Algorithms to support point-based cadcam

This paper presents a system that supports a point-based approach to CADCAM that was first suggested by McLaughlin. The core to the approach is the ability to interpolate a grid of points in a geometrically meaningful way that does not suffer from the disadvantages of the standard interpolation schemes based on NURBS. The essential features of the approach are based on recursive subdivision between existing points to generate intermediate points that are consistent with a smooth curvature profile. There are many advantages to this approach. Time-consuming surface fitting is not necessary; there are no problems with ensuring continuity between surfaces; data exchange can be carried out exactly. By chosing to work entirely with points, all of the standard interrogations available in CAE systems, including visualisations, FE analysis and NC machining, which are dependent on NURBS curves and surfaces have to be replicated. The feasibility of the point-based approach is illustrated by showing how geometric interrogations and machine tool paths can be accurately generated using just points.     

组合曲面造型的符号操作

根据当前几何造型的发展趋势，制造业对非闭曲面设计的迫切需求，以及为发展集成几何造型系统的造型手段，本文对一般组合曲面的造型理论作了探讨，提出了组合曲面邻域半空间新概念，建立了空间点对组合曲面的分类体系。为组合曲面造型手段的符号化奠定了理论基础。在此基础上，作者研究了基于组合曲面的集合运算、欧拉操作，并提出了对组合曲面操作的一个新的符号算子──ＴＧ操作。     

Geometric modeling of the linear motor driven electrical discharge machining (EDM) die-sinking process

Based on Z-map method, in this paper the development of a geometric model for the linear motor equipped EDM die-sinking process is described. Firstly discussed are the advantages and benefits of the introduction of the linear motor into EDM die-sinker. The current model has been employed to calculate the minimum gap distance for sparks to occur and to analyze the possibility of spark generation between the workpiece and electrode surfaces. Also calculated is the crater formed by a single spark. The final machined surface topography is predicted. The influence of peak current and discharge duration on the average surface roughness is simulated. The experiment has been conducted to study the effects of machining conditions as well as to verify the effectiveness of the developed geometric model.     

The influence of component inclination on surface finish evaluation using digital image processing

Many researchers have so far used Machine Vision and digital image processing for grabbing images of machined surfaces, improving their quality by pre-processing and then analysed them for evaluation of surface finish with a reasonable success. In the conventional mechanical stylus method used for roughness evaluation, many of the fundamental requirements are taken care of during measurement which includes alignment of component with the stylus pick up movement, tracing length, filter cut off length, etc. Practical use of Machine Vision for surface roughness estimation faces many challenges, as in this case only image is used for evaluation and not the component. For example, if the component is kept at an angle during imaging, there is a possibility of getting distorted information and the consistency of evaluation/quantification would become a problem. Therefore, there is a need to ensure that the measured surface is kept horizontal when the image is being taken. In this work, estimation of the surface roughness has been done and analysed using digital images of machined surfaces obtained by a Machine Vision system deliberately maintained at varying angles. The optical surface finish values (G_a) estimated in all such cases using Machine Vision approach are compared with that obtained using conventional stylus method (R_a). An artificial neural network (ANN) is trained and tested to arrive at the R_a values using the input obtained from the digital images of inclined surfaces which include optical roughness parameters estimated and angle of inclination of test parts. The experimental result indicates that the surface roughness could be estimated/predicted with a reasonable accuracy using Machine Vision and ANN, respectively. In addition, a shadow removal algorithm is used to improve the quality of the images of inclined surfaces and then the optical roughness parameter is estimated. All the results are compared with that obtained using stylus method and analysed in this paper.     

