Applied Mechanics and Materials Vols. 16-19

Abstract: This paper deals with the dimensional synthesis of a 2UPS-UPR parallel mechanism tool newly designed by Northeastern University. On the basis of establishing kinematics equations and obtaining Jacobian matrix, the performance index of dimensional synthesis is given which is the average of 729 values of the condition number of Jacobian matrix corresponding to 729 positions in the workspace. With MATLAB software, the effects are simulated which the structural parameters of parallel machine tools have on dimensional synthesis, their change laws are gained, and then dimensional synthesis of parallel machine tools is conducted based on these laws.

Abstract: The influence of process parameters on isothermal precision forging of a screw propeller is studied by means of FEM (Finite Element Method) simulation. The even degree of deformation, distributions of the flow line and effective strain within the billet and the forging load are analyzed. Notable difference of the effective strain is existed between the blades and the wheel hub of the screw propeller. Large deformation of the blade has been obtained, which is favorable for the blade strength. The material flow and the distribution of deformation can be adjusted by changing the process parameters and the forming quality can be improved. Both the forming temperature and punch speed have large influence on the forming load but less influence on the distribution of deformation. The result of simulation shows that the precision forging of screw propellers can be formed with the isothermal precision forging satisfactorily.

Abstract: The objective of this research work is to develop a direct metal rapid mould using layered manufacturing process. The approach relate to direct slices of CAD models to generate process planning instructions, incises the metal sheets layer by layer process and bonds them by diffusion weld technology. Instead of slicing the model from STL data, this methodology direct slices of CAD models using a constant layer thickness in EUCLID-IS based CAD system. The cross section contour profiles are then converted to CNC machine instructions for fabrication. Fabricated sample shows that the new process is one of the feasible methods for the layered manufacturing of metal moulds.

Abstract: In this paper, we present a novel method of using the continuous rolling to fabricate three-dimensional sheet metal. The core bendable roller is composed of the flexible axis and the controllable equipment. The transversal shape of the sheet metal can be realized by regulating the controllable equipment to make the axis of bendable roller bent; the longitudinal shape is formed by driving the three bendable rollers rotated and the top roller making a displacement synchronously. Some experiments were performed and typical 3D surface parts were formed. Based on the results of the experiments, the effects of the thickness and the rolling times are discussed. The results of the research will be beneficial to define the parameters and perfect the theory of continuous multipoint forming of multiform 3D parts.

Abstract: In this paper a three-dimensional numerical computation on temperature and crown of rolls in hot strip rolling was evaluated based on finite element method and parallel computation technology with multiple CPUs. A comparison between calculated results and actual data collected from rolling mills was presented, which indicated the high accuracy of the model. The calculated results indicated that a significant impact in thin layer of work roll surface was brought by thermal load, while much weaker in the core. Furthermore, the temperature field and thermal crown of hot mill work rolls would reach a stabilized condition only when several rolling cycle be finished.

Abstract: The tool position based on the general interpolation arithmetic will make sharp changes which bring a harmful influence to the mixed control of pose and position as well as the normal force in grinding process. In this paper, a new type of shape-adaptive tool is proposed for the common NC lathe. The effective of shape-adaptive and the stability of polishing force is studied utilizing the dynamic analysis software ADAMS, at the same time, the structural is optimized. The simulation outcome indicates that the tool could both adapt to the surface of workpiece and remove the influence brought by interpolation arithmetic.

Abstract: In laser cutting of glass with controlled fracture, thermal stress induces a fracture and the material is cleaved along the cutting path by fracture propagation. Compared with CO2 laser, YAG laser has many advantages in cutting glass with controlled fracture. As a volumetric heat source, YAG laser can penetrate through the glass. Therefore, the temperature distribution is uniform across the thickness of the glass and the fracture propagates from the top and bottom surface to the middle so that better cutting quality can be acquired and multi-layer glasses can be cut simultaneously. In this paper, a 1064nm YAG laser is applied to cut two-layer and four-layer glasses. Fracture propagation mechanism is studied by examining the temperature and stress fields using finite element software ANSYS11.0. Good cutting qualities of fracture surfaces for all the layer glasses are acquired and the cutting efficiency is greatly improved by this technique as well. Additionally, due to smaller laser spot size the glasses that are closer to the focal point have higher laser power density inside glass, which may lead to ablation and evaporation phenomenon. But lower laser power density is not enough for fracture initiation and expansion. Therefore, it’s important to find a proper laser power for all the layer glasses. Small tensile stresses on the top and bottom surfaces will make the material separate from up and down to middle, whereas the compressive stresses in the middle ensure stable fracture propagation. Moreover, the stable fracture propagation always lags behind the laser beam spot. High tensile stresses are distributed throughout the thickness of the glass in the leading and trailing edges, which leads to unstable fracture extension in the leading and trailing edges.

Abstract: This paper describes the grinding temperature characteristics in peel grinding. Some mathematical models such as average heat flux, triangular heat flux distribution and workpiece temperatures in the contact area are built. Using triangular heat flux model, the heat flow transferred to wheel and workpiece are analyzed. A 2D FEM model for thermal aspects of peel grinding process is presented and a finite element algorithm is implemented to solve the nonlinear problem. Finally, a peel grinding thermal field experiment was present.

Abstract: Porous materials have been successfully used in an aerostatic bearing. In this paper, the dynamic stiffness and damping of partial porous aerostatic thrust bearings are analyzed by numerical calculation method. Firstly, the pressure distribution function of the bearing is divided into the static and dynamic pressure distribution functions through minor perturbation method. Then, the static and dynamic pressure distribution functions are calculated by FEM. Finally, the dynamic stiffness and damping coefficients of the bearing are solved. The result indicates that the dynamic stiffness increases obviously with the increment of supply pressure and first increases then decreases with the increment of frequency, and that there is negative damping in the low frequency band and the supply pressure has a great impact on the stability of the bearing.

Abstract: The spiral mark is one of the quality defects on the tube surface in cone-type rotary pericing process. In this paper, the numerical simulation study was carried out for cone-type rotary piercing process using rigid-plastic finite element method. From the simulation results, the axial load applied on piercing plug and mandrel bar were then obtained. Taking the elastic deformation of mandrel bar into consideration, the variation of plug location under axial load during pericing process and the non-homogeneous wall thickness were investigated. The formation mechanism of the spiral mark on the tube surface can be found in the obtained results.