ENVELOPING THEORY BASED METHOD FOR THE DETERMINATION OF PATH INTERVAL AND TOOL PATH OPTIMIZATION FOR SURFACE MACHINING

An enveloping theory based method for the determination of path interval in three axis NC machining of free form surface is presented, and a practical algorithm and the measures for improving the calculating efficiency of the algorithm are given. Not only the given algorithm can be used for ball end cutter, flat end cutter, torus cutter and drum cutter, but also the proposed method can be extended to arbitrary milling cutters. Thus, the problem how to strictly calculate path interval in the occasion of three axis NC machining of free form surfaces with non ball end cutters has been resolved effectively. On this basis, the factors that affect path interval are analyzed, and the methods for optimizing tool path are explored.

Dual Drive Curve Tool Path Planning Method for 5-axis NC Machining of Sculptured Surfaces

The problem of finished surface being not first-order continuous commonly exists in machining sculptured surfaces with a torus cutter and some other types of cutters. To solve this problem, a dual drive curve tool path planning method is proposed in this article. First, the maximum machining strip width of a whole tool path can be obtained through optimizing each tool position with multi-point machining （MPM） method. Second, two drive curves are then determined according to the obtained maximum machining strip width. Finally, the tool is positioned once more along the dual drive curve under the condition of tool path smoothness. A computer simulation and cutting experiments are carried out to testify the performance of the new method. The machined surface is measured with a coordinate measuring machine （CMM） to examine the machining quality. The results obtained show that this method can effectively eliminate sharp scallops between adjacent tool paths, keep tool paths smooth, and improve the surface machining quality as well as machining efficiency.

Analytical modeling of geometric errors induced by cutter runout and tool path optimization for five-axis flank machining

The cutter runout effect has significant influence on the shape of cutter swept surface and the machining surface quality. Hence,it is necessary to integrate the cutter runout effect in cutter swept surface modeling,geometric error prediction and tool path optimization for five-axis flank machining. In this paper,an envelope surface model considering cutter runout effect is first established,and geometric errors induced by runout effect are derived based on the relative motion analysis between the cutter and part in machining. In the model,the cutter runout is defined by four parameters,including inclination angle,location angle,offset value and the length of cutter axis. Then the runout parameters are integrated into the rotation surface of each cutting edge that is used to form the final cutter envelope surface for the five-axis machining process. Thus,the final resulting geometric errors of the machined surface induced by cutter runout can be obtained through computing the deviations from the nominal cutter swept surface. To reduce these errors,an iterative least square method is used to optimize the tool paths for five-axis flank machining. Finally,a validation example is given for a specific ruled surface. Results show the effectiveness and feasibility of the analytical model of geometric errors induced by cutter runout,and also show that the geometric errors can be reduced significantly using the proposed tool path planning method.

Tool path generation and optimization for freeform surface diamond turning based on an independently controlled fast tool servo

Diamond turning based on a fast tool servo(FTS)is widely used in freeform optics fabrication due to its high accuracy and machining efficiency.As a new trend,recently developed high-frequency and long-stroke FTS units are independently driven by a separate control system from the machine tool controller.However,the tool path generation strategy for the independently controlled FTS is far from complete.This study aims to establish methods for optimizing tool path for the independent control FTS to reduce form errors in a single step of machining.Different from the conventional integrated FTS control system,where control points are distributed in a spiral pattern,in this study,the tool path for the independent FTS controller is generated by the ring method and the mesh method,respectively.The machined surface profile is predicted by simulation and the parameters for the control point generation are optimized by minimizing the deviation between the predicted and the designed surfaces.To demonstrate the feasibility of the proposed tool path generation strategies,cutting tests of a two-dimensional sinewave and a micro-lens array were conducted and the results were compared.As a result,after tool path optimization,the peak-to-valley form error of the machined surface was reduced from 429 nm to 56 nm for the two-dimensional sinewave by using the ring method,and from 191 nm to 103 nm for the micro-lens array by using the mesh method,respectively.

