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This study presents an unconventional flow processing technique that uses glass microspheres instead of abrasives. The fundamentals of flow machining with glass microspheres, including microsphere flow burnishing (MFB) and the conditions necessary for cutting or plastic deformation of a surface to occur during MFB, are determined. Details on such conditions are lacking, and therefore, this study attempts to define these conditions. To this end, MFB was experimentally confirmed to be a burnishing process, and the effects of MFB and abrasive flow machining (AFM) on 2017A aluminum alloy were compared. Both processes achieved a surface roughness (Sa) of < 0.5 μm, while MFB yielded higher values of surface microhardness and compressive stress. The effects of basic process parameters on the MFB and AFM results (workpiece weight loss and Sa) were compared experimentally, and the corresponding mathematical models were established. Utilizing these relationships, MFB parameters can be selected so as to obtain the most favorable surface layer for the expected operating conditions. [ABSTRACT FROM AUTHOR]

Precision polishing of aeroengine blades involves a complex material removal process, primarily due to the presence of numerous abrasive grains bonded on the polishing tool. Therefore, understanding the surface formation mechanism at the microscale, as a result of a single abrasive grain's interaction with the workpiece, is pivotal for deciphering the collective effect of numerous abrasive actions. Since conducting single-grain cutting experiments at the microscale presents significant challenges, the finite element method (FEM) is considered an effective method for revealing microscopic physical phenomena and conducting in-depth research on cutting mechanisms. In this research, the simplified single-grain scratch experiment was conducted first, and then, the adaptive remeshing technique in Abaqus was utilized to simulate the elastic and plastic deformation of the workpiece surface during the polishing process, supplementing the physical measurement results that are difficult to achieve in the scratch experiment. The single-grain scratch experiment results show that elastic deformation of the workpiece material persists throughout the grain cutting process, and the elastic deformation FEM simulation results show that the pure rubbing phase is confined to an extremely short length after the interference occurs between the grain and the workpiece. To delve into the plastic deformation of workpiece surface in FEM simulation, the material pile-up ratio was used, and the effect of polishing variables such as cutting speed, cutting depth, and grain size on microscopic surface creation was focused on. Among them, cutting depth and grain size significantly affect the surface creation of workpiece material. In addition, the microscopic plastic deformation when the abrasive grain cut-in and cut-out phases during the polishing process is different. The outcomes of these simulations are anticipated to inform future experimental strategies and foster advancements in the development of more efficient and precise aeroengine blade polishing techniques. [ABSTRACT FROM AUTHOR]

In recent years, additive-subtractive hybrid manufacturing (ASHM) technology has become a research hotspot. To realize high-precision manufacturing of complex parts and avoid machining interference, alternating additive manufacturing (AM) and subtractive manufacturing (SM) are valuable to be adopted. In this paper, a finite element numerical model was established to simulate the temperature history, stress distribution, and deformation trend of the thin-walled parts alternately fabricated by AM and milling process. Then, 316L stainless steel thin-walled samples were built by the alternating ASHM process. The molten pool temperature, the surface residual stress, and the surface contour of samples were measured and analyzed. The results show that high tensile stress is exhibited at the junction of the AM segment with the substrate or the previous SM segment. With the increase of deposition height, the tensile stress decreases first and then increases. After the subsequent milling, the surface residual stress level shows a decreasing trend, which is because the milling-induced compressive stress offsets the initial residual tensile stress. Moreover, the deformation of the two ends and the top of the AM segments is more significant than that of the bottom. After SM, the deformation in the top area of the SM segments is still slightly more extensive than the bottom area. The subsequent AM process results in a small increase in the residual stress of the milled segment, but had little effect on its surface deformation. Finally, the repeated cutting height between two segments was studied. Compared with the previous work, this strategy considers the effect of the alternating ASHM process on the residual stress and deformation of thin-walled parts. This study has certain guiding significance for the manufacture of thin-walled parts such as turbine blades and parts with internal structure by alternating ASHM process. [ABSTRACT FROM AUTHOR]

The real-time support variation of the machine tool is a source of systematic errors that cannot be ignored and has a great impact on the machining accuracy. The calculation and representation of moving support variation are important basis for improving machining accuracy. Different from the traditional data-based methods of static deformation measurement and compensation, this paper proposes a real-time continuous moving support deformation error model-based method to establish a systematic spatial-variably volumetric error model, which realizes the model decoupling of complex error sources of machine tools. The real-time deformation of moving support under multiple working conditions by FEM simulation is converted into the joint surface deformation of the moving system, and the translational and rotational position-dependent geometric errors (PDGE) are analyzed through the positional geometry of four sliders as joint surface, and the continuous moving variation errors along the single-axis and dual-axis motion space is generated. Further, based on the homogeneous transformation theory, the multi-axis 6-DOF PDGE are fused to construct a spatial-variably volumetric error model. In addition, this paper adopts a machining optimization method, which can efficiently identify the optimal machining space for the machine tool according to the machining features of the workpiece and the spatial-variably volumetric error model. In the case study, the proposed method is applied to a horizontal machining center, the detailed characterization of the spatial-variably error is given, and the optimal machining space is identified for different sample workpieces, which proves that it can effectively improve the machining accuracy of the machine tool. [ABSTRACT FROM AUTHOR]

Surface roughness with topography modeling is one of the most important indicator for evaluating the surface quality in the machining process. This paper establishes a 3D surface roughness prediction model for bevel milling by considering the factors such as milling geometry, motion trajectory, and elastic-plastic deformation. Most of the existing roughness prediction models for bevel milling are based on regression models combined with multiple methods, which makes these models cannot well applied in complicated applications. Aiming at the change of contact area between tool and workpiece in bevel milling, the concept of effective cutting edge is introduced to establish a surface topography simulation model. Furthermore, this model fully considered the milling method, machine perpendicularity, and elastic-plastic deformation. Combined with the international standard of three-dimensional surface roughness, the roughness is predicted according to the residual height of each point on the surface topography. In order to verify the model accuracy and to explore the influence of process parameters on roughness and milling force in bevel and plane milling, two orthogonal experiments are designed in this paper. The experimental results show that the surface topography simulation results are consistent with the actual shape characteristics. The average relative error of roughness prediction is 7.93%, and the minimum is only 0.84%. In addition, the experimental results show that the two factors that have a great influence on the roughness are the spindle speed and feed rate, while the cutting depth and step distance greatly impact on the milling force. [ABSTRACT FROM AUTHOR]

The temperature gradient rolling (GTR) method effectively addresses the issue of uneven deformation of surface and core in the rolling of extra-thick plate. Different from the traditional near uniform temperature rolling (UTR) process, GTR involves a significant temperature gradient along the thickness direction of the rolled piece. As a result, the rolling force prediction model used in uniform temperature rolling cannot be directly applied in GTR. Rolling force prediction model is crucial for process control models of plate mill and serves as the foundation for plate thickness control. However, there has been limited research on rolling force prediction methods specifically for GTR. In order to predict the change of rolling force in GTR process and enhance the control of the rolling process, the current paper proposed a simplified method based on the deformation resistance model, temperature distribution fitting, differential method, and loop iteration. The precision of the method was examined by using a finite element model and plane strain experiment, demonstrating a mean error between the method and FEM was less than 5%. [ABSTRACT FROM AUTHOR]

