自由曲面加工中考虑干涉的刀具路径安排

研究了自由曲面加工中无干涉刀具路径的安排,推出了一种创新的干涉检查方法,将干涉检查和加工刀具路径安排分别进行,加快了数控加工过程,提高了精度,并将该方法应用于三种常用的刀具体,通过实例验证了本法的合理性.规划刀具路径时,先按照某个参数方向的曲率半径和最大弦偏差确定加工步长,然后再按照另一个参数方向的曲率半径和残瘤高度来确定相邻两条刀具路径间的加工步距,最后跳过识别出的干涉区域安排加工路径.     

机械加工刀具的绿色设计

阐述绿色制造是人类社会可持续发展战略的重要组成部分,根据绿色制造“节约能源、利用资源、减少污染．有利于环境保护”的指导思想,详细介绍绿色刀具应遵循的设计原则、技术设计时应满足的基本要求和几何参数的设计特点。     

Combined reparameterization-based spiral toolpath generation for five-axis sculptured surface machining

Reparameterization-based toolpath generation methods are usually adopted for machining triangular meshes, trimmed surfaces and compound surfaces. The quality of the reparameterization has an important effect on that of the surface. In this paper, a combined reparameterization procedure is introduced to generate an optimal mapping between the designed surface and a specified planar circular region with relatively less distortion both in length and in angle. Then, for five-axis sculptured surface machining the mathematical model of spiral guide path with maximum path interval is constructed in the circular region. Cutter contact paths are obtained by inversely mapping the guide path onto the designed surface. Under constraints of gouging and collision, continuous and optimal cutter orientations are subsequently calculated. Finally, the results of simulation and experiment of the machining process are given to illustrate the feasibility and applicability of the proposed method.     

Generating efficient toolpath by cutter posture optimization in five-axis machining based on inverse feedback mechanism

This paper proposes a tool posture optimization method in five-axis machining using configuration space (C-Space) transformation according to the inverse feedback message. In conventional computer numerical control (CNC) manufacture process, the machining status information transmission is in single direction, and the CNC system interpolates the toolpaths without feedback. However, considering the drives’ acceleration and deceleration, the interpolation situation would greatly affect the machining efficiency and the trajectory should be adjusted in CNC. In this case, the toolpath efficiency is deteriorated and unable to be evaluated exactly by traditional c omputer-aided manufacturing (CAM) system, where the efficiency is approximately estimated by the length of toolpath. In this paper, an inverse feedback mechanism is proposed; the simulated information on CNC system interpolation can be feedback to CAM system to help evaluate the toolpath efficiency. An axis-based dynamic confined feedrate schedule model is used to find the feed sensitive zones of the toolpaths. A C-Space method is adopted to adjust the tool postures in the sensitive zones. Several examples are given to verify the method, and the machining efficiency is raised by 10% on the whole after feedback optimization.     

An accurate surface error optimization for five-axis machining of freeform surfaces

This paper presents an accurate surface error interpolation algorithm for five-axis machining of freeform surfaces. One of the most important steps in the interpolation process is to calculate the next cutter contact (CC) point according to the present one. In this paper, the next CC point is calculated by an accurate chord evaluation method. This method is developed based on the cutting simulation process, which can be vividly described as firstly planting dense grasses on the tool path curve and then cutting them when the tool moves by. The left lengths of the grasses either positive or negative are considered to be the machining error. The method is accurate also because the tool geometry and the tool orientation changes during five-axis machining are taken into consideration. With this method, the chord errors between CC points are controlled uniform along the tool path. The proposed interpolation algorithm is compared with the commercial CAM systems like PowerMILL and UG. The results show that the proposed algorithm can significantly reduce the number of cutter locations meanwhile confine the chord error. A real cutting experiment is implemented, and the result indicates its promising value in industrial applications.     

Grain mapping to freeform surface for machining using parameter-based incremental tracking method

This paper presents a novel method for mapping a texture for machining onto a freeform surface. When a grain texture designed on a 2D plane is projected onto a freeform surface simply, the texture is distorted along the curvature of the surface in the projection direction. Therefore, a method is required to suppress this distortion. The algorithm proposed in this paper rapidly generates a point cloud that represents a texture with less distortion on a simply connected parametric surface. Specifically, four equations that express local geometry constraints instead of conventional parameterization methods are presented to reduce the distortion between adjacent points on the point cloud. Solving these equations can generate grain textures on freeform surfaces. This paper examines two grain images mapped to two freeform surfaces that were prepared as case studies to demonstrate the effectiveness of the proposed method.     

