基于散乱数据点的数控加工刀位直接生成

研究了测量得到的散乱数据点在平面上投影点的边界轮廓提取算法；以抬刀次数最少为优化目标，通过引入计算几何中单调链的概念，确定了最佳的行切加工方向和最少单调链数；给出了在平面区域内行切法加工的刀位计算与Z字形刀位连接方法，该方法适用于模具型腔的刀位规划；针对圆环刀、球头刀和平头刀，提出了不发生干涉的曲面三轴加工刀位计算方法，可基于散乱点测量数据直接生成数控加工刀位，此刀位计算方法也可用于模具型腔的修复。最后，通过数值仿真验证了算法的可行性。     

舱体零件型腔加工轨迹生成模块开发

舱体零件是航天飞行器的关键零部件,而型腔面是舱体类零件的主要加工特征,舱体的型腔面具有数量多、形状复杂以及带有孤岛的特性,加工轨迹生成较为复杂。常用的UG NX等商业软件可以实现复杂型腔的加工轨迹生成,但是价格昂贵且难以和自主开发的加工软件集成。因此有必要依托三维几何引擎开发型腔的加工轨迹自动生成模块。基于三维几何引擎AnyCAD平台及相应的功能函数,建立了带孤岛复杂型腔的加工轨迹生成方法,针对舱体型腔的圆弧面特征,建立了型腔面的局部坐标系,提取了型腔的轮廓线以及加工轨迹线并利用局部坐标系进行平面投影,实现在平面中进行有效加工刀位点的判断,生成了有效刀位点集合。针对行切逐行扫描轨迹生成中存在的大量空行程导致的加工效率低下问题,提出了基于连续区域划分的加工轨迹生成算法,实现了高效的加工轨迹生成,最终基于AnyCAD平台开发了舱体零件复杂型腔面的加工轨迹生成模块,为自主加工软件开发提供了核心功能模块。     

平面型腔行切加工刀轨生成算法

型腔加工是CAM软件中一个重要的加工方式，被广泛应用于航空、汽车、模具制造业等领域。在型腔加工中，有两种常用的刀具轨迹走刀方式：环切方式和行切方式。在图1中，环切加工通过连续偏置型腔轮廓，构造当前环形轨迹的Voronio图来计算下一条环形轨迹，计算复杂且耗时。与环切加工相比，行切加工刀具轨迹主要由一系列与某一固定方向平行的直线段组成，计算简单。     

复杂型腔刀位轨迹规划的优化算法

针对行切法加工复杂型腔,对型腔边界与岛屿轮廓进行扫尾处理时,如何得到最短且合理的刀位轨迹,提出了一种优化算法。首先利用最小树得到环与环之间的最短连通路径。但是无序的最小树却无法映射为扫尾处理的最短刀位轨迹,因此应对同一父节点下的同层子节点进行排序,通过生成最小有序树得到最短的刀位轨迹,减少了空行程从而提高加工效率。该优化算法易于实现,已在自行研制的模具CAM软件中得到成功的应用。     

POCKET加工算法研究

本文提出了一个Ｐｏｃｋｅｔ加工算法,该算法不仅适合直线,圆弧围成的区域,而且也适合任何曲线和组合线围成的区域。同时提出了“端点同环优先”Ｐｏｃｋｅｔ行切算法,该算法具有仅产生一次进刀一次抬刀的特点,并具有最短路径寻优特性。     

复杂型腔加工区域的自动识别

为了解决型腔加工中交互式定义型腔和岛屿的不足,提出了一种简单有效的加工区域自动识别方法。为了识别型腔加工区域,首先构建了环关系矩阵,通过查询环关系矩阵的方式完成了轮廓环树的构建。在获得轮廓环树后,通过评估节点的深度来达到自动识别复杂型腔的目的。该方法无需用户直接参与,减轻了用户的负担,避免了出错的可能性。实例表明,该方法能自动有效地识别型腔加工区域,从而简化了数控编程步骤,提高了编程效率。     

球头铣刀曲面加工的刀具切触区域解析建模

针对球头铣刀三维曲面加工,提出一种刀具切触区域仿真的通用解析模型。采用微分方法,将曲面加工过程离散为一系列连续的微小斜平面稳态加工。以每一小斜面切削过程为研究对象,建立描述刀具进给方向变化的数学模型,针对不同的进给方向并基于空间坐标系旋转变换,提出一组确定刀具切触边界曲线及各边界交点的解析公式,以精确界定刀具切触区域的封闭几何。通过与Z-Map模型的切触区域仿真对比,验证了本文模型的有效性及其精确高效的特点。     