Effect of grit-blasting on substrate roughness and coating adhesion

Statistically designed experiments were performed to compare the surface roughness produced by grit blasting A36/1020 steel using different abrasives. Grit blast media, blast pressure, and working distance were varied using a Box-type statistical design of experiment (SDE) approach. The surface textures produced by four metal grits (HG16, HG18, HG25, and HG40) and three conventional grits (copper slag, coal slag, and chilled iron) were compared. Substrate roughness was measured using surface profilometry and correlated with operating parameters. The HG16 grit produced the highest surface roughness of all the grits tested. Aluminum and zinc-aluminum coatings were deposited on the grit-blasted substrates using the twin-wire electric are (TWEA) process. Bond strength of the coatings was measured with a portable adhesion tester in accordance with ASTM standard D 4541. The coatings on substrates roughened with steel grit exhibit superior bond strength to those prepared with conventional grit. For aluminum coatings sprayed onto surfaces prepared with the HG16 grit, the bond strength was most influenced by current, spray distance, and spray gun pressure (in that order). The highest bond strength for the zinc-aluminum coatings was attained on surfaces prepared using the metal grits.     

Surface characterization of Ti-7.5Mo alloy modified by biomimetic method

Titanium and its alloys have been used in dentistry due to their excellent corrosion resistance and biocompatibility. It was shown that even a pure titanium metal and its alloys spontaneously form a bone-like apatite layer on their surfaces within a living body. The purpose of this work was to evaluate the growth of calcium phosphates at the surface of the experimental alloy Ti-7.5Mo. We produced ingots from pure titanium and molybdenum using an arc-melting furnace. We then submitted these ingots to heat treatment at 1100 °C for one hour, cooled the samples in water, and cold-worked the cooled material by swaging and machining. We measured the media roughness (Ra) with a roughness meter (1.3 and 2.6 μm) and cut discs (13 mm in diameter and 4 mm in thickness) from each sample group. The samples were treated by biomimetic methods for 7 or 14 days to form an apatite coating on the surface. We then characterized the surfaces with an optical profilometer, a scanning electron microscope and contact angle measurements. The results of this study indicate that apatite can form on the surface of a Ti-7.5Mo alloy, and that a more complete apatite layer formed on the Ra = 2.6 μm material. This increased apatite formation resulted in a lower contact angle.     

基于SOFM和NURBS的散乱数据点自由曲面重构

提出了利用NURBS实现曲面散乱点数据几何建模的方法。首先利用Unigraphics软件设计原始曲面,在所设计的原始曲面上划分若干条曲线,并在曲线上随机设置大量的散乱点数据;然后用自组织神经网络SOFM对原始曲面上的散乱数据点进行聚类,构建NURBS曲线并完成曲面重构。最后通过仿真实验分析了重构曲面相对原始曲面的误差,实验表明所提出的几何建模方法是有效的,并能较精确拟合原始曲面。     

系列示波冲击断口三维形貌几何特征和断裂性能

应用示波冲击试验技术测量了Ｐ４６０ＮＬ１钢不同温度系列下的动态断裂性能。利用扫描电镜立体对技术,图像处理与分析和计算视觉方法对示波冲击断口形貌进行了三维重建和定量分析。     

Enhanced virtual machining for sculptured surfaces by integrating machine tool error models into NC machining simulation

Sculptured surface machining is a time-consuming and costly process. It requires simultaneously controlled motion of the machine axes. However, positioning inaccuracies or errors exist in machine tools. The combination of error motions of the machine axes will result in a complicated pattern of part geometry errors. In order to quantitatively predict these part geometry errors, a new application framework ‘enhanced virtual machining’ is developed. It integrates machine tool error models into NC machining simulation. The ideal cutter path in the NC program for surface machining is discretized into sub-paths. For each interpolated cutter location, the machine geometric errors are predicted from the machine tool error model. Both the solid modeling approach and the surface modeling approach are used to translate machine geometric errors into part geometry errors for sculptured surface machining. The solid modeling approach obtains the final part geometry by subtracting the tool swept volume from the stock geometric model. The surface modeling approach approximates the actual cutter contact points by calculating the cutting tool motion and geometry. The simulation results show that the machine tool error model can be effectively integrated into sculptured surface machining to predict part geometry errors before the real cutting begins.     

