开式三元叶轮高效率数控粗加工策略

论述了五轴数控粗加工的高效铣削策略和关键技术,对于影响数控粗加工效率的主要因素进行了分析,对于高速钢铣刀和硬质合金铣刀采用侧铣和插铣数控加工方法以及刀具选择进行了简要叙述,并且通过大量三元叶轮实际加工总结了一种面向三元叶轮加工特征、考虑刀具寿命的粗加工策略的原则,使三元叶轮的加工效率大大提高。     

A five-axis rough machining approach for a centrifugal impeller

A clear trend shows that most products or mechanical components, especially those regarding aerospace applications, are designed to fit the requirements of free form surface features. When a 3-axis computer numerical controlled (CNC) machining centre is used to produce a typical centrifugal impeller, great difficulties, i.e., collisions between the cutting tool and impeller, need to be overcome. In this case, sophisticated five-axis machines have to be utilised. Presently, most commercial computer-aided manufacturing (CAM) systems for five-axis control are lacking generality, and functions for the rough tool-path generation are far less than required. The rough machining is recognised as the most important procedure influencing the machining efficiency and is critical for the success of the following finishing process. However, great difficulties are expected to arise in performing five-axis rough machining. The main objective of the present study is to overcome this problem by combining related machining technology. As a result, CL data based on the geometry model of blade and hub of the impeller are generated. Finally, the CL data is confirmed through software simulation. The results of verification prove the machining methodology and procedure to be successful.     

Integrated rough machining methodology for centrifugal impeller manufacturing

In mechanical engineering, most products or components, especially those for aerospace applications, are designed to fit the requirements of free-form surface features. The impeller often required by 5-axis machine operations is a key component of the aerospace industry. When 3-axis CNC machining center is used to manufacture the impeller, great difficulties, i.e., collisions between the cutting tool and impeller, need to be overcome. Presently most commercial CAM systems for 5-axis control lack generality, and functions for the rough tool-path generation are far from sufficient. Although the rough machining is the most important procedure influencing the machining efficiency and the condition for the following finishing process, many difficulties arise in performing 5-axis rough machining. The main objective of the present study is to overcome this problem by integrating the state-of-art machining technology, and consequently effective rough tool-paths are to be generated. This study aims to implement the algorithm of the constant scallop height method to improve tool-path planning of rough machining. As a result CL data based on the geometry model of blade and hub are generated. The CL data are confirmed by comparing them with original CAD model through software simulations and later by machining experiments. The verification results show that the machining methodology and procedure adopted turn out to be a successful case.     

Cutting of polished single-crystal silicon by wire electrical discharge machining

Smoothly polished single-crystal silicon plates were cut by wire electrical discharge machining (WEDM) in water and in oil in order to investigate the effect of WEDM on the polished surfaces. For cutting in water, polished surfaces near cut sections have chips and cracks, and are extremely rough; the rough regions are upheaved. Examinations suggest that the upheaved region is silicon dioxide and results from oxidization of the surfaces by WEDM. Moreover, the polished surfaces far from the cut section are somewhat rough. For cutting in oil, polished surfaces near a cut section are smooth and almost flat although they have chips and cracks. These findings indicate the WEDM in oil is better than that in water for cutting polished single-crystal silicon to obtain high-quality surfaces.     

A novel surface analytical model for cutting linearization error in fast tool/slow slide servo diamond turning

Fast tool/slow slide servo (FTS/SSS) technology plays an important role in machining freeform surfaces for the modern optics industry. The surface accuracy is a sticking factor that demands the need for a long-standing solution to fabricate ultraprecise freeform surfaces accurately and efficiently. However, the analysis of cutting linearization errors in the cutting direction of surface generation has received little attention. Hence, a novel surface analytical model is developed to evaluate the cutting linearization error of all cutting strategies for surface generation. It also optimizes the number of cutting points to meet accuracy requirements. To validate the theoretical cutting linearization errors, a series of machining experiments on sinusoidal wave grid and micro-lens array surfaces has been conducted. The experimental results demonstrate that these surfaces have successfully achieved the surface accuracy requirement of 1 μm with the implementation of the proposed model. These further credit the capability of the surface analytical model as an effective and accurate tool in improving profile accuracies and meeting accuracy requirements.     

