Turbine blades, produced by the directional solidification(DS) process, often require high dimensional accuracy and excellent mechanical properties. A critical step in their production is the fabrication of wax patter...Turbine blades, produced by the directional solidification(DS) process, often require high dimensional accuracy and excellent mechanical properties. A critical step in their production is the fabrication of wax patterns. However, the traditional manufacturing process has many disadvantages, such as long-term production, low material utilization rate, and the high cost of producing a complex-shaped wax pattern. Selective laser sintering(SLS) is one of the most extensively used additive manufacturing techniques that substantially shortens the production cycle. In this study, SLS was adopted to fabricate the wax pattern instead of the traditional manufacturing process. The orthogonal experiment method was carried out to investigate the effects of laser power, scanning speed, scanning space, and layer thickness on the dimensional precision and morphologies of the SLS parts. The SLS parts showed a minimum dimensional deviation when laser power, scanning speed, scanning space, and layer thickness were 10 W, 3000 mm·s-1, 0.18 mm, and 0.25 mm, respectively. In addition, the tensile strength and fracture morphologies were closely associated with the laser volumetric energy density(VED). The tensile strength reached a maximum when the VED was 0.0762 J·mm-3, with an evident brittle fracture morphology. The wax pattern manufactured in this way meets the accuracy and strength requirements for investment casting. This research offers a novel path for the production of wax patterns for complex-shaped turbine blades by SLS.展开更多
Based on upper echelons theory and using a sample of private Chinese A-share listed firms from 2008 to 2020,this paper studies the impact of executives’overseas experience on firms’labor investment efficiency.The re...Based on upper echelons theory and using a sample of private Chinese A-share listed firms from 2008 to 2020,this paper studies the impact of executives’overseas experience on firms’labor investment efficiency.The results show that executives with overseas experience significantly enhance firms’labor investment efficiency.After distinguishing between different types of overseas experience,the results show that executives with only study experience or with both study and work experience abroad have a significant positive effect on firms’labor investment efficiency,while executives with only overseas work experience have no significant effect.A cross-sectional analysis based on labor adjustment costs shows that the positive impact of executives’overseas experience is more pronounced in labor-intensive firms,firms with a greater proportion of R&D investment and firms with a higher percentage of highly educated employees.The mechanism tests show that executives with overseas experience can optimize labor investment efficiency by lowering agency costs,attracting analyst attention and alleviating financing constraints under conditions of underemployment.This study enriches the literature on the characteristics of executive teams and the efficiency of labor investment,providing reference and inspiration for firms to attract more high-quality returnees and optimize their labor resource allocation.展开更多
基金financially supported by National Science and Technology Major Project(2017ZX04014001-002)China-EU(European Union)Science&Technology Cooperation in Aviation+1 种基金Horizon 2020 Framework Programme for Research and Innovation(2014-2020)of EU(No.690725)National Natural Science Foundation of China(No.51374137)
文摘Turbine blades, produced by the directional solidification(DS) process, often require high dimensional accuracy and excellent mechanical properties. A critical step in their production is the fabrication of wax patterns. However, the traditional manufacturing process has many disadvantages, such as long-term production, low material utilization rate, and the high cost of producing a complex-shaped wax pattern. Selective laser sintering(SLS) is one of the most extensively used additive manufacturing techniques that substantially shortens the production cycle. In this study, SLS was adopted to fabricate the wax pattern instead of the traditional manufacturing process. The orthogonal experiment method was carried out to investigate the effects of laser power, scanning speed, scanning space, and layer thickness on the dimensional precision and morphologies of the SLS parts. The SLS parts showed a minimum dimensional deviation when laser power, scanning speed, scanning space, and layer thickness were 10 W, 3000 mm·s-1, 0.18 mm, and 0.25 mm, respectively. In addition, the tensile strength and fracture morphologies were closely associated with the laser volumetric energy density(VED). The tensile strength reached a maximum when the VED was 0.0762 J·mm-3, with an evident brittle fracture morphology. The wax pattern manufactured in this way meets the accuracy and strength requirements for investment casting. This research offers a novel path for the production of wax patterns for complex-shaped turbine blades by SLS.
基金support from the Ministry of Education of Humanities and Social Science Project(21YJC630055)the Guangdong Province Philosophy and Social Sciences Coconstruction Project(GD23XGL069).
文摘Based on upper echelons theory and using a sample of private Chinese A-share listed firms from 2008 to 2020,this paper studies the impact of executives’overseas experience on firms’labor investment efficiency.The results show that executives with overseas experience significantly enhance firms’labor investment efficiency.After distinguishing between different types of overseas experience,the results show that executives with only study experience or with both study and work experience abroad have a significant positive effect on firms’labor investment efficiency,while executives with only overseas work experience have no significant effect.A cross-sectional analysis based on labor adjustment costs shows that the positive impact of executives’overseas experience is more pronounced in labor-intensive firms,firms with a greater proportion of R&D investment and firms with a higher percentage of highly educated employees.The mechanism tests show that executives with overseas experience can optimize labor investment efficiency by lowering agency costs,attracting analyst attention and alleviating financing constraints under conditions of underemployment.This study enriches the literature on the characteristics of executive teams and the efficiency of labor investment,providing reference and inspiration for firms to attract more high-quality returnees and optimize their labor resource allocation.
