Investigation of cavitation erosion using X-ray residual stress analysis

In this paper it will be shown that by X-ray residual stress analysis it is possible to obtain information on the cavitation process after only short cavitation times. To clarify the correlation between cavitation erosion and changes in residual stress, samples of various steels were tested in a flow cavitation device. The residual stress measurements showed that cavitation leads to the development of compressive residual stresses in the surface of the samples. The rate at which these residual stresses develop depends on the intensity of cavitation. Cavitation-induced changes in residual stress may also be observed in samples with pre-existing residual stresses due to handling, e. g. mechanical working, heat treatment etc. After very short cavitation times the local variation in cavitation intensity may be very clearly seen in the residual stress distribution in the surface. After a longer period of cavitation, compressive residual stresses reach a limiting value which is not exceeded even at points of highest cavitation intensity.     

Ultrasonic deburring

Burrs are always present in metal cutting and moulding processes and removal of burrs has always been a difficult engineering problem. The removal of burrs from high-strength materials with generic features that have blind or difficult-to-access burrs have made many deburring processes useless. Although some processes such as electro-chemical and thermal energy deburring methods are able to perform well for this purpose, there are serious health and safety considerations. There are also other limitations such as the requirement for materials to be electrically conductive for electro-chemical methods.In this paper, the ultrasonic deburring process has been used and developed to deburr thick metallic and non-metallic burrs which previously could not be deburred. The ability of ultrasound to propagate through elastic media and the fact that it does not require any tooling makes this technique very useful to treat surfaces that are generic in nature and difficult to access.     

Experimental investigations of sideward burr formation in rotary machining

Burrs can be formed on the feed mark ridges and the edges of the machined parts in machining operations. These burrs are undesirable in terms of the surface quality, the precise dimensioning of the machined parts and the safety of operators. This paper demonstrates the effectiveness of using a rotary tool on minimizing the sideward burr formation in machining. In particular, the experimental relationships between the size of sideward burr and the cutting parameters (including tooling mechanism) are established first in rotary machining. Methods to control the size of sideward burr are then explained. The possible application of a rotary tool for deburring operations while engaged in machining is also explored.     

Deburring of burrs in spring collets by abrasive flow machining

Micro burrs occurring inside the small and large diameters adversely affect the properties of products. Manual deburring of micro burrs in particular damages the processed surface and reduces production efficiency. In this study, spring collets made of chrome-molybdenum are used to test the deburring of the surface of collets including crossed micro grooves by abrasive flow machining. This revised version was published online in October 2004 with a correction to the issue number.     

A study on deburring of magnesium alloy plate by magnetic abrasive polishing

Drilling is one of the most important machining operations in manufacture process. When drilling process is applied, unexpected burrs will be formed on the surface of workpiece. Even a small burr can cause unwanted problems, resulting in low quality products. In order to get better drilled parts, it is very important to know characteristics of burr formation and to remove the burr from the drilled surface with machining process. In this study, magnetic abrasive polishing (MAP) was used to research the deburring factors of magnesium alloy. Moreover, design of experiments was performed to evaluate parameters’ effect on the MAP process. As a result, it was seen that the MAP was useful to remove the burrs on the workpiece without damage from its original surface.     

Cutting tool wear monitoring for reliability analysis using proportional hazards model

Electrochemical machining (ECM) is an important technology in machining difficult-to-cut materials and to shape free-form surfaces. In ECM, material is removed by electrochemical dissolution process, so part is machined without inducing residual stress and without tool wear. To improve technological factors in electrochemical machining, introduction of electrode tool ultrasonic vibration is justifiable. This method is called as ultrasonically assisted electrochemical machining (USAECM). In the first part of the paper, the analysis of electrolyte flow through the gap during USAECM has been presented. Based on computational fluid dynamic methods, multiphase, turbulent and unsteady electrolyte flow between anode and cathode (under assumption that cavitation phenomenon occurs) has been analysed. Discussion of the obtained solutions is the base to define optimal conditions of electrolyte flow in case of USAECM process. The second part of the paper is connected with experimental investigations of USAECM process. Classic experimental verification of obtained results in case of machining is extremely difficult, but influence of the ultrasonic vibration can be observed indirectly by changes in technological factors (in comparison to machining without ultrasonic intensification), whereas results of numerical simulation give possibility to understand reason and direction of technological factors changes. Investigations proved that ultrasonic vibrations change conditions of electrochemical dissolution and for optimal amplitude of vibration gives possibility to decrease the electrode polarisation.     

柴油机零件加工去毛刺方法及特点分析

阐述了柴油机零件加工毛刺的产生及其危害,介绍了柴油机零件去毛刺的几种方法,并分析了几种方法的优缺点,以为柴油机制造工作者参考.     

