Tool path generation for ultra-precision machining of free-form surfaces

The generation of tool paths for ultra-precision machining is still a limiting factor in the manufacturing of parts with complex optical surfaces. In conventional machining as well as in complex five axes machining the application of CAD- and CAM-software for the generation of tool paths is state of the art. But these software solutions are not able to generate tool paths according to the high requirements of ultra-precision machining. This paper describes possible ways to generate tool paths for ultra-precision machining when the optical surface can be analytically described or when the surface data is derived from optical design software. Ultra-precision milling experiments with different tool paths have been carried out and the quality of the machined geometry has been evaluated concerning the achievable form accuracy.     

Surface roughness prediction using measured data and interpolation in layered manufacturing

Layered manufacturing (LM) technology can efficiently fabricate 3D physical models without the restriction of geometric complexities. However, because of the LM process itself, the surface quality of processed parts is often unsatisfactory compared to that of machined parts made using traditional numerically controlled manufacturing technology. Hence, the surface roughness has become a matter of utmost concern despite the many potential advantages of LM. In the initial step of the LM process, reasonable process planning can be achieved by predicting the surface roughness in advance. Therefore, we propose an elaborate methodology to predict the surface roughness of LM processed parts. Theoretical and real characteristics of surface roughness distributions are investigated to reflect actual roughness distributions in the predictions, and a roughness distribution expression that can obtain surface roughness values for all surface angles is introduced using measured roughness data and interpolation. A prediction application is presented, and the validity and effectiveness of the proposed approach are demonstrated through several application examples.     

An accurate,efficient envelope approach to modeling the geometric deviation of the machined surface for a specific five-axis CNC machine tool

Geometric deviation, defined as the difference between the nominal surface and the simulation model of the machined surface, is the fundamental concern of five-axis tool path planning. Since the machined surface is part of the cutter envelope surface generated by the cutter motion, it is necessary to calculate the envelope surface in order to obtain the geometric deviation. In the stage of tool path planning, current approaches calculate the cutter envelope surface by using the cutter motion along the given tool path. However, the cutter motion of practical machining on a specific five-axis CNC machine tool is different from the given tool path. Moreover, the computation is very challenging when the accurate cutter motion of practical machining is applied to calculate the envelope surface. To overcome these two problems, a geometric envelope approach with two major distinctions is proposed in this paper. First, the envelope surface of the cutter undergoing a general motion is efficiently obtained as a closed-form vector expression. Second, the accurate cutter motion, which is determined by machine kinematic and interpolation scheme in practical machining, can be easily applied to calculate the accurate envelope surface. With the envelope surface, the geometric deviation is calculated to estimate the overcut or undercut in five-axis milling. An example is given to demonstrate the validity of the proposed method.     

Feed speed scheduling method for parts with rapidly varied geometric feature based on drive constraint of NC machine tool

As the existence of rapidly varied geometric feature and during the NC manufacturing process of this kind of parts, the actual moving speed of the workbench of the NC machine tool cannot reach the feed speed set in the NC program timely due to the drive constraint of NC machine tool. Furthermore, the machine tool would vibrate violently with the drive constraint when employing the constant machining parameter to process the parts with rapidly varied geometric feature, which seriously restricts the improvement of processing this kind of parts with high quality and high efficiency. In order to manufacture such parts with high quality and high efficiency, a sub-regional processing method with variable machining parameters is proposed. Firstly, the generation mechanism of the machining error is studied, and its mathematical model is built. Then the change rule of the machining error influenced by the curvature and the NC programmed feed speed is found out. Finally, taking the drive constraint and the machining error requirement into account, the relationship between the programmed feed speed and the curvature is established, and the corresponding programmed feed speeds to different curvatures are obtained. Taking the NC machining of the edge line of spiral microstrip antenna, which is an equiangular spiral, for example, the experiment results show that compared with the machining result with constant machining parameter, the maximum machining error of the sub-regional processing method with variable machining parameters decreases by 35.51% and the average value of the machining error decreases by 46.65%. For another example, the clover rose line is machined and the processing quality is also improved. This study proves that the method distributing the programmed feed speeds based on the curvature variation can improve the machining precision and ensure processing efficiency, and provides an effective method to manufacture parts with rapidly varied geometric feature.     

