Ultrasonic machining (USM):
Ultrasonic waves are sound waves which propagate at a frequency, beyond the human ear to respond. The vibrating tool oscillating at ultrasonic frequency is used to remove the material from work surface. Slurry of abrasive particles is drawn in between tool and work surface. The tool is pressed against the work piece with a small load and is fed downwards continuously. The tool never comes in contact with work piece. The shape of tool is a mirror image of desired cavity shape.
The arrangement consists of an acoustic head having frequency generator and magneto strictive transducer. It converts the mechanical motion into high frequency vibrations and these vibrations are transmitted to the tool. Tool should have high fatigue strength as it has to transfer vibrations. The tool is made of ductile and rough material. It has a shape of cavity to be produced in workpiece. The tool is made to vibrate against the workpiece surface. Gravity type or spring loaded feed mechanism is provided to the tool to apply working force. The slurry of abrasive particles is maintained between the workpiece and the tool. The tool imparts the necessary force on workpiece for cutting action. A gap of the order of 0.02 to 0.1 mm is maintained between the tool and the workpiece. The abrasive particles erode the workpiece to produce desired shape. Counterweight is applied to provide feed mechanism and to apply working force during machining.
Very little heat is produced in this process.
Extremely hard and brittle materials like ceramics, diamond, sapphire, glass can be machined by this process.
This process is suitable for electrical conductive as well as non conductive materials. Higher surface finish can be obtained.
The tool is commonly made of soft steels and nickel.
Ultrasonic waves can be generated by piezoelectric or magneto strictive effects.
A surface finish of 0.02 to 0.8 microns can be attained by this process. Holes, as small as 0.1 mm can be drilled by this method.