查看更多>>摘要：High quality micro mould tools are critical for ensuring defect-free production of micro injection moulded products.The demoulding stage of the micro injection moulding can adversely affect the surface integrity due to friction,adhesion and thermal stresses between the metallic mould and polymeric replicated part.In the present work,we propose the use of precision electropolishing(EP)as a shap-ing and polishing process to control the draft angle and fillet radius of micro features in order to ease demoulding.Typical defects that occur in replicated polymer parts include cracks,burrs and distorted features.A nickel mould having multiple linear ridges and star shape patterns was designed for the present investigation to have characteristic dimensions rang-ing from 10 μm to 150 μm and with various aspect ratios to study the effect of electropolishing on modifying the shape of micro features and surface morphology.A transient 2D computational analysis has been conducted to anticipate the effect of shaping on the Ni mould after electrochemical pol-ishing with non-uniform material removal rates,based on the distribution of current density.The experimental results indicate that after shaping using EP,the draft angle of star-patterns and linear patterns can be effectively increased by approximately 3.6°,while the fillet radius increases by up to 5.0 μm.By controlling the electropolishing process,the sur-face roughness can be maintained under 50 nm.This work uses a green and environmental friendly nickel sulfamate electrolyte which can be effective for shaping of nickel micro features without causing any surface deposition.
查看更多>>摘要：Currently,simultaneous buffer and service rate allocation is a topic of interest in the optimization of manu-facturing systems.Simultaneous allocation problems have been solved previously to satisfy economic requirements;however,owing to the progress of green manufacturing,energy conservation and environmental protection have become increasingly crucial.Therefore,an energy-efficient approach is developed to maximize the throughput and min-imize the energy consumption of manufacturing systems,subject to the total buffer capacity,total service rate,and predefined energy efficiency.The energy-efficient approach integrates the simulated annealing-non-dominated sorting genetic algorithm-Ⅱ with the honey badger algorithm-his-togram-based gradient boosting regression tree.The former algorithm searches for Pareto-optimal solutions of sufficient quality.The latter algorithm builds prediction models to rapidly calculate the throughput,energy consumption,and energy efficiency.Numerical examples show that the pro-posed hybrid approach can achieve a better solution quality compared with previously reported approaches.Further-more,the prediction models can rapidly evaluate manufac-turing systems with sufficient accuracy.This study benefits the multi-objective optimization of green manufacturing systems.
查看更多>>摘要：The exploration of component states for opti-mizing maintenance schedules in complex systems has gar-nered significant interest from researchers.However,current literature usually overlooks the critical aspects of system flexibility and reconfigurability.Judicious implementation of system reconfiguration can effectively mitigate system downtime and enhance production continuity.This study proposes a dynamic condition-based maintenance policy considering reconfiguration for reconfigurable systems.A double-layer decision rule was constructed for the devices and systems.To achieve the best overall maintenance effect of the system,the remaining useful life probability distri-bution and recommended maintenance time of each device were used to optimize the concurrent maintenance time win-dow of the devices and determine whether to reconfigure them.A comprehensive maintenance efficiency index was introduced that simultaneously considered the maintenance cost rate,reliability,and availability of the system to char-acterize the overall maintenance effect.The reconfiguration cost was included in the maintenance cost.The proposed policy was tested through numerical experiments and com-pared with different-level policies.The results show that the proposed policy can significantly reduce the downtime and maintenance costs and improve the overall system reliability and availability.
查看更多>>摘要：Reducing the short-circuit rate and increasing the effective discharge rate are important targets for improv-ing the servo control effect of micro-electrical discharge machining(micro-EDM),as these two indicators are closely related to the machining efficiency and quality.In this study,a feed-pulse collaborative control(FPCC)method is pro-posed for micro-EDM based on two dimensions(space and time).In the spatial dimension,a feed control strategy with a discharge holding process is adopted.Meanwhile,in the time dimension,a forward-looking pulse control strategy is adopted,in which the pulse interval is adjusted based on a sequence analysis of feed commands and discharge states.Process experiments are carried out to determine the key parameters used in this method,including the discharge holding threshold and pulse interval adjustment value(Toffadj).The feed smoothness and discharge sufficiency anal-yses of the experimental results show that compared to the traditional double threshold average voltage method,the FPCC method reduces the number of long-distance retreats by 64％and improves the effective discharge time by 40％.
查看更多>>摘要：Profile grinding is the most crucial method for the ultra-precision machining of special-shaped surfaces.However,profile grinding produces a unique machining profile,and many random factors in the machining process lead to complex surface characteristics.In this study,the structural and probabilistic characteristics of the profile grinding of a special-shaped surface were analyzed,and a probabilistic algorithm for the forming and 3D characteriza-tion of special-shaped surfaces under profile grinding was developed.The forming process of a GH738 blade tenon tooth surface was considered as an example to demon-strate the algorithm.The comparison results showed that the simulation results had similar surface characteristics to the measurement results,and the relative error range of the 3D roughness parameter was 0.21％-19.76％,indicating an accurate prediction and characterization of the complex special-shaped surface under the action of multiple factors.
