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  • Calibration of ductile fracture criterion from shear to equibiaxial tension using hydraulic bulge test
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-15
    Mohammad Javad Mirnia; Mostafa Vahdani

    Phenomenological ductile fracture criteria have defining parameters to be determined from experimental fracture tests. For a precise calibration of a ductile fracture criterion, fracture experiments should cover a wide range of stress states. To this end, sheet metal specimens with different geometries are tested using various experimental setups, such as uniaxial tension, Nakazima, and butterfly tests. Usually, a combination of these tests is performed to capture a wide range of stress states, which makes the calibration procedure more difficult and tedious. In contrast, in the present research, only the hydraulic bulge test with a circular die is utilized to calibrate a ductile fracture criterion with three defining constants. To cover a wide range of stress triaxiality from the pure shear to the equibiaxial tension, circular blanks with different geometries are designed and developed with the aid of the finite element (FE) simulation. Among the presented geometries, there is an innovative specimen for reproducing the in-plane shear state using the hydraulic bulge test. In the present research, the ductile fracture of the AA6061-T6 aluminum alloy sheet is investigated. By comparing results of the FE modeling and the experiment of the hydraulic bulging, it is shown that the pressure, the bulging height, and the sheet thickness at the instant of fracture onset can be predicted with a reasonable accuracy by the ductile fracture model calibrated using the proposed test. Therefore, the designed specimens allow the hydraulic bulge test to be implemented for investigating the ductile fracture of sheet metals under a wide range of stress conditions.

    更新日期:2020-01-15
  • Control of residual stresses by roller leveling with regard to process stability and one-sided surface removal
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-15
    Markus Grüber; Lutz Kümmel; Gerhard Hirt

    Roller leveling is a widely used production process to eliminate the coil set from metal strips. Therefore, this process aims mainly on removing the sheet curvature, while the created residual stresses are not systematically adjusted. Nonetheless, a straight strip can possess a disadvantageous residual stress distribution leading to a curvature when cutting the strip into parts or when applying a one-sided surface removal. Thus, it is desirable to address both curvature removal and residual stress distribution by roller leveling. Therefore, a seven-roll levelling machine is investigated to check for possible degrees of freedom to address those two target values. A respective control concept is introduced employing the different load triangles of a leveling machine. In order to investigate the possibility to influence curvature as well as residual stresses, first a numerical parameter study is conducted. In particular, the influence of the three individual load triangles of such a machine on the resulting residual stresses is investigated. The first load triangle is used to set a defined overstretch to the outer sheet fiber and the center load triangle is used as an actuator on the residual stress distribution. In all cases, the last load triangle is able to provide a straight sheet after leveling. To check for the influence of the achieved residual stress distributions on subsequent production processes, investigations on process robustness as well as a one-sided surface removal are done. For both cases it is possible to define an optimized set of roll positions.

    更新日期:2020-01-15
  • A calculation model to predict the impact stress field and depth of plastic deformation zone of additive manufactured parts in the process of ultrasonic impact treatment
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-14
    Changping Zhou; Fengchun Jiang; De Xu; Chunhuan Guo; Chengzhi Zhao; Zhenqiang Wang; Jiandong Wang
    更新日期:2020-01-14
  • Optical surface generation on additively manufactured AlSiMg0.75 alloys with ultrasonic vibration-assisted machining
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-13
    Yuchao Bai; Zhuoqi Shi; Yan Jin Lee; Hao Wang

    Additive manufacturing technology provides a feasible solution to directly manufacture optical components with complex functional structure. However, the poor surface quality and low relative density result in the limitation on its rapid application. In order to overcome the above shortcomes, process optimization and ultrasonic elliptical vibration-assisted machining (UEVAM) were used in the fabrication of optical surfaces on selective laser melted (SLM) AlSiMg0.75 alloy. The optimised energy density in the SLM process was identified to range from 65 to 130 J/mm3 with the highest achievable relative density of 99.6%. Post-processing heat treatment changes the cellular/dendritic microstructure of as-built samples to an α-Al matrix embedded with Si particles, which reduces the microcutting forces by 27.67% and improves the machined surface roughness (Ra) by 8.7% during conventional microcutting. In contrast, the UEVAM process is capable of further improving the surface quality from 11.03 to 5.1 nm Ra, without heat treatment. Poor machined surface quality was attributed to the formation of oxide particles during the SLM process. Chip morphology analysis and finite element method simulations revealed the benefits of UEVAM in tackling the issue of precipitation and extends our understanding of the applications of UEVAM.

    更新日期:2020-01-13
  • Active Gap Capacitance Electrical Discharge Machining of Polycrystalline Diamond
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-13
    Xiangzhi Wang; Shuang Yi; Mark Easton; Songlin Ding

    This paper introduced a novel active gap capacitance electrical discharge machining (AGC-EDM) method for high efficiency machining of polycrystalline diamond. Graphene was used for the first time in an EDM process to increase the gap capacitance, which would result in enlarged inter-electrode discharge explosive force and higher processing stability. The new principle and machining mechanisms were introduced; an equivalent circuit model was established; and factors that affect the machining performance were analyzed. In order to valid the theory and assumptions and investigate the effectiveness of the new approach, EDM experiments and comparative study were conducted. Test results showed that discharge explosive force in the new AGC-EDM was increased dramatically and the machining process became more stable. The material removal rate in AGC-EDM was found to be more than 10 times higher than that of the normal EDM while the relative electrode wear was reduced by 70%.

    更新日期:2020-01-13
  • Internal characteristic of droplet and its influence on the underwater wet welding process stability
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-11
    Changsheng Xu; Ning Guo; Xin Zhang; Hao Chen; Yunlong Fu; Li Zhou

    Based on an X-ray imaging system, the characteristic of underwater wet welding droplets was revealed, which was deemed to be the essential factor contributing to the unstable underwater wet welding process. By observing the X-ray images, it is confirmed that the inflation-exhaustion process in the droplet occurred during the entire process from the droplet forming to entering into the molten pool. The void in the droplet leaded to lower gravity and greater repulsive force and deteriorated the welding process stability. On the one hand, the spatter-like droplet transfer mode was relatively easy to occur, increasing the frequency of the droplet repelled spatter. On the other hand, the arc easily broke and the arc stability was deteriorated. In addition, the droplet rupture process tended to promote the generation of gas escaping spatter. The process was effected by material gas solubility, the surface tension, the temperature according to the establishing force models.

    更新日期:2020-01-13
  • Modeling and identification of cutting forces in milling of Carbon Fiber Reinforced Polymers
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-11
    R. Mullin; M. Farhadmanesh; A. Ahmadian; K. Ahmadi

    Mechanistic cutting force models are commonly used to compute milling forces in terms of the machining parameters such as feedrate, axial, and radial depths of cut. In isotropic (e.g. metallic) materials, the parameters of mechanistic models are treated as constants that are identified using well-established experimental procedures. Mechanics of chip formation in anisotropic Carbon Fibre Reinforced Polymers (CFRP) varies depending on the fibre cutting angle, which continuously changes as the tool rotates in milling operation. To address this variation, a mechanistic model with parameters that depend on fibre cutting angle is proposed. Also, a new experimental method is presented to identify the parameters of the proposed model. The model parameters are assumed to be periodic functions of the fibre cutting angle, and the Fourier coefficients of the periodic function are identified from the milling forces measured during a set of milling operations at various feedrates and fibre orientations. The experimental validation of the presented force modelling approach confirms its accuracy to predict forces in milling of Unidirectional as well as Multi-directional CFRP.

    更新日期:2020-01-13
  • Microstructural Evolution Mechanism of Semi-solid Slurry: A Study Using Phase-Field-Lattice-Boltzmann Scheme
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-11
    Wenying Qu; Min Luo; Zhipeng Guo; Xiaogang Hu; Ang Zhang; Fan Zhang; Hongxing Lu; Yongzhong Zhang; Daquan Li

    The formation mechanism study of a spherical crystal is the theoretical basis for preparing high-quality semi-solid slurries with homogeneous spherical microstructure. The interaction between thermal-solute diffusion during solidification and solid-liquid interface migration determines the morphology evolution of microstructure according to the representation theory. Comprehensive research about the effects of local variates on the microstructural evolution of semi-solid slurry in a Representative Elementary Volume (REV) by 2D cases was conducted. A modified Phase-Field-Lattice-Boltzmann scheme using techniques of parallel computing and adaptive mesh refinement (Para-AMR) was adopted. Actual processing parameters were coupled with the numerical scheme. Mesoscopic results were upscaled by averaging them over the simulation domain. Five aspects, growth space, initial undercooling degree, cooling rate, natural convection, and forced convection, were investigated. It is found that the formation of spherical grain requires a specific initial undercooling degree, cooling rate, and nuclei density. Study results indicate that melt convection has little effect on the morphological evolution of grain in the case of rapid isotropic growth, which was verified by experiments using the SEED process. Besides, forced convection has a significant effect on the morphology evolution of grain controlled by solute diffusion, which provides a possibility of an extension of the process window about pouring temperature and alloys with narrow solidification range for preparing semi-solid slurries.

