Thin-walled Components Research Articles

Optimizing microstructure and strength of CMT-wire arc additive manufactured WE43 Mg alloy through a novel active cooling technique

Cold metal transfer (CMT)-Wire arc additive manufacturing (WAAM) has been widely utilized in the production of large Magnesium (Mg) alloy components. However, the thermal cycling and heat input inherent in the CMT-WAAM process can adversely affect the microstructure and properties of Mg-Rare earth (RE) alloys. Currently, there is a lack of effective, low-cost, and easy-to-implement methods to mitigate these issues. In this study, an active cooling technique (ACT) comprising base cooling and bypass cooling was proposed. The ACT facilitates in-situ cooling of CMT-WAAMed WE43 components through uninterrupted water flow in the substrate and bypass plate, offering advantages in cost-effectiveness, safety, and ease of implementation. It was found that the CMT-WAAMed WE43 alloy thin wall component manufactured with the ACT assistance had fewer hard-brittle eutectic phases and finer grains due to the accelerated cooling rate. ACT effectively reduced the heat accumulation and peak temperatures in the component. Furthermore, it inhibited the transformation of the β1 phase to the β phase and suppressed the coarsening of the β1 phase. ACT also improved the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of the CMT-WAAMed WE43 component by 11.7 %, 5.8 %, and 72.3 %, respectively. This study provides a novel approach for the microstructure optimization of CMT-WAAMed Mg-RE alloy, which is crucial for the production of high-performance and large-size components in the aerospace industry.

Reduction in residual stress and distortion of thin-walled inconel 718 specimens fabricated by selective laser melting: Experiment and numerical simulation

Residual stresses were induced in the fabrication of thin-walled Inconel 718 specimens through selective laser melting (SLM) due to rapid heating and cooling, which yield distortion and have a detrimental impact on their mechanical performance. Reducing the process-induced residual stress and distortion is of great importance for practical applications. For achieving this aim, accurate measurement of residual stress and distortion is required. In the present work, residual stresses of SLMed samples were measured through hole drilling method (HDM), taking into account their anisotropic features. The distortion induced by the release of residual stress after manufacturing was measured using digital image correlation (DIC). The effect of thickness of thin-walled samples on residual stress and distortion was investigated. The results indicate that by reducing the thickness of sample, the residual stress could be reduced, whereas the distortion was increased. Furthermore, it was revealed that by manufacturing a pair of side samples in one printing job, the distortion and residual stress of the thin-walled component fabricated by SLM can be evidently reduced. The obtained results were clarified by using thermal-mechanical simulations of SLM.

Effect of heat treatment on the microstructure and mechanical properties of Mg-Gd-Y-Zr alloys fabricated by wire arc additive manufacturing

ABSTRACT Wire arc additive manufacturing (WAAM) technology is expected to be used for the fabrication of large and complex magnesium alloy components. In this work, Mg-9.54Gd-1.82Y-0.44Zr (wt.%, GW92) alloy thin-walled components were fabricated by cold metal transfer (CMT) arc in CMT-Advance mode. The microstructure of the WAAMed GW92 alloy consists of fine equiaxed ɑ-Mg grains with an average size of ∼17 μm, eutectic phases, β" phase, cubic phases, and Zr particles. The short-term high-temperature solution treatment at 525 ℃ for 25 minutes significantly reduced the content of the eutectic phase, resulting in a significant increase in elongation (EL) (13.5 ± 0.3%). The peak aging time of the solution-treated GW92 alloy at 225 ℃ for 12 h. The WAAM-T6 sample showed a significant increase in strength while maintaining good ductility, with a yield strength (YS) of 235 ± 3 MPa, ultimate tensile strength (UTS) of 360 ± 7 MPa, and elongation of 10.8 ± 1.7%. The synergistic strength and ductility properties of Mg-Gd-Y-Zr alloys fabricated by the WAAM process were significantly impacted by the short-term high-temperature solution + aging treatments to preserve the fine grain and high-density.

Wire-arc directed energy deposition of high performance heat treatment free Al-6Mg-0.3Sc alloy

The release of residual stress during heat treatment of additively manufactured components could lead to significant deformation, particularly for those with thin-wall features and variable cross-sections. In this study, high performance heat treatment free Al-6Mg-0.3Sc alloy components were fabricated using the wire-arc directed energy deposition (DED) technique, achieving a yield strength of 223.0 ± 0.9 MPa, tensile strength of 408.5 ± 3.2 MPa, and elongation of 20.6 ± 1.7 %. The results indicate that compared to the CMT arc mode, the CMT + PA arc mode leads to a more pronounced bimodal microstructure, resulting in improved elongation. The mechanical property enhancement mechanism relies more on solid solution strengthening and grain boundary strengthening than on precipitation strengthening. Additionally, this study establishes for the first time a correlation between droplet transition and microstructure evolution. The research presented herein lays a theoretical foundation for wire-arc DED in the direct manufacturing of large thin-walled components without the need for heat treatment.