Incorporated tool selection system using object technology

Tool selection is perhaps one of the most important functions in a process planning system because the selection of a tool affects the selection of machining parameters, jig and fixture selection, production rate, cost of the product, and the resulting accuracy. Therefore computer-aided tool selection (CATS) is an essential element within a computer-aided process planning (CAPP) system (C. Koulamas, Tool requirements in multi-level machining systems, International Journal of Production Research, 29 (2) (1991) 417–437.), and in turn in a Computer Integrated Manufacturing (CIM) environment. This paper proposes an object–oriented methodology for selecting the tooling parameters for parts in a CIM environment. As this system can be incorporated into both static and dynamic process planning systems, it is termed as Incorporated Tool Selection Systems (ITSS). The steps of the methodology are discussed in detail, together with an example.     

The form error prediction in side wall machining considering tool deflection

In this research, an effective method for the form error prediction in side wall machining with a flat end mill is suggested. The form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. The developed model can predict the surface form error accurately about 300 times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.     

Application of micro-EDM combined with high-frequency dither grinding to micro-hole machining

This research presents a novel process using micro electro-discharge machining (micro-EDM) combined with high-frequency dither grinding (HFDG) to improve the surface roughness of micro-holes. Micro-EDM is a well-established machining option for manufacturing geometrically complex small parts (diameter under 100 μm) of hard or super-tough materials. However, micro-EDM causes the recast layer formed on the machined surface to become covered with discharge craters and micro-cracks, resulting in poor surface quality. This affects the diameter of the micro-hole machined and undermines seriously the precision of the geometric shape. The proposed method that combines micro-EDM process with HFDG is applied to machining high-nickel alloy. As observed in SEM photographs and surface roughness measurement, HFDG method can reduce surface roughness from 2.12 to 0.85 μm Rmax with micro-cracks eliminated. Our results demonstrated that micro-holes fabricated by micro-EDM at peak current 500 mA followed by HFDG at 40 V can achieve precise shape and good surface quality after 6–8 min of lapping.     

Geometric prediction of conic tool in micro-EDM milling with fix-length compensation using simulation

Micro-EDM milling is an effective machining process for three-dimensional micro-cavity of high hardness materials. However, tools wear sharply in micro-milling, thus several compensation methods are applied. The present study examines the fix-length compensation method, and the initial experiments show that a cone-shaped tool end is formed with this compensation method. Because the cone angle is of great importance in the determination of the fix-length compensation parameters in the machining procedure, a clear explanation of the forming mechanism and precise prediction are of great necessity. First, the tool and the workpiece were geometrically and mathematically modeled as two-dimensional matrices. Second, the machining process was divided into three parts including sparking, horizontal feeding and vertical feeding. Finally, a series of experiments were conducted in order to verify the accuracy of the simulation. The results show that the relative error of the simulation compared to the experimental data is within 4% under most machining conditions. The developed model can thus be used to predict the machined surface of the tool and the workpiece and can also provide a better understanding for the mechanism of the cone shaped tool end.     

Virtual EDM simulator: Three-dimensional geometric simulation of micro-EDM milling processes

In this paper a three-dimensional geometric simulation method of micro-EDM milling processes is proposed, which introduces a Z-map algorithm to precisely represent the geometries of a machined workpiece and the evolution of the tool shape caused by tool wear during the machining. The micro-EDM milling process is mathematically and geometrically modeled. In order to verify the performance of the developed simulator, an actual square cavity is machined and compared to the simulation result. The developed EDM simulator can be used for tool path generation for tool wear compensation as well as for prediction of tool wear.     

聚晶金刚石电火花磨削加工效果预测和加工参数优化仿真系统

建立了聚晶金刚石电火花磨削加工效果预测及加工参数优化仿真系统，可以预测聚晶金刚石电火花磨削加工后的效果，具有较高的精度，并能实现加工参数的优化，进行优势因素分析。通过工艺数据库的建立，该仿真系统可以适用于各种材料的加工工艺，有助于进一步提高聚晶金刚石加工的自动化程度和开发智能化系统。     

The Computer Integrated Manufacturing (CIM) of net shape forged bevel gears

Computer Integrated Manufacturing (CIM) offers American industry a method of improving forge tool quality while lowering forge part costs. These costs savings are achieved by reducing machining stock allowances and eliminating trial and error tool development. The development of forge tooling for most new parts is normally a trial and error process. This is especially true when developing tooling for net or near-net shape forged bevel gears. Even with years of experience, the tool designer relies on numerous trials to design and manufacture forge tooling. The CIM approach takes the guesswork out of the design, analysis and manufacture of forge tooling for net shape bevel gears. Computer techniques have been developed which enable the design and manufacture of forge tooling, while bypassing the trial and error stage of tool development. This paper discusses the application of CIM techniques in the design and manufacture of forge tooling for net shape bevel gears.     

