Major Project Report on Ajm

8/19/2019 Major Project Report on Ajm

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A PROJECT REPORT ON

AJMSubmitted in partial fulfillment of the requirements

For the award of the

DEREE OF EN!NEER!N

!N

"""""""""""""""""""""""""""""""""""" EN!NEER!N

S#$%!TTED $&

-------------------- (--------------)

--------------------- (---------------)

--------------------- (---------------)

DEPART%ENT OF """"""""""""""""""""""" EN!NEER!N

""""""""""CO''EE OF EN!NEER!N

AFF!'!ATED TO """"""""""" #N!(ERS!T&


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CERTIFICATE

This is to )ertif* that the dissertation wor+ entitled

AJM is the wor+ done b*

"""""""""""""""""""""""""""""""""""""""""""""""submitted in partial

fulfillment for the award of ,$AC-E'OR OF EN!NEER!N. in

""""""""""""""""""""""""""En/ineerin/ from"""""""""""""" Colle/e of

En/ineerin/ affiliated to """"""""" #ni0ersit*1

________________ ____________

(Head of the department,______) (Assistant Professor)

EXTERNAL EXAMINER


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ACN!"LE#$EMENT

The satisfa)tion and euphoria that a))ompan* the su))essful )ompletion of an*

tas+ would be in)omplete without the mentionin/ of the people whose )onstant

/uidan)e and en)oura/ement made it possible2 3e ta+e pleasure in presentin/

before *ou1 our pro4e)t1 whi)h is result of studied blend of both resear)h and

+nowled/e2

3e e5press our earnest /ratitude to our internal /uide1 Assistant Professor

""""""""""""""1 Department of %e)hani)al1 our pro4e)t /uide1 for his )onstant

support1 en)oura/ement and /uidan)e2 3e are /rateful for his )ooperation and his

0aluable su//estions2

Finall*1 we e5press our /ratitude to all other members who are in0ol0ed either

dire)tl* or indire)tl* for the )ompletion of this pro4e)t2


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#ECLARATI!N

3e1 the undersi/ned1 de)lare that the pro4e)t entitled %A&M'1 bein/ submitted in partial fulfillment for the award of En/ineerin/ De/ree in %EC-AN!CA'

En/ineerin/1 affiliated to """"""""" #ni0ersit*1 is the wor+ )arried out b* us2


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Definition:

In abrasive jet machining, a focused stream of abrasive particles, carried by

high pressure air or gas is made to impinge on the work surface through a

nozzle and the work material is made to impinge on the work surface

through a nozzle and work material is removed by erosion by high velocity

abrasive particles.

Process:

!n Abrasi0e 4et ma)hinin/ abrasi0e parti)les are made to impin/e on wor+ material

at hi/h 0elo)it*2 Jet of abrasi0e parti)les is )arried b* )arrier /as or air2 The hi/h

0elo)it* stream of abrasi0es is /enerated b* )on0ertin/ pressure ener/* of )arrier

/as or air to its 6ineti) ener/* and hen)e hi/h 0elo)it* 4et2 No77les dire)ts abrasi0e

4et in a )ontrolled manner onto wor+ material2 The hi/h 0elo)it* abrasi0e parti)les

remo0e the material b* mi)ro8)uttin/ a)tion as well as brittle fra)ture of the wor+

material2


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This is a pro)ess of remo0al of material b* impa)t erosion throu/h the a)tion of

)on)entrated hi/h 0elo)it* stream of /rit abrasi0es entrained in hi/h 0elo)it* /as

stream2 AJ% is different from shot or sand blastin/1 as in AJ%1 finer abrasi0e /rits

are used and parameters )an be )ontrolled more effe)ti0el* pro0idin/ better )ontrol

o0er produ)t qualit*2

!n AJ%1 /enerall*1 the abrasi0e parti)les of around 9: mi)rons /rit si7e would

impin/e on the wor+ material at 0elo)it* of ;:: m Fine parti)les ?:2:;9mm@ are a))elerated in a /as stream

> The parti)le are dire)ted towards the fo)us of ma)hinin/

> As the parti)les impa)t the surfa)e1 it )auses a mi)ro fra)ture1 and /as )arries


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fra)tured parti)les awa*

> $rittle and fra/ile wor+ better

INTRODUCTION

Abrasive water jet machine tools are suddenly being a hit in the

market since they are quick to program and could make money on short

runs. They are quick to set up, and offer quick turnaround on the machine.

