Chatter in machining processes: A review

Chatter is a self-excited vibration that can occur during machining operations and become a common limitation to productivity and part quality. For this reason, it has been a topic of industrial and academic interest in the manufacturing sector for many years. A great deal of research has been carried out since the late 1950s to solve the chatter problem. Researchers have studied how to detect, identify, avoid, prevent, reduce, control, or suppress chatter.This paper reviews the state of research on the chatter problem and classifies the existing methods developed to ensure stable cutting into those that use the lobbing effect, out-of-process or in-process, and those that, passively or actively, modify the system behaviour.     

Computer simulation and experimental investigation of sheet metal bending using laser beam scanning

Computer simulation and experimental investigation of the sheet metal bending into a V-shape by the laser beam scanning without an external force exerted onto it have been performed. A 3-D FEM simulation has been carried out, which includes a non-linear transient indirect coupled thermal-structural analysis accounting for the temperature dependency of the thermal and mechanical properties of the materials. The bending angle, distribution of stress–strain, temperature and residual stresses have been obtained from the simulations. The sheet metal bending had been performed for different materials, thicknesses, scanning speeds and laser powers. The measurement of real-time temperature and bending angle was carried out. The bending angle is affected by the mechanical and thermal properties of the sheet metal material, the process parameters, and the output of laser energy. The bending angle is increased with the number of laser beam scanning passes and is the function of the laser power and the laser beam scanning speed. The simulation results are in agreement with the experimental results.     

High surface quality micro machining of monocrystalline diamond by picosecond pulsed laser

In micro machining of monocrystalline diamond by pulsed laser, unique processing characteristics appeared only under a few ten picosecond pulse duration and a certain overlap rate of laser shot. Cracks mostly propagate in parallel direction to top surface of workpiece, although the laser beam axis is perpendicular to the surface. This processed area can keep diamond structure, and its surface roughness is smaller than R_a = 0.2 μm. New laser micro machining method to keep diamond structure and small surface roughness is proposed. This method can contribute to reduce the polishing process in micro machining of diamond.     

Predicting surface roughness in machining: a review

The general manufacturing problem can be described as the achievement of a predefined product quality with given equipment, cost and time constraints. Unfortunately, for some quality characteristics of a product such as surface roughness it is hard to ensure that these requirements will be met. This paper aims at presenting the various methodologies and practices that are being employed for the prediction of surface roughness.The resulting benefits allow for the manufacturing process to become more productive and competitive and at the same time to reduce any re-processing of the machined workpiece so as to satisfy the technical specifications. Each approach with its advantages and disadvantages is outlined and the present and future trends are discussed. The approaches are classified into those based on machining theory, experimental investigation, designed experiments and artificial intelligence (AI).     

A new approach for the friction identification during machining through the use of finite element modeling

Finite Element Modeling (FEM) of chip formation has proved great sensitivity to tool/chip friction coefficient. This parameter cannot be adequately identified through conventional tests, because thermal and mechanical loadings during these tests are far from those encountered during machining. In this study, the inadequacy of using constant Coulomb's friction coefficient in FEM is showed. Although a good agreement is found for cutting force and chip thickness variables, significant differences can be found for feed force and tool–chip contact length. Differences of more than 50% are observed in some cases for those variables when FEM results are compared with experimental ones. A new approach to identify a friction model after experimental tests will be detailed. This new approach involves application of a variable friction coefficient at the tool–chip interface, which allows obtaining a better agreement between numerical results (differences close to 10%) regarding the feed force.     

基于Simulink的重物举升液压控制系统建模与仿真

以液压系统的典型应用－重物举升系统为例,从预测系统动态响应的角度出发,分析了液压系统仿真的特点和基于节点法的仿真建模方法。利用动态系统仿真软件包Simulink建立了通用液压元件的非线性仿真模型,实现了图形化交互方式下的系统仿真模型构建和元件参数修改。最后,给出了系统一个工作过程的仿真结果。     

基于VRML的虚拟NC加工仿真技术的研究

针对数控加工仿真的特点，探讨了VBML的技术特征及其在解决数控加工仿真中的关键技术和存在问题，并采用AutoCAD与VRML2．0相结合进行了数控仿真的初步实践，取得了成功的应用。     

A review on current research trends in electrical discharge machining (EDM)

Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. A pulse discharge occurs in a small gap between the work piece and the electrode and removes the unwanted material from the parent metal through melting and vaporising. The electrode and the work piece must have electrical conductivity in order to generate the spark. There are various types of products which can be produced using EDM such as dies and moulds. Parts of aerospace, automotive industry and surgical components can be finished by EDM. This paper reviews the research trends in EDM on ultrasonic vibration, dry EDM machining, EDM with powder additives, EDM in water and modeling technique in predicting EDM performances.     

