Study on magnetic polishing of free-form surfaces

Magnetic polishing technology applicable to free-form surfaces such as the die/mold manufacturing field, has been studied using two types of magnetic polishing tool. Finishing efficiency and final surface roughness can be satisfactorily achieved at the same time by magnetic polishing using two types of magnetic polishing tool. One is an abrasive wheel type and the other is a magnetic brush type. The possibility of free-form surface polishing has been confirmed by use of the magnetic polishing technology because it has flexibility of profiling and does not need any complex tool-path control, with respect to workpiece surfaces. Magnetic force was estimated and measured. A two-stage magnetic polishing experiment has been executed using the magnetic polishing tools and mini CNC milling machine without tool-path control. A realization of efficient polishing of curved surfaces is possible using the two-stage magnetic polishing method, and it was also confirmed that automation of free-form surface polishing is possible by this method.     

基于环境模型优化的机器人磨抛阻抗控制

对比传统加工机床,机器人的刚度与定位精度较低,为提高机器人辅助磨削的加工质量,需要控制其加工过程中的接触压力。基于球形弹性磨具磨削时的接触特性,以磨具的下压量为自变量,磨具与工件的接触压力为因变量进行有限元仿真,对下压量-接触压力仿真结果进行曲线拟合,并通过接触实验验证其准确性,以此建立基于环境模型修正的阻抗力学控制模型,从而进行自由曲面力控实验。结果表明:建立的基于环境模型修正的阻抗控制方法能有效改善球形弹性磨具的力控性能,自由曲面力控精度达到±0.5 N,且可为球形弹性磨具复杂曲面的磨削加工提供稳定的磨削压力。      

倾斜喷涂圆弧喷枪新模型的建立与轨迹优化

针对复杂自由曲面中犄角型曲面的喷涂机器人圆弧喷涂轨迹的优化和涂料浪费问题,基于已有的喷枪模型,运用微分几何面积放大定理建立了考虑涂料流量的倾斜喷涂圆弧喷枪新模型。并基于此模型对一具有外犄角特征的组合曲面进行了喷枪变向倾斜喷涂的轨迹规划,建立了喷涂轨迹优化目标函数。最后仿真实验验证了此模型和喷涂方案的有效性和可行性,为完善喷涂机器人离线编程系统提供了依据。     

模具自由曲面抛光过程的分析与研究

针对模具自由曲面抛光中受几何、物理及力学等因素的影响,从抛光工具与自由曲面之间的接触及摩擦角度分析,深入研究自由曲面的抛光机理,并对影响抛光工艺过程的主要因素进行分析,探讨自由曲面抛光过程中获取高质量表面的方法。     

Automatic polishing process of plastic injection molds on a 5-axis milling center

The plastic injection mold manufacturing process includes polishing operations when surface roughness is critical or mirror effect is required to produce transparent parts. This polishing operation is mainly carried out manually by skilled workers of subcontractor companies. In this paper, we propose an automatic polishing technique on a 5-axis milling center in order to use the same means of production from machining to polishing and reduce the costs. We develop special algorithms to compute 5-axis cutter locations on free-form cavities in order to imitate the skills of the workers. These are based on both filling curves and trochoidal curves. The polishing force is ensured by the compliance of the passive tool itself and set-up by calibration between displacement and force based on a force sensor. The compliance of the tool helps to avoid kinematical error effects on the part during 5-axis tool movements. The effectiveness of the method in terms of the surface roughness quality and the simplicity of implementation is shown through experiments on a 5-axis machining center with a rotary and tilt table.     

Development of 3 DOF Ultrasonic Vibration Tool for Elliptical Vibration Cutting of Sculptured Surfaces

A new machining method is proposed to obtain sculptured mirror surfaces by applying elliptical vibration cutting. The tool is vibrated elliptically unlike rotated end mills and fed along the sculptured surface in the proposed method. A 3 DOF ultrasonic vibration tool is developed, which can generate an arbitrary ultrasonic elliptical vibration in the 3D space so that it is suitable to machine the 3D sculptured surfaces. A precision machine tool is also developed, and the proposed method is successfully applied to mirror surface machining of hardened die steel.     

A new method of automatic polishing on curved aluminium alloy surfaces at constant pressure

This paper presents original research results of automatic polishing on curved surfaces of aluminium alloy moulds at constant pressure. The automatic polishing of aluminium alloy material is achieved. A parameter S is defined, which can express the comprehensive influential factors in the automatic polishing process and give a relationship among the polishing quality and the various machining variables. Based on this, a new method for comprehensive control of polishing quality is suggested.     

