Machining and dimensional inspection of spatial cams on 5-axis machine tools

An analytical methodology is developed for NC data generation to produce and measure spatial cams on 5-axis machine tools. The Denavit-Hartenberg notation is used for expressing the ability function of the employed machine tool and in the generation of the desired cutter/measuring-probe location. NC data equations are determined by equating the corresponding elements of the machine tool's ability function to the desired tool location matrices. To validate this methodology, a designed cam was machined and its surfaces were measured by an online measurement system equipped with a touch-trigger probe on a 5-axis machine tool. The resultant cutting speed and material-removal rate during machining are also investigated. This methodology is a general one and is applicable to various spatial cams. It also combines the activities of design, manufacturing, and measurement, thus making the production process more flexible, automatic, and controllable.     

NC data generation for 6-axis machine tools to produce a helical drill

This study presents a design methodology for grinding a specific helical drill on a CNC 6-axis grinding machine. The proposed methodology comprises three steps: (1) deriving a mathematical model of the helical drill, (2) establishing the ability matrix of the multi-axis grinding machine according to Denavit-Hartenberg (D-H) notation, and (3) constructing configuration matrices to express the required grinding wheel positions and orientations while machining the flute and flank surfaces of the drill. The NC data for the motion values of each axis are obtained by equating the corresponding elements of the CNC ability matrix and the configuration matrices of the grinding wheel. To verify the proposed methodology, a designed helical drill is machined on a 6-axis CNC tool-grinding machine. The methodology presented in this study integrates the drill design and manufacturing activities, thereby making possible the implementation of a more flexible, automatic, cost efficient and controllable design and production process.     

复杂曲面零件在线检测与误差补偿方法

复杂曲面零件的高精度加工与精密检测一直是数字化制造领域的研究热点。为提高复杂曲面零件的加工精度、检测精度,提出一种集数控机床在线检测、加工误差分解与补偿加工为一体的集成化方法。介绍集成化在线检测方法及补偿系统的基本原理,分析数控加工后曲面零件测点数据的误差组成,提出一种基于空间统计分析的加工误差分解方法,在建立基于B样条曲面的确定性曲面回归模型的基础上,对回归模型残差进行空间独立性分析,分解出系统误差和随机误差,进而通过数控代码的修改,实现零件加工过程的系统误差补偿。列举一个曲面零件的加工与检测实例,进行方法有效性验证。通过加工工件的在线检测、误差分解、代码修改及补偿加工等环节,实例零件的加工精度有了大幅提高,而该系统的检测精度也通过与三坐标测量机(Coordinate measuring machine, CMM)检验结果的对比,得到了有效验证。     

慢走丝电火花线切割粗加工仿真系统的开发

为对电火花线切割加工机理有更深刻的认识,了解加工参数对加工精度的影响规律,介绍了一个电火花线切割加工粗加工的仿真系统。仿真系统通过对放电点的探索、工件的去除以及对线电极丝振动的分析,将实际的加工现象形象地再现于计算机上。为证实仿真系统的正确性,将仿真结果与试验结果进行了比较。在试验结果的获取中,为能够得到很难测量的线电极周围的放电间隙和工件形状数据,提出一种新的三维形状测量方法。通过对仿真结果和试验结果的比较,定性地证明了仿真方法的正确性。研究结果表明:改变线电极张力及伺服电压值时,从仿真过程得到的加工形状结果与试验得到的加工形状结果其倾向基本一致;加工缝端部的形状呈凸形还是呈凹形,取决于加工过程中放电爆发力和静电引力的相对大小。     

A Study on an Open Architecture CNC System with a NURBS Interpolator for WEDM

This paper deals with the design and implementation of an open architecture CNC system for wire electrical discharge machining (WEDM) with a consideration of the differences between WEDM and NC cutting machines. Work using open architecture controllers (OACs) has focused mainly on metal cutting machines. WEDM has many aspects similar to milling machines. However, there are differences in the machining processes and control strategies. To close the gap between previous general work on OAC and the WEDM specific needs, an open architecture NC model for WEDM comprised of a synchronisation kernel and an NC functional module is proposed. The proposed CNC system is applied to an existing commercial WEDM system by a retrofitting method. A precise NURBS interpolation function is implemented and sample runs are conducted with a NURBS interpolator that is added to the proposed system.     

