Optimization of modern machining processes using advanced optimization techniques: a review

Thorough literature review of various modern machining processes is presented in this paper. The main focus is kept on the optimization aspects of various parameters of the modern machining processes and hence only such research works are included in this work in which the use of advanced optimization techniques were involved. The review period considered is from the year 2006 to 2012. Various modern machining processes considered in this work are electric discharge machining, abrasive jet machining, ultrasonic machining, electrochemical machining, laser beam machining, micro-machining, nano-finishing and various hybrid and modified versions of these processes. The review work on such a large scale was not attempted earlier by considering many processes at a time, and hence, this review work may become the ready information at one place and it may be very useful to the subsequent researchers to decide their direction of research.     

Investigation into reduction of die-cavity deflection in micro-hydroforming processes using FEA

Within the field of micro-technology, merchandised products as well as research activities show an important demand for complex-shaped tubular micro-components, for example, for medical devices or micro-fluidic applications. Concerning such micro-components made from metal materials, manufacturing techniques for the economic mass production of adequate tubular parts are often missing. Hydroforming, as a proven technology in the mass production of conventional-size components, offers miscellaneous advantages also for micro-part manufacture. However, due to the comparatively large forming loads involved, strategies for compensation of the elastic deflection of the forming tool elements resulting from these loads are particularly of interest when greater accuracy of the forming operation is required. Against this background, this paper presents a strategy to reduce elastic tool deflection in micro-hydroforming processes, verified by systematic finite element simulations.     

Micro-manufacturing: research, technology outcomes and development issues

Besides continuing effort in developing MEMS-based manufacturing techniques, latest effort in micro-manufacturing is also in non-MEMS-based manufacturing. Research and technological development in this field is encouraged by the increased demand on micro-components as well as promised development in the scaling down of the traditional macro-manufacturing processes for micro-length-scale manufacturing. This paper highlights some EU funded research activities in micro/nano-manufacturing, and gives examples of the latest development in micro-manufacturing methods/techniques, process chains, hybrid processes, manufacturing equipment and supporting technologies/device, etc., which is followed by a summary of the achievements of the EU MASMICRO project. Finally, concluding remarks are given, which raise several issues concerning further development in micro-manufacturing.     

Precision and efficiency of laser assisted jet electrochemical machining

Laser assisted jet electrochemical machining (LAJECM) is a hybrid process, that combines a laser beam with an electrolyte jet thereby giving a non-contact tool electrode that removes metal by electrochemical dissolution. The laser beam effectively improves the precision of LAJECM as it is able to direct the dissolution to specifically targeted areas. This prevents the machining from unwanted areas due to stray current. This parallel application of a laser beam with the electrolyte jet enables an improvement of machining accuracy, also productivity. LAJECM has shown that machining with laser assistance can effectively facilitate material removal of 20, 25, 33, and 54% for Hasteloy, titanium alloy, stainless steel and aluminium alloy, respectively. There is also a noticeable improvement in the shape accuracy and slight decrease in surface roughness of the holes and cavities produced due to more focused machining (the order of 20%). The measured reduction in taper is of the order of 38, 40, 41, 65% for aluminium alloy, stainless steel, Hasteloy and titanium alloy, respectively.     

超精密加工精度分析

介绍超精密加工技术概要;从加工精度角度出发分析超精密加工技术国内外动态及今后发展的目标;探讨进一步提高主轴和导轨运动精度以及微进给和超精密测量精度等的可能性和关键技术问题;展望超精密加工技术在微细加工领域的发展前景。     

Monitoring and processing signal applied in machining processes – A review

In machining processes several phenomena occur during material cutting. These phenomena can affect the production through the reduction of quality or accuracy, or by increasing costs (tools, materials, time). Thus, an understanding of machining phenomena is needed not only to define the cutting parameters for maximizing production, but also to ensure worker safety. An easy way to identify these phenomena is by monitoring machining processes, such as the measurement of cutting force, temperature and vibration. The acquired signal can have information about tool life, quality of cutting and defects in the workpiece. This review paper discusses the first steps involved in choosing and defining various techniques that may be used to monitor machining processes. Furthermore, this paper also outlines the techniques to acquire and process the signals of the monitoring processes. Hence, the objective of this paper is to help the reader understand the procedures for monitoring machining processes, and define methods, parameters, targets and other factors involved in doing so.     

