Journal of Manufacturing Processes最新文献

The high roughness of titanium alloy specimen fabricated by laser powder bed fusion (LPBF) may limit the application of LPBF technology. Plasma electrolytic polishing (PEP) can effectively reduce the surface roughness of metal samples. In this study, an orthogonal test was designed to investigate the effects of polishing time, voltage and electrolyte temperature on the reduction of roughness and wall thickness of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si specimens fabricated by LPBF. The surface roughness of the specimen decreased from Ra = 49.1 μm to Ra = 9.1 μm and the thickness decreased from 1.72 mm to 1.38 mm after the PEP. Due to the recoil pressure induced by rupture of vapor-gaseous envelope (VGE) and the annealing effect caused by electron impact, the width of α/α' grains on the surface of TC11 specimen decreased from 0.51 μm to 0.46 μm; the mean value of geometrically necessary dislocations (GND) increased by 9.8 %; the proportion of high angle grain boundaries (HAGBs) increased from 75.2 % to 80.8 %; the proportion of twin grain boundary length increased from 2.9 % to 11.9 %, and the activated twin variant type increased from 2 to 4. The number of pores in the samples reduced from 85 to 2 after PEP, which resulted in the improvement of tensile and fatigue properties. The ultimate strength and elongation of the tensile specimens increased by 6.2 % and 53.5 % respectively. The infinite fatigue life maximum stress of the high cycle fatigue specimen increased by 62.5 %. Another reason for the improvement of mechanical properties may be the self-healing of microcracks and the electroplasticity in the specimens.

Ultrasonic plastic welding (UPW) is an efficient and environmentally friendly method for joining carbon fiber reinforced thermoplastic (CFRTP). A crucial aspect of UPW is the design of the energy director (ED). In this study, ultrasonic embossing technology was used to process flat EDs to obtain a new type of ED, named embossed ED. The effect of embossed EDs on the joint formation in ultrasonic welding of continuous carbon fiber reinforced PEEK was investigated in terms of tensile shear properties, macro and micro-morphologies, and fracture morphology. The results show that the use of embossed EDs makes a more homogeneous temperature distribution at the welding interface which significantly reduces defects in the joint. The use of embossed EDs increases the failure load of welded joints by about 50 % (up to 39.6 MPa) and reduces the variation of the joint quality compared with the use of flat EDs. In the optimal condition, the joints made with embossed EDs experiences interlaminar failure of the base material.

Electrical Arc Machining (EAM) presents an efficient technique for processing difficult-to-cut materials such as Inconel 718. However, despite its extremely high machining efficiency, the high energy density in machining makes it difficult to achieve a desirable surface quality that can be compatible with the subsequent cutting process. To solve this issue, this study explores the application of a magnetic field to enhance the performance of Blasting Erosion Arc Machining (BEAM), namely Magnetic Field assisted BEAM (M-BEAM). It leads to an increased Material Removal Rate (MRR) and reductions in both the Tool Wear Ratio (TWR) and the Surface Roughness (represented by Sa) with the increasing magnetic field strength, attributed to the improvements of the arc deflection and molten metal expelling. Moreover, the electromagnetic force is positively correlated with the discharge energy, which can further improve the machining performance of BEAM, especially when the hydrodynamic force is hard to act at large discharge energy. The MRR and Sa are enhanced and reduced by 14.52 % and 41.86 % respectively due to the stronger control effect at large energy. After multi-objective optimization, the optimized MRR in M-BEAM achieves a 9.22 % enhancement and Sa also decreases by 25.96 % and 60.61 % in the roughing and finishing process. This advancement also elevates machining precision as well as mitigates defects such as debris adhesion, overburning, and cracks. Moreover, the recast layer is significantly reduced by 88.59 % and 89.96 %. Consequently, M-BEAM promises extensive applications in aerospace industries for machining Inconel 718 and even for other difficult-to-cut materials with high efficiency and quality.

Functional gradient materials (FGMs) have garnered increasing interest for their potential in material and structural design. Additive manufacturing, as a kind of free manufacturing and near-net shaping technology with in-situ controllability of materials, is the dominant technology for fabricating FGMs. While numerous studies have been conducted on titanium alloy FGMs, there is still a lack of research on the structure and properties of the material with the number of transitional layers. This study employs double-wire arc additive manufacturing to fabricate FGMs composed of TC4 and TC11 alloys. The study examines the utilization of direct and continuous transition forms in conjunction with stress relieving and solution aging heat treatment processes. The composition, grain morphology, microstructure, and mechanical properties of FGMs are analyzed. Results indicate that in samples employing direct transition, higher heat treatment temperatures and durations lead to a more uniform composition and microstructure. Additionally, the interface morphology becomes increasingly indistinct, and transversal elongation at the interface is enhanced by the strain compensation of the two materials. In continuous transitional samples, an increase in the number of transitional layers results in a more uniform microstructure near the interface, leading to a reduction in interface morphology and an enhancement of mechanical properties. The fracture position tends to shift closer to the TC4 side, with both process forms exhibiting ductile fractures. The plasticity of the TC4 part is superior, and the ductile fracture morphology is more pronounced. This study offers a valuable experimental foundation for investigating the direct and continuous transition of titanium alloy FGMs.

