INTRODUCTION In the era of high competition, every ever y manufacturing industry want to increase their productivity, quality for satisfying their customer customer at the minimum production cost. Failure cost has the major role in the production p roduction cost. Hence the ideas of DRILL !!L !!L D"#$%!%&&R come in to picture 'y us. (ecause the main fault in the manufacturing industry, in production line the failure of drill 'it. )henever the wor* is perform on the +#+ the cause of failure of drill 'it is the difference in the composition of material in the another lot and when the operator wor*s at manual drilling machine the cause of failure may 'e over pressure or load applied ap plied 'y the operatorwor*er. Hence the implementation of our project can reduce or eliminate this failure, 'ecause with the help of drill tool dynamometer wor*er can see the load applied on the wor* piece and he can stop the machine or can change the wor* -material if the load e/ceed to the strength of drill 'it,so that the failure of drill 'it can 'e avoided.
1
$ strain gauge type drilling dynamometer and its major components.
2
TYPES OF DRILL MACHINES SR.NO.
DRILL MACHINE
1
0pright 1ensitive Drill 2ress
2
Radial $rm Drill 2ress
3
3ang Drill %achine
4
%ultiple 1pindle Drilling %achine
5
%icro Drilling %achine
6
urret ype Drilling %achine
3
APPLICATION
BASIC TYPES OF DRILLING MACHINES
Drilling machines or drill presses are one of the most common machines found in the machine shop. $ drill press is a machine that turns and advances adva nces a rotary tool into a wor* piece. he drill press is used primarily for drilling holes, 'ut when used with the proper tooling, it can 'e used for a num'er of machining operations. he most common machining operations performed on a drill press are drilling, reaming, tapping, counter 'oring, countersin*ing, and spot facing. here are many different types or configurations of drilling machines, 'ut most drilling machines will fall into four 'road categories4 upright sensitive, upright, radial, and special purpose.
Uprig! "#$"i!i%# &ri'' pr#""
4
he upright sensitive drill press -Figure 5 is a light6duty type of drilling machine that normally incorporates a 'elt drive spindle head. his machine is generally used for moderate6to6light duty wor*. he upright sensitive drill press gets its name due to the fact that the machine can only 'e hand fed. Hand feeding the tool into the wor* piece allows the operator to 7feel7 the cutting action of the tool. he sensitive drill press is manufactured in a floor style or a 'ench Fig(r# 1 Uprig! 1 Uprig! "#$"i!i%# &ri'' pr#""
style.
Uprig! &ri'' pr#"" he upright drill press -Figure 8 is a heavy duty type t ype of drilling machine normally incorporating a geared drive spindle head. his type of drilling machine is used on large hole6producing operations that typically involve larger or heavier parts. he upright drill press press allows the operator to hand feed or power feed the tool into the wor* piece. he power feed mechanism automatically advances the tool into the wor* piece. 1ome types of upright drill presses are also manufactured with
Fig(r# 2 Uprig! 2 Uprig! &ri'' pr#""
automatic ta'le6raising mechanisms.
5
R)&i)' )r* &ri'' pr#"" he radial arm drill press -Figure 9 is the hole producing wo r* horse of the machine shop. he press is commonly refered to as a radial drill press. he radial arm drill press allows the operator to position the spindle directly over the wor*piece rather than move the wor*piece to the tool. he design d esign of the radial drill press gives it a great deal of versatility, versatility, especially on parts too large to position easily. Radial drills offer power feed on the spindle, as well as an automatic mechanism to raise or lower the radial arm. he wheel head, which is located on the radial arm, can also 'e traversed along the arm, giving the machine added ease of use as well as versatility. Radial arm drill presses can 'e equipped with a trunion ta'le or tilting ta'le. his gives the operator the a'ility to drill intersecting or angular holes in one setup.
6
Fig(r# 3 R)&i)' )r* &ri'' pr#""
SPECIAL PURPOSE DRILL MACHINES here are a num'er of types of o f special purpose drilling machines. he purposes of these types of drilling machines vary. 1pecial purpose drilling machines include machines capa'le of drilling 8: holes at once or drilling holes as small as :.:5 of an inch.
G)$g &ri'' pr#""
7
he gang style drilling machine -Figure ; or gang drill press has several wor* heads positioned over a single ta'le. his type of drill press is used when successive operations are to 'e done. For instance, the first head may 'e used to spot drill. he second head may 'e used to tap drill. he third head may 'e used, along with a tapping head, to tap the hole. he fourth head may 'e used to chamfer. Fig(r# 4 G)$g 4 G)$g &ri'' pr#""
M('!i"pi$&'# &ri'' pr#""
8
he multiple spindle drilling machine is commonly refered to as a multispindle drill press. his special purpose drill press has many spindles connected to one main wor* head -Figure <. $ll of the the spindles are fed into the wor*piece at the same time. his type of drilling machine is especially useful when you have a large num'er of parts with many holes located close together.
Fig(r# 5 M('!i"pi$&'# 5 M('!i"pi$&'# &ri'' pr#""
Mi+r, &ri'' pr#"" he micro drill press is an e/tremely accurate, high spindle speed drill press. he micro drill press is typically very small -Figure = and is only capa'le of handling very small parts. %any micro drill presses are manufactured as 'ench top models. hey are equipped with chuc*s capa'le of holding very small drilling tools.
9
Fig(r# 6 Mi+r, 6 Mi+r, &ri'' pr#""
T(rr#! !-p# &ri''i$g *)+i$# urret drilling machines are equipped with several drilling heads mounted on a turret -Figure =. &ach turret head can 'e equipped with a different type of cutting tool. he turret allows the needed tool to 'e quic*ly inde/ed into position. %odern turret type drilling machines are computer6 controlled so that the ta'le can 'e quic*ly and accurately positioned.
Fig(r# 6 CNC 6 CNC !(rr#! !-p# &ri''i$g *)+i$#
10
TYPES OF DRILL BITS Sr.N,.
N)*# , T,,' Bi!"
1
ungsten +ar'ide Inserts
2
Roller +one 'its
Sp#+ii+)!i,$
&ach cone has teeth made of hard steel, tungsten6car'ide
3
1elf 1harpening (its
4
2oly +rystalline Diamonds -2D+
5
Fishing tools
11
DRILL TOOL SPECIFICATIONS I$+
M*
S#g*#$!
5;>
=
568.
<5=>
A
568.
9A>
5:
568.
B>
58
568.
C5=>
5;
568.
<A>
5=
568.
5A
568.
8:
568.
@A>
88
568.
5>
8<
568.
9:
568.
565;>
98
568.
569A>
9<
568.
5658>
9A
568.
;:
568.
;<
568.
569;>
12
8>
<:
568.
THE MECHANISM OF CUTTING $ssuming !rthogonal +utting 6 assumes that the cutting edge of the tool is set in a position that is perpendicular to the direction of relative wor* or tool motion. his allows allows us to deal with forces that act only in one plane.
