Analysis–synthesis of dimensional deviation of the machining feature for discrete-part manufacturing processes

Dimensional deviation analysis has been an active and important research topic in mechanical design, manufacturing processes, and manufacturing systems. This paper proposes a comprehensive dimensional deviation evaluation framework for discrete-part manufacturing processes (DMP). A generic, explicit, and transmission model is developed to describe the dimensional deviation accumulation of machining processes by means of kinematic analysis of relationships between fixture error, datum error, machine tool geometric error, fixturing force inducing error and the dimensional quality of the product. The developed modeling technology can deal with general fixture configurations. In addition, the local contact deformations of the workpiece–fixture system are determined by solving a nonlinear programming problem of minimizing the total complementary energy of the frictional workpiece–fixture subsystem in machining system. Moreover, the deviation of an arbitrary point on machining feature can be also evaluated based on a point deviation model with prediction dimension deviation from the transmission model. The dimensional error transmission within the machining process is quantitatively described in this model. A systematic procedure to construct the model is presented and validated. This model can be also applied to process design evaluation for complicated machining processes.     

面向先进制造装备的网络化技术研究

分析了先进制造业现状，建立了数控加工网络化总体框架，提出了几何造型和NC加工的网络化实现方法，介绍了图形设计及走刀过程校验图形的网络浏览与发布，完成了用户标识，为实现数控加工的资源共享及网络化奠定基础。     

A study of materials swelling and recovery in single-point diamond turning of ductile materials

This paper presents an investigation of the effect of materials swelling in ultra-precision machining of ductile materials. The combined influence of materials swelling and recovery was found to affect the surface roughness in single-point diamond turning. It is interesting to note that the effect of materials swelling for ductile materials would be overwhelmed by the impact of recovery when the depth of cut is extremely small and the front clearance is small. In addition, radically different surface roughness profiles were found for different materials even though they are machined under the same cutting conditions. The difference in the machining behaviour could not be accounted by the elastic recovery alone but by the plastic deformation induced in the machined layer. The findings in the present study provide an important means for improving the surface roughness in ultra-precision machining.     

Form-accuracy analysis and prediction in computer-integrated manufacturing

The manufacturing of high-quality products at low costs is one of the greatest challenges of every company today. Form accuracy is among the quality parameters of machined parts and is directly related to functional performance. Control and improvement of form accuracy is to be performed under the computer-integrated manufacturing (CIM) concept. This paper investigates the form accuracy of mechanical machining and studies the essential aspects and procedures of form-accuracy simulation. The emphases are on the integration of form-accuracy analysis and the simulation into the CIM database construction and virtual manufacturing. Form-accuracy analysis in this paper reveals that the inherent drawbacks in design will directly affect the geometric quality of a workpiece, and proper process planning can enhance the manufacturability of parts with the required geometric quality. The simulation procedure implemented in this paper can be used at the design stage to predict the form accuracy of a machined part and functional performance. The procedure can also be used at the process planning stage to predict and control form accuracy during the machining process.     

Accuracy improvement of wire-EDM by real-time wire tension control

In this paper, a closed-loop wire tension control system for a wire-EDM machine is presented to improve the machining accuracy. Dynamic models of the wire feed control apparatus and wire tension control apparatus are derived to analyze and design the control system. PI controller and one-step-ahead adaptive controller are employed to investigate the dynamic performance of the closed-loop wire tension control system. In order to reduce the vibration of wire tension during wire feeding, dynamic absorbers are added to the idle rollers of wire transportation mechanism. Experimental results not only demonstrate that the developed control system with dynamic absorbers can obtain fast transient response and small steady-state error than an open-loop control system, they also indicate that the geometrical contour error of corner cutting is reduced with approximately 50% and the vertical straightness of a workpiece can be improved significantly.     