In-process surface roughness prediction using displacement signals from spindle motion

A method to predict surface roughness in real time was proposed and its effectiveness was proved through experiment in this paper. To implement the proposed method in machining process, a sensor system to measure relative displacement caused by the cutting operation was developed. In this research, roughness of machined surface was assumed to be generated by the relative motion between tool and workpiece and the geometric factors of a tool. The relative motion caused by the machining process could be measured in process using a cylindrical capacitive displacement sensor (CCDS). The CCDS was installed at the quill of a spindle and the sensing was not disturbed by the cutting. The workpiece was NAK80 and TiAlN coated carbide end mills were used in the test. Model to predict surface roughness was developed. A simple linear regression model was developed to predict surface roughness using the measured signals of relative motion. Close relation between machined surface roughness and roughness predicted using the measured signals was verified with similarity of about 95%.     

基于曲率自适应的自由曲面测量点分布

针对自由曲面测点布置问题,采用曲率自适应形状特征的测点自适应分布。分析自由曲面的数学模型,为自由曲面参数化建模提供数学基础;研究自适应形状特征法,采用曲面形状函数的采样算法,使测点自适应分布;设计曲面,进行实际测点的布置,得到自适应测点分布图,并对测点数据进行CMM检测验证。     

薄膜理想台阶的制备方法研究

目的 研究台阶的形貌对台阶仪测试的影响,准确测试薄膜的厚度。 方法 分析制备台阶中存在的问题,针对这些问题设计了中轴线位置带掩膜条的掩膜板,并采用该新型掩膜板,在不同衬底上制备台阶,用台阶仪对薄膜的厚度进行测定。 结果 在薄膜中轴线附近做出的台阶,坡度陡峭,上下表面清晰。 Mo 衬底上制备出的薄膜厚度重复性较好;单晶硅衬底上制备的薄膜表面粗糙度较大;石英衬底上制备薄膜形成的台阶上下表面均较为平滑。 结论 使用新型掩膜板在石英衬底上制备出理想台阶,可较为准确地测试薄膜的厚度。     

Surface characterization of AISI 316L biomaterials obtained by electropolishing in a magnetic field

The paper deals with comparison of the results obtained by electropolishing AISI 316L surfaces in an externally applied magnetic field with those of a standard electropolishing process. All electrochemical investigation methods, electrochemical impedance spectroscopy (EIS), polarization curve measurements, and surface analytical methods such as surface roughness measurements and scanning electron microscopy were carried out to determine the efficacy of electropolishing in a magnetic field.     

反求工程在具有内型面零件的快速集成制造中的应用

以实际工程中的发动机缸盖零件为例，阐述了对于具有内型面零件进行反求制作的方法和RE与CAD复合建模技术。以硅橡胶翻制零件的内型面，将零件内型面硅橡胶模型的外表面应用逆向工程技术，获取零件内型面的三维CAD模型，对零件其它特征进行常规三维CAD建模，并将此CAD模型与反求获得的曲面进行拼合即进行复合建模，从而获取零件的完整的CAD模型。     

A vision system for surface roughness characterization using the gray level co-occurrence matrix

Computer vision technology has maintained tremendous vitality in many fields. Several investigations have been performed to inspect surface roughness based on computer vision technology. This work presents a new approach for surface roughness characterization using computer vision and image processing techniques. A vision system has been introduced to capture images for surfaces to be characterized and a software has been developed to analyze the captured images based on the gray level co-occurrence matrix (GLCM).Three standard specimens and 10 machined samples with different roughness values have been characterized by the presented approach. Three-dimensional plots of the GLCMs for various captured images have been introduced, compared and discussed. In addition, some statistical parameters (maximum occurrence of the matrix, maximum occurrence position and standard deviation of the matrix) have been calculated from the GLCMs and compared with the arithmetic average roughness R_a. Furthermore, a new parameter called maximum width of the matrix is introduced to be used as an indicator for surface roughness.     

