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Abstract Aircraft parts are often designed as thin-walled structures to reduce the weight of the aircraft. However, thin-walled structures are prone to deformation during the milling process, leading to a decrease in machining accuracy. To address this problem, a method combining milling and electrochemical machining, known as electrolytic milling, is proposed to minimize deformation and enhance the accuracy of thin-walled parts. The factors that affect the machining accuracy of electrolytic milling were analysed, and a model for predicting the thickness of the material removed was established. Electrolytic milling experiments were designed, and the model was solved. Based on the built model, the influences of feed rate, spindle speed, radial cutting depth, voltage and electrolyte concentration on material removal thickness were investigated. Compared with the milling method, the electrolytic milling method can improve the machining accuracy of thin-walled parts. Electrolytic milling experiments were conducted on box-shaped parts to verify the reliability of the proposed method.

Machining chatter is likely to occur during milling of thin-walled parts. The structural differences in thin-walled parts and the magnitude of the milling force can lead to varying degrees of chatter in different areas of the machining process. Predicting machining stability using dynamic modeling methods can be time-consuming. In this study, a method for establishing a particle swarm optimization-back propagation (PSO-BP) neural network model is proposed to predict the modal parameters of thin-walled parts and the surface vibration of machined parts. Based on measurements of the length, height, wall thickness, and position of the thin-walled parts, the modal parameters of the workpiece were predicted using the PSO-BP neural network model. Additionally, the average milling force was included as an input parameter to predict the displacement of surface vibrations on thin-walled parts using the PSO-BP model. The predictive results of the modal parameters and surface vibration displacement are evaluated using the evaluation function, which indicates that the PSO-BP neural network model can reliably predict the modal parameters and surface vibration depth of thin-walled parts.

Accurate obstacle detection and proper behavior planning are key factors in the success of transmission line inspection robots. To achieve the autonomous location and identification of line obstacles in the operation of transmission line inspection robots, we propose a method in which information from various sensors is used to control a robot such that it can reliably and stably approach, locate, and identify obstacles. The accuracy and real-time requirements of obstacle information in the autonomous operation of the inspection robot are analyzed, a multi-sensor integrated structure for line obstacle location and identification is proposed, and an obstacle location and identification algorithm is designed for each stage. The principle of monocular vision ranging is used to control the robot such that it approaches obstacles and enters the short-range location stage, where the reliable location of obstacles is achieved via collision-encoder-current sensor data fusion. Obstacles are identified and the identification results are combined with those of the approaching rolling phase. The robot state vector is constructed according to the obstacle detection information and information measured by the robot sensors. Based on the current state vector, combined with the robot obstacle surmounting process, an obstacle surmounting behavior planning method based on multi-sensor fusion is implemented. Experiments were conducted using laboratory-simulated lines to verify the effectiveness of the proposed method for obstacle detection and behavior planning during transmission line inspection.

Machining vibrations often occur when working with thin-walled workpieces. One effective method to mitigate these vibrations is by using a damper, which can enhance machining accuracy, surface finish, and tool life. However, traditional contact dampers have a drawback in that they require direct contact with the workpiece, leading to friction, wear, increased cutting forces, and reduced machining accuracy. In contrast, electromagnetic eddy current dampers are noncontact dampers that can effectively suppress machining vibrations without the need for physical contact. In this study, a method to suppress machining vibrations in thin-walled workpieces using electromagnetic eddy current dampers is proposed. By establishing a theoretical model for the electromagnetic damper, the damping force and equivalent damping of the damper are determined. Subsequently, the impact of electromagnetic dampers on frequency response functions and machining vibrations are investigated through hammer impact tests. The results indicate that increasing the surface damper voltage and reducing the air gap both enhance the equivalent damping of the electromagnetic eddy current damper. Moreover, cutting experiments are conducted to analyze the surface roughness of thin-walled workpieces with and without dampers. The results demonstrate that the eddy current damper can effectively increase the equivalent damping and provide the necessary damping force to suppress machining chatter. Overall, the proposed method utilizing electromagnetic eddy current dampers presents a promising solution for suppressing machining vibrations in thin-walled workpieces.