Modeling for plastic instability in multi-directional rotary forging of thin-walled components with three ribs

Multi-directional rotary forging has the great potential to form thin-walled components with three ribs because of its incremental deformation characteristic and smaller forging load. However, for the components with thin-walled sterna and thick ribs, the plastic instability is easier to occur at the bottom of thick ribs in multi-directional rotary forging, resulting in the waste of components. Therefore, the aim of this paper is to establish the model for predicting plastic instability in multi-directional rotary forging of thin-walled components with three ribs. Firstly, the models for calculating actual and critical radial stresses on both sides of rib are established by analyzing complicated stress states caused by time-varying thinning deformation of sterna and thickening deformation of rib. It is found that the critical radial stress is mainly determined by ratio of deformation energy and external force work, while the actual radial stress is mainly determined by dissipated power and metal flow velocity. By combining actual and critical radial stresses, a unified model for simultaneously predicting plastic instability of ribs at different positions is proposed. Then, the influence laws of different technical parameters on critical conditions of plastic instability are revealed. It is found that the plastic instability is mainly determined by initial thickness of workpiece and width of rib, i.e., the critical deformation amount increases with increasing initial thickness of workpiece or decreasing width of rib, and vice versa. Finally, the experiments are conducted to verify that the proposed model for predicting plastic instability in multi-directional rotary forging of thin-walled components with three ribs is reliable. This paper provides a guideline to establish the model for predicting plastic instability under complicated stress states and metal flow modes.

Wire-arc directed energy deposition of metal using a tendon-driven soft robotic gun: prototyping and conceptual validation

ABSTRACT Most directed energy deposition (DED) implementations employ a rigid end effector to deposit material layer-by-layer, which is insufficient in cases with space constraints. To enhance the flexibility, this paper proposes a novel soft-robotic gun (SRG) based DED technology. The ideology is to replace the rigid weld gun with a tendon-driven omnidirectional-steering continuum manipulator, which a computer can numerically control. To this end, both requirements and concepts of the SRG-DED are introduced. A prototype system is designed and implemented before dedicated kinematic modelling and trajectory planning mechanisms are presented. As demonstrated by the experimental results, the developed trajectory planning algorithm improves the computational efficiency of tendon variables and enhances the consistency of trajectory tracking. The prototype system can deposit a complex path on an inclined substrate and fabricate a thin-wall component within a pipeline. The validation work confirms the feasibility and applicability of the prototype system for metal additive manufacturing applications.

A global springback compensation method for manufacturing metallic seal ring with complex cross-section and submillimeter precision

The fabrication of complex thin-walled components with irregular cross-sectional geometries often necessitates multi-pass forming processes. The springback phenomena at the microscale level contribute significantly difficulty to the precise control of geometrical accuracy for such components. To achieve submillimeter precision control of micro features in metal seal rings, this research proposed a global springback compensation method to facilitate the attainment of the optimized surfaces of dies. Through the analysis of changes in cross-sectional shape, stress distribution and bending moment in the multiple stages, several partition points were set up to divide the cross-section into four zones. For a partitional control of the manufactured surface, the compensation magnitudes for each segment are determined by iteratively refining the compensation factors using the secant method. The iteration of compensation factors is based on the deviation of dimensions measured by finite element simulation, which greatly saves experimental costs. The experimental results indicate that the predictive dimensional alterations by the global compensation agree with the experimental ones exhibiting a maximum error of less than 3 %. Furthermore, the springback behavior during the unloading and trimming stages coupling caused a dimensional error of 14.9 % for the wave width and 8.3 % for the peak width. Following the application of coupled compensation through two iterations, a distinct decrease in the relative average errors of springback values for both part width and peak width, achieving reductions to 2.4 % and 0.6 %, respectively. Compared to the traditional single springback compensation technique, the global compensation strategy effectively mitigates the out-of-tolerance issues induced by the trimming process.