)e can o'tain orthogonal cutting 'y ' y turning a thin walled tu'e, and setting the lath 'it cutting edge perpendicular to the tu'e a/is. #e/t, we can 'egin to consider cutting forces, chip thic*nesses, etc. First, consider the physical geometry of cut
13
#e/t, we assume that we are also measuring two perpendicular cutting forces that are horiEontal, and perpendicular to the figure a'ove. his then allows us to e/amine specific forces involved with the cutting. he cutting forces in the figure 'elow -Fc and Ft are measured using a tool force dynamometer mounted on the lathe.
14
1.2.1 F,r+# C)'+(')!i,$"
5.8.5.5 6 Force +alculations
15
he forces and angles involved in cutting are drawn 'elow,
Having seen the vector 'ased determination of the cutting forces, we can now loo* at equivalent calculations
16
he velocities are also important, and can 'e calculated for later use in power powe r calculations. he elocity elocity diagram 'elow can also 'e drawn to find cutting velocities.
17
$ final final note of interest to readers not completely co mpletely familiar with vectors, the forces Fc and Ft, are used to find R, from that two other sets of equivalent forces are found.,
1.2.1.2 / M#r+)$!0" F,r+# Cir+'# i! Dr)!i$g Op!i,$)' %erchantGs Force +ircle is a method for calculating the various forces involved in the cutting process. his will first first 'e e/plained with vector diagrams, these in turn will 'e followed 'y a few formulas. he procedure to construct a merchants force circle diagram -using drafting techniquesinstruments is,
18
5. 1et up /6y /6y a/is la'eled la'eled with with forces, forces, and and the origin origin in in the centre centre of the page. page. he scale should 'e enough to include 'oth the measured forces. he cutting force -Fc is drawn horiEontally, and the tangential force -Ft is drawn vertically. -hese forces will all 'e in the lower left hand quadrant -#ote4 square graph paper and equal eq ual / y scales are essential e ssential 8. Draw in the resultant -R of Fc and Ft. 9. Locate the centre of o f R, and draw a circle that encloses vector R. If done correctly co rrectly,, the heads and tails of all 9 vectors will lie on this circle. ;. Draw in the cutting tool in the upper right hand quadrant, ta*ing care to draw the correct ra*e angle - from the vertical a/is. <. &/tend the line that is the cutting face of the tool -at the same ra*e angle through the circle. his now gives the friction vector -F. =. $ line can now 'e drawn from the head of the friction vector, to the head of the resultant vector -R. his gives the normal vector -#. $lso add a friction angle -J 'etween vectors R an d #. $s a side side note recall that any vector can 'e 'ro*en down into components. herefore, mathematically, R K Fc Ft K F #. @. )e ne/t use the chip thic*ness, compared co mpared to the cut depth to find the shear force. o do this, the chip is drawn on ' efore and after cut. (efore drawing, select some magnification factor -e.g., 8:: times to multiply 'oth values 'y. Draw a feed thic*ness line -t5 parallel to the horiEontal a/is. #e/t draw a chip thic*ness line parallel to the tool cutting face. A. Draw a vector from the origin -tool point towards the intersection of the two chip lines, stopping at the circle. he result will 'e a shear force vector -Fs. $lso measure the shear force angle 'etween Fs and Fc. C. Finally add the shear force normal -Fn from the head of Fs to the head of R. 5:. 0se a scale and protractor to measure off all distances -forces and angles. he resulting diagram is pictured 'elow,
19
CONCEPT OF TOOL DYNAMOMETER he cuttin cutting g force force measur measureme ements nts allow in the past past to analyEe analyEe and develop develop accurate conventional cutting methods. #owadays with a constant demand for high precision machining oriented to high accuracy and even smaller dimensions also, the
20
deve develo lopm pmen entt of reli relia'l a'lee and sens sensit itiv ivee meas measur urin ing g inst instru rume ment ntss assu assume mess a wide wide importance. In fact they have a fundamental role in the analysis, optimiEation and monitoring of a machine processes, selecting machines, tools and materials. Force measurements are also fundamental for the definition of optimum cutting conditions, the 'rea*age 'ehavior of the micro end mills, the process of chip formation and how they influence the cutting forces and the machining process. +utting speed, depth of cut, feed rate, wor* piece material, tool material, cutting geometry, geometry, wear of the tool and cutting cutting fluid are the main factors determining the magnitude and direction of cutting forces. However the small diameter of the tools requires high rotational speeds to ahieve a reasona!le utting speed and material removal rate" #ith suh rotational speed$ in the order of ten thousand of rotation per minute$ the tool e%itation on the wor& piee has high frequen'" (his requires measuring sensors with a orrespondingl' high natural frequen' in order to avoid resonane" )oreover the fore pea&s are ontained in the range of few newtons"
1.1 GENERAL ASPECTS ASPECTS he term dynamometer refers to an instrument used to measure force. It can also
'e used to refer to a testing machine capa'le of applying force of a given precision. $ dynamometer dynamometer is composed composed of a transducer transducer comprising comprising a metallic metallic test specimen which receives the force to 'e measured and deforms elastically 'y the application of this force. In modern transducers such deformation -strain is communicated to a miniature electric electric circuit attached to the test specimen, specimen, resulting in a modificati modification on of the electric electric resistanc resistance. e. his resistance resistance variation variation is measured measured 'y the )heatston )heatstonee 'ridge method, where'y two legs of the electric circuit are supplied with an analog voltage, continuous or intermittent and an analogue voltage varia'le according to the force applied to the dynamometer is collected 'etween the two other legs in the circuit. he necessary equipment to supply voltage, collect and process the output signal and display usa'le values constitutes the electronic element connected to the transducer. radi raditi tional onal electr electroni onicc instru instrumen ments ts sta'il sta'iliEe iEed d and multim multimete eterr supply supply can 'e used. used.
21
ransduc ransducer er manufacture manufacturers rs have developed developed specific specific electronic electronic equipment equipment allowing allowing to optimiEe settings, measurement conditions and precision. he latest advances in the technique of dynamometers consist in integrating the electronic equipment associated to the digitaliEation of the signal and the transducer, so as to constitute a single device that powered 'y 88: , releases an output digital signal according to the force applied to the transducer. )hen the relationship 'etween the force applied to a dynamometer and the measur measureme ement nt of its output output signal signal cannot cannot 'e accura accurately tely determin determined ed 'y means means of a calculation, it is necessary to cali'rate the dynamometer, which consists in esta'lishing the e/act relationship 'etween the force applied to a dynamometer 6 input 6 and the electrical signal it releases 6 output. In essence, the operation consists in applying forces that can 'e accurately measured to a dynamometer and registering the values provided 'y the electronic equipment connected to the transducer. his operation is generally performed 'y applying the protocol esta'lished 'y the international standard I1! 9@=. his standard provides for a classification of the dynamometer according to precision criteria. criteria. he results of the cali'ration cali'ration of a dynamometer dynamometer lead to the determinati determination on of a mathematical polynomial of 8nd or 9rd degree, which allows calculating the value of the force applied to the dynamometer 'ased on the indication provided 'y the electronic equipment. he formula allowing calculating the level of uncertainty of this value is also part of the cali'ration. Dynamometers are often used as the sensitive element of weighing instruments. In this case, the shape of the test specimen is determined so as to o'tain an output signal that is e/actly proportional to the mass of the specimen placed on the of the instrument loading tray.