They complement e!isting tools used for either primary or secondary

operations and could make parts quickly out of virtually out of any material.

"ne of the major advantages is that they do not heat the material. All sorts

of intricate shapes are easy to make. They turns to be a money making

machine. #o ultimately a machine shop without a water jet is like a

carpenter without a hammer. #ure the carpenter can use the back of his

crow bar to hammer in nails, but there is a better way. It is important to

understand that abrasive jets are not the same thing as the water jet

although they are nearly the same. $ater %et technology has been around

since the early &'()s or so, and abrasive jets e!tended the concept about

ten years later. *oth technologies use the principle of pressuring water to

e!tremely high pressure, and allowing the water to escape through opening

typically called the orifice or jewel. $ater jets use the beam of water e!iting

the orifice to cut soft stuffs like candy bars, but are not effective for cutting

harder materials. The inlet water is typically pressurized between +)))) and

)))) -ounds -er #quare Inch -#I/. This is forced through a tiny wall in the

jewel which is typically .))(0 to .)&10 diameter ).&2 to ).3mm/. This


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creates vary high velocity beam of water. Abrasive jets use the same beam

of water to accelerate abrasive particles to speeds fast enough to cut

through much faster material.

In abrasive jet machining, a focused stream of abrasive particles, carried by

high pressure air or gas is made to impinge on the work surface through anozzle and the work material is made to impinge on the work surface

through a nozzle and work material is removed by erosion by high velocity

abrasive particles.

COMPONENTS OF ABRASIVE JET MACHINING CENTER

The components of A%4 centre include 5

Abrasive 6elivery #ystem

7ontrol #ystem

-ump

8ozzle

4otion #ystem

Process:

In Abrasive jet machining abrasive particles are made to impinge on

work material at high velocity. %et of abrasive particles is carried by carrier

gas or air. The high velocity stream of abrasives is generated by converting

pressure energy of carrier gas or air to its 9inetic energy and hence high

velocity jet. 8ozzle directs abrasive jet in a controlled manner onto work

material. The high velocity abrasive particles remove the material by micro

cutting action as well as brittle fracture of the work material.


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This is a process of removal of material by impact erosion through the action

of concentrated high velocity stream of grit abrasives entrained in high

velocity gas stream. A%4 is different from shot or sand blasting, as in A%4,

finer abrasive grits are used and parameters can be controlled more

effectively providing better control over product quality.

In A%4, generally, the abrasive particles of around 1) microns grit size would

impinge on the work material at velocity of +)) m:s from a nozzle of I6

).1mm with a standoff distance of around +mm. The kinetic energy of the

abrasive particles would sufficient to provide material removal due to brittle

fracture of the work piece or even micro cutting by the abrasives.


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-hysics of the -rocess5

• ;ine particles ).)+1mm/ are accelerated in a gas stream

• The particle are directed towards the focus of machining

• As the particles impact the surface, it causes a micro fracture, and gas

carries fractured particles away

• *rittle and fragile work better

"verlook : total part of an A%4/


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Abrsi!e De"i!er# S#ste$

A simple fi!ed abrasive flow rate is all that


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Gs Pro&'"sion S#ste$

#upplies clean and dry air. Air, 8itrogen and carbon dio!ide to propel the

abrasive particles. ?as may be supplied either from a compressor or a

cylinder. In case of a compressor, air filter cum drier should be used to avoid

water or oil contamination of abrasive powder. ?as should be nonto!ic,

cheap, and easily available. It should not e!cessively spread when

discharged from nozzle into atmosphere. The propellant consumption is of

order of ).))2 m>:min at a nozzle pressure of 1 bar and abrasive flow rate

varies from + to 3 gm:min for fine machining and &) to +) gm:min for

cutting operation.

Abrsi!e Fee(er

@equired quantity of abrasive particles is supplied by abrasive feeder. The

filleted propellant is fed into the mi!ing chamber where in abrasive particles

are fed through a sieve. The sieve is made to vibrate at 1)) z and mi!ing

ratio is controlled by the amplitude of vibration of sieve. The particles are

propelled by carrier gas to a mi!ing chamber. Air abrasive mi!ture movesfurther to nozzle. The nozzle imparts high velocity to mi!ture which is

directed at work piece surface.

