Abstract: Some turbine blades are produced by casting, using the lost wax process. The blades may include cooling air passages and the wall thickness of these is tested ultrasonically i.e. by transmitting and receiving acoustic pulses from and to, a common transducer.Lately the blades, having been cast, are directionally solidified. This process changes the grain structure such that during inspection, pulses received by the blade, have been dissipated. The invention provides ultrasonic testing ability by using a unidirectional pulse transmission system, resulting in pulses which, having passed outwards through the passage wall, still have sufficient energy to effect an indication of wall thickness.

Abstract: The production of passages in workpieces is described by an electrical method which simultaneously utilizes electrochemical and electrical discharge machining with a single electrode and dilute electrolytes. The method overcomes the metallurgical defects inherent in the recast layer left by electrical discharge machining which is removed by electrochemical machining. The method is particularly suited to producing cooling passages in the turbine blades of gas turbine engines and can be used to produce venturi shaped holes with rounded edges.