Microstructure and Mechanical Properties of Ultra-Narrow Gap Laser Weld Joint of 100 mm-Thick SUS304 Steel Plates J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-17 Yang Wuxiong, Xin Jijun, Fang Chao, Dai Wenhua, Wei Jing, Wu Jiefeng, Song Yuntao
A defect-free welded joint of 100 mm-thick SUS 304 steel plates is produced by ultra-narrow gap laser welding with filler wire in the laser conduction mode in 42 layers. The laser beam concurrent heating of the groove side walls and bottom ensures the adequate side wall fusion, with the angle distortion belowed 1°, and the average fusion ratio of the whole weld of about 11%. The microstructure is composed of cellular grains adjacent to the fusion line and fine equiaxed grains. The average tensile strength of the weld joint is 658 MPa, which corresponds to ~95% of that of the base metal. The fracture occurs near the fusion line in the cellular grain zone of the weld joint. The microstructure morphology difference in the weld joint implies the uneven distribution of microhardness which values in the equiaxed grain zone significantly exceed those the cellular zone.
Foaming behavior of blowing- and stabilization-agent-free aluminum foam precursor during spot friction stir welding J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-17 Yoshihiko Hangai, Keisuke Takada, Hidetoshi Fujii, Yasuhiro Aoki, Takao Utsunomiya
ADC12 die-casting precursors containing many gas pores were fabricated by the friction stir welding (FSW) route and were foamed by the FSW foaming process only using the friction heat during the indentation of the tool used for spot FSW. ADC12 precursors can be foamed by the friction heat generated during spot FSW without using TiH2 as a blowing agent. ADC12 foams can be obtained without using Al2O3 as a stabilization agent. This is considered to be due to impurities contained in the ADC12 die-castings. ADC12 foams with Al2O3 exhibited a larger expansion ratio than those without Al2O3. ADC12 foams with Al2O3 had significantly finer pores than those without Al2O3. The pore diameters of the ADC12 foams with Al2O3 were approximately half of those of the foams without Al2O3. This is considered to be due to the higher viscosity of the ADC12 substrate containing Al2O3.
Ultrasonic vibration-assisted metal forming: constitutive modelling of acoustoplasticity and applications J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-16 Hossein Sedaghat, Weixing Xu, Liangchi Zhang
This paper presents a new physics-based constitutive model to accurately describe the deformation behaviour of metals during ultrasonic vibration assisted (UVA) forming. Dislocation dynamics and acoustic energy transformation mechanisms in materials under ultrasonic vibration were considered in the modelling. A user defined subroutine was also developed for modelling the UVA forming processes using the finite element method. To assess the proposed model, upsetting forming, press forming, and incremental forming were simulated separately, and the predicted results were compared with their corresponding experiments. It was found that the application of the ultrasonic vibration can significantly decrease the material flow stress, making the material softer in forming. A large vibration amplitude results in a large reduction in flow stress. Relevant experimental measurements showed that the model has captured the material behaviour and the major mechanics in UVA forming. Different forming processes, due to their difference in tool-workpiece contact condition, would have different acoustic energy and stress transformation efficiency.
The Influence of Process Parameters on Vertical Surface Roughness of the AlSi10Mg Parts Fabricated by Selective Laser Melting J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-16 Tao Yang, Tingting Liu, Wenhe Liao, Eric MacDonald, Huiliang Wei, Xiangyuan Chen, Liyi Jiang
The role of vacuum degree in the bonding of Al/Mg bimetal prepared by a compound casting process J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-15 Guangyu Li, Wenchao Yang, Wenming Jiang, Feng Guan, Haixiao Jiang, Yao Wu, Zitian Fan
Schedule and electrode design for resistance spot weld bonding Al to steels J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-15 Nannan Chen, Hui-Ping Wang, Min Wang, Blair E. Carlson, David R. Sigler
A 2-step schedule, consisting of a pre-cleaning step followed by a welding step, and an electrode design incorporating a multistep face geometry were developed to address issues of inclusions in the aluminum fusion zone and over thickening of intermetallic compound (IMC) layer in weld bonding of aluminum to steel. The pre-cleaning phase used a multi-pulse current to expel the adhesive from the contacting faces. The subsequent welding phase created a sound joint by growing aluminum nugget diameter while limiting IMC thickening and breaking down remaining inclusions. The multistep electrode contributed to effectiveness of the cleaning by boosting expulsion in the pre-cleaning stage. It also reduced reaction between the electrode and the outer surface of the aluminum via breaking down the oxide film of the aluminum and hence reducing contact resistance. The uncured RSWB joints, generated from the 2-step schedule together with the multistep electrode, had approximately 95% improvement in lap shear peak load compared to joints fabricated using the conventional 1-step welding schedule with a dome electrode. The cured RSWB joints achieved approximately 20% and 80% improvement in the peak load and energy absorption, respectively, in coach peel tests.
Electrochemical direct-writing machining of micro-channel array J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-16 X.L Chen, B.Y. Dong, C.Y. Zhang, H.P. Luo, J.W. Liu, Y.J. Zhang, Z.N. Guo
Bipolar plate is an important component in proton exchange membrane fuel cell. The machining of micro-channel array is a key process for the fabrication of metallic bipolar plate. This paper proposed a novel approach named electrochemical direct-writing machining for generating micro-channel array on thin metallic plate at one time, showing a high machining efficiency. In this method, an insulated mask with a row of micro through-holes was integrated to a metallic nozzle, the electrolyte ejected from the nozzle reached to the workpiece through micro through-holes, and then the micro-channel array could be generated from dots to lines by controlling the movement of workpiece. In the machining process, the non-processing zones were covered by the insulated mask, which avoided the stray corrosion. By analyzing the results of simulation and experiment, it was found that due to the accumulation of electrolytic product in the ending point, the profile of this point was different from that of the starting point. The parameters with the voltage of 20 V and pulse duty cycle of 20% were useful for preparing micro channel with good profile and low dimensional difference. And compared with other pulse frequencies, the pulse frequency of 2 kHz could obtain a deeper micro channel. With other parameters unaltered, the dimension of micro channel was decreased with the increasing moving speed of workpiece. At last, with the optimized parameters (voltage = 20 V, pulse duty cycle = 20%, pulse frequency = 2 kHz, and moving speed = 20 μm·s-1), ten micro channels with the length of 60 mm were generated at one time on a metallic plate with the thickness of 0.5 mm. The width was 302 ± 3.53 μm (Mean ± SD) and the depth was 95.9 ± 1.34 μm, showing a satisfied dimensional consistency.
