Inspection of pistons

Inspection of an electron beam weld on large-bore pistons

Task:
An electron beam weld seam is located near the piston groove of a certain type of large-bore pistons. The weld seams are currently checked by using penetrant testing. This method does not, however, reliably detect defects. Distinguishing between cracks and pores yields ambiguous results. When cracks are suspected the pistons are now separated.
As part of this application an inspection using eddy currents is being prepared. The permissible defect sizes and quality requirements are specified in DIN 8563-12. Scattered pores are permitted, but cracks are not permitted.

Solution:
A probe that is adapted to the shape of the weld seam in the ground of the groove of the piston was developed. This probe is currently used in a static mode in a manual inspection. With its high degree of sensitivity, even minute pores, wormholes and circumferential defects are detected. One great advantage over the previously used penetrant testing turned out to be the detection of hidden defects right below the surface.
Compared to the penetration testing that has been used so far, the advantage of eddy-current inspection is the very fast and considerably more reliable evaluation of the quality of the weld seams. This inspection may be automated later. Thus the subjective evaluations of the inspector become obsolete.