Stress corrosion cracking of leaded brass in a sulphuric acid environment

Free-cutting leaded brass is commonly used as sleeve fittings (also termed clamping ferrules) on polytetrafluoroethylene-lined flexible hoses for the filling and distribution of compressed gases, e.g., oxygen, nitrogen and carbon dioxide, for various industrial and medical applications. Some of the gas-filling and gas distribution facilities are located in the proximity of highly industrialized areas for the convenience of transportation, application and customer service. Therefore, the gas-filling and gas distribution gears are frequently exposed to the environment containing various chemical substances, which in the presence of ambient moisture and under the influence of mechanical and residual stresses in the material can effect an undesirable material degradation reaction. Stress corrosion cracking (SCC) has been identified to occur in C36000 Cu–Zn–Pb leaded brass ferrules under the synergistic reactions of a sulphuric acid production environment in a sustained tensile stress environment. The tensile stress was imparted to the material by the mechanical crimping process applied on the ferrules, and superimposed by cyclical high-pressure gas-cylinder-filling operations. The chemical species responsible for the SCC originated from the gaseous vapours and/or ionic derivatives of S-containing substances emitted from a neighbouring sulphuric acid production plant, which reacted with water and moisture condensates on the brass ferrule surfaces and effected the chemical corrosion reaction(s). SCC of the leaded brass ferrules gave rise to predominantly intergranular failures with fracture surfaces heavily decorated by corrosion products of various configurations. Most corrosion products were found to have embedded on the grain-boundary planes of the fracture surfaces, suggesting that grain-boundary short-circuit diffusion may have served as a viable mechanism for the SCC of C36000 leaded brass under the operating conditions of this case study.     

Study of milling force variation in ultrasonic vibration-assisted end milling

Ultrasonic vibration cutting has been proved to be an effective cutting technology for its excellent cutting performance and has been widely applied in turning and drilling process. However, this kind of technology is rarely tried in milling process. In cutting process, cutting force is an important process parameter, which affects surface finish and tool wear. This paper investigates the milling force variation in ultrasonic vibration-assisted end milling process through a series of slot-milling experiments. The main research contents include two parts, one is the effect of the externally excited vibration on milling force in milling process, and the other is the influence of milling and vibrating parameters matching on milling force value. Experimental results show that ultrasonic vibration can change traditional milling conditions, realize separate-type milling, obtain similar pulse-like profiles of cutting forces, reduce average cutting force value; and the peak value of the feed direction cutting force can also be greatly decreased by adopting reasonable vibration amplitude, an optimal combination of machining parameters is of great benefit to achieving small cutting force. According to the experimental findings, ultrasonic vibration-assisted milling is a prospective technology to achieve precision milling of small part.     

Time-dependent behaviour of clay-concrete interfaces with different contact surface roughnesses under shear loading

Mechanics of Time-Dependent Materials - Mechanical properties of the interface between a pile and soil greatly affect the bearing capacity of a pile. The creep of soil causes a long-term strength...     

Heat release in a gas flow at the junction of channels with different surface roughnesses

A measurement is made of the thermal polarization which develops in a gas flow in a nonuniform channel due to the dependence of the mechano-caloric heat flux on surface roughness.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 3, pp. 466–470, September, 1990.     

Optimization for friction welding parameters with multiple performance characteristics

Friction Welding is a variation of pressure welding method. Though some experience has already been accumulated in the industrial application of friction welding, achieving the optimal processing parameters is still a difficult task. This work is putting a step forward to achieve the best possible design. This paper presents an investigation on the optimization and the effect of welding parameters on multiple performance characteristics (tensile strength and the metal loss) obtained by friction welded joints. A plan of experiments based on the Taguchi method was designed. The output variables were the tensile strength and metal loss of the weld. These output variables were determined according to the input variables, which are the Heating Pressure (HP), Heating Time (HT), Upsetting Pressure (UP) and Upsetting Time (UT). The main objectives of this study are maximization of tensile strength and minimization of metal loss. By statistical analysis, an optimal level of combination of processing parameters is achieved. To validate the optimization, experience were conducted at optimum parameters.     