1.2 DYNAMOMETER $ dynamometer dynamometer or 7dyno7 for short is a machine machine used to measure torque and rotational speed speed -rpm rpm from which power which power produced produced can 'e measured.
1.2.1 D#"ig$ Cri!#ri,$" )$& M)!#ri)' , D-$)*,*#!#r
22
1ensitivity, 1ensitivity, rigidity, elasticity, elasticity, accuracy, easy cali'ration, cost and relia'ility in the cutting environment have 'een ta*en into account in designing the dynamometer. Dimensions, shape and material of dynamometer are considered to 'e effective factors on dynamic properties of the dynamometer. $ dynamometer essentially consists of an important ring element. he rigidity, high natural frequency, corrosion resistance and high heat conductivity factors were ta*en into consideration while selecting the ring materials. $lso, $lso, deformation under the load should conform c onform to that of strain gauges. 1.3 TYPES OF DYNAMOMETER SR.NO.
DYANMOMETER
SPECIFICATION
1
&ddy +urrent Dynamometer
2
%agnetic 2owder Dynamometer
3
Hysteresis (ra*e Dynamometer
4
&lectric %otor3enerator Dynamometer
5
1train 3auge ype Dynamometer
1"3"1 *dd' +urrent ,'namometer &+ dynamometers are currently the most common a'sor'ers used in modern chassis dyno. he &+ a'sor'ers provide the quic*est load change rate for rapid load settling. 1ome are air cooled, 'ut many require e/ternal water cooling systems. &ddy current dynamometers require the ferrous core or shaft, to rotate in the magnetic field to
23
produce torque. Due to this, stalling a motor with an eddy current dyno is usually not possi'le.
1"3"2 )agneti -owder ,'namometer $ magnetic powder dynamometer is similar to an eddy current d ynamometer, 'ut a fine magnetic powder is placed in the air gap 'etween the rotor and the coil. he resulting flu/ lines create 7chains7 of metal particulate which are constantly 'uilt and 'ro*en apart during rotation creating great torque. 2owder dynamometers are typically limited to lower R2% due to heat dissipation issues.
1"3"3 H'steresis ,'namometer Hysteresis dynamometers, such as %agtrol IncMs HD series, use a proprietary steel rotor that is moved through flu/ lines generated 'etween magnetic pole pieces. his design allows for full torque to 'e produced at Eero speed, as well as at full speed. Heat dissipation is assisted 'y forced air. Hysteresis dynamometers are one of the most efficient technologies in small dynamometers.
1"3"4 *letri )otor./enerator ,'namometer &lectric &lectric motorgenerator motorgenerator dynamom dynamomete eters rs are a specia specialiE liEed ed type of adjusta'le6 speed drives. he drives. he a'sorptiondriver unit can 'e either an alternating current -$+ current -$+ motor or a direct current -D+ current -D+ motor. &ither an $+ motor or a D+ motor can operate as a generator which is driven 'y the unit under test or a motor which drives the unit under test test.. )hen )hen equip equipped ped with with appr appropr opria iate te contr control ol units units,, elect electri ricc moto motor rge gener nerat ator or dynamometers can 'e configured as universal un iversal dynamometers. he control unit for an $+
24
motor is a varia'le6frequency drive and drive and the control unit for a D+ motor is a D+ drive. drive. In 'oth cases, c ases, regenerative control units can transfer power from the unit under und er test to the electric utility. )here permitted, the operator of the dynamometer can receive payment -or credit from the utility for the returned power.
1.3.5 D-$)*,*#!#r i! S!r)i$ G)(g# he traditional configuration of a dynamometer for cutting force measurements in drilling drilling operations operations consists consists of four elastic elastic octagonal octagonal rings on which strain strain gages are mounte mounted d with with the necess necessary ary connect connection ion to form form the )heat )heatsto stone ne measur measuring ing 'ridge. 'ridge. 1emiconductor strain gages are small in siEe and mass, low in cost, easily attached and highly sensitive to strain 'ut insensitive to am'ient or process temperature variations. 1train gages required simple construction 'ut tend to change resistance with the time so they are suita'le for test of short duration the rings are fi/ed and held 'etween two metal plates. his his type type of dynamom dynamomete eterr produc produces es an output output voltag voltagee corres correspond ponding ing to the elastic deformation of its structure under an applied force. !ne of the critical pro'lems is the the stif stiffn fnes esss of the the comp compon onen ents ts that that is in conf confli lict ct with with the the sens sensit itiv ivit ity y of the the dynamometer however the main limitation is the low 'an dwidth of the system.
1.4 STRAIN GAUGE It is a device used to determine the strain at a specified place. he smallest gauge
developed and sold commercially to date is the electric resistance type. his gauge is prepared from an ultra thin alloy foil which is photo etched to produce the intricate grid construction with a gauge of :.8mm. !n the other hand, mechanical strain gauges are still employed in civil engineering structural application where the gauge length is 8::m 8: :mm m -( -(er erry ry st stra rain in gau gauge ge. . h hes esee (e (erry rry gau gauge gess ar aree ru rugg gged ed,, si simp mple le to us usee an and d suff su ffic icie ient ntly ly acc accur urat atee in st stru ruct ctur ural al ap appl plic icat atio ion n wh wher eree th thee st stai ain n di dist stri ri'u 'uti tion on is appro/imately linear over the 8::mm gauge length.
25
1train gauge system has four 'asic characteristics namely gauge length, sensitivity,, range of strain and the accuracy or precision. sensitivity •
3auge length is the distance 'etween two *nife edges in contact with the
•
specimen and 'y the width of mova'le *nife edges in a mechanical strain gauge. 1ensitivity is the smallest value of strain which can 'e read on the scale
•
associated with the strain gauge. Range represents the ma/imum strain which can 'e recorded without resetting
•
the strain gauge. 2recision is ery ery sensitive instruments are quite prone to errors unless they the y are employed with at most precision.
1train 3auges are 'roadly classified as follows
%echanical !ptical &lectrical $coustical
1.4.1 E'#+!ri+)' S!r)i$ G)(g# &lectrical 1train 3auges are classified as 'ellow
1.4.1.1 R#"i"!)$+# S!r)i$ G)(g# he resistance of an electrically conductive material changes with dimensional changes which ta*e place when the conductor is deformed elastically. )hen such a material is stretched, the conductors 'ecome longer and narrower, which causes an increase in resistance. his change in resistance is then converted to an a'solute voltage 'y a wheatstone 'ridge. he resulting value is linearly related to strain 'y a constant called the gauge factor. his is the type of strain gauge are 'eing used in the la'oratory. la'ora tory.