Pilot Investigation of Feedback Electronic Image Generation in Electron Beam Melting and its Potential for In-Process Monitoring J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-16 Hay Wong, Derek Neary, Sohail Shahzad, Eric Jones, Peter Fox, Chris Sutcliffe
Electron Beam Melting (EBM) is an additive manufacturing technique increasingly used by many industrial sectors, including the medical and aerospace industries. The application of this technology is, however, challenged by the lack of process monitoring and control systems to monitor process repeatability and component quality reproducibility. Various monitoring systems, mainly involving thermal and optical cameras, have been employed in previous attempts to study the quality of the EBM process. However, these systems have limitations, which include: (1) images generated unavoidably include monitoring-irrelevant regions beyond the processing area and (2) images are subject to keystone distortion. In this paper, a digital electronic imaging system prototype is described for the Arcam A1 EBM machine. This paper aims to: (1) disseminate the prototype design, (2) demonstrate the prototype ability to overcome limitations of the existing thermal and optical imaging systems, (3) showcase the potential for the prototype to serve as an alternative EBM monitoring technique, and (4) serve as a pilot study for future in-process EBM monitoring research with electronic imaging. Digital electronic images were generated by detecting both secondary electrons and backscattered electrons originating from interactions between the machine electron beam and the processing area using specially designed hardware. Prototype capability experiments at room temperature and approximately 320°C were conducted with digital images being generated and analysed from a Ti-6-Al-4 V (as demonstrator material) test build. Results suggest that this prototype has significant potential to be used for in-process monitoring of EBM in many manufacturing sectors.
Microstructures and mechanical properties of copper-stainless steel butt-welded joints by MIG-TIG double-sided arc welding J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-12 Zhi Cheng, Jihua Huang, Zheng Ye, Yu Chen, Jian Yang, Shuhai Chen
Two-step heating transient liquid phase bonding of Inconel 738LC J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-12 A. Amirkhani, B. Beidokh, K. Shirvani, M.R. Rahimipour
Abrasive-free surface finishing of glass using a Ce film J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-12 Junji Murata, Kazuki Goda
A novel form of abrasive-free polishing is described, using Ce film deposited on a polishing pad by vacuum evaporation. Polishing using metallic films other than Ce, such as Al and Cu, generates defects on the glass surface with almost negligible material removal rates (MRRs), whereas Ce film with deionized (DI) water achieves smooth, scratch-free surfaces with noticeable MRR. If DI water is not supplied to the pad, there is significant deterioration in polishing performance. MRR increases with greater thickness of Ce film, and extremely smooth surface with sub-nanometer roughness is achieved using Ce film of thickness 2.5 μm. Polishing performance is dependent on conditions such as pad rotation rate and polishing pressure. By adding potassium hydroxide (KOH) to the polishing solution, the MRR almost matches that obtained with conventional abrasive polishing, but achieves ultra-smooth surface finish (Ra: 0.388 nm). The polishing method presented here uses approximately 94% less Ce compared with conventional abrasive polishing, thereby dramatically reducing consumption of this valuable rare earth element.
Effects of travel speed on mechanical properties of AA7075-T6 ultra-thin sheet joints fabricated by high rotational speed micro pinless friction stir welding J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-11 Y. Ni, L. Fu, H.Y. Chen
0.5 mm thick AA7075-T6 ultra-thin sheets were joined successfully by high rotational speed friction stir welding using a pinless tool. Friction stir welding was performed under a high rotational speed of 6000 rpm, and the travel speed ranged from 300 mm/min to 1200 mm/min. Zero thickness reduction and delamination phenomenon were observed in the nugget zone when the travel speed was 1200 mm/min. In this condition, the dynamic recrystallization occurred in the lower part of the nugget zone is incomplete. The mechanical properties gradually improved with the increasing in the travel speed. All the tensile specimens fractured along the boundary between the thermo-mechanically affected zone and the nugget zone, and the morphology showed a shear fracture mode. The maximum tensile strength of 482 MPa (equivalent to ~90% of base metal) was obtained at the travel speed of 1200 mm/min, which presented a ductile fracture mode and a large amount of η phase (MgZn2) precipitates and thick tear ridges were detected on the fracture surfaces.
High Precision Shape Model and Presetting Strategy for Strip Hot Rolling J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-11 Jianwei Zhao, Xiaochen Wang, Quan Yang, Qiuna Wang, Chao Liu, Guangyi Song
The effect of stress release on the shape and deformation of strip between stands are rarely considered or quantified in the traditional strip shape model. In order to make up this deficiency, a high precision shape model is established by the mechanism of the strip shape forming and the deformation of roll system in this paper. Special concentration is placed on the effect of roll wear, roll thermal expansion, metal transverse flow and stress release on the shape. In addition, a tolerance factor which is used to describe the attenuation and tolerance abilities of each stand for longitudinal strain difference is proposed as a foundation for a presetting strategy. Compared to the traditional presetting strategies using the empirical coefficient or Shohet theory, the presetting strategy on the basis of the tolerance factor can better play the control ability of each stand. A systematical description of the presetting strategy and the modeling process of the high precision shape model is given in the present study. The calculated results agree well with experiments, and the actual production data show that the shape model has satisfactory accuracy.
Determination of formability considering wrinkling defect in first-pass conventional spinning with linear roller path J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-09 S.W. Chen, P.F. Gao, M. Zhan, F. Ma, H.R. Zhang, R.Q. Xu
Flange wrinkling is one of the common defects that occur in conventional spinning process, severely restricting the improvement of forming quality and formability. How to universally determine the formability dependent on flange wrinkling is a critical issue in conventional spinning process. For this end, such a determining method for the formability in the process is proposed to rationally design the forming parameters to prevent flange wrinkling. The method is as follows: firstly, the maximum circumferential stress during the process is calculated at the outer edge of the flange, where the circumferential stress is considered as the combining result of the shrinkage of flange diameter and the bending of flange; then, the formability is determined by comparing the maximum circumferential stress to critical circumferential stress for wrinkling defect. Based on the method, a formability analytical model considering wrinkling defect in the first-pass conventional spinning process with a linear roller path is established. The formability model is validated by experiments and FE simulations at different spinning conditions. Sequentially, the influences of forming parameters and their interaction on the formability considering wrinkling defect are systematically analyzed. Furthermore, the forming diagrams considering wrinkling defect for the first-pass conventional spinning are established. It is found that the feed ratio has the most significant effect on the formability, followed by the blank thickness, the hardening exponent, the feed ratio-hardening exponent interaction and the feed ratio-sheet blank thickness interaction. The smaller feed ratio and hardening exponent, thicker sheet blank and greater relative sheet blank radius are helpful to increase the formability. The research results could provide a theoretical basis and guidance for the selection of forming parameters in the actual production of the first-pass conventional spinning.
Microstructure evolution and metallurgical characteristic of bead-on-plate TIG welding of Ti-6Al-4V alloy J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-09 Kamlesh Kumar, Manoj Masanta, Santosh Kumar Sahoo
The bead geometry of autogenous bead-on-plate tungsten inert gas (TIG) welding performed on Ti-6Al-4 V alloy inside an argon inert box chamber was measured for different processing conditions. The microstructural evolution of the weldment was evaluated through optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) technique. The development of residual stress and the texture in the weldment were assessed through the XRD techniques. The full penetration melting for bead-on-plate welding was obtained for high current and low scan speed combination that induces maximum heat input within the experimental domain. Owing to intense heat of the TIG arc, a complex microstructural evolution occurred in the Ti-6Al-4 V alloy, which causes transformation of initial β phase to martensitic α’ phases. The transformation of initial α + β phase to martensitic α’ phase enhances the hardness value of the melt pool upto 365 HV0.2, and further at heat affected zone (upto 385 HV0.2) owing to grain refinement. The residual stress developed in the weld melt pool was recorded tensile type, and for increasing the welding current, due to the enhancement of induced heat, the residual stress increased from 140-200 MPa (for 80 A) to 240-270 MPa (for 100 A).
