Computer numerical control (CNC) machine tools are widely used in various industrial fields ranging from aerospace, automotive, ship building, and the die/mould to manufacture products. However, tool paths of most CNC machine tools are composed of a series of linear motion commands (G01), which will inevitably cause the discontinuity in curvature and feedrate at the junctions between adjacent linear tool path segments, deteriorating the surface quality with unfavorable marks and decreasing the machining efficiency. To solve this problem for obtaining the steady and continuous motions of machine tools, the local corners have to be smoothed. Generally, the existing corner smoothing methods can be classified as the global smoothing and the local corner smoothing, where the specially designed transition curves or the directly planned motion of machine tools are adopted to generate the geometrically corner-free tool path. Moreover, some new methods that focus on developing different transition or rounding strategies are also developed for further improving the kinematics performance of machine tools. In this paper, the recent advances and researches on corner smoothing methods are reviewed from different categories, and the conclusions, remaining challenges and future directions in corner smoothing are also presented.
Carbon fiber-reinforcement plastics (CFRP) have been widely applied in modern aerospace industry with aluminum alloy in the form of thin-walled stacks due to their superior mechanical and physical properties. However, for CFRP, the heat accumulation occurs easily during countersinking process in consequence of low thermal conductivity. The surface thermal damage of CFRP caused by excessive heat would affect the fatigue and stealth performance of aircraft. Consequently, the countersinking temperature is an important indicator to judge the feasibility of CFRP countersinking process. In this paper, to investigate temperature of countersinking process, the application of rotary ultrasonic machining technology to CFRP/Al thin-walled stacks countersinking process under different stiffness conditions with drilling-countersinking integrated tool is carried out by FEA (Finite element analysis) and experiments. And the influences of cutting temperature on countersunk wall quality are discussed. The results demonstrate that the maximum countersinking temperature increases with the decrease of axial stiffness, and the ultrasonic vibration can effectively reduce maximum countersinking temperature by 22.9%-26.2%. Furthermore, analysis of the surface quality of countersunk wall shows that the countersunk wall roughness and defects gradually deteriorate with the increase of the maximum countersinking temperature. Meanwhile, the ultrasonic vibration can improve countersunk surface quality by reducing maximum countersinking temperature effectively.
Abstract: Mg-2Zn-1Al alloy was used as the matrix, and 0.2wt% Ca, 0.2wt% Gd, and 0.2wt% Ca+0.2wt% Gd were added into it. The target alloys with four components were extruded at 200℃ and extruded bars with good surface quality were obtained. Optical microscope (OM), scanning electron microscope (SEM), X-ray (XRD) and tensile mechanics experiment were adopted to analyze the effect of trace Ca and Gd on the microstructure and mechanical properties of Mg-2Zn-1Al alloy. It is found that the grain size of the as-cast matrix alloy can be refined by adding Ca and Gd, and the effect of grain refinement was the superposition of the two effects added separately. This is due to the heterogeneous nucleation of Al2Ca and the segregation of Gd in front of the solid-liquid interface leads to the inhibition of grain growth. Furthermore, the addition of Ca and Gd can make the extruded micro-structure fine and uniform, which can weak the texture to improve the mechanical properties of the alloy. And the composite addition has the best refinement effect and texture weakening effect. Therefore, the alloy with the composite addition of the two showed the best mechanical properties.
Abstract: Tool deflection is severe in the micro milling process with flexible tools. Existing models usually predicted the machining errors caused by tool deflection through time-consuming iteration algorithms. This article presents an efficient method to predict the machining errors caused by tool deflection in the side-wall milling process. The concept of equivalent modulus is proposed to describe the tool deflection behavior under cutting loads. It is found that the radial cutting force at the immersion angle of π is the actual cause of the machining errors. To describe the influence of instantaneous actual cutting direction shifts in the down milling process with flexible tools, the cutter is regarded as pressing into the workpiece during the cutting process, and the total cutting load is regarded as the combination of cutting forces and the press force. The material piling up and strain hardening is included in this model. Verifications show that the proposed model can greatly save the computational time without losing prediction accuracy.
Currently, manual detection of wall welds and surface microcracks on ships and oil tanks is not only inefficient but also potentially hazardous. This study proposes a 4SRRR legged wall-climbing robot with redundant actuation, designed to accommodate the characteristics of permeable materials, to address this issue. First, the robot's gait is examined, followed by a thorough examination of its stability on both vertical and horizontal surfaces. For vertical surfaces, a statics analysis is conducted to prevent the risk of falling, whereas, for horizontal surfaces, the margin of stability is evaluated. To determine the required degrees of freedom for the robot to complete its assigned tasks, the screw theory is applied. The De-navit-Hartenberg (D-H) method is then used to analyze the forward and inverse kinematics of the robot. In addition, the La-grange balance method is used to analyze the swing leg's dynamics. A control algorithm for impedance is developed for situations in which the swinging leg collides with the ground. A prototype is then designed and tested to assess the wall-climbing performance and the efficacy of the impedance control strategy when the swinging leg experiences an impact. This research seeks to provide a solid theoretical foundation and technical support for the engineering application of wall-climbing robots, thereby enhancing the efficiency and safety of wall weld and surface microcrack detection processes in ships and oil tanks.