The results of numerical research on boiling heat transfer of R410A refrigerant in an elliptic tube with four microchannels and micro fins are presented in this paper. The boiling performance of elliptic microchannel tubes with different inlet vapor qualities is studied, keeping saturation temperature constant at 278.15 K corresponding to the saturation pressure at 93,623 Pa with 3 kW/m2 heat flux and 150 kg/(m2s) mass flux. The Martinelli parameter, heat transfer coefficient, pressure drop, and so on are investigated in the present paper. The CFD results are compared with and verified by the previous two-phase heat transfer correlations. The discrepancies in flow rate, heat transfer performance, and two-phase flow pattern between the middle and the two sides of the elliptic tube are compared. The velocity field and flow trajectory of gas-liquid two-phase flow in the elliptic tube microchannels are discussed and analysed. The results show that when the inlet vapor quality is high, there will be a distinct heat transfer deterioration area in the microchannels during the boiling process. The large area of gas film can weaken the heat transfer performance of the microchannel heat exchanger up to 35.42 % in the region without micro fin. The local highest heat transfer coefficient can reach 2,886.8 W/(m2K) in the physical model. The micro fins can not only increase the heat transfer area and enhance the nucleate boiling but also divide the gas film to form a local annular flow pattern and inhibit the deterioration of boiling heat transfer. The present paper is of great significance for scientific utilization and optimization of the heat exchanger, the reduction of energy consumption, and the enhancement of the exergy efficiency of the system.

In order to improve the cleaning effect of the castor shelling mixture, an air-sieve castor cleaning device was developed. The structure of the cleaning device was optimized by experiment and simulation based on the discrete element method. The results show that the sieving efficiency of the square distribution is 98.23% and the loss rate is 2.39%, both of which are better than the triangular distribution. The sieving efficiency in the condition of a 14 mm sieve hole diameter is 98.23%. For the conditions of 15 mm and 16 mm sieve hole diameters, the sieving efficiencies are 96.64% and 96.69%, respectively. Therefore, a sieve hole diameter of 14 mm is more beneficial for the sieving of castor capsules. The sieving efficiency is 94.0–99.5%, and the loss rate is 0.5–3.0% under 5–9° sieve inclination. The cleaning effect is better through comprehensive analysis when the sieve surface inclination is 8°. The parameters of maximum sieving efficiency combination, minimum loss rate combination, and optimal cleaning effect were obtained by optimizing the operating parameters of the cleaning device. The operating parameters were adjusted, and then the three combinations of parameters were tested. It is found that the impurity content of castor seeds is within 1%, which meets the requirements of the device design. This study can provide a reference for developing high-efficiency castor cleaning devices.

This paper elaborates on a digital simulation study on supernormal particle flow used to investigate and analyze the process of picking up jujube branches, which was a meaningful attempt to search for accurate and effective advanced numerical analogy methods in the agricultural field. In this paper, the meshless technology based on the element-free Galerkin method was used for the first time to present the effects of particle size, particle number and particle acting force on the movement of irregular particles, and the influence of the gear rotation speed, the feeding amount, and the jujube branch size on the movement behavior as well as the picking rate. It can describe not only the particles’ dynamic movement in the process of picking up jujube twigs, such as feeding, collision, throwing and rolling, but also the effect of the quality and shape caused by the particle size, which in turn affects the surface force of particles and interparticle acting force, thereby affecting the weight function in the analytical solution, the total feeding amount and the effect of the acting force resulting from the particles’ contact, roll and collision caused by gear rotation. The findings reveal that the digital simulation, based on the meshless Galerkin technology and Rocky software, is effective in dealing with issues related to supernormal particle flow. By eliminating the influence of geometric shapes on calculations, the method boasts an effective solution to the movement problems of irregularly shaped particles, which would be further applied in the agriculture field.

In order to solve the problem of low mechanization level of hairy vetch harvesting, a feeding device for an anti-winding hairy vetch harvester was designed. Firstly, the physical properties of hairy vetch stalk were studied. According to the mechanical properties of hairy vetch stalk, the key components of the feeding device were designed and analyzed, the structure and working principle of the feeding device were described. Secondly, the discrete element method was used to simulate and analyze the movement performance of the feeding device. On this basis, the ternary quadratic regression orthogonal rotation combination test was established with the vertical drum, the machine forward speed, and the spiral conveyor speed as the test factors and the stem loss rate as the test index. The simulation results showed that when the vertical drum was 1037.5 r/min, the machine forward speed was 2.76 m/s, the spiral conveyor speed was 348.88 r/min, and the straw loss rate was 2.38%, and the feeding device performs best at this time. Finally, the on-site performance test of the feeding device was carried out. The results showed that: all the test indicators met the requirements of the national standard; the actual cutting width was 1.66 m; the cutting stubble height was 6.41 mm; the over stubble loss rate was 0.45%; the missed cutting loss rate was 0.20%; and the stem loss rate was 3.00%, which verified the rationality of the design of the feeding device. In order to solve the problem of low mechanization level of hairy vetch, which easily becomes entangled in the working process, an anti-winding feeding device for hairy vetch harvesting was designed.