Selection of an optimal parametric combination for achieving a better surface finish in dry milling using genetic algorithms

In machining, coolants improve machinability, increase productivity by reducing tool wear and extend tool life. However, due to ecological and human health problems, manufacturing industries are now being forced to implement strategies to reduce the amount of cutting fluids used in their production lines. A trend that has emerged to solve these problems is machining without fluid – a method called dry machining – which has been made possible due to technological innovations. This paper presents an experimental investigation of the influence of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on machining performance in dry milling with four fluted solid TiAlN-coated carbide end mill cutters based on Taguchi’s experimental design method. The mathematical model, in terms of machining parameters, was developed for surface roughness prediction using response surface methodology. The optimization is then carried out with genetic algorithms using the surface roughness model developed and validated in this work. This methodology helps to determine the best possible tool geometry and cutting conditions for dry milling.     

Time modeling in high-speed machining of mold pocket

Numerical control milling (NCM) at high speed is the most used machining process in the manufacture of molds because it offers high productivity and workpiece surface quality. The aim of this work is to establish a methodology to evaluate the rough machining time, during high speed milling. In pocket machining, a 2.5D milling has been considered. The proposed approach considers the roughing cutting time as the ratio of the pocket volume by the removed material rate. The pocket is divided into volumes distributed according to the real radial depth. Since the radial depth varies during machining, the removed material rate is not constant. In this paper, an experimental study is carried out to validate models of machining time calculation. The obtained results show that the proposed method offers fast and easy calculation of the machining time of pocket roughing.     

大型船用螺旋桨桨毂粗加工刀具路径规划研究

针对大型船用螺旋桨毛坯余量较大,相邻桨叶间存在重叠区,现有加工方法吊装复杂、需要二次装夹且叶根桨毂加工周期长等问题,提出了一种多轴对称加工叶根桨毂方案,并依据加工方案,应用定轴加工方法研究桨毂粗加工刀具路径规划.根据桨毂曲面特征,计算走刀行距与步长;基于定向包围盒(Oriented Bounding Box,OBB)干...     

开式整体叶盘四坐标侧铣开槽粗加工轨迹规划

为了提高开式整体叶盘的粗加工稳定性，在粗加工阶段，提出采用将自由曲面蜕变为直纹面的方式简化开式整体叶盘通道开槽加工的难度，实现稳定切削。讨论了直纹面逼近自由曲面的算法，提出了一种新的刀轴矢量计算方法，并基于直纹面给出了开式整体叶片通道四坐标侧铣粗加工数控编程方法，规划出了无干涉的刀位轨迹。实例验证表明，采用该方法可快速有效地实现开式整体叶盘的开槽粗加工，并可提高开式整体叶盘加工中的稳定性。     

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。     

Cutting parameter and tool path style effects on cutting force and tool deflection in machining of convex and concave inclined surfaces

Convex and concave inclined surfaces are frequently encountered in the machining of components in industries such as aerospace, aircraft, automotive, biomedical, and precision machinery manufacturing and mold industries. Tool path styles, generated by different cutting strategies, result in various cutting forces and tool deflection values that might lead to poor surface integrities. In cost-effective manufacturing, it is helpful to make known their effects on machinability. Thus, the first aim of this study is to investigate optimum cutting parameter values in ball end milling of EN X40CrMoV5-1 tool steel with three coated cutters. The parameters taken into consideration are cutting speed, feed rate, step over, and tool path style. The second aim of the study is to determine the effects of tool path styles in ball end milling of inclined surfaces. As a result, the most effective parameter within the selected cutting parameters and cutting styles for both inclined surfaces and different coatings was step over. In terms of tool coatings, the most rapidly deteriorating coating was TiC coating for cutting forces in both inclined surfaces and for tool deflection in convex inclined surface. In addition, the response surface methodology is employed to predict surface roughness values, depending on the cutting forces obtained. The model generated gives highly accurate results.     

