Study On A Integration System Of Online Measuring And Machining

Automobile body exterior styling and interior design, as indispensable steps in the automobile design, are key parts of the new model development. Clay models with 1:1 scale are used to verify the design. Any improvements on the dissatisfied parts should be tested. The new improvement is made, and the corresponding clay model is built, and that cycle repeats. The clay model verification can’t be ended until the design is completed. Traditional manufacture craft of the clay model makes use of artificial template matching technology and three-coordinate measuring machines (CMM for short) to modify and measure the model. It takes a lot of labor hour. And the developing speed of new product is greatly limited.With the development of automobile industry, automobiles are upgraded faster and faster. The time spent on the artificial ways to make clay models and the precision of the ways are all hard to meet design demands. In recent years, some foreign enterprises, like TARUS in the United States, MORA in Germany and CMS in Italy, have developed a variety of products with the function of measure and machining. In the products manufacturing, designed digital model is directly shaped up by numerical control machining, instead of the way to artificial template matching. The production efficiency and manufacturing precision of the model can be improved a lot. These products are successfully applied to famous automobile manufacturers, such as Ford, BMW, Volkswagen, Mercedes Benz, and so on. China is still in the early stage of this field. A new product, which is a function integration of numerical control machining and online measuring, is designed to meet the application requirements of domestic automobile manufacturers.The main research work of this paper can be summarized as follows:1. Design of mechanical host system of the product is described. Cantilever structure, which can supply enough space to make and handle models, is applied in the host system. The overall system solution of the product is made. Requirements of automobile manufacture are collected on the basis of enough communications, which include products’ functions, precision indexes, stroke and machining period for the equipment to finish a clay model with 1:1 scale. Developments of the similar equipment aboard are surveyed. Combined with the domestic machining technology, host systems, which use cantilever structures, are designed. Double host systems and double guide rail are applied in the product. The control system adopts LinuxCNC, achieving the integration control of online measuring and machining. Control codes of measuring and machining are programed by RationDmis and PowerMill respectively.2. Structure design of the host system is mentioned. Column and wishbone structures are designed. Finite element analysis and calculations of the structures are conducted and the results are used to optimize the structures. Therefore, structures weight and stiffness are optimum. Some other key structures are designed, such as precision transmission components and guidance parts, z-axis weight balancing devices, outsides covers, the index plate of milling motorized spindle, and so on.3. Design of calibration system is discussed. Firstly, the effects of model and fixing position of cutter tool on calibration system are investigated in theory. Based on some comparative analysis, electric signal device of the calibration system, which adopts electric contact principle, is designed, so does its bottom support structure.4. Online measurement and control system is developed. There is no controller to meet the demand of integration control of online measuring and machining. After the investigation, LinuxCNC software system is applied in the product. Its fine expansibility brings the relevant functions of automatic measuring into the whole machining software structure. It makes possible to integrate the online measuring and machining.5. Precision test of the prototype is performed. Based on the evaluation criteria of precision testing, the measuring accuracy and machining accuracy of the host system are tested. Two indicators is used to show measuring accuracy. They are single axis positioning accuracy and indication error of measuring. For the single axis positioning accuracy, a value is obtained per 100mm and the acquisition time is 6 during a reciprocating movement. For the indication error, there are 5 standard blocks and each block is set in 7 azimuths. Test is performed 3times at each azimuth. So there are 105sets of data in total. Machining accuracy is evaluated by two indexes. They are geometric accuracy and sample machining precision. Geometric accuracy is evaluated by 6 sets of data, including three-axis straightness and three-axis verticality. For sample machining precision, a sample ball with a diameter of 200 mm, which is made up of epoxy tooling board, is machined. A dial indicator is used to measure the diameter in three azimuths. The maximum difference between the measure value and the theoretical value 200 mm is the machining precision.The following considerations should be made in the future.1. Five-axis coordinated mechanism should be design in the host system. It has incomparable advantages over the three-axis coordinated mechanism. Approximation normal machining of the machining tool can make the surface quality of workpiece better. A workpiece, which just needs to be fixed one time, can be processed by using the technology of multiple surfaces and multiple machining operations. It will shorten the machining cycle and avoid the error caused by some times of fixation. Then the accuracy can be improved.2. Linear motor should be used to drive the product. Because of the simple structure of linear motor, drive system of the product can be greatly simplified. The reverse backlash of mechanical transmission caused by rotary motor can be eliminated and the positioning precision is high. The product equipped linear motor has properties of short response time and high sensitivity.