Midas NDT Systems Ltd. have introduced a new patented ultrasonic inspection technique for the analysis of ‘single-shot’ box-section components. The need to inspect the stringer area of a component has, to date, precluded the single-shot manufacture of box section components. A typical box section needs a primary inspection of the skins and stringers prior to component assembly and a secondary inspection of the bond areas after final component assembly.
This problem has precluded manufacture of components in a single-shot process due to the lack of access in order to safely inspect the stringer areas. Although many possibilities, such as miniature transducers on long arms, have been tried, to date there has been no acceptable method for achieving 100% inspection of this style of component. |
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The technique utilises a set of internal mirrors creating a prismatic affect to guide the sound wave through the component. As can be seen in the illustration, the component is located in an immersion ultrasonic inspection system with the automated head driving the sensor in a raster pattern over the surface of the component.
The sound wave from the sensor is injected through the surface of the component onto a primary mirror, this mirror diverts the sound wave to travel at 90 degrees into the support strut. The sound wave travels through the support strut onto a secondary mirror at 180 degrees to the support strut, this secondary mirror diverts the sound wave back through the support strut and onto the primary mirror, the primary mirror in turn diverts the sound wave back through the component outer surface to the sensor for measurement.
In simplicity the prismatic technique allows a sound wave to be sent through the component and received back for analysis, the analysis being carried out by standard accepted methods. |
| To demonstrate the technique a piece of box section, as illustrated, was cut from an actual aircraft component. A number of artificial defects, manufactured from 16 mm x 3 mm lead tabs were attached to the sample in different configurations. The majority of the defects (five) were located on the stringer, with a single defect being located on the outer skin to prove that the inspection was carried out through the component. |
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A c-scan was carried out at a frequency of 5 MHz using a standard medium pulse transducer and a collimator, a gate was positioned over the internal reflector (prism) and the amplitude of reflected signals monitored. Although the A-scan seems complicated, the computer is able to interpret the data and present a C-scan clearly identifying all six defects. |
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| The first RTM Inspection System was supplied to Bombardier Aerospace in October 2005, a 7500mm x 2750mm x 1000mm immersion system with twin manipulators allowing full two channel inspection under full computer control.
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