    更新日期:2020-01-13
  • Efficient process planning of laser peen forming for complex shaping with distributed eigen-moment
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-09
    Mingsheng Luo; Yongxiang Hu; Lan Hu; Zhenqiang Yao

    Laser peen forming (LPF) is a flexible forming process that brings many challenges for complex shaping. This study aims to develop an effective optimization method to complete efficient process planning of LPF to generate the desired geometry shape. The eigen-moment is proposed as a new intermediate variable to describe the bending deformation to relate the LPF process parameters and the geometry shape. The governing equation of eigen-moment is derived to characterize the bending deflection with a PDF equation. The numerical computation method is developed by the PDE weak form and finite element method to predict the bending shape. To achieve process planning of complex shaping, the distributed eigen-moment on both plate surfaces is prescribed, and a PDE-constrained optimization is utilized to define the process planning problem of LPF. Then, the eigen-moment field is optimized by adopting the interior-point algorithm to obtain the desired shape. The proposed eigen-moment is verified to be an intrinsic physical quantity to describe the bending behavior of LPF. A complex shape with saddle geometry is used as a typical case to demonstrate the process planning method. The experiments conducted with the planned LPF process parameters are validated to produce a shape consistent with the designed geometry.

    更新日期:2020-01-09
  • 更新日期:2020-01-07
  • Effects of high-pressure coolant on cutting performance of high-speed ultrasonic vibration cutting titanium alloy
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-07
    Zhenghui Lu; Deyuan Zhang; Xiangyu Zhang; Zhenlong Peng

    As a novel machining process, high-speed ultrasonic vibration cutting (HUVC) has been successfully applied for high-speed machining of titanium alloys recently. To sufficiently exploit its cutting advantage over conventional cutting (CC), advanced cooling method should be employed in HUVC. In this research, high-pressure coolant (HPC) was firstly introduced to HUVC process and its influences on cutting performance of HUVC titanium alloy were studied, including tool life and wear mechanism, surface quality, cutting temperature and cutting force. The results showed that when cutting speed is 400 m/min, the tool life in HUVC can reach 7.3 times of that in CC if HPC of 200 bar was applied. Besides, the machined surface quality in a successive cutting process in HUVC was significantly improved by applying HPC. In addition, the temperature in HUVC can be reduced for 55% at 300 m/min compared to CC. Furthermore, the analysis of wear mechanism showed that HUVC with HPC can successfully suppress the occurrence of adhesion wear.

    更新日期:2020-01-07
  • Modelling and analysis of generation mechanism of micro-surface topography during elliptical ultrasonic assisted grinding
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    Qiuyan Wang; Zhiqiang Liang; Xibin Wang; Shuowei Bai; Swee Hock Yeo; Shun Jia

    Elliptical ultrasonic assisted grinding (EUAG) is considered a promising technique for difficult-to-machine material grinding. However, it has yet to be fully developed because the topography generation mechanism of a workpiece surface evolved using EUAG has not been elaborately addressed. Compared with other conventional grinding parameters, the ultrasonic vibration parameters (amplitude and frequency) during EUAG are the most critical factors in the generation of the surface topography. However, it is difficult to tune such parameters freely during an experiment, owing to the technical restrictions of current ultrasonic vibrators. Further, a pass-by-pass analysis of the surface material removal process is not possible to achieve during an experiment. Thus, a 3D ground surface topography generation method is developed in this study, and the surface generation process of four typical ground surfaces are analysed based on the calculated results. The four typical ground surfaces are then machined on the monocrystal silicon workpieces. The experimental results agree well with the surface topography predictions, which validates the effectiveness of the topography model. The material removal mechanism under different ultrasonic vibration parameters during EUAG is explained in this study according to the simulated abrasive cutting trajectory and ground surface. This method has shown its powerful ability to conduct a pass-by-pass analysis of the grinding process. Further, it can be used for a future investigation into the grinding vibration, cutting chips, and forces, and is not limited to EUAG, but is also applicable to other machining processes.

    更新日期:2020-01-02
  • Joining aluminium profiles to composite sheets by additive manufacturing and forming
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    R.J.S. Baptista; J.P.M. Pragana; I.M.F. Bragança; C.M.A. Silva; L.M. Alves; P.A.F. Martins

    This paper explores the application of the ‘mortise-and-tenon’ concept for joining hollow section aluminium profiles to composite strips or sheets. Wire arc additive manufacturing is combined with joining by forming to fabricate the tenons and to obtain the mechanical interlocking with the mortises available in the strips (or sheets). The workability limits are established by means of an analytical model that combines plastic deformation, instability and fracture. Experimental and finite element modelling are utilized to develop the overall joining process and to validate the round ‘mortise-and-tenon’ design resulting from the analytical model. Pull-out and shear destructive tests are carried out to evaluate the overall strength of the joints and results allow concluding that the new joints can easily and effectively replace existing solutions based on welding, fastening or adhesive bonding. The proposed joining process also circumvents the need to design extra fixing and interlocking features in low cost hollow section aluminium profiles for easy assembling.

    更新日期:2020-01-02
  • Influence of reinforcing particle distribution on the casting characteristics of Al-SiCp composites
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    Xinliang Yang; Nilam S. Barekar; Shouxun Ji; Brij K. Dhindaw; Zhongyun Fan

    SiC particulate reinforced A356 alloy metal matrix composites (MMCs) are synthesized using intensive melt shearing. The effect of reinforcing particle distribution on the fluidity of cast A356/10 vol.% SiCp composites is studied. Spiral length representing the fluidity of the composite melt was measured and liquid flow and solidification behaviour were analysed. Improvement in the fluidity of composites is attributed to the uniform distribution of reinforcing particles by intensive melt shearing treatment. From the casting performance point of view, uniform dispersion of reinforcing particles achieved with the aid of intensive shearing improves the mechanical properties of A356/10 vol.% SiCp cast composites. Improved strength, rigidity and wear resistance of composites is attributed to the bulk homogeneity, significantly reducing casting defects.

    更新日期:2020-01-02
  • Joining Mechanism of Bulk Metallic Glasses in their Supercooled Liquid Region
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    Qi Peng; Yiling Xie; Bo Zhu; Wen Chen; Jan Schroers; Mingxiang Chen; Ze Liu
    更新日期:2020-01-02
  • Hyperplasticity mechanism in DP600 sheets during electrohydraulic free forming
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    Qiuli Zheng; Haiping Yu

    This work discussed the multi-scale mechanisms of hyperplasticity during the high strain rate electrohydraulic forming (EHF) process by exploring the formability of DP600 sheets in a state of uniaxial tensile stress. The experimental results showed that the limit strains and limit dome heights of the deformed specimens obtained by EHF were improved by 15%-27% and 22.54%, respectively, as compared with quasi-static specimens, showing a hyperplasticity characteristic. The inertial effects that occurred during the EHF process were responsible for the macro-scale enhancement in terms of formability, which could generate an additional principal stress along the direction of stretching that slowed the velocity gradient of the necked elements to restrain uneven deformation, resulting in a 60% broadening of the action zone of maximum Y-displacement. The proportion of inertial effects that contributed to the plastic deformation of the deformed specimens was 87.1%, indicating that the vast majority of the deformation in the EHF process occurred as a result of inertial effects after the electrical energy was completely discharged. A larger dislocation density and a more uniform dislocation distribution were observed in the EHF specimens, which were regarded as the micro-scale causes of the hyperplasticity in the EHF process. Multiplication and entanglement of dislocations caused by the significant shear stress, together with the extensive nucleation of new dislocations caused by the high strain rates, demonstrated the micro-scale mechanism of hyperplasticity during EHF.

    更新日期:2020-01-02
  • Improvement in mechanical, thermal conductivity and corrosion performances of a new high-thermally conductive Al-Si-Fe alloy through a novel R-HPDC process
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2020-01-02
    Mingfan Qi; Yonglin Kang; Jingyuan Li; Beiyan Shang

    A low-cost, new casting Sr-modified Al-7.5Si-0.8Fe alloy with high-thermal conductivity was prepared into large thin-wall heat-dissipating shells for 5 G communication base stations using a traditional high pressure die-casting (HPDC) process and a rheological HPDC (R-HPDC) technique. Their microstructure, tensile property, hardness, thermal conductivity, and corrosion behavior were analyzed. The R-HPDC Al-7.5Si-0.8Fe alloy shows a refined microstructure in terms of α1-Al particles, α2-Al grains, fibrous β-Al5FeSi, and granular eutectic silicons when compared to traditional HPDC alloys. The R-HPDC alloy has a thermal conductivity, elongation-to-failure value, ultimate tensile strength, yield strength, and Vickers hardness of 186 W/(m.K), 12.4%, 235 MPa, 114 MPa, and 70 HV, respectively. These values are respectively 6%, 91%, 22%, 14%, and 11% higher than those reported for conventional HPDC alloys. Moreover, the R-HPDC Al-Si-Fe alloy shows a superior corrosion resistance in comparison to HPDC alloys. This observation is supported by scanning Kelvin probe (SKP) measurements and electrochemical tests. The improved performances arise mostly from the refinement of the iron-rich intermetallics (β-Al5FeSi) and eutectic silicons, the increase in the area proportion of α2-Al grains relative to eutectic silicon, and the reduction in the potential difference between the aluminum matrices and the iron-rich intermetallics.