Tolerancing for manufacturing via cost minimization

The purpose of dimensioning and tolerancing for process planning is to determine the dimensions and tolerances that are to be produced at each stage in the manufacture of a component in order that the design dimensions and tolerances specified on the engineering drawing of the component are satisfied. Three proposed objective functions for cost minimization are developed in this paper according to various situations. When cost information is available average cost per acceptable unit produced in minimized, otherwise ratio of number of components to be machined to output is minimized. If residual tolerances exist sum of manufactured tolerances are maximized by assigning weights according to their process capabilities. Combining these objective functions a computerized optimization program has been developed which determines the optimum set of dimensions and tolerances which satisfies the specified design dimensions and tolerances and the permissible machining allowances, with the cost of producing all dimensions to the respective tolerances to be minimal.

This system takes into account machining cost, scrap and where in the production process it occurs, manufactured dimensions and their distributions, allocated tolerances and process capabilities.     

Modeling system error in batch machining based on genetic algorithms

During batch machining under a static cutting-tool setting, machining errors of workpieces always have an ascending trend with the order of workpieces. Here the error trend is called the system error in batch machining. To compensate for the machining system error and enhance machining accuracy, modeling the system error is the key process. This paper first analyses several popular modeling methods and identifies their deficiencies when used in system error modeling. Subsequently, a new method of system error modeling based on Genetic Algorithms (GA) is introduced. Finally, a real-life application example using the new method and a comparison with other modeling methods are given, which indicate that the proposed GA based method is good. The paper also points out the essence that the proposed modeling method is a polynomial regression one in a broad sense, and is useful in the modeling of non-uniform error series.     

Manufacturing data analysis of machine tool errors within a contemporary small manufacturing enterprise

The main focus of this paper is directed at the determination of manufacturing errors within the contemporary smaller manufacturing enterprise sector. These can manifest themselves as machine tool, fixturing or programming errors, experienced during the manufacture of 2 1/2D components on a 3-axis vertical machining centre. The manufacturing error diagnosis is achieved through the manufacturing data analysis of the results obtained from the inspection of the component on a co-ordinate measuring machine. This manufacturing data analysis activity adopts a feature-based approach and is conducted through the application of a forward chaining expert system, termed, the Product Data Analysis Distributed Diagnostic Expert System, which forms part of a larger prototype feedback system entitled the Production Data Analysis framework. This paper introduces the manufacturing error categorisations that are associated with milling type operations, knowledge acquisition and representation, conceptual structure and operating procedure of the prototype manufacturing data analysis facility. The paper concludes with a brief evaluation of the logic employed through the simulation of manufacturing error scenarios. This prototype manufacturing data analysis expert system provides a valuable aid for the rapid diagnosis and elimination of manufacturing errors on a 3-axis vertical machining centre in an environment where operator expertise is limited.     

Compact machining module for laser chemical manufacturing

The size of machines for the manufacture of micro-components commonly stands in gross disproportion to the component size. The achievable accuracy is limited by inaccuracies of mechanical positioning elements and external disturbances. Micro-machining of metals can be realised in manifold ways by laser processes. In this paper, a compact module for laser chemical processing using continuous wave laser radiation is presented. For the laser-induced chemical machining the material removal is a result of thermochemical reactions between an etchant and the surface of a metallic workpiece at low laser power densities. Laser-induced chemical machining results in improved surface quality of the machined workpiece and it also avoids stress and strain of the material. Through the use of a micro-mirror array (DMD) for flexible beam shaping a 2-dimensional machining of the workpiece is possible. The laser chemical machining method now allow for the first time to connect the DMD technology with laser-based micro-machining for compaction of the machining module.     

Small-wavelength form error compensation during hydrodynamic polishing

This paper proposes a process control strategy for removing small-wavelength form error during hydrodynamic polishing, that is, by planning a tool dwelling time appropriate to accurately remove the form error. Volume removal analysis suggests that removal of an arbitrary error profile requires the tool to dwell at a given position for a period that is a linear function of the error profile. The dwelling-time distribution of the tool is solved by the non-negative least squares method. The residual error between the actual and desired profile is induced by this strategy. Residual error occurs mainly at the peaks and valleys of the profile, in addition to the boundaries of the machining area. Results indicate that the dominant factors in deciding residual error are the size of the machining zone, tool step, and wavelength and amplitude of the error profile. It is shown that larger residual error occurs in bands with wavelengths smaller than the machining zone, and vice versa. If the wavelength is sufficiently large, a small tool step effectively reduces the residual error. Furthermore, large variations in the amplitude of the error profile can be effectively reduced when the wavelength is large. Experimental results confirm that the proposed polishing strategy can remove an arbitrary profile and automatically reduce the small-wavelength errors. However, it is not effective when the wavelength of the error profile is near the size of the machining zone.     

