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Impeller with narrow-vane is a typical thin-walled structural part of the turbine engine. The high-accuracy requirement for the impeller is difficult to achieve in the machining process due to its low structural stiffness and narrow machining domain. This paper proposes a framework for enhancing the milling accuracy of the thin-walled narrow-vane turbine impeller, which is made of NiAl-based superalloy. The proposed framework consists of a machinability study of the impeller material, a machining deformation analysis, and an error compensation. By studying the milling force and tool wear behavior experimentally, the machinability study yielded optimized process parameters for machining NiAl-based superalloy. A cantilever beam–based tool deformation model and a finite element analysis method model were developed respectively to analyze and predict the deformation of the milling tool in machining the impeller. A flexible and iterative compensation method was studied for decreasing the machining error when milling the impeller. The effectiveness of the proposed framework has been validated experimentally. The results show that the milling accuracy of the turbine impeller has been enhanced significantly. [ABSTRACT FROM AUTHOR]

To improve the neck-spinning processing quality of plunger components, a reliable finite element (FE) model was established and validated by the experimental spinning force. In the advanced FE model, an additional analysis step was added to obtain the pulling-out force, the axial clearance, and the swing angle of the plunger components after the neck-spinning process. Thus, the neck-spinning quality of the plunger components can be predicted. The results show that the simulated results using the FE model agree with the experimental results very well. The radial and axial spinning forces are approximate 3 and 2 times of the tangential spinning force, respectively. Finally, the influences of spinning parameters (e.g., feed rate and rotating speed) on the finished pulling-out force, axial clearance, and swing angle were evaluated in detail. The pulling-out force increases with increased feed rate, which tends to be stable with increased rotating speed. Compared with the stable tendency of axial clearance affected by feed rates, the axial clearance decreases significantly with increased rotating speeds. The swing angle of plunger components remains stable with different feed rate and rotating speed after the neck-spinning process. [ABSTRACT FROM AUTHOR]

In the present research, three typical cutting tool wear mechanisms (abrasive wear, adhesive wear, and diffusive wear) were taken into consideration in the FE simulation of cutting tool with a specific user-defined subroutine. Based on the influence of temperature on the cutting tool wear form, a novel wear rate model was built integrating Usui, Takeyama, and Attanasio wear rate equation. The high-speed cutting tests were carried out on Ti6Al4V to determine the proposed wear rate model constant. The cutting forces and rack face wear morphologies obtained from FE simulation match well with those from experimental cutting tests. Finally, the effect of cutting parameters on tool wear was studied by FEM. The simulation results show that the impact of the cutting speed on the cutting tool life is more significant than that of feed rate, and the preferred ranges of cutting speed and feed rate for extending cemented carbide cutting tool in high-speed dry cutting Ti6Al4V are 90–150 m/min and 0.10–0.20 mm/r, respectively. [ABSTRACT FROM AUTHOR]

Abstract A finite element model (FEM) of single-grain surface grinding of SiC has been established to understand the effects of the cutting-edge radius and grinding wheel speed on SiC chip formation. Based on the mechanic deformation behavior of SiC, the critical chip formation thickness and critical ductile-brittle transition thickness were found. Results obtained show that critical ductile-brittle transition thickness has a peak value at R c = 1.25 µm and v s = 80 m/s respectively. Normal grinding force increased firstly with the increasing cutting edge radius and then declined. The critical cutting edge radius R c = 1.25 µm and grinding wheel speed v s = 80 m/s were determined depending on the variation of critical chip formation thickness, critical ductile-brittle transition thickness, grinding force, ground surface quality. Finally, the simulation results were verified experimentally by an indirect single diamond grain scratching SiC ceramics test. [ABSTRACT FROM AUTHOR]