Fabrication and Evaluation of Monolayer Diamond Grinding Tools by Hot Filament Chemical Vapor Deposition Method J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-05 Xiaotian Shen, Xinchang Wang, Fanghong Sun
Microstructural Evaluation of Hydrogen Embrittlement and Successive Recovery in Advanced High Strength Steel J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-04 Quentin S. Allen, Tracy W. Nelson
Advanced high strength steels (AHSS) have high susceptibility to hydrogen embrittlement, and are often exposed to hydrogen environments in processing. In order to study the embrittlement and recovery of steel, tensile tests were conducted on two different types of AHSS over time after hydrogen charging. Concentration measurements and hydrogen microprinting were carried out at the same time steps to visualize the hydrogen behavior during recovery. The diffusible hydrogen concentration was found to decay exponentially, and empirical relations were found for both types of steel. Hydrogen concentration decay rates were determined to be -0.355 /hr in TBF-980, and -0.225 /hr in DP-980. Hydrogen concentration thresholds for embrittlement were found to be 1.04 mL/100 g for TBF, and 0.87 mL/100 g for DP steel. TBF steel is predicted to recover from embrittlement within 4.2 hours, compared to 7.2 hours in DP steel. A two-factor method of evaluating recovery from embrittlement, requiring hydrogen concentration threshold and decay rate, is explained for use in predicting recovery after exposure to hydrogen. Anisotropic hydrogen diffusion rates were also observed on the surface of both steels for a short time after charging, as hydrogen left the surface through <001> and <101> grains faster than grains with <111> orientations. This could be explained by differences in surface energies between the different orientations.
Effects of dilution on alloy contents and microstructures in multi-pass steel welds J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-03 Y.L. Sun, G. Obasi, C.J. Hamelin, A.N. Vasileiou, T.F. Flint, J. Balakrishnan, M.C. Smith, J.A. Francis
A computational investigation of Equal Channel Angular Pressing of molybdenum validated by experiments J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-04 E. Priel, B. Mittelman, N. Trabelsi, Y. Cohen, Y. Koptiar, R. Padan
Quantification of thermal residual stresses relaxation in AA7xxx aluminium alloy through cold rolling J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-01 Ran Pan, Thilo Pirling, Jinghua Zheng, Jianguo Lin, Catrin M. Davies
Residual stresses (RS) are often induced through quenching of aluminum alloys and present a potential risk of developing crack or distortion in subsequent manufacturing processes. Study of methods to minimise the RS in quenched components is of practical importance. In this paper, cold rolling (CR) has been carried out to remove the RS in quenched AA7050 blocks. The CR effect on relaxing RS in quenched AA7050 blocks has been evaluated via the neutron diffraction (ND), X-ray diffraction (XRD) and contour techniques. The results reveal that although CR transforms near-surface residual stresses from large compression to large tension along the rolling direction, it results in remarkable RS relief in the core part of the material. An integrated finite element model for RS evolution through the CR process was put forward and has been validated by the experimental results.
Theoretical and experimental aspects of laser cutting with elliptically polarized laser beams J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-01 Gonçalo C. Rodrigues, Joost R. Duflou
The strong effect that beam polarization has on the performance of industrial laser cutting is well known. The linear and circular polarization states were widely investigated for CO2 lasers. These two states are, in fact, special cases of elliptically polarized laser beams. Theoretical models have predicted an optimal cutting performance for a specific ellipse ratio (b/a = 0,75), but experimental validation was never reported. The main reason is that this characteristic is difficult to obtain in practice. With the technology shift towards solid state lasers, different optical solutions become available for polarization control of high power laser beams (e.g. transmissive beam retarders). This paper reports on the novel design of an elliptically polarized laser beam with a continuous control of the ellipse axes ratio. Starting with a full description of the concept, the equations describing the control of the optical elements are deduced using Jones calculus formalism. A motorized optical module has been built to transform the output of a linearly polarized laser beam into a given elliptic polarization characteristic. Beam analysis equipment was used to validate the experimental setup. Cutting experiments were realized for 2 mm thick 304 L stainless steel and compared with a simulation model. Both results show a comparable nonlinear effect on the achievable maximum cutting speed. The influence of the beam shape is also considered, revealing a strong interaction with the beam polarization. With the help of simulation tools, the applicability of such concept is investigated and, in agreement with the experimental results, the obtained output confirms that the optimal ellipse beam ratio is much closer to b/a = 0 than anticipated in literature.
Capacitor discharge welding of nuts to steel sheets J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-01 Xiaobing Cao, Zhaoyao Zhou, Jiehan Luo, Chunhua Zou, Chunya Zou
This study is to investigate capacitor discharge welding (CDW) of M8 hexagonal flange welding nuts to Al-Si coated 22MnB5 steel sheets. Pullout tests, microstructural analysis, and fracture examination were conducted. The welding voltage has the biggest effect on mechanical performance and nugget size. The peak load and nugget size gradually increase and then decrease with increasing welding voltage. A modified criterion was established to calculate the minimum diameter to guarantee pullout fracture for nut projection welding. Microstructural evolution was analysed in detail. Three failure modes of the welded joints were examined: interfacial fracture (IF), partial interfacial fracture (PIF) and pullout fracture (PF).
Investigation of dynamic deformation behaviour of large-size sheet metal parts under local Lorentz force J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-10-02 Qixian Zhang, Liang Huang, Jianjun Li, Fei Feng, Hongliang Su, Fei Ma, Kai Zhong
Friction Stir Welding of High Density Polyethylene – Carbon Black Composite J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-30 J.Y. Sheikh-Ahmad, Dima S. Ali, Suleyman Deveci, Fahad Almaskari, Firas Jarrar
This investigation elucidates the important role of process temperatures in the friction stir welding of polymers. Measurements of the material temperatures were performed by means of an infrared camera and embedded thermocouples under the weld line. An inverse heat conduction method was also utilized to determine the temperature distribution in the workpiece numerically. The weld quality was determined in terms of the amount of defects present in the stir zone and the tensile strength of the joint. It was found that considerable melting occurred under the rotating shoulder and on the trailing side of the rotating pin. Movement of the molten material by the rotating tool created macro- and micro-voids in the stir zone. Crystallinity and nano-hardness measurements indicated that crystallinity was higher under the tool shoulder due to exposure to high temperatures. Tensile strength of the joint was mainly attributed to fusion welding on the top region and hot forging at the root. Decreasing the welding speed and increasing the penetration depth helped improve the weld quality.
