26756896 a Grinding System

8/14/2019 26756896 a Grinding System

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A Grinding System works on four factors working in tandem:

• Abrasive Product Factor,

• Machine Tool Factor,

• ork Material factor and

• !"erational Factor#

All these factors working together at o"timum efficiency results in "arts with re$uired Surface $uality

resulting into com"onents "erformance at o"timum cost#

%ust consider: A grinding wheel lower in "rice may be giving more no of com"onents but with a higher &

re'ection# Though the grinding cost "er com"onent may a""ear low, the total cost of such an o"eration is

definitely high# (esides the cost of re'ections, the cost of time s"end in checking and segregating

re'ections, dressing cost ) all of this considered together will show a much higher cost incurred in such

grinding system#

What is Total Cost of Grinding System?

*n any Grinding System, the Total +ost is the summation of:

• Abrasive +ost heel "rice - Parts "er heel

• Machine +ost Machine hour rates - Parts "er hour

• .abor +ost .abor hour rates - Parts "er hour

• /ressing +ost /resser Price - Parts "roduced "er dresser

• /owntime +ost 0Time of downtime1 2 0Machine 3 .abor hour

4ates1 - Parts "er downtime#

• 5nergy +ost 05nergy "er hour1 2 Power tariff - Parts "er hour#

A"art from these $uantifiable "arameters, the Total cost also includes factors like

• 4e'ection cost

• *P-in6"rocess material on sho" floor#

• Abrasive *nventory carrying cost

• Possible thru6"ut increase#

Most of our efforts on im"rovisation in a Grinding "rocess are focused on im"roving one of the following

)

• Parts "er wheel

• Parts "er dress• Productivity etc#

*t is very well "ossible that a Grinding wheel with higher initial "rice thereby higher Abrasive cost "er

com"onent will still result in lower Total cost "er com"onent ) which finally drives the "rice and margins

for a "roduct#

Tools to optimize the Abrasive Cost:

Field Instrumentation System

The technical out"ut from F*S can be collected and analysed to arrive at the 5conomic as"ects of

Grinding# These economic as"ects then hel"s us to arrive at the 5conomic out"ut i#e Total +ost of

Grinding system#

http://www.grindwellnorton.co.in/GrindingTech/gt_FIS.htm

http://www.grindwellnorton.co.in/GrindingTech/gt_FIS.htm



o! to "al"ulate Cost per "omponent?

At Grindwell 7orton ltd# e have arrived at a table, which hel"s us to arrive at the cost "er com"onent

considering all the as"ects of the grinding system simultaneously# for more details "lease mail to:

charu#'oshi8saint6gobain#co#in

The Field *nstrumentation System 0F*S1 is a tool develo"ed by Saint Gobain Abrasive9s iggins Grinding

Technology +enter 0GT+1, orcester to offer solutions to customers using the conce"t of ;SystemA""roach9# The System A""roach utili<es all "arts of the grinding system to influence the microsco"ic

interactions of the "rocess# *t integrates science-engineering-management as"ects of the "rocess

simultaneously thereby o"timi<ing the out"uts from a System ) both Technical and 5conomical#

Today, ma2imi<ing System out"uts is attem"ted thru Trial and 5rror a""roach ) using only the =uality of

com"onents "roduced as the source of information# The F*S gives an insight into the ;Process9 and hence,

aids the user to ado"t a more scientific a""roach to Process o"timi<ation# F*S +ollects and analyses the

macrosco"ic variables like "ower consumed, slide velocity, "art si<e change, wheel behavior v-s time

ela"sed# This collection and analysis of macrosco"ic data hel"s to understand the microsco"ic

interactions taking "lace at the grinding <one# aving established thisThese macrosco"ic variables can

then be controlled to get the desired microsco"ic interaction and thereby desired "erformance fromgrinding system#

The F*S consists of hardware for measurement of "ower and slide "osition with res"ect to time and a

software 0 develo"ed by GT+ 1 to analy<e these signals#

The F*S has been used and found beneficial for the following )

>#Grinding Cy"le #ptimization $ The F*S can be used to study the "ower drawn by the "rocess at

different Material removal rates 0M441# This can be used to find the forces in grinding ) Tangential and

