An integrated surface modeling and machining approach for a marine propeller
Abstract
For given data points on different cylindrical section curves of marine propeller during the design period,the fair fitting method with the least squares of the cubic B- spline curve has been used to form cylindrical section curves with different radius.
Then the control points of the cylindrical section curves were used as new data points to process fair fitting in another direction, and the pressure surface and the suction surface of the propeller can be
acquired at last.
Aims to overcome disadvantages of the present machining method of propeller, such as lower machining precision and efficiency, repeated clamping, and limited machining scope, a new machining method—the second order osculating machining method—has been presented.
By using this method, not only the cylindrical cutter and the machined surface can keep line contact, but also the propeller can be machined with one clamping. It’s very suitable for the machining of propeller with larger projected area ratio and the machining precision and efficiency will be improved.
Introduction
The performance of a ship mainly depends on the hull, main engine and propeller; while the propeller efficiency is primarily dependent on the design and manufacture of the marine propeller. The propeller blade can be divided into pressure surface and suction surface. The middle area of the pressure surface is designed by using a helical surface with a constant pitch ratio or variable pitch ratio normally, and
the areas near the leading and the trailing edges are designed by using the streamline method.
The suction surface of the marine propeller is determined by the pressure surface and the section thickness of the marine propeller. Due to the complexity of the propeller blade, presently, marine propellers are basically manufactured by using NC technology, primarily by using five-axis machine
tools. In order to machine a propeller blade, the geometrical description of the propeller blade is needed first. In general, the given data points on different cylindrical section curves of the marine propeller have been fitted into a free-form surface.
Considering most free-form surfaces used in engineering are restricted by hydrokinetic restrictions, Ye [1] presented a design method of free-form surface and used it in marine propeller. In this method, the normal vectors of the surface have been used as physical restrictions, and then the problem of surface design can be translated into a fair fitting process with the least squares of B-spline surface. At present, the point milling method and the flank milling method are often used for the machining of free-form surface [2].