Development of monitoring system on the diamond tool wear

Recently, ultra-precision machining using a single crystal diamond tool has been developing very rapidly, especially in the fields of production processes for optical or magnetic parts such as magnetic discs, laser mirrors, polygon mirrors and copier drums. As a result, it has been successfully extended to machine various soft materials, generating mirror-like surfaces to sub-micron geometric accuracy with the ultra-precision CNC machine and the single crystal diamond tool. With the real cutting operation, the geometric accuracy and the surface finish attainable in machined surfaces are mainly determined by both of the sharpness of a cutting tool and stability of the machine vibration. In this study, for monitoring the progress of machining state for assuring the machining accuracy and the surface quality, a new monitoring method of machining states in face-cutting with diamond tool is proposed, using the frequency response of multi-sensors signal, which includes wear state of tool in terms of the energy within the specific frequency band. A magnetic disc is machined on the ultra-precision lathe.     

Experimental analysis of dimensional error vs. cycle time in high-speed milling of aluminium alloy

Manufacturers of machined aluminium parts are among the principal users of high-speed milling. The excellent machinability of aluminium allows this technology to be used with severe cutting conditions, and at the same time permits the machining of complex shapes. There are many factors influencing the quality of manufactured aluminium parts and the economics of the manufacturing process, but little corresponding data is available, making process planning enormously difficult.The aim of the work presented in this article is to experimentally analyse the influence of some of these factors, specifically the feed rate, the type of interpolation and the toolholder, on the dimensional accuracy of the product and the cycle time. Design of experiments (DoE) is used to determine which experiments have to be conducted to obtain a mathematical model that relates the mentioned factors with the responses.The results show that the toolholder has considerable influence over dimensional accuracy and that the type of interpolation appreciably affects the cycle time. Details of the first-order interactions between factors have been included.     

Tooling and binder design for sheet metal forming processes compensating springback error

Part shape error due to springback can be a manufacturing defect in sheet metal forming processes. This manufacturing problem can be corrected by using appropriate designs of the tooling and the binder shape together with a binder constraint. In the present work a methodology for tool and binder design based on inverse springback calculations is developed and demonstrated. The design procedure invokes finite element analysis of the manufacturing process. The proposed method was demonstrated for two cases of forming of channel geometries (two-dimensional and three-dimensional) with an aluminum alloy sheet. The tooling needed to form the desired parts was numerically designed using the proposed algorithm then constructed with the aid of CNC machining. The designed tooling was found to produce the desired part shapes demonstrating both the accuracy of the numerical simulations and the success of the proposed tooling design algorithm.     

基于净切削比能的钛合金清洁切削加工表面完整性研究

目的 探究钛合金清洁切削过程中能量消耗的变化与加工表面完整性的关系，通过切削参数优化选择，以实现加工表面质量的控制，从而提高钛合金高效洁净制造零件的使用寿命和服役性能。方法 本文提出一种基于能量消耗的过程签名方法，来描述多工步清洁切削加工过程与加工表面完整性的相互影响。建立了净切削比能计算模型，结合钛合金两工步铣削试验，分析了粗加工参数变化对粗加工、精加工切削力，以及净切削比能的影响规律，并进一步对两工步加工过程中的净切削比能展开研究。本文研究了不同粗加工参数条件下粗加工和精加工表面残余应力及微晶尺寸的变化规律。结果 切削力和切削参数的变化均会影响净切削比能的大小。多工步切削加工过程中，粗加工和精加工切削参数的不同会改变净切削比能，进而引起表面完整性的变化。对切削比能影响最大的是径向切深，其次是进给量、切削速度。随着进给量和径向切深的增大，切削比能降低；随着切削速度的升高，净切削比能先增大后减小。净切削比能较大时，加工表面层残余应力较大，微晶尺寸较小。结论 在保证加工质量的前提下，从节能降耗的角度出发，选取合适的切削速度、较大的切削深度、进给量，从而降低净切削比能、减少能量消耗，提高加...     

