Ultrasonic Machine Tool
Ultrasonic Machine Tool
a machining unit for shaping various solid materials. In an ultrasonic machine tool, ultrasonic vibrations are transmitted to a tool and then to the material through abrasive particles in a slurry.
A distinction is made between all-purpose and specialized ultrasonic machine tools. The all-purpose machine tools are used to machine workpieces made of hard brittle materials, such as glass, ceramic, quartz, sapphire, silicon, germanium, and hard alloys. They may be employed in, for example, the production and lapping of hard-alloy female dies, the cutting of billets, the preliminary grinding of lenses made of optical glass, the cutting of crystals for germanium- and silicon-wafer semiconductor devices, the etching of patterns on semiconductor wafers, the stamping of parts made of brittle and hard materials, the machining of holes in ferrite plates, and the production of deep holes in crystals.
The bed of the Soviet-made model 4773A ultrasonic machine tool supports a moving table whose position coordinates are controlled from a separate panel and contains both a tank that holds the abrasive slurry and a pump for supplying the slurry under pressure. The spindle of the machine tool, which carries a magnetostrictive transducer, and the tool move in the vertical plane. A hole with a diameter of 10-60 mm can be machined to a maximum depth of 50 mm. The ultrasonic vibration system used in the machine tool is of the rod, or wave-guide, type and operates at a frequency of 22 kilohertz (kHz).
The USSR and other countries manufacture ultrasonic machine tools with transducers having power ratings of 0.1-1.5 kilowatts (kW) and small, low-power ultrasonic machine tools with ferrite magnetostrictive transducers. Examples include a unit for machining shallow holes not more than 5 mm in diameter with a power of 25 watts available as the transducer input and an ultrasonic broaching tool with an abrasive-carrying electrolyte for the combined electrochemical and ultrasonic machining of through holes, blind holes, and cavities of complicated shape. The broaching tool is used to machine workpieces made of conducting materials and alloys, such as dies, draw dies, and molds, in two passes. Preliminary machining to grade 6 of surface roughness is accomplished by the combined ultrasonic and electron chemical effect on the material; the workpiece is finished to grade 7-8 by ultrasound alone. In the USSR, the model 4770U, 4B772, and 4772A units are the most widely used.
Specialized ultrasonic machine tools are used for a limited number of operations, such as the cutting of internal threads in workpieces made of heat-resistant materials that are difficult to machine. A 2.5-kW transducer is mounted on the die head of the Soviet-made model 40-7018 machine tool. When a thread is cut, the tap simultaneously rotates about the thread axis, moves forward along the axis, and vibrates at a frequency of 18-24 kHz with an amplitude of several micrometers. The vibrations ensure that the tap functions without jamming; that is, the machine can be operated, without frequent tool replacement, to a thread accuracy of grade 2-3 and a surface roughness of grade 5-6. A UZG-10/22 ultrasonic oscillator generates the vibrations.
Specialized ultrasonic machine tools are also employed, for example, to bore holes with diameters of 0.3-1.2 mm in diamond draw dies and to cut disks from germanium and silicon wafers; the Soviet-made model ME-22 and ME-46 units, respectively, are used for these operations. Such machine tools can provide an accuracy of ±15 micrometers.
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B. V. PROTOPOPOV