Highlights • The tension-shear coupled fracture criterion was proposed to simulate the brittle-ductile transition phenomenon in the brittle materials machining process. • Tension-shear coupled fracture criterion is more suitable than the equivalent plastic strain fracture criterion for the simulation of brittle materials precision machining. • The equivalent plastic strain parameter could be used to distinguish the materials removed in ductile mode or brittle mode. • Even though the materials removed in brittle mode, the plastic deformation may happen and residual stress may be left on the machined surface or subsurface. Abstract Despite great efforts have been made to understand the machining mechanism of brittle materials, few numerical models are available to describe the brittle-ductile transition (BDT) in engineering ceramic grinding due to the fracture mechanism difference in brittle and ductile removal modes. This paper introduces the tension-shear coupled (TSC) fracture criterion for the finite element method (FEM) analysis of the brittle material machining that is capable of describing BDT. With TSC fracture criterion, simulation results of single diamond grain grinding of silicon carbide (SiC) ceramic, including the ground surface/subsurface morphology, grinding forces, and equivalent plastic strain, were compared with those under effective plastic strain (EPS) fracture criterion, the one widely adopted by commercial finite element software. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion. Graphical abstract Image, graphical abstract Up to now, few numerical models are available to predict the brittle-ductile transition phenomenon of materials removal mode in engineering ceramics grinding process due to different fracture mechanisms of brittle removal mode and ductile removal mode. To that problem, a new fracture criterion (tension-shear coupled (TSC) fracture criterion) was proposed in the present work to simulate the brittle materials machining process with finite element method. The simulation results (e.g. ground surface/subsurface morphologies, grinding force and equivalent plastic strain) with TSC fracture criterion were compared with those of effective plastic strain (EPS) fracture criterion, which was widely implemented into the commercial finite element software, e.g. ABAQUS, Ls-Dyna etc. The results show that TSC fracture criterion can better characterize BDT in SiC grinding than EPS criterion, via ground surface/subsurface morphology and tangential grinding force. To experimentally validate the proposed TSC fracture criterion, single diamond grain grinding tests were conducted on SiC with various maximum undeformed chip thickness to demonstrate BDT and compare with the simulation results. The measured ground surface morphology evolution and BDT with the increased undeformed chip thickness matched the results of the FEM simulation with TSC fracture criterion. [ABSTRACT FROM AUTHOR]

In this article, the finite element model containing the varied coefficients of friction is established in order to improve the prediction accuracy of surface grinding temperature of particulate reinforced titanium matrix composites (PTMCs). The coefficients of friction, such as 0.46 for conventional-speed grinding and 0.21 for high-speed grinding, respectively, are determined according to the grinding forces ratios measured. Results obtained show that the relative error of experimental and predicted grinding forces is limited within 2∼9 %, while the relative error of experimental and predicted grinding temperatures values is controlled at 7∼15 %. The prediction accuracy is improved significantly based on the varied coefficients of friction in surface grinding of PTMCs. [ABSTRACT FROM AUTHOR]

This article investigates the brazing-induced residual stresses in the polycrystalline cubic boron nitride (PCBN) abrasive grains based on finite element simulation. The effects of embedding depth and gap thickness on the residual stress distribution in brazed PCBN grains are discussed. Results obtained show that, compared with the Ag-Cu-Ti alloy joining CBN grains and AISI 1045 steel substrate, the AlN binder materials in the polycrystalline CBN grains always have a greater effect on the brazing-induced residual stresses; meanwhile, large residual tensile stresses usually exist at the interface between the microcrystalline CBN particles and AlN binders. In comparison to the embedding depth, the gap thickness has little influence on the brazing-induced residual stresses. Furthermore, compared with the other embedding depth, in the case of the embedding depth of 40 %, the residual stresses in the brazed PCBN grain are generally the lowest in the grain bottom and the largest in the grain top surface. Finally, the finite element model applied in the current simulation work is validated through measurement experiments of the brazing-induced residual stresses in the monocrystalline CBN grain. [ABSTRACT FROM AUTHOR]

This paper carries out a finite element (FE) analysis to investigate the effects of grinding speed (20 ∼ 400 m/s) and undeformed chip thickness (1 ∼ 8 μm) on chip formation during single grain grinding of nickel-based superalloy Inconel 718. Three factors related to the Johnson-Cook (J-C) constitutive model, i.e., the strain hardening, strain-rate hardening, and thermal-softening, were taken into account to determine the critical grinding speed. The results show that the chip segmentation frequency increases linearly with increasing the grinding speeds. It was found that the critical grinding speed is 150 m/s based on the variations of equivalent plastic strain, von Mises stress, and grinding force. It was also revealed that the effects of strain hardening and strain-rate hardening on the chip formation are more significant than that of the thermal softening when a grinding speed is below 150 m/s. However, if the grinding speed exceeds this critical value, thermal softening becomes a dominant factor. [ABSTRACT FROM AUTHOR]