7ormal# Measuring deflections in the system 0 using "rocess with and without s"ark6out 1 and using the

forces in grinding, the System Stiffness can be calculated# The System Stiffness decides the "art si<e

re"eatability and drives the +"k values in an o"eration# +ombining Stiffness values along with relation

between "ower and M44, new grinding cycles can be designed to yield )

a# (etter Process +a"ability#

b# *m"roved Productivity#

?#%valuation of &e! produ"ts ' *n any "rocess, change of any in"ut variable has an im"act on the

"rocess, which is generally inter"reted from the out"ut "art $uality ) in the absence of measurement of

"rocess# The F*S gives an insight into the effect of in"ut variable on microsco"ic interactions in the

"rocess and hence, "rovides better insight on 4eal "erformance of any 7ew "roduct#

@#Complaint Analysis ' The FIS "an be used to understand

a# Slide Position re"eatability#

b# 4e"eatability of feed rates 0 rate of change of dis"lacement 1

c# ariations in grinding "ower

d# ariations in *dle "ower

This hel"s in understanding of 7on ) "erformance of a "roduct and can attribute the reasons to

the right factor#

The F*S has been in use in *ndia for the last B years and has been found very beneficial at

all accounts where it was used#

mailto:[email protected]

mailto:[email protected]



What Is Centerless Grinding?

enterless grinding is an !/ grinding "rocess# *t differs from other

ylindrical "rocesses in that the work "iece is not mechanically

onstrained# *tCs the relationshi" among these three basic com"onentsD

• Grinding wheel,

• 4egulating wheel and• ork blade

Why Centerless Wor(s

the work "iece rests on a flat work blade that is on center with the

gulating and grinding wheels, the contact "oints form three sides of a

$uare# As the "art is ground in this setu", any high s"ot on the work "iece

ill shift the work slightly on the blade, allowing the grinding wheel to

ut a directly o""osite low s"ot# !ver time this setu" will create three

bes on the work "iece that may be dimensionally accurate but far from

und#

Setting an angled work blade so

it slo"es toward the regulating

wheel and su""orts the work

"iece centerline above the

centerline of the regulating and

grinding wheels is how the

centerless o"eration is able to

generate roundness# *n this setu" if a high s"ot comes in contact with either

the blade or the regulating wheel, it does not create a directly o""osite lows"ot because of the angle created between the centerlines of the wheels and

work "iece#

*nstead of grinding a lobe sha"e in the work "iece, the high s"ot is gradually

reduced by the action of the grinding wheel# So rather than creating a low

s"ot on the "eri"hery of the work e$ual to the high s"ot, the grinding wheel

generates a "ro"ortionally smaller low s"ot at its contact with the work

"iece#

The angle of the work blade hel"s kee" the work "iece in contact with and

under the control of the slower rotating regulating wheel to resist anyndency to Es"in u"E to the s"eed of the grinding wheel# *n some cases, a s"in6u" can take a work "iece from H

m to near IH,HHH r"m in the blink of an eye#

etup )eys

• +enters of grinding wheel J regulating wheel should be in the same line

• ork blade is inclined towards the regulating wheel# Angle should be in between H to B degK 0best is @H deg1

stee"er blade means faster rounding action, for large J longer work shallow blade angle is best#

• +enter eight of the 'ob should be half the dia of 'ob from centerline of grinding J regulating wheel and

ma2imum >H mm above the center

• Too high ) will "roduce chatter marksK Too low6 will "roduce work out of roundness

• 4egulating wheel runs at a slower s"eed than grinding wheel# (est s"eed of regulating wheel is @H 4PM# *t is

Setting the centerline of a work "iece on

the centerlines of the grinding and

regulating wheels will not "roduce

rounding# *n this setu", any high s"ot will

create a diametrically o""osite low s"ot#

!ver time, the work "iece will look like

the e2aggerated sha"e shown at the

bottom#

o enable the centerless grinding

rocess to create rounding action on the

work "iece, it must be "laced above the

enterline of the wheels# *n this setu",

igh s"ots no longer create

iametrically o""osed low s"ots#

nstead, the high s"ots are ground and a

radual rounding of the work "iece

akes "lace#



used to control the s"eed of revolution J through feed of the work "iece#

• (est blade for resisting wear is tungsten carbide but this can scour the work when

