Digital Manufacture Techniques for Large Hydro Turbine’s
Blades
LAI Xide，ZHANG Qinghua，ZHOU Yunfei，YAN Sijie
(1 .School of Energy & Environment Xihua University, Chengdu 610039, China， E-mail: laixd@ mail. xhu. edu. cn; 2. School of Mechanical Science, Huazhong University of Science and Technology, Wuhan 430074, China )
Abstract: Blades are one of the vital components and most difficulty in manufacturing of large hydra turbines. In order to cost-effectively and productively manufacture these kinds of blades a series of digital techniques in manufacturing have been developed，which includes digital design of hydro turbine blades based on manufacture’ requirements Computer-aided location and the machined error evaluation by using 3-dimensional digitized measuring,tool path generation strategy to meet requirements of en-hancing machining efficiency and controlling deviation in NC machining, tool path generation and NC machining simulation by establishing a virtual NC machining environment for blades,and reasonable and feasible strategy and the systematic scheme for manufacturing of large blades by using 5-axis simultaneous CNC machining.The developed digital manufacture techniques have been successfully applied in manufacturing of both the large Kaplan and Francis hydraulic turbine blades;it shows that higher efficiency and the
better surfaces finish accuracy can be achieved.
Key words: digital manufacture; hydraulic turbine; blade; NC Machining;CAD/CAM
1 Introduction
Hydro turbine blades,such as Francis and Kaplan types,are usually
designed by means of detailed hydrodynamics methods and simulations of computational fluid dynamics(CFD), or digitized from the models. Traditionally, the large size hydraulic turbine blades were machined by using manual grinding operations and inspections with sets of combined templates, which cannot satisfy for rapid developments of large hydro turbine and also cannot ensure accuracy of finished blades. Hydro turbine manufacturers have been trying to machine these large blades using CNC machining techniques in recent year. As the surfaces of a large blade to be machined are usually from several to tens of square meters and involve bulk metal removal while machining from the casting, it tends to be non-productive to machine these kinds of blade using traditional 3-axis machining with ballend cutters. With the advent of large size multi-axis CNC machines, an innovative 5-axis simultaneous CNC machining technology has become not only feasible but also cost effective for large parts with sculptured surfaces. As a large hydro turbine blade is closed with more than 10 sculptured surfaces that have irregular curvature distribution and its thickness also intensely changes, so it is much
difficult to mill the blades by using 5-axis CNC Machining. In practice, the 5-axis CNC machining not only offers many advantages over the 3-axis machining, which include the higher productivity and improved surfaces finish, but also brings about more complex technological problems. Such as highly complex algorithms for gouging avoidance and collision detection, complex surface machining errors that result from the traditional CNC programming methods, etc. However, a reasonable strategy and systematic scheme of blade's manufacturing with the right combination of a series of digital manufacture techniques can solve those complex problems in engineering and made them operational feasibility in technology. We had developed a series of digital manufacture techniques for large blades, which mainly include:(1)Digital design and 3D modeling of blades based on manufacture's requirements; (2)Computer-aided localization for position&setup by means of 3D digitized measuring of blades casting;(3)Making of machining strategy and tool path planning with the help of computer-aided geometrical analysis;(4)5-axis machining tool path generation for different surfaces of a blade;(5)Computer simulation for machining of a large blade to verify the gouges and collisions between machine tool and blade& fixtures;(6)Computer-aided inspection and the machined error evaluation for the finished blade surfaces by means of 3D digitized measuring; With the right combination of the developed digital manufacture techniqucs,
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