A study on dual laser beam separation technology of KDP crystal

KDP crystal is an important optic-electro material in various laser systems, at present, the greatest difficulty is the cutting of large-scale crystals. In this study, a dual laser beam separation technology (DLBS) for KDP crystal has been developed by skillfully combining femtosecond laser and continuous fiber laser for the first time. The principle of DLBS is expounded. The effects of laser separating parameters, including laser output power, scanning speed, focal position and focal length on separating accuracy and quality (flatness and surface roughness S_a of the separated sidewall) were investigated. The key parameters were determined and optimized for the separating of raw materials with the minimal flatness and the separating of the end product crystals with minimal S_a. The results show that a clean crystal surface and an average S_a of 2.6843 μm separated sidewall without any pollution, subsurface damage and limbic fragmentation could be achieved by DLBS. The separating speed of DLBS is at least 20 times faster than that of the conventional method. A numerical simulation to analyze the mechanism of DLBS separating KDP crystal was developed, which is in good agreement with the theoretical analysis and experimental results.     

Substrate pre-treatment of cemented carbides using abrasive flow machining and laser beam ablation

A significant driver in research activities of manufacturers and university institutions is the improvement of tool life for cutting tools. Recent publications have shown that the substrate pre-treatment prior to coating as well as defined rounding of cutting edges are key factors for cutting tool life. Different technologies are used for substrate pre-treatment, depending on the machining task, flexibility of the process and economic aspects. However regarding the surface quality two opposing requirements come into conflict. While high surface quality supports the chip removal during machining, the film adhesion between substrate and coating is greater on rough surfaces. This paper presents a comparison of the abrasive flow machining (AFM) and laser ablation technologies as pre-treatment processes for cemented carbides. With respect to the relevant processing parameters, the effects of a pre-treatment using AFM and laser ablation on roughness, surface topography, mechanical activation and chemical composition have been determined.     

Diamond machining of silicon: A review of advances in molecular dynamics simulation

Molecular dynamics (MD) simulation has enhanced our understanding about ductile-regime machining of brittle materials such as silicon and germanium. In particular, MD simulation has helped understand the occurrence of brittle–ductile transition due to the high-pressure phase transformation (HPPT), which induces Herzfeld–Mott transition. In this paper, relevant MD simulation studies in conjunction with experimental studies are reviewed with a focus on (i) the importance of machining variables: undeformed chip thickness, feed rate, depth of cut, geometry of the cutting tool in influencing the state of the deviatoric stresses to cause HPPT in silicon, (ii) the influence of material properties: role of fracture toughness and hardness, crystal structure and anisotropy of the material, and (iii) phenomenological understanding of the wear of diamond cutting tools, which are all non-trivial for cost-effective manufacturing of silicon. The ongoing developmental work on potential energy functions is reviewed to identify opportunities for overcoming the current limitations of MD simulations. Potential research areas relating to how MD simulation might help improve existing manufacturing technologies are identified which may be of particular interest to early stage researchers.     

Prediction of local sintering in laser beam machining of green Y-TZP ceramic

Laser beam machining of Y-TZP engineering ceramic material is carried out in green stage to increase the material removal rate. The generation of hot spots may cause local sintering of the ceramic material leading to a decrease of the mechanical properties of the final sintered component. This paper presents the implementation of alternative laser beam paths to reduce the hot spots occurrence. A thermal finite element model has been developed to support the experimental analysis as well as the prediction of local sintering. The experimental validation of the newly developed toolpath strategies confirmed the reduction of local sintering.     

Modeling and simulation of cylindrical electro-chemical magnetic abrasive machining of AISI-420 magnetic steel

The objective of the present research is to simulate cylindrical electro-chemical magnetic abrasive machining (C-EMAM) process for magnetic stainless steel (AISI-420). C-EMAM is a new hybrid machining process used for high efficiency finishing of cylindrical jobs made of advanced engineering materials. The material is removed from the workpiece surface due to simultaneous effect of abrasion and electrochemical dissolution. Finite element method is used to calculate the distribution of magnetic field between the magnetic poles in which cylindrical shaped workpiece is placed. The cutting forces responsible for abrasion are calculated from the magnetic forces due to gradient of magnetic field in the working gap. The effect of electrochemical dissolution and abrasion-assisted dissolution are incorporated into the C-EMAM process model using empirical relation for average anodic current. The empirical relation is correlated with the input parameters in the present system based on experimental results. Finally a surface roughness model is developed by considering total volume of material removed with the assumption of triangular surface profile. The simulation results for material removal and surface roughness are validated using experimental results. The simulated results agree with experimental observations.     

