A Study And Application For Initiative Locating And Precision Machining In Complex Shaped Workpiece Manufacturing Process

In modern manufacturing engineering, complex shaped workpieces are grown more and more.The positioning and orientation errors of workpieces is one of most important factors that affect directly product quality, productivity and response time to market. A machining system of complicated product is usually a serial-parallel multi-error-source multi-operation manufacturing process, in which the final product locating dimensional errors are a accumulation or stack-up of error from all machining stages. There are coupling relationships between errors from stages while different errors exist in a single stage. Those dimensional errors will be introduced, increased decreased, stack-up, propagated, and become the final product errors when one workpiece goes through the whole machining system. Currently, the complicated products have been machining with high precision, high efficiency and high reliability. More and more researchers and engineers are much concerned with the workpiece installation problems, especially in the production of small quantity with high varieties or in the trial-manufacture of a new product.This main research work and contributions can be summarized as follows:(1) Based on the concept of variation stream, this work describes the propagation regularity of positioning and orientation errors for complex shaped workpieces in a multi-stage machining process. Through analyzing the geometry relationship between key product characteristics error and error resource, the procedures are introduced for expressing he influence and dynamical changes of errors in fixtures and locating datum features. Using homogeneous transformation approach, key characteristics variations is mapped into changeable state variables when a workpiece goes through the whole machining process. According to characteristics of Discreted Event Dynamic Systems(DEDS), Error Propogation Model for Multi-operation Machining bades on IL&SM Fixturing System (EPMM)is proposed and developed by a linear state space modelling theory. In IL&SM fixturing system, the position variation of the workpiece is derived from four error resources, such as workpece itself, IL&SM box, initial locators for workpece and the simple locating equipment for IL&SM box on the machine tool worktable. In order to revolve the principle between the four error resource and workpiece actual position, workpiece is acted as a rigid body. Analysis of the workpiece location characteristic in IL&SM, an integrated machining coordinate system is constructed to describe the relation of the four error resource and the workpiece locating error. In order to revolve the principle between the four error resource and workpiece actual position, workpiece is acted as a rigid body. Analysis of the workpiece location characteristic in IL&SM, an integrated machining coordinate system is constructed to describe the relation of the four error resource and the workpiece locating error. Based on rigid body kinematics with small error assumption and homogeneous coordinate transformation method, a geometric relationship between the adjacent IL&SM box is represented, an initial installation error expression for workpiece in IL&SM Fixturing System and a installation error expression for IL&SM Fixturing System on the machine tool worktable are derived respectively. Based on the above expression formula, coefficient matrix EPMM model are derivation in detail.(2) On the basis of the analysis above, a initiative locating fixturing method is presented, at the meaning time, Error Control Model for Multi-operation setup based on IL&SM fixturing system(ECMM) is constructed in order control the errors derived from multi-processes setup changing in a multi-stage machining process. The workpiece or the fixtures are not required to be the only one correct position on the initial fixturing system or the machine tool worktable. There are two kinds of searching approach, one is trigger probe type for the outer curve.and the other is non-contact type. Where visualization is a key technique for the intelligent searching and is very useful for the inner curve. By the searching measure system, the workpiece and fixtures information are studied to measure. A method of minimum squares is adopted to fit measure data to with standard data in three-dimensional space, the principle is to make it satisfy the quadratic sum of distance from each measuring point to standard cuverd surface is the minimum. a way is studied to measure and identify the correct location of the workpiece or the fixtures based on the measuring system, then confirm the allude relationship between the workpiece coordinate system,fixtures coordinate system and the machine tool coordinate system according to the real fixed location. At last, we adjust the process to control the tool contrail on the machine tool coordinate system according to the allude relationship. By this means, we can figure out the real place of surface in the space, therefore eliminating the location error. processing method proposed and realized can solve effectively the problem of error compensation during operation changing. It provides reliable and accurate processing information basic for the technology of initiative location and fixturing.(3) As well as having a locating function, fixtures must also ensure that the manufactured component quality can be achieved. Based on the initiative locating fixturing method and Error Control Model for Multi-operation setup based on IL&SM fixturing system(ECMM),research and development of initiative locating fixturing method for the complex revolving shaped parts. A state searching adaptive locating approach for part locating and calmping is researched and has been designed to achieve high precision installation and position conversion. First, the workpiece is located at the initial locators roughly to form the initial fixturing entity, then is assembled rapidly and precisely during the locating interface unit on the machine tool. Compared with the exiting method, the above has high fixturing accuracy and operating controlled. Integrated the aboved Initiative Locating techniques, a special fixturing system is developed successfully and applied to machine the radome. The initial installation system can make radome to have initial positioning and fixturing, then, it will form a workpiece and fixture system. And then, the whole entity can be quickly and accurately installed at machine tool or the CMM by a rapid location conversion interface unit. Through the structure design and variations stream analysis, the mechanical system tolerance will be reasonably distributed which can ensure the location error controlled in a certain range. The key parts of the mechanical system are designed.(4) Based on the study of the state searching and distributed set up theory, the prototype fixturing system is used to machine radome is developed to machine and measure the inner and outer surface, which includes three main modules: an initial installation system, a searching system and a rapid location conversion interface unit. The results of geometry thickness measuring test show that the geometry thickness deviation of the inner and outer surface is less than the results with the exiting method, and has a good consistent along the centerline of the radome. The research fruit makes some contribution to the high accurate guiding missile development.The experimental results show that the proposed research method, models and installation technology for complex shaped workpieces in a multi-operation machining;process are feasible and effective.