Ultrasonic machining characteristics and application of ultrasonic machining

    When it comes to ultrasonic processing, many consumers probably don't know much about it, and they feel that ultrasonic processing is far away from us. In fact, many products are processed by ultrasonic now. Let's take a look at the characteristics and application of ultrasonic processing with a small series for your reference.

     Ultrasonic machining characteristics

    It is not limited by whether the material is conductive or not;The macro-acting force on the tool workpiece is small, and the thermal influence is small, so thin-walled workpieces, narrow-slit workpieces and thin-slice workpieces can be machined; The greater the brittleness of the processed material, the easier it is to process; the harder the material or the greater the strength and toughness, the more difficult it is to process; Because the crushing of workpiece materials mainly depends on the action of abrasive, the hardness of abrasive should be higher than that of processed materials, while the hardness of tools can be lower than that of workpiece materials. It can be combined with other machining methods, such as ultrasonic vibration cutting, ultrasonic EDM and ultrasonic electrochemical machining.

     Ultrasonic machining is mainly used for drilling (including round holes, special-shaped holes and curved holes), cutting, slotting, nesting, carving, deburring of small parts in batches, surface polishing of molds and grinding wheel dressing of various hard and brittle materials, such as glass, Shi Ying, ceramics, silicon, germanium, ferrite, gems and jade.

     The range of ultrasonic hole diameter is 0.1 ~ 90 mm, the processing depth can reach more than 100 mm, and the accuracy of the hole can reach 0.02 ~ 0.05 mm. The surface roughness can reach 1.25 ~ 0.63 μ m when W40 boron carbide abrasive is used to process glass and 0.63 ~ 0.32 μ m when cemented carbide is processed.

     Ultrasonic processing machine is generally composed of three parts: power supply (i.e. ultrasonic generator), vibration system (including ultrasonic transducer and horn) and machine tool body.

  The ultrasonic generator converts alternating current into ultrasonic frequency electric power output, with power ranging from several watts to several kilowatts, up to 10 kilowatts. Commonly used ultrasonic transducers are magnetostrictive and electrostrictive. Magnetostrictive transducers can be divided into two types: metal and ferrite. Metal transducers are usually used in high-power ultrasonic processing machines with a power of more than kilowatts.Ferrite is usually used in low-power ultrasonic processing machines below kilowatts. The electrostrictive transducer is made of piezoelectric ceramics and is mainly used in low-power ultrasonic processing machines.

      Amplitude horn plays the role of amplifying amplitude and gathering energy, and it has cone shape, exponential curve shape, catenary shape, step shape, etc. according to the change law of cross-sectional area. Generally, there are two types of machine tools: vertical and horizontal, while the ultrasonic vibration system is placed vertically and horizontally.

      Ultrasonic processing and application 

      1. Forming processing

     Ultrasonic processing of round holes, cavities, grooves, special-shaped through holes, curved holes, micro holes, nesting and so on of various hard and brittle materials. Although its productivity is not as good as that of EDM and ECM, the machining accuracy and the surface quality of the workpiece depend on EDM and ECM. For example, in production, using hard metallurgy instead of alloy tool steel to make deep die, wire drawing die and other dies, its durability can be increased by 80-100 times. When EDM is used, micro-cracks often appear on the surface of the workpiece, which affects the surface quality and service life of the die. However, ultrasonic machining has no such defect, and the dimensional accuracy can be controlled within 0.01-0.02mm, and the inner hole taper can be trimmed to 8'. The processing of silicon and other semiconductor hard and brittle materials such as nesting shows the characteristics of ultrasonic processing. For example, on a silicon wafer with a diameter of 90mm and a thickness of 25mm, 176 components with a diameter of only 1mm can be machined by nesting. The time is only 1.5min, the qualification rate is as high as 90%-95%, and the machining accuracy is plus or minus 0.02 mm. In addition, in recent years, ultrasonic machining has removed its obstacles to the field of micro-machining.

    2. Cutting and processing 

  Ultrasonic cutting of hard and brittle materials such as semiconductors, ferrites, Shi Ying, precious stones, ceramics, diamonds, etc. has the advantages of thinner slices, narrower cut, higher precision, higher productivity and better economy than cutting with diamond cutters. For example, by ultrasonic cutting a germanium wafer with a height of 7mm and a width of 15-20mm, a slice with a thickness of 0.08mm can be cut in 3.5min. Ultrasonic cutting of monocrystalline silicon wafers can cut 10-20 wafers at a time. For example, in the components for ceramic thick film integrated circuits, when processing 8mm and 0.6mm thick ceramic pieces, 4 pieces can be processed in 1min. 

  3. Welding processing 

  Ultrasonic welding is to use ultrasonic frequency vibration to remove the oxide film on the surface of the workpiece, so that the new surface of the workpiece can be exposed, and the two molecules on the surface of the welded workpiece will rub and heat up under the impact of high-speed vibration. Affinity and bonding together. It can not only weld nylon, plastic and aluminum products with oxidized strands on their surfaces, but also hang tin, silver and coat thin layers on nonmetallic surfaces such as ceramics. Because ultrasonic welding does not need additional heat and flux, the welding heat affected zone is very small, and the applied pressure is very small, so it can weld different metal materials with very small diameter or thickness (0.015-0.03), as well as plastic thin fibers and hard thermoplastic with irregular shape. At present, ultrasonic welding has been widely used for wire connection of large scale integrated circuits. 

  4. Ultrasonic cleaning and processing 

  It is mainly used for the fine cleaning of medium and small precision parts with complex geometry and high cleaning quality, especially the small holes, micropores, bent holes, blind holes, grooves, narrow slits and other parts on the workpiece. Other cleaning methods are ineffective or even impossible to clean, while ultrasonic cleaning has good effect and high productivity. At present, it is used in the cleaning of semiconductor and integrated circuit components, instrument parts, electric vacuum devices, optical parts, precision mechanical parts, medical devices, radioactive pollution, etc. Generally speaking, ultrasonic cleaning is the result of cavitation effect of cleaning liquid (water-based cleaning agent, chlorinated hydrocarbon solvent, petroleum flux, etc.) under the action of ultrasonic wave. The strong shock wave produced by cavitation directly acts on the dirt on the cleaned part and makes it fall off; Cavitation bubbles generated by cavitation penetrate between the dirt and the surface of the cleaned part, and promote the dirt to fall off; When the dirt is dissolved by the cleaning solution, the cavitation effect can accelerate the dissolution process. During ultrasonic cleaning, the working frequency and sound pressure intensity should be reasonably selected to produce good cavitation effect and improve cleaning effect. In addition, the temperature of the cleaning solution should not be too high, so as to prevent the cavitation effect from weakening and affecting the cleaning effect.