Laser surface modification of UNS S31603 stainless steel. Part II: cavitation erosion characteristics

Austenitic stainless steel UNS S31603 was laser surface alloyed with various elements (Co, Ni, Mn, C, Cr, Mo, Si) and alloys/compounds (AlSiFe, Si₃N₄ and NiCrSiB) as presented in Part I together with the microstructures and the corrosion characteristics of the alloyed specimens. In Part II, the cavitation erosion characteristics of the alloyed specimens in 3.5% NaCl solution at 23°C were studied by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 μm. The hardness profile and the compositional profile of the alloyed layers were investigated by a Vickers hardness tester and by EDX respectively. The cavitation erosion resistance of specimens alloyed with AlSiFe, C and NiCrSiB were highest, reaching 11.1, 10.5 and 7.9 times that of the substrate respectively. The damage mode was identified to be ductile fracture for specimens containing austenite as the major phase, and brittle fracture when the major phase was ferrite or intermetallic. Cavitation erosion was initiated at the phase boundaries where there was an abrupt change in mechanical properties (e.g. hardness) and then propagated into the weaker phase. It was also noted that large improvement in cavitation erosion resistance and corrosion resistance could not be simultaneously achieved in the present study.     

C2680黄铜箔微弯曲回弹规律研究

微型化导致微弯曲变形与宏观弯曲有明显差异.研制了一套三点微弯曲模具,并基于CMT8502型微机控制电子万能试验机平台,使用C2680黄铜箔进行三点微弯曲正交实验,获得了一系列三点微弯曲力和冲头位移曲线.研究表明,坯料厚度越小,弯曲半径越大,相对厚度越大时,回弹量越大.在本试验中,坯料厚度对回弹的影响最明显,其次是相对厚度,弯曲半径对回弹的影响程度最小.     

A comparative analysis of copper and brass surface films in contact with tap water

A study of the surface oxide films naturally grown on copper and brass in contact with drinkable water is presented. The investigation focuses on the influence of Zn as alloying element on the corrosion resistance of brass. Artificial tap water, employed as electrolyte, simulates a practical application of these materials. The surface films were grown at open circuit potential for 2 and 192 hours. Diverse in-situ techniques such as cyclic voltammetry, polarization curves, electrochemical impedance spectroscopy and UV-Vis reflectance spectroscopy were employed. Even when the surface layer is mainly composed of cuprous oxide, Zn(II) species are incorporated in the surface film grown on brass. At longer ageing times, the thickness increases, without affecting the composition of the surface films. The corrosion current was calculated for both materials using various techniques. The corrosion current density and the anodic currents in the polarization curves decreased as the ageing time increased, particularly in the case of brass. This improvement in the performance of the film on brass can be attributed to the incorporation of Zn(II) species into the surface layer, particularly as the film consolidates at longer times.     

Surface damages and tool wear mode in end milling of hastelloy‐C276 under dry and wet conditions

Hastelloy‐C276 is a nickel based superalloy that is widely used in chemical, petro‐chemical, environmental and nuclear industries due to its outstanding performance in a wide range of corrosive mediums. The superior properties of nickel based superalloys impair their machinability which increases the difficulty in obtaining a good surface finish. Because most of the components' failures are initiated from surface defects, several researchers have been concerned about surface integrity in machining aerospace superalloys particularly Inconel‐718. Due to the lack of studies done on machining corrosion‐resistant superalloys, this study aims to investigate surface damages and tool wear modes in milling Hastelloy‐C276 under dry and wet conditions. The absence of cooling and lubricating actions in dry machining resulted in the formation of craters, severe plastic deformation, voids, debris re‐deposition and materials drag. The breakage of the nucleated carbide phases resulted in the formation of nucleated cavities on the machined surface in both wet and dry machining. Adhesive tool wear was less in dry machining due to the formation of oxide layers on tool faces which suppressed the formation of built‐up edges due to the weak adhesion properties of oxide compounds which resulted in less surface roughness at v_c = 50 m/min. On the other hand, the higher temperature and friction in dry machining resulted in severer tool coating delamination.     

On-line condition monitoring of tool wear in end milling using acoustic emission

The monitoring of tool wear is important in maintaining the quality of workpieces produced. This paper presents a methodology to monitor on-line tool wear in end milling using acoustic emission. It is well known that the root-mean-square (RMS) value of the acoustic emission is directly proportional to the power expended in turning. A mathematical model has been developed to predict the RMS value of the acoustic-emission signal in milling. This mathematical model incorporates the machining parameters as variables. The accuracy of the model has been verified by a series of experiments. The experiments were carried out on a Bridgeport milling machine and data was collected and analysed by using an on-line computer data acquisition system. A comparison of the experimental and theoretical RMS values indicates a very good agreement between them. A control strategy similar to the moving average/moving range charts has been developed for monitoring on-line tool wear. The limits for the control charts were obtained from the theoretical equation of statistical quality control. An observation of the control charts clearly indicates the region of tool failure and the time at which the tool failed. The philosophy behind the use of control charts is based on the ease of implementation and widespread use in industry.     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Analysis and control/monitoring of the direct linear drive in end milling

