Ultrasonic impact treatment

Ultrasonic impact treatment (UIT) is a metallurgical processing technique, similar to work hardening, in which ultrasonic energy is applied to a metal object. This technique is part of the High Frequency Mechanical Impact (HFMI) processes. Other acronyms are also equivalent: Ultrasonic Needle Peening (UNP), Ultrasonic Peening (UP). Ultrasonic impact treatment can result in controlled residual compressive stress, grain refinement and grain size reduction. Low and high cycle fatigue are enhanced and have been documented to provide increases up to ten times greater than non-UIT specimens. Ultrasonic impact treatment (UIT) is a metallurgical processing technique, similar to work hardening, in which ultrasonic energy is applied to a metal object. This technique is part of the High Frequency Mechanical Impact (HFMI) processes. Other acronyms are also equivalent: Ultrasonic Needle Peening (UNP), Ultrasonic Peening (UP). Ultrasonic impact treatment can result in controlled residual compressive stress, grain refinement and grain size reduction. Low and high cycle fatigue are enhanced and have been documented to provide increases up to ten times greater than non-UIT specimens. In UIT, ultrasonic waves are produced by an electro-mechanical ultrasonic transducer, and applied to a workpiece. An acoustically tuned resonator bar is caused to vibrate by energizing it with a magnetostrictive or Piezoelectric ultrasonic transducer. The energy generated from these high frequency impulses is imparted to the treated surface through the contact of specially designed steel pins. These transfer pins are free to move axially between the resonant body and the treated surface. When the tool, made up of the ultrasonic transducer, pins and other components, comes into contact with the work piece it acoustically couples with the work piece, creating harmonic resonance. This harmonic resonance is performed at a carefully calibrated frequency, to which metals respond very favorably, resulting in compressive residual stress, stress relief and grain structure improvements. Depending on the desired effects of treatment a combination of different frequencies and displacement amplitude is applied. Depending on the tool and the Original Equipment Manufacturer, these frequencies range between 15 and 55 kHz, with the displacement amplitude of the resonant body of between 20 and 80 μm (0.00079 and 0.00315 in). UIT is highly controllable. Incorporating a programmable logic controller (PLC) or a Digital Ultrasonic Generator, the frequency and amplitude of UIT are easily set and maintained, thus removing a significant portion of operator dependency. UIT can also be mechanically controlled, thus providing repeatability of results from one application to the next. Examples of mechanical control employed with UIT include: