Allowance Optimization Based On Geometric Features And Research Of Machining Simulation

With the widely useing of numerical control technology, the manufacturing process is improved a lot. But there are also some parts with backwardly manufacturing process whose allowance are small and uneven distribution. If the distribution of allowance is uneven, the allowance of some surfaces might be too large and the other might be not enough. The insufficient allowance might cause scrapped parts. And the current allowance distribution is accomplished by artificial marking and repeated measurement.Aiming at this situation, this paper focuses on the method of allowance optimization to distribute the allowance and to use the machining simulation to validate the result of allowance optimization. The main work is as follows:1. Initial position adjusting based on the feature of one plane and two holes. The method of using the feature of one plane and two holes to build local coordinate system to adjust the initial position of measured data and design model is proposed. Base on the spatial relation of axis of the cylindrical hole and the plane, the features which are suitable for the construction of coordinate system are discussed. The planes and cylindrical holes of these features are fitted by least square method in measured data. Finally the local coordinate system is built by these planes and holes, and the initial position adjusting is done.2. Precise optimization calculation. The mathematical model of precise optimization calculation is proposed based on the least squares method. To improve computational efficiency the measured data is reduced by uniform sampling method. Then design model is tessellated into point cloud data. And Delaunay triangulation is created with theses points by a modified incremental insertion method to search the closet point for measured point. To the same measured point, the closest point is chosen between the closest vertices on the grid and the projection point. If the projection point is not located on the grid, the closest point is the closest vertice. If it is, to compare the two distances, the samller one is the closest point. One of the distances is calculated between the closest vertice and the measured point, the other is calculated between the projection point and the measured one. The closest vertice of the measured point is searched through the process that design model is tessellated into triangular mesh surfaces by Delaunay triangulation. The projection point of the measured one is calculated on these surfaces which contains the closest vertice. Finally the mathematical model is solved by Genetic Algorithms. 3. Machining simulation. The result of allowance optimization is validated through machining simulation. First, the machine simulation model is built. And the Numerical Control System is compounded for it. Then the stock is assembled on the machine worktable with the location method under the most optimization Attitude. Finally the experiment is done to validate the result.