To meet the requirements of higher speeds, greater accuracies and improved reliability, direct linear drives are increasingly employed in new machine tools. In this paper, the modelling, control and monitoring of a direct linear drive for end milling are studied. First, a direct linear drive and its advantage are addressed; then, a dynamical model of the direct drive for end milling is proposed. Second, the friction and damping characteristic of the guideways and its relation to axis velocity and temperature as well as the cogging force of the drive resulting from the interaction of the primary (active) and secondary (passive or stator) part are analysed in detail. Third, possibilities to improve the motion behaviour of the direct linear drive by compensation of disturbances, friction and cogging forces are discussed, and a self-adjusting compensation controller and a state-space controller are proposed. Finally, a practical case demonstrates that the high-frequency cutting force can be tracked by the linear motor current. Then a tool breakage monitoring method by sensing linear motor current with a smoothing non-linear energy operator is proposed and tested with the practical case.     

Optimization of burnishing parameters and determination of select surface characteristics in engineering materials

The present study is aimed at filling the gaps in scientific understanding of the burnishing process, and also to aid and arrive at technological solutions for the surface modifications based on Burnishing of some of the commonly employed engineering materials. The effects of various burnishing parameters on the surface characteristics, surface microstructure, micro hardness are evaluated, reported and discussed in the case of EN Series steels (EN 8, EN 24 and EN 31), Aluminum alloy (AA6061) and Alpha-beta brass. The burnishing parameters considered for studies principally are burnishing speed, burnishing force, burnishing feed and number of passes. Taguchi technique is employed in the present investigation to identify the most influencing parameters on surface roughness. Effort is also made to identify the optimal burnishing parameters and the factors for scientific basis of such optimization. Finally, a brief attempt is made to construct the Burnishing maps with respect to strength level (in this case, average micro hardness of unburnished material).     

Experimental study on the meso-scale milling of tungsten carbide WC-17.5Co with PCD end mills

Tungsten carbide is a material that is very difficult to cut, mainly owing to its extreme wear resistance. Its high value of yield strength, accompanied by extreme brittleness, renders its machinability extremely poor, with most tools failing. Even when cutting with tool materials of the highest quality, its mode of cutting is mainly brittle and marred by material cracking. The ductile mode of cutting is possible only at micro levels of depth of cut and feed rate. This study aims to investigate the possibility of milling the carbide material at a meso-scale using polycrystalline diamond (PCD) end mills. A series of end milling experiments were performed to study the effects of cutting speed, feed per tooth, and axial depth of cut on performance measures such as cutting forces, surface roughness, and tool wear. To characterize the wear of PCD tools, a new approach to measuring the level of damage sustained by the faces of the cutter's teeth is presented. Analyses of the experimental data show that the effects of all the cutting parameters on the three performance measures are significant. The major damage mode of the PCD end mills is found to be the intermittent micro-chipping. The progress of tool damage saw a long, stable, and steady period sandwiched between two short, abrupt, and intermittent periods. Cutting forces and surface roughness are found to rise with increments in the three cutting parameters, although the latter shows signs of reduction during the initial increase in cutting speed only. The results of this study find that an acceptable surface quality (average roughness R_a<0.2 μm) and tool life (cutting length L>600 mm) can be obtained under the conditions of the given cutting parameters. It indicates that milling with PCD tools at a meso-scale is a suitable machining method for tungsten carbides.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00298-y     

Modeling of flow and debris ejection in blasting erosion arc machining in end milling mode

Blasting erosion arc machining (BEAM) is a typical arc discharge machining technology that was developed around 2012 to improve the machinability of difficult-to-cut materials. End milling BEAM has been successfully developed and preliminarily applied in industry. However, owing to the high complexity of the flow field and the difficulty of observing debris in the discharge gap, studies of the flow and debris in end milling BEAM are limited. In this study, fluid dynamics simulations and particle tracking are used to investigate the flow characteristics and debris ejection processes in end milling BEAM. Firstly, the end milling BEAM mode is introduced. Then the numerical modeling parameters, geometric models, and simulation methods are presented in detail. Next, the flow distribution and debris ejection are described, analyzed, and discussed. The velocity and pressure distributions of the axial feed and radial feed are observed; the rotation speed and milling depth are found to have almost no effect on the flow velocity magnitude. Further, debris is ejected more rapidly in the radial feed than in the axial feed. The particle kinetic energy tends to increase with increasing milling depth, and smaller particles are more easily expelled from the flushing gap. This study attempts to reveal the flow field properties and debris ejection mechanism of end milling BEAM, which will be helpful in gaining a better understanding of BEAM.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00328-9     

