Automated Ultrasonic Testing of Billets for Gas-Turbine Engine Shafts

Abstract

An apparatus for automatic ultrasonic testing of billets used in the manufacture of gas-turbine engine shafts is described.In order to ensure a high degree of flight safety, it is necessary that critical parts of gas-turbine engines (GTEs) be subjected to nondestructive testing. The ultrasonic technique has been widely used to test the most critical parts, GTE shafts, at different stages of their production. The problem of detecting defects early in the manufacture of GTE shafts using acoustic methods of nondestructive testing was raised in the early 1990s. The technique for manual inspection of GTE-shaft billets was brought into use in 1992. Since that time, this techniques high efficiency has been demonstrated by the detection of cracks due to hardening on three shafts. However, the manual inspection technique has a number of drawbacks: primarily, low reliability and low significance of test results and, in addition, its laboriousness. For this reason further refinement of the procedure for testing shaft billets was focused on its automation.Since the early 1980s, KTB UZD (Design and Technology Bureau for Ultrasonic Flaw Detection) has been engaged in the automation of ultrasonic nondestructive testing and has gained much experience in developing automatic systems for ultrasonic testing of various samples (e.g., disks, blades, rods, and gear wheels). The main problems in rendering the inspection of shafts automatic are the intricate configuration of the shafts (these are long-length bodies of revolution with varying cross sections) and the necessity to maintain acoustic contact with them. The latest achievement in automating ultrasonic inspection is the development of the VAL automatic system for nondestructive testing (VAL ASNT) of shaft billets.The VAL ASNT is used to test blanks of shafts for gas-turbine engines ( èë -90A), gas-transfer facilities, and power plants. Testing is performed with the aim of detecting internal flaws that make up the discontinuities of metal parts-cracks, layering, porosity, voids, cavities, and nonmetal inclusionsand are located in easy-to-reach places that yield an ultrasonic-wave reflection signal that falls within the limits of the method's sensitivity.The pulse-reflection ultrasonic method has been selected for testing billets. An immersion version of the method is used: ultrasonic vibrations are coupled into the shaft through a water layer on the outside of the shaft, and the signals reflected from the discontinuities are then detected.The directions of ultrasonic-waves incidence of ( Fig. 1) were selected so as to allow the most probable (in view of the shaft-manufacturing technology) flaws to be revealed. As a result, five directions of longitudinal and shear waves were selected. The longitudinal waves are incident perpendicularly to the surface, and the shear waves propagate in the radial ACOUSTIC METHODS1 2 3 4 5 1 Fig. 1. Directions of incidence of ( 1 ) longitudinal and ( 2 -5 ) shear ultrasonic waves.

Design of an advanced automatic inspection system for aircraft parts based on fluorescent penetrant inspection analysis

“…It can detect deep defects with high accuracy and without any part preparation. Unfortunately, UT only works well on large parts and structures such as turbine engine shats [7] , or even bigger components such as wind turbine blades [8] . Another popular NDT method used in the aerospace industry, ECT, uses coils to produce a magnetic ield, which then generates an alternate electrical current (eddy current) on the test-piece.…”