Free-form die-cavity pocketing

This paper deals with the tool path optimisation procedure in free form die-cavity pocketing. Many researchers have investigated pocket machining problems, and most of them focused on the tool-path element generation problem, which has been regarded as the key issue in the pocketing tool-path generation. However, free form die-cavity pocketing involves many other problems, such as machining area extraction, uncut removal, local tool path linking and global tool path linking. All these problems should be solved to optimise pocketing tool path and each of them involves its own geometrical and technological issues. The objective of this paper is not to develop a new algorithm, but to achieve the global optimisation of pocket machining by considering all issues and solutions in pocketing.     

Generation of Tool Paths for Machining Free-Form Pockets with Islands Using Distance Maps

In this paper, we present a new procedure for generating tool paths using discrete distance maps, especially for dealing with free-form shaped pockets with multiple islands. In this procedure, a discrete distance map is computed by shading a right circular cone having the height of a given offset distance, while moving its apex along the boundary curve segments. Using the discrete distance maps, the proposed algorithm effectively extracts the characteristic points or the valid self-intersection points of offset curve segments. For an offset distance, one or more offset profiles are constructed without the topological problems by offsetting the boundary curve segments within the parameter values specified by these chararteristic points, and connecting them into closed profiles using the topological information contained in the distance map. The gouging-free tool path is constructed by connecting these offset profiles, starting from the innermost offset profile. In the proposed method, we do not need any artificial bridges for a pocket with multiple islands to merge the pocket profile and the island profiles into a single boundary profile.     

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.     

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

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一种新的型腔铣削刀轨生成算法

在对型腔外轮廓和岛屿轮廓分别考虑的基础上,对各封闭环路进行简化,提出了一种新的干涉标志量递推规则,实现了多种等距环交点情况的统一处理,降低了算法复杂度.文中给出了由该算法生成的带岛屿型腔刀位轨迹的实现步骤及计算实例.测试表明,该算法计算速度快,稳定性好.     

带任意多岛屿的型腔环切加工刀轨生成

对带任意多岛屿的型腔环切加工刀轨生成进行了研究 ,提出了一种等距环互交处理的快速简便算法 ,设计了多个岛屿之间、岛屿与型腔之间的干涉处理方法 ,算法在超人CAD/CAM软件中实现 ,实践表明 ,该功能模块运行速度快 ,稳定性好 ,具有工程应用价值。     

Modeling an envelope generated by 3D volumetric NC tool motion

Simulation and verification of numerically controlled (NC) manufacturing processes require efficient visualization and analysis of the swept volume generated by the motion of freeform NC tools along complex 3D paths. State-of-the-art methods are either based on approximation techniques (thus lacking the level of accuracy required in NC manufacturing) or are based on analytical solutions with high computational complexity, which are not suitable for real-time applications. In addition, until recently, modeling the self-intersection of a generated volume was thought to be obstructed by seemingly complex mathematics. This paper proposes solving the sweeping problem by using the sweep-envelope differential equation (SEDE). This method has advantages over other methods in terms of low computational complexity and high accuracy. Moreover, this method includes efficient tools for self-intersection detection and modeling. In this paper, we present an enhanced self-intersection algorithm and apply the SEDE algorithm on a ball-end cutter that is swept along non-intersecting and self-intersecting cutter paths.     

NC Machining of Freeform Pockets with Arbitrary Wall Geometry Using a Grid-Based Navigation Approach

A tool path must be determined in an efficient manner to generate NC (numerical control) code for machining. This is particularly important when machining freeform pockets with arbitrary wall geometry on a three-axis CNC machine. In this paper, a grid-based 3D navigation algorithm for generating NC tool-path data for both linear interpolation and a combination of linear and circular interpolation is presented for three-axis CNC milling of general pockets with sculptured bottom surfaces. The pocket surface is discretised by defining a grid and the navigation algorithm plans the tool motion. The grid size and the cutter diameter are chosen so that a predefined tolerance for surface roughness is satisfied. The grid-based navigation algorithm is simulated graphically and verified experimentally.     