非典型叶轮数控5轴技术的研究

由于非典型叶轮结构复杂,无法使用主流CAD/CAM软件提供的叶轮5轴模块,在粗加工阶段采用3轴定向加工时,残余毛坯留量体积大形状不规则,严重影响了5轴加工的效率和质量。为此,一方面对于叶轮开式区域采用双圆柱面投影法获得驱动曲面,从而实现4轴联动粗加工,切削刚性大效率高;对于非开式区域则通过构建驱动曲面获得5轴联动刀轨,刀轨连续且刀轴矢量无突变。另一方面,提出了一种基于NC程序的刀轴矢量评价方法,可快速直观地评价5轴编程质量。实际使用结果表明:基于驱动曲面的刀轴矢量优化法能够显著提高复杂工件5轴加工的效率和质量。     

An Improved Sculptured Part Surface Design Method with Jerk Continuity Consideration for Smooth Machining

This paper presents an investigation of jerk continuity in milling operations for sculptured surfaces of mechanical parts. It has been realised that chattering in machining operations can cause detrimental effects on the quality of machined parts as well as on the life of the cutting tool. One of the major reasons of chattering is known to be the rough transition of cutter accelerations when traversing through desired part sur-faces. The problem becomes serious when machining sculptured surfaces of parts. In this work, an effective computer-aided sculptured surface design technique is proposed. The ultimate goal is to achieve smooth and near chattering-free machining for producing precision parts. The proposed surface design scheme models the part’s sculptured surfaces in such a way that it warrants a smooth "jerk" transition at the boundaries of common surface patches on the part. This results in a drastic reduction of large step changes of cutter accelerations during machining operations which will in turn eliminate a good portion of the chattering effects. Three theorems concerning the necessary jerk continuity conditions for surface patches connections are developed and their proofs are presented. Examples of an aerofoil and a concept car model are implemented, using the proposed modelling approach, to demonstrate its effectiveness.     

INTERFERENCE-FREE TOOL POSTURE GENERATION FOR 5-AXIS NC MILLING FREE-FORM SURFACES WITH CYLINDRICAL MILL

The 5-axis NC machining offers the potential of efficient and accurate machining. However, the present CAM system for 5-axis control is still an unsolved problem due to interference between tool and surrounding objects. A new method is presented. There are two steps in this procedure. First, it detects the interference by calculating the shortest distance between the tool-axis and the surrounding surfaces. Then upon the maximum gouging, the interference-free tool posture for 5-axis NC cylindrical milling free-form surfaces is obtained by adjusting tool. The validity of the proposed method has been confirmed by machining an impeller.     

Effect of very high cutting speeds on shearing, cutting forces and roughness in dry turning of austenitic stainless steels

Behavior of austenitic stainless steels has been studied at very high cutting speeds. Turning tests were carried out using the AISI 303 austenitic stainless steel. In particular, the influence of cutting speed on tool wear, surface quality, cutting forces and chip geometry has been investigated. These parameters have been compared when performing machining at traditional cutting speeds (lower than 350?m/min) versus high cutting speeds. The analysis of results shows that the material undergoes a significant change in its behavior when machining at cutting speeds above 450?m/min, that favors the machining operation. The main component of cutting forces reaches a minimum value at this cutting speed. The SEM micrographs of the machined surfaces show how at the traditional cutting speeds the machined surfaces contain cavities, metal debris and feed marks with smeared material particles. Surfaces machined at high cutting speeds show evidence of material side flow, which is more evident at cutting speeds above 600?m/min. Tool wear is located at the tool nose radius for lower cutting speeds, whereas it slides toward the secondary edge when cutting speed increases. An analysis of chips indicates also an important decrement in chip thickness for cutting speeds above 450?m/min. This study concludes that there is an unexplored range of cutting speeds very interesting for high-performance machining. In this range, the behavior of stainless steels is very favorable although tool wear rate is also significant. Nevertheless, nowadays the cost of tool inserts can be considered as secondary when comparing to other operation costs, for instance the machine hourly cost for high-end multitasking machines.     

A cutting force model considering influence of radius of curvature for sculptured surface machining

A new cutting force model considering influence of radius of curvature is introduced in this research for sculptured surface machining with ball-end mill. In this model, first the whole cutting region near the cutter contact (CC) point on the sculptured surface is approximated by a spherical surface, and the radius of this spherical surface is used as the radius of curvature at the CC point. Then equations to estimate the cutting forces at a differential element on the cutting edge are established. By obtaining the cutter-workpiece contact areas based on geometries of the cutter and the sculptured surface, the mathematical model for estimating the total cutting forces in different directions is then developed. Experiments have also been conducted to measure the cutting forces considering different radii of curvatures on the sculptured surfaces. The analytically estimated cutting forces match well with the actual cutting forces obtained through experiments.     