六面顶压机油缸加工机的研制

我们研制了一种新型超精加工设备,用来修磨加工六面顶压机油缸的内孔.通过采用有效可行的工艺,特殊的超精磨具,保证了不易加工的大直径设备内孔的尺寸精度与表面粗糙度的要求.用该设备加工近百台压机油缸,经检验全部合格.该设备结构简单、维护方便、使用寿命长、有效地解决了六面顶压机油缸泄露问题,值得推广使用.     

表面微结构对冰粘附强度的影响

目的研究试片表面粗糙度及分形维数对冰粘附强度的影响。方法通过对裸铝表面进行化学刻蚀及氟硅烷修饰,制备不同表面试片,测试试片表面的粗糙度和分形维数,应用冰粘附强度实验装置测试不同试片表面的冰粘附强度。结果粗糙度(x)与粘附强度(y)的关联式为:y=1.0966x+51.816(亲水表面),y=-0.67x+74.98(疏水表面)。分形维数(z)与粘附强度(y)的关联式为:y=-146.6z+493.5(亲水表面),y=95.45z-209.9(疏水表面)。结论亲水表面试片冰粘附强度随粗糙度的增加而增加,随分形维数的增加而减小,疏水表面试片的变化趋势则相反。冰粘附强度与粗糙度及分形维数之间存在较强的线性关系。表面粗糙度相同的试片经氟硅烷修饰后,冰粘附强度降低,且表面粗糙度越大,冰粘附强度下降越多。     

Surface roughness inspection by computer vision in turning operations

The use of computer vision techniques to inspect surface roughness of a workpiece under a variation of turning operations has been reported in this paper. The surface image of the workpiece is first acquired using a digital camera and then the feature of the surface image is extracted. A polynomial network using a self-organizing adaptive modeling method is applied to constructing the relationships between the feature of the surface image and the actual surface roughness under a variation of turning operations. As a result, the surface roughness of the turned part can be predicted with reasonable accuracy if the image of the turned surface and turning conditions are given.     

陶瓷球高效超光滑磁流变柔性抛光新工艺研究

目的为实现陶瓷球表面的高效超光滑抛光,提出一种集群磁流变抛光陶瓷球的新工艺。方法在传统V型槽抛光陶瓷球的基础上增加集群磁极和上盘旋转动力,配制适当的磁流变抛光液,通过在上下抛光盘的集群磁极,形成磁流变抛光垫包覆陶瓷球,进行研磨抛光加工。然后,基于陶瓷球工件几何运动学和动力学分析得到球体各运动参数的影响关系,利用机械系统分析软件ADAMS对成球过程进行动态仿真,可以看出该抛光方法能够主动控制球体的运动,实现球面抛光轨迹的快速均匀全包络。最后,根据仿真结果,通过调整上下抛光盘的转速比、偏心距和加工间隙等参数,控制陶瓷球的自转角,实现球面的快速高效超光滑抛光。结果用自行设计的陶瓷球集群磁流变抛光实验装置,对氮化硅陶瓷球进行抛光2.5 h,表面粗糙度Ra从60 nm左右下降到10 nm左右,球形误差为0.13μm,达到了陶瓷球轴承氮化硅球的国家标准(G5水平)。结论集群磁流变抛光方式可以实现球面抛光轨迹的快速均匀全包络,实现陶瓷球表面的高效超光滑抛光,值得进一步深入探讨研究。     

VUV-induced micro-folding of acrylate-based coatings: 2. Characterization of surface properties

The surface properties of micro-folded, “physically matted” acrylate coatings prepared via vacuum UV (VUV) treatment are described. By comparing micro-structured and smooth surfaces, static and dynamic friction values were determined. The topography of micro-wrinkled areas was scanned by an optical profiler and correlated to the gloss. In addition, the reproducibility of surface structure formation and their spatial frequency spectrum roughness have been analyzed using the power structural density functions calculated from the measured surface topographies. Since the high energy 172 nm photons (7.2 eV) are able to generate radicals in acrylates even in the absence of any photoinitiator, a highly crosslinked acrylate matrix was formed in the near surface range. As a result of the increased cross-link density, the micromechanical properties such as the surface hardness were improved. Selected data are presented.