grinding with softer materials# *n this case a cast iron blade should be used#

inds #f Centerless Grinding

he two most common centerless grinding techni$ues are infeed and thrufeed#

The work "iece is "laced between the wheels, and the grinding

cycle begins# After s"ark6out, the finished "art is removed and

the ne2t one goes in# *nfeed centerless grinding is analogous to

"lunge grinding on a center6ty"e machine in that the work"iece

is static in the a2ial direction# For continuous, "roduction6ty"e

centerless grinding, the thrufeed method is very effective#

Thrufeed grinding is accom"lished by "assing the work"iece

between the grinding and regulating wheel# (asically, raw

material goes in one side of the grinding <one, and finished

work"ieces come out#

The work is driven a2ially between the wheels by inclination of

the regulating wheel relative to the grinding wheel# (ecause all of the "oints to be ground

on the work"iece contact all the "oints on the wheels, this centerless grinding method is

best a""lied to straight cylindrical "arts without shoulders or other interfering features#

*n thrufeed grinding, the regulating wheel is inclined, creating a feed angle relative to the

grinding wheel# This feed angle allows the regulating wheel to "erform the dual "ur"ose

of rotating the work"iece against the grinding wheel and driving the work"iece across the

face of the grinding wheel#

he regulating wheel can be swiveled relative to the grinding wheel# owever, to do its 'ob and use the full width of

e grinding wheel, line contact between the work"iece, grinding wheel and regulating wheel must be mLaintained#

herefore, the regulating wheel must be trued with a diamond block located on the truing attachment# The diamond

ock is a device that ad'usts the diamond contact relative to the work"iece height above the grinding and regulating

heel centerline#

A $uick check to see if the thrufeed setu" is running correctly,E says Mr# Payne, Eis to look at the wear line across

e to" of the workblade# This line should be "arallel to the to" of the blade# *f it runs u"hill, from front to back, there

too much diamond block offset# *tCs the o""osite if the line runs downhill#E

hrufeed grinding is

enerally a""lied to

ontinuous, volumeroduction a""lications#

he wheels are dressed in

uch a way that the

work"iece is driven

hrough the cutting <one,

cross the face of the

rinding wheel# !ften a

ingle "ass is sufficient to

nish the work"iece#

*nfeed centerless

grinding is analogous to

"lunge grinding on a

center6ty"e machine#

The work is "laced on

the blade, and the

regulating wheel moves

into a "rogrammed feed

to begin the grind# The

work does not move

a2ially in this ty"e ofcenterless grinding#



Centerless Grinding For *ou?

raditionally, centerless grinding is found in sho"s involved in high

olume "roduction runs# ThatCs still an im"ortant segment for the

chnology#

ncreasingly, though, the advantages of centerless grinding, such as"id rounding and accuracy, are finding a""lication in sho"s that run

latively shorter 'ob lot si<es# The enabler for this is the a""lication

f +7+ and servomotor technology to the centerless grinding

achine# ith electromechanical actuation of slides, dressers and

uing attachments, setu" of the centerless machine is a much less

aunting and time consuming e2ercise# Moreover, the ability to

rogram grinding and regulating wheel contours using +7+ actuated

uing attachments eliminates the need for "rofile cams, which take

me to manufacture and are usually less accurate# +enterless grinding

successfully a""lied to manufacture of "arts ranging from

y"odermic needles to bowling balls# The "rinci"les of the "rocessmain the same regardless of the work"iece# .ike most metalworking

rocesses, centerless grinding is not magic, if you understand the

undamentals#

There are 6 factors which affect the choice of a grinding wheelspecification.

1. Material to be ground and its hardness.2. Amount of stock removal and finish required.3. Whether the grinding is done wet or dry.4. Wheel seed.!. Area of grinding contact.". #everity of the grinding oeration.

