Wear characteristics of diamond tool in ultraprecision raster milling

Ultraprecision freeform raster milling is a very complex machining process, and long machining time is used for small components. Therefore, the diamond tool wear is a crucial factor that not only raises the machining cost but also limits the cutting performance in ultraprecision raster milling. In this paper, the methods of process monitoring and wear evaluating of single-crystal diamond tools during the raster milling of copper are studied in two types of cutting environment: with lubrication and without lubrication. Experimental results indicate that the impact and free vibration are important dynamic characteristics in raster milling process that result in the obvious microchipping wear on the cutting edge.     

Novel tool wear monitoring method in ultra-precision raster milling using cutting chips

Tool wear monitoring is a popular research topic in the field of ultra-precision machining. However, there appears to have been no research on the monitoring of tool wear in ultra-precision raster milling (UPRM) by using cutting chips. In the present research, monitoring tool wear was firstly conducted in UPRM by using cutting chips. During the cutting process, the fracture wear of the diamond tool is directly imprinted on the cutting chip surface as a group of ‘ridges’. Through inspection of the locations, cross-sectional shape of these ridges by a 3D scanning electron microscope, the virtual cutting edge of the diamond tool under fracture wear is built up. A mathematical model was established to predict the virtual cutting edge with two geometric elements: semi-circle and isosceles triangle used to approximate the cross-sectional shape of ridges. Since the theoretical prediction of cutting edge profile concurs with the inspected one, the proposed tool wear monitoring method is found to be effective.     

Iso-scallop tool path generation in 5-axis milling

This paper presents a new method of computing constant scallop height tool paths in 5-axis milling on sculptured surfaces. Usually, iso-scallop tool path computation methods are based on approximations. The attempted scallop height is modelled in a given plane to ensure a fast computation of the tool path. We propose a different approach, based on the concept of the machining surface, which ensures a more accurate computation. The machining surface defines the tool path as a surface, which applies in 3- or 5-axis milling with the cutting tools usually used. The machining surface defines a bi-parametric modelling of the locus of a particular point of the tool, and the iso-scallop surface allows to easily find iso-scallop tool centre locations. An implementation of the algorithms is done on a free-form surface with a filleted end mill in 5-axis milling.     

An integrated study of surface roughness for modelling and optimization of cutting parameters during end milling operation

The aim of this study is to develop an integrated study of surface roughness to model and optimize the cutting parameters when end milling of AISI 1040 steel material with TiAlN solid carbide tools under wet condition. A multiple regression analysis using analysis of variance is conducted to determine the performance of experimental measurements and to show the effect of four cutting parameters on the surface roughness. Artificial neural network (ANN) based on Back-propagation (BP) learning algorithm is used to construct the surface roughness model exploiting a full factorial design of experiments. Genetic algorithm (GA) supported with the tested ANN is utilized to determine the best combinations of cutting parameters providing roughness to the lower surface through optimization process. GA improves the surface roughness value from 0.67 to 0.59 μm with approximately 12% gain. Then, machining time has also decreased from 1.282 to 1.0316 min by about 20% reduction based on the cutting parameters before and after optimization process using the analytical formulas. The final measurement experiment has been performed to verify surface roughness value resulted from GA with that of the material surface by 3.278% error. From these results, it can be easily realized that the developed study is reliable and suitable for solving the other problems encountered in metal cutting operations as the same as surface roughness.     

铣磨复合加工齿轮的切削参数优化

为减少齿轮复合加工的切削时间,提高加工效率,对铣磨复合加工齿轮切削参数进行了研究,并结合机床的各项约束条件,建立了以最小加工时间为目标函数的铣磨复合加工数学模型,使用改进的量子行为粒子群优化算法对切削参数进行寻优计算. 将寻优计算所得结果与齿轮模数进行最小二乘拟合,得到优化加工时间与齿轮模数、磨齿进给量与齿轮模数的函数关系拟合方程,实现了加工时间最少的目标,并且充分发挥了机床的性能.     