基于HyperMILL的整体叶轮五轴数控加工

在HyperMILL软件的基础上,对整体叶轮的五轴加工策略进行分析和实现.首先拟定加工路径和工艺方案,确定加工参数,然后计算出叶轮的加工刀轨路径,生成机床加工代码,最后加工出合格的零件.该方法有效地减少了加工循环次数、减少加工步骤、提高加工精度和加工效率.     

Optimal CNC plunge cutter selection and tool path generation for multi-axis roughing free-form surface impeller channel

Plunge milling is the most effective way for rough machining of impeller parts, but previous research had not considered the optimization of plunge cutter selection and tool path. In this paper, a new method for optimizing the plunge cutter selection and tool path generation in multi-axis plunge milling of free-form surface impeller channel is proposed in order to improve the efficiency in rough machining. Firstly, in the case of fixing a rotation axis at a certain angle in five-axis machine, a mathematical representation is formulated for the geometric model of the cutter interfering the impeller, and an optimization model of the cutter size is established at a cutter contact point on the impeller channel surface, so the largest tool could be determined. Secondly, by analyzing the machine tool movement characteristics, the geometric constraint model of the plunge tool path which relative to the largest tool, step distance, and row space is established, and a tool orientation calculation method of impeller channel machining is given, and then, the plunge tool path and tool orientation could be obtained. Finally, the generated tool path and tool orientation are simulated and verified in practical processing. Simulation and experimental result shows that the rough machining efficiency of the impeller part is improved up to 40 % with this method.     

面向特征库的整体叶轮刀轨规划方法

针对整体叶轮曲面曲率变化大、流道为特殊型腔的特点,提出了一种面向特征的刀轨规划方法。分析了整体叶轮加工型面的特征及加工难点,建立由叶片、流道、进出水边、叶根等不同型面刀轨构成的特征库。设计叶轮加工型面与特征刀轨库间的匹配规则,开发了整体叶轮加工型面特征刀轨规划系统。算例仿真表明,该方法可有效减少叶轮加工曲面的刀路数量,提高整体叶轮自由曲面叶片的加工质量和效率。     

A state-of-the-art review of ductile cutting of silicon wafers for semiconductor and microelectronics industries

Silicon is a typical functional material for semiconductor and optical industry. Many hi-tech products like lenses in thermal imaging, solar cells, and some key products of semiconductor industry are made of single crystal silicon. Silicon wafers are used as substrate to build vast majority of semiconductor and microelectronic devices. To meet high surge in demand for microelectronics based products in recent years, the development of rapid and cost efficient processes is inevitable to produce silicon wafers with high-quality surface finish. The current industry uses a sequence of processes such as slicing, edge grinding, finishing, lapping, polishing, back thinning, and dicing. Most of these processes use grinding grains or abrasives for material removal. The mechanism of material removal in these processes is fracture based which imparts subsurface damage when abrasive particles penetrate into the substrate surface. Most of these traditional processes are extremely slow and inefficient for machining wafers in bulk quantity. Moreover, the depth of subsurface damage caused by these processes can be up to few microns and it is too costly and time consuming to remove this damage by heavy chemical–mechanical polishing process. Therefore, semiconductor industry requires some alternative process that is rapid and cost effective for machining silicon wafers. Ductile cutting of silicon wafer has the potential to replace the tradition wafer machining processes efficiently. If implemented effectively in industry, ductile cutting of silicon wafers should reduce the time and cost of wafer machining and consequently improve the productivity of the process. This paper reviews and discusses machining characteristics associated with ductile cutting of silicon wafers. The limitations of traditional wafer fabrication, the driving factors for switching to ductile cutting technology, basic mechanism of ductile cutting, cutting mechanics, cutting forces, surface topography, thermal aspects, and important factors affecting these machining characteristics have been discussed to give a systematic insight into the technology.