The drawing above

illustrates how the

diamond block can be

set to obtain true line

contact on the

regulating wheel# The

drawing on the right

illustrates a $uick check

to determine if the

thrufeed setu" is

correct# The wear lineon the workblade

should be "arallel to the

to" of the blade edge#



Abrasives+itrified grinding !heels: 6

itreous glass is used to bind traditional abrasive grains of Aluminum !2ide, +eramic Aluminum

!2ide and Silicon +arbide1 in a controlled "orosity matri2#

Aluminum o,ide: 6

• Aluminium !2ide abrasives are well suited for

Steels and ferrous metals

+arbon SteelsAlloy Steels

igh S"eed Steel

Annealed Malleable *ron

rought *ron

(ron<e

• *t is a bulky, hard grain and denoted by A

52am"les would include @A, IA, A, IBA, ?A etc#

the numbers are the wheel manufacturer9s way of denoting different ty"es of aluminum o2ide#

•

The biggest factor se"arating different ty"es of aluminum o2ide is a "ro"erty we callNfriability#O

Friability: 6 is a measure of the grain9s ability to fracture and break down during use#

• hite aluminum o2ide 0ty"ically a white wheel ) think a manual tool and cutter wheel1 is the

most friable ty"e of aluminum o2ide 0i#e# breaks down easiest1#

• A brown aluminum o2ide 0ty"ically a gray wheel ) think a bench grinder1 is the least friable

0i#e# the most durable1#

07ote this is the durability of the grain, not the wheel# All vitrified wheels are basically made of

glass and e2tremely fragile#1

Cerami" aluminum o,ide 0ceramic1: 6

is a high performance version of aluminum oxide. Grain manufactures basically fire ty"ical aluminum

o2ide grains to create an e2tremely hard resilient grain which has a "ro"erty we refer to as Nmicro

fracturing#O As the name suggests, each grain micro6fractures, allowing it to hold its sha"e and remain

shar"er for a longer "eriod of time than ty"ical aluminum o2ide# This ty"e of grain is sometimes

referred to as NSG,O which is Saint6Gobain-7orton9s trade name for this material# Ty"ically, grinding

wheel manufactures call out this ty"e of grain by de"icting a NGO in the first "osition of the marking

system# Generally the NGO will be accom"anied by a digit that designates the "ercentage of ceramic in

the wheel# Ty"ical mi2es are >H, @H and H& ceramic# The balance is usually a ty"e of friablealuminum o2ide# There is also an e2truded ceramic grain called NTargaO develo"ed and "atented by

Saint6 Gobain# *t9s used in high Material 4emoval 4ate 0M441 a""lications where coolant delivery

and chi" clearance are crucial#



• +eramic should be used for materials that are difficult to grind due to hardness and/or toughness.

• +eramic can also be used when you9re trying to e2tend wheel life, decrease cycle times by

increasing material removal rates, or increase the form holding capability of a "rocess#

• +eramic "erforms best when "ushed because the grains need high unit "ressure to "erform the

microfracturing "rocess# This is why ceramic does not work well when grinding soft materials

like aluminum# The grains would never break down, which leads to dulling, rubbing, and

ultimately loading of the wheel unless it was made e2ceedingly soft# !n the other hand, if the

wheel is too soft it will sim"ly release the ceramic aluminum o2ide grains and not allow the enduser to fully utili<e the higher "erformance grain#

• sing a ceramic wheel requires high quality diamonds in your truing device# +eramic has the

re"utation of "rematurely wearing diamond tools# That9s true under certain circumstances, but a

high $uality diamond tool or roll will greatly reduce this "roblem#

• Another "oint to remember is that due to the shar"ness of the grain, ceramic will ty"ically leave a

dee"er scratch than aluminum o2ide grains of the same si<e# Therefore it is sometimes necessary

to decrease grit si<e by one to reach re$uired finishes versus aluminum o2ide# 4emember the

following when considering ceramic wheels for your grinding o"eration:

o orse"ower and machine stiffness is critical to the "erformance of the grain

o

As a general rule, decrease dress de"th by H& when switching from aluminum o2idewheels

o /ue to shar"ness of grain, it9s sometimes necessary to move to a finer grit si<e vs#

aluminum o2ide to reach re$uired surface finishes

• Pay attention to total "rocess cost rather than wheel cost with ceramic grain wheels

-ir"onia Alumina: 6

*t is used for rough grinding o"eration, like cutoff o"eration#

Sili"on Carbide 0Si+1: 6

• Grey *ron

+hilled *ron

(rassSoft (ron<e

Aluminium

Stone

4ubber

+ast iron

7on6ferrous metals

7on6metallic materials .