The level of automation and precision in aircraft assembly determines the effectiveness and quality of aircraft manufacturing. In contrast, the unstable localization accuracy resulting from the layout pattern of flexible track drilling robot has limited their further development and applications in domains with high machining accuracy requirements, such as aircraft assembly. This study begins by presenting the paradox between the need for high-precision drilling tasks during aircraft construction and the accuracy of automated drilling equipment. The problem of precision loss due to flexible track drilling devices is examined in a new application scenario where the overall position and pose layout change with the location of the process station. Then, the characteristics of the weak rigidity of the transmission system of the flexible track drilling robot at the joint surface and the variation of the transmission axial load due to variations in the position and pose of the drilling process station are examined. In addition, an equivalent stiffness model is developed to predict the incremental error of the entire process station, and the incremental error conjecture due to the elastic deformation of the coupling surface of the transmission system is proposed as an optimization algorithm for global position accuracy compensation. Finally, experimental results showed that the incremental error compensation method optimized 68.67% of the total error. [ABSTRACT FROM AUTHOR]

Process monitoring is essential to enable process parameter optimization, deformation prediction, and fault diagnosis in robotic milling. However, expensive costs and installation requirements limit the use of industrial sensors in machining process. This paper proposed a sensorless method to predict force-induced deformation and surface waviness. First, the tracking errors of tooltip was calculated based on the robot joint tracking errors and the robot kinematic model. Subsequently, the idle running and cutting process signals monitored by the robot controller were used to calculate the cutting force acting on tooltip based on Kalman filter and robot static model. On this base, the force-induced deformation, considering the posture error of the robot flange coordinate system, was calculated using the estimated milling force and the flexible model. Finally, the effectiveness of the proposed method was verified by a series of cutting experiments. [ABSTRACT FROM AUTHOR]

In the aerospace industry, high-precision components like impellers and blisks present considerable challenges in machining due to their intricate geometries and the need for reliable performance. Blades, often classified as thin-walled parts with complex, free-form surfaces, are crucial in ensuring the efficiency and safety of aircraft engines. Their geometries and materials require strict control over cutting parameters, such as tool path and orientation, to avoid deformation and maintain surface integrity. This study investigates the impact of tilt angle variation during ball end milling of Ti6Al4V thin-walled parts. Four different tilt angles (15°, 30°, 45°, and 60°) were analysed to evaluate their effect on dimensional accuracy and surface roughness. The results show that tilt angle significantly influences surface quality and dimensional precision. A tilt angle of 30° achieved the best balance between surface finish and dimensional tolerances, with flatness values ranging from 0.038 mm at 30° to 0.101 mm at 60°, representing a 152.5% increase in flatness. The findings provide practical guidelines for optimizing ball end milling of thin-walled components, emphasizing the importance of tool orientation in reducing deformation and enhancing surface quality. [ABSTRACT FROM AUTHOR]

The thin-walled titanium alloy parts have the poor structural stiffness, and the surface deformation error can hardly be improved under heavy processing load, so that has poor machinability for this kind of materials. Based on the comprehensive investigation, liquid nitrogen (LN2) cooling can change obviously the mechanical properties of alloy materials and reduce greatly the cutting heat, and it has been widely used in difficult-to-process materials. In this paper, the deflection and angle models of cutting deformation of titanium alloy thin-walled parts were established. A series of machining experiments were conducted using LN2 and traditional flood cooling strategies, and the influence of milling temperature on machining deformation was analyzed. The results show that the deflection and angle of machining deformation are mainly related to milling force and elastic modulus. When the cooling temperature is reached −130 ℃, there are few burrs on the machined surface. The brittle chip fracture is realized for cutting thin-walled parts, the milling force is increased, and the machining error is decreased clearly. Meanwhile, the location of the occurred deflection and angle has risen significantly near 10 mm, and the machining deformation is reduced obviously compared to the flood cooling. In cryogenic cooling, the increase of cutting stiffness, the change of chip breaking form, and the reduction of deflection are the main reasons for the improvement of thin-walled milling deformation defects. Furthermore, the cryogenic cooling strategy can effectively improve the deformation problem and obtain better machinability for the thin-walled titanium alloy parts. [ABSTRACT FROM AUTHOR]

The surface topography has an important influence on the SCC behavior of stainless steel. Pre-stress grinding has the potential to improve the SCC resistance of the surface. Therefore, theoretical and experimental studies ought to be carried out to explore the improvement effect of pre-stress grinding on topography. Aiming to consider the influence of deformation effect on surface topography, the grinding force, and heat model considering the properties of stainless steel material and grinding wheel was established at the beginning. Then, to make the simulation more accurate, the grains' position with random distribution, the bulge height obeying non-Gaussian distribution, and possessing autocorrelation length were expressed, respectively; finally, the surface topography model considering deformation and plow effect in pre-stress grinding was established, and experimental tests were conducted for the model validation. The simulation results showed good agreement with the experimental results. The results suggest that appropriate pre-stress could flatter the ground surface and decrease the amount of grinding surface defects, such as grinding areas, indentations, and deep grooves. With the increase of pre-stress, Ra, Rz, and aspect ratio of grooves tend to fall, which are conducive to improving the SCC resistance of the surface. The mechanism of the improvement introduced by pre-stress may be that pre-stress improves the rigidity of the grinding surface and reduces the thermal deformation during the grinding process, which makes the material easy to be cut and reduces the probability of surface defects; the spring-back effect after pre-stress release would further close the minor defects on the surface, and further improve the surface corrosion resistance. [ABSTRACT FROM AUTHOR]

The support point layout has an important influence on the working performance of the machine tool, when the material, manufacturing process, and internal structure of machine bed are given. In order to ensure the performance, stability, and anti-interference of precise machine tool, this paper presents an optimized design method of 3-point support for T-shaped bed of precision horizontal machining center. This article first establishes the statics model of the T-shaped bed and analyzes grillage beam model used to characterize the main static deformation trend of the bed based on the singular function method. After verifying the rationality of the model through simulation, the optimized 3-point support position can be obtained. Then this paper measured the deformation of the upper surface of a simple bed due to gravity. The deviation between the experimental results and the simulation results is less than 20%, which verifies the reliability of the simulation and theoretical results. Based on the ISIGHT multidisciplinary optimization platform, this paper completes the multi-objective optimization of the support point layout of the bed, and the optimization results prove the accuracy of the theoretical model. This paper takes the bed of M800H precision horizontal machining center as an example to illustrate the application process of the proposed method. Then, the optimization effect of the bed and the static characteristics of the whole machine by simulation are compared. The maximum deformation of the bed has reduced by 27.1%. In the whole machine status, the deformation of the spindle end has reduced by 50.8%, and the maximum deformation of the workpiece end has reduced by 50.0%. Finally, a verification experiment of the relative position deviation between the end of the spindle and the worktable on the complete machine was carried out. The error of the simulation and experiment results was about 22%, which proves the effect of the optimization of the support position. [ABSTRACT FROM AUTHOR]