Incomplete mesh-based tool path generation for optimum zigzag milling

The majority of mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation and physical considerations for better machining productivity with guarantee of machining safety are the most important issues in milling tasks. In this paper, we present an optimized path-generation algorithm for zigzag milling, which is commonly used in the roughing stage as well as in the finishing stage, based on an incomplete two-manifold mesh model, namely, an inexact polyhedron that is widely used in recent commercialized CAM software systems. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the tool path obtained from geometric information has been successful to make a desirable shape, it seldom considers physical process concerns like cutting forces and chatter. In order to cope with these problems, an optimized tool path that maintains constant MRR in order to achieve constant cutting forces and to avoid chatter vibrations at all times is introduced and the result is verified. Additional tool path segments are appended to the basic tool path by using a pixel-based simulation technique. The algorithm was implemented for two-dimensional contiguous end-milling operations with flat end mills and cutting tests were conducted by measuring the spindle current, (which reflect machining situations) to verify the significance of the proposed method.     

Tool path generation and modification for constant cutting forces in direction parallel milling

This paper presents an optimized path generation algorithm for direction parallel milling, which is commonly used in the roughing and finishing stages. First, a geometrically efficient tool path generation algorithm using an intersection points graph is introduced. Second, the generated tool path is modified as an optimized tool path that maintains a constant material removal rate to achieve a constant cutting force and avoid chatter vibration, and the results are verified. Additional tool path segments are appended to the basic tool path through a pixel-based simulation technique. The algorithm is implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests are conducted by measuring the spindle current, which reflects the changing machining situations, to verify the performance of the proposed method.     

Accurate spiral tool path generation of ultraprecision three-axis turning for non-zero rake angle using symbolic computation

An accurate spiral tool path generation method of ultraprecision three-axis turning free form surface is proposed based on symbolic computation in this paper. Many analytic optical free form surfaces often need to be machined to submicron in form error, such as optical nonaxisymmetric aspheric surfaces, but current mainstream CAM systems usually use nonuniform rational basis spline (NURBS) to describe the designed surface and generate tool path. If we want to use these systems, the analytical optical surfaces must be approximated using NURBS surfaces, but it will introduce approximation error and may be difficult to achieve the approximation error less than submicron. More importantly, there is no effective tool path generation method for the special three-axis turning machine tool in current mainstream CAM systems. In this context, we propose to calculate the tool path directly from these analytic surfaces by using symbolic math. The proposed method can be used to generate accurate spiral tool paths for zero/negative/positive rake angle in a unified way. Finally, several examples are given to prove its effectiveness.     

Gouging elimination through tool lifting in tool path generation for five-axis milling based on faceted models

Five-axis milling may be performed with a constant tool-orientation or varying optimal tool-orientation. When applying a constant tool orientation, the inclination angle, the angle between the tool axis and the normal vector of a contact point (cc-point), is kept constant along the tool path. On the other hand, when applying a varying optimal tool orientation, the tool inclination angle is dynamically optimized along the tool path in order to maintain the tool to be as close as possible to the surface without gouging. In both tool orientation methods, tool lifting is one of the crucial components and involved in tool path generation, especially when it is used for gouging elimination. For the constant tool orientation, the tool is lifted immediately when the specified inclination angle causes gouging with the part surface. In the case of varying optimal tool orientation, the minimum rotation angle (inclination angle) has to be found first to avoid gouging. If the gouging still occurs (e.g. due to limited rotational axes of the milling machine), then the tool is lifted. In this paper, gouging elimination through tool lifting for five-axis milling based on a faceted model is presented. The tool is lifted based on the types of gouging. These types of gouging are described and the tool lifting procedure has been developed and implemented for gouging elimination in both tool orientation methods.     

Iso-parametric CNC tool path optimization based on adaptive grid generation

The iso-parametric tool path is broadly used in CAM systems to machine sculptured surfaces. To satisfy tolerance constraints CAM systems usually adopt the smallest intervals across discrete tool paths, leading often to overlap and inefficient tool path. This paper presents a novel optimization scheme based on adaptive grid that can produce the optimal tool path on the basis of iso-parametric tool path and introduces the numerical method of generating the adaptive grid. When the generated optimal tool path has the same number of discrete tool path as the iso-parametric tool path, the optimal tool path will produce smaller machining errors. Or when the generated optimal tool path produces the same errors as the iso-parametric tool path, the optimal tool path will have fewer discrete tool paths and higher efficiency. This optimization scheme is robust, concise, and easy to be integrated into CAM systems to produce the optimal tool path automatically.     

数控铣削加工曲面时刀具轨迹的研究

数控铣削加工曲面过程中,刀具的运动轨迹是影响加工质量的一个重要因素.研究了数控铣削加工过程中刀具轨迹的生成,以及不同轨迹形式对加工质量有何影响等内容.     