Research on virtual dynamic optimization design for NC machine tools

Virtual dynamic optimization design can avoid the repeated process from de-sign to trial-manufacture and test.The designer can analyze and optimize the productstructures in virtual visualization environment.The design cycle is shortened and the costis reduced.The paper analyzed the peculiarity of virtual optimization design,and put for-wards the thought and flow to implement virtual optimization design.The example to opti-mize the internal grinder was studied via establishing precise finite element model,modi-fying the layout of Stiffened Plates and designing parameters of the worktable,and usingthe technology of modal frequency revision and the technology of multiple tuned damper.The result of optimization design compared the new grinder with the original grinder showsthat the entire machine's first orders natural frequency is enhanced by 17%,and the re-sponse displacement of the grinding-head has dropped by 28% under the first order natu-ral frequency and by 41% under second order natural frequency.Finally,the dynamic per-formance of the internal grinder was optimized.

OPTIMAL ALGORITHM FOR NO TOOl-RETRACTIONS CONTOUR-PARALLEL OFFSET TOOL-PATH LINKING

A contour-parallel offset （CPO） tool-path linking algorithm is derived without toolretractions and with the largest practicability. The concept of ＂tool-path loop tree＂ （TPL-tree） providing the information on the parent/child relationships among the tool-path loops （TPLs） is presented. The direction, tool-path loop, leaf/branch, layer number, and the corresponding points of the TPL-tree are introduced. By defining TPL as a vector, and by traveling throughout the tree, a CPO tool-path without tool-retractions can be derived.

Generation of tool path for flank milling in divided areas

Presents the division of non developable ruled surface into divided small areas and flank milling in these divided areas to improve machining efficiency and machined surface quality by controlling the machining error for each area, and the algorithms developed for generation of tool path and calculation of errors, and concludes from computer simulation results that the algorithms are correct.

Series Design of Large-Scale NC Machine Tool

Product system design is a mature concept in western developed countries. It has been applied in war industry during the last century. However,up until now,functional combination is still the main method for product system de-sign in China. Therefore,in terms of a concept of product generation and product interaction we are in a weak position compared with the requirements of global markets. Today,the idea of serial product design has attracted much attention in the design field and the definition of product generation as well as its parameters has already become the standard in serial product designs. Although the design of a large-scale NC machine tool is complicated,it can be further optimized by the precise exercise of object design by placing the concept of platform establishment firmly into serial product de-sign. The essence of a serial product design has been demonstrated by the design process of a large-scale NC machine tool.

Tool Orientation Optimization and Path Planning for 5-Axis Machining

Tool path generation is a fundamental problem in 5-axis CNC machining, which consists of tool orientation planning and cutter-contact(CC) point planning. The planning strategy highly depends on the type of tool cutters. For ball-end cutters, the tool orientation and CC point location can be planned separately;while for flat end cutters, the two are highly dependent on each other. This paper generates a smooth tool path of workpiece surfaces for flat end mills from two stages: Computing smooth tool orientations on the surface without gouging and collisions and then designing the CC point path. By solving the tool posture optimization problem the authors achieve both the path smoothness and the machining efficiency. Experimental results are provided to show the effectiveness of the method.

自由曲面NC加工无干涉刀具轨迹生成

对自由曲面ＮＣ加工中的干涉情况和现有处理方法进行分析．以曲面模型→刀具接触点数据→无干涉刀位数据为基本求解策略，综合多种优化措施。

Tool Path Generation for Clean-up Machining of Impeller by Point-searching Based Method

Machining quality of clean-up region has a strong influence on the performances of the impeller. In order to plan clean-up tool paths rapidly and obtain good finish surface quality, an efficient and robust tool path generation method is presented, which employs an approach based on point-searching. The clean-up machining mentioned in this paper is pencil-cut and multilayer fillet-cut for a free-form model with a ball-end cutter. For pencil-cut, the cutter center position can be determined via judging whether it satisfies the distance requirement. After the searching direction and the tracing direction have been determined, by employing the point-searching algorithm with the idea of dichotomy, all the cutter contact （CC） points and cutter location （CL） points can be found and the clean-up boundaries can also be defined rapidly. Then the tool path is generated. Based on the main concept of pencil-cut, a multilayer fillet-cut method is proposed, which utilizes a ball-end cutter with its radius less than the design radius of clean-up region. Using a sequence of intermediate virtual cutters to divide the clean-up region into several layers and given a cusp-height tolerance for the final layer, then the tool paths for all layers are calculated. Finally, computer implementation is also presented in this paper, and the result shows that the proposed method is feasible.