In the robotic belt grinding process, the elastic contact condition between the flexible tool and the workpiece is a critical issue which extremely influences the surface quality of the manufactured part. The existing analysis of elastic removal mechanism is based on the statistic contact condition but ignoring the dynamic removal phenomenon. In this paper, we discussed the dynamic contact pressure distribution caused by the non-unique removal depth in the grinding process. Based on the analysis of the removal depth of a single grit, we obtained the topology of a single groove. With the coupling analysis of the topology single groove and grit trajectories in elastic removing procedure, an elastic grinding surface topography model was established with the consideration of the dynamic contact condition in the removing process. Robotic belt grinding experiments were accomplished to validate the precision of this model, while the result showed that the surface roughness prediction error could be confined to 11.6%, which meant this model provided higher accuracy than the traditional predicting methods. [ABSTRACT FROM AUTHOR]

An unintended anisotropic deformation of a polycrystalline billet has been observed in micro-extrusion, which implies that the extruded billet shows a curved shape rather than an intended straight curve. Although the deformation is considered to originate from the anisotropy of crystal grains, three-dimensional computational analyses are yet to be conducted owing to computational challenges. In this study, the anisotropic deformation behavior of a polycrystalline billet during micro-extrusion was investigated by performing three-dimensional finite element analyses based on the anisotropic elastoplastic constitutive model of a single crystal and its robust algorithm. To explain the effect of grain size on the unintended deformation of billet in micro-extrusion, several simulations for two extrusion dies were performed considering polycrystalline billets containing crystal grains between 100 and 20,000 in number, and the results were statistically analyzed. Anisotropic deformation appeared in the billets with fewer grains, owing to the anisotropy of the single crystal. The grain size, normalized with respect to the billet diameter at which the anisotropic deformation began to appear, was quantitatively estimated. These results are in agreement with the corresponding experiments. Furthermore, simulation results indicated that the extruded crystallographic texture decreased the anisotropic deformation in the case of large grains. [ABSTRACT FROM AUTHOR]

Adhesively bonded sandwich structure with dissimilar materials becomes an important means of lightweight for the next generation of autobody closure panels. However, during the baking process, the complicated change of physical properties of the adhesive can lead to structural mismatch deformation. In this paper, a multi-physics coupling numerical model of the curing process is proposed to reveal the deformation mechanism of adhesively bonded sandwich structures quantitatively. The material constitutive model of the one-component hemming adhesive hemming adhesive is established, considering evolution of curing properties. The curing process of typical aluminum alloy and steel-bonded sandwich structure is simulated in COMSOL Multiphysics. The predicted surface deformation of the component is verified by experiment using Digital Image Correlation (DIC) technique, which captures the full-field displacement in a non-intrusive manner. Then, the development process of surface deformation of the outer panel and residual internal stress of the adhesive layer is analyzed, and the influence of temperature cycle on the maximum deformation of the component is discussed. The results show that at the beginning of holding stage, the deformed component slightly rebounds, which is related to the chemical shrinkage. Mechanical strain caused by the coefficient of thermal expansion (CTE) and stiffness difference of the inner and outer panels is dominant in the adhesive layer. Reducing the curing rate and maximum holding temperature can reduce the overall deformation of the structure. [ABSTRACT FROM AUTHOR]

During milling of free-form surfaces, cutting force varies due to the variation of workpiece surface curvature, which can seriously affect machining quality. In this study, a layered strategy was proposed for flexible machining of complex parts with variable curvatures. By taking a blade as the research object, we first considered a constant cutting force as the starting point. The relationship between the machining allowance and the radius of curvature of the workpiece under a certain cutting force was established. By analyzing the curvature of each position of the blade, a reasonable cutting allowance was set for each layer and the machining process was carried out layer by layer, such that a stable cutting force was maintained on the workpiece surface during machining of each layer. Second, the blade surface deformation law was determined by using the T-spline surface characteristics and an improved offset algorithm, and a series of deformation surfaces was obtained. Finally, the feasibility of the proposed method was verified by using finite element simulations and validated by experiment, and the advantages of the proposed method were verified by comparison with the existing main blade processing methods. [ABSTRACT FROM AUTHOR]

In order to explore the influence of cutting process (CP) pretreatment on surface integrity in ultrasonic rolling process (URP), we build a composite cutting–ultrasonic rolling process (CURP) model of 7N01 aluminum alloy based on finite element (FE) software and obtain the deformation mechanism of surface material in CURP treatment through plane ultrasonic rolling experiments. The results show that under CP pretreatment at different feed rates, after URP treatment, surface roughness is reduced by more than 70% compared to after CP treatment; after CURP treatment, surface roughness increases with increasing feed rate; maximum surface microhardness reaches 185 HV, and hardened depth rises to 500 μm. Cutting depth makes the greatest difference to residual stress in CURP; both the amount and depth of residual stress increase with increasing cutting depth; when the cutting depth is 0.6 mm, the residual stress after CURP treatment reaches – 350 MPa. FE analysis reveals that during URP, the surface micro-elements will pass through three deformation zones—extrusion, impact, and recovery. The coupling of mechanical stress and thermal stress will turn the residual tensile stress caused by CP treatment into a compressive stress. [ABSTRACT FROM AUTHOR]

Ceramic particle-reinforced metal matrix composites (PRMMCs) have been widely applied in modern industry with excellent mechanical characteristics. Meanwhile, the addition of high hardness reinforcements also produces a significant challenge for precision machining of PRMMCs and leads to poor machinability and higher time consumed in the subsequent surface treatment process. To investigate the machining mechanism of PRMMCs, a 2D mesoscopic-based finite element (FE) model reinforced with randomly distributed polygon particles was developed. Elastoplastic and failure behavior of aluminum alloy, high hard-brittle and fracture characteristics of reinforcements and particle-matrix-tool interactions were considered comprehensively. Systematic cutting experiments show that the proposed FE model accurately predicts deformation mechanism and surface quality of PRMMCs. Particle fracture and debonding are mainly determined by the stress distribution and strain value. Serrated chips primarily are formed along shear plane and accompanied with the generation and propagation of microcracks. In addition, cracks around particles are easier to propagate to chip root and promote the formation of segmented chips. Cutting depth significantly affects the surface quality, subsurface damage, and cutting force. Moreover, a proper cutting speed is beneficial to improve efficiency and machinability of PRMMCs. [ABSTRACT FROM AUTHOR]