Analysis of the effects of fixture clamping sequence on part location errors

Several fixture-related error sources are known to contribute to part location error, which can lead to poor part quality. In addition to typical error sources, such as fixture geometric error and elastic deformation of the fixture and part due to clamping forces, the clamping sequence used can also influence part position and orientation. In this paper, the effect of clamping sequence on workpiece location error is modeled analytically for a fixture–workpiece system where all major compliance sources and fixture geometric error are considered. Part location error is quantified by the displacement of a response point on the part surface. An algorithmic procedure designed to understand how forces and deformations change as clamps are applied sequentially is presented. The effect of clamping sequence on part location error and locator reaction force is examined through model simulations and experiments via an example involving a 3-2-1 machining fixture.     

A process planning strategy for removing an arbitrary profile by hydrodynamic polishing process

A process planning strategy for removing an arbitrary profile by a deterministic polishing process is proposed. This strategy suggested that to remove an arbitrary profile the time-distribution of the tool motion at themachining area can be designed to be a linear function of the profile. Because the area of the instantaneous machining zone is finite and the machining rate distribution at this zone is not uniform, this strategy may cause a difference between the desired and machined profiles. The possible errors are classified into two groups: the machining time-distribution error and the ripple error. It is shown that the machining time-distribution error is significant only at the boundary of the machining area. By increasing the size between two conjoint tool positions, this error can be reduced. The size of the instantaneous machining zone has little effect on this error if the size ratio between this zone and two conjoint tool positions is fixed. On the other hand, the ripple error will occur over the whole machining area. The smaller the distance between two conjoint tool positions, the smaller the ripple error will be. The experimental study indicated that the analytical prediction is correct and an arbitrary profile can be accurately removed according to this proposed strategy.     

基于多体系统理论的车铣中心空间误差模型分析

数控机床的误差建模是进行机床运动设计、精度分析和误差补偿的关键技术,也是保证机床加工精度的重要环节.本文利用多体系统理论来构建超精密数控机床的几何误差模型,该模型简便、明确,不受机床结构和运动复杂程度的限制,为计算机床误差、实现误差补偿和修正控制指令提供了理论依据.在机床实际应用中,可以利用由精密机床误差建模所推导出的几何位置误差来修正理想加工指令,控制机床的实际运动,从而实现几何误差补偿,提高机床加工精度.     

Derivation of machine tool error models and error compensation procedure for three axes vertical machining center using rigid body kinematics

Volumetric positional accuracy constitutes a large portion of the total machine tool error during machining. In order to improve machine tool accuracy cost-effectively, machine tool geometric errors as well as thermally induced errors have to be characterized and predicted for error compensation. This paper presents the development of kinematic error models accounting for geometric and thermal errors in the Vertical Machining Center (VMC). The machine tool investigated is a Cincinnati Milacron Sabre 750 3 axes CNC Vertical Machining Center with open architecture controller. Using Rigid Body Kinematics and small angle approximation of the errors, each slide of the three axes vertical machining center is modeled using homogeneous coordinate transformation. By synthesizing the machine's parametric errors such as linear positioning errors, roll, pitch and yaw etc., an expression for the volumetric errors in the multi-axis machine tool is developed. The developed mathematical model is used to calculate and predict the resultant error vector at the tool–workpiece interface for error compensation.     

