Study On Three-dimensional Carving Technique By Laser Ablation Of Hard Materials

As an advanced manufacturing technology, laser machining has already been applied in many fields. Different kinds of laser forming techniques have been developed. Among the existing laser carving techniques, there seems not the laser carving technology that can fabricate three-dimensional (3D) graphics directly on the surface of hard materials. In this dissertation, a new technology, namely 3D laser carving that can fabricate the true 3D graphics on the surface of hard materials was presented, and some concerned fundamental scientific problems such as software development, control system design and carving process exploration of the 3D laser carving system were studied based on the principle of layered manufacturing. Following are the main results on the subject:STL (StereoLithography) file was used as the data interface between CAD modeling software and the 3D laser carving software. The concerned software functional modules such as topologic reconstruction, on-line slicing, regional filling, processing simulation, process control and human-machine interaction were developed, and the slicing algorithm and scanning algorithm were studied further with a view to improve the speed of data processing. Due to the redundancy of geometric information and the lack of topological information, the geometric elements of STL model should be sorted and merged firstly, and then the adjacent-side lists were built to gain time for slicing. In order to track the adjacent triangles successfully during slicing STL model , the five intersection relationships among slicing planes and triangle facets were converted into the intersection relationship among slicing plane and two sides of the triangle facet. To reduce the times of intersection and improve the sorting efficiency, the active-side list was established to make full use of the consistency of the side and the scanning line. In view of the profile with islands, the divisional linear scanning algorithm was put forward and implemented to optimize the scanning paths.The hardware platform for 3D laser carving system was established by upgrading an existing 3D working table. Based on the study of several existing computer-controlled modes and the real-time ability of operating system, the open NC systemic architecture of PC + intelligent control cards was used in the control system of 3D laser carving, in which Windows2000 was chosen as the software platform. The hardware architecture of control system, electrical circuit and systemic performance were analyzed specially, in addition, the framework and the calling mechanism of the device driver in Windows2000 were studied and the details of the development of device driver and interface were given.The technological process, namely doing laser carving experiments to obtain the optimum parameters related to one single-layer carving depth firstly and then carrying out 3D laser carving based on these data, was laid down for 3D laser carving. Laser carving on Al2O3 ceramic plate with different processing parameters was done to study the effects of laser processing parameters on single-layer carving depth and carving quality, and in the mean time to analyze the physical process of laser carving, and to uncover the removing rules of redundant materials in the course of laser carving. In the experiments on ceramics, the main mechanism that contributes the laser carving mechanisms is that laser beam with high peak power ablate the ceramic surface which induced the pit spallation. By establishing the mathematical model for carving depth, the relationships between carving depth and the main processing parameters such as laser power, scanning speed and repetition rate were disclosed mathematically, which can give the theoretical guidance to rapidly get the process parameter data. In order to simulate the mathematical model conveniently, the laser beam energy within one single laser pulse was calculated by the average estimate method. The mathematical model for carving depth is as follows: In addition, the nonlinear mapping relationship between carving depth and the process parameters was established by ANN (artificial neural network). The BP was trained by using the existing data obtained by laser carving experiments, and the ANN model was built based on the training results. By ANN model, the finite data from experiments can be generalized to the overall range, which effectively improved the optimizing rate of process parameters and was very helpful to build the parameter database for 3D laser carving. On the basis of making full analysis of the carving errors in aspect of carving principle, equipment and technology, the complete error-evaluation system was established for 3D laser carving. By analyzing the CAD model error, slicing error, motion error, scanning error, carving surface roughness error, carving vertical error and their forming mechanisms, many effective ways were explored to improve the carving precision and quality. The ideal model for carving surface roughness of horizontal plane is And the ideal model for carving surface roughness of vertical plane isAccording to the characteristics of 3D laser carving, the temperature-field model and the thermal-stress model for 3D laser carving were established and simulated tentatively on the basis of the existing temperature filed model of the instantaneous point heat source, the existing calculation method of thermal stress and a series of assumptions.Summing up above mentioned, the technology and equipment of 3D laser carving have created a new laser processing technology with fast, flexible, high efficiency and low cost, as well as the ability to fabricate 3D micro-graphics and carve the hard and/or brittle materials. 3D laser carving technology has a great potential industrial application prospect in the field of mould/die, craft production, 3D mark, security and MEMS/MEOMS.