VADODARA INSTITUTE OF ENGINEERING. KOTAMBI.

ACTIVE LEARNING ASSIGNMENT ONProduction technology

Topic : ultrasonic machining. ( USM )

Enrolment no : 130800119551 : Niraj

140803119701 : Anupam140803119702 : Milan140803119703 : Sunil

Introduction• Ultrasonic machining (USM) is the removal of hard and

brittle materials using an axially oscillating tool at ultrasonic frequencies [18–20 kHz]

• During that oscillation, the abrasive slurry of B4C or SiC is continuously fed into the machining zone between a soft tool (brass or steel) and the workpiece.

• The abrasive particles are, therefore, hammered into the workpiece surface and cause chipping of fine particles from it.

• The oscillating tool, at amplitudes ranging from 10 to 40 μm, imposes a static pressure on the abrasive grains and feeds down as the material is removed to form the required tool shape.

USM - Components

Principles of Ultrasonic MachiningIn the UM process, a low-frequency electrical signal is

applied to a transducer, which converts the electrical energy into high-frequency (~20 KHz) mechanical vibration (see Figure 2).

This mechanical energy is transmitted to a horn and tool assembly and results in a unidirectional vibration of the tool at the ultrasonic frequency with a known amplitude.

The standard amplitude of vibration is typically less than 0.002 in.

The power level for this process is in the range of 50 to 3000 watts. Pressure is applied to the tool in the form of static load.

A constant stream of abrasive slurry passes between the tool and the workpiece.

Commonly used abrasives include diamond, boron carbide, silicon carbide and alumina, and the abrasive grains are suspended in water or a suitable chemical solution.

In addition to providing abrasive grain to the cutting zone, the slurry is used to flush away debris.

The vibrating tool, combined with the abrasive slurry, abrades the material uniformly, leaving a precise reverse image of the tool shape.

Main Elements of an USM

Magnetostrictor

• It has a high-frequency winding wound on a magnetostrictor core and a special polarizing winding around an armature.

• Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization.

• The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ.

• Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build actuators and sensors.

Material Removal Process

Material removal mechanism of USM involves three distinct actions:

1. Mechanical abrasion by localized direct hammering of the abrasive grains stuck between the vibrating tool and adjacent work surface.

2. The microchipping by free impacts of particles that fly across the machining gap and strike the workpiece at random locations.

3. The work surface erosion by cavitation in the slurry stream.

Material Removal Process• The relative contribution of the cavitation effect

is reported to be less than 5 per cent of the total material removed.

• The dominant mechanism involved in USM of all materials is direct hammering.

• Soft and elastic materials like mild steel are often plastically deformed first and are later removed at a lower rate.

• In case of hard and brittle materials such as glass, the machining rate is high and the role played by free impact can also be noticed.

• When machining porous materials such as graphite, the mechanism of erosion is introduced.

• The rate of material removal, in USM, depends, on the frequency of tool vibration, static pressure, the size of the machined area, and the abrasive and workpiece material.

• MRR and machinability by USM depends on the brittleness criterion which is the ratio of shearing to breaking strength of a material.

Material Removal Rate

USM Performance

Factors affecting MRRTool Oscillation or Vibration• Amplitude of the tool oscillation has the greatest

effect of all the process variables.• MRR increases with a rise in the tool vibration

amplitude. • Vibration amplitude determines the velocity of the

abrasive particles at the interface between the tool and workpiece.

A greater vibration amplitude may lead to the occurrence of splashing, which causes a reduction of the number of active abrasive grains and results in a decrease in the MRR.

. Abrasive Grains• Both the grain size and the vibration

amplitude have a similar effect on the removal rate.

• According to McGeough (1988), MRR rises at greater grain sizes until the size reaches the vibration amplitude, at which stage, the MRR decreases.

The MRR obtained with silicon carbide is about 15 % lower when machining glass, 33 % lower for tool steel, and about 35 % lower for sintered carbide

Workpiece Impact Hardness• MRR is affected by the ratio of tool hardness to

workpiece hardness.• In this regard, the higher the ratio, the lower will

be MRR.• For this reason soft and tough materials are

recommended for USM tools.Tool Shape• Increase in tool area - decreases the machining

rate; due to inadequate distribution of abrasive slurry over the entire area.

Rise in static pressure - enhances MRR up to a limiting condition, beyond which no further increase occurs

Applications of USM• USM should be applied for shallow cavities cut

in hard and brittle materials having a surface area less than 1000 mm2.

• Drilling and coring.

Ultrasonic sinking and contour machining

• During USM sinking, material removal is difficult for depth > 5 to 7 mm.

• Under such conditions, the removal of abrasives at the interface becomes difficult and hence the material removal process is impossible.

• Moreover, manufacturing of such a tool is generally complex and costly.

Ultrasonic Polishing• Polishing occurs by vibrating a brittle tool

material (graphite or glass) into the work piece at an ultrasonic frequency and a relatively low amplitude.

• Fine abrasive particles abrade the high spots of the work piece surface, typically removing 0.012 mm of material or less.

Other Applications• Cutting off of parts made from

semiconductors at high removal rates compared to conventional machining methods.

• Engraving on glass as well as hardened steel and sintered carbide.

• Parting and machining of precious stones including diamond.

Advantages of ultrasonic machining include:

The process is non-thermal, non-chemical, and non-electrical, leaving the chemical and physical properties of the work piece unchanged. This low-stress process translates into high reliability for your critical applications.

Multiple features can be machined at the wafer or substrate level simultaneously, and the process is scalable. Our process is often the highest quality and lowest cost solution

Ultrasonic machined features have vertical side walls, enabling you to preserve valuable space for your designs that translate into higher productivity.

Thank you.