Virtual simulation of five-axis machine tool with consideration of CNC interpolation,servo dynamics,friction, and geometric errors

Abstract

A virtual machine tool (VMT) simulation system which considers tool center point (TCP) interpolation, geometric errors, servo dynamics, and friction effects for a five-axis machine tool is developed in this paper. A novel five-axis interpolation method is proposed to ensure that maximum velocity constraints for each axis can be satisfied. The geometric error model, including lead screw, straightness, angular and squareness errors is built to analyze the volumetric errors within the working space. The model which includes rigid body motion, friction model and servo control loops is utilized to evaluate servo dynamics and non-linear effects. The errors caused by the locations, servo dynamics, and friction effects are integrated into the VMT simulation program. Simulation results of TCP trajectory are represented by small line segments to generate NC codes. Then the NC codes are fed into VERICUT software to perform virtual cutting. To evaluate the interpolation design, cutting experiments are carried out on the five-axis engraving machine with a PC-based controller. The performances using the proposed interpolation method are comparable with the commercial CNC controller from Heidenhain. The effects of different error sources on the surface are demonstrated by cutting the sculpture of a human face. Path overcut caused by servo dynamics is found at sharp corners, and volumetric errors cause obvious tool marks and poor surface roughness. The proposed methodology can serve as a useful tool in evaluating the behaviors of error sources during the design stage.     

数控机床整机动态特性评价方法

动态特性是衡量机床性能的一项重要指标,但目前并没有较好的数控机床整机动态特性评价方法。利用真实的动态切削力对数控机床进行激励,能够快速获取机床在切削力作用下的动态特性。鉴于切削参数会影响各频率成分对应的切削力幅值,基于不同工件材料和切削参数下的动态切削力,建立动态激振力模型,通过分频段激励来检验数控机床在不同频段下的动态特性。通过有限元仿真分析,判断数控机床在各个频段下的动态特性;对振动信号进行快速傅里叶变换,得到机床振动时的主要频率成分,为优化机床动态特性提供指导;对比各种动态切削力激振下不同机床的动刚度,评价不同机床动态特性的优劣。最后,通过激振试验验证了仿真结果的准确性。结果表明上述方法简单实用,能快速评价数控机床的动态特性,具有一定的实用价值。     

Evaluation method of dynamic characteristics of whole NC machine tool

The dynamic characteristics is an important index to measure the performance of machine tools.However, there is no better method to evaluate the dynamic characteristics of whole NC (numerical control) machine tool. Through the excitation of real dynamic cutting force to the NC machine tool, the dynamic characteristics of the machine tool under the action of cutting force can be quickly obtained. In view of the fact that the cutting parameters would affect the amplitude of cutting force corresponding to each frequency component, a dynamic excitation force model was established based on the dynamic cutting forces under different sample materials and cutting parameters.The dynamic characteristics of the NC machine tool in different frequency bands could be tested by frequency band excitation. Through the finite element simulation analysis, the dynamic characteristics of NC machine tool in each frequency band was judged. The main frequency components in the vibration of machine tool were obtained by fast Fourier transform of vibration signal, which could provide guidance for optimizing the dynamic characteristics of machine tool. The dynamic stiffness of different machine tools under excitation of various dynamic cutting forces was compared to distinguish which machine tool had better dynamic characteristics. Finally, the simulation results were verified by the excitation test. The results indicate that the above method is simple and practical, and can quickly evaluate the dynamic characteristics of NC machine tool, which has certain practical value.     

炭/炭复合材料切削加工试验研究

探讨了Ｃ／Ｃ复合材料结构和机构物理性能的特殊性及机构切削加工的特点。用ＳＥＭ观察了不同切削条件下切屑的断口形貌。用５种不同的刀具材料、刀具角度及几何开头相同的刀具，在一定的切削工艺参数条件下，对该材料进行切削试验，以刀具有前刀面和／或后刀面的磨损率为判据，最佳刀具材料为ＹＧ８，在切削Ｃ／Ｃ复合材料的过程中，轨具的磨损极为严重，刀具磨损的主要机理是粘着磨损和磨粒磨损。     

Fundamental Turning Characteristics of Inconel 718 by Applying Ultrasonic Elliptical Vibration on the Base Plane