Mc)inin* c)$ber

It is well closed so that concentration of abrasive particles around the

working chamber does not reach to the harmful limits. 4achining chamber is

equipped with vacuum dust collector. #pecial consideration should be given

to dust collection system if the to!ic materials like beryllium/ are being

machined.


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AJM no++"e

A%4 nozzle is usually made of tungsten carbide or sapphire usually life B

>)) hours for sapphire , +) to >) hours for $7/ which has resistance to

wear. The nozzle is made of either circular or rectangular cross section and

head can be head can be straight, or at a right angle. It is so designed that

loss of pressure due to the bends, friction etc is minimum possible. $ith

increase in wear of a nozzle, the divergence of jet stream increases resulting

in more stray cutting and high inaccuracy. Aluminum o!ide Al+">/ #ilicon

carbide #i7/ ?lass beads, crushed glass and sodium bicarbonate are some

of abrasives used in A%4. #election of abrasives depends on 4@@ , type of

work material , machining accuracy.


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ABRASIVES

Abrsi!es Grin Si+es A&&"ictionAluminum o!ideAl+">/ &+, +), 1) microns ?ood for cleaning, cutting

and deburring

#ilicon carbide #i7/ +1,3) micron Csed for similar

application but for hard

material

?lass beads ).>1 to &.+(mm ?ives matte finish6olomite +)) mesh Dtching and polishing

#odium bi carbonate +( micros 7leaning, deburring and

cutting of soft material

Eight finishing below 1))7

Process &r$eters

;or successful utilization of A%4 process, it is necessary to analyze the

following process criteria.

&. 4aterial removal rate

+. ?eometry and surface finish of work piece

>. wear rate of the nozzle

owever, -rocess criteria are generally influenced by the process parameters

as enumerated below5

• Abrsi!es

a/ material B Al+"> #i7 ?lass beads 7rushed glass #odium bi carbonate

b/ shape B irregular:regular

c/ #ize B &) to 1) microns

d/ 4ass flow B ++) gm:min

• Crrier Gs

a/ 7omposition B Air, 7"+, 8+

b/ 6ensity B &.> kg:m>

c/ Felocity 1)) to ()) m:s

d/ -ressure + to &) bar


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e/ ;low rate 1 to >) microns

• Abrsi!e

a/ material B Al+"> #i7 ?lass beads 7rushed glass #odium bi carbonate

b/ shape B irregular:regular

c/ #ize B &) to 1) microns

d/ 4ass flow B ++) gm:min

• Crrier Gs

a/ 7omposition B Air, 7"+, 8+

b/ 6ensity B &.> kg:m>

c/ Felocity 1)) to ()) m:s

d/ -ressure + to &) bare/ ;low rate 1 to >) microns

• Abrsi!e Jet

b/ Felocity &)) to >)) m:s

c/ 4i!ing ratio B Folume flow rate of abrasives:Folume flow rate of gas

d/ #tandoff distance B #"6 ).1 to &1mm.

e/ Impingement angle B ) to ') deg.

• No++"ea/ 4aterial B $7:#apphire

b/ 6iameter B ).+ to ).2 mm

c/ Eife B >)) hours for sapphire, +) to >) hours for $7

Process c&bi"it#

&. 4aterial removal rate B ).)&1 cm>:min

+. 8arrow slots B ).&+ to ).+1mm ± ).&+mm

> #urface finishes ).+1 micron to &.+1 micron3 #harp radiuses up to ).+mm is possible

1. #teel up to &.1mm ,?lass up to .>mm is possible to cut

. machining of thin sectioned hard and brittle materials is possible .


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A&&"ictions

&. This is used for abrading and frosting glass more economically as

compared to etching or grinding

+. 7leaning of metallic smears on ceramics, o!ides on metals, resistive

coating etc.

>. A%4 is useful in manufacture of electronic devices , drilling of glass

wafers, de burring of plastics, making of nylon and Teflon parts permanent

marking on rubber stencils, cutting titanium foils

3. 6eflating small castings, engraving registration numbers on toughened

glass used for car windows

1. Csed for cutting thin fragile components like germanium, silicon etc.

. @egister trimming can be done very easily and micro module fabrication

for electrical contact , semiconductor processing can also be done effectively.

