Applied Mechanics and Materials Vols. 201-202

Abstract: Shape from shading (SFS) is one of the critical techniques in 3D shape recovery in computer vision. The task of SFS is to reconstruct 3D shape of the visible surface of an object from one single picture using its gray variation. Analyzing the 3D shape of welding pool is important to evaluate the welding quality. During the disk laser welding experiments, a high-power laser was used as the auxiliary illuminant, and a high-speed image acquisition system with infrared filter was applied to capture the welding pools in real time. The slant and tilt of illuminant source were estimated by statistics to reconstruct the 3D shape of welding pool visible surface by using the localization method of SFS. Methods of median filter and cubic spline interpolation were used to denoise images and smooth the image shapes. Experimental results showed that the proposed technique could reconstruct parts of welding pool effectively.

Abstract: In order to improve the quality and accuracy of blanking workpiece, reasonable measures have been proposed during the production process. Firstly, the quality precision of blanking workpiece has been classified into three grades, corresponding to each type of dimensional accuracy, reasonal range of blanking clearance has been selected. Then the relationship of blanking clearance size with blanking quality has also been analyzed, and the affection of blanking clearances to dimensional accuracy has also been analyzed.At last, the method to improve the workpiece quality has been proposed, and the measure has been put forward to solve problems of quality and accuracy. The results refer useful references to improve the quality of stampings.

Abstract: During deep penetration laser welding, a keyhole is formed in the molten pool. The characteristics of keyhole are related to the welding quality and stability. Analyzing the characteristic parameters of a keyhole during high power fiber laser welding is one of effective measures to control the welding quality and improve the welding stability. This paper studies a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, and an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. A combination filtering system with a filter length of 960-990nm in front of the vision sensor was used to obtain the near infrared image and eliminate other light disturbances. The width, the area, the leftmost point, the rightmost point, the upmost point and the bottommost point of a keyhole were defined as the keyhole characteristic parameters. By using the image preprocessing method, such as median filtering, Wiener filtering, threshold segmentation and Canny edge detection methods, the characteristic parameters of a keyhole were obtained. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters could reflect the quality and stability of laser welding effectively.

Abstract: Owing to a strong capability of penetration, the radiography can be used to observe and analyze the formation of a molten pool inside weldments during laser deep penetration welding. The shape of a molten pool and the thermal transmit of laser through keyhole can be monitored and analyzed in real-time. During a high-power fiber laser bead on plate welding of Type 304 stainless steel, a high-speed radiography camera was employed to capture the molten pool images. These captured X-ray images were degraded by the disturbance and noises from the welding process and radiography devices. This paper proposes an efficient arithmetic to restore and enhance the X-ray images of molten pools. The point spread function (PSF) of X-ray image degeneration was obtained through blind deconvolution, And the PSF was applied as a parameter to implement the constrained least squares filtering of X-ray image of a molten pool. Also, the X-ray image was enhanced by contrast stretching transformation. Experimental results showed that the proposed arithmetic of image restoration and enhancement could improve the quality of X-ray images efficiently and protrude the contour feature of a molten pool.

Abstract: In order to solve the problem that traditional flutters can’t reach the requirements of vibration-assisted machining (VAM), a miniature modularized electro-hydraulic high-frequency flutter was proposed, which can output large force in high frequency. The structure and working principle of the flutter were elaborated in this paper. The equations of the valve in this flutter can be obtained based on equations of tradition valves, which established the mathematical model of the flutter. The flutter output waveforms were analysed by MATLAB in different input frequencies. The simulation results show that the flutter amplitude reach the maximum value in resonant frequency.

Abstract: Serious vibration and noise exists in the circular saw cutting process. In order to reduce the cutting vibration and noise, this paper uses the finite element numerical calculation and modal testing analysis to study the dynamic characteristics of the circular saw blades, obtain the circular saw’s kinetic parameters, such as each order natural frequency, the main vibration mode and damping ratio, evaluate the circular saw system’s dynamic response. Through the optimization of slotted design and experimental analysis, a circular saw with reasonable structure reduces the maximum vibration displacement of 11.1% which increases the circular saw blades cutting quality, prolongs the service life and reduces the cutting noise.

Abstract: This paper presents a new structure of electro-hydraulic flutter device, taking into consideration the high frequency response and low inertia. A simulation model is established based on AMEsim and simulated the vibration of the flutter. The dynamic characteristics of the flutter device and the flow field in the chamber of the flutter are investigated by experiment. Basically the experimental results were in accord with the simulation results. The results show that the electro-hydraulic flutter device can get a high frequency vibration performance. The average chamber pressure of the flutter device is half of the system pressure without the exciting valve pressure drop.The amplitude is 4um in 1572Hz and 3um in 1853Hz.

Abstract: The application of air-decked blasting technology has enabled the efficient use of explosion energy, which proves that the air-decked blasting technology can overcome many disadvantages caused by column charge effectively, getting ideal explosion effect. Based on the JHC model of concrete damage evolution, the dynamic stress characteristics and failure mechanism of blast-hole near-field about bottom-air-decked charge structure is studied by numerical simulation. Result shows that the failure mechanism of typical elements changes from compression-shear failure into shear-tensile failure gradually with the increase of their position, for the effecting factors of the freedom and the loading from the hole. Comparing the dynamic stress characteristics of different detonating manners, indirect initiation can improve the static function intensity and delay the time of detonation gas, so it is easier to destroy the bottom rock of hole.

Abstract: Detecting the weld pool width is prerequisite to control the welding quality. However, in an arc welding process, it is difficult to obtain a clear image of weld pool due to strong arc disturbance. A method is proposed to lessen the arc disturbance and obtain the width of a weld pool. A camera was used to capture the weld pool images during the arc welding process. The frequency domain filter combined with spatial processing algorithms were used to depress the noises in the pool image. During arc welding, the weld pool was in a liquid state and showed specular reflection due to the arc light effects. Because of the specular reflection, edges of the weld pool exhibited different brightness from that of the internal weld pool where a camera hangs. According to this phenomenon, it was easy to recognize the outlines of the internal and external weld pool. After the image noise of the weld pool was eliminated by an image filtering algorithm, then the line scanning on the image was carried out. It was crystal-clear that the external edge and internal edge demonstrate different grey levels. Therefore the method could be utilized to identify and extract the internal weld pool width and external weld pool width.

Abstract: Technology of EDG has been widely applied in aviation aerospace field recently. In the process of EDG honeycomb ring (GH536) which as the important part of aircraft engine, analysis software of ABAQUS is used to conduct the simulation analysis to temperature field, then obtained the distribution of temperature field with honeycomb ring. Through analysis and calculation meanwhile conducting a lot of simulation tests that repeatedly validated, simulation process by ABAQUS are accurate and rapidly, and it is also applied to optimize the craft of EDG other related thin-walled parts, at the same time it can be used to provide the theory basis of calculating precisely the thermal stress and residual stress in EDG processing.