Inconel 718, a nickel-based superalloy, exhibits desirable properties over a wide temperature range, and it is widely used in industry. However, Inconel 718 is typically difficult to cut because of its strong work hardening, high temperature tensile strength, and shear strength. To improve the machinability of Inconel 718, this study proposes ultrasonic turning by applying elliptical vibration to the base plane. The principle and features of the ultrasonic elliptical vibration are discussed in detail. Experiments were conducted on a commercial ultrasonic cutting unit installed onto a commercial numerical control (NC) lathe; the cutting forces were found to be lower in the new method than in conventional turning (CT). Microchip particles were observed on both chip and work surface in CT but were almost absent on the surfaces prepared by ultrasonic elliptical vibration assisted turning (UEVT). Furthermore, the cutting tool used in CT developed built-up edge (BUE), and its flank wear became heavier; in contrast, negligible BUE and less flank wear were found on the cutting tool used in UEVT. The theoretical surface roughness of UEVT was calculated and it agreed much well with the measured surface roughness.     

数控刀具材料的研究进展

数控刀具是数控加工技术中的重要基础装备之一,在保证制造技术的有效实施方面有着十分重要的作用。本文主要介绍数控机床刀具的分类、数控刀具材料的现状和发展趋势。     

Application of bivariate parameter design to the optimization of the operating conditions of a turning process

Parameter design, introduced by Taguchi, has been shown to be an effective approach for improving quality and productivity at low cost. The present article reports a case study of the application of parameter design to the determination of the optimal operating conditions of an integrated numerical control (NC) lathe such that the roundness and surface roughness of the cylindrical workpieces, which are processed on the NC lathe, can be improved. An orthogonal array, signal-to-noise ratio and analysis of variance are employed to carry out the bivariate parameter design and its corresponding data analysis. Through this study, not only can the optimal operating conditions for the integrated NC lathe be obtained, but also significant parameters that affect the roundness and surface roughness of the workpieces can be determined. Experimental results are provided to confirm the effectiveness of this approach.     

硝化纤维素细断新工艺技术研究

为了解决我国目前的硝化纤维素细断（粉碎）过程能耗高、效率低、污染严重的问题,文章利用双圆盘粉碎机对硝化纤维素进行了细断试验。重点研究了粉碎时间、磨刀类型、磨刀间距及浆料浓度等因素对细断效果的影响,得出了合适的工艺条件。与传统锥形细断机相比,该技术与设备节能45％,提升了我国硝化纤维素细断工艺技术水平。     

Comparative study of the effect of surface texturing on cutting tool in dry cutting

Recent researches in the field of dry machining have indicated that surface texture has the potential to influence tribological conditions. Researchers have studied the application of controlled surface microtextures on cutting tool surfaces to improve machining performance by changing the tribological conditions at the interfaces of tool–chip and tool–work piece. An experiment to study the performance of the microtextured high-speed steel cutting implement within the machining of steel and aluminum samples was performed. Surface textures were introduced using Rockwell hardness tester, Vickers hardness tester, and by scratching with diamond dresser on the face of single point cutting tool. Machining in dry conditions was applied on mild steel (EN3B) and aluminum (AA 6351) samples using lathe machine with microtextured and traditional cutting tool for the constant range of feed, depth of cut, and for varying range of cutting speeds. Measurement of cutting force, cutting temperature, and surface roughness of the work surfaces after machining were made. The results showed reduction in cutting forces and cutting temperature with textured tools in comparison with those of the untextured tool. Chips collected from different samples were studied under a microscope and the results showed that textures created on the tool surface by various methods exhibited variations in chip formation. Cutting tools without texture and with texture were comparatively studied and the outcomes of the experimental study are presented in this paper.     

Adaptive and dynamic process planning using neural networks

Although feature-based process planning plays a vital role in automating and integrating design and manufacturing for efficient production, its off-line properties prevent the shop floor controller from rapidly coping with dynamic shop floor status such as unexpected production errors and rush orders. This paper proposes a conceptual framework of the adaptive and dynamic process planning system that can rapidly and dynamically generate the needed process plans based on shop floor status. In particular, the generic schemes for constructing dynamic planning models are suggested. The dynamic planning models are constructed as neural network forms, and then embedded into each process feature in the process plan. The shop floor controller will execute them to determine machine, cutting tools, cutting parameters, tool paths and NC codes just before the associated process feature is machined. The dynamic nature of process planning enables the shop floor controller to increase flexibility and efficiency in unexpected situations.     