(. Csed for drilling , cutting , debarring etching and polishing of hard and

brittle materials.

2. 4ost suitable for machining brittle and heat sensitive materials like glass,

quartz, sapphire , mica , ceramics germanium , silicon and gallium.'. It is also good method for debarring small hole like in hypodermic needles

and for small milled slots in hard metallic components.

A(!nt*es


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-article size in microns/ #urface roughness in microns/

&) ).&1+ to ).+)>+1 to +( ).>11 to ).(1

1) 1) ).'1 to &.+(

&. igh surface finish can be obtained depending upon the grain sizes

+. 6epth of damage is low around+.1 microns/

>. It provides cool cutting action, so it can machine delicate and heat

sensitive material

3. -rocess is free from chatter and vibration as there is no contact between

the tool and work piece

1. 7apital cost is low and it is easy to operate and maintain A%4.

. Thin sections of hard brittle materials like germanium, mica, silicon, glass

and ceramics can be machined.

(. It has the capability of cutting holes of intricate shape in hard materials.

Dis(!nt*es ,-i$ittions


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&. Eimited capacity due to low 4@@. 4@@ for glass is 3) gm:minute

+ Abrasives may get embedded in the work surface, especially while

machining soft material like elastomers or soft plastics.

>. The accuracy of cutting is hampered by tapering of hole due to

unavoidable flaring of abrasive jet.

3. #tray cutting is difficult to avoid

1. A dust collection system is a basic requirement to prevent atmospheric

pollution and health hazards.

. 8ozzle life is limited >)) hours/

(. Abrasive powders cannot be reused as the sharp edges are worn and

smaller particles can clog the nozzle.

2. #hort standoff distances when used for cutting, damages the nozzle.

Mc)inin* c)rcteristics

;ollowing are the A%4 process criteria

&. 4aterial removal rate

+. ?eometry and surface finish of work piece

>. $ear rate of the nozzle-rocess criteria are generally influenced by the process parameters

The characteristics of above process parameters on process criteria are as

follows


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.. Effect of brsi!e f"o/ rte n( *rin si+e on MRR

It is clear from the figure that at a particular pressure 4@@ increase

with increase of abrasive flow rate and is influenced by size of abrasive

particles. *ut after reaching optimum value, 4@@ decreases with ;urther

increase of abrasive flow rate. This is owing to the fact that 4ass flow rate of

gas decreases with increase of abrasive flow rate and hence mi!ing ratio

increases causing a decrease in material removal rate because of decreasing

energy available for erosion.

01 Effect of e2it *s !e"ocit# n( brsi!e &rtic"e (ensit#

The velocity of carrier gas conveying the abrasive particles changes

considerably with the change of abrasive particle density. The e!it velocity of

gas can be increased to critical velocity when the internal gas pressure is

nearly twice the pressure at e!it of nozzle for the abrasive particle density is

zero. If the density of abrasive particles is gradually increased e!it velocity


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will go on decreasing for the same pressure condition. It is due to fact that

9inetic energy of gas is utilized for transporting the abrasive particle.

31 Efect of Mi2in* rtio on MRR

Increased mass flow rate of abrasive will result in a decreased velocity of

fluid and will thereby decrease the available energy for erosion and

ultimately the 4@@. It is convenient to e!plain to this fact by term 4IGI8?

@ATI". This is defined as


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41 Effect of No++"e &ress're on MRR

The abrasive flow rate can be increased by increasing the flow rate of the

carrier gas. This is only possible by increasing the internal gas pressure as

shown in the figure. As the internal gas pressure increases abrasive mass

flow rate increase and thus 4@@ increases. As a matter of fact, the material

removal rate will increase with the increase in gas pressure

9inetic energy of the abrasive particles is responsible for the removal of

material by erosion process. The abrasive must impinge on the work surface

with minimum velocity for machining glass by #I7 particle is found to be

around &1)m:s.


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51 Stn( off (istnce.

Standoff distance is defined as the distance between the face of the nozzle

and the work surface of the work. SOD has been found to have considerable

effect on the work material accuracy. A large #"6 results in flaring of

jetwhich leads to poor accuracy. It is clear from figure that 4@@ increase

with nozzle tip distance or #tandoff distance up to certain distance and then

decreases. -enetration rate also increases with #"6 and then decreases.