26
1.4.1.2
C)p)+i!)$+# S!r)i$ G)(g#
+apaci +apacitan tance ce devices, devices, which depend depend on geometr geometric ic featur features, es, can 'e used used to measure strain. he capacitance of a simple parallel plate capac itor is proportional to4 N-5.5 )here4 C is the capacitance, ) is the plate area, is is the dielectric constant, and ! is the separation 'etween plates. he capacitance can 'e varied 'y changing the plate area OaG or the gap OtG. he elect electri rical cal prope propert rties ies of the the mate materi rial alss used used to form form the the capac capacit itor or are are rela relati tivel vely y unim unimpo port rtan ant. t. 1o capac capacit itan ance ce stra strain in gauge gauge mate materi rial alss can can 'e chos chosen en to meet meet the the mechani mechanical cal requir requireme ements nts.. his his allows allows the gauges gauges to 'e more more rugged rugged,, provid providing ing a significant advantage over resistance strain gauges.
27
1.4.1.3 P,!,#'#+!ri+ S!r)i$ G)(g# $n e/tensometer -an apparatus with mechanical levers attached to the specimen is used to amplify the movement of a specimen. $ 'eam of light is passed through a varia'le slit, actuated 'y the e/tensometer, and directed to a photoelectric cell. $s the gap opening changes, the amount of light reaching the cell varies, causing a varying intensity in the current generated 'y the cell.
1.4.1.4 S#*i+,$&(+!,r S!r)i$ G)(g# In pieEoelectric materials, such as crystalline quartE, a change in the electronic charge across the faces of the crystal occurs when the material is mechanically stressed. he pieEoresistive effect is defined as the change in resistance of a material due to an applied stress and this term is used commonly in connection with semiconducting materials. he resistivity of a semiconductor is inversely proportional to the product of the electronic charge, the num'er of charge carriers, and their average mo'ility. he effect of applied stress is to change 'oth the num'er and average mo'ility of the charge carriers. (y choosing the correct crystallographic orientation and doping type, 'oth positive and negative gauge factors may 'e o'tained. 1ilicon is now almost universally used for the manufacture of semiconductor strain gauges.
1.4.2 Op!i+)' S!r)i$ G)(g# 1.4.2.1 P,!,#')"!i+ S!r)i$ G)(g# )hen )hen a photo photo elasti elasticc materi material al is su'ject su'jected ed to a load load and illumina illuminated ted with polariEed light from the measurement instrumentation -called a reflection polariscope, patterns of color appear which are directly proportional to the stresses and strains within the material. he sequence of colors o'served as stress increases is4 'lac* -Eero stress, yellow, red, 'lue6green, yellow, red, 'lue6green, yellow, red, etc. he transition lines seen 'etween the red and green 'ands are *nown as 7fringes.7 he stresses in the material increase proportionally as the num'er of fringes increases. +losely spaced fringes mean a steeper stress gradient, and uniform color represents a uniformly stressed area. area. Hence, Hence, the overall overall stress stress distri'u distri'utio tion n can easily easily 'e studie studied d 'y o'serv o'serving ing the
28
numerical order and spacing of the fringes. Furthermore, a quantitative analysis of the dire direct ctio ion n and and magn magnit itude ude of the the stra strain in at any point point on the the coat coated ed surf surface ace can can 'e performed with the reflection polariscope and a digital strain indicator. indicator.
1.4.2.2 M,ir# I$!#r#r,*#!r- S!r)i$ G)(g# %oire interferometry is an optical technique that uses coherent laser light to produce a high contrast, two6'eam optical interference pattern. %oire interferometry reveals planar displacement fields on a partMs surface, which is caused 'y e/ternal loading or other source deformation. It responds only to geometric changes of the specimen and is effective for diverse engineering materials. +ontour maps of planar deformation fields can 'e generated from / and an d y components of displacements.
1.4.2.3 H,',gr)pi+ I$!#r#r,*#!r- S!r)i$ G)(g# Holographic interferometry allows the evaluation of strain, rotation, 'ending, and torsion of an o'ject in three dimensions. 1ince holography is sensitive to the surface effects of an opaque 'ody, e/trapolation into the interior of the 'ody is possi'le in some circumstances. In one or more dou'le6e/posure holograms, changes in the o'ject are recor recorde ded. d. From From the the frin fringe ge patt patter erns ns in the the reco recons nstr truct ucted ed image image of the the o'je o'ject ct,, the the interference phase6shift for different sensitivity vectors are measured. $ computer is then used to calculate the strain and other deformations.
1.5 BASIC CHARACTERISTICS OF A STRAIN GAUGE
29
he gauge should 'e of e/tremely small siEe -gauge length and width so as
to adequately estimate strain at a point. he gauge should 'e of significant mass to 'e permit the recording of
dynamic strain. he strain sensitivity and accuracy of the gauge should 'e significantly high. he gauge should 'e unaffected 'y temperature, vi'ration, humidity and other am'ient condition. he gauge should 'e capa'le of indicating 'oth static and dynamic strains. It should 'e possi'le to read the gauge gaug e either on location or remotely. he gauge should e/hi'it linear response to strain. he gauge and associated equipment should 'e availa'le at reasona'le cost. he gauge should 'e suita'le for use as a sensing element or other transducer systems.
1.6 ADANTAGES 7 DISADANTAGES OF STRAIN GAUGE
•
he advantages of strain gauge are4 1mall siEe and mass &ase of production over a range of siEes • Ro'ustness • 3ood sta'ility, repeata'ility and linearity over large strain range • 3ood sensitivity • Freedom from -or a'ility to compensate for temperature effects and other • environmental conditions 1uita'ility for static and dynamic measurements and remote recording •
30
•
Low cost
T# &i")&%)$!)g#" , "!r)i$ g)(g# )r#8 • • •
Relatively high temperature sensitivity 1emiconductor types are e/tremely nonlinear he semico semiconduc nductor tor gauge gauge is consid considera era'ly 'ly more more e/pens e/pensive ive than than ordina ordinary ry metallic gauge
D#"ig$ r#9(ir#*#$!" ,r T,,' : ,r+# D-$)*,*#!#r" For consistently accurate and relia'le measurement, the following requirements are considered during design and construction of an y tool force dynamometers 4 S#$"i!i%i!- 4 the dynamometer should 'e reasona'ly sensitive for precision measurement Rigi&i!- 4 the dynamometer need to 'e quite rigid to withstand the forces without causing much deflection which may affect the mach ining condition Cr,"" "#$"i!i%i!- 4 the dynamometer should 'e free from cross sensitivity such that one force -say 2 does not affect measurement of the other forces -say 2 and P Q 2 " 1ta'ility against humidity and temperature uic* time response
31
High frequency response such that the readings are not affected 'y vi'ration within a reasona'ly high range of frequency +onsistency, i.e. the dynamometer should wor* desira'ly over a long period.