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.     

基于模糊评判的机床类型选择及切削参数优化

对影响机床选择的各个因素进行了分析,利用模糊数学理论,根据零件几何特征、机床装夹尺寸、加工范围、加工精度、加工表面粗糙度等因素建立了机床优化选择的理论模型,并利用模糊综合评判法确定了机床选择的隶属度及最大综合评判指标,在创成式CAPP系统中实现了机床的合理自动选择.建立了ABAQUS有限元模型,对机床的钻削过程进行仿真,分别得到了理论上和经验上的切削参数与切削力、切削参数与加工表面残余应力的关系曲线图,从而找到了最优的切削参数.     

Design optimization of cutting parameters for side milling operations with multiple performance characteristics

In this paper, a grey relational analysis is applied to a set of two-stage experiments designed to determine the cutting parameters for optimizing the side milling process with multiple performance characteristics. The cutting parameters to be considered are cutting speed, feed per tooth, axial depth of cut, radial depth of cut, overhang length and flank wear of peripheral cutting edge. L₃₆ and L₉ orthogonal arrays are used in the experiments and lower-the-better is used as a qualitative characteristic to evaluate the results. It is found that using the grey relational analysis coupled with a deliberate design of the two-stage experiments is simple and efficient in determining an optimal combination of the cutting parameters. The results of the confirmation test also show that this new approach can greatly improve the cutting performance of side milling process.     

PCBN刀具铣削灰铸铁时铣削用量优化的研究

采用单因素分数优选法进行PCBN刀具铣削灰铸铁的耐用度试验,根据最大刀具耐用度的原则给出了最佳铣削速度.应用正交试验法,研究PCBN刀具的铣削用量对刀具耐用度的影响,建立了PCBN刀具耐用度和铣削用量的经验公式,根据试验结果,给出了PCBN刀具铣削灰铸铁的合理铣削用量范围.     

The effects of cutting parameters on tool life and wear mechanisms of CBN tool in high-speed face milling of hardened steel

High-speed face milling of AISI H13 hardened steel is conducted in order to investigate the effects of cutting parameters on tool life and wear mechanisms of the cubic boron nitride (CBN) tools. Cutting speeds ranging from 400 to 1,600 m/min are selected. For each cutting speed, the metal removal rate and axial depth of cut are fixed, and different combinations of radial depth of cut and feed per tooth are adopted. The tool life, tool wear progression, and tool wear mechanisms are analyzed for different combinations of cutting parameters. It is found that for most of the selected cutting speeds, the tool life increases with radial depth cut and then decreases. For each cutting speed, the CBN tool life can be enhanced by means of adopting suitable combination of cutting parameters. When the cutting speed increases, the normal wear stage becomes shorter and the tool wear rate grows larger. Because of the variations of cutting force and tool temperature, the tool wear mechanisms change with different combinations of cutting parameters even at the same cutting speed. At relatively low cutting speed, in order to acquire high tool life of the CBN tool, the tool material should possess sufficient capability of resisting adhesion from the workpiece. When relatively high cutting speed is adopted, retention of mechanical properties to high cutting temperature and resistance to mechanical impact are crucial for the enhancement of the CBN tool life.     

Contour parallel milling tool path generation for arbitrary pocket shape using a fast marching method

Contour parallel tool paths are among the most widely used tool paths for planer milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, the applicability of various offsetting methods is restricted because of limitations in dealing with pocket geometry with and without islands, the high computational costs, and numerical errors. Generation of cusps, segmentation of rarefied corners, and self-intersection during the offsetting operations and finding a unique offsetting solution for pocket with islands are among the associated problems in contour tool path generation. Most of methods are inherently incapable of dealing with such problems and use complex computational routines to identify and rectify these problems. Also, these rectifying techniques are heavily dependent on the type of geometry, and hence, the application of these techniques for arbitrary boundary conditions is limited and prone to errors. In this paper, a new mathematical method for generation of contour parallel tool paths is proposed which is inherently capable of dealing with the aforementioned problems. The method is based on a boundary value formulation of the offsetting problem and a fast marching method based solution for tool path generation. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an “entropy condition” in its numerical implementation. The appropriate modifications are carried out to achieve higher accuracy for milling operations. A number of examples are presented, and computational issues are discussed for tool path generation.