Machining of free-form surfaces. Part II: Calibration and forces

In the machining simulations of 3D free-form surfaces by ball-end milling, calibration coefficients play very critical role in force predictions. In other words, obtaining the calibration coefficients from calibration tests is a very influential process in the prediction of cutting forces. Accurately obtained calibration coefficients lead to better force predictions. In the literature, the calibration coefficients are assumed to be independent of start and exit angles of the engagement region, thus they are assumed to be identical for any engagement region. Calibration coefficients are obtained from the horizontal slot cutting tests and these tests are repeated for different depth of cuts. In this paper, in order to achieve more accurate force predictions in free-form machining simulations, a new modification algorithm for calibration coefficients is presented. In this research, with theoretical analysis and experimental force signals, it is shown that the inclination angle has a great importance in calibration and in force simulation of 3D free-form machining.     

超光滑表面加工技术的发展及应用

超光滑表面加工技术是超精密加工体系的一个重要组成部分,超光滑表面在国防和民用等领域都有着广泛的应用.本文针对超光滑表面的需求,介绍了超光滑表面制造技术的发展过程,对各种超光滑表面加工原理与方法进行了简单描述与评价,最后提出了一种基于流体二维振动的超光滑表面加工技术,为超光滑表面的加工提供了新的方法.     

Machineability in NURBS interpolator considering constant material removal rate

Increasing demands on precision machining of three-dimensional free-form surfaces have necessitated that the tool move smoothly and at varying feedrates. To achieve this, parametric interpolators, such as the Non-Uniform Rational B-Spline (NURBS) interpolator, have been introduced in CNC machining systems. Such interpolators reduce the data burden in the Numerical Control (NC) code, increase data transfer rate into the NC controller, and finally give smooth motion while machining. In this research, a new concept to control cutting load in a NURBS interpolator based on the degree of curvature was tried. This protects the cutting tool and improves machineability. To prove the system, cutting force and surface topography were evaluated. From the experimental results, the interpolator is adequate for machining a free-form surface.     

Combined ultrasonic vibration and chemical mechanical polishing of copper substrates

This paper introduces an ultrasonic, vibration-assisted, chemical mechanical polishing (UV-CMP) method and an ultrasonic, vibration-assisted, traditional diamond disk (UV-TDD) dressing method. A copper substrate is polished by traditional CMP and UV-CMP. UV-CMP combines the functions of traditional CMP and ultrasonic machining (USM) with small-amplitude, high-frequency tool vibration to improve the fabrication process and machining efficiency. The removal rate of the copper substrate, torque force, and polished surface morphology of CMP and UV-CMP are compared. The polishing pad is also dressed by traditional diamond disk (TDD) and UV-TDD. The pad cut rate, torque force, and pad surface profiles of TDD and UV-TDD are also investigated in experiments. Experimental results reveal that UV-TDD can produce twice the pad cut rate and reduce torque force compared to TDD. Consequently, a dressing time reduction by half is expected, and hence, the diamond life is extended. It is found that the removal rate of the copper substrate polished by UV-CMP is increased by approximately 50-90% relative to that of traditional CMP because in UV-CMP, a passive layer on the copper surface, formed by the chemical action of the slurry, will be removed not only by the mechanical action of CMP but also by ultrasonic action. In addition, the surface roughness improves and the torque force reduces dramatically. This result suggests that the combination processes of CMP/USM and TDD/USM are feasible methods for improving polishing and dressing efficiency.     

五自由度虚拟轴机床刚—柔耦合动力学仿真研究

针对一种用于研磨自由曲面的新型虚拟轴机床，建立基于Lagrange方程的空间刚—柔耦合动力学模型，并通过动力学仿真研究说明各支链驱动力、运动具有相似性。该方法为虚拟轴机床动力学研究提供了新的思路。     

超声振动磨削放电复合加工SiCp／Al试验研究

针对SiCp／Al的加工,提出一种超声振动磨削放电复合加工的方法．从加工效率、加工稳定性及表面质量等方面与电火花加工进行了对比试验研究。分析了两种加工方法的脉冲宽度和峰值电流对加工速度和表面粗糙度的影响,结果表明：电火花加工的表面粗糙度平均值为尺04．5μm,超声振动磨削放电复合加工的表面粗糙度平均值为Ra2μm：超声振动磨削放电复合加工的稳定性比电火花加工好,但加工速度较低。通过扫描电镜对两种加工方法下零件表面形貌和重熔层进行了观测,对试件表面进行了X射线衍射分析,表明采用超声振动磨削放电复合加工SiCp／Al复合材料可获得较好的表面质量。     

自由曲面上等斜率曲线的跟踪算法

为了提高自由曲面加工质量,提出一种等斜率曲线跟踪算法.算法首先利用曲面内部法矢量的连续性,采用二分法求出初始点,采用密切圆法进行跟踪,然后再用梯度法精化.数值计算结果表明,该算法具有较高的计算效率和精度,能准确地对曲面进行分区处理,为三轴加工加工策略的实施提供重要依据.     