The evaluation of process capability for a machining center

The machining center methodology is widely applied to production systems within the fast-developing processing industry. The automated machining center can simultaneously perform certain processes, such as milling, drilling, boring, and reaming, on the same machine at the same time, and manufactures limited quantities of multiple-type products. These products usually have numerically important quality characteristics with high accuracy. However, a machining center is unable to measure process capability on its own. Thus, we reflect the process capability of a machining center by measuring the quality characteristics of its processing products. In this paper, we propose the three integrated process capability indices (PCIs) C _p^mc, C _a^mc, and C _pm^mc to evaluate the integrated process precision, accuracy, and actual capability respectively. Furthermore, we develop a process capability monitoring figure (PCMF), which not only displays the status of the process precision and accuracy by the color management method [1], but it also forecasts the integrated process capability of the next productive time (batch) through the analysis of time series. Using the PCMF, engineers will be assisted with tasks such as monitoring the process quality, deciding the period of the borer’s replacement, and designing the process parameters.     

OPTIMIZATION OF ELECTRO-CHEMICAL MACHINING PROCESS PARAMETERS USING GENETIC ALGORITHMS

ECM and ECM-based processes (derived and hybrid processes) are one of the most widely used advanced machining processes (AMPs) to make complicated shapes of varying sizes in the products made of electrically conducting but difficult-to-machine materials such as superalloys, Ti-alloys, alloy steel, tool steel, stainless steel, etc. These materials are extensively used in aerospace, automobile, space, nuclear, defense, cutting tools, dies and mold making applications. ECM offers some unique advantages over other conventional and advanced machining processes but its use incurs relatively higher initial investment cost, operating cost, tooling cost, and maintenance cost. Use of optimum ECM process parameters can significantly reduce the ECM operating, tooling, and maintenance cost and will produce components of higher accuracy which is very important in some critical areas such as aerospace, space, defense, nuclear applications. Therefore, choice of optimum process parameters is essential to ensure the most cost-effective, efficient, and economic utilization of ECM process potentials. This paper describes optimization of three most important ECM process parameters namely tool feed rate, electrolyte flow velocity, and applied voltage with an objective to minimize geometrical inaccuracy subjected to temperature, choking, and passivity constraints using real-coded genetic algorithms. Comparison of the obtained optimization results with the results of past work in this direction shows an improvement in terms of geometrical accuracy.     

Micro wire electrode electrochemical cutting with low frequency and small amplitude tool vibration

For removing electrolysis products and renewing electrolyte, the low frequency and small amplitude micro-tool vibration which direction is parallel to wire electrode axis is adopted. A wire electrochemical micro-machining system with micro-tool vibration unit has been developed. A mathematical model of overcut is presented. The micrometer scale wire electrodes of 10, 5, and 2???m in diameter have been electrochemically in situ fabricated. The influence of micro-tool vibration on processing stability, overcut, machining accuracy, and repeatability accuracy of micro wire electrode electrochemical cutting is investigated. With electrodes in various diameters, influence of electrode diameter on overcut is experimentally studied. To investigate the influence of machining parameters and work-piece thickness on the machining, comparative experiments are carried.     

微小型结构件的微细切削技术

高深宽比微小型结构件是微小型系统的重要组成部分。微细切削技术是面向金属与合金等非硅材料微小型结构件精密加工需求的关键技术。本文结合微小型结构件的特点和加工需求,分析了微细切削的主要形式、适用范围和技术体系。在此基础上讨论了微细切削在加工材料、三维加工能力等方面的技术优势,以及在加工精度和批量生产能力等方面的局限性。认为微机电引信和微惯性器件将是微细切削的主要应用方向。     

A new approach for force measurement and workpiece clamping in micro-ultrasonic machining

Micro-ultrasonic machining (micro-USM) is a promising micromachining technique to meet the increasing demands of high accuracy in processing the micro-components of hard and brittle materials. Unlike the well-established conventional USM, micro-USM still lacks in its commercial viability. The major concerns in micro-USM process are the accuracy of the setup and dynamic behavior of the system associated with precise force monitoring and robust workpiece clamping. In this study, a new micro-USM system with regards to measurement and monitoring of static force as well as tooling and workpiece clamping is developed. A force measurement and control system is proposed which is well suited for machining conditions in micro-USM. Furthermore, a reliable and quick setup for the vacuum chuck is introduced, which is capable of consistently transmitting the ultrasonic vibration from horn to the workpiece. Measurement of acoustic characteristics as well as experimental investigations is carried out to validate the functionality of the proposed system.     