查看更多>>摘要：Model design and slicing contour generation in additive manufacturing(AM)data processing face chal-lenges in terms of efficiency and scalability when stereo-lithography files generated by complex functionally graded structures have millions of faces.This paper proposes a hybrid modeling and direct slicing method for AM to effi-ciently construct and handle complex three-dimensional(3D)models.All 3D solids,including conformal multigra-dient structures,were uniformly described using a small amount of data via signed distance fields.The hybrid rep-resentations were quickly discretized into numerous disor-dered directed lines using an improved marching squares algorithm.By establishing a directional HashMap to con-struct the topological relationship between lines,a connect-ing algorithm with linear time complexity is proposed to generate slicing contours for manufacturing.This method replaces the mesh reconstruction and Boolean operation stages and can efficiently construct complex conformal gra-dient models of arbitrary topologies through hybrid mod-eling.Moreover,the time and memory consumption of direct slicing are much lower than those of previous methods when handling hybrid models with hundreds of millions of faces after mesh reconstruction.
查看更多>>摘要：The problems of severe sawtooth wear,harsh sawing noise,and low surface quality during the process-ing of circular saw blades need to be solved.To improve the cutting performance of TiC-based cermet saw blades,microtextures parallel to the cutting edge were fabricated on rough and fine sawteeth by laser machining.The cutting tests were performed on a sawing platform under lubricated conditions.Models of the sawing arc length and working sawtooth cutting force variations were developed for saw-ing steel pipes,and the accuracy of the sawing force model was verified experimentally.The results indicate that the variations in the sawing force are proportional to the saw-ing arc length.The circular saw blades with microtextures that did not penetrate the sawtooth rake face exhibited the lowest cutting force,sawing noise,and highest machined surface quality.Furthermore,the worn-out distance of the rougher and finisher sawteeth was reduced by approximately 7.4％and 44.1％,respectively,compared with conventional circular saw blades.The main failure modes of sawteeth were tip wear,rake face adhesion,and oxidative wear.In addition,the mechanism by which the textures improve the cutting and wear properties of TiC-based circular saw blades was discussed.This study provided a significant concept for enhancing the cutting performance of circular saw blades and improving the machined surface quality.
查看更多>>摘要：The real-time monitoring of the weld pool dur-ing deposition is important for automatic control in plasma arc additive manufacturing.To obtain a high deposition accuracy,it is essential to maintain a stable weld pool size.In this study,a novel passive visual method is proposed to measure the weld pool length.Using the proposed method,the image quality was improved by designing a special visual system that employed an endoscope and a camera.It also includes pixel brightness-based and gradient-based algo-rithms that can adaptively detect feature points at the bound-ary when the weld pool geometry changes.This algorithm can also be applied to materials with different solidifica-tion characteristics.Calibration was performed to measure the real weld pool length in world coordinates,and outlier rejection was performed to increase the accuracy of the algo-rithm.Additionally,tests were carried out on the intersection component,and the results showed that the proposed method performed well in tracking the changing weld pool length and was applicable to the real-time monitoring of different types of materials.
查看更多>>摘要：Ultrasonic-vibration-assisted milling(UVAM)is an advanced method for the efficient and precise machining of difficult-to-machine materials in modern manufacturing.However,the milling efficiency is limited because the ultra-sonic vibration toolholder ER16 collet has a critical cutting speed.Thus,a 2D UVAM platform is built to ensure preci-sion machining efficiency and improve the surface quality without changing the milling toolholder.To evaluate this 2D UVAM platform,ultrasonic-vibration-assisted high-speed dry milling(UVAHSDM)is performed to process a tita-nium alloy(Ti-6Al-4V)on the platform,and the milling temperature,surface roughness,and residual stresses are selected as the important indicators for performance analy-sis.The results show that the intermittent cutting mechanism of UVAHSDM combined with the specific spindle speed,feed speed,and vibration amplitude can reduce the mill-ing temperature and improve the texture of the machined surface.Compared with conventional milling,UVAHSDM reduces surface roughness and peak-groove surface profile values and extends the range of residual surface compressive stresses from-413.96 MPa to-600.18 MPa.The excellent processing performance demonstrates the feasibility and validity of applying this 2D UVAM platform for investigat-ing surface quality achieved under UVAHSDM.
查看更多>>摘要：The maximum flyer impact velocity based on a dynamic solidification cracking mechanism is proposed to describe the upper limit of collision welding process win-dows.Thus,the upper limit of the weld window is governed by the evolution of dynamic stresses and temperatures at the weld interface.Current formulations for the upper limit of the collision weld window assume that both the flyer and target are made of the same material and approximate stress propagation velocities using the acoustic velocity or the shear wave velocity of the weld material.However,collision welding fundamentally depends on the impacts that generate shockwaves in weld members,which can dominate the stress propagation velocities in thin weld sections.Therefore,this study proposes an alternative weld window upper limit that approximates stress propagation using shock velocities cal-culated from modified 1-D Rankine-Hugoniot relations.The shock upper limit is validated against the experimental and simulation data in the collision welding literature,and offers a design tool to rapidly predict more accurate optimal col-lision weld process limits for similar and dissimilar weld couples compared to existing models without the cost or complexity of high-fidelity simulations.
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