Study on discrete form algorithm of cutter location surface in CNC milling of freeform surface

A novel discrete form algorithm of cutter location surface is proposed to produce 3D tool paths in computer numerical control (CNC) 3-axis milling of freeform surface. As compared with the normal form algorithm, it can be applied to the complex curve surface and irregular shape cutter. The research objective is to identify the discrete form algorithm of cutter location surface. First, the cutter working surface and the machined curve surface were dispersed to be two-point clouds, respectively. Next, the tangency mode of their point clouds was established to produce the cutter location surface. Then, CNC milling experiments were carried out to identify the machined form errors for discrete and normal form algorithms. Finally, the effects of discrete form parameters and workpiece surface posture were investigated on the discrete form accuracy. Experimental results show that the machined form errors for the discrete form algorithm is identical to that for normal form algorithm, but its large form errors are mainly distributed on the large workpiece slope location. On decreasing searching interval and lattice grid size, the discrete form accuracy increases. Moreover, the workpiece surface posture greatly influences the discrete form accuracy, but there exists such a workpiece surface posture that the best discrete form accuracy may be achieved. It is concluded that the discrete form algorithm is feasible to produce the cutter location surface for CNC milling of freeform surface by controlling lattice grid size and searching interval and choosing a suitable workpiece surface posture.     

锥铣刀加工端面螺旋面法及误差计算

介绍了波形弹簧成形模具凸、凹螺旋面参数的计算公式,提出了锥铣刀在铣床上利用挂轮装置铣削端面螺旋面的方法及刀具选择方法,用螺旋面加工理论建立刀具坐标系及工件坐标系,推导了本文所述加工方法的加工误差计算公式及铣刀安装角度的优化计算公式,推证了螺旋面波谷的曲率半径与工件半径成线性关系的公式.用实例进行了系统计算,锥铣刀加工方...     

Constrained deformation of freeform surfaces using surface features for interactive design

There is an increasing demand in conceptual design for more intuitive methods for creating and modifying freeform curves and surfaces in CAD modeling systems. The methods should be based not only on the change of the mathematical parameters but also on the user's specified constraints and shapes. This paper presents a new surface representation model for freeform surface deformation representation. The model is a combination of two functions: a displacement function and a function for representing an existing NURBS surface called a parent surface. Based on the surface model, the authors develop several novel deformation methods which are named SingleDef (Single-point constraint based deformation method), MultiDef (Multiple-points constraints based deformation method), CurDef (Curve constraints based deformation method) and FeatDef (Feature constraint based deformation method). The techniques for freeform surface deformation allow conceptual designers to modify a parent surface by directly applying point constraints, curve constraint or a surface constraint to the parent surface. The deformation methods are implemented in an experimental CAD system. The results show that designers can easily and intuitively control the surface shape.     

基于加工仿真的立铣刀三维参数化设计

基于CATIA软件平台进行二次开发,开发出基于加工仿真的高速立铣刀三维参数化设计的CAD软件系统。设计人员输入立铣刀的使用参数和主要结构参数,根据系统的数据库和相关程序自动生成立铣刀的三维CAD模型以及加工立铣刀的砂轮刀位轨迹及NC代码,调用VERICUT软件进行立铣刀磨削加工仿真,从而保证立铣刀参数化设计的三维模型的可加工性,保证刀具设计的质量和缩短刀具设计和制造周期。     

基于改进遗传算法求取加工自由曲面的最大刀具尺寸

为选取合适的加工刀具尺寸以对自由曲面实现无曲率干涉加工,提出了改进遗传算法并应用于自由曲面全局最大主曲率求取,确定无曲率干涉最大刀具尺寸.根据主曲率特点设计了一种新的非线性自适应度函数,避免算法过早收敛于局部最优值,并给出了新的复制原则.改进遗传算法应用算例分析表明,该算法在500代内能有效求取自由曲面全局最大主曲率,比传统的离散法效率高,选择的最大刀具尺寸满足自由曲面加工无曲率干涉加工的要求.     