薄壁零件加工变形分析及控制方案

介绍了有限元在分析薄壁件铣削加工变形中的应用，并提出一种数控补偿方法来减少让刀误差，从而控制薄壁件的加工精度。通过分析和实验建立切削力模型，运用ANSYS有限元分析软件对典型薄壁框体零件的加工变形进行了分析计算，结果与实际加工情况相符。根据有限元分析结果，提出在精加工时，在数控编程时让刀具在原有走刀轨迹中按变形程度附加一个偏摆，补偿因变形而产生的让刀量，可基本消除让刀误差。     

Using wire electrical discharge machining for improved corner cutting accuracy of thin parts

The wire electrical discharge machining process (WEDM) allows one to achieved ruled surfaces along intricate contours in hard materials. When one intends to use such a machining process, one has to analyze both the magnitudes of the corners’ radii and the corner’s angles that are formed between adjoining surfaces. Some experimental research work carried out unveiled the systematic occurrence of machining errors when WEDM is used to obtain outside sharp corners, especially in small thickness workpieces. A permanent bending at the crest of sharp corners, which leads to a substantial deviation from the prescribed geometrical shape, was found. The deviation form depends on the magnetic properties of the workpiece material. The research was focused on establishing a means for characterizing this shape error. Moreover, the influence exerted by certain factors, such as the corner angle and the thickness of the workpiece on the above-mentioned machining error was quantified.     

Original models for the prediction of angular error in wire-EDM taper-cutting

Taper-cutting is a common application of the wire electrical discharge machining (WEDM) process used for the production of parts with complex geometry such as extrusion dies in wear-resistant materials, cutting dies, etc. During cutting, the wire is subject to deformation, resulting in deviations in the inclination angle of machined parts. This fact causes dimensional errors and loss of tolerances that can lead to the rejection of high added-value tooling. Currently, WEDM machine manufacturers propose time-consuming experimental trial-and-error methodologies for the correction of the errors. To reduce the experimental load and to contribute a more general approach to the problem, two original models for the prediction of angular error in WEDM taper-cutting are presented here. Results show that part thickness and taper angle are the most influencing variables in the problem. Experimental validation of the proposed models shows that angular error can be reduced below 3′45′′ in 75% of cases.     

Development of a virtual reality wire electrical discharge machining system for operation training

Wire electrical discharge machining (WEDM) uses a metallic thin wire to cut a programmed profile with high strength having sharp edges such as extrusion dies and blanking punches. However, the cost of purchasing and maintaining of WEDM equipment is very high for both the industry and general education institutions. Therefore, there are potential demands to reduce the expensive machine operation training cost, provide off-line collision-free simulation verification of the tool path, and examine the correctness of the programmed wire cutting NC codes. This paper presents the development of a virtual reality-based WEDM full machine simulation system which can emulate major functions of a real controller related to operation training and education. These functions include the tool path simulation, NC program interpretation and processing, kinematics of the machine mechanism, workpiece origin setting, etc. To demonstrate the developed system and illustrate the adopted method, the system capability is explained and shown in this paper. The research result can be used as a cost-effective interactive 3D digital tutoring system that has the benefits of improving on the inefficient, dangerous, and costly drawbacks in traditional learning and training for operating the real WEDM machine.     