Based on the theory of small deflection bending of a thin-walled part, a mechanical model of thin-walled planar members under the action of vacuum adsorption was established. Combined with finite-element simulation and testing, the deformation mechanism and law of the thin-walled flat members was studied under the action of vacuum adsorption. Vacuum clamping caused clamping residual stresses on the upper and lower surfaces of the thin-walled flat parts and resulted in torque along the middle surface. When the vacuum clamping was unloaded, the rebound of the thin-walled flat parts that was caused by the torque was the fundamental cause for the clamping deformation. The residual stress and deformation on the surface of the thin-walled flat parts tended to increase and level off with an increase in vacuum. From the initial stage to the stable clamping stage, the radial and tangential stresses in the 200 mm × 2.2 mm workpiece increased by –10 MPa and –27 MPa, respectively, and the relative displacement in the load direction increased by 0.026 mm. Under the effect of vacuum clamping, the maximum deformation capacity of thin-walled flat parts was affected mainly by their initial surface profile error. The stiffness of the workpiece was affected mainly by its thickness; a greater thickness led to a greater stiffness, and a larger vacuum was required for the workpiece to reach a stable clamping state. [ABSTRACT FROM AUTHOR]

We introduce an autonomous laser kirigami technique, a novel custom manufacturing machine system which functions somewhat similar to a photocopier. This technique is capable of creating functional freeform shell structures using cutting and folding (kirigami) operations on sheet precursors. Conventional laser kirigami techniques are operated manually and rely heavily on precise calibrations. However, it is unrealistic to design and plan out the process (open loop) to realize arbitrary geometric features from a wide variety of materials. In our work, we develop and demonstrate a completely autonomous system, which is composed of a laser system, a 4-axis robotic arm, a real-time vision-based surface deformation monitoring system, and an associated control system. The laser system is based on the Lasersaur, which is a 120-Watt CO2 open-source laser cutter. The robotic arm is employed to precisely adjust the distance between a workpiece and the laser lens so that a focused and defocused laser beam can be used to cut and fold the workpiece respectively. The four-axis robotic arm provides flexibility for expanding the limits of possible shapes, compared to conventional laser machine setups where the workpiece is fixed on rigid holders. The real-time vision-based surface deformation monitoring system is composed of four low-cost cameras, an integrated AI-assisted algorithm, and the sensors (detachable planar markers) mounted on the polymer-based sheet precursors, and allows real-time monitoring of the sheet forming process with a geometric feature estimation error less than 5% and delay time around 100 ms. The developed control system manages the laser power, the laser scanning speed, the motion of the robotic arm based on the designed plan, and the close-loop feedback provided by the vision-based surface deformation monitoring system. This cyber-physical kirigami platform can operate a sequence of cutting and folding processes in order to create kirigami objects. Hence, complicated kirigami design products with various different polygonal structures can be realized by undergoing sequential designed laser cuts and bends (at any folding angles within designed geometric tolerance) using this autonomous kirigami platform. [ABSTRACT FROM AUTHOR]

This paper focuses on an unconventional laser powder bed fusion (LPBF) technique in which the LPBF and machining processes were executed alternately to fabricate higher quality parts compared to those obtained using subtractive machining processes. The additional machining process modified the stress distribution inside the built part, resulting in the deformation of the surface morphology in the final part. The phenomenon resulting in the combined LPBF and machining-process-based fabrication was investigated, and the influence of the process parameters on the formation of surplus part and the deformation of machined surface was evaluated. In addition, a laser scanning and machining strategy were formulated to improve the surface quality of the built part. The surplus buildup at the edge of the fabricated part occurred owing to the difference in the thermal properties between the solidified part and the deposited metal powder. The principal factors affecting the formation of the surplus part were the laser-irradiated position at the first layer buildup and the energy density. Moreover, the formation of the surplus part was improved using the laser scan strategy, in which the laser-irradiated position was shifted inward. The peripheral face of the built part formed periodical steps, owing to the deformation induced by the change in the thermal distribution inside the built part. These steps could be reduced using a machining strategy combining the rough machining process with a finishing allowance and stepwise finishing process. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration has been widely utilized in the forming and processing of metallic materials due to its advantages of reducing forming force and improving deformation ability and surface quality. However, the effect of ultrasonic vibration on the deformation mechanism of metallic material is still unclear. Based on the method of segmented resonant design, an ultrasonic vibration tensile device was developed, and its vibration performance was evaluated in this work. Furthermore, the ultrasonic vibration tensile tests were carried out to investigate the influence of ultrasonic vibration parameters on the properties of the 6061-T6 Al material. The results showed that the design error of 3.3% and ultrasonic vibration amplitude of 8.7 μm were achieved. Ultrasonic vibration reduced the stress required for 6061-T6 Al material deformation, but did not change Young's modulus and strain hardening rate. The stress reduction was proportional to the square of the ultrasonic vibration amplitude, indicating that ultrasonic softening was attributed to the changed dislocation of 6061-T6 Al material. Meanwhile, the ultrasonic vibration has no permanent effects on the tensile behavior of 6061-T6 Al material. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical simulation model of cross wedge rolling (CWR) was developed to analyze the influence law of die parameters on internal voids during CWR using a rigid-plastic finite element method (FEM), where particular attention has been given to the internal void generation mechanism during CWR of shaft parts from the analyses of morphology, stress, and strain. The main reason for the internal voids during CWR is the extremely uneven deformation of the core and surface of the rolled product. By adjusting the key die parameters in CWR, the influence of die process parameters on internal voids in CWR was studied. As a result, the larger the forming and widening angles, the smaller the diameter of the rolled workpiece after rolling, and when the distribution coefficient of area reduction is about 1, the more difficult it is for loose defects to occur. According to the simulation results, a new CWR die structure was proposed and rolling experiments were performed. No looseness was found in the center, which proved that optimizing the die was feasible. [ABSTRACT FROM AUTHOR]

The influence of high strain rate on the forming limit curves of AA6082-T6 aluminum alloy sheets, 1 mm in thickness, was investigated by means of dynamic tensile and hemispherical punch tests carried out until the onset of sample failure using a Split Hopkinson Bar (SHB) system, at a punch speed of 7500 and 12000 mm/s. The equipment used was designed according to the standard EN ISO 12004-2 but properly scaled to adapt it to the SHB apparatus. A finite element analysis was performed to quantify the strain rate values reached during tests (around 600 and 1000 s-1 associated at the punch speeds of about 7500 and 12000 mm/s, respectively). The limit strains were determined on different sample geometries undergoing deformation in the range from the uniaxial and balanced biaxial stress states typical for sheet metal forming processes. The major and minor strain distributions, acquired through an accurate image analysis by analyzing the deformation of a previously imprinted grid on the specimen surface, allowed to plot the dynamic forming limit curves at different high strain rate values. Such forming limit curves were compared with those provided by samples deformed under quasi-static loading condition, using the same equipment and specimen geometries, in order to evaluate the influence of the loading rate on the formability. It was observed that the formability of AA6082-T6 aluminum alloy strongly improves as the strain rate increases from quasi-static to dynamic conditions. [ABSTRACT FROM AUTHOR]