    更新日期:2020-01-02
  • AgrawalResidual stress inclusion in the incrementally formed geometry using Fractal Geometry Based Incremental Toolpath (FGBIT)
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-27
    Harish Kumar Nirala; Anupam Agrawal

    Single Point Incremental Sheet Forming (SPISF) is a well-known flexible alternative to conventional generative manufacturing processes. In SPISF, the geometry to be formed is fragmented into series of 2D slices and the plastic deformation is achieved through layer by layer movement of a Numerically Controlled (NC), hemispherical or ball end forming tool. The whole plastic deformation is the sum of all localized strains developed during each increment. Spiral, constant z incremental toolpaths, and their variants are common conventional toolpaths for SPISF. Several researchers have investigated these toolpaths extensively. Fractal Geometry Based Incremental Toolpath (FGBIT) is a recently developed toolpath for SPISF that improves the process formability and stress distribution. Unlike conventional toolpaths, FGBIT deforms the base region of the formed geometry which induces work hardening and residual stresses into the work piece. This may lead to the forming of high strength components. The residual stress distribution over the base region of the formed component (square cup) has been investigated in this study. Further, a comparison based on residual stress distribution between FGBIT and conventional incremental toolpaths is presented. Residual stresses have been measured by using nanoindentation technique. Pile up generation near the periphery of the indent is investigated for conventional and FGBIT based toolpaths. It has been observed from the experimental results that, the strength of the formed component increases due to induced compressive surface residual stresses while using FGBIT hence, metal components with high fatigue life and better strength-to-weight ratio can be formed.

    更新日期:2019-12-27
  • Development of an aluminum compound casting process - experiments and numerical simulations
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-26
    Stefan Heugenhauser; Erhard Kaschnitz; Peter Schumacher

    The casting of liquid melt on a preheated substrate layer to produce a metallurgical compound represents a direct approach towards clad aluminum strips. To investigate this direct process route and the formation of a metallurgical bond at the interface, a small-scale pilot plant to cast pure aluminum on strips of aluminum alloy 7075 under controlled conditions was developed. Composite casting plates were produced at varying casting parameters (preheating temperature of the substrate, clad layer thickness, casting speed, melt temperature) and subsequently analyzed by metallographic means to classify the bond quality. Suitable thermal conditions for the melt flow in the casting device were found by numerical simulation using a commercial fluid flow and solidification software package. Additional meso- and micro-modeling of the casting and the bonding zone supported the understanding of the bonding mechanism. The heat transfer in the macro-model of the casting device was calibrated using measured temperatures obtained during compound casting experiments. A finer meshed two-dimensional meso-model of the casting device was derived from the macro-model to gain more accurate information about the temperature distribution in the vicinity of the bonding zone. This interface between the pure aluminum and the aluminum alloy was modeled in extremely high temporal and spatial resolution (micro-model) as temperatures are not accessible there by direct measurements. These simulation results show the time-resolved re-melting and re-solidification of the aluminum alloy during compound formation. The obtained simulation results correlate very well with electrochemically etched cross sections of cast bilayer aluminum strips. The experiments show that the oxide layer at the interface has to be removed completely during the casting process to obtain high quality compounds. The assumed mechanism of detachment and transport of the fractured oxide is shown schematically and necessary thermo-mechanical conditions for the removal of the oxide skin are discussed.

    更新日期:2019-12-27
  • Multi-mode distortion behavior of aluminum alloy thin sheets in immersion quenching
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-26
    Z.X. Li; M. Zhan; X.G. Fan; X.X. Wang; F. Ma; R. Li

    Aluminum alloy thin sheets are widely used to produce light-weight high-strength components and the sheets are generally quenched before forming (Q-F) to improve the final mechanical properties of components. However, the distortion in quenching will significantly affect the quality and stability of the following forming process. In this study, the distortion behavior of 2219 aluminum alloy thin sheets and its forming mechanism in quenching process were investigated through experiments and finite element analysis (FEA). The results indicate that, the quenched thin sheets basically present three distortion modes, namely saddle-shape, shovel-shape and arch-shape. The distortion modes of the quenched thin sheets are determined by the bending modes of distortion zone which is the zone of the thin sheet near the water surface. When the bending mode is one-half sine wave, the quenching thin sheets always show saddle-shape. However, for the cases where the bending mode changes to three-half sine wave and the bending of distortion zone is suppressed, the quenching thin sheets show shovel-shaped and arch-shaped distortion modes, respectively. The reasons behind the variations of the bending mode are finally analyzed based on a buckling criterion under laterally constrained conditions. These results will provide an in-depth understanding of quenching distortion behavior and lay a basic guidance for controlling the distortion of thin sheets in quenching process.

    更新日期:2019-12-27
  • Deformation characteristics and surface generation modelling of crack-free grinding of GGG single crystals
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-26
    Chen Li; Yueqin Wu; Xuliang Li; Lianjie Ma; Feihu Zhang; Han Huang

    Gallium gadolinium garnet (GGG) single crystals are the primary host material for making the high-power solid-state lasers. GGG single crystals are difficult-to-machine materials due to their high hardness and brittleness. Ultra-precision grinding experiments of GGG crystals was carried out, which generated the ground surface and subsurface free of brittle fracture and cracks. The TEM examination demonstrated that the plastic formation of GGG crystals induced by ultra-precision grinding was dominated by the slippage of (114) crystal planes, as well as nanocrystallization and amorphization. Morphology and roughness of the ground surfaces were measured by AFM. A theoretical model was developed for predicting the surface morphologies and surface roughness by considering the random distributions of the radius, location and protrusion height of abrasive grits. The simulated results were found to be in good agreement with the experiment. This model is thus useful for understanding the effect of material deformation and removal on the surface finish in ultra-precision grinding of hard and brittle crystals, and can provide meaningful guidance for optimizing the process parameters of grinding of hard and brittle crystals.

    更新日期:2019-12-27
  • Inverse identification of the work hardening law from circular and elliptical bulge tests
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-23
    A.F.G. Pereira; P.A. Prates; M.C. Oliveira; J.V. Fernandes

    An inverse identification strategy is proposed to characterize the hardening behaviour of metal sheets up to high strains, regardless of the material anisotropy. The Levenberg-Marquardt method is used to minimize the gap between the experimental and numerical, pressure vs. pole height curves, of bulge tests with circular and elliptical dies, by iteratively updating the work hardening and the Hill’48 parameters of the numerical model. The optimization of the Hill’48 parameters is used only to ensure that the yield surface is conveniently described in a region close to the stress paths that occur in the circular and elliptical bulge tests, in order to improve the identification of the hardening parameters. The strategy aims to be accurate and simple from an experimental point of view, using only the results of pressure vs. pole height. The results are compared with those of the membrane theory procedure standardized in ISO 16808 (2014) and experimentally validated for two materials, DP600 steel and Al5754 aluminium alloy. For anisotropic materials, the proposed methodology represents a clear improvement when compared to the membrane theory procedure since it avoids the equibiaxial stress state assumption.

    更新日期:2019-12-23
  • Theoretical and experimental analysis of material removal and surface generation in novel fixed abrasive lapping of optical surface
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-23
    Bin Lin; Xiang-Min Jiang; Zhong-Chen Cao; Tian Huang; Kai-long Li

    Fixed abrasive machining, which overcomes the lack of determinacy and efficiency of current loose abrasive polishing or lapping processes, is an alternative technology for fabricating large-aperture aspheric surfaces with high finishing efficiency and high-quality surface finish. A novel fixed abrasive lapping (NFAL) tool, which combines computer-controlled optical surfacing and conventional fixed abrasive lapping process, is introduced in this study to produce off-axis aspheric surfaces efficiently while surface state is controlled and subsurface damage (SSD) is avoided. The removal mechanism analysis shows that fused quartz glass is primarily removed in ductile regime and the SSD depth is 14.7 μm when the tool load is 25 N. The material removal volume is linear with the machining time under the ductile removal mode. The material removal and surface generation models are developed on the basis of the calculation of the spatial distribution of abrasive particles, the pad–particle–workpiece interactions, the single-particle abrasion mechanism, and the linearly cumulative removal of surface generation in the NFAL process. The models are verified through a series of spot and surface lapping experiments. Results show that the theoretical model can be successfully used to predict and optimize the NFAL process. The spot lapping experiments indicate that the material removal volume is linear with the rotation speed, and the maximum depth is limited to the specific value that depends on the stiffness of lapping tool. The surface roughness Ra and Rz values of the measured and simulated surface data decrease with the increase in feed rate and increase with the increase in raster spacing. The power spectral density analysis indicates that high feed rate can distinctly improve the high-frequency errors, and the selection of the raster spacing can principally affect the low-frequency and middle-spatial frequency errors.

