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  DIGITAL HOLOGRAPHY TECHNOLOGY

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Holography has been used since the 1970’s for tire inspection. Before the development of electronic holography or electronic speckle interferometer (ESPI) cameras, film holography cameras were used in combination with vacuum stress. Early film holography cameras were also use to solve a major production issue in the inspection of abradable turbine engine components.

Since the 1970’s turbine aircraft engines have used abradable seals in the compressor stages of the engine to achieve high-pressure ratios per stage, reducing the turbine power required to drive the compressor, engine weight and increasing performance. The loss of this material can affect engine performance and inspection of the bond line in production or engine overhaul is required.


Ultrasonic through transmission C-Scan is capable of detecting disbonds in parts where the shroud geometry is a straight or slightly conical cross section. However, in most engines, the design of the compressor shrouds includes brazed stators, material thickness changes, flanges and other features that obscure or shadow the abatable seal material.

In 1982, a holography NDT technique entered production at Pratt & Whitney, combining time average holography with a low frequency ultrasonic vibration applied to the compressor shroud. Holography provided excellent disbond detection with easily interpreted images essentially identical to UT results, but not affected by part geometry, material thickness changes. Early systems used film holography with a one step chemical process, invented by the author, which produced production quality holograms in approximately 10 seconds. The results were viewed on a video monitor. Electronic holography currently using mega-pixel CCD cameras has radically improved system operation speed and reliability. Since1982, holography has been the inspection standard for Feltmetal and plasma sprayed aircraft abradable seals.

Holography inspection has eliminated compressor seal bond failures, yielded large financial savings to the manufacturers and greatly enhanced customer satisfaction and cost savings. Similar applications of holography with vibration part excitation of bonded metallic materials on human orthopedic implants have shown dramatic improvement in product quality. Highly automated systems that monitor all system parameters have been FDA approved. Together, these two applications of holography have yielded significant cost savings, manufacturing quality and provide a means for engineering improvements to processes.




LTI's DH-8000
Holographic Inspection Station

 



Composite Display of Abraidable
Seal Test Standard after Inspection

1055 West Germantown Pike, Norristown PA