GENERATION METHOD FOR FIVE-AXIS NC SPIRAL TOOL PATH BASED ON PARAMETRIC SURFACE MAPPING

A new spiral tool path generation algorithm for 5-axis high speed machining is proposed in this paper.Firstly,the voltage contours are calculated to satisfy the machining parameters in the mapping parametric domain by means of the electrostatic field model of partial differential equations.Secondly,the mapping rules are constructed and the machining trajectory is planned out in the standard parametric domain in order to map and generate the spiral trajectory in the corresponding parametric domain.Finally,this trajectory is mapped onto the parametric surface for the obtainment of the spiral tool path.This spiral tool path can realize the machining of complicated parametric surface and trimmed surface without tool retractions.The above-mentioned algorithm has been implemented in several simulations and validated successfully through the actual machining of a complicated cavity.The results indicate that this method is superior to the existing machining methods to realize the high speed machining of the complicate-shaped cavity based on parametric surface and trimmed surface.

正交型五轴虚拟机床NC刀具路径仿真加工研究

利用Creo设计出五轴虚拟数控机床模型,用Creo设计工件模型及五轴加工NC代码,然后由VERICUT NC切削加工模拟软件整合前两者的资料,即可开始进行五轴切削仿真验证,监控数控机床加工中可能的超程、过切、干涉等潜在问题,消除程序中的错误,从而在VERICUT7.14环境下,实现了Mikron_ucp800五轴虚拟数控机床仿真加工多面体零件的全过程。

机床空间误差完备建模方法与NC代码优化补偿技术

空间误差是机床几何误差元素综合作用的结果,但现阶段空间误差模型大多存在缺失若干几何误差元素的问题,直接影响着机床空间误差的预测精度。为此,提出一种机床空间误差完备建模方法,以多体系统理论及齐次坐标变换为分析研究手段,在充分考虑体间坐标系初始位置关系及原始误差特征矩阵的基础上,确保模型包含机床全部几何误差元素。进而,针对传统基于NC代码的空间误差补偿技术中存在残差的局限性,提出将NC代码坐标的逆向叠加过程转化为最优化设计问题,并借助遗传算法对该问题进行求解计算,达到消除空间误差补偿残差的目的。最终,以某型卧式加工中心为研究对象进行计算分析与实验验证,结果表明:依据所提方法构建的空间误差完备模型包含加工中心全部21项几何误差元素,空间误差预测结果较精确;所提NC代码优化补偿技术使加工中心空间定位精度得到进一步提升,补偿后定位精度增幅最高达90.92%。研究成果可为数字制造装备精度问题探索提供较重要的理论与工程技术支撑。

基于NC程序的五轴数控加工刀位信息提取算法

研究了从NC代码中逆向提取刀位点的计算方法,通过UG软件仿真得到数控加工模型的刀位文件,再经后置处理得到模型的数控加工NC文件。经过研究后置处理理论,推导了从NC文件中的数据点反算刀位文件中的刀位点坐标及刀轴矢量,实现了从NC程序中提取曲面上刀位点及刀轴矢量的目标,为进一步实现数控加工信息的逆向提取提供了理论基础。最后通过VC编程实现逆向提取计算过程得到逆向提取的刀位点,经过与UGNX软件所得的刀位点进行对比验证,所得结论正确。

