MECHANICAL BASED ENERGY PROCESS

ME2026 UNCONVENTIONAL MACHINING PROCESSES

UNIT 2

MECHANICAL ENERGY BASED PROCESS

By

G.NANTHINI,

LECTURER,

DEPT OF MECHANICAL,

KRCE, Trichy.

SYLLABUS

Abrasive Jet Machining (AJM)

Water Jet Machining (WJM)

Abrasive Water Jet Machining (AWJM)

Ultrasonic Machining. ( USM)

Working Principles – equipment used – Process

parameters – MRR-Variation in techniques used –

Applications.

ABRASIVE JET MACHINING

(AJM)

Principle

In Abrasive Jet Machining process, a

high speed stream of abrasive particles mixed with

high pressure air or gas which is injected on the

work piece through nozzle

Schematic Representation

Typical AJM Parameters

Abrasives used.

Aluminum Oxide (Al o ) 10 to 50 mic

Silicon Carbide (Sic) 25 to 50 mic

Glass Powder. 0.3 to 0.6 mm

Dolomite 200 grit size

Working Medium.

Dry air

Gases ( Nitrogen or carbon dioxide)

Nozzle Material

Tungsten Carbide

Silicon carbonate

ABRASIVE MATERIALAbrasive material Grit size (μin) Orifice diameter (in)

Aluminum oxide 10 - 50 0.005 - 0.018

Silicon carbide 25 - 50 0.008 - 0.018

Glass beads 2500 0.026 - 0.05

ADVANTAGES

Low capital cost

Less vibration

No heat generated in the work piece

Eco friendly

Only one tool is required

DISADVANTAGES

Low metal removal rate

Abrasive powder can not be reused

The machining accuracy is poor

Nozzle wear rate is high

Water Jet Machining

Principle

In WJM, the high velocity of water jet

comes out of the nozzle and strikes the material, its

kinetic energy is converted into pressure energy

including high stress in the work material. when this

exceeds the ultimate shear stress of the material,

small chips of the material get loosened and fresh

surface is exposed.

Schematic Representation

PROCESS PARAMETERS

Material removal rate(MRR)

-Depends on the reactive force of the jet

Reactive force = Mass flow rate (m) X jet

velocity (V)

Geometry and finish of work piece

Wear rate of the nozzle

Advantages of water jet cutting

There is no heat generated in water jet cutting; which

is especially useful for cutting tool steel and other

metals where excessive heat may change the

properties of the material.

Unlike machining or grinding, water jet cutting does

not produce any dust or particles

Disadvantages of water jet cutting

One of the main disadvantages of water jet cutting is that a limited number of materials can be cut economically.

Thick parts cannot be cut by this process economically and accurately

Taper is also a problem with water jet cutting in very thick materials.

Taper is when the jet exits the part at different angle than it enters the part, and cause dimensional inaccuracy.

Applications Of WJM Process

Water jet cutting is mostly used to cut lower strength

materials such as wood, plastics and aluminum.

When abrasives are added, (abrasive water jet

cutting) stronger materials such as steel and tool steel

can be cut.

Abrasive Water Jet Machining

Principle:

In abrasive water jet machining process a

high stream of abrasive jet particles is mixed with

pressurized water & injected through the nozzle on

the work piece.

Schematic Representation

Advantages of Abrasive water jet

cutting

In most of the cases, no secondary finishing required

No cutter induced distortion

Low cutting forces on work pieces

Limited tooling requirements

Little to no cutting burr

Typical finish 125-250 microns

Smaller kerfs size reduces material wastages

No heat affected zone

CONTD…

Localizes structural changes

No cutter induced metal contamination

Eliminates thermal distortion

No slag or cutting dross

Precise, multi plane cutting of contours, shapes, and

bevels of any angle.

Disadvantages of Abrasive water jet

cutting

Cannot drill flat bottom

Cannot cut materials that degrades quickly with

moisture

Ultrasonic Machining

Principle

In the Ultrasonic Machining process the material is removed by micro-chipping or erosion with abrasive particles.

The tool forces the abrasive grits, in the gap between the tool and the work piece, to impact normally and successively on the work surface, thereby machining the work surface.

Contd….

In USM process, the tool , made of softer material

than that of the work piece, is oscillated by the

Booster and Sonotrode at a frequency of about 20

kHz with an amplitude of about 25.4 um(0.001 in).

Schematic Representation

Schematic Representation

PROCESS PARAMETER

Effect of amplitude and frequency of vibration

on MRR

MRR is directly proportional to the first power of

frequency for a fixed amplitude

Theoretical

M

R

R

Frequency

Actual

M

R

R

High

amplitude

Low

frequency

High

frequency

CONTD…

EFFECT `VELOCITY`

MRR IS DIRECTLY PROPORTIONAL TO THE PARTICLE

VELOCITY

M

R

R

Feed forceMean grain

diameter

Surface

rough

CONTD..

EFFECT OF STATIC LOADING OR FEED

FORCE:

- MRR increases with an increase in feed

force.

EFFECT OF GRAIN SIZE:

1. - Grain size increases with an increase in

MRR

Advantages of USM

There is no cutting forces therefore clamping is not required except for controlled motion of the work piece

Extremely hard and brittle materials can be easily machined

There is no heat affected zone.

Can machine harder metals

Faster than EDM

No tool wear at all.

No heat affected zone.

Better finish and accuracy.

USM Applications

Hard, brittle work materials such as ceramics, glass,

and carbides.

Also successful on certain metals, such as

stainless steel and titanium.

Shapes include non-round holes, holes

along a curved axis.

“Coining operations” - pattern on tool is

imparted to a flat work surface

Thank you