TOOL DYNAMOMETER
he dynamo dynamometer meterss 'eing commonly used now6a6 now6a6days days for measur measuring ing machi machining ning force forcess desira'ly accurately and precisely -'oth static and d ynamic characteristics are either strain gauge type or pieEoelectric type 1train 1tr ain gaug gaugee ty type pe dyn dynamom amomete eters rs are ine ine/pen /pensiv sivee 'ut les lesss acc accura urate te and con consis sisten tent, t, whereas, the pieEoelectric type are highly accurate, relia'le and consistent 'ut very e/pensive for high material cost and stringent construction.
T(r$i$g D-$)*,*#!#r urning dynamometers may 'e strain gauge or pieEoelectric type and may 'e of one, two or three dimensions capa'le to monitor all of 2 , 2 and 2 . Q " P For ease of manufacture and low cost, strain gauge type turning dynamometers are widely used and prefera'ly of 8 S D -dimension for simpler construction, lower cost and a'ility to provide almost all the desired force values. Design and construction of a strain S gauge type 8 S D turning dynamometer are shown schematically in Fig. 5:.A and photographically in Fig. 5:.C wo full 'ridges comprising four live strain gauges are provided for 2
P
and 2 channels which are connected with Q
the strain measuring 'ridge for detection and measurement of strain in terms of voltage which provides the magnitude of the cutting forces through cali'ration. Fig. 5:.5:
32
pictorially shows use of 9 S D turning dynamometer having pieEoelectric transducers inside.
2hotographs of a strain gauge type 8 S D turning dynamometer dynamometer and its major components.
0se of 9 S D pieEoelectric type t ype turning dynamometer.
Dri''i$g &-$)*,*#!#r
33
2hysical construction of a strain gauge type 8 S D drilling dynamometer for measuring torque and thrust force is typically shown schematically in Fig. 5:.55 and pictorially in Fig. 5:.58. Four strain gauges are mounted on the upper and lower surfaces of the two opposite ri's for 2 S channel and four on the side surfaces of the other two ri's for the Q torque channel. (efore use, the dynamometer must 'e cali'rated to ena'le determination of the actual values of and 2 from the voltage values or reading ta*en in 1%( or 2+. Q
1chematic view of construction of a strain gauge type drilling dynamometer.
Mi''i$g &-$)*,*#!#r 1ince the cutting or loading point is not fi/ed w.r.t. w.r.t. the jo' and the dynamometer, d ynamometer, the jo' platform rests on four symmetrically symmetrically located supports in the form of four !6rings. he
34
forces on each !6ring are monitored and summed up correspondingly for getting the total magnitude of all the three forces in Q, " and P direction respectively. Fig. 5:.59 shows schematically the principle of using !6ring for measuring two forces 'y mounting strain gauges, ; for radial force and ; for transverse force.
Fig. 5:.5; typically shows configuration of a strain gauge type 9 S D milling dynamometer having ; octagonal rings. 2ieEoelectric type 9 S D dynamometers d ynamometers are also availa'le and used for measuring the cutting forces in milling
$ typical strain gauge type 9 S D milling dynamometer. d ynamometer.
Gri$&i$g &-$)*,*#!#r he construction and application of a strain gauge type -e/tended !6ring grinding surface dynamometer and another pieEoelectric type are typically shown in Fig. 5:.5< and Fig. 5:.5= respectively.
35
$ typical typical strain S gauge type 8 S D grinding dynamometer d ynamometer
2ieEoelectric type grinding dynamometer in operation. 0nli*e strain gauge type dynamometers, the sophisticated pieEoelectric type -TI1L&R dynamometers can 'e used directly more accurately and relia'ly even without cali'ration 'y the user.
36
CHAPTER 2
D#"ig$ )$& F);ri+)!i,$ , Dri'' T,,' D-$)*,*#!#r AIM8 o determine determine the cutting tool forces on the wor* piece using drill tool dynamometer.
THEORY8 he strain gauge 'ased Drill ool Dynamometer designed to measure hrust orque orque during drilling operation and effect of speed, feed cut on these forces. he unit consists of a mechanical sensing unit or test piece holder and digital force indicator. he e/istence of some physical varia'les li*e force, temperature etc and its magnitude or strength cannot 'e detected or quantified directly 'ut can 'e so through their effects only. only. For e/ample, a force which can neither 'e seen nor 'e gripped 'ut can 'e detected and also quantified respectively 'y its effects and the amount of those effects li*e elastic deflection, deformation, pressure, strain etc. hese effects, called signals, often need proper conditioning for easy, accurate and relia'le detection and measurement.
1chematic view of construction of a strain gauge type drilling dynamometer.
37
$ strain gauge type drilling dynamometer and its major components.
OB
• •
o minimiEe minimiEe the num'er of parts in the e/perimental setup -simple in
construction. o have a more accurate and relia'le e/perimental setup. &asy to understand and simple in operation. &asy in handling and digital d igital force indicators to measure two forces • simultaneously.
METHODOLOGY8 In order to assem'le the drill tool dynamometer, the important components needed are strain gauges and 2hysical construction of a strain gauge type drilling dynamometer for measuring torque and thrust force consists Four strain gauges are mounted on the upper and lower surfaces of the two opposite ri's. he ends of the strain gauges connected to the strain indicator using wires. )hen the load is applied on a mem'er, the force is produced in a mem'er will 'e e/perienced 'y the strain gauges and are shown on the strain indicator.
38
ITEMS RE=UIRED8 • • • • • •
%echanical 1ensing 0nit with strain 3auge. Digital Force Indicator. ; 1train gauges. Uo' holder. Fi/ed mem'er. #ecessary ca'les, wires, solder etc.
RESULTS E>PECTED8 $ccurate cutting forces can 'e o'tained during the drilling process on the wor* piece using the drill tool dynamometer through the digital force indicator. indicator.
39
MODEL CONTENT TABLE TABLE SR.NO.
COMPIONENT NAME
SPECIFICATION
1
D.+.%otor
58volt permanent magnet type motor
2
3ears
Rac* $nd 2inion type
3
ransformer
586:65: D.+. transformer
4
Rectifier
5
Resistance
6
Load cell
%a/ Load +apacity 5<: Tg.
?
Display
Digital display
@
2ower 1upply
88: olt $c.,9olt Dc.
+apacitor
MODEL CONTENT SPECIFICATIONS
40
(,+( ,+ )otor
Faradays used oersteds discovered, that electricity could 'e u sed to produce motion, to 'uild the world first electric motor in in 5A85. en en years later, using using the same logic in reverse, faraday was interested in getting the motion produced 'y oersteds e/periment to 'e continuous, rather then just a rotatory shift in position. position. In his e/periments, faraday thought in terms of magnetic lines of force. He visualiEed how flu/ lines e/isting around a current carrying wire and a 'ar magnet. He was then a'le to produce a device in which the different lines of force could interact a produce co ntinues rotation. he 'asic faradays motor uses a free6swinging wire that circles around the end of a 'ar magnet. he 'ottom end of the wire is in a pool of mercury. )hich allows the wire to rotate while *eeping a complete electric circuit.