复杂形状区域行切加工刀具轨迹生成

讨论了由任意多段直线、圆弧、自由曲线及其组合构成边界轮廓，且边界内包含多个岛屿的复杂区域加工刀具轨迹计算问题。详细介绍了岛屿分解、边界轮廓刀具干涉处理、加工路线规划及刀具轨迹生成原理与算法。     

起落架深孔复杂型腔拉镗加工工艺研究

通过型腔拉镗加工工艺技术在起落架典型深孔复杂型腔零件上的应用,介绍了航空产品深孔加工技术现状,型腔拉镗加工工艺技术的工作原理、专用刀杆技术参数以及型腔拉镗法的工艺实施过程,对行业的发展和改进有着非常重要的意义。     

复杂型腔行切轨迹生成算法研究

复杂型腔类零件的加工是数控编程中的一个难点。本文从提高加工算法的稳定性和加工效率的角度出发，提出了一个复杂平面型腔数控加工的优化算法，即通过二维环的等距，自交，集全等基本运算，按“端点同环最短距离优先剖面线算法”规划并优化刀具轨迹。最衙给出了应用实例。     

A mapping-based spiral cutting strategy for pocket machining

Almost 80 % of the milling operations to produce mechanical parts are produced by NC pocket milling, especially in aerospace and automobile industry. At present, for 2.5D pocket machining, direction-parallel and contour-parallel machining strategies have gained nearly universal acceptance. However, in such tool path, abrupt change of path direction, frequent acceleration and deceleration, and sharp velocity discontinuous are found to significantly limit the machining efficiency of pockets. To address these problems, this paper introduces a method for generating a spiral tool path that maintains a steady-state cutting process by as smoothly as possible curvature evolution of the tool path for pocket machining. First, the machined region of a layer of a pocket is mapped onto a circular domain by means of mesh mapping, which reduces the task of tool path generation from the geometrically complex pocket region to a topologically simple disk. On this disk, a guide spiral is constructed according to a mathematical function constrained by the calculated path interval map. Using the mapping from the pocket to the disk as a guide, the guide spiral is inversely mapped into the interior of the pocket and then a smooth low-curvature spiral path is derived. The generated tool paths are guaranteed to not inherit any corners in the subsequent interior tool paths and allows cutting of the pocket without tool retractions during the cutting operations. Finally, the proposed method is implemented and tested on several typical sample pockets to demonstrate its validity and significance.     

Effects of inclination angles on geometrical features of machined surface in five-axis milling

With the development of manufacturing technology, five-axis milling has been one of the most important solution strategies in machining field. To deepen the understanding of multi-axis processing and improve the application level of the technology, the current work was carried out. This paper investigated the effects of tilt and lead angle on the scallop height, surface roughness, surface topography, and surface damages in five-axis ball-end milling process. Both geometrical analysis and experiment research are conducted to investigate the scallop height after five-axis milling, and variation of the surface roughness and surface topography with tool inclination angle obtained from the experiments was analyzed. Surface damages under the different inclination angles were also observed and analyzed with optical profiler. Several conclusions are made as follows. The inclination angles of the ball-end mill have no effect on the scallop height when only the spherical part of the cutter participates in the cutting process according to the geometrical analysis. Surface roughness with regard to tilt angles presents symmetrical characteristic around 0°. Surface texture feature, especially the texture direction, is closely related with the tool posture. The surface concave pits, convex marks, microscopic cracks, and spot corrosions are mainly the damage forms of the machined surface. More surface blemishes appeared when small inclination angles are adopted in cutting. As a result, the recommendatory inclination angle values for inclination angle are proposed. A better understanding of the five-axis machining process would be given by the detailed analysis of generation reason of the machined surface features, and the results could provide support for process parameter optimization.     

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.     

Selection of optimal set of cutting tools for machining of polygonal pockets with islands

Selection of the optimal set of cutting tools is one of the most important steps in process planning for 2.5-D pocket machining. Conventional CAM software requires considerable input from the user in terms of selection of tool sizes and machining strategy. This trial-and-error procedure to determine the optimal process sequence tends to generate conservative and suboptimal results. This paper presents a methodology for optimal selection of a sequence of tools to minimize the total time required to end mill a non-convex polygonal pocket with or without islands using the staircase milling strategy. The algorithm decomposes the pocket geometry into convex regions and mills each region independently by selecting a sequence of tools based on the accessibility of various tools to the region. Strategies have been developed for machining the main pass and the subsequent leftover areas in order to obtain the final pocket geometry. Subsequently, the machining times for each decomposed area are aggregated while accounting for the need to use multiple passes, non-cutting time, and the tool change time. A dynamic programming approach is used to determine the optimal set of tools which minimizes the total processing time. The effect of varying the non-cutting speed and tool change time on the tool path length and number of tool selection is studied.     