• Traditionally, before diamond6grinding wheels were readily available, silicon carbide

wheels were the wheels of choice for grinding carbide6cutting tools#

•

heels containing silicon carbide grain are almost always either black or green in colorand will be ty"ically called out in the marking system by the letter N+#O Another way to

easily identify silicon carbide is sim"ly by looking at the wheel# heels containing silicon

carbide will Ns"arkleO when tilted to the light#

• A number of factors make silicon carbide uni$ue# Silicon carbide is e2tremely hard and

shar", like ceramic, but is also very friable# This "ro"erty allows silicon carbide to

"erform well on both e2tremely hard materials 0due to its shar"ness1 and e2tremely soft

materials 0due to its friability, or Nre6shar"eningO "ro"erty1# *t is $uite a versatile grain in

environments where the material is either too hard for aluminum oxide to "enetrate or

too soft to create an environment for aluminum oxide grains to breakdown#

Grit Size:Grit si<e is the second "osition in the grinding wheel marking system, and will ty"ically

range between BI and ??H on vitrified bonded abrasive wheels# 0There are uses for grits down to B



and u" to over IHH in various bonded abrasive a""lications#1 The lower the grit si<e number, the

larger the grain si<e# The chart below de"icts this relationshi":

A Grit

Grit size has a direct effect on the rate at which the material is removed as well as the scratch

depth that remains afterwards. The first things to consider when selecting a grit si<e are the re$uired

surface finish and any radiuses that need to be ground in the "art# The chart below is a good reference,

but it9s 'ust a starting "oint# These factors can vary de"ending on dressing and grinding "arameters#

As a rule, coarser grit is selected for fast6cutting action and fine grit where a high

finish is re$uired#

Grain .enetration*t9s also im"ortant to understand grain "enetration when considering grit si<e# *n a given

o"eration, the smaller the grit si<e the higher the unit "ressure "er grain, as illustrated below:S



ize

Avage .arti"le Siz

This hel"s understand the ne2t crucial "oint: Many users mistakenly move to a courser gritsi<e when burn is "resent on a ground com"onent, but that is the opposite of what they should doQ

Moving to a finer grain can help alleviate a burn. (urns are often caused by rubbing of the grain

on the ground surface# (y moving to a smaller grit si<e you create more unit "ressure on the grain,

therefore allowing for better grain "enetration into the material#

• A relatively fine grit6si<e works best on hard and brittle material#

• A coarser grit ca"able of taking heavier cuts can be used advantageously on soft and

ductile materials# To e2"lain, on hard materials the increased number of cutting "oints, on

the face of a moderately fine grit wheel 0Fig# >1 will remove stock faster than the fewer

cutting "oints "resented by a coarser wheel 0Fig# ?1# The larger abrasive grains in a coarser

grit wheel can not "enetrate as dee"ly into the hard work6"iece without burning it#

!n soft ductile materials, however, the larger grains "enetrate easily and "rovide the necessary

chi" clearance to minimise wheel loading 0Fig# @1 and heat generation#

Grade:

Grade is the measurement of the relative hardness of the grinding wheel# Manufacturers

create different grades by varying the ratio of bond to abrasive grain in the wheel# Grade is called

out by a letter in the @rd "osition of the marking system# The letter NAO would be the softest grade

and the letter NRO would be the hardest# (y ad'usting the grade, you allow the wheel to release

grains at an increased or decreased rate# Ty"ical "recision grinding o"erations using vitreous

bonded wheels will usually use a grade between / and M# The grade of the wheel affects its

material removal rate, as a softer wheel offers the constant "resence of new shar" grains and the

release of older dull grains# Grade also affects the form holding capability of the wheel# *t is

difficult to hold a tight "art form with a soft wheel grade# The chart below covers these "oints and

more:



A harder grade can be used on soft, easily "enetrated materials than on hard materials

which naturally tend to dull the wheel faster# owever, the softer grade wheel releases the dulled

grains more readily, enabling the new, shar" grains lying under it to do the work#

Stru"ture:

The structure of a grinding wheel is a measurement of its "orosity, or the amount of airrelative to other com"onents# Structure is re"resented by a number that generally ranges from B to

@H# The lower the number, the less "orous the wheel# A B, or I structure would be considered a

very dense wheel# At the other end of the s"ectrum, ?B ) @H structure wheels are very "orous#

Manufacturers ty"ically induce structures over an by "utting an additional ingredient into the

mi2 that will burn off during firing and leave small hollows in the wheel# Porosity can be

NengineeredO into the construction of a Targa wheel, which has an e2truded ceramic grain#

High porosity leads to better coolant delivery into the cut "lus better removal of the swarf

from the grind <one, so "orous wheels are ty"ically used in surface and cree"feed grinding

a""lications# The downside of a "orous wheel is shorter wheel life.