High repetition rate femtosecond laser heat accumulation and ablation thresholds in cobalt-binder and binderless tungsten carbides J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-27 Kendrick Mensink, Elías H. Penilla, Pablo Martínez-Torres, Natanael Cuando, Suveen Mathaudhu, Guillermo Aguilar
Novel rotating-vibrating magnetic abrasive polishing method for double-layered internal surface finishing J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-27 Jiang Guo, Ka Hing Au, Chen-Nan Sun, Min Hao Goh, Chun Wai Kum, Kui Liu, Jun Wei, Hirofumi Suzuki, Renke Kang
Formation of a Highly Conductive Thick Film by Low-Temperature Sintering of Silver Paste Containing a Bi2O3-B2O3-ZnO Glass Frit J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-27 Wanchun Yang, Qin Sun, Qing Lei, Wenbo Zhu, Yufeng Li, Jun Wei, Mingyu Li
A new Pb-free Ag paste containing a Bi2O3-B2O3-ZnO glass frit was developed for Al2O3 substrate metallization. First, Bi2O3-B2O3-ZnO glass frits with various compositions and glass transition temperatures (Tg) of 322 °C-440 °C were synthesized by using a traditional melt-quenching method. Then, silver pastes containing different contents of the glass frit were sintered on an Al2O3 substrate at temperatures ranging from 450 °C to 600 °C. The glass frit content and the sintering temperature had significant impacts on the electrical resistivity and shear strength of the product. The experimental results indicated that the silver film formed from the paste containing 7 wt.% glass frit and sintered at 600 °C for 15 min had a low electrical resistivity of 2.5 μΩ cm and a high strength of 28.5 MPa. These properties resulted from the formation of a stable glass network that supported the Ag network. Furthermore, ZnAl2O4 was observed to form close to the interface of the Al2O3 substrate, which could improve the shear strength. Moreover, the Bi-based glass frit could be a suitable substitute for Pb-based glass frits in the preparation of environmentally friendly silver pastes for forming thick Ag films on Al2O3 substrates.
Tribological and Mechanical Properties of MoS2 Enhanced Polyamide 12 for Selective Laser Sintering J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-26 Jiaming Bai, Jie Song, Jun Wei
The solid lubricant MoS2 was used as the reinforcement filler for the Polyamide12 material for the additive manufacturing process – selective laser sintering. The tribological and mechanical properties of the laser sintered PA12/MoS2 and PA12 were investigated by the linear reciprocating ball-on-flat wear and impact tests. Results show that by incorporating the MoS2 filler into the PA12 matrix, the impact properties was improved. The coefficient of friction and wear rate of the laser sintered PA12/MoS2 were reduced significantly. The worn surface formed in the wear test was shallow and smoother for the PA12/MoS2, where only mild wear occurred. The XPS testing suggested the involvement of the mechanical-chemical reaction, which resulted the decomposing of the MoS2 and the enhancement of the wear properties of the PA12/MoS2.
Flat Friction Stir Spot Welding of Three 6061-T6 Aluminum Sheets J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-26 Yufeng Sun, Hidetoshi Fujii, Shijie Zhu, Shaokang Guan
Three 6061-T6 aluminum sheets with a thickness of 1 mm for each were subjected to the flat friction stir spot welding technique, which contains two steps of welding process. In step 1, a specially designed back plate with a pre-drilled dent was used in order to form a protuberance on the bottom side of the joint. In step 2, the keyhole and the protuberance were removed by using a probe-less rotating tool and a smooth back plate. The optimized welding condition for the three sheet spot welding was 700 kg/550 rpm/2 s in step 1 and 1000 kg/600 rpm/2 s in step 2. Two sheet/sheet interfaces were formed in the bowl-like stir zone. The stir zone showed a grain size varied from 4.2 to 8.6 μm, much smaller than the 17.6 μm of the base metal. Three different tensile test modes were used to evaluate the failure behavior of the joints. The interface between the top and middle sheet showed a longer bonding length of 11.5 mm and a higher fracture load of about 6438 N. While the interface between the middle and the bottom sheet showed a bonding length of 5.2 mm and a fracture load of about 4450 N. The step 2 joints showed plug-type failure mode during the shear tensile tests.
Scaling laws for the laser welding process in keyhole mode J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-26 Remy Fabbro
This study shows that the keyhole model derived for determining the scaling laws of keyhole depths for laser welding when high power incident laser beams are used (typically in the multi-kW incident power range), can be also applied to determine the melted depths observed during the Selective Laser Melting process, where much lower incident powers of typically few hundred watts are focused on very small focal spots. The solution of the thermal analysis of this keyhole configuration is described by only three independent dimensionless parameters that are also involved for the analysis of a more general problem of heat conduction using similar input parameters. This global approach and the keyhole model describing the process of laser welding have been also validated by analyzing the melted depths generated by the Selective Laser Melting process. The dependence of the melted depths on the operating parameters of this process has been established, as well as the formation thresholds of the keyhole.
An approach to enhancement of Mg alloy joint performance by additional pass of friction stir processing J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-22 Q. Shang, D.R. Ni, P. Xue, B.L. Xiao, K.S. Wang, Z.Y. Ma
Profuse extension twins were successfully introduced to the whole stir zone of friction stir welded AZ31 alloy, and the joint turned out to be a two-layered structure after an additional pass of friction stir processing with a different tool under appropriate parameters. The detailed twinning characteristics and resultant texture evolution in various regions were then investigated. The strengthening effect of twin lamellae and the weakened strain localization in deformation gave rise to a significant improvement of joint mechanical properties. The yield strength of the joint was raised from 96 MPa to 122 MPa and the tensile strength was enhanced to be roughly equal to that of the base material with no reduction of elongation.
Development of Auto Ejection Melt Spinning (AEMS) and its application in fabrication of cobalt-based ribbons J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-24 A.A. Shirzadi, T. Kozieł, G. Cios, P. Bała
Auto Ejection Melt Spinning (AEMS) is a new variant of melt spinning processes in which spontaneous ejection of the alloy occurs as soon as it is fully melted. Unlike the conventional laboratory melt spinning processes, there is no need for a skilled operator to monitor the melt temperature and/or manually release the ejection gas at the right moment. This new process substantially reduces the uncertainties associated with temperature measurement and human errors. On the request of the authors, the capability of the new process was independently tested and verified by the design engineers of a renowned manufacture of laboratory melt spinners in Germany [Edmund Bühler GmbH]. The application of the new process for fabrication of high melting point cobalt-based ribbons is also described and the key findings are outlined.
Effects of welding speed on bubble dynamics and process stability in mechanical constraint-assisted underwater wet welding of steel sheets J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-24 Jianfeng Wang, Qingjie Sun, Zuchen Pan, Jie Yang, Jicai Feng
Microstructure evolution and mechanical performance of underwater local dry welded DSS metals at various simulated water depths J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-21 Yu Hu, Yonghua Shi, Kun Sun, Xiaoqin Shen
Microstructure and mechanical properties of cold metal transfer welding-brazing of Titanium alloy (TC4) to stainless steel (304L) using V-shaped groove joints J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-19 Gang Mou, Xueming Hua, Dongsheng Wu, Ye Huang, Wenhu Lin, Peizhi Xu
Wire feed speeds of 3.5, 4.5, and 5.5 m/min and offset positions of 1 and 2 were employed for this study with an ERCuSi-A weld wire. The microstructures of the joints, which include a Cu/Ti interface layer consisting of Ti2Cu, TiCu, and AlCu2Ti, a Cu-matrix seam consisting of Cu and petal-shaped Fe-Si-Ti intermetallics, and a Cu/Fe interface layer consisting of α-Fe and Cu, were studied. The formation enthalpy calculated from the Miedema model can explained the microstructure evolution mechanism. The interface thickness and ultimate tensile strength were found to increase with wire feed speed. The highest tensile strength of the joint was 294 MPa, fracturing at the Cu/Ti interface. Offsetting the welding torch to the TC4 side increased the amount and size of the Fe-Si-Ti intermetallics, degrading the tensile strength. Four fracture modes were proposed to differentiate the crack propagations in the joints, which were determined by the interfacial bonding strength and the Fe-Si-Ti intermetallics in the weld seam.
