Nowadays, there are urgent demands of micro structure/parts which have high strength in hightemperature environment in the fields such as aerospace, energy, power, biomedical, etc. Nickel-based superalloy with high strength and high hardness under high temperature is the suitable material for manufacturing this kind of micro parts. Aimed at the problem of the complicated cutting force variation rule when micro-end milling nickel-based superalloy, the cutting forces model during micro-end milling of nickel-based superalloy processing is studied. Firstly, micro-end milling hole experiments are carried out to establish the radical run-out prediction model of cutting edge, which lays the foundation for establishing the cutting thickness calculation model during micro-end milling. Then, based on the minimum cutting thickness value, micro-end milling of nickel-based superalloy process is divided into two different cutting processes: shear-dominant regime cutting process and ploughing-dominant regime cutting process. Moreover, cutting forces prediction model during sheardominant regime cutting process is developed based on the cutting forces in proportion to cutting layer area, which takes the effect of ploughing into account. Meanwhile, cutting forces prediction model during ploughing-dominant regime cutting process is developed based on the cutting force in proportion to interference volume between the flank surface of cutting tool and the workpiece. The experiment results verify that the cutting forces prediction results and experiment results are well matched.
Purpose The purpose of this paper is to solve the problem that the analytic solution model of spatial three-dimensional coordinate measuring system based on dual-position sensitive detector (PSD) is complex and its precision is not high. Design/methodology/approach A new three-dimensional coordinate measurement algorithm by optimizing back propagation (BP) neural network based on genetic algorithm (GA) is proposed. The mapping relation between three-dimensional coordinates of space points in the world coordinate system and light spot coordinates formed on dual-PSD has been built and applied to the prediction of three-dimensional coordinates of space points. Findings The average measurement error of three-dimensional coordinates of space points at three-dimensional coordinate measuring system based on dual-PSD based on GA-BP neural network is relatively small. This method does not require considering the lens distortion and the non-linearity of PSD. It has simple structure and high precision and is suitable for three-dimensional coordinate measurement of space points. Originality/value A new three-dimensional coordinate measurement algorithm by optimizing BP neural network based on GA is proposed to predict three-dimensional coordinates of space points formed on three-dimensional coordinate measuring system based on dual-PSD.
Wind tunnel balance is one of the most important measurement equipments in aerodynamic testing. In this paper, a new six-component piezoelectric balance is developed to measure the dynamic impact loading force in the wind tunnel. The arrangement mode of the triaxial piezoelectric load cells is confirmed based on the theory analysis. Furthermore, the mathematical model is established according to the calibration experimental results. Support vector machine is proposed to develop the piezoelectric balance calibration. It is an effective method to predict the model using small samples and reduce the duration of the calibration. The results of prediction are compared to the conventional calibration and the dynamic step response. The linearity and repeatability of the balance are within 0.2% and 0.5%, respectively, and the interference error has been reduced using the support vector machine method. The experimental results have shown that the four supports arrangement mode can reduce the area of attack and enhance the measuring range of the balance. The dynamic characteristics of the piezoelectric balance performed by the step response test show that the designed balance is feasible to measure the dynamic impact airloads in a wind tunnel.
In the process of manufacturing and operation of mechanical equipment, accurate measurement of vector force provides an important basis for real-time control of working conditions and process adjustment to ensure the performance. Piezoelectric three-component force unit can be used to measure three-axis force with the characteristics of high frequency and stiffness, great dynamic response, and resistance to harsh conditions. Piezoelectric dynamometer consisting of four three-component force units can measure six-axis force/torque, which is widely used in vector force measurement. However, because of the limitation of manufacturing capability and assembly process, dimension coupling caused by assembly error of three-component force unit restricts improvement of test accuracy for itself and piezoelectric dynamometer. To reduce dimension coupling caused by displacement and angle assembly error, this article establishes a theoretical model of assembly error of three-component force unit. To achieve that the dimension coupling of threecomponent force unit is less than 3%, stiffness of relevant components is obtained by simulation analysis and experiment, and assembly tolerance range of three-component force unit is proposed. Four three-component force units are assembled to meet assembly tolerance range, and the calibration experiment is performed. The results show that the maximum of dimension coupling is less than 2.5%, which verifies the rationality of assembly tolerance range and further proves the reliability of the theoretical model. The theoretical model of assembly error clarifies the assembly accuracy of three-component force unit to ensure its test accuracy, which can further improve test accuracy of dynamometer. This article will also provide theoretical reference basis for this kind of sensors.
Piezoelectric force sensors are widely used in precision measurement and machining applications. Sensitivity is one of the significant parameters determining the precision of these sensors. The influence of factors, such as the piezoelectric coefficient, sensor structure, and temperature on sensitivity had previously been studied except the roughness of sheets. For design optimization, the effect of roughness on the sensitivity of piezoelectric force sensors was investigated. A sensitivity model was built based on the electromechanical relationships and measurement systems. Fractal theory and classic statistics model were used to define the roughness of the sheets. The stiffness effect and thickness effect were used to probe the relationship, and two types of experiments with sheets of different roughness were performed to verify the models. The results indicated that the roughness of the sheets affected the sensitivity of the piezoelectric dynamometers due to the stiffness effect and thickness effect. In terms of the thickness effect, rough sheets induced high sensitivity; however, in terms of the stiffness effect, as the roughness decreases, the sensitivity first improved and then decreased. A method was proposed to optimize the roughness of the sheets to improve the sensor performance.
A piezoelectric dynamometer can produce thermal forces because of temperature fluctuations, thus affecting measurement precision. To investigate the influence of the thermal force on the dynamometer, this article proposes a hypothesis of decreasing the conduction power and establishes the function of a thermal force over time in an ordinary dynamometer based on the heat conduction differential equation. A novel double-sensor thermal compensation dynamometer is designed, with static calibration in constant temperature and force/heat coupling experiments, to solve the problem of the thermal force. The experimental results indicate that the nonlinearity and repeatability of the double-sensor thermal compensation dynamometer are less than 1% full scale (FS) of the static calibration at a constant temperature; in the force/heat coupling experiments, at a heating rate of 0.4 ℃/s to 110 ℃ with a loading force of 500 N, the maximal output deviation is less than 1.06% (FS), realizing the unidirectional thermal force compensation of the structure. The double-sensor thermal compensation dynamometer can be utilized in sharp temperature fluctuations environment, like rocket engine forces measurement.
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