超声波椭圆振动加工技术的研究进展

超声波椭圆振动加工是功率超声加工技术的重要分支之一,在硬脆性材料加工方面具有非常广阔的应用前景。综述了超声波椭圆振动加工系统的研究进展和超声波椭圆振动加工技术在车削、镗削、钻削、铣削、磨削、化学机械抛光、砂轮修整、表面滚压与焊接等方面的最新应用,最后对超声波椭圆振动加工技术的发展方向提出了一些建议。     

Machining of free-form surfaces. Part I: Analytical chip load

In the machining simulations of 3D free-form surfaces with ball-end mill, determinations of instantaneously changing tool-workpiece engagement regions and chip load play very critical roles in force and surface quality predictions. Cutting force models for ball-end milling are based on the undeformed chip load. Undeformed chip load can be constructed from the boundaries of instantaneous engagement region between the ball-end mill and workpiece. In order to predict the cutting forces accurately, precise determination of the varying engagement regions is important. In the literature, there are two main engagement region constructing methods; one is the Z-mapping and the other one is using solid modeler based on Boolean operation method. Both methods construct the engagement region within accuracy limits, on the other hand the computational time for these methods are long such that it is not possible to calculate the forces at the same time of CL-point construction. This paper presents development of a new analytical method for fast and accurate determination of the instantaneous engagement regions in the 3D machining of monotonic free-form surfaces. The analytical tool is grid size independent, thus it is much faster than discretization and Boolean methods. In addition to that, the analytical tool gives the most precise and exact engagement regions.     

Feedrate scheduling strategies for free-form surfaces

Free-form machining is one of the commonly used manufacturing processes for several industries such as automobile, aerospace, die and mold industries. In 3D complicated free-form surfaces, it is critical, but often difficult, to select applicable cutting conditions to achieve high productivity while maintaining high quality of parts. It is essential to optimize the feedrate in order to improve the machining efficiency of the ball-end milling. Conservative constant feedrate values have been mostly used up to now since there was a lock of physical models and optimization tools for the machining processes.The common approach used in feedrate scheduling is material removal rate (MRR) model. In the MRR based approach, feedrate is inversely proportional to either average or instantaneous volumetric removal rate. Commonly used CAM programs and NC code generators based on only the geometric and volumetric analysis, but they do not concern the physics of the free-form machining process yet. The new approach that is also introduced in this paper is based on the mechanics of the process. In other words, the force-based models in which feedrate is set to values which keep either average or instantaneous machining forces to prescribed values. In this study, both feedrate scheduling strategies are compared theoretically and experimentally for 3D ball-end milling of free-form surfaces. It is shown that MRR based feedrate strategy outputs higher feedrate values compared to force based feedrate strategy. High feedrate values of the MRR strategy increase the cutting forces extensively which can be damaging to the part quality and to the CNC Machine.When the new force based feedrate-scheduling strategy introduced in this paper is used, it is shown that the machining time can be decreased significantly along the tool path. The force-based feedrate scheduling strategy is tested under various cutting conditions and some of the results are presented in the paper.     

Fundamental study of ultrasonic polishing of mold steel

Ultrasonic Machining (USM) is conventionally used for machining hard and brittle materials. As polishing of steel mold has been a serious concern in the industry, an innovative cost-effective ultrasonic polishing system is developed for this purpose. The ultrasonic tool moves in a patterned path to cover the entire surface to be polished. Microcutting, plowing and indentation by abrasives are observed on the polished surface. The experiment was conducted on typical mold steel with the emphasis on the effects of the abrasive size and the static load on the surface finish. The optimal abrasive size depending on the surface roughness prior to polishing is identified. Large static loads possess an advantage in that the abrasives are more effectively activated for polishing.     

超声加工技术的研究现状及其发展趋势

结合近年来超声加工技术的发展状况,综述了超声振动系统的研究进展和超声加工技术在深小孔加工、拉丝模及型腔模具研磨抛光、难加工材料的加工、超声振动切削、超声复合加工等方面的最新应用,并阐述了超声加工技术的发展趋势.     

一种切削加工机器人运动功能方案的解析设计方法

本文提出了一种以加工表面和刀具为输入信息,基于解析方法的切削加工机器人的运动功能方案设计方法。该方法可以突破传统设计模式的约束,为切削加工机器人的方案设计提供理论依据