Holographic watermarks and steganographic markings for combating the counterfeiting practices of high-value metal products J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-18 Krystian L. Wlodarczyk, Marcus Ardron, Nicholas J. Weston, Duncan P. Hand
This paper describes recent advances in direct laser writing of tamper-proof holographic structures on metal surfaces for preventing counterfeiting of high-value metal products, e.g. luxury watches, medical tools and implants, collectible coins, etc. Each of these holographic structures consists of an array of optically-smooth craters arranged in such a way to generate diffractive images comprising, e.g. a company logo and/or a string of alphanumeric characters, providing a unique method for the traceability of genuine products. The craters are less than 10 μm across and less than 500 nm deep. They are generated on metals by UV nanosecond laser pulses (355 nm wavelength and 35 ns pulse duration) that lead to localized melting and evaporation of the material. This paper demonstrates various methods for combining the holographic structures with standard marking patterns, such as QR codes and Data Matrices, in order to form aesthetic holographic markings concealing secret messages about the products. By merging a few holographic patterns together it is also possible to generate so called “holographic watermarks”. Finally, this article describes a few approaches for making the holographic structures particularly difficult to replicate and counterfeit. This includes the generation of multi-level holograms as well as the formation of optically-smooth protrusions (bumps) in selected places within the holographic structures in order to create hidden identifiers and/or miniature signatures which cannot be detected by the naked eye.
Joining of tubular carbon fiber-reinforced plastic/aluminum by magnetic pulse welding J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-17 Junjia Cui, Ya Li, Quanxiaoxiao Liu, Xu Zhang, Zhidan Xu, Guangyao Li
Tailored Microstructures of Gadolinium Zirconate/YSZ Multi-layered Thermal Barrier Coatings Produced by Suspension Plasma Spray: Durability and Erosion testing J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-15 Satyapal Mahade, Dapeng Zhou, Nicholas Curry, Nicolaie Markocsan, Per Nylén, Robert Vaßen
This work employed an axial suspension plasma spray (SPS) process to deposit two different gadolinium zirconate (GZ) based triple layered thermal barrier coatings (TBCs). The first was a ‘layered’ TBC (GZ dense/GZ/YSZ) where the base layer was YSZ, intermediate layer was a relatively porous GZ and the top layer was a relatively dense GZ. The second triple layered TBC was a ‘composite’ TBC (GZ dense/GZ + YSZ/YSZ) comprising of an YSZ base layer, a GZ + YSZ intermediate layer and a dense GZ top layer. The as sprayed TBCs (layered and composite) were characterized using SEM/EDS and XRD. Two different methods (water intrusion and image analysis) were used to measure the porosity content of the as sprayed TBCs. Fracture toughness measurements were made on the intermediate layers (GZ + YSZ layer of the composite TBC and porous GZ layer of the layered TBC respectively) using micro indentation tests. The GZ + YSZ layer in the composite TBC was shown to have a slightly higher fracture toughness than the relatively porous GZ layer in the layered TBC. Erosion performance of the as sprayed TBCs was evaluated at room temperature where the composite TBC showed higher erosion resistance than the layered TBC. However, in the burner rig test conducted at 1400 °C, the layered TBC showed higher thermal cyclic lifetime than the composite TBC. Failure analysis of the thermally cycled TBCs and eroded was performed using SEM and XRD.
Application of Tailor Heat Treated Blanks Technology in a Joining by Forming Process J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-15 Matthias Graser, Sebastian Wiesenmayer, Martin Müller, Marion Merklein
The usage of modern materials in the automotive industry for the body in white construction leads to increasing requirements for the manufacturing process. Due to the limited formability of high-strength aluminium alloys and steels, joining by forming of these dissimilar materials is still a big challenge, which requires suitable and innovative manufacturing technologies. In sheet forming processes the Tailor Heat Treated Blank (THTB) technology allows enhancing the formability of high-strength aluminium alloys. Therefore, the applicability of the THTB technology for the shear-clinching technology is investigated in this paper. Up till now, this innovative joining by forming technology is only qualified to join ductile aluminium alloys and high-strength steels, but the combination of high-strength aluminium and high-strength steel has not been realized yet. In this research work, the limits of the shear-clinching process have been extended to successfully join the material combinations of AA7075 on the punch side and HCT780X, as well as press hardened 22MnB5 on the die side by using aluminium specimens with different heat treatment layouts. Further, this paper shows the possibility to adjust the material flow of the shear-clinching process by local and short-term heat treatment.
Reducting stray corrosion in jet electrochemical milling by adjusting the jet shape J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-14 Xindi Wang, Ningsong Qu, Xiaolong Fang
Jet electrochemical (Jet-EC) milling, using a movable nozzle as the cathode, can fabricate complicated structures flexibly. With the dissolution restricted to a limited area by the electrolyte jet, high removal localization and good surface quality can be obtained. However, the edge of the machined groove is usually subject to stray corrosion because of the low current density in the edge area. In this paper, it is confirmed that the jet shape, which is determined by the working parameters, has a notable influence on the edge condition. Through experiments and analysis, the interrelation between the working parameters, jet shape and edge condition in Jet-EC groove milling is established. It is found that the stray corrosion on the edge can be reduced significantly by adjusting the jet shape, and the necessary conditions to completely eliminate the stray corrosion are established. Furthermore, based on the conclusions, a groove with both a sharp edge and a smooth surface is fabricated via a two-pass process. A deep groove (1.208 mm) with a sharp edge is produced via multiple-pass milling with downward cathode feeding.
A combined numerical and experimental approach for determining the contact temperature in an industrial ironing operation J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-15 Esmeray Üstünyagiz, Chris V. Nielsen, Peter Christiansen, Paulo A.F. Martins, Taylan Altan, Niels Bay
Tribological conditions in forming operations depend on several parameters such as tool-workpiece interface pressure, surface expansion, sliding length, sliding speed, tool and workpiece materials and the roughness of the parts. Among indirect parameters, the most influential one is the tool-workpiece interface temperature, which directly influences the lubricant performance. Prior to testing new tribo-systems to determine their limits of lubrication, it is therefore important to find the interface temperature. However, measurement of the interface temperature in metal forming is difficult. The present work investigates the determination of the interface temperature in an industrial ironing operation, where severe process parameters lead to lubricant film breakdown and galling after several strokes. The methodology combines finite element simulations and experimental measurements. The overall procedure is based on a steady-state thermal analysis to determine the temperature distribution within the tool and a transient thermo-mechanical analysis of the ironing process when steady-state conditions are achieved. Results show that the proposed methodology applied to a single stroke can effectively and accurately predict the interface temperature in the test tool, thus avoiding the otherwise required thermo-mechanical FEM analyses of hundreds of strokes to reach steady-state. Furthermore, the influence of parameters, such as the predicted steady-state tool temperature, the friction coefficient and the heat transfer coefficient on the contact temperature, is analysed. It is concluded that the frictional heating is the primary cause for the peak temperature. By calibration of the friction coefficient and the heat transfer coefficient to ensure matching of the numerical results and the experimental measurements, a maximum tool-workpiece interface temperature of 158 °C was determined during the forward stroke and 150 °C during the backward stroke.