BASIC MOTOR ACTION
41
$lthough FaradayMs motor was ingenious. It could not 'e used to do any an y practical wor*. his is 'ecause its drive shaft was enclosed and it could only produce an internal or'ital motion. It could not transfer its mechanical energy to the outside for deriving an e/ternal load. However it did show how the magnetic fields of a conductor and a magnet could 'e made to interact to produce continuous motion. Faradays motor or'ited its wire rotor must pass through the magnetGs lines of force.
)hen a current is passes through the wire ,circular lines of force are produced around the wire. hose flu/ lines go in a direction descri'ed 'y the left6hand rule. he lines of force of the magnet go from the # pole to the 1 pole "ou can see that on one side of the wire, the magnetic lines of force are going in the opposite direction as a result the wire, s flu/ lines oppose the magnetGs magn etGs flu/ flu/ line since flu/ lines ta*es the path of least resistance, more lines concentrate on the other side of the wire conductor, the lines are 'ent and are very closely spaced. he lines tend to straighten and 'e wider spaced. (ecause of this the denser, curved field pushes the wire in the opposite direction.
42
he direction in which the wire is moved is determined 'y the right hand rule. If the current in the wire went in the opposite direction. he direction of its flu/ lines would reverse, and the wire would 'e pushed the other way.
R('#" ,r *,!,r )+!i,$ he left hand rule shows the direction of the flu/ lines around a wire that is carrying current. )hen the thum' points in the direction of the magnetic lines of force. he right hand rule for motors shows the direction that a current carrying wire will 'e moved in a magnetic field. )hen the forefinger is pointed in the direction of the magnetic field lines, and the centre finger is pointed in the direction of the current in the wire the thum' will point in the direction that the wire will 'e moved.
TOR=UE AND ROTATORY MOTION In the 'asic action you just studied the wire only moves in a straight line and stops moving once out of the field even though the current is still on. $ practical motor must develop a 'asic twisting force called torque loop. )e can see how torque is produced. If
43
the loop is connected to a 'attery. +urrent +urrent flows in one direction one side of o f the loop, and in the opposite direction on the other. herefore herefore the concentric direction on the two sides. If we mount the loop in a fi/ed magnetic field and supply the current the flu/ lines of the field and 'oth sides of the loop will interact, causing the loop to act ac t li*e a lever with a force pushing on its two sides in opposite directions. he com'ined forces result in turning force, or torque 'ecause the loop is arranged to piot on its a/is. In a motor the loop that moves in the field is called c alled an armature or rotor. he overall turning force on the armature depends upon several factors including field strength armature current strength and the physical construction of the a rmature especially the distance from the loop sides to the a/is lines. (ecause of the lever action the force on o n the sides are further from the a/isV thus large armature will produce greater torques.
In the practical motor the torque determines the energy availa'le for doing useful wor*. he greater the torque the greater the energy. If If a motor does not develop enough torque to pull its load it stalls.
R)+ )$& Pi$i,$
44
slope.. Rac* and pinion animation along a steep slope
he rac* and pinion arrangement is commonly found in the steering steering mechanism mechanism of cars or other wheeled wheeled,, steered vehicles. his arrangement provides a lesser mechanical advantage than advantage than other mechanisms $ r)+ )$& pi$i,$ is a pair of gears gears which which convert rotational motion into linear motion. he circular pinion circular pinion engages engages teeth on a flat 'ar 6 the rac*. Rotational Rotational motion motion applied to the pinion will cause the rac* to move to the side, up to the limit of its travel. For e/ample, in a rac* railway, railway, the rotation of a pinion mounted on a locomotive locomotive or or a railcar engages engages a rac* 'etween 'etween the rails and pulls a train such as recirculating 'all, 'all, 'ut much less 'ac*lash less 'ac*lash and and greater feed'ac* , or steering 7feel7. he use of a varia'le rac* was invented 'y $rthur & (ishop, (ishop,W5X so as to improve vehicle response and steering 7feel7 on6centre, and that has 'een fitted to many new vehicles, after he created a hot forging process forging process to manufacture the rac*s, thus eliminating an y su'sequent need to machine the form of the gear teeth.
RESISTANCE
45
Resistance is the opposition of a material to the current. It is me asured in !hms -
. $ll $ll conductors conductors represent represent a certain certain amount of resista resistance, nce, since since no conductor conductor is is
5::Y efficient. o control the electron flow -current in a predicta'le manner, we use resistors. &lectronic circuits use cali'rated lumped resistance to control the flow of current. (roadly spea*ing, resistor can 'e divided into two groups viE. fi/ed adjusta'le -varia'le resistors. In fi/ed resistors, the value is fi/ed cannot 'e varied. In varia'le resistors, the resistance value can 'e varied ' y an adjuster *no'. It can 'e 'e divided into -a +ar'on composition -' )ire wound -c 1pecial type. he most common type of resistors used in our projects is car'on type. he resistance value is normally indicated 'y colour 'ands. &ach resistance has four colours, one of the 'and on either side will 'e gold or silver, this is called fourth 'and and indicates the tolerance, others three 'and will give the value of resistance -see ta'le. For e/ample if a resistor has the following mar*ing on it say red, violet, gold. +omparing these coloured rings with the colour code, its value is 8@::: 8@: :: ohms or 8@ *ilo ohms and its tolerance is Z
CODE
(lac*66666666666666666666666666666666666666666666666666666: (rown66666666666666666666666666666666666666666666666666665 Red66666666666666666666666666666666666666666666666666666668 !range6666666666666666666666666666666666666666666666666669 "ellow6666666666666666666666666666666666666666666666666666; 3reen66666666666666666666666666666666666666666666666666666< (lue66666666666666666666 (lue6666666666666666666666666666666 666666666666666666666 666666666666666666666666= 66666666666666= iolet6666666666 iolet66666666666666666666 666666666666666666666 666666666666666666666666666666666@ 6666666666666666666666@ 3rey666666666666666666666666666666666666666666666666666666A )hite6666666666666666666 )hite66666666666666666666666666666 6666666666666666666666666666666666C 666666666666666666666666C
46
he first rings give the first digit. he second ring gives the second digit. he third ring indicates the num'er of Eeroes to 'e placed after the digits. he fourth ring gives tolerance -gold Z
, it will will have have three three dials dials each
having ten ten gaps i.e. i.e. ten resist resistance ance coils coils each of of resistance resistance 5:[
ten ten resi resist stan ance cess each each of of 5::[ 5::[
. he third third dial dial will will have
.
he dial type of resistance 'o/es is 'etter 'ecause the contact resistance in this case is small constant.
