Ultrasonic machining process (USM)

WORKING PRINCIPLE OF ULTRASONIC MACHINING PROCESS AND ITS MACHINING APPLICATIONS

1. Ultrasonic Machining Process (USM ) BY, ARAVINDKUMAR B

2. Ultrasonic Machining Process (USM) Ultrasonic machining (USM) is a mechanical material removal process. It is used to erode material in the form of fine holes and cavities in hard or brittle workpiece through the use of formed tools, vibrations of high frequency along with the use of a suitable abrasive slurry-mix. The Ultrasonic Machining (USM) process is suitable for machining brittle materials such as glass, ceramics and semiconductors for increasingly complex operations to provide intricate shapes and workpiece profiles.

3. The USM is a non-thermal and non-chemical process which creates no change in the chemical, physical or metallurgical properties of the workpiece . It is therefore being widely used in the manufacturing of hard and brittle materials which are normally unfeasible to machine by the traditional methods. The cutting is actually performed by the abrasive particles which are suspended in the slurry (fluid). Ultrasonic machining accomplishes the material removal through the abrading action of the grit-loaded slurry which circulates between the tool and the workpiece . Small amplitudes and high frequency of vibrations are given to the tool,typically in the range of 10–20 μm at 20–40 kHz.

4. The hard abrasive particles in the slurry are accelerated towards the workpiece surface by the oscillating action of the tool -through repeated abrasions, the tool further machines a cavity of cross section identical to its own. The material removal takes place is the form of fine grains by shear deformation. Different mechanisms could be attributed to this material process such as brittle fracturing of the work material, impact action of abrasives, cavitation and chemical reaction due to the slurry. The workpiece shape and dimensional accuracy is directly dependent on the geometry of the tool.

5. Mechanism of Material Removal Mechanical abrasion : Occurs due to the hammering effect of abrasive particles on workpiece through the tool. Impact : The freely moving particles impact with a certain velocity on the work piece resulting in micro chipping. Erosio n: Due to cavitation effect of the abrasive slurry, erosion of the work surface occurs. Chemical : Due to fluid employed, chemical effect can come into consideration.

6. Advantages of USM In USM process, there are no physical, chemical or thermal changes. There is no direct contact of the tool and workpiece due to the slurry used, it makes it a wet cutting process. The surfaces produced are free from stress and damages. The process is free from burrs and distortions. The process is suitable for any materials, irrespective of electrical conductivity The process is very much suitable for machining brittle materials The process offers good surface finish and structural integrity.

7. Disadvantages / Limitations of USM Soft materials like lead and plastics are not suitable for machining by the USM process, since they tend to absorb the abrasive particles rather than to chip under their impact. The USM process consumes higher power and has lower material-removal rates compared to traditional fabrication processes. The tool wear rate in USM process is fast. The areas of machining and higher depths are the constraints in USM. As the USM process continuous, the lateral wear of the tool increases gradually and it tends to make the holes tapered. The sharp corners of the tool get rounded off thereby requiring tool replacement essential for producing accurate blind holes. The accuracy of the machined surface gets lost due to setting up of strong lateral vibrations. This occurs if the axis of the tool and horn, which are brazed together, are not properly aligned with the transducer axis. In such a case, the tool needs to be redesigned. The holes produced in USM have a tendency to break out at the bottom owing to the static load and high amplitudes. While producing deeper holes through USM method, there is ineffective slurry circulation leading to presence of a fewer active grains under the tool face. Due to this, the bottom surfaces of blind holes tend to become slightly concave.

8. Applications of USM USM process is used in machining hard and brittle metallic alloys, semiconductors, glass, ceramics, carbides etc. In machining of advanced ceramics for applications in auto-engine components. In machining, wire drawing, punching or blanking of small dies Machining ceramic substrates for drilling holes in borosilicate glass for the sensors used in electronic industries Drilling small holes in helicopter power transmission shafts and gears.