Theoretical Investigation of the Influence of Combined Machining Modes on the Value and Character of Residual Stresses in the Surface Layer of Cylindrical Friction Pairs

In this paper, analysis of influence of residual stresses in the surface layer of cylindrical friction pairs on the operational wear resistance index is carried out. Stresses of the first kind after application of combined machining are investigated. Combined machining is consecutive electromechanical machining and diamond burnishing. A formula for calculation of residual stresses originating in the surface layer after the combined machining is obtained. For computational convenience, a computer program calculating the residual stress parameter is written in Visual studio 2017 C#. The combined machining method creates a potential for improving performance indices due to creation of compressive residual stresses.     

Influence of material microstructure changes on surface integrity in hard machining of AISI 52100 steel

Residual stresses are a consequence of thermo-mechanical and microstructural phenomena generated during the machining operation. Therefore, for improving product performance in machined hardened steels, material microstructure changes (commonly referred to as white and dark layers) must be taken into account. This paper presents a finite element model for white and dark layers formation in orthogonal machining of hardened AISI 52100 steel. In particular, a hardness-based flow stress and empirical models for describing the white and dark layers formation were developed and implemented in the finite element code. A series of experiments was carried out in order to validate the proposed simulation strategy and to investigate the influence of material microstructure changes on residual stresses. As main results, it was firstly demonstrated by surface topography analysis as both the white and dark layer are the result of microstructural alterations mainly due to rapid heating and quenching. Furthermore, it was found as both the presence of white and dark layers influence the residual stress profile. Particularly, the former significant impacts on the magnitude of maximum residual stress and on the location of the peak compressive residual stress; the latter reduces the compressive area.     

Modeling of machined surface characteristics in cryogenic orthogonal turning of inconel 718

The determination of the optimal machining conditions for assuring desired machined surface characteristics of a part is one of the main goals in a machining process. In this article, the impact of a cooling lubrication fluid, its delivery phase and location, as well as machining parameters, on residual stresses have been investigated. The workpiece material under observation is Inconel 718. For measuring residual stress profiles, X-ray diffraction technique has been used. Additionally, besides the experimental work, modeling with the finite element method model was implemented and correlated with experimental results. The results show that residual stresses are influenced by the cooling lubrication scenario, even though the machining parameters are kept constant. However, flood and cryogenic machining show more compressive residual stresses than a dry machining case. On the other hand, the results have shown also that machining parameters influence residual stresses, where stresses increase with their increase (v_c and f).     

二维切削中切削方向毛刺与亏缺的界限转换条件

建立了二维切削中切削方向毛刺与亏的生成模型,给出了切削方向毛刺与亏缺的判别准则,并对影响切削方向毛刺与亏缺转换的主要因素进行了实验研究和相应的理论分析,提示出切削方向毛刺与亏缺的界限转换条件为：剪切应变ε≤3,为亏缺;3＜ε＜4,为过渡区;ε＞4,为毛刺。并且,切削方向毛刺与亏缺的界限转换条件因切削条件变化而变化。为进一步深入研究切削毛刺的生成与抑制理论提供了科学的基础。     

Wear mechanisms and residual stresses in alumina-based laminated cutting tools

The outstanding performances of the Al₂O₃ cutting tools in terms of potential cutting speed can lead to substantial economies in the machining of metallic materials.Nevertheless, their widespread use is limited by some drawbacks such as the tendency to edge chipping and to the propagation of microcracks, which can lead to premature failures.These shortcomings are due to the intrinsic low toughness of the ceramic material, which is in turn related to its characteristics non-metallic bonds.A well-recognised method of increasing the toughness of brittle materials is the introduction of surface compressive stresses, which can be obtained through a suitable lamination geometry of the tools as consequence of the different coefficients of thermal expansion (CTE) of the constituent layers.The performances of an alumina/zirconia laminated cutting tool used for machining steel have been investigated and compared to those of a non-laminated commercial alumina/zirconia cutting tool. The different wear mechanisms are explained on the basis of the different microstructures and chemical compositions. We have shown that residual compressive stresses, measured by Piezo-Spectroscopy, are effective in avoiding the microchipping on the flank zone but cannot avoid larger fractures caused by the residual porosity.     

HARD TURNING PLUS GRINDING–A COMBINATION TO OBTAIN GOOD SURFACE INTEGRITY IN AISI O1 TOOL STEEL MACHINED PARTS

The establishment of adequate machining guidelines requires the study of several factors (residual stresses, roughness, hardness, microstructural changes, etc.) that define the surface integrity generated in the part by a machining operation. This work studies the surface integrity generated in AISI O1 tool steel by four hard turning (conventional, laser assisted, MQL and conventional with worn tool) and two grinding (production and finishing) processes, as well as by a combined machining process (conventional hard turning + finishing grinding). Hard turning generates tensile stresses and strong structural changes in the machined surface while grinding causes compressive stresses and negligible structural changes. Below the surface, grinding generates slightly tensile or nearly null stresses whereas turning generates strong compressive stresses. The results obtained show that an optimum machining process would imply the combination of hard turning plus a slight final grinding.     