POER SUPPLY In altern alternati ating ng curren currentt the electr electron on flow flow is altern alternate ate,, i.e. i.e. the electr electron on flow flow increases to ma/imum in one direction, decreases 'ac* to Eero. It then increases in the other direction and then decreases to Eero again. Direct current flows in one direction only. Rectifier converts alternating current to flow in on e direction only. )hen the anode
47
of the diode is positive with respect to its cathode, it is forward 'iased, allowing current to flow. (ut when its anode is negative with respect to the cathode, it is reverse 'iased and does not allow current to flow. his unidirectional property of the diode is useful for rectification. $ single diode arranged 'ac*6to6'ac* might allow the electrons to flow during positive half cycles only and suppress the negative half cycles. Dou'le diodes arranged 'ac*6to6'ac* might act as full wave rectifiers as they may allow the electron flow during 'oth positive and negative half cycles. Four diodes can 'e arranged to ma*e a full wave 'ridge rectifier. Different types of filter circuits are used to smooth out the pulsations in amplitude of the output voltage from a rectifier. he property of capacitor to oppose any change in the voltage applied across them 'y storing energy in the electric field of the capacitor and of inductors to oppose any change in the current flowing through them 'y storing energy in the magnetic field of coil may 'e utiliEed. o remove pulsation of the direct current o'tained from the rectifier, different types of com'ination of capacit capacitor or,, induct inductors ors and resist resistors ors may 'e also also 'e used used to increa increase se to action action of filtering.
NEED OF POER SUPPLY 2erhaps all of you are aware that a Opower supplyG is a primary requirement for the Oest (enchG of a home e/perimenterGs mini la'. $ 'attery eliminator can eliminate or replace the 'atteries of solid6state electronic equipment and the equipment thus can 'e operated 'y 89:v $.+. mains instead of the 'atteries or dry cells. #owadays, the use of commercial 'attery eliminator or power supply unit has 'ecome increasingly popular as power source for household appliances li*e transreceivers, record player, player, cassette players, digital cloc* etc.
48
CAPACITORS It is an electronic component whose function is to accumulate charges and then release it.
49
o understand the concept of capacitance, consider a pair of metal plates which all are placed near to each other without touching. If a 'attery is connected to these plates the positive pole to one and the negative pole to the other, electrons from the 'attery will 'e attracted from the plate connected to the positive terminal of the 'atter y. If the 'attery is then disconnected, one plate will 'e left with an e/cess of electrons, the other with a shortage, shortage, and a potential or voltage difference will e/ists 'etween them. hese plates will 'e acting as capacitors. +apacitors are of two types4 6 -5 i#& !-p# li*e ceramic, polyester, p olyester, electrolytic capacitors6these names refer to the material they are made o f aluminium foil. -8 )ri);'# !-p# li*e gang condenser in radio or trimmer. In fi/ed type capacitors, it has
two leads and its value is written over its 'od y and varia'le type has three leads. 0nit of measurement of a capacitor is farad denoted 'y the sym'ol F. It is a very 'ig unit of capacitance. 1mall unit capacitor are pico6farad denoted 'y pf -IpfK55:::,:::,:::,::: f $'ove $'ove all, in case of electrolytic capacitors, itMs two terminal are mar*ed as -6 and - so chec* it while using capacitors in the circuit in right direction. %ista*e can destroy the capacitor or entire circuit in operational.
LOAD CELL $ load cell is an electronic device -transducer -transducer that is used to convert a force into an electrical signal. his conversion is indirect and happens in two stages. hrough a mechani mechanical cal arrange arrangemen ment, t, the force 'eing sensed sensed deform deformss a strain gauge. gauge. he strain gauge converts the deformation -strain -strain to electrical signals. $ load cell usually consists
50
of four strain gauges in a )heatstone 'ridge configuration. 'ridge configuration. Load cells of one or two strain gauges are also availa'le. he electrical signal output is typically in the order of a few millivolts and requires amplification 'y an instrumentation amplifier 'efore 'efore it can 'e used. he output of the transducer is plugged into an algorithm to algorithm to calculate the force applied to the transducer. $lthough strain gauge load cells are the most common, there are other types of load cells as well. In industrial applications, hydraulic -or hydrostatic is pro'a'ly the second most common, and these are utiliEed to eliminate some pro'lems with strain gauge load cell devices. $s an e/ample, a hydraulic load cell is immune to transient voltages -lightning so might 'e a more effective device in outdoor environments. !the !therr types types incl includ udee pieEo6electric load load cells cells -usefu -usefull for dynami dynamicc measur measureme ements nts of force, and vi'rating wire load cells, which are useful in geomechanical applications geomechanical applications due to low amounts of drift. drift. &very load cell is su'ject to 7ringing7 when su'jected to a'rupt load changes. his stems from the spring6li*e 'ehavior of load cells. In order to measure the loads, they have to deform. $s such, a load cell of finite stiffness must have spring6li*e 'ehavior, e/hi'iting vi'r vi'rat atio ions ns at its its natural natural frequency frequency.. $n oscillating data pattern can 'e the result of ringing. Ringing can 'e suppressed in a limited fashion 'y passive means. $lternatively, a control system can use an actuator to to actively damp out the ringing of a load cell. his method offers 'etter performance at a cost of significant increase in comple/ity.
H, i! ,r" / S!r)i$ G)(g# L,)& C#'' $ strain strain gauge is a long length of conductor arranged in a EigEag pattern on a mem'rane. )hen it is stretched, its resistance increases. 1train gauges are mounted in the same direction as the strain and often in fours to form a full M)heatstone (ridgeM.
51
he diagram a'ove represents what might happen happ en if a strip of metal were fitted with four gauges. $n downward 'end stretches the gauges on the top and compresses those on the 'ottom. $ load cell may contain several similar strain gauges elements.
52
LOAD FORCE CELLS
he load or force cell ta*es many man y forms to accommodate the variety of uses throughout research and industrial applications. he majority of todayMs designs use strain gauges as the sensing element, whether foil or semiconductor. Foil gauges offer the largest choice of different types and in consequence tend to 'e the most used in load cell designs. 1train gauge patterns offer measurement of tension, compression and shear forces. 1emiconductor strain gauges come in a smaller range of patterns 'ut offer the advantages of 'eing e/tremely small and have ha ve large gauge factors, resulting in much larger outputs for the same given stress. Due to these properties, they tend to 'e used for the miniature load cell designs. 2roving rings are used for load measurement, using a cali'rated metal ring, the movement of which is measured with a precision displacement transducer. $ vast num'er of load cell types have developed ove r the years, the first designs simply using a strain gauge to measure the direct stress which is introduced into a metal element when it is su'jected to a tensile or compressive force. $ 'ending 'eam type design uses strain gauges to monitor the stress in the sensing element when su'jected to a 'ending force.
53
%ore recently the measurement of shear stress has 'een adop ted as a more efficient method of load determination as it is less dependent on the way and direction in which the force is applied to the load cell. he M1M or MPM (eam Load +ell
$ simple simple design load cell where the structure is shaped as a M1M or MPM and strain gauges are 'onded to the central sensing area in the form of a full )heatstone 'ridge. he )heatstone (ridge +ircuit
& K &/citation oltage-typically 5:
dc.