基于网络优化的复杂型腔刀具轨迹规划算法

复杂型腔零件的加工是数控编程中的一个难点。从提高加工算法的稳定性和加工效率的角度出发,提出了基于网络优化的复杂平面型腔数控加工刀具轨迹优化算法,分析了轮廓环的等距、自交、集合运算等基本运算,详细论述了基于网络优化的刀具轨迹规划方法并优化了刀具轨迹。     

Research on an algorithm for an NC machining hypoid pinion

Based on the flexibility characteristics of the NC machine tool, which means that various motions can be performed arbitrarily on NC machine tools, a new algorithm for manufacturing a hypoid pinion is proposed. This gets rid of the limitation of traditional mechanical machine tools and their algorithms. When the cutter tilt method is combined with the modification method, a method of manufacturing the pinion with a prescribed-size cutter on an NC machine tool can be realised. This helps to simplify cutter specifications and realise the error compensation of the cutter size. In this paper the algorithm is derived. According to the equations of cutting, the machine settings are calculated.     

MasterCAM在数控车床自动编程中的应用

在数控机床上加工复杂模具的凹模，可以用手工编程，但是难度很大。如果利用MasterCAM软件中的铣槽加工方法，则很容易实现NC程序，还可以通过模拟加工，验证程序的可行性。本文主要介绍了MasterCAM软件对于铣槽加工刀具路径生成的过程，并通过复杂零件实例说明加工不同类型凹槽(Pocket)时的刀具路径，既考虑保证零件尺寸精度同时又能提高工效。     

飞机结构件槽特征加工路径优化算法研究

提出了一种基于分治法思想的加工路径优化算法。该算法将槽特征加工路径的优化近似为旅行商问题(TSP),根据槽的分布对TSP路径进行几何分区,分别应用正交路径法、最近邻算法等求解,并将结果合并为完整路径。最后通过实际应用验证了该算法实现简单,求解速度快,优化结果同人工编排的加工路径非常接近,具有可行性和有效性。     

Chatter prediction based on frequency domain solution in CNC pocket milling

Chatter has been a problem in CNC machining process especially during pocket milling process using an end mill with low stiffness. Since an iterative time-domain chatter solution consumes a computing time along tool paths, a fast chatter prediction algorithm for pocket milling process is required by machine shop-floor for detecting chatter prior to real machining process. This paper proposes the systematic solution based on integration of a stability law in frequency domain with geometric information of material removal for a given set of tool paths. The change of immersion angle and spindle speed determines the variation of the stable cutting depth along cornering cut path. This proposed solution transforms the milling stability theory toward the practical methodology for the stability prediction over the NC pocket milling.     

Exact Tool Sizing for Feature Accessibility

This paper presents an algorithm for calculating the volume of a 2D-profile, accessible by a given diameter of milling cutter. The method is independent of the generation of cutter tool paths, and exploits facilities commonly found in kernel modellers. Exact results are obtained despite the simplicity of the procedure. As a proof of the concept, the algorithms have been implemented in the Heriot-Watt University feature recogniser as a pre-processor for a part programming system. The aim of these algorithms is to assist and optimise the selection of multiple tools for the machining of complex components. The methodology has applications in process planning research where it is currently common to assume that a single tool will machine each feature. Although cutter selection is a critical step in planning the manufacture of components, computer-aided process planning (CAPP) systems rarely make any attempt to analyse the trade-offs involved. Perhaps this is because, traditionally, exact tool accessibility calculations have been viewed as a side effect of generating a cutter tool path. Consequently, accessibility calculations are not carried out explicitly but they appear implicitly in the results of a complex geometric algorithm (i.e. cutter path generation). Because this implicit checking of tool accessibility is carried out, downstream from the higher-level reasoning about set-up and sequencing, the results are generally available only after a detailed process plan has been generated.     

