Ultrasonic Machining

Ultrasonic machining, or strictly speaking the "Ultrasonic vibration machining", is a subtraction manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm (0.002 to 0.005 in.). The fine abrasive grains are mixed with water to form a slurry that is distributed across the part and the tip of the tool. Typical grain sizes of the material range from 100 to 1000, where smaller grains (higher grain number) produce smoother surface finishes.

Ultrasonic vibration machining is typically used on brittle materials as well as materials with a high hardness due to the microcracking mechanics.

Process

An ultrasonically vibrating mill consists of two major components, an electroacoustic transducer and a sonotrode, attached to an electronic control unit with a cable. An electronic oscillator in the control unit produces an alternating current oscillating at a high frequency, usually between 18 and 40 kHz in the ultrasonic range. The transducer converts the oscillating current to a mechanical vibration. 

The transducer vibrates the sonotrode at low amplitudes and high frequencies. The sonotrode is usually made of low carbon steel. A constant stream of abrasive slurry flows between the sonotrode and work piece. This flow of slurry allows debris to flow away from the cutting area. The slurry usually consists of abrasive boron carbide, aluminum oxide or silicon carbide particles in a suspension of water (20 to 60% by volume). The sonotrode removes material from the work piece by abrasion where it contacts it, so the result of machining is to cut a perfect negative of the sonotrode's profile into the work piece. Ultrasonic vibration machining allows extremely complex and non-uniform shapes to be cut into the workpiece with extremely high precision.

Advantages

Ultrasonic vibration machining is a unique non-traditional manufacturing process because it can produce parts with high precision that are made of hard and brittle materials which are often difficult to machine. Additionally, ultrasonic machining is capable of manufacturing fragile materials such as glass and non-conductive metals that can not be machined by alternative methods such as electrical discharge machining and electrochemical machining. Ultrasonic machining is able to produce high-tolerance parts because there is no distortion of the worked material. The absence of distortion is due to no heat generation from the sonotrode against the work piece and is beneficial because the physical properties of the part will remain uniform throughout. Furthermore, no burrs are created in the process, thus fewer operations are required to produce a finished part

Disadvantage

Because ultrasonic vibration machining is driven by microchipping or erosion mechanisms, the material removal rate of metals can be slow and the sonotrode tip can wear down quickly from the constant impact of abrasive particles on the tool.^[1] Moreover, drilling deep holes in parts can prove difficult as the abrasive slurry will not effectively reach the bottom of the hole. Note, rotary ultrasonic machining is efficient at drilling deep holes in ceramics because the absence of a slurry cutting fluid and the cutting tool is coated in harder diamond abrasives.^[1] In addition, ultrasonic vibration machining can only be used on materials with a hardness value of at least 45 HRC.

Source: Wikipedia