Method and apparatus for ultrasonic peening of axial recesses for the attachment of blades to a rotor

A method of surface treating and compressively prestressing by peening a wall of at least one oblong cavity formed in a part, said cavity opening to the outside via a lateral mouth and having two ends presenting frontal openings, said method comprising the steps of:

• a) providing a sonotrode arranged within a sleeve, said sonotrode having a vibratory surface and ultrasonic means for vibrating said vibratory surface, and said sleeve having opposed closing-off means capable of closing off the frontal openings of said cavity;
• b) placing a plurality of beads of a predetermined diameter on said vibratory surface of said sonotrode with said sonotrode arranged in an intermediate position in which said sleeve surrounds said vibratory surface;
• c) placing said lateral mouth of said cavity facing said sonotrode,
• d) moving said sonotrode, supporting said plurality of beads, together with said sleeve substantially vertically toward a raised peening position in which said closing-off means close off said frontal openings of said cavity and in which said sonotrode is disposed facing said lateral mouth to delimit, together with said sleeve, said closing-off means and said cavity, a chamber sealed to said beads;
• and
• e) operating said ultrasonic means to vibrate said vibratory surface of said sonotrode whereby said beads are mobilized in said chamber to conduct ultrasonic peening of said wall of said cavity.