Continuous flexible rolling is a novel plastic forming process for 3D curved parts. In this work, asymmetry forming technology was firstly applied in continuous flexible rolling process, which can effectively compensate the lack of longitude bending deformation caused by work hardening. In the process of asymmetry forming technology, by changing the relative longitude elongation between the tensile surface and compressive surface of the sheet metal, the adjusting of longitudinal bending deformation is achieved. In this paper, the finite element model with different friction ratio was designed; the effect of asymmetry forming technology on longitude curvature radius of 3D curved parts was studied. As results demonstrate that: When the friction ratio between the upper (compressive) and lower (tensile) surface are 0.2:0.2, 0.2:0.15, 0.2:0.10, 0.2:0.05 and 0.2:0.2, 0.15:0.2, 0.10:0.2, 0.05:0.2 in turn, the corresponding longitude curvature radiuses of convex curved parts are 226 mm, 236 mm, 254 mm, 272 mm and 226 mm, 219 mm, 207 mm, 199 mm in turn. When the friction ratio between the upper (tensile) and lower (compressive) surface are 0.2:0.2, 0.2:0.16, 0.2:0.12, 0.2:0.08 and 0.2:0.2, 0.16:0.2, 0.12:0.2, 0.08:0.2 in turn, the corresponding longitude curvature radius of saddle curved parts are 330 mm, 321 mm, 315 mm, 306 mm and 330 mm, 339 mm, 345 mm, 350 mm in turn. The longitude bending deformation of sheet metal can be effectively adjusted in the asymmetry forming technology, so the feasibility of this technology is verified. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional finite element model is utilized to analyse the top edge burr formation in orthogonal slotting copper finned tubes. To describe the top edge burr generation, a conceptual model is developed to explain the material shear failure. The normalized Cockroft-Latham criterion is employed for a general understanding of the plastic behaviour and burr formation, and the critical damage value is obtained to qualify the burr geometries by tensile tests. Based on material side flow and the progressive deformation behaviour, the characteristics and mechanism of top edge burr formation are further investigated. The results show that the top edge burr is formed by a combination of material tear and sideward flow. The top edge burr formation process can generally be divided into three phases: the initiation of the deformation bulge, the development of the deformation bulge, and tear formation. The characteristics of the top edge burr also consist of three parts: basal deformation area, tensile area, and top tear area. The three parts of the burr characteristics correspond to the three phases of the burr formation process. Additionally, the influences of rake face, feed rate, and cutting speed on the burr size are studied based on a quantitative method. The study provides a basis for the minimization of top edge burr formation and optimization of machining parameters. [ABSTRACT FROM AUTHOR]

In the majority of electromagnetic tube forming system, the distribution of Lorentz force acting on tube is restricted and has poor controllability, which leads to the tube being unable to meet the requirement of manufacturing flexibly. A new electromagnetic tube-forming method based on the two-stage coils system, which consists of two coils and two independent capacitor banks, has been proposed to improve the distribution mode and controllability of Lorentz force. With higher deformation depth and less occurrence of cracking compared with the conventional one single-coil system; this method has been proved to be effective in improving the deformation behavior of tube in electromagnetic forming through experiments. However, the deformation behavior of tube in this forming method still needs further studies. In this paper, the effect of pulse width of middle-coil current on AA1060 aluminum tube deformation behavior under two-stage coil system is investigated through simulation model, which is based on the combination of current filament method and finite element method. Results show that the short pulse width of the middle-coil current can achieve larger deformation depth of tube under relatively small discharging energy, and the long pulse width of the middle-coil current has good performance in deformed profile. Moreover, the thickness reduction in the case of long pulse width of middle-coil current is less than the case of short pulse width of the middle-coil current under equal deformation depth of tube. [ABSTRACT FROM AUTHOR]

Support structures are required in selective laser melting process to support overhanging surfaces in order to remove heat away from the process and to reduce geometrical distortions. Heat stress and warping may occur due to heat accumulation in overhangs. These ultimately affect the dimensional and geometrical accuracy of the part. Therefore, this work introduces an approach to mitigate heat stress by maximizing the heat conduction of support structures. The minimum thermal compliance is set as an objective function to use a method of three-dimensional topology optimization to generate lattice support structures. In addition, fabrication experiments were conducted to investigate the warpage and levelness of the final built cantilever parts supported by our support structures and the three conventional support structures including pillar, wall, and "IY" support structures. The experiment results revealed that the warpage deformation of the cantilever part supported by our support structures is the lowest. Compared with the pillar, wall, and "IY" support structures, the top surface warp deformation of the cantilever supported by our support structures is reduced by 25.4, 31.75, and 17.65%, respectively. Moreover, the experiment results also indicated that the collapse and cracking of the built cantilever part supported by our support structures is significantly reduced compared with the conventional support structures. [ABSTRACT FROM AUTHOR]

In ultra-precision manufacturing, the prediction of workpiece deformation induced by loading of the fixture–workpiece system is critical for manufacturing workpieces with high-quality surfaces. However, the influence of any errors resulting from the differences between the surface profiles of the fixture and the workpiece on the clamping deformation is always neglected. This results in a low processing accuracy of low-rigidity workpieces. Moreover, the effects of different structural parameters of the workpiece and the vacuum fixture on the clamping deformation have not been thoroughly investigated. In this study, a comprehensive finite element analysis (FEA) model considering the surface profile error between the vacuum fixture and the low-rigidity flat parts was established to predict the clamping deformation under various clamping pressures in the vacuum fixture–workpiece system. Furthermore, the relationship between the clamping deformation, as well as the structural parameters of the flat parts and the vacuum fixture, was evaluated. A detailed comparison between the predictions and experimental results verified the accuracy of the proposed analytical method. Finally, based on the analysis results, the position angle of the vacuum fixture–workpiece system was optimized to reduce the clamping deformation caused by the differences between the surface profiles. [ABSTRACT FROM AUTHOR]

Laser shock peening is one of the most effective surface strengthening techniques, which uses laser shock-induced plastic deformation to optimize surface stress state and microstructures of target material. In this paper, dislocation dynamics simulation was used to investigate laser shock induced ultra-high strain rate plastic deformation of face-centered cubic (FCC) nickel and body-centered cubic (BCC) iron. Molecular dynamics was employed to calculate dislocation mobility. Based on the obtained dislocation mobility coefficient, dislocation dynamics models of nickel and iron were established. Results show that the velocity of dislocation motion increases as temperature decreases. Under ultra-high strain rate deformation, dislocation density of nickel increases while dislocation density of iron decreases as temperature rises. Moreover, iron exhibits thermal softening while nickel exhibits thermal hardening under laser shock loading. Plastic deformation dominated by dislocations is sensitive to loading direction, depending on the Schmidt factor of the slip system. The ultra-high strain rate induced by laser shock can effectively increase dislocation density by promoting dislocation multiplication and suppressing dislocation annihilation. [ABSTRACT FROM AUTHOR]

