Chatter suppression in micro end milling with process damping

Micro milling utilizes miniature micro end mills to fabricate complexly sculpted shapes at high rotational speeds. One of the challenges in micro machining is regenerative chatter, which is an unstable vibration that can cause severe tool wear and breakage, especially in the micro scale. In order to predict chatter stability, the tool tip dynamics and cutting coefficients are required. However, in micro milling, the elasto-plastic nature of micro machining operations results in large process damping in the machining process, which affects the chatter. We have used the equivalent volume interface between the tool and the workpiece to determine the process damping parameter. Furthermore, the accurate measurement of the tool tip dynamics is not possible through direct impact hammer testing. The dynamics at the tool tip is indirectly obtained by employing the receptance coupling method, and the mechanistic cutting coefficients are obtained from experimental cutting tests. Chatter stability experiments have been performed to examine the proposed chatter stability model in micro milling.     

Process control and dynamic process planning

Real time machine tool control and the planning activities which precede manufacture are usually interfaced through a low level language which allows little more than position, feed, and speed information to be passed between the two systems. The higher level systems used to describe geometry and tool paths also lack an adequate capability to describe manufacturing processes. The authors discuss the provision of a much richer interface between the planning and control activities which both facilitates the identification and scheduling of suitable monitoring tasks and allows the updating of process plan data from real time measurements. The result of such integration is an improvement in the efficiency of real time optimisation, and perhaps most importantly the possibility of quasi real time process planning. A system that is able to perform both initial process planning and plan refinement based upon low level feedback must also encompass the path generation activity, such a system is referred to by the authors as a dynamic process planning system. The paper describes the fundamentals of the process models, identification algorithms, control strategies, and low level process plan generation used within such an integrated system.     

Thermo-mechanical analysis and optimal tension control of micro wire electrode

The tension control of the micro wire electrode is a key technology for the micro wire electro-discharge machining (WEDM). Based on the coupled thermo-mechanical analysis, both the three-dimensional temperature and the stress distribution in the micro wire are determined. As a result, the tension of the micro wire electrode during the WEDM process can be optimized in accordance with the discharge energy, which is sampled and fed back to the tension control system in real time. Then the development of an optimal tension control system characterized by the form of master–slaver structure makes it possible to keep the wire tension optimal in the process of WEDM. The results of the machining experiments show that the optimal wire tension control is effective on the improvement of the machining accuracy with the prevention of wire breakage for the micro WEDM.     

数字微小流量阀的试验研究

本文介绍了一种新型数字微小流量阀,并通过试验研究介绍了其静动态特性。     

Wear behaviour in a combined micro blanking and deep drawing process

A one stroke micro blanking and deep drawing process is used to produce micro cups in a high quantity (200 strokes per minute) with an outer diameter of 1 mm. For cutting and deep drawing one single hollow punch is used. The outer diameter punches the circular blank while the inner diameter serves as drawing ring. Investigations regarding the tool life show that the punching edge wears out quicker than the rest of the tool. Furthermore it is shown that the positioning of the tool has a high influence on the wear behaviour.     

Accuracy improvement of wire-EDM by real-time wire tension control

In this paper, a closed-loop wire tension control system for a wire-EDM machine is presented to improve the machining accuracy. Dynamic models of the wire feed control apparatus and wire tension control apparatus are derived to analyze and design the control system. PI controller and one-step-ahead adaptive controller are employed to investigate the dynamic performance of the closed-loop wire tension control system. In order to reduce the vibration of wire tension during wire feeding, dynamic absorbers are added to the idle rollers of wire transportation mechanism. Experimental results not only demonstrate that the developed control system with dynamic absorbers can obtain fast transient response and small steady-state error than an open-loop control system, they also indicate that the geometrical contour error of corner cutting is reduced with approximately 50% and the vertical straightness of a workpiece can be improved significantly.     

A review of the evolution of microcontroller-based machine and process monitoring

This paper reviews the evolution of intelligent, distributed, microcontroller based machine and process monitoring systems. It considers basic building blocks that support such systems through the development of fault diagnostic methods, intelligent system based approaches and sensor-based machine monitoring. It then identifies three approaches that may be utilised when designing monitoring system architecture: integrated, distributed and embedded. Current applications of these approaches, when deployed individually and in combination with each other, are then discussed. In particular, the paper considers the efficacy of microcontroller based embodiments, in both current and future monitoring activities.     