Grade/Stru"ture Shifts

Structure can affect wheel life "ositively or negatively# This creates a "roblem when

ad'usting more than one wheel "arameter at a time# *n general, shifting the structure by three

"oints is e$uivalent to one letter grade# So if you move from an N5O grade N>O structure to an NFO

grade in a N?>O structure you will have two wheels which act the same as regards hardness# The

below chart demonstrates this fact:

The bond ty"e is called out by the th "osition in the marking system#

• The vitrified call6out letter is almost always a N,O while the others vary de"ending on the

grinding wheel manufacturer#

• !ne of the most im"ortant things to remember when using vitrified grinding wheels is that

they are extremely fragile. The manufacturing "rocess is very similar to that of chinadinner "lates# *t is a glass bond fired in a kiln at high tem"eratures 0a""ro2imately ?@HH

F1 for a set time# As the wheel si<e increases, so does the Nburn time,O or length of time in

the kiln#

• itrified bonds wear by "ressure breaking the bond "osts in the grinding wheel# The

ma'ority of vitrified grinding wheel wear comes from the truing "rocess# This is why an

increase in "arts "er dress is directly related to an increase in wheel life# !ther key "oints

to remember about vitrified bonds versus other bonds:

52cellent resistance to abrasion from the "art

Good form holding ability

Free cutting bond 0"orosity1

52cellent ability to draw coolant into grind <one NSelf shar"eningO bond 0releasing of dull abrasive grains1

itrified bonded wheels are generally used for fast6cutting action and commercial finish#

4esinoid, 4ubber and Shellac bonded wheels "roduce the highest finish

0ond 1odifi"ation:

Abrasive Grain Grit Size Grade Stru"ture

0ond Type 0ond 1odifi"ation

2SG 34 ' 5 6 + .

The Ith and last "osition in the wheel marking system is what we call the bond

modification# This is basically the wheel manufacture9s way to internally identify the differences

in the bond system# *t designates, among other things, bond traits, s"eed limitations, and s"ecialty

bonds for s"ecific abrasives# And wheel manufacturers generally do not release the meanings of

each modification#



Whether the grinding is done wet or dryGenerally for "recision grinding, coolant is necessary# owever, in some cases 0e#g# Tool

4egrinding1 the "rocess may be dry, in which case a softer grade wheel may be necessary#

hereas for wet grinding, a one grade harder wheel can be used as the coolant reduces the

heat generated in grinding#

W%%5 S.%%7• The s"eed at which the grinding wheel is to be o"erated often dictates the ty"e of

bond#

• itrified (onded wheels should not be used at "eri"heral s"eeds over @@ meters

"er second e2ce"t for s"ecially designed wheels#

• Standard organic bonded wheels 0resinoid, rubber and shellac1 are used in most

a""lications of over @ meters u"to B meters "er second, and s"ecially designed

wheels for s"eeds u"to H meters "er second#

• The s"eed at which a grinding wheel revolves is im"ortant# Too slow a s"eed

means wastage of abrasive without much useful work achieved, whereas an

e2cessive s"eed may result in a hard grinding action and may introduce the danger

of breakage# ence the safe o"erating s"eed marked on the wheel or blotter, in

revolutions "er minute must never be e2ceeded#

• As a general rule, it is best to o"erate a grinding wheel at somewhere near the

s"eed recommended for a certain grinding o"eration# Some of the more common

o"erating s"eed guidelines for "articular ty"es of grinding wheels are listed below,

in surface meters "er second# A mild abrasive such as IA, @?A or @A is best



Con"lusion

The grinding wheel is a uni$ue "art of the grinding "rocess# Abrasive cost is ty"ically only

?6B& of the entire "rocess cost# (ut that ?6B& can affect more than >& of your "rocess cost by

im"roving cycle times, im"roving $uality, and combining o"erations# hen you look at the

grinding "rocess as a system you can "ermanently im"rove it, leading to meaningful savings: The

ty"e of savings that will hel" you com"ete in the global economy#



Surface Grinder

Different Grinding Processes



Grinding: IntroductionGrinding is a finishing process used to improve surface finish, abrade hardmaterials, and tighten the tolerance on flat and cylindrical surfaces by removing asmall amount of material. Information in this section is organized according to thesubcategory links in the menu bar to the left.