Deformation is an unavoidable phenomenon in a thin-walled milling operation, which causes the radial cutting depth to deviate from the initial position and change the tool-workpiece meshing boundary. Milling force is an important factor in the deformation; thus, the phenomenon of machining deformation mechanism is revealed and a machining error prediction model based on the force-deformation coupling relationship is developed in this paper. Discrete micro-cutting disks of the thin-walled parts take into account the deformations and milling cutting force of different contact relationships in the cutting area. The tool-workpiece contact relationship (single-flute cutting and double-flute cutting) is determined by different cutting parameters and the deflection of thin-walled parts is introduced. A detail iterative strategy is developed to calculate the milling force after deformation and the tool-workpiece meshing boundary. By modifying the instantaneous chip thickness of each micro-cutting disk, a new force-deformation coupling relationship and a time-based deformation matrix of different contact relationships are obtained. The machining error is calculated by considering the part deformation and the surface generation mechanism. After finishing systematic experiments, a comprehensive comparison between the model in mechanical prediction and experiments proves that the model captures the material removal mechanism that produces machining error. The results show that the proposed method can effectively predict the machining error. [ABSTRACT FROM AUTHOR]

An approach to analyzing three-dimensional vertical rolling is presented on the basis of energy method. The double parabola function model is applied to describe dog bone shape in the deformed region between the vertical rolls. The DSF (dual stream function) method is utilized to obtain three-dimensional velocity and strain rate fields. The values of dog bone shape dimensions and roll force are obtained when the total power functional achieves minimum, which is received according to double parabola model, velocity field, and the first variational principle. The validity of the proposed approach is discussed by contradistinguishing the present predictions with other models' results and measured data in a hot strip plant in miscellaneous rolling conditions. Moreover, the impacts of different rolling conditions on the dog bone shape and stress state coefficient are researched, respectively. [ABSTRACT FROM AUTHOR]

Stiffened plates are widely used in components of airplane for its light weight and high stiffness and ultrasonic peening (UP) is the key forming technology. However, insufficient bending deformation and poor mechanical properties usually appear during free UP, and elastic prestressed UP is adopted. The effect of prebending curvature radii on bending deformation and surface properties is experimentally conducted. The results show that chordwise peening path contributes to enhancement of chordwise bending strain and smaller spherical deformation. Compared with free UP, more sufficient bending deformation, larger surface hardness with smaller surface roughness, and larger and deeper compressive residual stress are generated in prestressed UP. Spherical deformation coefficient is adopted to quantitatively describe the spherical deformation. With decrease of prebending curvature radius, bending deformation, surface hardness, and absolute value of maximum compressive residual stress are significantly increased; meanwhile, the spherical deformation coefficient is obviously decreased. More uniform surface morphology and larger total depth of compressive residual stress are acquired by applying a prebending moment before UP. [ABSTRACT FROM AUTHOR]

Electromagnetic forming (EMF) was used to conduct elongated hole flanging in this work. The investigation showed that the low geometry accuracy around the elongated hole flanging attributed from an uncoordinated deformation occurred, including unequal flanging heights and different rebound amounts between the straight edges and the circular edges. The uncoordinated flanging height resulted from different strain distribution. The strain distribution of the circular edges was similar to circular hole flanging, while the strain distribution of the straight edge regions was similar to sheet stretch bending. The uncoordinated rebound amount resulted from different deformation mechanisms, stress distribution, and structural stiffness within the forming regions. To improve the geometry accuracy of the elongated hole flanging, a two-step method combined geometric compensation electromagnetic forming (GC-EMF) and electromagnetic calibration (EM calibration) was proposed. GC-EMF was used to achieve equal flanging height by optimizing the prefabricated hole, while EM calibration after GC-EMF was used to improve the forming accuracy by reducing the amount of rebound. The difference in the flanging heights between the straight edges and the circular edges was only 0.1 mm after the GC-EMF process, when the compensation dimension on both sides of the straight edges of a prefabricated hole was 3.4 mm. The gap between the die and the straight edges was 0.2 mm, the gap between the die and the circular edges was 0.1 mm, after EM calibration. Therefore, the improved geometry accuracy of the elongated hole flanging was achieved by combining the GC-EMF with EM calibration. The results obtained and the method proposed in this work present significant guidance for the process of elongated hole flanging or other irregular hole flanging by EMF. [ABSTRACT FROM AUTHOR]

Diamond burnishing (DB) is a static mechanical surface treatment based on severe surface plastic deformation aimed at significant improvement in the surface integrity and operating properties of the treated component. Very often, DB is unjustifiably perceived of as typical smoothing burnishing. In the present article, it is shown that DB can be conducted as smoothing, deep, or mixed burnishing depending on the particular combination of process governing factors employed. Optimizations of the DB process for 41Cr4 steel under different criteria are conducted in order to obtain the optimal parameters of different DB processes. The choices of governing factors and objective functions (roughness and fatigue limits), which are obtained on the basis of planned experiments and regression analyses, are fully justified. By means of one-objective optimizations, the uncompromising optimum values of the objective functions and the corresponding optimum values of the governing factors of smoothing and deep DB processes are obtained. A new optimization procedure for solving a multi-objective optimization task is developed in order to obtain compromise optimal values simultaneously with the objective functions and governing factors of the mixed DB process. In order to highlight the advantages of the proposed optimization procedure, the multi-objective task solution is compared with the results obtained via some known methods, i.e., the compromise weight vector and function of the losses methods. [ABSTRACT FROM AUTHOR]

Cellular structures are promising applicants for additive manufacturing (AM), due to their best capabilities over solid ones such as high strength-to-weight ratio, having porosity, and light in weight. New vintile cellular structures and with the existing five different cellular structures namely cubic, tetrahedron, hexagon, octagon, and rhombic dodecahedron were designed and the effect of unit size, lattice topology, porosity, and optimization of cellular structures on the mechanical properties were discussed in this study. Eighty-four samples with different cell sizes, lattice topologies, and porosities were printed using VisiJet M3 Crystal material on Projet 3510 HDMax 3D printer. Then, electro-optical microscopic is used to determine the pore size. Based on predesigned cellular structures, finite element analysis (FEA) and experimental work were performed to estimate and evaluate the mechanical properties of cellular structures. Results shown that the cellular structure with vintile lattice topology performs less stress and less deformation than the other cellular structures. The experiment results were in good conformance with the result obtained from simulation. This study is not only limited to cellular structure design for biomedical applications but also compared the mechanical performance of uniform density and variable density cellular structures. Both non-optimized and optimized vintile cellular structures is finally tested with FEA and experiments have been carried out on samples fabricated by material jetting, and both results have shown that the optimized cellular structure had much less stress and lower deformation than the non-optimized cellular structure. [ABSTRACT FROM AUTHOR]

The coupler knuckle of railway wagon is a complex forging component with big section change. In this paper, a near-net-shape forming process for coupler knuckle based on closed-die forging without flash was proposed and the preforming operation was designed and optimized. Firstly, the shape and the dimension of the preforging were preliminarily designed based on the geometric features of forged knuckle and the flow characteristics of metal in the forging process, and then a multi-objective optimization approach based on the filling capacity, deformation homogeneity, and damage degree of forgings was established, and the response surface method combined with the finite element simulation was used to obtain the optimum geometric parameters of preforging. In order to verify the effectiveness of the near-net-shape forming process and the optimized results on preform design, forming experiments and measurements were carried out; the analyzed results show that based on the designed preforging, near-net-shape forming process is capable of producing coupler knuckle of high quality and without forming defect. [ABSTRACT FROM AUTHOR]

