Statistical study of the spindle dilatation phenomena—Application to a NC lathe

Spindle dilatation in one of the most important causes of defects on parts machined on CNC lathes. Experiments and models have been established to determine the average value of the spindle's dilatation. The problem of determination of confidence interval associated to those predictions remains open. If the average value of dilatation can be estimated, any existing model can predict how near or far from the average value will be the spindle's dilatation. This work deals with the problem of type of dilatation measures repartition. A Khi-2 test done on dilatation measures reveals that dilatation measures spread under a normal repartition law. So, a model to determine the confidence interval associated to the dilatation prediction is presented. The repartition law of the samples of dilatation allows to set up this model. Then, a method to calculate an upper bound of the standard deviation of the dilatation repartition law is proposed. The model proposed can be used to determine the confidence interval of spindle dilatation phenomenon. This determination allows a useful prediction of the dilatation because of the confidence interval that can now be associated to the prediction.     

心轴法在偏心齿轮加工检验中的应用

本文介绍了心轴法在加工偏心齿轮中的应用,通过心轴法能够有效保证偏心齿轮的加工精度。     

加工中心几何精度检验的探讨

本文简要的论述了加工中心整机几何精度检验合理的实施方法， 分析了新颁国际标准（ 草案） ＩＳＯ／ＤＩＳ１０７９１ 的几何精度部分同原机械工业部部颁标准ＪＢ／ＧＱ１１４０ － ８９ 加工中心精度部分二者的差异与劣优， 差重指出ＩＳＯ／ＤＩＳ１０７９１ 新标准仍有漏检或易引起争议的一些尚待商榷的问题， 提出了制订我国加工中心几何精度检验新标准的具体建议。     

Fuzzy control of spindle torque for industrial CNC machining

Developing a dedicated control system for each and every machining process or machine is costly and time-consuming. Such a practice has obviously undermined the usefulness of many current systems. This paper presents a fuzzy control system that can be used for different machining processes. This system consists of a basic fuzzy logic controller, a fuzzy rule base, and a tuning mechanism used to enhance the adaptability of the system. Industrial tests have been carried out for both end milling and turning processes. The control signal is spindle torque, readily available on many CNC machines. The test results show that the system performs well on both end milling and turning operations and can easily adapt to tool changes as well as workpiece material changes.     

A study on the development of a multi-purpose spindle system for quality productive machining

A compact multi-purpose spindle for multi-tasking machine tools has been developed such that it can provide high power and torque for lower speed ranges while it rotates at high speeds for light duty machining. The innovative design based on the dual direct drive concept has been adopted such that the size of the spindle can stay the same as a conventional spindle of its class. For optimizing the design process, a method based on the complete virtual approach using 3D solid models has been studied and developed. Machining performance has been verified through a physical prototype.     

机床主轴系统的动态优化设计

以降低主轴产端动柔度值为优化目标，综合利用传递矩阵法和子结构的概念，寻找薄弱模态和计算共能量分布率，并编制了相应的计算机程序，使调参能方便地在微机上进行。     

Position geometric error modeling,identification and compensation for large 5-axis machining center prototype

This paper presents a position geometric error modeling, identification and compensation method for large 5-axis machining center prototype. First, regarding the prototype as a rigid multi-body system, a geometric error model has been established, which supports the identification of position geometric error associated with a translational axis by using laser interferometer, and a rotational axis by using laser tracker. Second, based on this model, an improved identification approach named as virtual rigid-body is put forward for calculating positioning error of each large translational axis. Detailed derivation of a generalized matrix equation is given. Third, analytical models based on the least-squares theory were adopted to compute error values at an arbitrary position for error compensation. Finally, the identified position geometric errors were compensated by using recursive software-based error compensation method. The results show that the position accuracy of large machining center prototype has been improved with compensation and up to the design requirements.     

Compensation of thermo-dependent machine tool deformations due to spindle load: investigation of the optimal transfer function in consideration of rough machining

The thermal behavior of a machine tool is an important indicator for the grade of production accuracy and indirectly for the market success. The load-dependent temperature distribution and the resulting deformation of the machine tool are influenced by a variety of design and thermo-technical parameters. The main spindle of a machine tool is, without any doubt, the major heat source within the machine structure. The object of the scientific investigation presented in this article is the development of an approach to robust compensation of thermo-dependent machine tool deformations due to spindle load in consideration of rough machining. The focus of the work concentrates on the identification of the model with the highest compensation performance. The underlying concept for the compensation of thermo-dependent machine tool deformations is the indirect approach by using the speed and the effective power of the main spindle for the calculation of the Tool Center Point (TCP) displacement. The presented modeling approach requires the knowledge of the TCP displacement in X-, Y- and Z-direction depending on the speed and the effective power of the main spindle. As a tool for modeling the thermo-dependent behavior of a milling machine, a load test rig for repeatable, defined long-term loading of the main spindle has been developed. It simulates the cutting force depending on the spindle speed and the torque and applies load to the main spindle. The spindle speed and the spindle effective power can be taken directly from the numerical control of the machine tool. An important advantage of the presented compensation method is the fact that it does not require any external sensors. The displacement of the TCP has to be measured, but only during modeling. The relationship between the speed/power of the main spindle as a cause and the displacement of the TCP in X-, Y- and Z-direction as an effect can be determined by a transfer function. This paper compares the compensation results depending on the transfer function and identifies the model with the best compensation performance. The validation of the compensation method is executed by using the example of two different speed and power spectra of the main spindle.     

Computer simulation applied to an orthogonal three-rod machine tool for machining a complicated three-dimensional surface

A computer simulation approach to machine a complicated three-dimensional surface by using a virtual orthogonal three-rod machine tool is presented. First, based on a Hunt’s parallel mechanism of three degrees of freedom, a three-dimensional virtual orthogonal three-rod machine tool with three degrees of freedom is created with advanced C software. Secondly, a tool spiral path base on the three-dimensional surface of workpiece is constituted. Thirdly, the tool spiral path base of the three-dimensional surface is assembled into a virtual orthogonal three-rod machine tool with some auxiliary links and a new virtual one-degree of freedom mechanism is created. Finally, by analyzing reversing motion, a reasonable input rotation function is determined, and the kinematic curves of the three rods and the feeding process are simulated and analyzed.     

Design and performance of AlTiN and TiAlCrN PVD coatings for machining of hard to cut materials

Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed.Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl₆V₄).It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al-Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10-30 nm enhances necessary properties of the coating.In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.