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Evaluation of dimensional accuracy and surface integrity of cylindrical array microelectrodes and cylindrical array microholes machined by EDM

Sun Yao, Gong Yadong, Wen Xuelong, Xin Bo, Yin Guoqiang, Meng Fantao, Tang Benjia

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e46, 2022

EN

In this study, the loss self-finishing method based on EDM reverse copy principle was proposed aiming to enhance the prepared efficiency of cylindrical array microholes. First, the effects of geometric parameters of microelectrodes on the diameter consistent error, inlet and outlet deviation, section profile, surface roughness parameters and the heat affected zone thickness were quantitatively investigated. The forming accuracy of cylindrical array microelectrodes obtained by self-finishing and multi-finishing methods were contrastively analyzed. Furthermore, 8 × 8 cylindrical array microelectrodes with diameter of about 185.18 μm and length of 2168.79 μm were fabricated by the loss self-finishing method for the first time. Besides, the size accuracy, surface morphology and surface roughness parameters of cylindrical array microholes machined using array microelectrodes prepared by loss self-finishing method were evaluated. Experimental results disclosed that the average consistent errors of inlet and outlet diameter for cylindrical array microholes, respectively, were 1.495 μm and 3.13 μm, indicating that the cylindrical array microelectrodes obtained by loss self-finishing method are capable to manufacture cylindrical array microholes with good surface quality and high dimensional accuracy.

2

Analytical and experimental study on micro-grinding surface-generated mechanism of DD5 single-crystal superalloy using micro-diamond pencil grinding tool

Sun Yao, Su Zhipeng, Gong Yadong, Ba Dsechun, Yin Guoqiang, Zhang Huan, Zhou Linhu

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

353--374

EN

Single-crystal superalloy is characterized by no grain boundary and widely used in the aviation and aerospace industry due to its high creep strength and high thermal fatigue resistance, especially applications in aero engine necessitate numerous micro-scale structures made of single-crystal superalloy material with high-dimensional accuracy and surface quality. Micro-grinding as one of micro-precision machining technology is capable to fabricate micro-parts and structures with high machining precision and quality. In this work, a series of diamond micro-pencil grinding tool (MPGT) with diameter ranged from about 100 to 800 μm are firstly prepared by hybrid processes. The surface-generated mechanism of micro-grinding process associated with effects of length ratio of rubbing, ploughing and chip forming were explored based on analytical and experimental investigations. In addition, a novel analytical force model for the DD5 material machined by MPGT is developed considering variable size effect under different length proportion, protrusion height distribution of MPGT and material mechanical properties, which can more accurately agree well with the measured results compared with the traditional micro-grinding force model. This study enabled an in-depth understanding of mechanical behaviour characteristics, surface formation and material removal mechanism under microscopic scale of single-crystal superalloy involved in micro-grinding.

3

Experimental study on fabricating micro-holes in DD5 single-crystal nickel-based superalloy using electrical discharge drilling

Gong Siqian, Sun Yao, Jin Liya, Su Zhipeng

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

337--352

EN

The single-crystal superalloy materials have been rapidly developed and widely used in advanced thermal structural components due to their excellent comprehensive physical and chemical properties under high-temperature service conditions. However, conventional micro-hole making results in defects such as edge breakage and burr. In this study, the electrical discharge drilling (EDD) combined with helical microelectrode is first adopted to fabricate DD5 single-crystal nickel-based superalloy. The effects of tool geometry and machining parameters on subsurface damage layer, micro-hole taper, surface morphology, surface roughness and machining time were investigated in detail. Experimental results indicated that helical microelectrode can obtained smoother surface without debris deposition and thinner subsurface damage layer depth lack of micro-cracks compared with cylindrical microelectrodes. Additionally, the computational fluid dynamics model was developed to analyze working fluid movement and reveal effective debris removal mechanism of helical microelectrode. The vortices will be generated in lateral gap fluid between micro-hole and helical microelectrode and have a certain delay time. The surface roughness and dimensional precision of micro-holes fabricated by helical microelectrodes are greatly improved and machining efficiency is also improved by 30.94% compared to cylindrical microelectrodes. This work could provide theoretical and process guidance to assist in realizing high surface quality and low subsurface damage of micro-holes obtained with EDD process.