Optimum tool path generation for 2.5D direction-parallel milling with incomplete mesh model

Many mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation, along with physical considerations for better machining productivity with guaranteed machining safety, are the most important issues in milling. In this paper, an optimized path generation algorithm for direction-parallel milling, a process commonly used in the roughing stage as well as the finishing stage and based on an incomplete 2-manifold mesh model, namely, an inexact polyhedron widely used in recent commercialized CAM software systems, is presented. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the tool paths obtained from geometric information have been successful in forming desired shapes, physical process concerns such as cutting forces and chatters have seldom been considered. In order to cope with these problems, an optimized tool path that maintains a constant MRR for constant cutting forces and avoidance of chatter vibrations, is introduced, and verified experimental results are presented. Additional tool path segments are appended to the basic tool path by means of a pixel-based simulation technique. The algorithm was implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests measured the spindle current, which reflects machining characteristics, to verify the proposed method.     

Influence of tool inclination on chip formation process and roughness response in ball-end milling of freeform surfaces on Ti-6Al-4V alloy

An experimental test part, which was made up of flat, concave, and convex surfaces of variable curvatures, was designed to be fabricated in a four-axis machining center. Aluminum alloy 7075 and titanium alloy Ti-6Al-4V were used for the fabrication. Within the finishing process, smeared/adhered material was found in some areas of the concave and convex surfaces of the titanium alloy. On the other hand, smeared/adhered material was not found in the aluminum alloy. To characterize the type of defects, the 3D roughness parameters of the surfaces were measured by confocal microscopy, and surface morphology was observed using optical microscopy and scanning electron microscopy. The kinematics of the ball-end milling process was modeled and it was found that the lead and tilt angles between the tool axis and surface normal vector vary continuously, producing transitions between oblique-plunge-push-up milling and oblique-reverse-push-up milling. This causes variation in the thickness behavior during the chip formation process. It was found that the lead angle has a moderate influence, while the tilt angle has a strong effect on the quality of the surfaces of the titanium alloy, with negative tilt angles producing the worst surfaces when there was the oblique-plunge-push-up milling process.     

球头刀铣削淬硬钢倾斜表面切削力试验研究

采用正交试验方法,使用PCBN涂层硬质合金球头铣刀,对不同铣削参数下的52HRC淬硬钢Cr12MoV倾斜表面进行了铣削试验。研究了各工艺参数对切削力的影响规律。试验结果表明:三向力中,Fz远大于Fx和Fy的切削分力,Fz为主铣削力;切削深度对主铣削力的影响大于进给速度、工件倾角和主轴转速对其的影响;工件倾角16.7°,主轴转速6000r/min,进给速度800mm/min,切削深度0.1mm为优选工艺条件。同时,对比试验表明,采用顺铣方式能有效减小切削力,改善铣削稳定性。本文研究结果对淬硬钢Cr12MoV铣削工艺参数的优化具有一定的参考价值。     

文字、图案数控凹凸雕刻加工计算机辅助编程系统

介绍作者研制的文字、图案数控凹凸雕刻加工计算机辅助编程软件系统的关键技术方法。该软件系统能够将以图形扫描方式和图形 Ｃ Ａ Ｄ方式得到的文字、图案的图象和图形文件,经过一系列的处理和转换,按照凹或凸的雕刻加工要求,自动生成数控铣床的加工程序。     

数控型腔铣削加工稳定性预测

数控型腔铣削加工过程中,铣刀进入拐角时,刀具-工件间啮合信息的变化通常会引起颤振。针对这一状况,在用半离散算法对刀具-工件啮合状况恒定铣削加工稳定性预测的基础上,结合数控型腔铣削加工过程中加工路径引起的刀具-工件间啮合信息的变化,针对给定的加工路径提出了型腔铣削加工稳定性预测的方法。试验证明,该方法能在数控加工时对型腔加工过程中的铣削稳定性进行成功预测。     

An Operation Planning System for Multi-Axis Milling of Sculptured Surfaces

Multi-axis milling of sculptured surfaces with cylindrical or toroidal cutters has many advantages compared to the use of three-axis milling with ball nose cutters. Surfaces to be machined are often of complex shape and characterised by convex, concave and saddle areas. Today, CAM-systems do not support the user in the selection of the different operations in order to finish the workpiece. This paper describes an operation planning system, which facilitates process planning for the multi-axis machining of sculptured surfaces. The core of the system is surface analysis, which divides the surfaces into regions, each characterised by a preferred milling direction and tool diameter. Further, for each region or set of regions, a drive surface is constructed that is used as the basis for the tool-path calculation. The drive surface approximates to the original workpiece as closely as possible, and the isoparametric lines which will be the tool-path feed direction lie in the preferred milling direction.