In grinding, an abrasive material rubs against the metal part and removes tinypieces of material. The abrasive material is typically on the surface of a wheel or beltand abrades material in a way similar to sanding. On a microscopic scale, the chip

formation in grinding is the same as that found in other machining processes. Theabrasive action of grinding generates excessive heat so that flooding of the cuttingarea with fluid is necessary.

Reasons for Grindingeasons for grinding are!

". The material is too hard to be machined economically. #The material mayhave been hardened in order to produce a low$wear finish, such as that in abearing raceway.%

&. Tolerances re'uired preclude machining. Grinding can produce flatnesstolerances of less than ().))&* mm #().)))" in% on a "&+ x "&+ mm #* x *in% steel surface if the surface is ade'uately supported.

achining removes excessive material.

Flat Surface GrindingThe figure below illustrates a typical flat surface grinding machine.

The figure above is of the horizontal spindle, reciprocating table type, as detailedbelow.

http://www.efunda.com/processes/machining/grind_tools.cfm

http://www.efunda.com/processes/machining/chip.cfm


http://www.efunda.com/processes/machining/grind_tools.cfm





Other Types of Flat Surface GrindingOther types of flat surface grinding machine configurations are shown below.



Surface Grinding Design Guidelines

". -s with other machining operations, set up changes should be minimized.This is possible if all flat ground surfaces are parallel and on the same side ofthe part.

&. agnetic chucks are typically used for holding down parts during surfacegrinding. If the part can be designed to be compatible with a magnetic chuck,convenience and throughput increase. se of a magnetic chuck re'uires aferrous #magnetic% material and a flat seating surface opposite the groundsurface.

/. Ground surfaces should be situated as high up above obstructions aspossible, as shown below.



Ground surfaces should be as continuous as possible and well supported since thegrinding wheel will be pressing down upon them.

Centered GrindingGrinding for surfaces of rotation #axially symmetric surfaces% can be eithercentered or centerless. 0entered grinding involves fixturing the part on a spindleaxis as it is ground, as illustrated below.

This configuration can be compared to fixturing a part on a lathe with or without a tail stock. The abrasive material is on a grinding

wheel that rotates in a direction such that rolling or sliding contact occurs where the wheel and work piece touch. 0entered grinding is

accurate and stable, but set$up takes time and through$put suffers.



Centered Grinding Part Design: External

". ndercuts should be avoided.

&. 1or inside corners, the best practice is to machine a relief at the corner priorto grinding so that a sharp ninety$degree male ob2ect can be placed in thecorner. This is illustrated below.

1or internal holes with sharp corners, the figure below illustrates recommended

practice.

/. 3lunge grinding is a centered form of grinding in which the wheel 4plunges4radially into the part. The four figures below illustrate good plunge$grindingdesign practices.

a. The figure below shows how inside radii merging with cylindricalsurfaces are to be avoided.



b. The illustration below shows how tapers and angular surfaces should bereplaced by straight surfaces if possible.

The illustration below shows how deep, narrow grooves are to beavoided. The tool re'uired has a thin, tall protrusion that breaks andwears easily and is not rigid.



c. The illustration below shows how complex surfaces are best avoided forplunge$ground parts.

Centered Grinding Part Design: Internal

". ndercuts should be avoided.

&. adii should be the same in order to simplify wheel dressing and minimizetool changes.

/. 5ole depth to diameter aspect ratio should be minimized. This is for the samereasons that bored holes are not too deep. -voiding length to diameter ratiosof more than six is a good practice.

6. If possible, blind holes should be avoided. 7lind holes restrict the flow ofcoolant.0ircumferential interruptions should be avoided. 8ven axial interruptionsshould be avoided.

*. -n option to consider is a hardened and ground liner. This option must beweighed against the tolerance build up and extra logistics involved.