6ecrease in #"6 improves accuracy, decreases kerfs width, and reduces

taper in machined groove. owever light operation like cleaning, frosting etc

are conducted with large


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#"6. #ay &+.1 to (1mm/

Materia remoa modes in A&M

Followin/ assumptions are made in deri0in/ the %aterial remo0al models for

AJ%2

2 Abrasi0e are spheri)al in shape and ri/id

;2 6ineti) ener/* of parti)le is )ompletel* used to )ut the material

B2 $rittle material are )onsidered to fail due to brittle fra)ture and fra)ture of

0olume

is )onsidered to be hemispheri)al with diameter equal to )hordal len/th of


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indentation

2 For Du)tile material 0olume of material remo0al is assumed to be equal to

indentation 0olume due to parti)ulate impa)t2

Abrasi0e parti)les are assumed to be spheri)al in shape ha0in/ diameter d/2

From the /eometr*


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DESCRIPTION OF COMPONENTS

Abrsi!e De"i!er# S#ste$

A simple fi!ed abrasive flow rate is all that


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F'n($ent" "i$ittion of tr(ition" CNC contro" s#ste$s1

istorically, water jet and abrasive jet cutting tables have used traditional

787 control systems employing the familiar machine tool H?code.H

owever, there is a rapid movement away from this technology for abrasive

jet systems, particularly those for shortrun and limited production machine

shop applications. ?code controllers were developed to move a rigid cutting

tool, such as an end mill or mechanical cutter. The feed rate for these tools is

generally held constant or varied only in discrete increments for corners and

curves. Dach time a change in the feed rate is desired programming entry

must be made. A water jet or abrasive jet definitely is not a rigid cutting

tool using a constant feed rate will result in severe undercutting or taper on

corners and around curves. 4oreover, making discrete step changes in feed

rate will also result in an uneven cut where the transition occurs. 7hanges in

the feed rate for corners and curves must be made smoothly and gradually,

with the rate of change determined by the type of material being cut, the

thickness, the part geometry and a host of nozzle parameters. The control

algorithm that computes e!actly how the feed rate should vary for a givengeometry in a given material to make a precise part. The algorithm actually

determines desired variations in the feed rate every ).)))1H ).)&+ mm/

along the tool path to provide an e!tremely smooth feed rate profile and a

very accurate part. Csing ?7ode to convert this desired feed rate profile

into actual control instructions for the servo motors would require a

tremendous amount of programming and controller memory. Instead, the

power and memory of the modern -7 can be used to compute and store theentire tool path and feed rate profile and then directly drive the servomotors

that control the G= motion. This result in a more precise part that is

considerably easier to create than if ?code programming were used.

013 P'$&:


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Intensifier &'$&s

Darly ultrahigh pressure cutting systems used hydraulic intensifier pumps

e!clusively. At the time, the intensifier pump was the only pump capable of

reliably creating pressures high enough for water jet machining. An engine

or electric motor drives a hydraulic pump which pumps hydraulic fluid at

pressures from &,))) to 3,))) psi ,')) to +(,)) k-a/ into the intensifier

cylinder. The hydraulic fluid then pushes on a large piston to generate a high

force on a smalldiameter plunger. This plunger pressurizes water to a level

that is proportional to the relative crosssectional areas of the large piston

and the small plunger. 7rankshaft pumps The centuriesold technology

behind crankshaft pumps is based on the use of a mechanical crankshaft to

move any number of individual pistons or plungers back and forth in a

cylinder. 7heck valves in each cylinder allow water to enter the cylinder as

the plunger retracts and then e!it the cylinder into the outlet manifold as the

plunger advances into the cylinder. 7rankshaft pumps are inherently more

efficient than intensifier pumps because they do not require a powerrobbing

hydraulic system. In addition, crankshaft pumps with three or more cylinders

can be designed to provide a very uniform pressure output without needing

to use an attenuator system. 7rankshaft pumps were not generally used in

ultrahigh pressure applications until fairly recently. This was because the

typical crankshaft pump operated at more strokes per minute than an

intensifier pump and caused unacceptably short life of seals and check

valves. Improvements in seal designs and materials, combined with the wide

availability and reduced cost of ceramic valve components, made it possible

to operate a crankshaft pump in the 3),))) to 1),))) psi +2),))) to

>31,))) k-a/ range with e!cellent reliability. The major breakthrough in the

use of such pumps for abrasive jet cutting.

