Ultrasonic Machining

Ultrasonic Machining (USM) is a special type of processing that uses high-frequency vibrations to produce small amplitude impacts on the surface of the workpiece. In this process, an abrasive material is suspended in a liquid, which acts as a medium to transfer the energy generated by the ultrasonic frequency to the workpiece.

Ultrasonic Machining is frequently utilized for various applications including piercing, cutting, welding, nesting, and polishing.

Working principle

The ultrasonic generator transforms standard AC power into an ultrasonic frequency oscillation with a specified power output.

The transducer then transforms this ultrasonic frequency oscillation into an ultrasonic mechanical vibration.

The tool attached to the end of the horn is vibrated ultrasonically through the amplitude amplifying rod (horn), causing the abrasive suspension to strike the surface of the workpiece at high speeds and polish it to form the desired shape.

Material used

Ultrasonic processing of plastic materials using corundum abrasives, processing of brittle materials with silicon carbide abrasives, machining of carbides using boron carbide abrasives, and processing of diamonds using diamond powder abrasives.

Main features of ultrasonic machining

Ultrasonic processing is not limited by the electrical conductivity of the material. It has a small macro force and minimal heat influence on the workpiece, making it ideal for processing thin-walled, narrow slit, and sheet workpieces. The brittleness of the material being processed is directly proportional to its ease of processing, while the hardness and toughness of the material make it more difficult to process. For the abrasive to effectively scrape the workpiece material, its hardness should be higher than that of the material being processed, and the tool’s hardness can be lower.

Ultrasonic processing can be combined with other processing methods, such as ultrasonic vibration cutting, ultrasonic EDM, and ultrasonic electrolysis. It is mainly used for perforating (including round, special, and curved holes), cutting, slotting, and engraving various hard and brittle materials such as glass, quartz, ceramic, silicon, germanium, ferrite, gemstones, and jade. It is also used for nesting, batch deburring of small parts, surface polishing of molds, and dressing of grinding wheels.

The aperture of ultrasonic perforation ranges from 0.1 to 90 mm, and the processing depth can reach over 100 mm with a precision of 0.02 to 0.05 mm. The surface roughness can reach 1.25 to 0.66 μm when processing glass with W40 boron carbide abrasive and 0.63 to 0.32 μm when processing cemented carbide.

Ultrasonic processing machines consist of three parts: the power source (an ultrasonic generator), the vibration system (including the ultrasonic transducer and horn), and the machine body. The ultrasonic generator transforms alternating current into ultrasonic frequency power output with a power range of a few watts to a maximum of 10 kilowatts.

Two types of ultrasonic transducers are commonly used: magnetostrictive and electrostrictive. Magnetostrictive transducers are available in metal and ferrite and are mainly used in high-power ultrasonic processing machines above kilowatts. Ferrite transducers are used in low-power ultrasonic machines below kilowatts. The electrostrictive transducer, made of piezoelectric ceramics, is mainly used in low-power ultrasonic processing machines.

The horn amplifies the amplitude and energy of the ultrasonic vibration. Horns come in various shapes, including cone, cosine line, exponential curve, catenary line, and step shapes. The machine body is available in both vertical and horizontal types and the ultrasonic vibration system is positioned accordingly.

Ultrasonic machining application method

(1) Ultrasonic Welding Method:

The welding head vibrates at an ultra-high frequency, producing ultrasonic waves and applying a moderate pressure. This causes the joint surfaces of the two plastics to instantly melt and join due to friction heat. The welding strength is comparable to the strength of the body. With appropriate workpieces and a well-designed interface, watertight and airtight seals can be achieved without the need for additional products, resulting in efficient and clean welding.

(2) Rivet Welding Method:

The ultrasonic welding head vibrates at an ultra-high frequency and is pressed against the protruding tip of the plastic product. This creates instant heat, melting the material into a rivet shape and mechanically connecting materials of different types.

(3) Implantation:

By adjusting the trajectory of the welding head and applying the right pressure, metal parts (such as nuts, screws, etc.) can be inserted into a plastic hole and fixed at a specific depth. The resulting tension and torque are comparable to those produced by traditional molding methods and avoid the drawbacks of injection mold damage and slow injection.

(4) Forming:

This method is similar to rivet welding. The concave welding head is pressed against the outer ring of the plastic product and vibrates at an ultra-high frequency, causing the plastic to melt and form a coating on the metal object being fixed. The result is a smooth and attractive appearance. This method is often used for fixing molds in electronic devices and horns, and for attaching lenses in cosmetics.

(5) Spot Welding:

Two plastic points are welded without pre-designing a welding wire, achieving the purpose of welding. For larger workpieces, it may not be easy to design a welding wire for point welding, but the welding effect can still be achieved by spot welding multiple points at the same time.

(6) Cutting Seal:

This method uses the ultrasonic vibration principle of ultrasonic waves to cut chemical fiber fabric, producing smooth, non-cracked or drawn slits.