Experimental investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel

Milling of hardened steel generates excessive heat during the chip formation process, which increases the temperature of cutting tool and accelerates tool wear. Application of conventional cutting fluid in milling process may not effectively control the heat generation also it has inherent health and environmental problems. To minimize health hazard and environmental problems caused by using conventional cutting fluid, a cryogenic cooling set up is developed to cool tool–chip interface using liquid nitrogen (LN₂). This paper presents results on the effect of LN₂ as a coolant on machinability of hardened AISI H13 tool steel for varying cutting speed in the range of 75–125 m/min during end milling with PVD TiAlN coated carbide inserts at a constant feed rate. The results show that machining with LN₂ lowers cutting temperature, tool flank wear, surface roughness and cutting forces as compared with dry and wet machining. With LN₂ cooling, it has been found that the cutting temperature was reduced by 57–60% and 37–42%; the tool flank wear was reduced by 29–34% and 10–12%; the surface roughness was decreased by 33–40% and 25–29% compared to dry and wet machining. The cutting forces also decreased moderately compared to dry and wet machining. This can be attributed to the fact that LN₂ machining provides better cooling and lubrication through substantial reduction in the cutting zone temperature.     

Carburising behaviour of low carbon steel with nanocrystalline surface layer induced by ball milling

Abstract

Ball milling, as a surface nanocrystallisation method, was employed to investigate the influence of severe plastic deformation on the carburisation treatment performed on low carbon steel. The results indicated an enhancement in the carburisation efficiency as a result of surface milling. This enhancement was attributed to the formation of a nanocrystalline layer in the surface of the treated samples. It was found that the main reasons for the accelerated kinetics of the carburisation process would be the considerable amounts of non-equilibrium defects and the finer austenite grains in the early and later stages of the treatment respectively, which facilitate the carbon diffusion.     

Effect of fiber orientation on surface microscopic characteristics of surface grinding of unidirectional C/SiC composites

Ceramic matrix composites have complex structures. For exploring the impact factors of machined surface quality and material removal mechanism, its internal structure must be decoupled, and then a unidirectional C/SiC composite was designed and fabricated in this paper. Through a series of representative surface grinding experiments, the machined surface of the composites was characterized by 3D profile test, and the microscopic characteristics and material removal mechanism of the grinding surface were discussed in detail. The results showed that the fiber orientation had a significant effect on the surface quality, and the order of 3D surface roughness was longitudinal > normal > transverse. On the basis of the systematic analysis of the microscopic characteristics of the machined surface, the brittle fracture was the dominant form of material removal in grinding process. Further, combined with 3D surface profile and surface micromorphology, the effect of fiber orientation on the removal mechanism of composites was revealed. The results not only enrich the machinability and improve the surface quality of unidirectional C/SiC composites, but also provide some guidance for grinding of the woven composites.     

进给速度对不同纤维方向CFRP铣削表面形貌的影响

采用金刚石涂层硬质合金铣刀对0°、45°、90°、135°4种纤维方向的碳纤维增强复合材料(CFRP)进行了顺铣加工试验。通过对铣削力和加工表面形貌的对比,分析了纤维方向和每转进给量对加工表面质量的影响。结果表明:主切削力随着每转进给量的增大而增大,0°方向纤维受到的主切削力最大,90°方向纤维受到的主切削力最小;0°方向纤维表面破碎树脂与纤维的残留随着每转进给量的增大而增多,135°方向纤维表面树脂粘附逐渐减小;90°方向纤维表面会有大小不同的微坑,同时在样件上、下表面易产生分层缺陷,45°方向纤维表面多呈现沟槽或波浪形形貌。     

仿生表面减磨特性的数值模拟研究

为探究颗粒冲蚀作用下的仿生表面减磨特性,基于沙漠蝎表面抗蚀结构,确定凹槽、凸包和凹槽+凸包3种形式的仿生表面,采用数值模拟方法计算其磨损率分布规律,并分析仿生结构对流场和颗粒场的影响.结果表明:在颗粒入射角小于70°时,3种仿生表面均有减磨效果,其中凹槽结构减磨效果显著,但凹槽表面两侧磨损率略微增大,引入凸包结构后磨损...