Abrasive processes for micro parts and structures

The demand for miniaturized products and functionalized parts is increasing, and many such products are made of hard and brittle materials machined by abrasive processes. The first part of this keynote paper is dedicated to a discussion of micro parts and micro structures machined – at least in part – by abrasive processes, followed by a discussion of the associated abrasive processes. The strengths and limitations of these processes, among which include dicing, micro grinding, micro abrasive blasting, and vibration and magnet field assisted finishing are discussed. The paper concludes with a discussion of future trends in the field.     

微细侧铣过程的有限元建模与仿真

建立了AISI 4340 微细侧铣的二维有限元模型。将Johnson Cook本构模型与Johnson Cook剪切失效模型相结合,对铣削刃旋转过程中的一个完整侧铣周期进行了仿真。由于没有考虑尺寸效应的影响,所得到的流动应力值偏小。因此,建立了应变梯度塑性模型,并应用其预测了切屑的形成、冯米斯应力和温度场。仿真结果显示：微细侧铣过程中存在尺度效应,与Johnson Cook本构模型相比,应变梯度塑性模型能够很好地描述微细侧铣过程中的尺寸效应。最后,将仿真结果与理论计算结果相比较,验证了所建模型的正确性。     

An on-line pulse trains analysis system of the wire-EDM process

Ignition delay time (Td) has been widely used to distinguish the abnormal discharges from the normal ones in wire electrical discharge machining (WEDM) process. In this paper an on-line analysis system for the causality of the Td data sequences was developed to evaluate the machining performance of WEDM process. The system is composed of a stand-alone Td processing circuitry and a user-friendly computer program for data analysis. The Td processing circuitry calculates and records the Td of every single electrical discharge in the first place, and then transmits the Td data via an embedded communication port to a desktop or notebook computer. The computer program, after performing the analysis tasks, will display the result in a graphic way. Two mathematical algorithms were employed for the analysis: autocorrelation function and Fourier transform. Through experiments under different working conditions, it was found that the autocorrelation function could be used to detect if arc or short circuit discharges take place consecutively, and to distinguish the WEDM process with similar Td distributions. On the other hand, the spectral analysis revealed that several factors were identified to be able to induce certain periodic patterns of Td data. These factors include the length of wire electrode, the water pressure, etc.     

Automated supply of micro parts based on the micro slide conveying principle

Part supply is a major bottleneck for successful automation in micro assembly. So far, vibratory conveyors working according to the micro throw principle are applied predominantly. However, missing flexibility, fault liability and abrasive wear are significant disadvantages. In this paper, a multi body simulation model describing the micro slide principle including all major influencing parameters for micro parts is presented. By means of experiments with an especially designed piezoelectric conveyor, the functionality and advantages of this principle are demonstrated and the model is validated. Furthermore, optimization of the conveyor by automation, miniaturization and modularization is shown.     

Non-destructive evaluation of the micro residual stresses of IIIrd order by using micro magnetic methods

Nanoscale coherent precipitates and the corresponding micro residual stresses play a dominant role in the strengthening process of materials. At present, there exists no experimental method for measuring micro residual stresses of IIIrd kind non-destructively. In the frame of the present work, it will be shown that micro-magnetic measurement techniques based on the tensile loading dependent maximum Barkhausen noise amplitude can be used for the analysis of micro residual stresses (MRS) of IIIrd kind (coherency residual stresses). For this purpose, Fe–Cu-alloys with well-defined contents of Cu-precipitates were produced and investigated.     

Experimental and numerical investigation on micro deep drawing process of stainless steel 304 foil using flexible tools

Flexible forming technology provides significant application potential in various areas of manufacturing, particularly at a miniaturized level. Simplicity, versatility of process and feasibility of prototyping makes forming techniques by using flexible tools suitable for micro sheet metal forming. This paper reports the results of FE simulation and experimental research on micro deep drawing processes of stainless steel 304 sheets utilising a flexible die. The study presents a novel technique in which an initial gap (positive or negative) is adopted between an adjustment ring and a blank holder employed in the developed forming system. The blank holder is moveable part and supported by a particular spring that provides the required holding force. The forming parameters (anisotropy of SS 304 material, initial gap, friction conditions at various contact interfaces and initial sheet thickness) related with the forming process are in details investigated. The FE models are built using the commercial code Abaqus/Standard. The numerical predictions reveal the capability of the proposed technique on producing micro metallic cups with high quality and large aspect ratio. To verify these results, number of micro deep drawing experiments is conducted using a special set up developed for this purpose. As providing a fundamental understanding is required for the commercial development of this novel forming technique, hence the optimization of the initial gap in accordance with each sheet thickness, thickness distribution and punch force/stroke relationship are detected.     