Tool wear and tool thermal expansion during micro-machining by spark assisted chemical engraving

Gravity-feed micro-hole machining using spark assisted chemical engraving (SACE) has achieved repeatable hole drilling up to few hundred microns in depth. However, the tool wear and tool thermal expansion were not included in these measurements. In this paper, quantitative results are presented for the tool wear and tool expansion for three tool electrode materials: tungsten, steel and stainless steel. A simplified lumped thermal model predicting tool expansion and its dynamics is presented. It is as well demonstrated how the tool electrode temperature can be controlled by pulsed voltage supply. These results will enable higher measurement accuracy and therefore more precise micro-machining by SACE.     

Design of a five-axis ultra-precision micro-milling machine—UltraMill. Part 1: holistic design approach, design considerations and specifications

High-accuracy three-dimensional miniature components and microstructures are increasingly in demand in the sector of electro-optics, automotive, biotechnology, aerospace and information-technology industries. A rational approach to mechanical micro machining is to develop ultra-precision machines with small footprints. In part 1 of this two-part paper, the-state-of-the-art of ultra-precision machines with micro-machining capability is critically reviewed. The design considerations and specifications of a five-axis ultra-precision micro-milling machine—UltraMill—are discussed. Three prioritised design issues: motion accuracy, dynamic stiffness and thermal stability, formulate the holistic design approach for UltraMill. This approach has been applied to the development of key machine components and their integration so as to achieve high accuracy and nanometer surface finish.     

IN-PROCESS TOOL CONDITION MONITORING USING ACOUSTIC EMISSION SENSOR IN MICROENDMILLING

Recently researchers and manufacturers have shown keen interest in fabricating micro-components through tool based mechanical micromachining processes namely micromilling, microdrilling, microturning, etc. In this scenario, microendmilling is used in the manufacture of micro-molds, micro-dies, micro-channel, micro-gear, etc. The major issue in microendmilling process is the unpredictable life of the micro-tool and its premature failure during operations. Therefore in this work, an attempt has been made to monitor the tool condition (in-process) using acoustic emission (AE) sensor in microendmilling of different materials such as aluminum, copper and steel alloys. From this study, it is observed that there is a strong relationship between the tool wear (flank wear) and acoustic emission (AE_RMS) signals, surface roughness (R_a) as well as chip morphology. In order to understand the mechanism of tool wear, SEM and EDAX analyses were carried out on the microendmill after machining. Scanning Electron Microscope (SEM) and energy dispersive X-ray spectroscopy (EDAX) analyses indicated occurrence of the tool wear mechanism such as adhesion and plastic deformation in all three materials. Coating delamination is also observed while machining steel alloy. This work provides significant and new knowledge on the usage of AE sensor in monitoring the tool condition and understanding the tool wear mechanism in microendmilling of different materials.     

Improving machinability of Inconel 718 with a new hybrid machining technique

In this paper, by joining three non-traditional machining methods — plasma-enhanced machining, cryogenic machining, and ultrasonic vibration assisted machining — a new hybrid machining technique for machining of Inconel 718 is presented. Cryogenic machining reduces the temperature in the cutting zone, and therefore decrease tool wear and increases tool life, while plasma-enhanced machining helps to increase the temperature in the workpiece to make it softer. Also, applying ultrasonic vibrations to the tool helps to improve cutting quality and to prolong tool life by lowering, mainly, the cutting force and improving the dynamic cutting stability. This study experimentally investigates the effect of cutting parameters on cutting performance in the machining of Inconel 718 and compares the results of hybrid machining and conventional machining (CM). It is found that the hybrid method results in better surface finish and improves tool life in hard cutting at low cutting speeds as compared to the CM method.     