Turning process is one of the most complex manufacturing processes to simulate. The ability to accurately simulate turning processes depends on the availability of accurate workpiece material properties as well as the workpiece flow stress behavior change with deformation parameters such as strain, strain rate, and temperature. The goal of this paper is to determine the parameters of constitutive equation of flow stress for hardened AISI630 steel according to Johnson-Cook (JC) and power viscosity law (PVL) models. The numerical analysis of turning process has been done based on the finite elements method (FEM). Predicted results have been compared with experimentally determined data like, cutting force, tool tip temperature, and chip shape to validate the FE models. The numerical simulation results indicate that the adeptness of PVL model in forecasting the plastic behavior of AISI630 steel is quite acceptable and the predicted results are very close to experimental results in comparison with JC model. In addition, the results showed that the serrated chip morphology was accurately predicted over a large range of machining parameters using PVL model. Furthermore, FE analysis and PVL model have been used to predict cutting forces and tool temperature during different turning conditions. It has been found that for low feed rates, the chip form will be changed from continuous to saw-tooth form, e.g., at 0.1 mm/rev feed, with increasing cutting speed from 28 to 62 m/min the chip form was changed from continuous to saw-tooth type. In addition, during machining at cutting speed of 28 m/min, the cutting force is stable, while at cutting speed of 62 m/min, the resultant cutting force is fluctuating. This fluctuating force along with the build-up edge formation increases machined surface roughness at a speed of 62 m/min unexpectedly. [ABSTRACT FROM AUTHOR]

Due to the complicated deformation of the billet in roll forming process and the lack of the theoretical understanding, there are still no unified methods to design and optimize roll profiles. Theoretical analysis of the deformation in roll forming process based on mathematical method is efficient and necessary. A qualified roll profile optimization method should be based on the accurate calculation of the spatial configuration of the billet. However, the existing models for calculating the spatial configuration of the billet in roll forming process cannot calculate the springback of the billet. In this paper, according to the mathematical model established by the author for calculating the spatial configuration of the billet, a roll profile optimization method for high-strength V channel roll forming process was proposed by taking the maximum edge membrane longitudinal strain as constraint conditions. After optimization, the number of roll stands required for final V channels was reduced from 8 to 5. Through analyzing and comparing the deformation of the billet in simulation results of bending and roll forming process, it is found that bending tests can also be used to verify the feasibility of the roll profile optimization method proposed in this paper. The bending tests were carried out using the original and optimized process parameters, respectively. The results show that the shape of the V channel obtained by the optimized process parameters is much closer to that of the designed V channel. [ABSTRACT FROM AUTHOR]

Precision forging is a choice for compressor blade fabrication. Pressure and suction surfaces could be forged to yield design requirements but the blade edge could not. A localization for machining blade edge, considering forging deformation and surface continuity, is discussed in this paper. Different from making machining allowance more balance in past researches, minimizing the difference between machined surface and design surface is adopted. Except machining allowance constraint, new constraints about form tolerance and geometry continuity are built up for localization. As a model for generating tool path, the machining surface of the blade edge is determined by adjusting a group of section curves under proposed constraints. At last, a precision forging blade is applied to verify the proposed localization method. [ABSTRACT FROM AUTHOR]

This review paper is devoted to the slide burnishing (SB) of metal components—state-of-the-art, achievements and perspectives. SB belongs to the group of static methods for mechanical surface treatment used largely in aerospace, automotive and other industries. By means of the plastic deformation of the surface layers, the surface integrity (SI) of the respective component is improved greatly in terms of minimum roughness, micro-hardness and introduced residual compressive stresses. As a result, fatigue crack resistance, crack corrosion resistance, wear resistance and corrosion resistance increase dramatically. The main feature of SB is the sliding friction contact between the deforming element and the surface being treated. Using the differential-morphological method, an integrated classification of the static methods is created and the area of SB is outlined. The proposed morphological matrix, which can be expanded and supplemented contains existing burnishing methods as well as combinations of elements and interactions that can be used to synthesize new burnishing methods and tools. In addition, a literature review of the publications devoted to SB has been conducted. Further, an analysis of the published studies on different criteria has been carried out and graphic visualizations of the statistical results have been made. On this basis, relevant conclusions have been made and the directions for future investigations of SB have been outlined. [ABSTRACT FROM AUTHOR]

Flexible rolling is a sheet metal forming process used to rapidly manufacture three-dimensional (3D) surface parts for various industries. In this paper, a flexible rolling method of 3D surface parts using auxiliary rolls is introduced, and a forming mechanism of curved surface parts is described. The generation of instability of a convex surface part in the rolling process was analyzed, and the calculation for longitudinal bending deformation was deduced to obtain an effective design method for the roll gap shape. Numerical simulations and experimentation were performed for two rolling processes, with and without auxiliary rolls, for surface parts, for which the curvature distribution and dimensional accuracy were measured and analyzed. The simulation results show that the flexible rolling process with auxiliary rolls offers a more stable rolling process with smaller curvature fluctuation of the formed parts. The experimental results further verify that the process with auxiliary rolls is better than that without auxiliary rolls, as indicated by the shape error that can be controlled in a narrower range and the smaller error value of fluctuation. Overall, the proposed flexible rolling process with auxiliary rolls offers a feasible method to effectively form 3D surface parts with good forming quality and accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes an approach for twist springback reduction using variable blank holder force (VBHF) trajectory that the blank holder force (BHF) varies through the stroke. In addition, the blank shape is optimized. Therefore, design optimization of VBHF trajectory and blank shape for twist springback reduction is performed. Springback of U-shaped product is a simple deformation, whereas the one of S-rail-shaped product shows more complicated behavior due to twisting. As the result, compared with the springback of U-shaped product, it is difficult to evaluate the twist springback. A novel evaluation method for the twist springback is proposed, and the optimal VBHF trajectory and blank shape for the twist springback reduction are determined under several design constraints. Numerical simulation of the S-rail-shaped product is so intensive that response surface approach is valid. In particular, a sequential approximate optimization that the response surface is repeatedly constructed and optimized is used to determine the optimal VBHF and blank shape. Through numerical result, the validation of the proposed approach is examined. [ABSTRACT FROM AUTHOR]