Size effect and underlying microstructural mechanism in cyclic deformation behavior of nickel-based superalloy sheet

The nickel-based GH4169 superalloy is widely used in the aerospace field, which has desirable oxidation resistance and strength in extreme environments. However, the size effect and underlying microstructural mechanism in the cyclic deformation of the GH4169 sheet are still not fully elucidated, which affects the forming accuracy precision of thin-walled components. To this end, the cyclic mechanical properties and microstructural evolution of the GH4169 sheets with different thicknesses and grain sizes were systematically investigated via cyclic shearing tests. The superalloy sheet exhibits obvious early re-yielding, instantaneous softening and permanent softening during the cyclic deformation and these cyclic deformation behaviors are obviously affected by size effect. To rationalize the cyclic mechanical responses and size effect, transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) tests were conducted. The results indicated that the dislocation slip patterns are principally planar array slip and cross slip in the cyclic shearing deformation. Meanwhile, the annihilation of unstable dislocation and the presence of carbides led to the instantaneous softening. Moreover, the change of loading direction, the reduction of texture strength, the proportion of low-angle grain boundary (LAGB), and geometrically necessary dislocation (GND) density together result in the occurrence of permanent softening. Based on the comparative analysis of the microstructure evolution of superalloy sheets with different size factors, the underlying mechanism of size effect on cyclic deformation was clarified. The findings in the research combine the cyclic mechanical response and microstructure evolution closely in the cyclic deformation of superalloy sheets and deepen the understanding of size effect under complex loading paths.

Ultrasonic impact surface strengthening treatment and fatigue behaviors of titanium alloy thin-walled open hole components

A double side surface strengthening method based on ultrasonic impact treatment (UIT) was developed to improve fatigue behaviors of titanium open hole structures. The surface property after strengthening was characterized. The surface strain under quasi-static load was analyzed by a 2D-DIC method, moreover, fatigue behaviors were also tested. The results showed that the hardness and microstructural characteristics were significantly improved by the strengthening method. The surface strain along tensile direction was restricted by the strengthened surface, while the strain level perpendicular to tensile direction increased after strengthening. As expected, an obvious increasing in fatigue life of strengthened specimens was observed, and the fatigue crack propagation was delayed by the strengthening. Specially, the optimal fatigue performance was generated by the combination strengthening of UIT and polishing.

A novel manufacturing process for intermetallic thin-walled components: Forming and hot pressing of thin-walled laminates prepared by laying/winding metal foil strips

To address the challenge of manufacturing NiAl intermetallic thin-walled components, an integrated manufacturing process using the preform prepared by laying/winding of metal foil strips was proposed. This method entails the initial fabrication of a stacked foil preform via the laying/winding of metal foil strips, followed by pre-sintering to prepare a laminated preform. Subsequently, precise shaping is achieved through hot bulging of the laminated preform, while the NiAl intermetallic phase is obtained through reaction synthesis of Ni and Al foils under hot pressing. The microstructure of Ni/Al/Ni laminated preforms under varied sintering parameters and different laminating methods were analyzed. Additionally, the deformation behaviors of these preforms at both room and high temperatures were investigated via tensile tests and bulge tests. Results show: (1) The micro-cracks and Ni-Ni interface delamination occurred in the brittle Ni2Al3 layer of the laminated preform. The deformation capability of laminated plates decreased as the thickness of the brittle Ni2Al3 layer increased with sintering time. (2) Tiny gaps between foils due to laying path and foil size deviations, causing reduced deformability and fractures when the tensile direction was perpendicular to these gaps. (3) These gaps and micro-cracks can be progressively eliminated through hot pressing sintering processes. The findings verify the preliminary feasibility of the proposed novel manufacturing process and provide a novel solution for manufacturing NiAl intermetallic thin-walled components.

Fully equiaxed grain structure and isotropic mechanical properties in wire arc additive manufactured Mg–Al-RE alloy

Wire arc additive manufacturing (WAAM) of Mg–Al-RE alloy is an essential technology for producing high-quality large-scale components with high manufacturing flexibility. In this study, WAAM was utilized to fabricate a thin-wall component made of Mg-8.2Al-0.6Y-0.4Ce (AE81) alloy. The microstructure and tensile properties of the fabricated component were investigated. The results showed that the as-built AE81 alloy exhibits superior isotropic tensile strengths and a homogeneous equiaxed α-Mg grains structure. Additionally, the alloy demonstrated a minimal growth in grain size after high-temperature solid solution treatment due to the presence of thermally stable Al11/rare earth (RE)3 phases at grain boundaries. Further ageing treatment induces the formation of high-density of β-Mg17Al12 precipitates within the α-Mg grains, resulting in a considerable precipitation strengthening effect. Consequently, the heat-treated AE81 alloy demonstrated significantly enhanced tensile strength of 280 MPa and acceptable ductility of 4.6%. The results also revealed that the formation of equiaxed grains during WAAM contributed to the isotropic mechanical properties. These findings can facilitate advancements in AM processes and the development of high-performance Mg alloys.