The dual-wire electron beam-directed energy deposition (EB-DED) process presents considerable advantages for fabricating titanium aluminide (TiAl) alloys via in situ reactions between Ti and Al. However, variations in the thermophysical properties of pure Ti, pure Al, and TiAl alloys pose challenges in achieving consistent droplet transition behavior and uniform chemical composition. This study explored the effects of wire feeding modes on the forming quality of TiAl alloys and droplet transition behaviors and discussed compositional homogenization and elemental evaporation in TiAl alloy components. Both single-side and double-side feeding modes were utilized, and the electron beam directly melted the Ti wire in the double-side mode, thereby achieving superior surface morphology. Random disturbances and suboptimal wire feeding angles led to the wires deviating from the electron beam center and then being inserted into or passing through the molten pool, thereby degrading the forming quality. By positioning the Al wire tip beneath the Ti wire tip, a common droplet emerged as the Ti droplets melted the Al wire. The droplet transition behavior was regulated by the distance between the wire tips and component surfaces, achieving a liquid bridge transition at distances ranging from 0.75 to 5.82 mm. Although the droplet composition was generally uniform owing to elemental evaporation, the fluctuations among the droplets exceeded those observed in the as-deposited components. The extensive molten pool and keyhole effect enhanced compositional homogenization within the TiAl alloy components. During the deposition process, the evaporation rate of Al surpassed that of Ti due to its higher saturation vapor pressure, consequently yielding a lower actual Al content. The loss rate of Al initially decreased and then increased as the calculated Al content increased, which was influenced by the Al content in the molten pool and temperature variations. This research advances the fundamental understanding of TiAl alloy fabrication via in situ reactions and contributes to the development of the EB-DED process.

Friction stir spot welding has important applications in the joining of thin metallic plates. However, the asymmetric thermomechanical action inherent in the single-sided friction stir spot welding inevitably generates the hook defect at the joint interface, and the defect deteriorates with the improvement of the interfacial metallurgical bonding, which causes the irreconcilable contradiction and significantly restricts the breakthrough of the process stability and welding efficiency. The synergistic double-sided probeless friction stir spot welding (SDP-FSSW) technology proposed in this study adopts a dual-axis synergistic control system, which introduces intense plastic deformation from both sides of the interface to form a wavy hook by accurate axial motion during the welding process. This innovative process solves the problem of hook warpage while realizing rapid metallurgical bonding and mechanical interlocking at the interface, thus obtaining AA2198-T8 aluminum‑lithium alloy spot joints with a tensile/shear strength exceeding 9kN in a short dwell time (0–3 s). Through response surface methodology, the optimal process parameters are identified, i.e. rotation speed of 603 rpm, dwell time of 3 s, and plunge depth of 0.26 mm, at which condition the average joint strength is 13.0 ± 0.5kN, a 47 % increase compared to an optimized joint of single-sided probeless friction stir spot welding (8.9kN). The optical microscope examination shows that the wavy hook can be adjusted by the rotation speed and the higher rotation speeds will make the wave disappear and produce an approximately straight interface. The fractographic analysis shows that the wavy hook can inhibit crack propagation and has good mechanical interlocking effect, but the flat hook at high rotation speeds leads to crack propagation directly along the interface, and the failure mode is changed from plug-pull fracture to interfacial fracture. Therefore, the joint strength at 1000 rpm is only 7.0kN, which decreases by about 47 % compared with the optimal strength. The electron backscattering diffraction analysis shows that continuous dynamic recrystallization occurs in the hook region and good metallurgical bonding is formed, and there are also some discontinuous dynamic recrystallized grains distributed between the large grains due to the larger strain rates and lower temperature at the interface during the SDP-FSSW process. It has been found that the wavy hook with good metallurgical bonding and mechanical interlocking can be introduced in spot welded joints by controlling the interface forming, which is a viable method to create high quality, efficient and reliable spot joints.

