加工中心刀具选配问题的研究

传统加工中心的刀具选配仅以满足加工点的需求为目的 ,没有考虑刀具的可调性和可代用性。本文从刀具的组成特点出发 ,提出了基于逻辑刀具的刀具选配方法 ,把某些可以归为一类的需求刀具用一个逻辑刀具来代替 ,通过集合覆盖方法求解逻辑刀具。在不同的加工工件之间 ,通过调整逻辑刀具的实例状态来满足数控程序中的刀具需求。基于逻辑刀具的刀具选配法 ,可有效减少刀具的准备数量 ,提高刀具利用率。本文介绍了有关概念及算法     

A technologically oriented approach for the economic tool selection and tool balancing of milled components

A technologically oriented tool selection and tool balancing system for milled components is presented. The system is capable of selecting the most economical tool set and, where necessary, adjusting the cutting conditions for all the features of a batch of components. Several key parts of the system such as the method for estimating the remaining tool life of a cutter used for selected different cuts, the cost equation used and the method of searching for the most economical tool set are discussed. The system has been used to analyse the tools required for the machining of a typical milled component. This analysis considered the influence of batch size, the number of repeat batches, the number of sister tools, inventory cost and of varying the cutting velocity within a given feature.     

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.     

Wear and Tool Life of CBN Cutting Tools

The wide application of precise high-quality components made of advanced structural materials is directly related to the accelerating use of superhard materials and tools made of them. When machining with these tools, the optimal choice of cutting process parameters is important, as the requirements concerning the parts can often only be satisfied by cutting under extreme conditions (small chip cross-section, high cutting speed, special materials, new wear forms, etc.). Polycrystalline CBN tools are widely used for the fine turning of parts made of construction, stainless, heat-resistant, acid-resistant or even hardened (60–70 HRC) HS steels. The experimental T = T(vc) tool life curves are of "dromedary" type. The tool life maximum point moves up and down according to changes of depth of cut and feed-rate values. The reasons for polyextreme tool life curves and moving maximum tool-life points are discussed in the paper. A new general tool life Eq. is outlined which reflects the physical principles of cutting phenomena more completely and exactly. The suggested form describes the polyextreme structure of the tool life function, while the position of the extreme values (along the T- and vc-axis) depend on the cutting parameters. ID="A1" Correspondence and offprint requests to: Professor A. G. Mamalis, Manufacturing Technology Division, Department of Mechanical Engineering, National Technical University of Athens, 42 28th October Avenue, 106 82 Athens, Greece. E-mail: mamalis@central.ntua.gr     

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.     

面向加工特征的刀具和切削参数计算机辅助选择系统

切削刀具制造商面临围绕大量工件材料和加工特征为客户提供合理刀具和切削参数的现状,切削工艺规划的核心步骤也是刀具和切削参数的确定。确定刀具和切削参数一般多从零件材料角度出发,可能导致工件与刀具不匹配。文中提出面向加工特征的刀具和切削参数计算机辅助选择系统的开发。系统包括车削特征、铣削特征、钻削和镗削加工特征,系统利用特征图形作为用户交互式接口,采用关系数据库结合数据驱动和规则推理逻辑来选择刀具和切削参数,利用数学模型计算过程参数包括单工步加工工时、切削功率、最大粗糙度等,并辅助制定工序。以车刀和车削参数选择为例,介绍该系统的实现方法。该系统可以辅助设计师及工艺人员选择合理的刀具和切削参数。     

一种支持型腔粗加工刀具序列高效优化的刀具筛选方法

型腔加工是现代数控加工中广泛面临的一类加工问题。刀具筛选是型腔粗加工刀具序列优化过程中的一个重要环节。现有的基于几何、设备和工艺等约束的刀具筛选方法并不能判别因刀具之间相互制约而产生的冗余刀具,降低了刀具序列优化的效率。通过对比刀具组合过程中因不同刀具的优势互补而产生的效益增量与因换刀带来的相关效益损失量,建立一种用于判断刀具序列是否有效的分析模型;在此基础上,从刀具序列的组合形态的角度构造并证明一种可以判别部分冗余刀具的规则,并将其与基于几何、设备和工艺等约束的刀具筛选方法相串联,得到一种可支持刀具序列高效优化的刀具筛选方法;研究新方法的实现技术,包括刀具加工能力的估算方法和刀具组合有效性的计算方法;算例结果表明所提方法在去除冗余刀具上的效果明显,能为刀具序列的高效优化提供有效支持。     