4

Reliability model of sequence motions and its solving idea

Sun Yao, Sun Zhili, Yin Mingang, Zhou Jie

Eksploatacja i Niezawodność

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2019

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Vol. 21, no. 3

359--366

EN

The missions of weapon systems are becoming increasingly complex. Thus, more mechanism motions than one are required to complete one mission. Under such conditions, a sort of mission has emerged, that needs a few mechanism motions to be executed in sequence. This means that the mission is not completed until all the motions have been executed successfully in strict sequence. This sequence motion system can be considered as a traditional series system with the motions treated as subsystems. Then, the system reliability can be analyzed with the traditional series system reliability method. However, this method cannot fully reflect the characteristics of a sequence. In this work, a reliability model of sequence motions and its solving idea are proposed. In this reliability model, the influence factors of each motion are included. Particularly, the performance function of the former motion is regarded as just one of the influence factors of the next motion, which is the most significant feature for the sequence motion system. Afterward, a solving idea with characteristics of a gradually shrinking sample space is proposed based on Monte-Carlo simulation. Finally, the reliability model of sequence motions and its solving idea are illustrated with a case study on the automatic chain shell magazine sequence motions of a self-propelled artillery.

PL

Misje systemów uzbrojenia stają się coraz bardziej złożone. Często, jedna misja wymaga wykonania przez układ zmechanizowany więcej niż jednego ruchu. W artykule omówiono misję, w której układ zmechanizowany wykonuje sekwencję kilku ruchów. Misja w takim układzie nie zostanie ukończona, dopóki wszystkie ruchy nie zostaną prawidłowo wykonane w ściśle określonej kolejności. Taki układ sekwencyjnych ruchów można rozważać w kategoriach tradycyjnego systemu szeregowego, traktując poszczególne ruchy jako jego podsystemy. Wówczas, niezawodność systemu można analizować za pomocą tradycyjnej metody analizy niezawodności systemów szeregowych. Jednak, metoda ta nie jest w stanie w pełni odzwierciedlić charakterystyki sekwencji. W niniejszym artykule zaproponowano model niezawodności ruchów sekwencyjnych oraz jego rozwiązanie.

5

Inconel-steel functionally bimetal materials by hybrid directed energy deposition and thermal milling: Microstructure and mechanical properties

Li Pengfei, Gong Yadong, Xu Yunchao, Qi Yang, Sun Yao, Zhang Huan

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 3

820--831

EN

Many engineering applications, particularly those in extreme environments, require com-ponents with properties that vary with location in the part. Functionally bimetal materials (FBM) that combine dissimilar materials, such as those with different density and thermal properties, provide a potential solution to this need. Directed energy deposition (DED) is convenient to fabricate all kinds of complicated parts and to clad different materials at specific locations. Milling can improve the surface quality and dimensional accuracy after DED. Hybrid DED and thermal milling manufacturing can fabricate FBMs and be applied to laser repair. This study used this new method to fabricate Inconel-steel FBM. Inconel 718 powder and 316L stainless steel powder were deposited on the thermal milling surface of parts prepared with DED. The interfacial characteristics of different cladding materials were compared. Microstructure, chemistry, phase composition, element segregation and micro-hardness varied with position and were characterized by energy dispersive spectroscopy, X-ray diffraction, scanning electron microscopy and microhardness testing. Finally, the tensile properties of the FBM were compared to other materials, and the fracture location and morphology were analyzed. The results showed that the yield strength (YS) reached 368 MPa, and the ultimate tensile strength (UTS) reached 516 MPa. The Vickers microhard-ness of the diffusion layer was approximately 250 HV.