Tailor welded blank (TWB) technology can be economical to produce large blanks by suitably welding smaller size sheets of C-103 (Nb-10Hf-1Ti (wt.%)) alloy, and subsequently deforming these blanks through single point incremental forming (SPIF) process to fabricate critical space components. The present work aims to weld highly oxidation-prone C-103 sheets by electron beam welding and to deform the successfully welded blanks at room temperature into conical and pyramidal frustums with constant wall angle employing a multi-stage SPIF process. In this SPIF process, a tool path strategy was designed to obtain a higher wall angle, overcoming challenges such as surface galling and tool failures. Moreover, a reduction in axial force on the tool was observed after implementing this strategy due to a gradual decrease in wall angle increments in subsequent stages safeguarding the tool. The welded blanks fractured at a wall angle of 52.85° and 43.83° during the fabrication of the conical and pyramidal frustums, respectively. These angles were found to be lesser than the corresponding wall angle of monolithic sheets (57.34° and 50.19°). This decrease in wall angle was attributed to early fracture in weld zone (WZ) due to its higher hardness and reduced ductility resulting from the presence of nano-sized HfO₂ precipitates. The above findings suggested that the proposed multi-stage SPIF strategy can be implemented to deform TWBs of C-103 material for the fabrication of complex space components. In order to get further insight into the deformation behavior, texture analyses were carried out near the fracture region of the frustums. It was found that random orientation in the WZ tended to orient towards Rotated Cube {001}〈110〉 in the deformed WZ specimens. However, the intensity of Rotated Cube, Cube {001}〈100〉, and $\gamma$-fiber weakened in the base region of the deformed C-103 specimens as compared to the undeformed specimen.

Feedforward/feedback control of laser powder bed fusion (L-PBF) was proposed over a decade ago but remains challenging. Despite numerous parameters involved, most studies have attempted to control the process by changing laser power only. On the other hand, previous studies have shown that reducing the time per layer ($\mathrm{TPL}$) increases the heat accumulation during the process. Thus, this feasibility study aimed to validate $\mathrm{TPL}$ as a potential parameter to control the top surface temperature of a nickel-based superalloy sample during L-PBF. First, a part-scale finite element thermal analysis with feedback control was performed to verify the temperature control strategy. Then, the sample was experimentally fabricated with the temperature control by changing $\mathrm{TPL}$. The measured temperature was successfully maintained at target values (400, 500, and 700 °C), which were switched every 100 layers. In the as-fabricated IN738LC sample with the temperature control, the cellular microstructures coarsened by more than 0.5 μm and the hardness increased by approximately 50 HV as the target temperature was set higher. While demonstrating the potential of $\mathrm{TPL}$ for temperature control, its limitations in practical manufacturing were also discussed.

Centrifugal impellers (CIs) boast advantages such as compact structure, lightweight characteristics, and high single-stage pressure ratio. These benefits make them essential across sectors such as aerospace, energy and power, and automotive. The manufacturing process of impellers plays a crucial role in determining their aerodynamic performance and production costs. It demands attention to diverse processing methods, the distinctive features of free-form surface and thin-walled blades, and factors affecting manufacturing accuracy and efficiency. Consequently, the manufacturing technologies for impeller machining have become the focal point of current research. The 5-axis milling manufacturing process for CIs has been extensively analyzed and reviewed. This thorough review scrutinizes and contrasts the attributes of 5-axis end milling and flank milling methods, covering processing principles, unique characteristics, and the implications of tool geometry. Regarding these two milling methods, the paper summarizes the current research findings on milling strategies for free-form surface blade fabrication and the evaluation and management of errors and deformations in the machining of thin-walled blades. Moreover, it delves into the challenges and innovative technological solutions in tool-path planning and deformation control within 5-axis milling. This paper aims to furnish technical guidance for the manufacture of CIs, thereby charting a path towards the realization of high-performance and cost-efficient CIs.

Constant monitoring of manufacturing processes is crucial for ensuring high-quality products and cost-effectiveness. Non-destructive testing (NDT) techniques, such as eddy current testing (ECT), offer a direct and accurate means of evaluating weld quality in real-time. ECT can assess microstructural changes in welded materials by measuring electrical conductivity. Establishing a robust correlation between electrical conductivity and microstructural changes induced by FSW process parameters remains a critical step to bridge existing knowledge gaps. In this study, electrical conductivity field analysis using eddy currents was conducted on AA6082-T6 FSW joints. A pivotal factor controlling process heat input and influencing defect formation and weld microstructural features is the ratios of FSW tool rotational speed (ω) to travel speed (v). Previous works often evaluated only one set of process parameters, while our study examines multiple combinations of ω and welding speed v to develop a more robust correlation between electrical conductivity and microstructural changes. Both defective and defect-free joints were obtained employing various ω/v ratio and electrical conductivity results were compared with hardness measurements and tensile test results. The analysis reveals a consistent trend between electrical conductivity variations, microstructural changes in weld zones, and microhardness as the ω/ν ratio varies. Our findings show that, at a constant travel speed, an increasing ω/ν ratio is associated with enhanced microhardness and decreased electrical conductivity, attributed to grain refinement. Conversely, at a constant rotational speed, a higher ω/ν ratio leads to increased electrical conductivity, due to the enhanced dissolution of strengthening precipitates. Furthermore, analyzing electrical conductivity profiles and identifying local maxima corresponding to weld failure zones could strengthen the correlation. This approach suggests the potential to assess variations in mechanical properties resulting from process drift, specifically influenced by changes in the ω/v parameter over time. Microstructural analysis through electrical conductivity evaluation emerges as a valuable and predictive tool for assessing weld properties, with promising applications in process monitoring.