    更新日期:2019-12-23
  • Al-NiO Energetic Composites as Heat Source for Joining Silicon Wafer
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-23
    Hongtao Sui; Nazmul Huda; Zhikang Shen; John Z. Wen

    Silicon wafers with the thickness of approximately 250 μm were joined successfully using Al/NiO nano-thermite composites and with an aluminum foil interlayer (thickness of 30 μm), due to energy production from the exothermic reaction between Al (40 nm) and NiO (50 nm) powders. This reaction heat was subsequently transferred across the silicon wafer and reached the Si-Al-Si interface. This joining method reduces the possibility of introducing unwanted impurity and residual from the thermite reaction and subsequently improves the joint quality. Experimental data shows, adding Al micro-powder (5 μm, 60% by mass) or Ni micro-powder (1 μm, 30% by mass) into the nano-thermite composite was necessary and effective in joining the silicon wafer. The micro-hardness of the joined zone was measured as 129.3 ± 15.5 HV and 42.3 ± 4.0 HV for the Al and Ni micro-powder modified nano-thermite composites, respectively. The localized yield strength data confirmed the Al micro-powder produced a higher yield strength (350.6 ± 17.8 MPa) than the Ni micro-powder (327.1 ± 55.0 MPa). Energy production from the nano-thermite composites with different mixing ratios with the additive was characterized by Differential Scanning Calorimetry (DSC), and the apparent activation energy of the respective thermite reaction were calculated to investigate the effects of reaction kinetics to the joining process. The reduced joint quality produced by the Ni micro-powder modified Al/NiO nano-thermite composite was due to the low energy release from its thermite reaction (1.06 kJ/g), which was not sufficient to melt the silicon wafer. Moreover, the large activation energy of this thermite reaction (696.09 kJ/mol) hindered the joining process. In contrast, the Al micro-powder modified Al/NiO nano-thermite composite, via a two-step energy release process, produced sufficient energy (1.89 kJ/g) which led to a superior joint quality. In the first step, a pilot reaction (corresponding to the activation energy of 332.96 kJ/mol) between Al (40 nm) and NiO (50 nm) nanoparticles was dominant. In the following step, the reaction between Al micro-powder (5 μm) and NiO (50 nm) nanoparticles became significant and contributed greatly to successful joining.

    更新日期:2019-12-23
  • Classification of weld penetration condition through synchrosqueezed-wavelet analysis of sound signal acquired from pulse mode laser welding process
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-23
    M.F.M. Yusof; M. Ishak; M.F. Ghazali

    Monitoring weld condition using acoustic method is quite challenging due to some factors, hence the importance to further explore the use of signal analysis method not only to diminish the effect of noise, but more importantly, to obtain a distinct correlation with weld condition. The main goal of this work is to determine the significance of the feature extracted from synchrosqueezed-wavelet analysis in classifying sound signals that derived from varied weld penetration conditions. In achieving the aim, sound signal was acquired during pulse mode laser welding process with variation in peak power and pulse width that produced half penetration and full penetration weld joints. The trends of time domain, frequency domain, and wavelet analysis features of the acquired sound from half and full penetration welds were compared prior to the support vector machine (SVM) classification analysis. The comparison between all the features displayed a clear distinction in signals between half and full penetration welds for the case of features extracted from synchrosqueezed-wavelet analysis. In SVM binary classification analysis, the use of same feature as input recorded 96.94% of average classification accuracy, which appeared to be the highest. Additionally, comparison with band power, exhibited 27.7% improvement in classification precision. From these findings, it is concluded that the use of features extracted from synchrosqueezed-wavelet analysis as input for classification of sound signals from various penetration conditions is indeed significant. This work contributes to an alternative way in dealing with random sound signals in view of developing an efficient weld penetration monitoring system in future.

    更新日期:2019-12-23
  • MANUFACTURING HYBRID BUSBARS THROUGH JOINING BY FORMING
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-23
    J.P.M. Pragana; R.J.S. Baptista; I.M.F. Bragança; C.M.A. Silva; L.M. Alves; P.A.F. Martins

    This paper focus on the production of hybrid busbars made from copper and aluminium by means of a joining by forming process that was recently developed by the authors. The process involves the combined use of partial cutting and bending with form-fit joining by compression in the direction perpendicular to strip thickness. The resulting joints are flat with the plastic deformed materials enclosed within the thickness of the overlapped strips. Design is performed by means of an analytical model and the overall manufacturing concept is validated through numerical and experimental modelling. Major process parameters are identified and their influence on the overall deformation mechanics and joining feasibility is investigated. The effectiveness and performance of the new joints is analysed by means of tensile-shear loading tests. Results show that joining by forming can be successfully utilized to produce form-fit joints with good shear forces in hybrid busbars for electrical applications.

    更新日期:2019-12-23
  • Current-independent metal transfer by utilizing droplet resonance in gas metal arc welding
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-19
    Xiaochao Zhang; Hongming Gao; Guangjun Zhang

    Separate control of heat input and metal transfer is an essential way to resolve the contradiction between low heat input and stable metal transfer in GMAW, to meet the possible requirement from different welding tasks, e.g., the thin plate welding. To this end, the resonance of the pendant droplet excited by mechanical means is utilized to achieve current-independent metal transfer at any reasonably low current that can sustain the arc. The natural frequency of the pendant droplet decreases with the rise of the droplet size. When the natural frequency declines to close to the excitation frequency with the droplet growth, resonance occurs, and the oscillation amplitude of the droplet increases significantly. In the resonant region, the downward inertial force resulting from the downward moving droplet induces the drop detachment in advance, resulting in much faster metal transfer and smaller detached drop diameter compared with conventional GMAW with the same welding parameters. The improved metal transfer process leads to an enhancement of the continuity and uniformity of the bead formation.

    更新日期:2019-12-19
  • Characterizing the back stress of ultra-thin metallic sheet via pre-strain tension/bending process
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-18
    Rui Zhang; Zhutian Xu; Yujun Deng; Linfa Peng
    更新日期:2019-12-19
  • Study on electroless composite plating for an Ni-P bond micro diamond wheel
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-18
    Tianfeng Zhou; Yupeng He; Qian Yu; Zhiqiang Liang; Shidi Li; Xiaohua Liu; Xiaobin Dong; Xibin Wang

    In this paper, nickel phosphorous diamond (Ni-P-D) composite plating is introduced as a new method to fabricate a micro diamond wheel with a diameter of φ450 μm. In the fabrication process, the steel substrate (SKD-11) is first ground to a ball end shape with a radius of 200 μm. Nickel phosphorous (Ni-P) and micro diamond particles with an average grain size of 3.5 μm are then electrolessly plated on the steel substrate tip, with a final plating thickness of approximately 25 μm. Parameters of the Ni-P-D plating conditions, including substrate rotation, stirring speed, and diamond grain density are then investigated. The topography of the micro wheel shows that diamond grains as the reinforced phase are embedded omnidirectionally and uniformly in the Ni-P plating along both the surface direction and the thickness direction. Energy dispersive spectrometer (EDS) results indicate that the ratio of diamond grains is approximately 27 wt%, and the Ni-P plating layer is an alloy in the amorphous state. Once fabricated, the micro diamond wheel performance is tested by grinding microgrooves on single crystalline silicon. The machined microgroove has a surface roughness of Ra 26 nm without obvious cracks. Micro tool wear after grinding proves that the bonding strength between diamond grains and Ni-P alloy, as well as the adhering strength between the Ni-P plating and steel substrate, are strong enough to meet the requirements of the micro grinding wheel.

    更新日期:2019-12-19
  • Experimental investigation and finite-element modeling of the short-time induction quench-and-temper process of AISI 4140
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-17
    D. Kaiser; J. Damon; F. Mühl; B. de Graaff; D. Kiefer; S. Dietrich; V. Schulze

    Induction hardening is a widely used surface treatment technique that has extensively been investigated. In contrast, induction tempering with short heating times ≤1 s has not been investigated thoroughly, nor by experiment neither by simulations. Also, the influence of rapid tempering on the residual stresses after induction surface hardening has only been investigated superficially. Induction quench and temper experiments were performed, both with heating times ≤1 s. A significant change of the residual stress state was observed, leading to a shift from compressive to tensile residual stresses in the surface layer. A multiphysical FE-model for the whole quench-and-temper process has been developed and validated. A good agreement with the experiments for the relevant mechanical properties hardness and residual stress could be achieved. The recently reported transformation induced plasticity during tempering has been found to play a key role in the development of residual stresses during tempering. The simulations further indicate that conventional heat treatment leads to more favorable residual stress states after tempering to a prescribed surface hardness. By accounting for tempering processes during austenitization, the hardening simulation could be generalized to different initial states and allows for the prediction of hardness minima in the transition zone.