Melt pool control-assisted additive manufacturing of thin-walled parts

Thin-walled aerospace components manufactured by laser directed energy deposition are susceptible to thermal accumulation effects owing to their deposition path and efficiency, further leading to the edge collapse. The melt pool width, as the carrier of thermal input, is an important geometric factor reflecting the state of the melt pool. Therefore, an in-situ melt pool control technique was proposed. The melt pool width as the control target was monitored using a coaxial camera, and the laser power was adjusted in real time based on the proportional-integral-derivative algorithm. A thermal accumulation model in conventional mode and a thermal suppression model in control mode were derived. The surface roughness, porosity, microstructure, and tensile properties of AISI 316 L stainless steel were compared between two modes. The results demonstrated that the roughness and porosity of thin-walled parts were respectively reduced by 45.3% and 82.7% after control. The periodic evolution of interlayer columnar and equiaxed crystals, and the increase in deformation twins contributed to a simultaneous increase in tensile strength and toughness, with a maximum increase of 35.7% in elongation.

Temporal and spatial determination of solidification rate during pulsed laser beam welding of hot-crack susceptible aluminum alloys by means of high-speed synchrotron X-ray imaging

Pulsed laser beam welding is primarily used to join thin-walled components. The use of 6xxx group aluminum alloys is characterized by good mechanical properties but these alloys are prone to hot cracking during solidification, i.e., requirements regarding strength and tightness, as increasingly important for electromobility related applications, cannot be fulfilled. The solidification rate has been identified as dominant factor in pulsed conduction welding which can be adjusted by the pulse shape, i.e., by varying the beam power over time for a single pulse.Pulse shapes with different, linear ramp-down slopes were studied to describe the interaction between beam power and resulting solidification rate for spot welds. Based on rotationally symmetric conditions of the spot welds, the solidification rate can be measured in radial and vertical directions. The welding process of EN AW 6082 alloy was examined by in situ high-speed synchrotron X-ray imaging at the European Synchrotron Radiation Facility (ESRF) for this reason. Frame rates up to 120,000 Hz and subsequent image analysis allowed in-depth analysis of the solidification processes, their dependence on different spatial directions, and the resulting effects on hot crack formation.

Investigation on mechanism in fabricating truncated cone with tooth features of titanium alloy via flexible free incremental forming at room temperature

It has been a challenge to efficiently make titanium alloy thin-walled components by sheet metal forming. Incremental sheet forming (ISF) method provides a promising way to increase the formability of low-ductility metallic sheets, but making titanium alloy sheet panels still needs heating by electricity or laser. The present work investigates the deformation mechanism in fabricating truncated cones of titanium alloy with tooth features realized by flexible free incremental sheet forming (FFISF) at room temperature. Experimental investigations on auxiliary sheets and tool path selections, analytical modeling, finite element simulation, and microstructure characterization have been conducted to evaluate the deformation mechanism in terms of the geometric deviation, thickness distribution and microstructure evolution of TA2 and TC4. Results indicate that the I-O loading path coupled with an optimized auxiliary sheets selection can ensure the successful fabrication of designed panel without defects. An analytical model is proposed to predict the free edge dependent law of thickness distribution in FFISF, indicating the material thinning is positively correlated with the distance from the free edge, while the thinning rate is inversely proportional to the yield strength. A more uniform thickness of TC4 panel is obtained compared with TA2. Finally, the improved formability of titanium alloys by FFISF can be attributed to grain subdivision, decreasing of intragranular deformation, and optimization of dislocation movement.

Sc/Zr microalloying on strength-corrosion performance synergy of wire-arc directed energy deposited Al-Mg

ABSTRACT WADED Al-Mg and Al-Mg-Sc-Zr aluminium alloy thin-wall components were produced. Heat treatment (350°C aging for 4 h) was further conducted. The effects of Sc/Zr addition on porosity, microstructure, mechanical properties and corrosion behaviour were investigated. With Sc/Zr adding, pore area fraction decreased from 0.208 to 0.005% and grain size decreased from 84.34 to 19.54 μm. In WADED Al-Mg-Sc-Zr component, microstructure showed refined equiaxed grains. Mechanical properties were improved with 360 MPa ultimate tensile strength (UTS), 185 MPa yield strength, and 23.31% elongation. After heat treatment, UTS increased to 388 MPa with good ductility (22.53%) maintained. The grain refinement and Al3(Sc, Zr) particles were the key factors for mechanical property improvement. The corrosion behaviour was improved with introduced Sc/Zr and further optimised after heat treatment. The corrosion exhibited layered characteristics due to the distribution of primary Al3(Sc, Zr) while minor-size secondary Al3(Sc, Zr) along grain boundaries improved the corrosion behaviour.