Design and implementation of a system for laser assisted milling of advanced materials

Laser assisted machining is an effective method to machine advanced materials with the added benefits of longer tool life and increased material removal rates. While extensive studies have investigated the machining properties for laser assisted milling(LAML), few attempts have been made to extend LAML to machining parts with complex geometric features. A methodology for continuous path machining for LAML is developed by integration of a rotary and movable table into an ordinary milling machine with a laser beam system. The machining strategy and processing path are investigated to determine alignment of the machining path with the laser spot. In order to keep the material removal temperatures above the softening temperature of silicon nitride, the transformation is coordinated and the temperature interpolated, establishing a transient thermal model. The temperatures of the laser center and cutting zone are also carefully controlled to achieve optimal machining results and avoid thermal damage. These experiments indicate that the system results in no surface damage as well as good surface roughness, validating the application of this machining strategy and thermal model in the development of a new LAML system for continuous path processing of silicon nitride. The proposed approach can be easily applied in LAML system to achieve continuous processing and improve efficiency in laser assisted machining.     

An analytical model for the prediction of temperature distribution and evolution in hybrid laser-waterjet micro-machining

A hybrid laser-waterjet micro-machining technology was developed for near damage-free micro-ablation recently. It uses a new material removal concept where the laser-softened material is expelled by a pressurised waterjet. The temperature field in this hybrid machining process is an essential quantity for understanding the underlying material removal mechanism and optimizing the process conditions. This study presents a three-dimensional (3-D) analytical model for the temperature field in this hybrid laser-waterjet micro-machining process. The interaction among the laser, waterjet, and workpiece is considered in the model. The absorption of laser by water, the formation of laser-induced plasma in water, the bubble formation and the laser refraction at the air-water interface are discussed. DuHamel’s principle is used to determine a closed-form temperature equation and a solution in a variable separation form is obtained. A calculation for silicon carbide is conducted. The results are illustrated by a group of 3-D temperature profiles intuitively and visually. It is shown that the temperatures are below the melting point during the process due to the cooling action of waterjet. The almost damage-free micro-machining can be achieved. Besides, the maximum temperature increases with the increased average laser power and waterjet offset distance and decreased nozzle exit diameter where the average laser power takes a major action.     

微细超声复合电加工技术与应用

为进行微器件及零件表面微结构的精微制作,提出微细超声复合电加工技术。构建、完善加工参数可较大范围调节的微细超声复合电加工系统,进行复合电加工机理研究;用组合放电微细加工方法,制作出可满足试验及实际加工要求的多种截面、尺寸的微细工具电极;进行多参数超声复合电加工试验研究,结果表明微细超声复合电加工技术具有加工效率高、精度好及成本低的技术优势。分析储油微结构对摩擦副表面摩擦学特性的影响规律,用超声复合电加工技术制作摩擦副表面储油微结构,摩擦学试验证明储油微结构可使摩擦副表面摩擦因数减小,磨损量降低。     

超声电解复合微细加工装置与试验研究

分析微细电解复合超声频振动加工过程机理,提出一种微细加工新方法--超声电解复合微细加工;设计、构造并完善复合微细加工装置;研究微细阴极制作工艺,利用微细组合电加工技术制作各类截面形状的微细阴极;进行超声电解复合微细加工试验,验证微细电解复合超声频振动实现微细加工的可行性及其在加工速度、精度、表面质量等方面的技术优势,探讨超声电解复合微细加工制作微结构的工艺规律。     

Machining of NiTi-shape memory alloys-A review

The emerging trends in the development of advanced smart materials with better unique properties under different environments for a particular application fascinate the researchers and industrialists. Nickel-Titanium based shape memory alloys are exotic materials due to their unique properties such as SME, SE, high damping characteristics, high corrosion and wear resistance and biocompatibility. This article presents an overview of machining processes that can be used to machine the NiTi and its surface induced characteristics such as microhardness, surface roughness, topography, induced layer, residual stress, fatigue and phase transformation. The surface integrity characteristics are discussed for machining of NiTi-SMAs under the category of traditional, non-traditional and micro-machining with the effect of input parameters such as cutting speed, feed, depth of cut, type of lubricant and type of coating material on cutting tool. The conventional machining of NiTi alloys are quite complicated due to high toughness, severe strain hardening, fatigue hardening and distinctive property of NiTi-SMAs such as pseudoelastic and shape memory effect. From this study, non-traditional process is significantly used to machine the NiTi-SMAs due to its better results on surface integrity characteristics. Consequently, future trends are also identified for machining the NiTi-SMAs and to improve the surface integrity characteristics.