    更新日期:2019-12-18
  • Two-step electropolishing of 316L stainless steel in a sulfuric acid-free electrolyte
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-17
    Wei Han; Fengzhou Fang

    The study is to electropolish 316 L stainless steel in a sulfuric acid-free electrolyte, consisting of phosphoric acid, glycerol and distilled water instead of the widely used sulfuric acid-based electrolyte. The influence of water concentration in the electrolyte on the electropolishing characteristics was investigated from the polarization curve, material removal rate and surface roughness Ra. It is confirmed that the limiting current density increases with increasing the water concentration, resulting in a high material removal rate. However, the surface roughness Ra increases because the electropolishing effect is lowered. The surface characteristics were analysed by X-ray photoelectron spectroscopy, and the mechanical properties were studied by nanoindentation. A two-step electropolishing method was proposed to enhance the electropolishing efficiency significantly by utilizing the electropolishing characterizations with different water concentrations. The method contains two electropolishing processes in high and low water concentration electrolyte, respectively. The experimental results show that the material removal rate is increased significantly compared with the one-step electropolishing method with a low water concentration, and the surface roughness is decreased obviously compared with the one-step electropolishing method with a high water concentration.

    更新日期:2019-12-18
  • Joining Dissimilar Thin-Walled Tubes by Magnetic Pulse Welding
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-17
    J. Lueg-Althoff; J. Bellmann; M. Hahn; S. Schulze; S. Gies; A.E. Tekkaya; E. Beyer

    Welding dissimilar metal tubes attracts <-- -->interest for a wide range of automotive, aeronautical, and plant engineering applications as well as other consumables. Hybrid driveshafts or structural elements can meet mechanical requirements at a reduced weight. However, joining materials with strongly different thermo-physical properties is a challenge for conventional fusion welding processes. In Magnetic Pulse Welding (MPW), the weld formation is based on the high-velocity collision between the joining partners, without additional heat input. This allows for the fabrication of sound “cold” welds. MPW of tubular parts is usually realized by the radial electromagnetic compression of the outer “flyer” part and the subsequent impact on the inner “parent” part. This impact represents a harsh loading for the parent, which therefore is usually designed as a thick-walled or solid part to avoid damage or unwanted deformations. To further increase the lightweight potential, the objective of the present manuscript is the comprehensive analysis of MPW with thin-walled parent parts. Experimental and analytical investigations are presented, which enable to reduce the parent thickness without affecting the joint strength. The approaches comprise the observation of the impact and deformation behavior by inline laser-based measurement technology as well as the development of adequate, re-usable mandrels to support the parent parts. The focus is on aluminum flyer parts, which are welded to steel and copper parent parts. Critical values for the parent wall thickness are deduced and recommendations for the process design of MPW with thin-walled tubes are given.

    更新日期:2019-12-18
  • Experimental and numerical analysis of rotary tube piercing process for producing thick-walled tubes of nickel-base superalloy
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-17
    Zhe Zhang; Dong Liu; Runqiang Zhang; Yanhui Yang; Yuhua Pang; Jianguo Wang; Hai Wang

    In order to overcome the problems of existing methods for preparing thick-walled tubes of nickel-base superalloy (TWNS), the rotary tube piercing (RTP) process was proposed. For this purpose, an improved piercing mill was designed, and the influences of process parameters on strain, temperature, biting condition, lose stability of mandrel, defects control and microstructure distribution were studied by the combination of finite element model (FEM) and experiments. Based on the control variable method, the ranges of process parameters corresponding to the second biting condition and the critical condition of mandrel instability were determined by the simulation results. The experiment results indicate that the external separation layer defect (ESLD) is significantly affected by roll speed and reduction rate. The internal separation layer defect (ISLD) is mainly controlled by reduction rate. The preferred process parameters are determined as temperature 1040℃, reduction rate 13%, roll speed 35 rpm, feed angle 8°, cross angle 15°, and plug advance against gorge 12 mm. The equiaxed grains with average grain size of 25 μm are obtained due to the complete dynamic recrystallization (DRX) process.

    更新日期:2019-12-18
  • 更新日期:2019-12-17
  • Argon-Helium mixtures as Laser-Powder Bed Fusion Atmospheres: Towards increased build rate of Ti-6Al-4V
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-16
    Camille Pauzon; Pierre Forêt; Eduard Hryha; Tanja Arunprasad; Lars Nyborg

    The effect of the gas thermal properties and density on the laser powder bed fusion (L-PBF) process was investigated by using inert argon, characterized by high density, and helium, characterized by high thermal conductivity and heat capacity, and their gas mixtures. The results highlighted that for L-PBF of Ti-6Al-4 V, the effect of residual impurities such as oxygen and nitrogen on the process stability and defect generation is prevailing the type of the process gas. However, by monitoring the residual oxygen level in the process atmosphere, the results showed that using the argon-helium mixtures allows to increase the produced material density upon higher build rates. High density, greater than 99.98 % is indeed achieved using a mixture of 50 % argon and 50 % helium, allowing for a build rate increase of 44 % in comparison to the standard build rate. The analysis of the produced material revealed the presence of thermal residual stresses attributed to an enhanced energy input when using the gas mixtures. The latter offer a positive balance of density and thermal properties, and in turn, probably reduce the accumulation of process by-products at the melt pool that interfere with and attenuate the laser radiation. The possible detrimental effect of the introduced residual stresses is efficiently eliminated by the conventional stress relieving treatment leading to the decomposition of α´martensite into a fine (α + β) microstructure. This study opens the perspective on the development of the gas recipes for improved process stability and increased productivity of L-PBF process.

    更新日期:2019-12-17
  • Damage-induced performance variations of cold forged parts
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-16
    Oliver Hering; A. Erman Tekkaya

    Forming processes play a key role in the manufacturing of metal components. They allow for the economical production of geometrical shapes with reproducibly high quality. Strain hardening and residual stresses affect the performance of the produced parts. These factors are controllable and can even be utilized to increase the performance of the component. This, however, does not apply to damage. Damage in metals describes the decrease of the load-bearing capacity due to the appearance and evolution of voids. The aim is to analyse, predict, and control the evolution of damage in cold forging, to allow for a production of cold forged components with a defined, load-adapted performance. It was investigated numerically to what extent the load path, which is responsible for the damage evolution, is affected in cold forging. Subsequently, the effect of load path changes on the product performance was determined experimentally in the region of the central axis where the load path is affected most by the extrusion parameters. Hereby, a correlation between the occurring triaxiality during forming and the product performance by means of number of cycles to failure in multi-step fatigue tests, impact energy and Young’s modulus was observed.

    更新日期:2019-12-17
  • Modeling A Scanning-Mask Projection Vat Photopolymerization System For Multiscale Additive Manufacturing
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-12
    Viswanth Meenakshisundaram; Logan D.Sturm; Christopher B.Williams

    Industries such as orthodontics and athletic apparel are adopting vat photopolymerization (VP) to manufacture customized products with performance tailored through geometry. However, vat photopolymerization is limited by low manufacturing speeds and the trade-off between manufacturable part size and feature resolution. Current VP platforms and their optical sub-systems allow for simultaneous maximization of only two of three critical manufacturing metrics: layer fabrication time, fabrication area, and printed feature resolution. The Scanning Mask Projection Vat Photopolymerization (S-MPVP1) system was developed to address this shortcoming. However, models developed to determine S-MPVP process parameters are accurate only for systems with an intensity distribution that can be approximated with a first order Gaussian distribution. Limitations of optical elements and the use of heterogeneous photopolymers result in non-analytic intensity distributions. Modeling the effect of non-analytic intensity distribution on the resultant cure profile is necessary for accurate manufacturing of multiscale products. In this work, a model to predict the shape of cured features using analytic and non-analytic intensity distribution is presented. First, existing modeling techniques developed for laser and mask projection VP processes were leveraged to create a numerical model to relate the process parameters (i.e. scan speed, mask pattern irradiance) of the S-MPVP system with the resulting cure profile. Then, by extracting the actual intensity distribution from the resin surface, we demonstrate the model's ability to use non-analytic intensity distribution for computing the irradiance for any projected pattern. Using a custom S-MPVP system, process parameters required to fabricate test specimens were experimentally determined. These parameters were then input into the S-MPVP model and the resulting cure profiles were simulated. Comparison between the simulated and printed specimens dimensions demonstrates the model”s effectiveness in predicting the dimensions of the cured shape with an error of 2.9%.