曲面笔式加工刀位点曲线的实时拟合

针对曲面高速高精度加工问题,给出一种刀位点轨迹实时生成算法。该方法的实现包括曲面上离散刀触点的生成和基于三次非均匀B样条曲线的刀位点轨迹实时高精度拟合两部分。第一部分,由导动曲线和刀触点轨迹的运动学关系,通过计算导动曲线参数,间接得到投影在曲面上的离散刀触点;第二部分,通过合理参数化、构建模长因子等实现刀位点参数曲线的分段实时拟合。仿真实例表明该算法简单易于编程,曲线拟合精度高,适用于自由曲面笔式加工中刀具路径计算与生成,从而满足复杂曲面高性能数控加工需求。     

最小有向距离算法在螺杆加工中的应用

从空间啮合原理出发 ,研究刀具与工件表面的接触规律 ,将最小有向距离算法应用于螺杆加工的数控编程中。在给定工件端截面参数方程的条件下 ,可采用该方法生成刀具运动轨迹 ,实现经济、高效的螺杆加工。该算法适用于各种截面廓型为一阶连续可微曲线的圆柱螺旋面螺杆加工 ,并可通过分段处理技术实现对截面廓型由多段曲线组合而成的螺杆进行自动编程加工。     

Machining of plate cam profiles on CNC machine tools using a highly integrated part programming system

The concept of NC (Numerical Control) and CNC (Computerised Numerical Control) in machine tools has contributed a great deal to automation and flexibility in manufacturing. In small/medium batch manufacturing, machining of complex contours with conventional machining is neither economical nor accurate. These can be achieved on a CNC machining centre more economically. The can machining system is designed to provide the necessary CNC program blocks for machining the plate cam profiles. The cam profiles can be defined by geometric curves, by follower motion or through a set of points. A promising new concept for approximating the tool path close to the defined cam profile, within the specified tolerance, has been proposed. The CLIP algorithm, presented in this paper, automatically chooses the best of the available interpolations (e.g. linear and circular interpolations) for selecting the intermediate points on the profile to guide the cutter for machining the profile. It provides the minimum number of intermediate points. This module can also be used for machining the elliptical profiles and pockets. The cam module, with little modification, is also used for machining the scroll threads of any pitch.     

五坐标端铣数控加工计算理论分析

本文介绍了五坐标端铣数控加工中的后跟角计算方法及刀位计算方法,分析了加工误差,包括直线逼近误差和刀轴摆动误差,提出了刀轴摆动误差补偿方法——刀具切触点偏置法,给出了走刀步长、走刀步距及刀具半径计算公式。     

基于散乱测量数据点的三轴数控粗加工刀位轨迹生成算法

提出了一种直接利用三维散乱测量数据点的三轴数控粗加工刀位轨迹生成算法。首先根据切层深度作一组垂直于Z轴的平面,去截取测量点云,得到一系列切层截面点集,再在每个切层面上组环并判断加工区域,规划出刀位轨迹,将每一分层平面上的刀位轨迹按适当的方式连接起来,就可构成零件的整体加工轨迹。该算法避免了由测量点构造曲面且由曲面来进行刀位轨迹生成的这一复杂过程。     

基于贪心-遗传算法的混合轨迹加工走刀空行程路径优化

针对数控自动编程中交互式图形文件存储图元的无序性,提出基于贪心算法和遗传算法的新型多轮廓混合轨迹加工路径优化方法,利用遗传算法对各个轮廓轨迹的前后加工顺序进行优化排序,并融合贪心算法对某种加工顺序中相邻轨迹段之间的空行路径的控制点进行选择,进而计算总空行程和个体的适应度,然后对个体进行评价选择、交叉、变异等遗传操作。该算法不仅简化了遗传算法的编码方式,而且还排除了无效解。经编程仿真及试验测试,结果表明：算法有效地缩短了刀具的空行程、减少了刀具的起落次数、提高了加工效率。