Research On The Technology Of Dimensional Measurement Of Hot Large Forging

Large forging is the key material of large heavy equipment; its development could improve the national defense capabilities, economic construction and the capabilities in large heavy equipment manufacturing. With the rapid expansion of power plants, petroleum and chemical processing, metallurgy and shipbuilding, great demand for large forgings will continually grow during the industrialization in the next 10 to 15 years. China is one of the main countries which manufacture large forgings. But right now, our country is still not a power country in large forging manufacturing field; some high technology critical forgings still rely on import from other countries.Precisely and promptly online measurement during the forging process could improve the productivity and reduce the raw material loss. With the support of Shanghai Hi-Tech Research and Development Program of China, the work developed a novel ,comprehensive measurement system for large hot forging based on time of flight and perpendicular coordinator, which can acquire the dimensional data of forgings precisely and promptly. This paper includes the following points: 1. A new large forging dimensional measurement method is presented based on laser range sensor, which could scan in a sector of 360°, and perpendicular coordinator, which could move along guide rail smoothly and precisely. The laser range sensor scans in a certain frequency, whenever it completes a sector of 360°, the dimensional data of the measurement section of the forging are acquired immediately, so this system could acquire a large of point cloud in a very little time. The coordinator has advantages of high definition, long range movement and easy to control. The laser sensor measures its surrounding in two-dimensional polar co-ordinates, plus the movement of coordinator, we can get the three-dimensional information of the forgings.2. According to specific demand of the measurement system, the hardware system is developed. Portal frame is adopted as the main frame, and the X direction rail use gear-driven mode and the Z direction rail belt-pulley; the high definition of the motor assures the high transmission accuracy; in order to monitor the forging field, image guided movement and get the temperature online, this system also equipped a CCD camera and a temperature sensor.3. VC++ 6.0 is adopted as the software development environment. We can get the acquisition data of the laser range sensor quickly and accurately by using CSOCEKT as the communication tool, and the system efficiency is greatly improved by multithread process. For the sake of image guided motion control, the CCD camera communication program is also developed.4. A nice calibration method for the frame mounting is designed for the convenience of data processing in the measurement process. By the method of least squares against the acquisition data we can obtain the sectional dimensional information and the overall straightness accuracy in a very little time.5. The feasibility and repeatability of the system get verified by times of laboratory experiments and field experiments. And also, in order to get a better measuring accuracy, the main errors are analyzed and the ways to prevent or reduce them are introduced by some MATLAB simulations.