    更新日期:2019-12-13
  • A novel magnetic field-assisted mass polishing of freeform surfaces
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-10
    Chunjin Wang, Chi Fai Cheung, Lai Ting Ho, Kai Leung Yung, Lingbao Kong
    更新日期:2019-12-11
  • Formation of Non-dendritic Microstructures in Preparation of Semi-solid Mg-RE Alloys Slurries: Roles of RE Content and Cooling Rate
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Cunlong Wang, Guohua Wu, Ming Sun, Liang Zhang, Wencai Liu, Wenjiang Ding

    The proper alloy composition ranges for rheo-forming of Mg-RE alloy was obtained through thermodynamic calculations. The low frequency electromagnetic stirring (LFEMS) process was used to fabricate semisolid slurries of Mg-Gd-Zn series alloys, and the role of solute Gd content and the cooling rate in the LFEMS process were systematically investigated. Both the Gd content and cooling rate show effective influences on the microstructure of the Mg-Gd-Zn alloy semisolid slurries. Fine and spherical primary Mg phase can only be obtained by decreasing the cooling rate to less than 1.4 C°/min and increasing the solute Gd content to no less than 9 wt.%. The formation mechanism of non-dendritic morphology of primary Mg phase in Mg-Gd-Zn alloy was proposed to be the dendrite arm root re-melting induced by curvature undercooling and ripening induced by low cooling rate.

    更新日期:2019-12-11
  • Effect of fractal parameters on optical properties of cold rolled aluminum alloy strips with induced surface deflection: simulations and experimental correlations
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Muhammad Arif Mahmood, Tsung-Ying Tsai, Yhu-Jen Hwu, Wei-Jr Lin, Lee-Cheng Liu, Jiing-Yih Lai, Jui-Wen Pan, Wang-Long Li, Jen-Fin Lin

    Cold rollings for Al5182 aluminum alloy strips are carried out to evaluate the optical parameters with the applications of two lubricants and various operating conditions. In order to obtain these optical parameters, the fractal parameters which includes periodic lengths (Lx, Ly) and fractal dimensions (Dx, Dy) in the modified three-dimensional formula for the fractal surface morphology have been solved first for the rolled surfaces. This three-dimensional formula can provide an effective way to correlate these fractal parameters with the optical parameters using TracePro software, which can help to define rolling conditions efficiently for the specific demand of optical properties. The deterministic results for fractal surface simulations using MATLAB in series and 20° incident angle simulation in TracePro software explain that an increase in Dx and Dy will yield dense profiles which elevates the maximum illuminance and lower down the minimum illuminance. While an increment in Lx and Ly would increase the characteristic distance between two predominant asperities and increase minimum illuminance and decrease maximum illuminance. Finite element analyses prove that different friction coefficients in the upper and lower rolls potentially induce surface deflection and thus affect the optical properties. A high illuminance uniformity can be achieved by making a compromise among the fractal parameters (Dx, Dy, Lx and Ly) such that a small difference in the maximum and minimum illuminances is available.

    更新日期:2019-12-11
  • An investigation of direct-chill cast 2024 aluminum alloy under the influence of high shearing with regards to different shear positions
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Xudong Liu, Qingfeng Zhu, Yanlei Kang, Yubo Zuo, Rui Wang, Zhimeng Li

    The 2024 aluminum alloy ingot with a diameter of 300 mm was prepared by a direct-chill (DC) cast with the application of a high-shear unit in the sump to study the influence of the intensive melt shearing on the 2024 aluminum alloy. During the DC casting process, the head of the high-shear unit was set to different positions in the sump and the corresponding temperature curves were recorded to further study the role of the position of the high shear unit in the DC casting process with the influence of the intensive melt shearing. The experimental results showed that the intensive melt shearing during the DC casting process results in uniform temperature distribution in the sump, significant grain refinement and reduction of negative centerline macrosegregation. The average grain size in the center of the ingot was reduced from 739.7 μm to 193.8 μm, and the negative centerline macrosegregation of Cu element was reduced from -0.094 to -0.041. It was also found that the shear position plays a significant role in uniforming temperature field, eliminating melt superheating and refining grains. When the high shear position lowered to slurry region, the morphology of grain in the center of the ingot transformed from equiaxed dendritic into finer globular equiaxed grain. The reduction of negative centerline macrosegregation is believed to be due to the forced convection caused by the intensive melt shearing and consequently refined microstructure and uniform distribution of floating grains through the whole section of the ingot.

    更新日期:2019-12-11
  • Pre-holed self-piercing riveting of carbon fibre reinforced polymer laminates and commercially pure titanium sheets
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Xianlian Zhang, Xiaocong He, Baoying Xing, Wenjie Wei, Jiawei Lu

    The new technique of pre-holed self-piercing riveting (PH-SPR) was proposed to improve the dissimilar joining of the carbon fibre reinforced polymer (CFRP) laminate and the commercially pure titanium (TA1) sheet. The joint quality, strength, failure behaviour and forming structure of the PH-SPR joints were analysed comparing with the regular SPR (R-SPR) joints. The effects of process parameters on the PH-SPR joint were discussed systematically and experimentally. It was concluded that a better mechanical interlock could be obtained using PH-SPR. The joint strength of the PH-SPR joints failed in the rivet pulled out was superior to those failed in the composite layer torn. Comparing with the R-SPR joints, a better hardening effect to the TA1 sheet and a relatively lower strength loss to the rivet brought a better joint strength for the PH-SPR joints. For the PH-SPR process, the joint strength is highly dependent on the interlock length, and the static failure mode of the joints was affected largely by the rivet head height. The remaining bottom thickness and interlock length was mainly determined by the plastic deformation capacity of the metallic sheet, and the rivet head height was primarily influenced by the joining force.

    更新日期:2019-12-11
  • A Study on Central Crack Formation in Cross Wedge Rolling
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Xianyan Zhou, Zhutao Shao, Catalin I. Pruncu, Lin Hua, Daniel Balint, Jianguo Lin, Jun Jiang

    Cross wedge rolling (CWR) is an innovative roll forming process, used widely in the transportation industry. It has high production efficiency, consistent quality and efficient material usage. However, the continual occurrence of crack formation in the centre of the workpiece is a critical problem excluding the CWR technique from more safety-critical applications, in particular, aerospace components. The mechanisms of central fracture formation are still unclear because of a combination of complicated stress and strain states at various stages of CWR. Thus, the aim of this study is to understand the stress/strain distribution and evolution during the CWR process and identify the key variables which determine central crack formation. A comprehensive investigation was then conducted to simulate 27 experimental cases. The stress and strain distributions in the workpiece were evaluated by finite element analysis. Various damage models from literature were applied and compared. A new fracture criterion was proposed, which was able to successfully determine the central crack formation in all 27 experimental cases. This criterion can be applied in CWR tool and process design, and the enhanced understanding may enable the adoption of CWR by the aerospace industry.

    更新日期:2019-12-11
  • A novel method to evaluate the high strain rate formability of sheet metals under impact hydroforming
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    Da-Yong Chen, Yong Xu, Shi-Hong Zhang, Yan Ma, Ali Abd El-Aty, Dorel Banabic, Artur I. Pokrovsky, Alina A. Bakinovskaya

    In this study, a novel method was proposed to evaluate high strain rate (HSR) formability of Al-Cu-Mg 2B06-O sheets by impact hydroforming (IHF). IHF was suitable to manufacture hard-to-form sheets, since it combined the advantages of flexible liquid and impact impulse loading. Both 2D and 3D HSR formability curves were established to describe the relationship between impact energy, drawing height ratio (DHR) and deep drawing ratio (DDR). Moreover, the novel evaluation method was realized by finite element (FE) modeling using Fluid-Structure Interaction (FSI) algorithm. FSI modeling was used to deal with the interaction of structure solid and flexible fluid. This evaluation means of FE modeling characterized with guiding production practice, saving evaluation costs, improving efficiency compared with corresponding experiments. The results obtained from FE modeling were in a remarkable agreement with those obtained from IHF experiments in the aspects of part shape, failure feature, thickness distribution. FE modeling showed that the limit deep drawing ratio (LDDR) and limit drawing height ratio (LDHR) were 1.99 and 1.04, respectively when the blank was completely deep drawn to the cavity of the die in one step only. FE modelling is proved to be reliable and efficient to estimate high strain rate formability of low formability metal sheets.