Compensation of systematic errors in five-axis high-speed machining

A method is described for the compensation of errors associated with tool path generation, particularly during five-axis high-speed machining (HSM). Information on machine tool performance and its dynamic features is used to calculate possible errors and convenient modifications of the NC program, thereby avoiding errors when parts are actually being machined. This 'preprocess method' by means of postprocessing with NC software is presented. The errors dealt with are mainly servo lag errors, but the explored approach can support most systematic errors associated with machine tool performance. These are briefly summarized. Research so far has largely been aimed at the implementation of compensation routines in the CNC controller and at corrections in real time. The problem is that most applications are only available for three-axis milling. The presented approach (compensation before machining by using software routines in a specially designed postprocessor) is based on a fuzzy logic expert system. The benefits can be summarized as data reduction, data improvement, precontrol of feed, and improved component accuracy. The applied procedure is also convenient for implementation in an industrial environment by retrofitting existing equipment. The suggested method provides improved control over machine dynamics, permitting high-speed machining centres to maintain a maximum or near-maximum feed rate despite axis reversals and tool path changes, even at corners. Two categories of results are presented, namely the management of NC data related to expected performance of the machine tool and improvements of the machine tool performance in terms of productivity and accuracy of the machined test components.     

Machine vision assisted characterization of machined surfaces

This paper demonstrates the feasibility of using an inexpensive machine vision system to compute non-contact, optical parameters for the characterization of surface roughness of machined surfaces. Two parameters were selected for online analysis, where surface roughness is measured during the rotation of a specimen on a lathe. The sensitivity of the vision-based optical parameters to differences in surface roughness, ambient light and spindle speed of a lathe during measurement was evaluated. Statistical analysis of data collected through experimentation revealed that the vision parameters can discriminate different surface roughness heights and are insensitive to changes in ambient lighting and speed of rotation during measurement. The results of the experimental analysis were used to conclude the feasibility of using machine vision for the evaluation of surfaces.     

Finite element analysis of bending occurring while cutting with high speed steel lathe cutting tools

The bending which occurs on a cutting tool during machining on a lathe affects tool life, surface roughness and dimension correctness. In this research, the bending which has been calculated by Castigliano theorem has been compared with the bending obtained by finite element method. Under the constant cutting conditions, material Ç1060 has been machined with high speed steel (HSS) lathe cutting tools having 60°, 75° and 90° of cutting edge angle. It was determined by using ANSYS finite elements program that the bending of the cutting tool generated by the forces, which varied between 1360 N and 1325 N and occurred during cutting, varied between 0.039958 and 0.04373 mm. According to the results, it has been observed that the bending that was calculated by Castigliano theorem and that varied between 0.03542 and 0.034505 mm was almost the same with the bending determined by finite elements method. In other words, it was seen that the calculated values approach to the analysed results up to 0.4% .     

Green manufacturing—performance of a biodegradable cutting fluid

Huge quantity of petroleum and mineral-based cutting fluids mixed with carcinogenic additives to increase their performance is used every year in the manufacturing industry. Application of such fluids poses a serious hazard to the environment, workers, and personnel who directly or indirectly come in contact with them. Disposal of these cutting fluids without neutralization has a high potential of contaminating the water bodies and affects the aquatic life. Various vegetable-based cutting fluids have been formulated from edible oils, but less work is reported on non-edible oils. In this work, non-edible neem oil was used as a base oil and a food grade emulsifier was used. Thus, the cutting fluid is totally biodegradable. Various cutting fluids were formulated, and then, experiments were done on EN8 with uncoated carbides on lathe machine and various results reported. The neem oil has inherent anti-microbial properties and thus prevents microbial contamination for a long period of time. This newly developed cutting fluid does not require any neutralization before disposal.     