Precision manufacturing process monitoring with acoustic emission

Current demands in high-technology industries such as semiconductor, optics, MEMS, etc. have predicated the need for manufacturing processes that can fabricate increasingly smaller features reliably at very high tolerances. In situ monitoring systems that can be used to characterize, control, and improve the fabrication of these smaller features are therefore needed to meet increasing demands in precision and quality. This paper discusses the unique requirements of monitoring of precision manufacturing processes, and the suitability of acoustic emission (AE) as a monitoring technique at the precision scale. Details are then given on the use of AE sensor technology in the monitoring of precision manufacturing processes; grinding, chemical–mechanical planarization (CMP) and ultraprecision diamond turning in particular.     

数字化焊接过程监视和控制

回顾了艾美特公司在焊接自动化控制领域进行的数字焊接自动化控制和系统集成技术方面的工作,介绍了在变极性等离子纵环组合焊接、CNC热丝TIG深孔堆焊、激光跟踪多丝深坡口埋弧等方面应用情况。为业内人士提供了一些数字焊接自动化的组态结构和质量控制方法。     

Boring and face grooving using micro turning tools

Micro turning tools with outside diameters of 25–50 μm were fabricated using cemented tungsten carbide by electrical discharge machining and used for micro boring and micro face grooving. The new process used could improve the hole circularity down to 0.25 μm and provide smooth-finished surfaces. From a set of experiments, the limit depth of cut and feed rate that can prevent tool breakage were determined. Compared with previous studies, the current study paved the way for applying removing processes with micro tools to boring and face grooving.     

A Bayesian network approach to root cause diagnosis of process variations

This paper addresses the challenges inherent in root cause diagnosis of process variations in a production machining environment. We develop and present a process monitoring and diagnosis approach based on a Bayesian belief network for incorporating multiple process metrics from multiple sensor sources in sequential machining operations to identify the root cause of process variations and provide a probabilistic confidence level of the diagnosis. The vast majority of previous work in machining process monitoring has focused on single-operation tool wear monitoring. The focus of the present work is to develop a methodology for diagnosing the root cause of process variations that are often confounded in process monitoring systems, namely workpiece hardness, stock size, and tool wear variations. To achieve this goal, multiple sensor metrics have been identified with statistical correlations to the process faults of interest. Data from multiple sensors on sequential machining operations are then combined through a causal belief network framework to provide a probabilistic diagnosis of the root cause of the process variation.     

Use of micro ultrasonic vibration lapping to enhance the precision of microholes drilled by micro electro-discharge machining

In microhole machining of metal, micro electro-discharge machining (MEDM) is an effective method that can easily create a hole with a diameter under 100 μm. Due to the poor surface quality and shape of MEDM, a machining method that compounds MEDM and micro ultrasonic vibration lapping (MUVL) is proposed here to allow the production of high precision microholes with high aspect ratios. In our investigations, first, a circular or stepped circular microtool was made by the MEDM process, and the tool was used to create a microhole on a small piece of titanium plate in the same machining process. Finally, the abrasive particles driven by the same tool were utilized to grind this hole in the MUVL procedure, and a hole with a diameter about 100 μm can be obtained. Owing to the microtool and workpiece not taking apart from the clamping apparatus during different machining steps, the microhole was processed in the co-axial situation, so the precise shape and perfect surface can be obtained easily. For example, the diameter variation between the entrances and exits of the microholes could reach a value of about 5 μm when the workpiece had a thickness of 500 μm, if the circular microtools was used. Meanwhile, the roundness of the microholes clearly improved, regardless of whether circular or stepped tools were used. However, owing to the perfect grinding effect between the microholes and microtools, the stepped circular tools produced high quality surfaces more easily than the circular tools.