    更新日期:2019-12-11
  • Meso-scale modelling of semi-solid deformation in aluminum foundry alloys: Effects of feeding and microstructure on hot tearing susceptibility
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-09
    F. Sheykh-jaberi, S.L. Cockcroft, D.M. Maijer, A.B. Phillion

    In the context of hot tearing susceptibility, the semi-solid constitutive behaviour of two commercially important foundry aluminum alloys at high solid fraction has been simulated. The numerical methodology combines solid mechanics, computational fluid dynamics, and microstructure modelling, i.e a meso-scale multi-physics approach. Feedable and un-feedable domains with different microstructures including equiaxed globular, equiaxed dendritic, and combined dendritic and eutectic were developed. Considering that it is the combined effects of a lack of liquid feeding and limited semi-solid ductility that contribute to hot tearing formation, the effect of feeding and mechanical deformation are studied and discussed. The model demonstrates that the microstructure type and the eutectic formation also have a considerable effect on the liquid channels pressure drop and semi-solid bulk stress and strain, and consequently on hot tearing.

    更新日期:2019-12-11
  • Effect of mechanical and solid-state joining characteristics on tensile-shear performance of friction self-piercing riveted aluminum alloy AA7075-T6 joints
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-05
    Yunwu Ma, Bingxin Yang, Ming Lou, Yongbing Li, Ninshu Ma

    Friction self-piercing riveting (F-SPR), as a combination of traditional self-piercing riveting and friction stir spot welding processes, has been proposed to solve the cracking issues in riveting low ductility materials. The F-SPR process creates mechanical and solid-state hybrid joints, which are quite different from existing spot welding/joining methods. However, the roles that mechanical interlocking and solid-state bonding play upon the mechanical behavior of the joints are unknown. To fill in this gap, the current body of work investigated the tensile-shear behavior and fracture mechanism of the F-SPRed AA7075-T6 aluminum alloy sheets. The results reveal that the ring-shaped solid-state bonding between aluminum sheets enhances the overall stiffness of the joints but shows a minor contribution to the tensile-shear performance. The solid-state bonding formed between the captured aluminum in the rivet shank and the lower sheet serves as an “anchor” to hinder the rotation of the rivet, which delays the action of rivet pull-out from the lower sheet and thus strengthens the joints significantly. The combination of a hard rivet, large rivet flaring and solid-state bonding inside the rivet shank is necessary to achieve the preferred rivet pull-out fracture mode, which shows a higher peak load and larger energy absorption compared to other fracture modes.

    更新日期:2019-12-05
  • Multiphase Modelling of the Transient Flow for Sn-15Pb and 357.0 Alloys in Semi-Solid Die Casting Process
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-05
    Wenying Qu, Daquan Li, Fan Zhang, Min Luo, Xiaogang Hu, Yongzhong Zhang

    The transient flow behavior of the semi-solid slurries for Sn-15Pb and 357.0 alloys during die casting process is investigated by experimental and numerical methods. A model for the transient-state three-dimensional multiphase flow based on the kinetic theory of granular flow is developed. This model is applied to investigate the distribution of solid concentration, flow state, pressure variation of the semi-solid slurry in the die casting process. The three important aspects in the multiphase flow, flow regime, particle-particle interaction, particle-liquid interaction, are interpreted according to the characteristic of the system. The model is verified by partial filling and in-situ observation experiments. Then it is applied for the phase segregation study of an elbow cavity encountered in practice. Results indicate that the 3D multiphase model can depict the flow characteristics of the semi-solid slurry very well. The inner arc side of the elbow cavity is easier to have liquid phase segregation than the outer arc side for the lower velocity gradients of the solid and liquid phases.

    更新日期:2019-12-05
  • Experimentally validated calculation of the cutting edge temperature during dry milling of Ti6Al4V
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-05
    A.W. Nemetz, W. Daves, T. Klünsner, C. Praetzas, W. Liu, T. Teppernegg, C. Czettl, F. Haas, C. Bölling, J. Schäfer
    更新日期:2019-12-05
  • Analysis of a Hybrid Process for Manufacturing Sheet Metal-Polymer structures Using a Conceptual Tool Design and an Analytical-Numerical Modelling
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-04
    Saeed Farahani, Veera Aditya Yerra, Srikanth Pilla

    This paper presents an experimental and numerical study on the hybrid process of polymer injection forming (PIF) developed to manufacture sheet metal-polymer structures in one single operation. Despite the wide potential application of the PIF process, several challenges have prevented conducting an in-depth analysis of the simultaneous injection/forming condition that occurs during this hybrid process. One such challenge is the lack of a special feature in the regular injection molding machine for an independent application and control of the blank holder force (BHF) from the preset clamping force. To enable such, a new concept-to-design tool is proposed in this work. Using this specialized setup, the influence of the BHF, injection rate and their interactions are experimentally determined focusing on the transient PIF process variables and the quality of the final hybrid product. The use of the fluid-structure interaction (SFI) method to perform a multi-physics simulation on the PIF process incurs such computational costs that it is unreasonable to conduct multiple simulations to investigate the effects of several process parameters and their interactions. To achieve both efficiency and accuracy, a new combined analytical-numerical approach is presented to enable fundamental understanding of the PIF process physics considering the interaction of filling, stretching and drawing mechanisms. The feasibility of the proposed numerical and experimental methodologies is demonstrated through a comparative analysis of the deformation of the AA1100 sheet during the injection of a Polypropylene compound with different injection rates and BHF settings.

    更新日期:2019-12-04
  • A new continuous tensile-compressive testing device with friction-counteracting and anti-buckling supporting mechanism for large strain
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-03
    Y. Chang, B.T. Wang, X.D. Li, C.Y. Wang, K.M. Zhao, H. Dong

    The forming process of sheet metal is a complicated procedure relating to tensile and compressive plastic deformation. The in-plane tensile-compressive test is a main way to understand the plastic behavior under the complicated loading paths. In this paper, a new device is developed to realize in-plane tensile-compressive tests in order to study the plastic behavior during tension and compression of sheet metal. The newly-developed device has the advantages of high efficiency and low cost. It can support a reliable continuous, large-strain tensile-compressive test for more materials with higher strength based on any common universal testing machine. A set of friction-counteracting supporting mechanism including T-shaped supporting plates, Teflon sheets and upper/lower fixtures is designed to prevent buckling deformation of sheet metal during compression. Moreover, the tensile-compressive tests of DP780 steel are conducted by using the new device to obtain the tensile-compressive stress-strain curve reflecting the Bauschinger behavior. The constitutive model of DP780 steel is established and the optimal model parameters are achieved for the simulation analysis. As a result, the simulated tensile-compressive curves match the experimental curves very well. The newly-developed device is favorable to accurately describe the plastic behavior under the complicated loading paths during forming and contribute to precise simulation analysis.

    更新日期:2019-12-04
  • Effects of an oscillation electromagnetic field on grain refinement and Al8Mn5 phase formation during direct-chill casting of AZ31B magnesium alloy
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-03
    Yonghui Jia, Jian Hou, Hang Wang, Qichi Le, Qing Lan, Xingrui Chen, Lei Bao

    The effects of an oscillation electromagnetic field (EMF) generated by low frequency pulse current on the grain refinement and phase formation in direct-chill (DC) casting of AZ31B magnesium alloy have been investigated experimentally. The macrostructure evolution was quantitatively examined in terms of the grain size and its distribution, and fine equiaxed grains can be obtained. Given the Lorentz force and velocity variations, temperature distribution and heat extraction process during DC in different electromagnetic conditions, the grain refinement mechanism and the phase composition and formation of AZ31B magnesium alloy were discussed in detail. The grain sizes decrease from 549 ˜ 1094 μm (without EMF) to 402 ˜ 486 μm at the frequency of 15 Hz, and columnar grain region decreases significantly. Forced convection induced by EMF can strengthen the heat extraction along the diametrical direction of billet, weaken the contact heat transfer between melt and mold wall. For the formation of Mn-containing phases, eutectic transformations are dominant in DC casting process of AZ31B magnesium alloy, and the area fraction of eutectic Al8Mn5 phase decreases from center to edge of billet, and its distribution is more homogeneous in the presence of EMF.

    更新日期:2019-12-03
  • Characterization of tribological conditions within direct hot stamping
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-03
    Patrik Schwingenschlögl, Marion Merklein

    The aim of this study is to create a detailed process understanding regarding the tribological conditions within direct hot stamping. Hot stamping has established as a common technology for manufacturing safety-relevant components in modern car bodies. However, due to the high forming temperatures within hot stamping applications, no suitable lubricants have been developed yet. As a consequence, high friction and severe wear occur during the forming. This affects the tool wear as well as the resulting part quality. For improving the robustness and the efficiency of industrial hot stamping processes, future measures to reduce the tribological loads have to be found. The key to the development of such measures is a detailed process understanding of the tribological conditions. Within this study, friction and wear are analyzed for different workpiece and tool temperatures, relative velocities and contact pressures. Based on the experimental results, detailed knowledge of the critical cause-effect relations between process parameters and tribological behavior is acquired. The friction behavior is analyzed via strip drawing experiments under hot stamping conditions. The amount of wear is determined via confocal microscopy measurements before and after the experiments. The results of this study help to improve the process understanding of the tribological conditions within the hot stamping process and to develop future measures for reducing tool wear.

