The Research On The Processing Error Theory Of The Large-scale Space Bending Steel Pipes

With the growing span and the more complex shapes of space elbow, the problems of transmission error and cumulative error in the manufacturing process of assembling the space bends become more and more prominent. The current production process of space elbow mainly takes two approaches to reduce the cumulative processing error produced after the manufacturing of the space elbow. First, further improve manufacturing precision of each segment elbow in the project. However, the acceptance norms in the construction of steel structure which is the basis in factory production has been given the most appropriate economic precision. The each additional level of accuracy on this basis will exponentially increase difficulties in the process. Second, the space elbow which has a large processing error should be taken mechanical correction and flame straightening method to achieve the tolerance range after completion of construction. But it will not only increase the cost of the extra time and labor costs, but will also cause residual stress in the pipe. in summary, there is no a complete set processing error theory of large-scale space elbow, which does not correspond to the current booming situation of the space steel structure. Therefore, we must develop a set of machining error control theory for large-scale space elbow.This paper takes the large-scale space elbow as the research object and choose the control of processing cumulative error as the core. The research for reducing the processing cumulative error is as following:(1) Using the UG software to automatically obtain the geometry information of space elbow for secondary development which is based on the basic theory of space curves and the key point expression method of the space elbow axis, and designs a three-dimensional coordinate point acquisition method to analyze the space elbow segment points.(2) Using the theory and finite element analysis software analyze the causes of elbow manufacturing error and assembly error which are the main factors in space elbow machining error. Researching on the permitted range of manufacturing errors in the norms and the technical measures to reduce the assembly error.(3) Researching on the cumulative manufacturing error and assembly error models and analyzing the assembled elbow to determine the specific linear displacement and angular displacement error. Analyzing the main factors and secondary factors of the cumulative error model in the context of a practical project.(4) Proposing dimension chain issue of the cumulative error based on the dimension chain theory and raising a mutual satisfied method in which positive deviation ring and negative deviation ring take turns. Establishing a further optimized mathematical model of the cumulative error which is according to the main factor the cumulative error model to achieve optimal control of the cumulative error.