Formulas determining the local critical stress of I-shape sections under axial compression

The I-shaped steel sections should be checked for local buckling conditions during design. When local buckling occurs, there is interaction between thin-walled components of the section. Design codes have provided formulas to determine local critical stress for I-shaped steel sections, but they do not account for this interaction. This paper proposes equations for determining the local ultimate stress of I-shaped sections under axial compression, considering web and flange interaction when ratios between the height and width of the section, the flange thickness and web thickness change. The local critical stress is determined by the semi-analytical finite strip method carried out in the CUFSM program. The equations are proposed based on the parametric study. The reliability of formulas is confirmed when comparison to published and numerical results.

Electroforming of Personalized Multi-Level and Free-Form Metal Parts Utilizing Fused Deposition Modeling-Manufactured Molds.

Adapting to the growing demand for personalized, small-batch manufacturing, this study explores the development of additively manufactured molds for electroforming personalized metal parts. The approach integrates novel multi-level mold design and fabrication techniques, along with the experimental procedures for the electroforming process. This work outlines design considerations and guidelines for effective electroforming in additively manufactured molds, successfully demonstrating the production of composite metal components with multi-level and free-form geometries. By emphasizing cost efficiency and part quality, particularly for limited-thickness metal components, the developed technique offers distinct advantages over existing metal additive manufacturing methods. This approach establishes itself as a flexible and durable method for metal additive manufacturing, expanding the scope of electroforming beyond traditional constraints such as thin-walled hollow structures, 2D components, and nanoscale applications.

Innovative high degree of freedom single-multipoint incremental forming system for manufacturing curved thin-walled components

This study proposed a new design and control framework for a novel high degree of freedom single-multipoint incremental forming (HDoF-SMIF) system to manufacture curved thin-walled components. First, a novel HDoF-SMIF system was designed based on the principles of HDoF-SMIF technology (including the description of the mechanical structure and network topology). Following that, to realize the process control of the HDoF-SMIF process, this study introduced a novel control strategy for the tool deflection angle specific to robotic incremental forming. It also developed a synergistic motion control approach for the lifting platform and an accelerated computation method to determine the forming parameters for a multipoint reconfigurable die. Then, a novel HDoF-SMIF principle prototype and control program were built for the designed HDoF-SMIF system structure and control method. Finally, the feasibility of the HDoF-SMIF system was verified with the forming test on the domed component, and the geometrical accuracy and wall thickness distribution of the samples were measured using a 3D optical scanner system to evaluate the forming quality of the established HDoF-SMIF system. The results showed that compared to the conventional single-point incremental forming (SPIF) process, the developed HDoF-SMIF system can provide a more uniform thickness distribution of the formed part with a lower overall thickness thinning rate. Furthermore, by increasing the tool deflection angle with a 1 mm elastomeric interpolator, the overall part's forming accuracy and surface quality can be effectively improved.

Strength-plasticity synergetic CF/PEEK composites obtained by adjusting melt flow rate

Short carbon fiber reinforced PEEK (CF/PEEK) composite materials with the advantages of excellent mechanical properties and easy processing, have been widely applied in the fields of aeronautics and astronautics, automotive engineering, and so on. However, their development in microinjection molding is hindered by the incompatibility between excellent plasticity and high mechanical properties. Herein, strength-plasticity synergetic CF/PEEK composites are prepared by adjusting the melt fluidity and crystallization behaviors, based on PEEK with different melt flow rate (MFR) and T800 carbon fiber. The rheological results showed that the melt viscosity of CF/PEEK composite was negatively related to the MFR of PEEK. Moreover, the mechanical properties of composites were increased by the crystallinity of PEEKs with high MFR. This work presents strength-plasticity synergetic CF/PEEK composites suitable for microinjection molding thin-walled and intricate components, offering new opportunities for next-generation portable electronic.

Forming quality optimization of 2219 aluminum alloy thin-walled complex components based on fracture constraint in spin forming

Forming quality optimization of 2219 aluminum alloy thin-walled complex components based on fracture constraint in spin forming