装夹定位误差的补偿方法

在数控机床上，利用数控程序测量，计算和补偿工件装夹定位误差，可降低对工件的装夹定位要求，提高了加工精度和生产效率。文章着重介绍了车床大拖板类异形零件装夹定位误差的测量，计算和数学模型的建立方法。     

A methodology for systematic geometric error compensation in five-axis machine tools

To enhance the accuracy, an efficient methodology was developed and described for systematic geometric error correction and their compensation in five-axis machine tools. The methodology is capable of compensating the overall effect of all position-dependent and position-independent errors which contribute to volumetric workspace. It was implemented on a five-axis grinding machine for error compensation and for the check of its effectiveness. Error compensation algorithm was designed, and a routine was written in Matlab software. The developed technique and software are based on an error table which interprets the function of axis through cubic spline technique and synthesis modeling of a machine tool. Recursive compensation methodology was used to remove the machine errors from the actual tool path and inverse technique was implemented to find the corrected positions of prismatic and rotary joints. Moreover, it can convert the corrected tool paths into practical compensated NC codes. The generated, corrected and modified NC codes directly fed to the controller of a five-axis machine tool. Validation of the technique was preceded by repeated experimentation of measurement and through machining of typical standard workpieces with some additional specific features. Experimental results exhibit effective compensation and remarkable improvement in the parametric and volumetric-workspace accuracy of the five-axis machine tool.     

端面正弦直纹曲面零件的线切割加工技术

为解决端面正弦直纹曲面的加工难题,提出了利用国产高速走丝电火花线切割机床进行加工的一种方法。依据正弦直纹曲面的形成原理,分析线切割加工的运动方式。通过数控回转台与线切割机床相结合,形成实现加工所需的运动,进行了样件的实验加工,实验结果表明,设计的加工方法合理有效。     

Surface integrity study of WEDM with various wire electrodes: experiments and analysis

Abstract

Wire electrical discharge machining (WEDM) is always significant for its high-precision machining. However, due to the generation of high discharge energy during machining, machined surfaces are often got distorted. These might be upgraded by choosing the correct tool with proper machining condition. The effects of the electrode materials and process parameters on different responses of WEDM like average surface roughness, recast layer thickness, and surface morphology are systematically examined here to enhance the knowledge of WEDM and its correlation with electrode property. The experiments have been carried out on one of the expensive steel namely Maraging steel 300 due to its applicability in tooling and aerospace industries. Plain brass wire, zinc-coated brass wire (ZCB), and silver-coated brass (SCB) wires are used as a tool electrode for analysis. Comparative experimental studies prove that among BW, ZCB, and SCB, the overall performance of SCB is commendable owing to the high-quality surface considering control parameters in low discharge energy level. However, the second-best performance is shown by ZCB.     

空间曲面线切割多轴联动加工系统开发及应用

开发了能实现空间曲面零件电火花线切割加工的多轴联动加工系统,分析了系统的组成和运动参数。依据空间解析几何直纹曲面形成原理,建立了五轴联动加工的数学模型体系,获得了五轴联动加工三导线曲面零件的数学模型。研制了多轴联动加工系统的执行机构转摆摆数控工作台及数控系统,加工出理想的实验样件。解决了空间曲面零件的加工难题,拓宽了高速走丝电火花线切割加工的应用范围。该方法在模具制造及空间曲面零件加工中得到广泛应用。     

Selection of optimal process parameters in WEDM while machining Al7075/SiCp metal matrix composites

Aluminium metal matrix composites (MMCs) reinforced with silicon carbide particulate (SiCp) find several applications due to their improved mechanical properties over the conventional metals for a wide variety of aerospace and automotive applications. However, the presence of discontinuously distributed hard ceramic in the MMCs made them as difficult-to-cut materials for conventional machining methods. The wire electrical discharge machining (WEDM), as a widely adopted non-traditional machining method for difficult-to-cut precision components, found an appropriate metal removal process for MMCs to enhance quality of cut within the stipulated cost. While machining the advanced materials like MMCs, a clear understanding into the machining performance of the process for its control variables could make the process uncomplicated and economical. In light of the growing industrial need of making high performance-low cost components, the investigation aimed to explore the machining performance characteristics of SiCp reinforced Al7075 matrix composites (Al7075/SiCp) during WEDM. While conducting the machining experiments, surface roughness, metal removal rate, and wire wear ratio are considered the responses to evaluate the WEDM performance. Response surface methodology is used to develop the empirical models for these WEDM responses. SiC particulate size and volume percentages are considered the process variables along with pulse-on time, pulse-off time, and wire tension. Analysis of variance (ANOVA) is used to check the adequacy of the developed models. Since the machining responses are conflicting in nature, the problem is formulated as a multi-objective optimization problem and is solved using the Non-dominated Sorting Genetic Algorithm-II to obtain the set of Pareto-optimal solutions. The derived optimal process responses are confirmed by the experimental validation tests, and the results are analyzed by SEM.     