Flower pattern and roll positioning design for the cage roll forming process of ERW pipes J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-14 Weiye Chen, Jinmao Jiang, Dayong Li, Tianxia Zou, Yinghong Peng
The cage roll forming process improves the flexibility of electrical resistance welding (ERW) pipes manufacturing by employing several groups of cage rolls, but poses great challenge to flower design and roll positioning, since the flower pattern and rolls’ positions are no longer one-to-one correlated as in conventional roll forming processes. In the present work, a forming flower design method for cage roll forming of ERW pipes is proposed, considering the transversal bending characteristics of the sheet metal, especially the existence of “non-bending area”. Furthermore, based on kinematic analysis of the cage roll frame, a roll positioning method is put forward by implementing flower pattern and enforcing the geometric constraint condition between rolls and the steel strip. The proposed flower pattern design and roll positioning methods are demonstrated by the cage roll forming of two ERW pipes. The forming processes by using the newly designed parameters and old experience based parameters are compared. The proposed method provides a science based process design method for cage roll forming processes. To the best of our knowledge, the present work is the first effort on developing flower pattern and roll positioning design methods for the cage roll forming process of ERW pipes.
SEMI-SOLID STATE MIXING OF Mg-Zn-RE ALLOYS—MICROSTRUCTURE AND MECHANICAL PROPERITES J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-13 Łukasz Rogal, Grzegorz Garzel
Fabrication of porous NiAl intermetallic compounds with a hierarchical open-cell structure by combustion synthesis reaction and space holder method J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-12 Yunmao Shu, Asuka Suzuki, Naoki Takata, Makoto Kobashi
We have developed a process to fabricate porous NiAl intermetallic compounds with a bi-modal porous structure by combining the combustion synthesis reaction and the space holder method. The fabricated porous NiAl showed large pores of the order of several tens of micrometers derived from the NaCl space holder and small pores of the order of several micrometers derived from the combustion synthesis reaction. The NaCl space holder acted as a heat absorber and contributed to the formation of small pores by preventing the melting of NiAl. Although the reaction was difficult to complete for large volume fractions of NaCl, it was possible to obtain single-phase NiAl by controlling the sintering conditions. We could finally obtain highly porous (porosity: >80%) single-phase NiAl with a hierarchical open-cell structure.
Observations of repair process by friction stitch welding in simulated wet conditions – flaws, microstructure and hardness evolutions in overlapping welds J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-12 Zhijiang Wang, Jinhu Teng, Dongpo Wang, Lei Cui, Hao Liu, Jiahang Yang, Yang Zhang, Han Zhu
The overlapping friction taper plug welding (FTPW) process influences the overlapped welds and bonding quality of the friction stitch weld, therefore, flaws, microstructure and hardness evolutions were observed with the progress of overlapping FTPW process in a simulated wet condition to study the forming mechanism of underwater friction stitch welding. DH36 plugs were used to repair the arc welded DH36 joint. Six burn-off distances (namely consumptions) of plug were chosen to observe the intermediate status of flaws, microstructure and hardness. With the increase in burn-off distance, bonding was firstly formed at the bottom, then at the sidewall and finally at the rounded corner. In the overlapping FTPW process, the microstructure was coarse lath martensite and hardness up to 410 HV10 in the center of stir zone while acicular ferrite and grain boundary ferrite with hardness from 290 to 320 HV10 was observed at the rounded corner of stir zone; fine lath martensite was observed and hardness was about 370 HV10 in the forged zone in upper part of the overlapping friction taper plug weld; the overlapped friction taper plug welds were tempered and the hardness was reduced with a minimum about 250 HV10. The overlapping FTPW process study shows increase in heat input at the location of flaws at the beginning of the process, improving material flow at the location of flaws, and good plug material selection will promote the weld quality in underwater friction stitch welding.
A modified electrode design for improving process performance of electric discharge drilling J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-12 Ravinder Kumar, Inderdeep Singh
The present experimental investigation aims at improvement of the response characteristics during electric discharge drilling process. It is a well-established fact that aspect ratio of a drilled hole in Electric Discharge Drilling (EDD) process is limited due to the occurrence of arcing and short circuiting, resulting from ineffectiveness of flushing at larger depth. The prevention of accumulation of debris during EDD is important in order to improve the material removal rate (MRR) and aspect ratio of the hole. This can be achieved by designing shaped tool electrodes which can easily evacuate the debris from the machining zone. In the present experimental investigation, a novel tool electrode has been fabricated by drilling an inclined through hole into the tool electrode (Patent application number: 201711005674). The proposed electrode was found effective in eliminating the accumulation of debris in the machining zone. Moreover, the need of flushing during the process has been totally eliminated making it a self-flushing electrode. The images captured using high speed camera supports the mechanism explained for the debris evacuation. The proposed electrode (diameter 0.8 mm) can drill a hole of depth greater than 9.8 mm in Ti6Al4V which is the highest depth ever reported in the literature for Ti6Al4V using electric discharge drilling. The effect on other response parameters such as machining time, hole taper and corner radius has also been investigated and compared with the holes drilled by solid cylindrical electrode. The fabrication time of the proposed electrode is lower than time reported in the literature. Therefore, the proposed electrode is capable of producing holes of high aspect ratio with minimum electrode fabrication time, thus, improving the overall productivity and reducing the cycle time.
Rapid and high-performance processing technology for large-area frequency selective surfaces J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-09 Jun Ai, Huiqing Xiang, Qifeng Du, Dongchu Chen, Jianguo Liu, Xiaoyan Zeng
Frequency selective surfaces (FSSs) with periodic smart structures have widespread applications in many areas, especially in electromagnetic wave filters. In this paper, a rapid and high-performance processing technology for large-area FSSs was presented. This novel technology combined laser direct writing lithography (LDWL) with wet chemical etching (WCE) (i.e., LDWL + WCE). Basing on experiments and in the condition of optimal parameters (i.e., 40 mW laser power, 1000 mm/s scan speed, single scan, 20 μm hatch space, pattern-profile scan path, and ferric chloride aqueous solution as etchant) of LDWL + WCE, a large-area (200 × 200 mm2) aperture type FSS with 625 square-loop units was fabricated within 8 minutes on a FR-4 copper-clad plate (with 12 μm-thickness copper layer). When the same FSS was prepared by commonly-used laser direct ablation (LDA) technology with itself optimal processing parameters, it needed about 62 min (nearly 8 times as much time as the former). Scanning electron microscopy (SEM) and surface probe profilometry analyses showed that the edges of the square-loop patterns fabricated by LDWL + WCE were steeper and smoother, and the FR-4 substrate had no damage. In an anechoic chamber, the electromagnetic wave filtering performances of the as-prepared FSSs were tested, and the results indicated that the FSS fabricated by LDWL + WCE had a bandpass response at 7.08 GHz with a transmittance of 97.75%. Its frequency response curve was in better agreement with the simulation result. The technology of LDWL + WCE also has the potential to rapidly fabricate large-area and/or non-planar FSSs with high performance.