整体硬质合金精密高效直槽扩挤刀

扩挤刀是汽车发动机高精度孔加工专用刀具。汽车发动机的进气管是发动机的重要部件,进气管喷油嘴孔的加工质量直接影响汽车的节油性能。过去加工喷油嘴孔大都使用国外进口的精密扩挤刀,价格昂贵,加工成本很高。为了降低加工成本,提高产品的市场竞争力,汽车刀具国产化...     

自由曲面三坐标加工等间距刀具路径规划

为提高自由曲面数控加工的切削效率,改善刀具的受力状态,提出了一种自由曲面三坐标加工等间距刀具路径规划方法.分析了在实际加工过程中可采用的几种刀具路径规划方法及其实现等距加工的约束条件.研究了等间距刀具路径的计算方法,并针对计算过程中出现的逼近误差校验和刀具路径延伸与裁剪问题给出了解决方法.对等参数线法和等距截面法进行了比较,表明应用该方法规划自由曲面刀具路径,可提高走刀路径对曲面形状变化的适应性和切削行间距分布的均匀性.     

自由曲面行距自适应五轴数控加工刀轨生成方法

在满足残留高度的前提下,增大行距能够有效减少加工刀轨的行数,从而减少刀轨总长度。针对自由曲面平底刀五轴加工,提出了一种行距自适应的刀轨生成方法。在刀具进给方向法平面上,以椭圆等效表示平底刀切削轮廓,基于曲面局部轮廓线和等残留高度点的几何特征提出迭代计算等残留高度点的方法;再根据等残留高度点、切削轮廓和曲面之间的几何关系,通过迭代调整下一行切削轮廓位置计算出满足残留高度要求的下一行刀轨信息;最后以下一行和当前行刀触点之间最小的参数差值作为自适应行距值规划刀轨。以叶片曲面为例生成刀轨,验证了算法的可行性和有效性。     

Geometry design model of a precise form-milling cutter based on the machining characteristics

This paper presents a new approach to design a form milling cutter for precisely obtaining the complex free-form surfaces. In this study, the intersection point of the rake surface, helix flute and clearance flank is appropriately defined due to its significant role in the design and grinding performance. The angle-solid-block analysis is developed to establish the new cutter geometry model. Hence, a new form-milling cutter satisfying the requirements of machining characteristics of workpiece can be designed. In addition, the cutter geometric model can be adopted to map out the measuring strategy with minimum measured points to attain the exact geometric feature of cutter.     

Prediction of surface reconstruction uncertainties for freeform surface inspection

A method is introduced to predict uncertainties of the B-spline freeform surfaces that are reconstructed from the measurement points for inspection of freeform surfaces. The uncertainties of a reconstructed B-spline surface are modeled by variances of coordinates of points on this freeform surface. Prediction of the uncertainty at any location on the reconstructed B-spline surface is carried out in two steps: (1) estimation of variances of the B-spline surface’s control points introduced by the surface reconstruction process, and (2) propagation of the variances from the control points to the points on the B-spline freeform surface. In this research, the variances of the control points of the reconstructed B-spline surface in all three directions are considered to improve the accuracy of uncertainty prediction in the regions with significant changes of geometric shapes. Both the errors and uncertainties at different locations on the reconstructed surface are considered in freeform surface inspection to compare the manufactured surface against the design surface and its tolerance. The developed method has been applied to two case studies to demonstrate its effectiveness.     

加工曲轴用可转位车拉刀的CAD/CAM

1　引言可转位车拉刀具有加工效率高、加工质量好、刀具寿命长、换刀和调刀方便等优点 ,是目前汽车曲轴粗加工首选的先进刀具。我国汽车行业所用车拉刀长期依赖进口 ,由于价格昂贵 ,大大增加了曲轴的加工成本。为了实现可转位车拉刀的国产化 ,近年来国内多家企业相继开发了车拉刀产品 ,但由于可转位车拉刀结构复杂 ,技术含量高 ,制造难度大 ,对加工条件及加工精度要求严格 (需在高精度五坐标数控机床上加工 ) ,且多数采用操作者手动编程加工 ,因此造成刀具制造周期长 ,加工精度不易保证 ,废品率较高。我公司利用ＳＵＮ图形工作站及美国ＳＤ…