ZH5120B立式钻削加工中心的造型设计研究

通过对北京第三机床厂ZH5120B立式钻削加工中心进行了结构与外观研究，本文分析了数控加工中心的造型形式法则、色彩设计、宜人性设计等，并完成了其造型的改良设计，从而为企业提高产品竞争力，做了有实际意义的实践工作。     

Greenhouse gases emitted in manufacturing a product—A new economic model

In this paper, we propose a machining microeconomic model that can optimize machining parameters and include all energy and environmental costs. A survey of microeconomic machining cost models is covered, with the result that a new cost model has been developed based on life cycle analysis (LCA) methodology. The scope includes the initial part production. Theoretical and actual experimental results are used to illustrate the model's implications with respect to carbon emissions and cost sensitivity. It is shown that for a manufacturing strategy, more certainty is required for inputs like carbon pricing to reduce financial risk. The limitations of the model, policy issues and future work are outlined.     

An oblique ultrasonic polishing method by robot for free-form surfaces

This paper develops a new ultrasonic machining system and methodology by which a robot polishes on free-form surfaces at an oblique angle with an elastic tool. On the basis of the theories of reflection of elastic waves and dynamic stress concentration, the conception is brought forward that ultrasonic elastic contact is not continuous, the physical process of the oblique ultrasonic polishing is studied and the cutting mechanism of the abrasive finish machining methods driven by ultrasonic vibration is ascribed to the joint action of the machining operation and shot-blasting. Experimental results verify that the new oblique ultrasonic polishing method by robot is an effective machining method for free-form surfaces.     

Improving the shape quality of bearing rings in soft turning by using a Fast Tool Servo

In machining of ring shaped components, the workpiece is deformed by the clamping forces of the chuck. This elastic deformation generates shape deviations in soft turning. Moreover, the machining process generates locally varying residual stresses which contribute to shape deviation of the workpiece. Hence, in machining of thin-walled bearing rings hexagonal out‐of‐roundness up to 200 μm occur. In order to minimize the shape deviations, a long stroke Fast Tool Servo (FTS) for controlling the depth of cut was developed. The applied FTS differs from other published FTS systems in the guidance design. The moving tool holder is suspended to the FTS frame by flexure joints instead of using a linear guidance. The flexure joints provide a low stiffness in moving direction and high stiffness in orthogonal directions. The high stiffness in cutting force direction is essential for a real time reduction of shape deviations in soft turning. In this paper, results of an experimental investigation for the reduction of the shape deviation by adapted non circular machining are presented, using the developed FTS. Based on the results, the influence of the cutting forces on part accuracy is discussed.     

The effectiveness of contouring control and a design for three-dimensional machining

Although many researches have been conducted on contouring control for machine tool feed drive systems, to the best of authors’ knowledge, its effectiveness has been verified only through comparative experiments with industrial non-contouring (independent axial) controllers, or conventional contouring controllers such as the cross-coupling controller. Because control performance largely depends on controller gains, such comparisons involve some difficulties in demonstrating the effectiveness of contouring control. In other words, a similar control performance can be achieved if the non-contouring controller gains are appropriately assigned. This paper discusses the effectiveness of contouring controllers both analytically and experimentally. A new contouring controller design for three-dimensional machining is presented, which is extended from the authors’ biaxial design based on coordinate transformation. The contouring controller is concluded to be effective through an analysis of the proposed design, in that it provides performance comparable to non-contouring controllers with less control input variance. This property reduces the damage to machine tool systems and saves control energy. In addition, because an inherent contour error exists in the coordinate transformation approach, a method for reducing this error is presented to enhance the effectiveness of the contouring controller. Experimental results support the claims of this paper.     

Tool deflection compensation in peripheral milling of curved geometries

This paper presents compensation of surface error due to cutting force-induced tool deflections in a peripheral milling process. Previous research attempts on this topic deal with error compensation in machining of straight geometries only. This paper is concerned with peripheral milling of variable curvature geometries where the workpiece curvature changes continuously along the path of cut. In the case of curved geometries, both process geometry and the cutting forces have shown to have strong dependence on workpiece curvature and hence variation of surface error along the path of cut. This calls for a different error compensation strategy than the one which is normally used for machining straight geometries. The present work is an attempt to improve accuracy in machining of curved geometries by use of CNC tool path compensation. Mechanistic model for cutting force estimation and cantilever beam model for cutter deflection estimation are used. The results based on machining experiments performed on a variety of geometries show that the dimensional accuracy can be improved significantly in peripheral milling of curved geometries.