Study Of Laser Processing CNC System And Process Monitoring Techniques

Laser processing has found extensive applications in machining the key components in aeronautics, astronautics, shipbuilding and other industries for its advantages such as comprehensive material applicability, high flexibility, efficiency and precision. Nowadays research activities of laser cutting CNC system are focusing on openness in architecture, multi-axis in dimension, integration of functions, automation in focus control and intelligence in machining process. Much attention is paid to the research activities on the mechanism of beam-material interaction and process monitoring of laser cutting.China is lagging behind western developed countries, namely the U.S.A, Japan and Europe, in laser processing technology, and technology blockage and strategic prohibition of high precision laser machining system have been enforced upon China for a long time. Based on the current prevailing open architecture motion control technology and the advanced software developing techniques, development of domestic-patented high-performance laser machining systems would greatly promote the laser machining industry and the equipment manufacturing industry. Therefore, this paper carries out research on (1) the development of laser cutting CNC system, (2) process monitoring of laser cutting and (3) laser machining of key aerospace materials.This paper firstly presents the composition and structure of the laser processing machine tool. After the analysis of the three typical implemention solutions of PC-Based open-architecture CNC system, an"NC embedded in PC"solution is selected to contruct the dual-CPU CNC system with a host industrial PC (IPC) and a programmable multi-axis motion controller PMAC where the PMAC performes the real-time tasks and the IPC is in charge of background management and man-machine interfadce (MMI).After the feasibility analysis of COM-based open-architecture CNC software, a COM-based hierachical-architecture CNC software is developed with three layers, namely the device layer, the function layer and the application layer. The software development is composed of two phases, the component development phase and the component deployment phase. In the first phase, the component server is divided into functional components to offer service to the CNC software, and in the second phase the CNC software, as the client of the component server, implements its functions based on the services of the components.For the harmony between the CNC system and the laser, a CNC-laser interface circuit and the laser control software component are developed for online control and monitoring of the laser parameters. Directly or indirectly would the process signals reflect the process stability and cut quality in laser cutting, and measures can be taken to prevent the influeces of process instability on cut quality by monitoring the process signals.This dissertation analyzes the generation mechanism of the acoustic signal, and performs data processing of the signal with wavelet denoising and Smooth Peudo Wigner-Ville time-frequncy Distribution (SPWVD) to acquire the influencing characteristics of laser cutting parameters on pulse-induced acoustic signal. The results show that the standard deviation of the pulsed acoustic sound can reflect the morphology information of the bottom dross. The characteristics of the acoustic signals of full-penetration and incomplete-penetration cutting conditions are analyzed and the differences between them are found. Therefore, a laser cutting monitoring method based on acoustic signal is proposed.Aiming at performing the laser cutting of the leaf-shaped holes of the ring parts of a certain aeroengine, experiments of Nd:YAG pulsed laser cutting of titanium alloy and superalloy sheets are carried out. Research is performed on the influences of laser cutting parameters on (1) the heat affected zone (HAZ), surface morphology and corrosion resistance of titanium alloy and (2) the recast layer of superalloy sheet. Finally, with the above-developed laser cutting CNC system, laser cutting of the leaf-shaped holes of dozens of ring parts is performed well meeting the developing requirement, which proves the system to be stable and reliable with satisfying performance.