To increase the cutting efficiency for castor stem, the castor harvester cutting device was developed. The structure of the disc cutting device was designed. Cutting blade angle, sufficient working and minor cutting edge lengths were determined, which were 20°, 73 mm and 19.8 mm, respectively. The finite element model of disc cutter for castor stem was established. The incision volume was selected as the cutting performance evaluation index. The cutting process of the cutter was simulated. The results show that the cutting performance of the trapezoidal cutter is preferable to that of the rectangular and the curved cutters. When cutting blade cuts the stem, the volume of the incision decreases first and then increases, and the size of the incision increases with the increase of cutting edge angle. When the blade angle is 10°, the cutter has the ideal cutting quality. Considering the blade angle, the slip angle, and the angle of the cutter head as factors, the virtual test of the cutter was made with the incision volume as the index. The response surface analysis was used to obtain the cutter structure parameters when the incision volume was the least. The result for the blade, slip and cutter head inclination angles are 14.06°, 19.93°, and 10.54°, respectively. The cutting efficiency evaluation index (one-time cutting) was established to optimize the cutter running parameters. The results show that when the cutter moving speed was 1.011 m/s and the cutter rotation speed was 282.0 r/min, the maximum cutting efficiency is 2.25 castor stems/s.

Hollow blades with honeycomb structures are increasingly used in the turbine engines for reducing weight and saving costs. The hollow blade is a typical thin-walled structural part with low stiffness, the machining system of which is often unstable and likely to chatter. The most effective solution to avoid the machining chatter is to guide the hollow blade to be machined in a stable machining zone. This paper proposes a measurement-based approach for modal analysis and stability prediction of turn-milling hollow blade. The impact test was carried out to achieve the FRF curves on the hollow blade and the milling tool. An extremum method was employed to obtain an equivalent FRF curve, from which the modal parameters involving the natural frequency, damping ratio, and stiffness were computed. Afterwards, the semidiscretization method was used to draw a stability lobe diagram to predict the stability when turn-milling hollow blades. The experimental results confirm the feasibility of the predicted stability lobe diagram.

The stability limit may change with the cutter’s location due to effect of curvature during the milling of a complex surface. The method for calculating the actual radial cutting depth is presented by accounting for the effects of curvature on the actual cutting parameters. The computed radial cutting depth is in turn used to determine the entrance/exit angles. Moreover, a milling system dynamic model is established based on the instantaneous milling force coefficients, and the stability limit is determined by means of the time-domain semidiscretization method. In addition, a location-dependent method for predicting the stability associated with the peripheral milling of a complex surface is put forward and simulation is carried out to generate a stability limit diagram. The effectiveness of the proposed method is verified through milling tests.

Castor is one of the important oil crop, the shelling process of which directly affects the quality of castor seeds. In the process of shelling, the shelling force of castor is an important index to study its damage. The castor capsule model was established and the shelling test machine was established based on the discrete element method. Then the extrusion law of castor capsule during shelling was analyzed. The shelling process is divided into three stages, which are the Initial stage, stable shelling stage and the final stage. The force law of shelling process is analyzed. The results show that with the increase of rotating speed, the maximum force decreases from 68.78 to 68.10 N, the maximum speed increases from 8.92 to 12.99 m/s, the force of inner drum increases from 509.34 to 533.14 N, and then decreases to 456.15 N. The shelling increases from 91.23% to 91.28%, and then decreases to 88.89%. With the increase of filling amount, the maximum force increases from 55.86 to 76.93 N, the maximum speed decreases from 12.99 to 10.86 m/s, the force of inner drum increases from 338.58 to 603.364 N, and the shelling rate changes from 91% to 90.05%. This study can provide theoretical support for the design of castor shelling machine. [ABSTRACT FROM AUTHOR]