    更新日期:2019-12-03
  • Development of an original electromagnetic damping-controlled horizontal cutting mechanism for microwire-EDM
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-02
    Shun-Tong Chen, Li-Wen Huang, Jin-Pin Kuo, Tin-Cheng Pai

    In this study, an original ‘electromagnetic damping-controlled horizontal cutting mechanism’ is designed and proposed for precisely controlling micro-scale wire-tension for cutting a microstructure array. The electromagnetic damper uses a set of three annular electromagnets equally distributed with their end-faces orientated toward a mild-steel disc. This arrangement is located at the front of the cutting mechanism. The cutting mechanism also consists of a set of microgroove rollers, a wire-electrode guide, and an auxiliary guide designed to suppress wire-wriggling and wire-swaying in order to deliver a tungsten wire of Ø13 μm diameter at a steady state over the long-term. Experimental verification is conducted on B-NPD (boron-doped nano-polycrystalline diamond), which possesses a high melting-point and high electrical resistivity characteristics, to establish the feasibility of cutting such difficult-to-machine materials. A 'one-cut one-skim' machining approach is used whereby the surface flatness and the dimensional accuracy of the slot-wall can be improved. Experimental results found that the wire feed-rate during the finish-cutting stage can be used at a rate greater than that of the rough-cutting stage. The resultant diamond microstructure array is of high-consistency and aspect-ratio at 1:22, demonstrating that the electromagnetic damping-controlled horizontal cutting mechanism can precisely and stably control the tension and running speed of the microwire.

    更新日期:2019-12-02
  • Effects of Laser Power on Geometry, Microstructure and Mechanical Properties of Printed Ti-6Al-4V Parts
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-02
    F.R. Kaschel, M. Celikin, D.P. Dowling

    This study investigated the effect of laser power on the properties of Ti-6Al-4V alloy parts produced by additive manufacturing. The printing study was carried out using the laser beam powder bed fusion (PBF-LB) technique (Renishaw RenAM 500M). The laser power was altered in the range of 100 to 400 W, in order to evaluate the effects of changing the input energy received by the powder particles on the as-built parts. The impact of changing laser power was investigated based on printed part dimensions, porosity, morphology, micro/nanostructure, wear, hardness and tensile properties. It was determined that laser power has a direct influence on part dimensional accuracy, with larger dimensions compared with CAD design under the processing conditions used, obtained at higher powers i.e. 2% at 250 W, while 4% at 400 W. The border thickness for rounded edges was found to be ∼0.2 ± 0.06 mm greater than that obtained for straight edges, printed on the same quarter circle samples. A more homogeneous morphology, along with an improved surface finish, was obtained for parts printed using the higher laser powers. The microstructure of the high power alloy, was characterised by wider prior β grains with longer and finer α' needles, along with superior as-built mechanical properties, when compared to parts produced using lower laser power (100 W). Additionally, shifts in the XRD peak position for parts printed at the lower and higher laser powers, indicate some reduction in the level of residual stress for parts produced at higher powers.

    更新日期:2019-12-02
  • Theoretical and experimental study on the producible rolling thickness in ultra-thin strip rolling
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-02
    Xiao Liu, Hong Xiao

    The cold rolling process of a thin strip is difficult to continue when the strip has been thinned to a certain thickness. A limit thickness, which is referred to as the limiting producible rolling thickness below which plastic deformation does not occur, exists even if the rolling force and the number of rolling passes are increased. The Stone formula is the most common approach for predicting this limit, but its results are inaccurate in experiments or in ultra-thin strip-rolling production. In this study, the variation laws of the contact profile and rolling pressure of ultra-thin strips with different thickness specifications at different reductions were obtained by finite element simulations, indicating that the Stone minimum thickness can be regarded as the critical thickness that exists when a neutral zone is present under a minimal reduction. A theoretical calculation model of producible rolling thickness for an ultra-thin strip based on Fleck theory was established and verified by experiments. When this model is used, the single-pass reduction can be obtained in accordance with the given unit width rolling force, the technical parameters of the rolling mill, the yield strength of the material, and the initial thickness of the strip. The formula for the conditional limiting producible thickness considering the restriction of rolling force was corrected. The relationship between single-pass reduction and the ratio of the initial thickness of the strip to the theoretical limiting producible thickness under the condition of the maximum allowable rolling force of the rolling mill was discussed. This study provides theoretical guidance for practical production by defining the product specification ranges and rolling regulations for existing rolling mills and determining the roller diameters and force and energy parameters for the design of rolling mills.

    更新日期:2019-12-02
  • Cutting force analysis considering edge effects in the milling of carbon fiber reinforced polymer composite
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-12-02
    Yanli He, Jamal Sheikh-Ahmad, Shengwei Zhu, Chunlin Zhao

    Machining damage incurred in milling carbon fiber reinforced polymer (CFRP) composite is closely related to the cutting force. However, the dynamic distribution of the cutting force arising from different cutting effects has not been fully investigated. In this study, a new two-region cutting model was used to analyze components of the cutting force resulting from the cutting and edge effects in the milling of CFRP. The friction coefficient was obtained as a function of the fiber cutting angle. The instantaneous magnitudes of the net cutting, pressing and friction forces were identified quantitatively. The variation of different force components and the corresponding specific cutting energies were studied in relation to the cutting mechanisms. The relationship between the cutting forces and machining damage was also investigated. A mechanistic milling force model is proposed. Comparison indicates that the model can produce better prediction of the milling force than the traditional model.

    更新日期:2019-12-02
  • 更新日期:2019-12-02
  • Methods for measuring large shear strains in in-plane torsion tests
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-11-29
    Heinrich Traphöner, Till Clausmeyer, A. Erman Tekkaya

    The in-plane torsion test achieves true strains far beyond 1.0 for sheet metals, especially using specimens with circular grooves. The accurate measurement of these high strains is a challenge for the conventional digital image correlation (DIC). Thus, the determination of flow curves is limited and fracture strains for very ductile materials cannot be measured. A new grooved specimen is introduced to avoid strain localization. Shear stress and shear strain along a defined area in the groove are constant so that strains can be measured independently of the DIC system setting without error due to strain localization. Furthermore, three methods for the measurement of very high shear strains in the in-plane torsion test are presented: Firstly, the limit of the optical strain measurement is extended by multiple renewal of the digital image correlation (DIC) pattern on the samples. Secondly, the shear strain for the planar specimen is calculated exactly from the rotation angle curve. Lastly, a new incremental method is presented. This method enables to determine shear strains for plane and grooved specimen exactly by only measuring the torque and the angle of rotation. All methods were applied for three steel sheet materials namely DP1000, CP1000 and DC04. The equivalent strain in a grooved in-plane torsion test of sheet steel DC04 was determined as 3.3 with the new incremental method. Such high strains far exceed conventional methods for determining the flow curve.

    更新日期:2019-11-29
  • Influence of surface nanocrystallization pretreatment on high-temperature vacuum carburizing behavior
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-11-26
    Meiling Dong, Xiufang Cui, Bingwen Lu, Xiangru Feng, Shengqiang Song, Guo Jin, Haidou Wang

    The supersonic fine particles bombarding (SFPB) pretreatment is adopted to assist vacuum carburizing for refining the microstructure and improving the mechanical properties of carburized layer. The microstructures, micrhardness and tribology properties of SFPB carburized sample and vacuum carburized sample were studied. The results showed that SFPB pretreatment could form random oriented, ultrafine-grained microstructure and high density dislocations in AISI 9310 steel, leading to the increase of case depth of carburized layer, the refinement of grain size and the promotion of the formation of twin martensite and carbides in carburized layer. Besides, the surface microhardness, maximum residual compressive stress and wear rate of carburized layer were enhanced by SFPB pretreatment, which was attributed to the formation of twin martensite, grain refinement, dispersion strengthening of carbides and the increase of high misorientation angle grain boundary.

    更新日期:2019-11-27
  • Control of nanoscale material removal in diamond polishing by using iron at low temperature
    J. Mater. Process. Tech. (IF 4.178) Pub Date : 2019-11-26
    Ning Yang, Wen Huang, Dajiang Lei

    Diamond is the most promising material for future applications in the fields of semiconductors and optics due to its extraordinary physical properties. The development of diamond processing technology, especially polishing, is of great importance for diamond applications. Diamond friction during polishing usually occurs at room temperature. In this paper, the material removal rate at low temperature (about the temperature of liquid nitrogen) is studied by using molecular dynamics (MD) simulation and designed experiments. This study reveals that the inhibitory effect of low temperature on diamond removal is an efficient way to control the diamond material removal rate in the nanoscale range and enables the control of material removal on an atomic scale in diamond polishing.

    更新日期:2019-11-27
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