纤维增强热塑性树脂复合材料与激光连接研究进展

为研究碳纤维增强复合材料和铝合金搭接激光焊接过程的温度变化规律,文中以6061铝合金和碳纤维增强尼龙66复合材料(CF/PA66)为研究对象,建立了基于热传导的有限元模型,使用SYSWELD软件对两种材料搭接激光焊接过程进行数值模拟,并通过试验验证了模型的准确性;在此基础上研究了激光功率、焊接速度、搭接宽度、冷却条件、工装导热条件对接头温度场的影响规律;研究发现, CF/PA66树脂熔化区域随着激光功率的增大而增加,随冷却速度的增大而减小,同种工艺参数下材料搭接尺寸对界面树脂最大熔化宽度无影响,水冷条件能够显著降低CF/PA66树脂熔化量,导热材料热导率越大,对PA66树脂熔化量的降低作用越显著.

     

Position geometric error modeling,identification and compensation for large 5-axis machining center prototype

This paper presents a position geometric error modeling, identification and compensation method for large 5-axis machining center prototype. First, regarding the prototype as a rigid multi-body system, a geometric error model has been established, which supports the identification of position geometric error associated with a translational axis by using laser interferometer, and a rotational axis by using laser tracker. Second, based on this model, an improved identification approach named as virtual rigid-body is put forward for calculating positioning error of each large translational axis. Detailed derivation of a generalized matrix equation is given. Third, analytical models based on the least-squares theory were adopted to compute error values at an arbitrary position for error compensation. Finally, the identified position geometric errors were compensated by using recursive software-based error compensation method. The results show that the position accuracy of large machining center prototype has been improved with compensation and up to the design requirements.     

Finite element simulation of magnesium alloys laser beam welding

In this paper, a three-dimensional finite element model is developed to simulate thermal history magnesium-based alloys during laser beam welding. Space–time temperature distributions in weldments are predicted from the beginning of welding to the final cooling. The finite element calculations were performed using Cast3M code with which the heat equation is solved considering a non-linear transient behaviour. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam dimensions and welding speed, and it is associated to moving boundary conditions. Experiments were carried out to determine temperature evolution during welding and to measure the laser weld width. By comparing the thermal model answers with the measurements, it is found that numerical simulations results are in a good agreement with the experimental data.     

Mathematical modeling and numerical simulation of layer growth and phase transformation during galvannealing process

In the galvannealing process, a galvanized sheet is given an annealing treatment to transform the zinc coating to the Zn–Fe intermetallic coating through diffusional reactions. In the present work, a mathematical model for predicting the growth of ζ (zeta), δ (delta), and Γ (gamma) during the galvannealing process has been developed by using fundamental diffusion data. The primary diffusion mechanism is the movement of zinc through the multiphase of the Zn–Fe intermetallics. The values of iron content in the coating were predicted and compared to the data obtained from experimental studies. With the increase of galvannealing temperature, the growth rate of the δ phase increases, while the growth rate of the ζ phase decreases. At the same iron content in the coating, the thickness of the Γ phase layer is thicker at a higher temperature. The new type of galvannealing process of first high annealing temperature and then low annealing temperature is validated as a better galvannealing process, which should be a range of practical application. The simulated results agree well with experimental observations, and the model can be utilized to optimize the galvannealing parameters.     

Fuzzy adaptive networks in machining process modeling: surface roughness prediction for turning operations

Due to the complexity of the machine tool structure and the cutting process, the dynamics of machining processes are still not completely understood. This is especially true due to the demand of high-speed machining to increase productivity. In order to model and control these complex processes, new approaches, which can represent complex phenomenon combined with learning ability, are needed. The combined neural–fuzzy approach appears to be ideally suited for this purpose. In this paper, the recently developed fuzzy adaptive network (FAN) is used to model surface roughness in turning operations. The FAN network has both the learning ability of neural network and linguistic representation of complex, not well-understood, vague phenomenon. Furthermore, it can continuously improve the initially obtained rough model based on the daily operating data. To illustrate this approach, a model representing the influences of machining parameters on surface roughness is established and then the model is verified by the use of the results of pilot experiments. Finally, a comparison with the results based on statistical regression is provided.     

An investigation of laser-assisted machining of Al2O3 ceramics planing

Laser-assisted machining (LAM), an alternative method of fabricating difficult-to-machine materials, uses primarily laser power to heat the local area (without necessarily evaporating or melting any material) before the material is removed. It not only efficiently reduces the cutting force during the manufacturing process but also improves the machining characteristics and geography with regard to difficult-to-machine materials, especially structural ceramics.This study on the application of laser-assisted machining to Al₂O₃ ceramics examines the measurements of cutting force and workpiece surface temperature as well as surface integrity and tool wear. Specifically, it uses the lattice Boltzmann method (LBM) to calculate the temperature distribution inside the ceramic workpiece during the LAM process and ensure that the laser energy causes no subsurface damage. The experimental results reveal that the LAM process efficiently reduces the cutting force by 22% (feed force) and 20% (thrust force) and produces better workpiece surface quality than conventional planing.