面向多刀具组合方案选择的加工成本评价模型的研究

针对数控加工中最佳刀具组合方式的选择问题,提出了一种适用于2.5维腔槽类零件加工的多刀具组合方式的评价策略,并建立了相应的加工成本计算模型.在该模型中,不仅考虑了刀具的切削时间、空走刀时间和换刀时间,还综合考虑了刀具磨损和机床折旧等因素的影响.为简化计算且便于管理,采用有向图表示法枚举和表示所有可能的刀具组合形式.同时,在扫描线填充算法的基础上,提出了刀具有效加工区域的计算新方法.实践证明,该方法简单可行,为数控程序设计和优化开辟了一条新途径.     

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.     

Optimisation of Multiple Tool CNC Rough Machining of a Hemisphere as a Genetic Algorithm Paradigm Application

This work presents the development of a method to achieve optimal roughing of a hemisphere in terms of least machining time and maximum material removal from the original material block. This is considered as a problem formulation case study in the field of genetic algorithm applications – a preamble to more complex and generic geometry. A genetic algorithm is used off-the-shelf as an optimisation tool. Three different process parameters are used to model the problem : the number of scallops, the height of each scallop, and the tools used. Multiple tools are considered, in particular their diameters, maximum depths of cut and maximum feed allowed, as defined in a tool database, whereas the strategy of the tool path on each slice (but not the path details) is taken as known. Fitness functions that can be used independently or combined are the cutting time and the remaining material. The proposed method results in a concentrated result table containing the sequence of the tools employed and the corresponding scallop heights. ID="A1"Correspondance and offprint requests to: Dr G. Vosniakos, Department of Mechanical Engineering, Manufacturing Technology Division, National Technical University of Athens, Iron Polytexneiou, 157 80 Zografou, Athens, Greece. E-mail: vosniak@central.ntua.gr     

刀具涂层材料的发展

采用涂层技术可有效提高切削刀具的使用寿命,使刀具获得优良的综合机械性能,从而大幅度提高机械加工效率.我国的刀具涂层材料经过多年发展,目前正处于关键时期,充分了解国内外刀具涂层材料的现状及发展趋势,有计划、按步骤地发展刀具涂层材料,对提高我国切削刀具制造水平具有重要意义.     

不同速度下切削钛合金刀具上温度场应力场的数值模拟

简单介绍了一下有限元计算软件的建模过程,并对在不同切削速度下,硬质合金刀具切削钛合金的过程进行了模拟,得到了切削过程中刀具上应力场和温度场的分布状况。通过对模拟结果的分析与研究,得到了刀具最易出现的磨损区域,并通过与试验结果相对照,证明了有限元模拟方法的可行性,其模拟结果可以为试验提供一定的指导。     

螺旋刀具轨迹规划的水平集方法

提出了一种新的螺旋线刀具轨迹生成方法。运用水平集边界推进技术，以型腔边界作为初始零水平集，通过求解水平集方程得到一系列等距线；同时运用曲率流技术平滑等距线的高曲率交点，避免高速加工过程中的刀具损伤。最后，使用相邻等距线的对角线来生成螺旋线刀具轨迹。该方法能够生成连续平滑的加工轨迹，适用于平面型腔的高速切削加工。     

Cutting tool strategies for multifunctional part configurations: Part II—Discussion of experimental and analytical results

The analytical models, developed in Part I [Int J Adv Manuf Technol (1992)7: 59–69] for the optimisation of multistep cutting tools, are evaluated using experimental data. The effectiveness of the proposed approaches utilising the mathematical models from Part I for multifunctional tools, including both multi-step and combination tools, are demonstrated through simulations. The solution schemes and heuristic algorithms used for optimising the aforementioned cutting tool designs are described and explained through simulation examples which involve several tool configuration situations often applicable in a production environment. When the aforementioned cutting tools are utilised in mass production applications, the advantages of lower production cycle time and cost, become obvious through the tutorial of the examples. These simulations clearly demonstrate the benefits obtained when the mathematical models and analytical schemes, developed in Parts I and II, are incorporated in the manufacturing process and system design optimisation analytical tools or expert systems for justifying the use of multi-functional cutting tools.     