HARD TURNING PLUS GRINDING-A COMBINATION TO OBTAIN GOOD SURFACE INTEGRITY IN AISI O1 TOOL STEEL MACHINED PARTS

The establishment of adequate machining guidelines requires the study of several factors (residual stresses, roughness, hardness, microstructural changes, etc.) that define the surface integrity generated in the part by a machining operation. This work studies the surface integrity generated in AISI O1 tool steel by four hard turning (conventional, laser assisted, MQL and conventional with worn tool) and two grinding (production and finishing) processes, as well as by a combined machining process (conventional hard turning + finishing grinding). Hard turning generates tensile stresses and strong structural changes in the machined surface while grinding causes compressive stresses and negligible structural changes. Below the surface, grinding generates slightly tensile or nearly null stresses whereas turning generates strong compressive stresses. The results obtained show that an optimum machining process would imply the combination of hard turning plus a slight final grinding.     

油井管螺纹加工中的去毛刺技术

油井管螺纹切削加工中产生的毛刺会直接影响螺纹检验的准确性和螺纹连接质量。根据油井管螺纹不同部位产生毛刺的特点 ,讨论了去除和控制毛刺的相应工艺方法。     

Effects of micro-stresses from machining and shot-peening processes on fatigue life

An investigation of the effects of tensile machining and compressive shot-peening residual stresses on fatigue life is presented. The paper is focused on fatigue life modelling using the finite element method (FEM). A representative broached notched specimen under three-point bending is modelled as a 2D plane stress geometry using the FEM. Inconel 718 mechanical and fatigue material properties at 600°C are used. Machining and shot-peening residual stresses are mapped to the macro FE models using mathematical algorithms around the notched area of the specimen and their influence on the fatigue life experiencing high cycle fatigue (HCF) and low cycle fatigue (LCF) is investigated. The results show that the compressive shot-peening residual stresses significantly increase the life at HCF compared to the LCF.     

切削参数对微铣毛刺尺寸影响的试验研究

以铝合金Al6061-T6为研究对象,采用单因素试验方法,利用MIKRON UCP800五轴联动加工中心进行了微铣槽试验,研究了主轴转速、切削深度和进给速度对顶部毛刺尺寸的影响,初步揭示了上述切削参数对顶部毛刺尺寸的影响规律,为主动控制微铣加工过程中的毛刺尺寸提供依据。     

Influence of the machining sequence on the residual stress redistribution and machining quality: analysis and improvement using numerical simulations

The manufacturing of aluminium alloy structural aerospace parts involves multiple steps, the principal ones being the forming (rolling, forging etc.), the heat treatments and the machining. During this last step, the final geometry of the part is obtained. Before machining, the workpiece has therefore undergone several manufacturing steps resulting in unequal plastic deformation and metallurgical changes which are both sources of residual stresses. On large and complex aluminium alloy aeronautical parts, up to 90 % of the initial workpiece volume can be removed by machining. During machining, the mechanical equilibrium of the part is in constant evolution due to the redistribution of the initial residual stresses.The residual stress redistribution is the main cause of workpiece deflections during machining as well as of post-machining distortion (after unclamping). Both can lead to the non-conformity of the part with the geometrical and dimensional tolerance specifications and therefore to a rejection of the part or to additional conforming steps. In order to improve the machining accuracy and the robustness of the process, the effect of the residual stresses has to be considered for the definition of the machining process plan. In this paper, a specific numerical tool [2] allowing to predict workpiece deflections during machining and post-machining distortion is used to study the influence of the machining sequence on the machining quality in taking into consideration the initial residual stresses. A first machining process plan defined as the reference case is simulated. Simulation results are then compared with experimental ones showing the feasibility to use the developed tool to predict the machining quality depending on the initial residual stresses, the fixture layout and the machining sequence. Using the computational tool, a method to optimise the machining quality depending on the initial workpiece and on the machining sequence is presented. A machining process plan allowing to respect the tolerance specifications is then defined. This demonstrates the feasibility to adapt and to optimise the machining process plan to ensure conformity of the part with the tolerance specifications.     

纳米ZrO2陶瓷超声振动磨削表面残余应力试验研究

采用超声振动磨削和普通磨削方式,利用X射线衍射分析仪,对纳米氧化锆陶瓷表面残余应力进行了研究.实验结果表明,纳米氧化锆陶瓷磨削表面产生的残余应力都表现为压应力;随着磨削深度的增加,超声振动磨削表面残余应力减小趋势较缓;磨削表面残余应力随着磨粒的增大呈上升趋势,且普通磨削表面残余应力上升的趋势较超声振动磨削的要快.     

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4___0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 Bin. Residual stresses attributed to 7-A1203 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2~u method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667_＋20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.