AUTOCAD图形环境下NC自动编程的实现

AUTOCAD是目前国内外最流行的CAD软件之一，它在机械、电子、化工、土木、服装等方面被广泛应用。然而由于其通用性目标，使AUTOCAD不可能在某一专项应用中有特别具体的辅助功能，本文叙述了在AUTOCAD（RELEASE11．0以上版本）图形环境下与C语言接口的一般方法，结合自己编程中的一些经验，介绍了在AUTOCAD图形环境下实现平面内含有多个不加工的岛的多个单连域的NC（NumericalControl）自动编程、干涉校验、轨迹仿真，该工作是对作者提出的复杂槽型机械加工普遍算法的具体实现，并输出了刀位数据文件，也可通过RS－232C串行通讯口直接送到数控机床实现DNC（DirectNumericalControl）控制。本文是AUTOCAD下用C语言进行二次开发的具体实例，实现了在CAD环境下直接利用CAD数据进行CAM（ComputerAidedManufacturing）。

Tool path strategy and cutting process monitoring in intelligent machining

Intelligent machining is a current focus in advanced manufacturing technology, and is characterized by high accuracy and efficiency. A central technology of intelligent machining--the cutting process online monitoring and optimization--is urgently needed for mass production. In this research, the cutting process online monitoring and optimization in jet engine impeller machining, cranio-maxillofacial surgery, and hydraulic servo valve deburring are introduced as examples of intelligent machining. Results show that intelligent tool path optimization and cutting process online monitoring are efficient techniques for improving the efficiency, quality, and reliability of machining.

参数曲线光滑处理的双向四阶Taylor拟合方法

为了使数控轨迹更加光滑,以进一步提高加工效率,提出一种基于空间轴的光滑曲线双向四阶Taylor拟合方法,通过优化使曲率更平缓来进一步降低拟合曲线的轮廓误差。首先,在参数曲线上选取有限均匀的数据点计算参数各阶导数以及曲率、挠率等微分几何量,以建立Frenet坐标系;然后,在第i区间始末两个数据点分别进行前向和后向四阶Taylor展开,根据刀位点在始末两个数据点形成的参数空间的相对距离确定耦合权重的拟合曲线;最后,通过坐标反变换得到机床坐标系XYZ下的优化轨迹。通过对原始轨迹和双向四阶Taylor拟合进行比较表明,随着阶数的提高,轮廓误差逐渐降低,曲率均值、曲率极差和曲率的导数极差均趋近原始曲线。通过对标准圆和高速列车车轮踏面LM-32进行拟合测试表明,相比拟合曲线,所提方法得到的优化曲线曲率变化连续,轮廓误差小4μm~5μm。

㶲耗散法对数控加工刀具路径能耗评估研究

针对数控加工中不同刀具路径加工的能耗问题进行研究,基于㶲(yòng)分析理论提出了一种㶲(yòng)耗散方法,对不同刀具路径加工进行能耗的评估;㶲耗散方法通过对加工过程中的切削热、切削液、机床待机、刀具切削磨损、压缩空气等能耗源进行分析,并对各个能耗源进行数学建模,计算不同刀具路径加工情况下的能耗,通过比较不同刀具路径加工能耗的大小,在保证加工质量的前提下选择能耗较少的刀具路径,达到节能目的;最后分别使用三种不同的刀具路径对曲面进行加工实验,通过实验结果证明:实际加工的能耗与㶲耗散法评估的能耗一致,等间距环形刀具路径比往复刀具路径的总㶲能耗降低了10.93%,等间距环形刀具路径比斜45°刀具路径的总㶲能耗降低了15.24%,说明㶲耗散法评估刀具路径加工能耗是可行的;创新点在于提出了㶲耗散法,通过㶲耗散把电能和物料能等不同类型的能量转化为同一形式进行计算,使能耗评估更加全面。

模拟退火遗传算法在自由曲面数控加工中的实验

在自由曲面的加工中,一直面临着加工时间长的问题,本研究以提高加工效率为目的,通过分析待加工自由曲面的面曲率、残余高度等参数,计算出合理的加工步长和行距,并以此为依据将待加工曲面离散成点云即为刀触点。将刀具路径规划问题转化为求解TSP问题的最优解,为避免遗传算法早熟陷入局部最优解,引入了模拟退火算法进行改进,使用改进后的混合算法进行刀具路径寻优。对优化方法进行了仿真加工、实验加工及测量,结果表明优化方法相比传统方法刀路长度最多减少303.4mm,相对缩短了12.3%,加工效率提升较为明显,并且加工表面也取得了较好的加工效果。