Price, delivery time, and capacity decisions in an M/M/1 make-to-order/service system with segmented market

In this paper, a method to determine the optimal tool orientation to make a more perfect impeller blade surface using a five-axis flank milling machine is presented. Verification of surface geometric accuracy using a 3D coordinate measuring machine is also shown. A mathematical formula is derived which includes the parameters of tool and curved surface to calculate the appropriate tool orientation, whose direction is named the optimal tool orientation. The 3D CAD software Unigraphics (UG) is used to plot models which include the curved surface and the tools of optimal tool orientation and other orientations. The reasonable overlap between curved surface and tool is obtained (overcutting) by checking the interference from the UG, its tool orientation is the optimal tool orientation. According to the optimal tool orientation and position at all cutting points on curved surface, a cutting location source file is derived, which can transform into the NC code for the five-axis tool machine to make the centrifugal impellers of various types. These impellers are measured by using the 3D Coordinate Measuring Machine to verify blade to be free of flaws, and with accurate geometry and the tool, marks are removed from its surfaces.     

Tool crater wear depth modeling in CBN hard turning

Hard turning has been receiving increased attention because it offers many possible benefits over grinding in machining hardened steel. The wear of cubic boron nitride (CBN) tools, which are commonly used in hard turning, is an important issue that needs to be better understood. For hard turning to be a viable replacement technology, the high cost of CBN cutting tools and the cost of down-time for tool changing must be minimized. In addition to progressive flank wear, microchipping and tool breakage (which lead to early tool failure) are prone to occur under aggressive machining conditions due to significant crater wear and weakening of the cutting edge. The objective of this study is to model the CBN tool crater wear depth (K_T) to guide the design of CBN tool geometry and to optimize cutting parameters in finish hard turning. First, the main wear mechanisms (abrasion, adhesion, and diffusion) in hard turning are discussed and the associated wear volume loss models are developed as functions of cutting temperature, stress, and other process information. Then, the crater wear depth is predicted in terms of tool/work material properties and process information. Finally, the proposed model is experimentally validated in finish turning of hardened 52100 bearing steel using a low CBN content tool. The comparison between model predictions and experimental results shows reasonable agreement, and the results suggest that adhesion is the dominant wear mechanism within the range of conditions that were investigated.     

Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (V_c) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al₂O₃ coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.     

对称多型腔粗加工刀轨快速生成算法

对具有对称特性的多型腔零件的刀轨规划方法进行了研究，提出了一种新的算法：首先生成其中一个型腔的刀轨，然后通过阵列生成其余刀轨，并对刀轨的进退刀进行处理，从而快速生成完整的、连续的、有序的刀具轨迹。该算法尤其适用于高速加工的刀轨规划，实践表明，可大大提高编程效率．节省加工时间。     

Development of an automatic arc welding system using SMAW process

In end milling of pockets, variable radial depth of cut is generally encountered as the end mill enters and exits the corner, which has a significant influence on the cutting forces and further affects the contour accuracy of the milled pockets. This paper proposes an approach for predicting the cutting forces in end milling of pockets. A mathematical model is presented to describe the geometric relationship between an end mill and the corner profile. The milling process of corners is discretized into a series of steady-state cutting processes, each with different radial depth of cut determined by the instantaneous position of the end mill relative to the workpiece. For the cutting force prediction, an analytical model of cutting forces for the steady-state machining conditions is introduced for each segmented process with given radial depth of cut. The predicted cutting forces can be calculated in terms of tool/workpiece geometry, cutting parameters and workpiece material properties, as well as the relative position of the tool to workpiece. Experiments of pocket milling are conducted for the verification of the proposed method.     

PREDICTION OF TOOL LIFE IN MACHINING WITH RESTRICTED CONTACT TOOLS

A semi-empirical method is described for predicting tool life in orthogonal machining with restricted contact tools. The method uses a well established machining theory to predict cutting forces, tool-chip contact length and cutting temperatures for the corresponding plane face tool i.e. tool having the same cutting edge geometry but no restricted contact. These predicted parameters and a set of empirical relations are then used to calculate the cutting temperatures and tool life for the restricted contact tool. A comparison has been made between predicted and experimental results obtained from the literature and from tests carried out by the authors.