ABSTRACT
Super nickel alloys have been developed for turbine blades which are able to withstand the high stresses and temperatures required for improved performance. A range of blades are manufactured using the ‘lost wax’ casting process to obtain the precise external aerofoil shape. Complex internal blade cooling passages are produced by the use of ceramic cores which are subsequently removed. These cores are supported during casting by platinum pins which are left protruding
from the aerofoil surface as shown in figure 1. These need to be removed without unduly affecting the aerofoil profile which directly influences the blades efficiency. At present the pins are removed using a manual linishing process which also removes up to 100 µ m from the blade surface, thus changing the precision cast form and reducing the polytropic efficiency of the turbine. In addition the process is expensive which has led to a programme aimed at identifying a new cost effective manufacturing technique to recover the aerofoil profile without contacting the precision cast aerofoil surface. A maximum protrusion of 25 µ m on the finished blade was specified as being acceptable.