Analyzing the surface layer after WEDM depending on the parameters of a machine for the 16MnCr5 steel

The efficient wire electric discharge machining (WEDM) technology is a trade-off between the cutting speed and the resulting surface quality. A typical morphology of a surface machined using WEDM contains a large number of craters caused by the electric sparks generated in the cutting process. The paper analyzes the influence of the cutting speed on the quantitative and qualitative evaluation of the craters formed on the surface of a workpiece made of the 16MnCr5 steel. Applying metallography to cross-section microscopic slides, diffusion subsurface damages were studied caused by the cutting. The diffusion processes taking place between the electrode and the material machined were studied using a local point EDX microanalysis applied both to the machined surfaces and to the cross sections. A detailed study was also carried out of the brass electrode to measure its wear rate caused by the cutting process as well as its degradation in terms of the quality of its morphology and the chemical composition of surface.     

数控电解车削装置及基础工艺试验

介绍数控电解车削加工原理及试验装置.利用直线刃阴极在试验装置上进行圆柱面和凸轮面的加工试验,并对试验结果进行分析.结果表明数控电解车削加工可用于回转件的加工.     

Improving the surface quality in wire electrical discharge machined specimens by removing the recast layer using magnetic abrasive finishing method

This study explores the feasibility of removing the recast layer formed on aluminum alloy cylindrical specimens machined by wire electrical discharge machining (WEDM) by using magnetic abrasive finishing (MAF). The WEDM is a thermal machining process capable of accurately machining parts with high hardness or complex shapes. The sparks produced during the WEDM process melt the metal’s surface. The molten material undergoes ultra-rapid quenching and forms a layer on the surface defined as recast layer. The recast layer may be full of craters and microcracks which reduce service life of materials tremendously, especially under fatigue loads in corrosive environments. This investigation demonstrates that MAF process, can improve the quality of WEDM machined surfaces effectively by removing the recast layer. The present work studies the effect of some parameters, i.e., linear speed, working gap, abrasive particle size, and finishing time on surface roughness and recast layer thickness using full factorial analysis. Three-level full factorial technique is used as design of experiments for studying the selected factors. In order to indicate the significant factors, the analysis of variance has been used. In addition, an equation based on regression analysis is presented to indicate the relationship between surface roughness and recast layer thickness of cylindrical specimens and finishing parameters. Experimental results show the influence of MAF process on recast layer removal and surface roughness improvement.     

新型电火花线切割机床的设计与可行性研究

现在通用的快走丝电火花线切割机床一般为线架与走丝部件固定在床身,工作台移动进给式结构,这样的结构对于一般的中小型工件可以满足加工要求,但是重型工件,由于对机床工作台的行程、电机的驱动能力要求过高,一般机床难以满足加工要求.这里提出一种新型的机床结构,对现有机床进行结构改造,并在改造前后的机床进行了一系列的切割实验,对切割效果进行分析比较分析,为新型线切割机床设计的可行性及生产提供了理论与工艺的支持.     

Five-Axis NC Machining of Sculptured Surfaces

This paper presents a new method for the determination of tool position and orientation for NC milling of sculptured surfaces with a five-axis NC machine. This method uses an analysis of local curvatures of the surface and the tool geometry. Based on matching these local properties, optimal tool axis orientations are selected so that the gouging error in machining is eliminated or controlled within a specific tolerance. An accurate technique is also proposed for the computation of cusp height of the machined surface. By eliminating gouging and controlling scallops within a specified tolerance, it is expected that the time-consuming manual grind-ing process could be greatly reduced or completely eliminated in the finish machining of complex die or mould surfaces.