Research progress of machine tool thermal error modeling technology

During cutting, machine tools are influenced by different heat sources, which induces machine thermal deformation, deviation and thermal error. In different machine errors, thermal error accounts for 40%~70% of total machine errors, which is the main influence factor of machining accuracy. In order to reduce machine thermal error and improve machining precision, there are mainly 3 ways at present: 1) Improving machine thermal stiffness by optimal design of machine structure; 2) Separating heat sources from machine tools; 3) Thermal error compensation, which reduces the influence of thermal distortions by predicting and compensating measures. In order to compensate thermal errors, thermal error modeling is the premise and foundation. Therefore, thermal error modeling technology is introduced in this paper firstly, and its recent development both at home and abroad is analyzed. The main obstacles in thermal error modeling field at present are summerized, and the future of the technology are presented

Comparison of four risk assessment scales in predicting the risk of intraoperative acquired pressure injury in adult surgical patients: a prospective study

Objective To develop and compare four predictive models for intraoperative acquired pressure injury (IAPI) in surgical patients. Methods One hundred patients undergoing various surgeries (hepatobiliary, pancreas, spleen, gastrointestinal, and cardiac surgeries) at Ruijin Hospital from November 2021 to September 2022 were included in this prospective cohort study. Four pressure injury risk assessment scales were used to measure the pressure injury risk: the Braden scale, Munro Pressure Injury Risk Assessment Scale, Scott Triggers tool, and CORN Intraoperative Acquired Pressure Injury Risk Assessment Scale. The patients were divided into the IAPI group and non-IAPI group. Results In total, 37% of patients (37/100) developed class I/stage pressure injury (erythema) after surgery, which resolved within 2 hours after surgery in 86.49% of cases and further progressed to class II/stage or higher pressure injury within 6 days in 15.63% of cases. The application effects of the four commonly used risk assessment tools were compared with the sensitivity, specificity, and area under the receiver operating characteristic curve. The Munro Scale showed the best sensitivity and area under the receiver operating characteristic curve among the four tools for postoperative assessment, but its specificity was only 20.63. Conclusions More appropriate assessment tools are required for IAPI risk evaluation

Study on Wear Mechanism of Helical Gear by Three-Body Abrasive Based on Impact Load

This study aimed to explore the wear characteristics and evolution mechanisms of large-scale wind power gears under the impact load of particles of the three-body abrasive Al2O3 (0.2 mg/mL) from four aspects: oil analysis, vibration analysis, amount of gear wear, and tooth-surface-wear profile analysis. A magnetic powder brake was used to simulate the actual working conditions. Combined with the abrasive particle monitoring and the morphology analysis of the tooth-surface-wear scar, by setting quantitative hard particles in the lubricating oil, the gears are mainly operated in the abrasive wear state, and wear monitoring and wear degree analysis are carried out for the whole life cycle of the gears. Oil samples were observed and qualitatively analyzed using a particle counter, a single ferrograph, a metallographic microscope, and a scanning electron microscope. The experiments demonstrate that the initial hard particles have a greater impact in the early wear stage of the gears (2O3 particles accelerate the gear wear during the running-in period. The loading method of the impact load on the oblique gear exacerbates the abrasion particle wear and expands the stress concentration, which reduces the surface of large milling particles on the surface, and reduces the width of the tooth (the part above the pitch line is severely worn), which causes the gear to break into failure. The research provides help for analyzing the mechanism of abrasive wear of gears and predicting wear life

Kinematic Characteristics Analysis of Orbiting Scroll and Structural Optimization of Oldham’s Coupling in Scroll Compression

The contact form of the orbiting scroll and Oldham’s coupling plays an important role in improving the operation stability of the scroll compressor. In this study, the kinematic simulation of key moving parts such as the orbiting scroll and Oldham’s coupling was carried out under the condition of low speed, and the reason for the impact between Oldham’s coupling and the orbiting scroll was revealed. Results showed that the clearance between the moving pairs causes the orbiting scroll to have a slight rotation tendency and causes the impact between Oldham’s coupling and the orbiting scroll. The angular velocity of the orbiting scroll in the x-axis direction can effectively characterize this impact. The impact of the Oldham’s coupling convex key on the mainframe keyway is more severe than that on the keyway of the orbiting scroll. By optimizing the structure of the convex key of Oldham’s coupling, the contact form between Oldham’s coupling and the orbiting scroll is improved, and the starting acceleration of the orbiting scroll is reduced by 53%, which greatly improved the working stability of the scroll compressor

Proximate Model of Gear Drive Units Based on Dimensional Analysis for Wear Process Evaluation

Excessive wear of gears will not only cause noise and vibration in the transmission system, but also reduce transmission efficiency and accuracy in severe cases, causing irreversible losses to the transmission system. It is desirable to develop a micro-gear unit model for evaluating the wear process and predicting the failure time of large gear units (such as wind turbine gear units), reducing losses due to sudden failures. Based on the Buckingham pi-theorem of dimensional analysis and Hertz formula, the similarity ratio of each parameter of the gear wear process was proposed. The maximum equivalent stress is calculated by establishing the FEM model and comparing it with the theoretical contact stress calculated by the Hertz formula, and the results were relatively consistent. Two pairs of gear friction and wear experiments with similar parameters were carried out to compare the wear evolution performance of two similar gears. The friction performance process of the test gears was observed by particle counter and analytical ferrograph. The results show that the friction and wear processes of the two groups of gears with similar parameters have a certain correlation, which was consistent with the proposed similarity model. The similarity model combined with the observation results of abrasive particles has a certain application value for the evaluation of the wear state of the transmission system

Prediction of Surface Roughness in Gas-Solid Two-Phase Abrasive Flow Machining Based on Multivariate Linear Equation

The main purpose of this study is to explore a surface roughness prediction model of Gas-Solid Two-Phase Abrasive Flow Machining. In order to achieve the above purpose, an orthogonal experiment was carried out. Q235 steel as processing material and white corundum with different particle sizes as abrasive particles were used in the experiment. Shape and spindle speed were the main reference factors. The range method and factor trend graph are used to comprehensively analyze the experimental results of different processing stages of the detection point, and the optimal parameter combination of A3B2C1D2 was obtained. According to the experimental results, a multiple linear regression equation was established to predict the surface roughness, and the experimental results were solved and significantly analyzed by software to obtain a highly reliable prediction model. Through experiments, modeling and verification, it is known that the maximum error between the obtained model and the actual value is 0.339 μm and the average error is 0.00844 μm, which can better predict the surface roughness of the gas-solid two-phase flow abrasive pool