Research On The Technology Of Online Inspection System For Machining Accuracy Of Free-form Surface Components

To meet the demand for higher machining precision and efficiency the technology of numerical control (NC) is playing an increasingly important part in manufacturing. At the same time, the inspection of high precision machining dimensions is confronted with a further challenge. Dimensional measurements using a coordinate measuring machine (CMM) have been commonly used in advanced manufacturing environments to ensure that the manufactured parts have a high dimensional accuracy. However, some problems still exist such as the errors occurring from the second fixing operation and disability to measure large parts. To conduct free-form components' dimensional inspection effectively in a computer-integrated manufacturing (CIM) environment, manufacturers and consumers are demanding a "free-form surface component online inspection system" (FCOIS) that will measure parts without removing them from the machine. Considerable effort has been devoted to developing a rapid and accurate FCOIS for dimensional inspection, but most of them are for the regular geometric features. Therefore, there is an urgent need to develop an FCOIS for complex geometries with free-form surfaces.In this thesis, an FCOIS is developed using a standard CAD STL format. During the course of the thesis the following points are addressed:i) Based on the state of the art of the inspection techniques, this thesis states some key problems of FCOIS that need to be solved and improved upon in the future. Then an outline of the requirements for an FCOIS for parts with free-from surfaces is presented.ii) Validating the precision of STL format to ensure that it has the required accuracy to transpose the geometric data. Based on the demands of contact measurement, the measurement points planned should be the least number possible but still provide sufficient information of the measured surface, a measurement point planning approach through polygonal mesh curvature is proposed.iii) Some of the key points for assessing surface's machining errors are analyzed and an approach of point-to-point error assessment is put forward.iv) A macrocode for outputting the measurement result in FANUC series NC machine is developed. With the API programming technology, the input and output module of the FCOIS software, communicating with NC machine at real time, is developed.v) Based on the Visual C++ 6.0 and OpenGL 3D graphics techniques, an on-line inspection system of machining tools for free-form surfaces is developed and is put in practice. An experiment to testify the precision of the FCOIS was implemented, measurement result of which showing this system to be a reliable and trustworthy measurement system.