Ti6Al4V零件铣削加工表面等效残余应力与作用深度的测量及其有限元分析

金属零件在切削加工后,其被加工表面会形成一残余应力层,其所引起零件的变形是影响精密弱刚性零件精度的重要的因素。为了预测Ti6Al4V零件因铣削加工表面残余应力而引起的变形,本文介绍一种测量表面等效残余应力及其作用深度的方法而达到此目的。通过对被加工面的对面进行两次腐蚀去除材料的操作使得零件的厚度和中性层的位置发生变化,测量此过程中零件挠度和表面应变的变化,进而计算得铣削加工引起的零件表面等效残余应力及其作用深度值。通过有限元分析验证该方法得到的结果,发现有限元计算得到的零件挠度和应变的变化与实际测量值非常吻合,因此可以断定该方法得到的结果是正确的,其可以正确评估铣削加工引起的表面残余应力性质和大小并能准确预测零件铣削加工后因表面残余应力而引起的工件的变形量,从而可以预测零件是否满足精度要求。     

Experimental determination of the friction coefficient on the workpiece-fixture contact surface in workholding applications

Surface flatness, geometric integrity and micro-surface finish characteristics are crucial for automotive industry to properly seal joints, reduce leakage and consequently increasing engines efficiency and reducing emissions. Optimum fixture layout is a key element in achieving this goal. Machining of flexible parts impose further challenges to the selection of a proper fixture scenario.Workpiece motion arising from localized elastic deformation at the workpiece/fixture contacts due to machining and clamping forces significantly affect the workpiece location accuracy and hence the machined part quality. The tangential friction force plays an important role in fixture configuration design as it can be utilized to reduce the number of fixture components, thereby the workpiece features accessibility to machining operations and providing a damping mechanism to dissipate input energy from machining forces out of the workpiece/fixture system.Although the literature is full of research on friction and its application, it lacks research that relates to the contact found in workpiece/fixture systems. This paper presents the results of an experimental investigation of the workpiece/fixture contact characteristics.     

Off-line modelling and planning of optimal clamping forces for an intelligent fixturing system

An intelligent fixturing system (IFS) for machining aims to adaptively adjust the clamping forces to achieve minimum deformation of the workpiece according to the cutter position and the cutting forces. This paper presents the concept, architecture, control scheme, models and methodologies for an IFS. Using off-line simulations and on-line experimental verifications, the performance of the proposed IFS is evaluated and verified. As adaptive clamping forces appropriate to the dynamic machining environment are employed, the IFS offers higher quality of machined parts and greater robustness to disturbances. This system is suitable for application in high-precision machining environment as well as flexible manufacturing systems (FMS).     

基于轴承毛坯表面分析的磨削材料去除率模型与应用实验

目的 在轴承套圈磨削加工中,传统基于动力学模型建立的磨削材料去除率模型仅考虑了磨削工件-砂轮-机床三者的弹性变形,未考虑毛坯零件表面不规则变形对模型的影响,导致传统理论模型在实际磨削应用中的效果不佳。针对此问题,基于轴承套圈毛坯表面形状分析建立了新的磨削材料去除率模型,并进行了应用实验。方法 基于轴承套圈毛坯零件表面形状的工艺研究,针对粗磨阶段毛坯零件表面不规则形状和弹性变形对磨削加工及产品质量的影响,建立不同偏心圆数量的轴承套圈结构分析方法,并提出一种以分段函数形式的磨削材料去除率模型,该模型充分考虑了轴承套圈毛坯零件表面不规则变形和偏心圆形状对磨削材料去除的影响,可有效反映轴承套圈实际材料磨削去除过程。最后,通过大量实验对所建的分段函数形式的磨削材料去除率模型进行应用实验研究。结果 与传统磨削材料去除率模型GPSM相比,所建的以分段函数形式的磨削材料去除率模型MMRG的准确率提高了96%以上,该模型可有效在线量化分析毛坯表面不规则大小及偏心圆结构。结论 该模型对指导毛坯零件制造,保证磨削加工质量和磨削加工效率有着重要的理论指导意义。     

A general approach to simulating workpiece vibrations during five-axis milling of turbine blades

Workpiece vibrations have a significant influence on the machining process and on the quality of the resulting workpiece surface, particularly when milling thin-walled components. In this paper a simulation system, consisting of an FE model of the workpiece coupled with a geometric milling simulation for computing regenerative workpiece vibrations during the five-axis milling process, is presented. Additionally, a modeling method for visualizing the resulting surface is described. In order to validate the simulation model, turbine blades were machined and the experimental results were compared to the simulation results.