Analytical and experimental bond strength investigation of cold forged composite shafts J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-09 Stefan Ossenkemper, Christoph Dahnke, A. Erman Tekkaya
Composite cold forging denotes the simultaneous processing of hybrid raw parts by cold forging operations. The objective is the manufacturing of composite components by means of joining by plastic deformation. For lightweight purposes, composite shafts were produced by forward rod extrusion of backward extruded steel cups, into which an aluminum core has been inserted. The final composite shafts possess a wear-resistant outer steel sleeve and a light aluminum core. An analytical model has been developed to predict the strength of the force fit of composite shafts produced by cold forging. Push-out tests were conducted in order to experimentally determine the bond strength for the validation of the model. The analytically estimated bond strengths are in good accordance with the experimental values determined by push-out tests. The bond strength can be increased significantly by structuring the inner surface of the cups for the hybrid raw part to cause a form fit between steel sleeve and aluminum core after forward rod extrusion. Metallurgical bonds are not established between steel and aluminum in the investigated composite cold forged shafts.
Expanding particle size distribution and morphology of aluminium-silicon powders for Laser Beam Melting by dry coating with silica nanoparticles J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-07 Michael Cornelius Hermann Karg, Alexander Munk, Bhrigu Ahuja, Manuel Veit Backer, Jana Petra Schmitt, Christopher Stengel, Sergey Vyacheslavovich Kuryntsev, Michael Schmidt
Microstructure and mechanical properties of 6061/7N01 CMT+P joints J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-08 Junjie Li, Junqi Shen, Shengsun Hu, Ying Liang, Qian Wang
6061/7N01 dissimilar aluminum alloys were welded by the cold metal transfer plus pulse (CMT + P) technology. With a decrease in the ratio of number of CMT stages to P stages in one CMT + P cycle (CMT/P ratio), the heat input increased and grain growth was observed in the weld metal. The grains in the heat-affected zone (HAZ) were equiaxed on the 6061 side, and the grains in the HAZ on the 7N01 side retained their strip shape. As the CMT/P ratio decreased, the widths of the partially melted zone (PMZ) and HAZ on both sides increased. Asymmetric hardness distribution profiles were observed for all the samples due to the obvious differences in the microstructure of the two base metals. Micro-hardness exhibited an increasing tendency from the HAZ to the PMZ on the 6061 side. The changes in the trend of micro-hardness on the 7N01 side were opposite of those on the 6061 side due to the adverse effect of Si impurities. When the ratio of CMT/P was 1:7, the strength of the weld joint was approximately 60% of the strength of the 6061 substrate due to the transformation and coarsening of the strengthening phase. The fracture site is located in the HAZ on the 6061 side. Dimples were uniformly distributed on the fracture surfaces, which indicates a typical ductile fracture.
Material instability under localized severe plastic deformation during high speed turning of titanium alloy Ti-6.5AL-2Zr-1Mo-1V J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-06 Jianfei Sun, Qingchan Ke, Wuyi Chen
High temperature, large strain and fast strain rate resulting from the severe plastic deformation will cause local material instability, then physical and chemical reactions such as phase transition, grain redistribution and fracture may occur during this process. This paper presents an in-depth investigation about the material instability and corresponding microstructures during the serrated chip formation of titanium alloy Ti-6.5AL-2Zr-1Mo-1 V by high speed turning. Firstly, intense deformation during high speed cutting was verified. Phase transition under different loading conditions including temperature, strain and strain rate were also explored, followed by the domination of equiaxed α-phase due to suitably localized severe plastic deformation and sufficient cooling. Secondly, criterion for initiation of fracture of material was introduced and applied to chip breaking. Finally, particle redistribution phenomenon was analyzed accordingly and the so-called severe plastic flow was further verified.
Direct fabrication of metal tubes with high-quality inner surfaces via droplet deposition over soluble cores J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-05 Hao Yi, Lehua Qi, Jun Luo, Daicong Zhang, Li Ni
Droplet-based 3D printing is very promising for the fabrication of complex thin-wall microwave devices such as antenna horns and waveguide tubes since it can print a shell by utilizing only several layers of droplets. However, due to the naturally scalloped shape of metal droplets, conventional droplet-based 3D printing methods cannot produce thin-wall tubes with high-quality inner surfaces that can meet the requirement of electromagnetic transmission. Here, combining the conventional casting procedure and droplet printing, a hybrid printing process is proposed. Uniform aluminum droplets were first rotationally deposited on a soluble core, and then the core was dissolved and left behind a tube with a high-quality inner surface. The deposition parameters (i.e., number of layers and deposition frequency) were adjusted according to the rotation of the core to form a dense shell over its surface. A hexagonal metal tube was fabricated by using the proposed method to prove its effectiveness. The standard Archimedes test shows that the density of the formed part was up to 98.89%. The industrial CT scanning results also prove a porosity-free inner structure. The inner surface roughness (Ra) was measured to be 4.38 μm by using a laser confocal microscope scanning, and the roughness is only 0.37% of the droplet diameter.
Trimming and Sheared Edge Stretchability of Automotive 6xxx Aluminum Alloys J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-05 Sergey. F. Golovashchenko, Nan. Wang, Quochung. Le
Edge quality produced by shearing processes often leads to reduced material formability which was observed in multiple studies and summarized in the reference literature. The intention to make the sheared edge performance more predictable has motivated the development of several experimental techniques such as the hole expansion test and the tensile test with one side of the sample sheared in various cutting conditions. The paper presents a review of published results for both of these techniques and illustrates very limited research dedicated to sheared edge performance of aluminum alloys. The experimental study was performed on three broadly used in automotive industry 6xxx serious aluminum alloys which have similar mechanical properties and chemical composition with some variation in processing regimes and individual elements quantities. The effects of cutting clearance on longitudinal, transverse and diagonal orientations of the trim line relative to the rolling direction were discussed for all three alloys. The results of standard tensile test of all three materials were very similar with rather small difference in work hardening and almost no difference in total elongations measured by an extensometer. Measurements of elongations as a result of stretching of samples along orthogonally trimmed sheared surfaces indicated that the increase of the cutting clearance above 5% for Alloy 1 and above 15 % for Alloy 2 usually leads to formation of burrs and reduced elongations of trimmed samples before fracture occurs. The effect of cutting clearance on sheared edge stretching performance for Alloy 3 is significantly less pronounced than for Alloys 1 and 2, which makes Alloy 3 very attractive for exterior panel automotive applications in which significant stretching of sheared edge can be anticipated. Detailed discussion of mechanism of blank separation during trimming process was based upon the results of 2D numerical simulation and interrupted trimming process with partially propagated cracks.