304不锈钢管滚压成形圆锥外螺纹组织及性能研究

滚压加工螺纹可以获得更高的螺纹强度、精度,其在加工效率和环保性方面的优越性不容忽视.同时,滚压加工可以解决某些工艺方法不能解决的问题,如对特大型缸体的加工,可以达到减少机床和夹具、提高工件加工精度、缩短加工周期和节约作业面积的效果.为此,本文采用一种四滚丝轮车床滚压加工得到了304不锈钢管圆锥外螺纹.通过金相分析、扫描电镜、显微硬度计和万能试验机等手段,研究了304不锈钢管滚压成形圆锥外螺纹的组织及性能,并与传统的套丝管螺纹进行对比.研究结果表明,套丝加工的管螺纹,齿表层出现孔洞、金属组织被切断,其内部显微组织仍是原有的等轴晶,齿形不完整;而滚压加工使得螺纹表层组织细化,形成了沿螺纹齿形连续分布的纤维组织.套丝加工后304钢管螺纹硬度有所提高,但幅度不大;与套丝加工相比,滚压加工后304钢管螺纹的抗剪拉力和硬度均有大幅提高.     

基于尺寸驱动参数化的产品结构设计系统研究

介绍了使用SolidWorks进行二次开发的建立方法进行了研讨;以SolidWorks为平台利用API和DLL技术,使用面向对象的VB语言,开发了五轴联动高速切削数控机床结构设计系统,通过尺寸驱动实现了机床零件的参数化设计,旨在提高机械产品结构的设计效率.     

MAGNETIC BEARING SPINDLES FOR ENHANCING TOOL PATH ACCURACY

Thin rib machining of electronic components or airframe structures can benefit from high speed machining for burr free cutting, improved surface quality and increased metal removal rate. It is suggested that the use of a magnetic bearing spindle can not only successfully provide the benefits of high speed machining but, more importantly, minimize tool path errors. In this paper the various sources of tool path error are discussed as functions of machine tool positioning errors and cutting force errors which are characterized as static, dynamic and stochastic. The operation of high speed magnetic bearing spindles is described and a control scheme whereby the spindle may be translated and tilted for minimizing tool path errors is discussed. This overall research activity is a cooperative effort between the University of Maryland, Cincinnati Milacron, Magnetic Bearings, Inc., The Uestinghouse Corporation, and The National Bureau of Standards.     

基于Web的数控编程动态仿真及可视化

根据硕士研究生学位公共课程“CAD/CAM基础理论与实践”网络化远程教学的需求,针对点位控制、直线控制、曲线控制等几种典型的数控类型,综合运用Java编程、数控G指令编程以及刀具切削原理等技术,开发具有动态交互及可视化功能的、能实时显示数控程序设计和执行过程的线切割、车削、铣削等基于Web的数控编程动态仿真Java软件。并将其集成在远程教学课件的Web信息架构中。     

圆柱表面微结构阵列超精密车削加工技术

辊子是光学薄膜模压制造的关键零件,其圆柱表面微结构复杂,表面粗糙度要求也极高.超精密车削成形作为微结构的一种高效加工方式,其加工的可达性、伺服刀具动态特性的制约、海量微结构的加工长时一致性等是高质量辊子微结构加工所需解决的关键问题.本文以圆柱球面微结构阵列为例,从其数学描述入手,分析了刀具几何尺寸、伺服系统动态特性与微结构加工可达性之间的制约关系,并在自主研制的超精密车床和快刀伺服系统上进行了两种球面微结构的加工实验,得到了预期的微结构形貌,并对加工实验中发现的切深不一致现象给出了初步的解释.     

Comparing the Effectiveness of Coatings on Carbide andCermet Cutting Tool Inserts

A series of metal cutting experiments was performed on a CNC lathe to evaluate the performance of various coatings on different tool substrates. The workpiece material was plain medium carbon steel and the cutting tool materials were carbide and cermet inserts coated with various single as well as multilayer coatings. Machining was done under various cutting conditions of speed and feed-rate, and for various durations of Cutting. The output parameters studied were the cutting forces (axial, radial and tangential), the surface roughness of the workpiece, as well as the tool wear (crater and flank wear). From these results, the performances of the various cutting inserts are evaluated and compared. Results show that cutting forces are significantly lower when using coated cermets than when using coated carbides although different coatings on the same substrate also result in different cutting forces. However, there is less difference in the surface roughness of the finished workpiece for the various coatings and substrates.