-de'uate access for coolant flow should be provided. This can be difficult sincethe coolant shed by the rotating grinding wheel provides an effective 4curtain4which prevents coolant exchange

Three ain Types of Grinding



0enterless grinding is similar to centered grinding except that there is no spindle.This allows high through$put since parts can be 'uickly inserted and removed fromthe process. There are three main types of centerless grinding!". Through$feed grinding.

&. In$feed grinding.

@# 8nd$feed grinding.

Through!Feed GrindingIn through-feed grinding, the part rotates between the grinding wheel and aregulating wheel as shown below.

1or through$feed grinding, one or both wheels of the centerless grinding machine

are canted out of the horizontal plane, as shown below. This imparts a horizontalvelocity component to the work piece, so that outside feed mechanisms are notnecessary.

The grinding wheel is canted with respect to the other two axes so that acomponent of its surface velocity pushes the part in the direction shown below.This auto feeding characteristic is useful for rapidly processing many parts in 'uickse'uence.

7ecause of the axial movement, through$feed parts can only have right circularcylindrical ground surfaces. The wheel cannot be dressed to grind more complex

shapes. 7elow are parts produced with the through$feed centerless grinding process. -s canbe seen from the 'uantities produced, through$feed grinding is primarily a mass$

http://www.efunda.com/processes/machining/#through-feed_grinding

http://www.efunda.com/processes/machining/#in-feed_grinding

http://www.efunda.com/processes/machining/#end-feed_grinding

http://www.efunda.com/processes/machining/#through-feed_grinding

http://www.efunda.com/processes/machining/#in-feed_grinding

http://www.efunda.com/processes/machining/#end-feed_grinding



production process because of its high throughput.

In!Feed GrindingIn-feed grinding differs from through$feed grinding in that the part is not fed axiallyso that the ground surface does not need to be a right circular cylinder. Thegrinding wheel can be dressed to accomodate the part. Once the work piece part isin place, the grinding wheel is fed in radially. 7ecause of the set up time involved for each part, in$feed griding does not have thehigh throughput of through$feed grinding. In$feed grinding is illustrated below.

End!Feed GrindingIn end-feed grinding, the part moves in axially between the grinding wheels, stops

for grinding, and then moves out again. The wheel can be dressed to form morecomplex shapes, but the part can only get progressively smaller in diameter. 8nd$



feed grinding is illustrated below.

Centerless Grinding Guidelines

". The largest diameter of the workpiece should have the ground surface, ifpossible. This allows through$feed grinding.

&. The axial length of a centerless$ground workpiece should be at least e'ual tothe diameter. 9hort workpieces are more susceptible to surfaces that deviatefrom right circular cylindricity.

/. adii should be as uniform as possible in order to simplify wheel dressingand:or set up changes.

6. 1or a flat at the end of a shaft, it is preferable to incorporate a matching flaton the opposite side of the shaft. This will prevent a high spot from formingopposite the flat. -lternatively, the flat can be brought inboard so that theend is a complete cylinder, as shown below in the right$hand view.



5oles with diameter to depth ratios of over four should be avoided unless wideningof the mouth of the hole can be accomodated, as illustrated below.

*. -s the following diagram shows, internal grinding should allow for as large adiameter tool support as possible. This illustration shows a hole with anentrance that is smaller than that of the ground area.

;hen face$grinding turned surfaces, ground undercuts should be avoided. -s thefigure below shows, face undercuts re'uire specially$dressed grinding wheels that



are expensive to maintain and replace.

If at all possible, blind holes should be avoided. If a blind hole must beimplemented, the middle two geometries of the following diagram can help withgrinding.

9ome examples of dimensioned centerless$ground parts are shown in centerless

grinding

Grinding "heel O#erall ShapesIllustrated below are some common grinding wheel forms. Of course, any shape ispossible, but these shapes have evolved because of their utility and robust nature.

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<. The figure below illustrates how ends of in$feed ground parts need to beterminated for satisfactory results. The included angle of the pointy endshould be less than "&) degrees. If in$feed grinding is not used, ends ofcylindrical parts should not be ground.



Grinding "heel Dressings7elow are shown some typical grinding wheel dressing shapes. The dimensions arerecommended for grinding accuracy and wheel longevity.

26756896 a Grinding System

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