Research on the localisation of the workpieces with large sculptured surfaces in NC machining

Localisation of workpieces with large sculptured surfaces can be difficult. Previously, such pieces were measured by the probe of the machine and adjusted manually. This process is arduous and time-consuming and an even allowance cannot be ensured for every measured point. Searching for the optimal location of surface matching by computer can realise computer aided localisation (CAL) and thus enhance the precision of localisation, saving a lot of time and greatly accelerating machining cycles while reducing machining cost.

In this paper, a method is proposed for a localisation problem that consists of rough surface matching and accuracy surface matching. Rough matching determines the variable range of the follow-up algorithms. Accuracy matching acquires the optimal location. Then fast localisation and a clamp can be implemented. A hybrid global optimisation method is adopted to cope with the accuracy matching. It shares the advantages of both genetic algorithms (GAs) and simplex algorithms. The method presented in this paper has been used in the 5-axis machining of both large Kaplan and Francis hydro turbine blades. It shows that the method is easy to realise and the algorithm is steady and robust.