Papers by Author: Jun Hu

Abstract: This paper proposed an optimized algorithm for discretization of cutter location points on the laser cutting path of three-dimensional surface. The initial discretization step size was calculated due to the curvature of the curve on the starting point and accuracy requirements. A reference sphere was established by taking the initial discretization step size as the radius. The initial cutter location point was located on the intersection of the reference sphere and the processing path. The radius of reference sphere was dynamically adjusted by dichotomy according to string height difference in order to get the optimal cutter location on the path to be processed. This algorithm has a high computational efficiency. And an automatic programming software used for three-dimensional laser cutting was developed based on this algorithm.

Abstract: Laser micro-adjustment as application of laser forming is a contact less and easily automated technology able to cause very small changes in shape to achieve high accuracies. In this study, a method using dual heating is introduced to reduce the temperature gradient across the thickness during laser micro-adjustment of actuators. The temperature field and deformation behavior using dual heating method are analyzed using a 3D finite element model. The in-plane angles are compared between using single heating and dual heating and the numerical results show that the in-plane angle using dual heating method can be predicted by the results by single heating.

Abstract: Based on a convergent nozzle and a conical nozzle, the simulation of the free jet of assemble nozzles by adopting a three-dimensional axial symmetrical model is presented in the paper. The study reveals the effect of cone angle of conical nozzle and the parabola equation of convergent nozzle on flow field by adjusting nozzles’ interior figure parameters. The distribution of pressure and velocity of gas jet are shown in the investigation. A conical nozzle with cone angle of 30° and a convergent nozzle described by the parabola equation of y=0.207x2 are designed and produced for the laser cutting experiment. Numerical simulation and experimental results are given at the end of the paper.

Abstract: In the laser forming of metal plates, there is a substantial waiting time required for cooling down the workpiece so that a steep temperature gradient can be reestablished during the next scan. Currently, there are no standard techniques that can be used to reduce this waiting time. This paper discusses the possibility of using non-natural cooling systems to cool down the workpiece. A numerical model of thermo-mechanical analyses with moving boundary conditions to simulate the traveling of laser beam and moving forced water cooling system is presented. Based on the proposed model, cooling effects under different laser powers and scanning velocities with various cooling conditions are investigated. The results show that the forced water cooling can significantly reduce the temperature with no adverse effect on the forming of plates.

Abstract: An improved interpolation method is presented based on B-spline curve back calculation which regards data points as control points. First, a B-spline surface reconstruction is done, and a favorable condition for real-time interpolation can be provided for NC machining. Then, by prejudging the trajectory feedrate, the tangent vectors of spline curve junction can be calculated, which can be used to establish the spline curve equations based on time. At last, with the equations mentioned above, the trajectory and feedrate profile can be generated simultaneously by the improved interpolation algorithm. An error analysis is also discussed and the feasibility of the improved algorithm is verified by the simulation results.

Abstract: A three-dimensional axial symmetrical model of laser cutting is established by adopting N-S equation in the paper, and numerical simulation is put up to analyze the flow field of assist gas in cutting channel. The investigation reveals the law about how channel width affects the dynamic characteristic of gas jet in the cutting process, and the distributions of pressure and velocity of gas jet with different channel widths are shown in the study. The study shows that the intensity of compressed wave and expanded wave in cutting channel declines remarkably with channel width increasing, and the kinetic energy at channel surface drops while the cutting quality is deteriorated. A taper nozzle with cone angle of 30°and a convergence nozzle comprised a parabola equation of are designed for the laser cutting experiment. The experimental results are given at the end of the paper.