Typical +):>) horsepower crank shaft driven triple! camp.


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D!perience has shown that an abrasive jet does not really need the full

),))) psi 3&3,))) k-a/ capability of an intensifier pump. In an abrasive

jet, the abrasive material does the actual cutting while the water merely acts

as a medium to carry it past the material being cut. This greatly diminishes

the benefits of using ultrahigh pressure. Indeed many abrasive jet operators

with ),))) psi 3&3,))) k-a/ intensifier pumps have learned that they get

smoother cuts and more reliability if they operate their abrasive jets in the

3),))) to 1),))) psi +(,))) to >31,))) k-a/ range. 8ow that crankshaft

pumps produce pressures in that range, an increasing number of abrasive jet

systems are being sold with the more efficient and easily maintained

crankshafttype pumps.

+.3 8ozzles

All abrasive jet systems use the same basic twostage nozzle as shown in

the ;I?. ;irst, water passes through a smalldiameter jewel orifice to form a

narrow jet. The water jet then passes through a small chamber where a

Fenturi effect creates a slight vacuum that pulls abrasive material and air

into this area through a feed tube. The abrasive particles are accelerated bythe moving stream of water and together they pass into a long, hollow

cylindrical ceramic mi!ing tube. The resulting mi! of abrasive and water

e!its the mi!ing tube as a coherent stream and cuts the material. It


35/45

wear is caused by the erosive action of the abrasive stream as it enters the

side of the chamber and is entrained by the waterjet. #ome nozzles provide

a carbide liner to minimize this wear. -recise alignment of the jewel orifice

and the mi!ing tube is critical to mi!ing tube life. This is particularly true for

The relatively small diameter ).)>)H ).(1 mm/.

Mi2in* T'be

The mi!ing tube is where the abrasive mi!es with the highpressure water.

The mi!ing tube should be replaced when tolerances drop below acceptable

levels. ;or ma!imum accuracy, replace the mi!ing tube more frequently. The

size of the kerfs and cutting performance are the best indicators of mi!ing

tube wear.

Motion S#ste$ :

G= Tables

In order to make precision parts, an abrasive jet system must have a

precision G= table and motion control system. Tables fall into three general

categories5

;loormounted gantry systems with separate cutting tables Integrated table:gantry systems

;loormounted cantilever systems with separate cutting tables

Dach type of system has its benefits and drawbacks.

.1F"oor6$o'nte( *ntr# /it) se&rte c'ttin* tb"e

A floormounted gantry with a separate cutting table is the most common

approach used by water jet system manufacturers. A framework that

supports the G= motion system is secured directly to the floor and straddles

a separate cutting table and catcher tank. The nozzles/ is mounted to a

carriage which moves along a gantry beam that straddles the table. The

gantry beam is supported on each end by a guide system and is moved by

ball screws, rack and pinion assemblies or drive belts located at each end.

The parallel drive mechanisms are either operated by two electronically


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coupled drive motors or by a single motor driving a mechanicallycoupled

drive system.

01Inte*rte(tb"e,*ntr# s#ste$

The integrated table:gantry system is very similar to the traditional gantrysystem previously described, e!cept that the guides for the gantry beam are

integrated into the cutting table. *ecause of this the G= motion system and

the material support table are part of the same overall structure and

unwanted relative motion between them is eliminated. In this type of

system, the floor is not a vital part of the system structure. This system is

typically more accurate than the more traditional separate gantry and table.

31F"oor6$o'nte( cnti"e!er s#ste$ /it) se&rte c'ttin* tb"eThis type of system uses a floormounted Ga!is and a cantilevered =a!is

mounted to the Ga!is carriage. The nozzle mounts to a carriage on the =

a!is. The cutting table is totally separate from the G= motion structure.

7OR8ING

A typical abrasive jet machining center is made up of the following

components5

igh pressure water starts at the pump, and is delivered through specialhigh pressure plumbing to the nozzle. At the nozzle, abrasive is typically/introduced, and as the abrasive:water mi!ture e!its, cutting is performed.

