋锥齿轮铣齿机变性法铣齿研究

研究了四轴数控螺旋锥齿轮铣齿机的运动规律，建立了铣齿机加工坐标系。基于空间坐标变换，分析了由传统铣齿机调整参数转化为四轴数控铣齿机调整参数的原理并提出了实现方法。参照传统的变性法加工原理，推导出工件与摇台间变性法展成运动的滚比变化关系。这样，在四轴数控铣齿机上可以实现变性法加工准双曲面齿轮。     

基于PLC的数控机床电气控制系统研究

数控机床在解决复杂、精密零件的加工方面起到了重要的作用,是具有典型机电一体化系统的数控机床。基于PLC的数控机床电气控制系统是数控技术发展的必然结果。PLC数控机床在应用中有很多优点,例如,电气控制系统通过采用工件自动夹紧、断刀检测和机械手自动换刀等实现了数控机床的自动化。本文探讨了加工中心的电气控制技术和设计方法,对确保机床的安全可靠,提高加工精度和生产率具有重要意义。