All non destructive test procedures need specimen with precisely defined reference defects for sensitivity determination. In addition to mechanical procedures, spark erosion is particularly suited to the manufacture of very high precision grooves and flat bottom slots with dimensions under 0,5 mm. BAM has already used this procedure for many years for the production of test defects with different dimensions, geometry and depth profiles. A sophisticated mounting plate system for the electrodes also enables the production of grooves in inaccessible places, for example in the inside of pipes or bushes.
An optical measuring microscope is used for determining not only the width and length of the cracks but also the depth. The reversing distance of the electrode at the end of the process can also be used as a mechanical method to estimate the depth. If a perpendicular view is not possible due to geometry, reference defects are consulted.
In the simplest case the grooves are straight; however they can also be semicircular or convoluted. Likewise it is possible to modify and adapt the depth profile to the surface curvature of the workpieces. The achievable groove dimensions and operating time depend predominantly on the material and the width/depth ratio.
At the end of the test, a clearly attributable certificate with an indication of the groove dimensions, a sketch or photograph of the test piece and a record of the measuring instruments used is provided for each test piece.
Edge of a rectangular groove, Width: 105 µm, depth: 200 µm
Example defect implemented over a material edge. Groove dimensions: depth: 0.95 mm, width: 0.11 mm
Example of an electrode, Length: 0.95 mm, width 0.05 mm
Valve with an artificial crack