"nce the jet has e!ited the nozzle, the energy is dissipated into the catch

tank, which is usually full of water and debris from previous cuts. The motionof the cutting head is typically handled by an G : =a!is structure. 7ontrol of

the motion is typically done via a computer following the lines and arcs froma 7A6 drawing.

AJM FEATURES

"btainable tolerances5

=ou need a machine with good precision to get precision parts, but there are

many other factors that are just as important. A precise machine starts with


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a precise table, but it is the control of the jet that brings the precision to the

part. A key factor in precision is software not hardware. This is also true for

cutting speed. ?ood software can increase cutting speeds dramatically. This

is because it is only through sophisticated software that the machine can

compensate for a Hfloppy toolH made from a stream of water, air, and

abrasive. "btainable tolerances vary greatly from manufacturer to

manufacturer. 4ost of this variation comes from differences in controller

technology, and some of the variation comes from machine construction.

#ignificant advances are made in the control of the process allowing for

higher tolerances.

Mteri" to $c)ine

arder materials typically e!hibit less taper, and taper is a big factor in

determining what kind of tolerances you can hold. It is possible to

compensate for taper by adjusting the cutting speed, and:or tilting the

cutting head opposite of the taper direction.

Mteri" t)ic9ness

As the material gets thicker, it becomes more difficult to control the behavior

of the jet as it e!its out the bottom. This will cause blowout in the corners,and taper around curves. 4aterials thinner than &:3H mm/ tend to e!hibit

the most taper which is perhaps the opposite of what you might e!pect./,

and with thicker materials, the controller must be quite sophisticated in

order to get decent cuts around comple! geometry.

Acc'rc# of tb"e

"bviously, the more precise is the positioning the jet , the more precise will

be the machine part.

Stbi"it# of tb"e

Fibrations between the motion system and the material, poor velocity

control, and other sudden variances

in conditions can cause blemishes in the part Hwitness marksH/,


38/45

The hardware that is out there varies greatly in stability and susceptibility to

vibrations. If the cutting

head vibrates relative to the part ,the part will be ugly.

Contro" of t)e brsi!e et

*ecause your cutting tool is basically a beam of water, it acts like a Hfloppy

toolH. The jet lags between where it first enters your material and where it

e!its.

MACHINING ASPECTS

.1Aro'n( c'r!es

As the jet makes its way around a radius, the jet down, and let the tail catchup with the head. And : or tilt the cutting head to compensate/

01Insi(e corners

As the jet enters the corner, the traverse speed must slow down to allow the

jets tail to catch up. "therwise the tail lag will cause the corner to Hblow outH

a little. As the jet e!its the corner, the feed rate must not be increased too

quickly, otherwise the jet will kick backend damage the part.

31Fee( rte:$hen the jet slows down, its kerf width grows slightly.

41Acce"ertion:

Any sudden movement like a change in feed rate/ will cause a slight

blemish as well. Thus for highest precision it is necessary to control the

acceleration as well as feed rate.

51 No++"e Foc's

#ome nozzles produce more taper than others. Eonger nozzles usually

produce less taper. #maller diameter nozzles also produce less taper. olding

the nozzle close to the work piece produces less taper as well.


39/45

;1 S&ee( of c'ttin*

Typically, the slower the cutting, the higher the tolerance. This is because as

the cutting is slowed down, the surface finish improves, and the taper begins

to disappear. owever in some cases it is possible to slow the cutting down

so much that tolerances begin to get worse due to reverse taper.

H : ).)(mm/. Eikewise, it is possible to make

ultrasmall abrasive jet nozzles, but they are problematic.

>1 Consistenc# of P'$& Press're

Fariations in water jet pump pressure can cause marks on the final part. It is

important that the pump pressure vary as little as possible while machining

is in progress to prevent these. This becomes an issue only when lookingfor better than K.))1H ).&+1mm/ tolerances, however/. Typically it is older

Intensifier type pumps that e!hibit this problem. #ome newer intensifiers,

and as far as I know all crankshaft driven pumps have smoother pressure

delivery, and this is not an issue.