Although there are methods to machine free-form surfaces, serious distortion in the concave–convex characteristic of the flattened-plane boundary, high deformation of the surface geometry, and single limitation of the surface topology are usually produced. Thus, a novel surface flattening method is proposed in this paper to retain the concave–convex characteristic and reduce the deformation, and a spiral path is generated to machine the free-form surface with various topologies. The machined surface is mapped to a planar region with a free boundary using a fusing constraint mapping method. First, the spring-mass-based stretching constraint is used to minimize the length differences of the triangular sides, which are caused by surface flattening. Subsequently, in order to flatten surfaces with an isometric deformation, we perform this operation under the constraint of hinge-based bending. Eventually, the global constraint, the minimization of the global energy, is employed to acquire a less distorted plane. Then, to generate a planar spiral path fit for machining various planes, which are concave, convex, simply-connected, or multiply connected, enrichment of the conventional Voronoi diagram, interpolation between the wave fronts, and rounding of the spiral polyline are implemented. For machining a free-form surface, by inversely mapping the planar path, a spiral tool path is planned. Experimental results are given to illustrate the effectiveness of the presented methods. [ABSTRACT FROM AUTHOR]

The objective of this research is to study the influence of cutting parameters on the quality and integrity of machined surfaces obtained by a longitudinal external turning in a sintered self-lubricating composite. Tests were performed at cutting speeds of 100 and 200 m/min, feed of 0.1 and 0.2 mm, and cutting depths of 0.5 and 1 mm for the materials manufactured by single and double pressing. The materials tested are composites with matrix composition of Fe-Ni-C-Si containing solid lubricants, which were subjected to the pressing process and subsequent sintering. The analysis of machined surfaces indicates that the large amount of ferrite in the microstructure of the matrix combined with the type of insert used in the tests caused high plastic deformation of the surfaces. However, solid lubricant particles were left exposed on the surfaces produced after machining. The roughness parameters Sdq (rms surface slope) and Str (texture aspect ratio) were influenced only by variations in the cutting speed. The roughness parameter Sq (root mean square height) was influenced by the variations in the cutting speed and feed as well as the material manufacturing route. Plastic deformation caused by machining led to the closing of pores, which affected the integrity of machined surfaces. The hardness of the surface boundary layer was approximately 30% higher compared with the boundary layer of sintered surfaces. [ABSTRACT FROM AUTHOR]

Preform design is one of the most important aspects in forging process design. An automatic method of preform optimal design based on the bi-directional evolutionary structural optimization is presented in this paper. The complete filling of die cavity with less flash and uniform deformation of material are the goals of the preform optimal design. A new criterion of element addition/deletion is proposed. The new criterion is associated with objective functions. The technique of element information tracking and transferring is introduced and the variables can be transmitted from the final mesh of the forging to the background grid that represents the preform. The method of boundary smooth fitting of the preform using the B-Spline curve is given. The preform optimal design for an H-shaped forging is carried out to demonstrate the effectiveness of the proposed method. A near net-shape forming is achieved meanwhile the uniform deformation is obtained. [ABSTRACT FROM AUTHOR]

The present work investigated the influence of the subarea scanning pattern on substrate deformation and residual stress distribution in direct laser-deposited Ti-6Al-4V. An island scanning pattern, adopted as a representative subarea scanning pattern, was compared with the successive scanning pattern experimentally. Additionally, different island scanning strategies with islands of different sizes (60 × 60, 40 × 40, and 20 × 20 mm2) and different island scanning orders (specified, outside in and inside out) were investigated in large-scale deposition. The results showed that the island scanning pattern reduces the deformation due to successive scanning pattern by 71% and causes a periodically oscillated residual stress distribution on the whole deposit. The island scanning order has a more basic effect than the island size on deformation and residual stress. The newly defined outside-in island scanning order remarkably minimizes deformation, while the randomly specified order induces the smallest residual stress; thus, their combination is appropriate for the fabrication of the large components. Moreover, buckling deformation unexpectedly occurs even if a 5-mm-thick substrate is used primarily due to the small temperature gradient generated by the small island size of 20 × 20 mm2. [ABSTRACT FROM AUTHOR]

The present study is focused on the disintegration effect of ultrasound-enhanced pulsating water jet (PWJ) technology on brass CW614N. The first part of the study discusses the effect of a combination of factors based on the full factorial design of experiments (DoE) 33. Traverse speed v (mm s−1), circular nozzle orifice diameter d (mm), and hydraulic power Ph (kW) are selected as the disintegration variable factors. Mass material removal Δm (mg s−1) is evaluated based on the change in these variable factors. In the next part, a verification experiment is performed with by varying the traverse speed between 0.2 and 1.4 mm s−1. The mathematical model calculated in DoE is confirmed. Moreover, the significant effect of hydraulic power Ph (kW) on the efficiency of the PWJ disintegration is demonstrated. The last part of the study discusses the surface and subsurface effects on a PWJ after brass CW614A erosion. A sample disintegration with hydraulic power Ph = 13 kW and circular nozzle diameter d = 1.321 mm is observed. Optical profilometry and scanning electron microscopy are performed to visualise the surface erosion of a selected groove. A significant mass material removal is observed from the groove surface, and the disintegrated surface is characterised by erosion and crater formation. A slight cold deformation with a maximum depth of 200 μm is detected in the subsurface layer. The experiment and results present a part of an extensive research focused on describing the PWJ disintegration efficiency for metallic materials. [ABSTRACT FROM AUTHOR]

A new auxetic structure, re-entrant chiral auxetic (RCA) structure, is proposed for the first time in this paper. The RCA structure combines the topological features of hexagonal re-entrant and anti-tetrachiral honeycombs. Additive manufacturing technique, stereolithography (SLA), and traditional waterjet machining (WJM) were employed to fabricate six samples made from photopolymer (VisiJet SL Flex) and aluminum alloy (6061), respectively. Quasi-static uniaxial tensile tests were conducted in the X and Y directions, respectively. Numerical models were developed using ANSYS/LS-DYNA and verified by experimental data. Deformation modes, stress-strain curves, and Poisson’s ratios were considered to examine the effects of loading directions and material types. A comparative study was conducted experimentally and numerically between the well-known hexagonal re-entrant honeycomb, and this newly developed RCA structure. The proposed RCA structure presented here was found to display lower density compared with re-entrant honeycomb. Moreover, it shows higher tensile properties and auxetic effect compared with re-entrant honeycomb when loaded in the X direction. The validated FEA models were employed to investigate the effect of friction on the deformation pattern and mechanical properties of the RCA structure when it is loaded in both directions. [ABSTRACT FROM AUTHOR]

Due to its low rigidity and poor stiffness, machining deformation in numerical control milling is a big obstacle to achieve accurate shape of thin-walled honeycomb-core sandwich structural parts. In this paper, the factors which affect the machining deformation of these structural parts are analyzed at first. Then, a finite element analysis model is established, which considers the affecting factors of workpiece original stress, fixture constraints and cutting forces, to simulate the magnitude and distribution of the machining deformation. Afterwards, a prediction model is developed by using back propagation neural network to build the relationship between the deformation and machining parameters. Finally, the milling and measurement experiments are performed to validate the proposed prediction model. By comparing the experimental result with the simulation result and the prediction result, it is found that the experimental result was 7.2 and 2.2% less than the simulation result and the prediction result, respectively. Thus, a conclusion is drawn that the machining deformation prediction methodology is feasible. [ABSTRACT FROM AUTHOR]