Ultrasonic processing - supersonic working

Ultrasound is a sound higher than audible sound, that is, a sound wave with a frequency of 16 kHz or more, which is beyond the audible range. This is a metal processing method that utilizes ultrasound. In this case, a magnetostrictive transducer that utilizes the magnetostrictive phenomenon, such as a nickel-AF alloy (13% aluminum, 87% iron), is usually used as the source of ultrasound. When ultrasound propagates through water, in water with a hydrostatic pressure of 1 atmosphere, if the sound intensity exceeds a certain level, the peak value of the sound pressure exceeds 1 atmosphere, generating negative pressure and creating cavities and bubbles in the water. The moment the pressure changes from negative to positive, the cavities disappear, and at that moment there is a strong destructive effect. This phenomenon is used to drill, cut, and polish brittle and hard materials such as quartz, germanium, gemstones, ceramics, and superhard alloys. For example, to drill a hole, if vibration is applied and abrasive grains are mixed into the water and supplied during that time, a hole will be made in the shape of the tool pressed against it.

[Muneaki Shimura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

可聴音よりも高い音、すなわち周波数が16キロヘルツ以上の、可聴範囲を超えた音波を超音波というが、これを利用した金属加工法。この場合、普通は超音波の発生源として、ニッケルAF合金（アルミニウム13％、鉄87％）などの磁気ひずみ現象を利用する磁歪(じわい)振動子などが用いられる。超音波が水中を伝播(でんぱ)する場合、静水圧が1気圧の水中では音の強さがある程度以上になると音圧の波高値は1気圧を突破して負の圧力を生じ、水中に空洞や気泡を生ずる。圧力が負から正に変わる瞬間に、空洞は消滅し、そのとき強烈な破壊作用がある。この現象を利用して水晶、ゲルマニウム、宝石、陶磁器、超硬質合金など、もろくて硬い材料に穴あけ、切断、研摩などを行う。たとえば穴あけは、振動を与え、その間に砥粒(とりゅう)を水に混ぜて供給してやると、押し付けた工具の形どおりの穴があく。

［志村宗昭］

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