40/45

.?1 C'ttin* s&ee(s:

Ideally, you want to make the most precise part possible in the least amount

of time, and for the least amount of money. 7utting speeds are a function of

the material to cut, the geometry of the part, the software and controller

doing the motion, the power and efficiency of the pump making the

pressure, and a few other factors such as the abrasive used5 ere are the

primary factors that determine cutting speed5 4aterial being cut And how

thick it is/

Hr(ness: ?enerally speaking, harder materials cut slower than soft

materials. owever, there are a lot of e!ceptions to this. ;or e!ample,

granite, which is quite hard, cuts significantly faster than 7opper, which is

quite soft. This is because the granite easily breaks up because it is brittle. It

is also interesting to note that hardened tool steel cuts almost as quickly as

mild steel. Though Habsolute blackH granite, which is tough as nails, actually

cuts a bit slower than copper./

T)ic9ness: The thicker the material, the slower the cut. ;or e!ample, a part

that might take & minute in

&:2H >mm/ steel, might take a half hour in +H 1)mm/ thick steel, andmaybe +) hours in &) inch +1)mm/ thick steel.

Geo$etr# of t)e &rt

It is necessary to slow the cutting down in order to navigate sharp corners

and curves. It also takes additional time to pierce the material. Therefore,

parts with lots of holes and sharp corners will cut much slower than simpler

shapes.

A6FA8TA?D# "; A*@A#IFD %DT5

a/ D!tremely fast setup and programming

8o tool changes required, so there is no need to program tool changes or

physically qualify multiple tools.


41/45

;or some systems, programming simply involves drawing the part. If you

customer gives you that drawing on disk, half the battle is won. This means

that for some machines/ you can make good money off single part and low

volume productionL

b/Fery little fi!ture for most parts

;lat material can be positioned by laying it on the table and putting a couple

of &) lb weights on it. Tiny parts might require tabs, or other fi!turing. At

any rate, fi!ture is typically not any big deal.

4achine virtually any +6 shape and some >6 stuff/

Including tight inside radii, 4ake a carburetor flange with holes drilled and

everything.

c/Fery low side forces during the machining

This means you can machine a part with walls as thin as .)+1H ).1 mm/

without them blowing out. This is

"ne of the factors that make featuring is so easy. Also, low side forces allow

for close nesting of parts, and 4a!imum material usage.

d/Almost 8o heat generated on your part

=ou can machine without hardening the material, generating poisonousfumes, recasting, or warping. =ou can machine parts that have already been

heat treated with only a tiny, tiny decrease in speed. "n

-iercing +H 1)mm/ thick steel, temperatures may get as high as &+)

degrees ; 1) 7/, but otherwise 4achining is done at room temperature.

Aerospace companies use abrasive jets a lot because of this.

e/8o start hole required

$ire D64, eat your heart out. #tart holes are only required for impossible topierce materials. #ome -oorly bonded laminates are about the only

materials I can think of offhand/

f/4achine thick stuff

This is one huge advantage Abrasive jets have over lasers.


42/45


43/45

-rogramming tool changes. -rogramming, #etup and 7lean up time is

reduced significantly, meaning you make more money because you can turn

more parts faster.

-IMITATIONS OF ABRASIVE JET5

6espite their simple design, abrasive jet nozzles can be troublesome at

times. There are many designs, but they share the same problems5

#hort life of an e!pensive wear part5 The mi!ing tube. Eike I said, the

abrasive jet can cut through just about anything including itself. This will

be a large part of your operating cost. 4ore on operating cost later/

"ccasional plugging of mi!ing tube5 Csually caused by dirt or large

particles in abrasive. This used to be a big problem with abrasive jet

nozzles, but not so much anymore./

$ear, misalignment, and damage to the jewel.

CONC-USION

The better performance, and the applications presented above statements

confirm that A*@A#IFD %DT 4A7I8I8? A%4/ will continue to e!pand.


44/45

Industry is convinced that the large aerospace segment will take off in near

the future, together with other segments that are currently showing interest

in A%4 method. ;rom operator e!periences the abrasive jets are capable of

anywhere from ).1mm).)+1mm precision. igh precision manufacturing

needs can be met by using A%4 method. 8ewer machines are capable of >6

machining thus making it an important in specialty manufacturing. The new

softwareMs used will minimize time and investments, thereby making it

possible for more manufacturers of precision parts to install A%4 centers .

@D;D@D87D#

&. -rocesses and 4aterials of 4anufacture by @.A. EI86*D@?

+. #D4I8A@ T"-I7 ;@"45 www.edufive.com:seminartopics.html


45/45

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