The stability of laser welding with an off-axis wire feed J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-05 Himani Siva Prasad, Jan Frostevarg, Alexander F.H. Kaplan
Correlation of structural and optical properties in as-prepared and annealed Bi2Se3 thin films J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-05 A.M. Adam, E. Lilov, E.M.M. Ibrahim, P. Petkov, L.V. Panina, M.A. Darwish
Bi2Se3 bulk alloys were synthesized using a standard mono-temperature melting process and used as source materials to deposit thin films on non-conductive super cleaned glass substrates by a vacuum thermal evaporation technique. Both bulk and thin-film samples were polycrystalline as confirmed by X-ray diffraction patterns. The film samples were subjected to the annealing process in air atmosphere at 250 and 300 ℃℃ for 3 h, aiming to boost the optical properties, in particular, to enhance the light transmission. The surface roughness, morphology and granular structure were investigated by atomic force microscope and scanning/transmission electron microscopes. The correlation between structural changes due to annealing and optical properties was observed. For a higher annealing temperature of 300 ℃℃, the coefficient of transmittance increased reaching 80-90% in the IR range. Consequently, the absorption coefficient greatly decreased by annealing, especially for low photon energies. The optical band gap corresponds to the direct transition and increased notably by annealing from 1.51 to 1.83 eV. The spectra of optical parameters including the refraction index, coefficient of extinction and complex-valued dielectric function were deduced from the transmittance/reflection measurements to evaluate the effect of annealing. The energy loss functions were also estimated demonstrating that the volume and surface energy losses are of the same order.
Microstructural adjustment of carburized steel components towards reducing the quenching-induced distortion J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-09-01 H. Farivar, U. Prahl, M. Hans, W. Bleck
It is crucial to control and minimize the geometrical distortions resulted from the application of carburizing and quenching processes. This is particularly of the utmost importance for high quality steel products such as power transmission components which require high performance and dimensional precision in the range of micrometers. Carburized steel components are quenched from hardening temperature to room temperature to acquire a very hard martensitic layer (case). During the quenching process, due to the phase transformation-induced volumetric expansion in case and the interior region (core), unwanted dimensional changes may occur. In the present work, the effects of a modified hardening temperature and different soaking times on the core microstructure, the final dimensional stability and the mechanical properties are systematically investigated. Navy C-ring specimens are employed to quantify and correlate the effect of the developed microstructural constituents, magnitude of distortion, distribution of residual stresses and hardness values (macro, micro and nanohardness). Mini-tensile specimens are additionally fabricated out of the Navy C-rings’ core to evaluate the overall tensile behavior of the developed microstructures. The results show that by application of the modified hardening temperature the quenching-induced distortion can be reduced up to 27% while retaining the hardness properties of the case and core similar to that in the reference specimens which are quenched from a typical hardening temperature. The overall tensile properties of the core microstructures developed by the reference and modified heat treatments also show a nearly similar behavior.
Texture control of 316L parts by modulation of the melt pool morphology in selective laser melting J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-08-31 Olivier Andreau, Imade Koutiri, Patrice Peyre, Jean-Daniel Penot, Nicolas Saintier, Etienne Pessard, Thibaut De Terris, Corinne Dupuy, Thierry Baudin
Parametric mapping of linear deposition morphology in uniform metal droplet deposition technique J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-08-31 Daicong Zhang, Lehua Qi, Jun Luo, Hao Yi, Wei Xiong, Yuanbing Mo
The parametric mapping of linear deposition morphology with different droplet spacing is first proposed, which provides a baseline for parameter selection in uniform metal droplet deposition technique. Experiments related to linear deposition are carried out with deviating droplet size and deposition placement. Deposition morphology is first categorized into inclined region, wave-shaped region and horizontal region. Horizontal region is further classified into overlapped sub-region, clustered sub-region and discrete sub-region. Mathematical models about classification of deposition morphology are established by these initial parameters: offset ratio, merge ratio, solidification angle, and maximum spreading diameter. After mathematical models are established, boundaries between regions are extracted, and then verified by CCD (Charge-coupled Device) photographs and experimental data. Based on the above models and experiment results, the parametric mapping is found and verified. The following conclusions can be drawn: uncontrollable wave-shaped and clustered regions are not suitable for forming parts, hence the selected process parameters should be avoided in the above regions; Controllable inclined, overlapped and discrete regions can be used to forming part, hence the process parameters should fall into these regions. Furthermore, some possible applications are explored corresponding to three controllable regions with the help of the parametric mapping.
On improving chatter stability of thin-wall milling by prestressing J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-08-31 Min Wan, Ting-Qi Gao, Jia Feng, Wei-Hong Zhang
Some long strip-like thin-walled workpieces such as blades usually need to be manufactured by milling with two ends being clamped on the machine table. This paper presents a stability improvement method in this kind of thin-wall milling by applying tensile prestress to the workpiece. The methodology is described by developing theories to establish the relationship between the needed tensile prestress and the expected critical axial depth of cut. Influence of the workpiece natural frequency on the critical axial depth of cut is theoretically explained for the first time. It is found that increasing the workpiece natural frequency can locally improve the stability in milling, and based on this conclusion, quantitative equations relating the expected critical axial depth of cut to the workpiece natural frequency are theoretically derived and solved in detail. With the aid of modal analysis from finite element simulation, problem on how much tensile prestress should be used to increase the workpiece natural frequency to the expected level is explained. In short, the stability lobe of a thin-wall milling system is shifted to the expected stable zone by manipulating tensile prestress to the clamping areas of long strip-like part. Besides, a prototype device, which has the capacity of fixing and prestressing the workpiece, is originally invented to check the effectiveness of the proposed methodology. The proposed method together with the invented prestressing device is experimentally validated by carrying out a series of milling tests with and without prestress.
Experiments and Simulations of Micro-hole manufacturing by Electrophoresis-assisted Micro-ultrasonic Machining J. Mater. Process. Tech. (IF 3.647) Pub Date : 2018-08-31 J.F. He, Z.N. Guo, H.S. Lian, J.W. Liu, Y. Zhen, Y. Deng
Electrophoresis-assisted micro-ultrasonic machining (EPAMUSM) is an effective method for solving the problem of using traditional micro-ultrasonic machining (MUSM) to fabricate micro-holes in materials that are hard and brittle, namely the low utilization ratio of abrasive particles. EPAMUSM uses an electric field to attract the abrasive particles to the processing area during processing, which is useful for improving both the utilization ratio of abrasive particles and the processing quality. Numerical simulations of the concentration distributions of abrasive particles in MUSM and EPAMUSM show that the abrasive concentration on the tool surface is much higher in EPAMUSM. The concentration increases rapidly from 1 mol/m3 to 4.68 mol/m3 after 10 s in EPAMUSM. Comparative experiments show that EPAMUSM has advantages over MUSM under the same processing conditions: the EPAMUSM edge chipping rate (0.03) is much less than the MUSM one (0.22) and the EPAMUSM material removal rate (1.916 × 10−4 mm3/min) is marginally better than the MUSM one (1.718 × 10−4 mm3/min). Single-factor experiments are used to study how varying certain parameters (namely DC voltage, ultrasonic power, and spindle speed) affects EPAMUSM manufacturing quality and efficiency. Finally, the processing parameters are optimized by means of response-surface experiments, and the optimum EPAMUSM processing parameters are determined (namely an applied voltage of 7.5 V, an ultrasonic power of 22.5 W, a spindle speed of 300 rpm, and a mass fraction of 10%).
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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