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2 Archives of Civil and Mechanical Engineering

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

100%

Gong S. , Sun Y. , Jin L. , Su Z.

2020

tom Vol. 20, no. 3

337--352

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.

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

75%

Sun Y. , Su Z. , Gong Y. , Ba D. , Yin G. , Zhang H. , Zhou L.

tom Vol. 21, no. 1

353--374

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.