!2 K !utput 1ignal he (ending (eam Load +ell
54
he strain gauges are 'onded on the flat upper and lower sections of the load cell at points of ma/imum strain. his load cell type is used for low capacities capac ities and performs with good linearity. Its disadvantage is that it must 'e loaded correctly to o'tain consistent results. he 1hear (eam Load +ell
he strain gauges are 'onded to a reduced part of the cross section of the 'eam in order to ma/imiEe the shear effect. hey are 'onded at ;< degree angles on either side of the 'eam to measure the shear strains.
55
0sed for medium to large capacities, the load cell has good linearity and is not so suscepti'le to e/traneous loading, in particular to side loads.
Mi$i)!(r# L,)& C#''"
%iniature load cells 'ecause of their compact siEe u sually use semiconductor strain gauges as the sensing element. hey are availa'le in many different configurations for 'oth tension and compression force measurement. hey offer good performance with high outputs and high overload capa'ilty for protection. 1peciality $utomotive$utosport Load +ells
56
%any more Load +ell designs e/ist and we will 'ring you details of these at a later stage.
LOAD CELL SPRING MEMBER DESIGN CONSIDERATIONS (ending4 1imple
FI30R& 5. (ending4 he simple cantilever (ending elements are low6force, generally less than 5,::: l'f range, high6deflection structures offering convenient and flat strain gauging surfaces where complete pushpull strain symmetry is maintained.
wo wo strain gauges may 'e mounted on the top surface of the 'eam with two strain gauges mounted on the 'ottom of o f the 'eam in equal and opposite strain fields. 1ince
57
strain gauges are directly opposite one another an d 'eam thic*ness tends to 'e small, little li*elihoode/ists that the strain gauges will operate at different temperatures providing generally good thermal performance. $lthough $lthough the cantilever 'eam structure provides e/cellent electrical nonlinearity, nonlinearity, due to electrical symmetry, symmetry, the point of load contact with the 'eam 'ea m translates curvilinearly, producing mechanical nonlinearities.
he ma/imum moment resisting movement of the 'eam occurs o ccurs at the rigid clamp with the ma/imum stress occurring according to %yI& where %K moment at the clamp, y K displacement from the centerline of the 'eam -neutral a/is, 5K area moment of Inertia and & K "oungMs "oungMs %odulus for the material used. 1ince the majority of the 'eam length serves only to increase the moment at the rigid clamp, various modifications of the simple 'eam are used to reduce the 'eam mass in the interest of maintaining a high natural frequency or to concentrate the strain at the strain gauge locations as shown in Figure 8.
Lastly, a review of 'eam 'ending characteristics of reveals that the surface strain present in the 'eam surface linearly varies from the point of force application to the clamp. his implies that the strain gauges will e/perience a strain gradient and provide an output equating to the average strain. +onstant stress 'eam sections can 'e fa'ricated 'y tapering the edges of the 'eam such that the tapered edges projected intersect at the point of load application to the 'eam as shown in top view Figure 8. In the end analysis, the load cell designer must weigh the performance p erformance 'enefits produced against the cost of incorporating the mechanical features shown.
58
FI30R& 8. 1imple +antilever &nhancements
(ending4 %ultiple %ultiple cantilever structures produce a 7multiple 'ending7 where tension and compression strain fields e/ist on the same surface of the 'eam as shown in Figure 9a. he advantage of multiple 'ending elements is realiEed when one considers that the point of load application to the structure translates linearly linearly along the loading a/is, there'y reducing or eliminating first order nonlinearities. )hen the peripheral support clamp is rigid and immo'ile, deflection of the 'ending 'eams also produces median plane tensile loads in the 'eam resulting in nonlinear outputs. )hen )hen the peripheral clamp is rigid and mo'ile, as shown in Figure 5, median plane tensile stresses are eliminated however, as the 'eams deflect, the moment arm reduces in leng th yielding yet another non6linear term and dou'ling the deflection of the load cell. #ote that 77 is used in the Figure to denote tensile strains and 7+7 is used to denote compressive co mpressive strain.
59
FI30R& 9. %ultiple (ending4
%ultiple 'ending can 'e implemented as shown in Figure ; where the sensitivity of the load cell to off6a/is loads is minimiEed. +oupled dual6'eam load cell configurations conveniently produce equal and opposite a/ial loads within each of the 'eams in response to e/traneous couples. 1ince the strain gauges can 'e wired to cancel the effects of a/ial loads, the result is a load cell structure largely insensitive to the point of load application and particularly well6suited to commercial weighing applications. $s the 'eams deflect, however, small changes in the moment arm lengths result producing geometric nonlinearities. $dditionally, $dditionally, a/ial forces produce nonlinearities in each 'eam 'ea m which tend to 'e equa l and opposing, thus canceling each ea ch other. $lthough $lthough strain gauging inside a drilled hole is more la'or intensive, the design lends itself to effective sealing. !ften vacuum degassed silicone gel materials are used to fill the interior strain gaged cavity waterproofing 'y the 7e/clusion7 principle. he 7'inocular7 dual 'eam design of Figure ;' is popular for low force commercial weighing applications. he thic*ened sections resist 'ending there'y reducing the
60
compliance of the design and ma/imiEing the natural frequency. #ote that the ma/imum strain occurs at the transduction Eones and is less than this value everywhere else within the structure. Low6profile 'ending6'ased load cells are usually configured as strain gaged diaphragms or multiple strain6gaged spo*e assem'lies.
!ften, low profile multiple6'ending designs possess four spo*es at C: degree intervals where strain gauges are wired to cancel off6a/is moment6induced strains. It should 'e notedV when in the process of designing any load cell structure, the designer must consider all 'ending as well as shear loads that the spring element must communicate. FI30R& ;. +oupled Dual6(eam +antilevers4
%any of the designs shown are depicted herein possessing right6angled corners. o minimiEe stress concentrations that will occur at geometric discontinuities, it is highly recommended that generous fillets 'e used with particular attention to possi'le discontinuities at surfaces tangent to radiused features. 1tress risers will often show local stresses in e/cess of the microyield strength of the material used, producing Eero insta'ilities and potential fatigue failures. Forty years ago sensor designers found that performance was almost always enhanced when the sensor was fa'ricated from a solid 'illet of material and attention paid to the elimination of structural discontinuities. oday oday we have a much more refined
61
understanding of materials and material 'ehavior along with the terminology to e/press these various attri'utes and characteristics. ch aracteristics.
B#$&i$g8 Ri$g he 'ending ring shown in Figure < has a rich history and is popularly *nown as the %orehouse proving ring. he original design having 'een appropriated from Russia. he %orehouse proving ring was and continues to 'e used as a transfer standard in 'oth sensor cali'ration systems and materials test systems. It is o'vious from the design of the ring that each leg of the ring must communicate a/ial loads while simultaneously e/periencing 'ending. he fact that 'oth a/ial and 'ending occur within the transduction Eone of the sensor characteriEes ring6style load cells.
he 'eauty of the proving ring with strain gauges installed as shown is the fact that all gauges of the wheatstone 'ridge ideally e/perience e/p erience identical a/ial strain, resulting in cancellation of a/ial strain effects in the output of the 'ridge. $nother attri'ute of the ring structure relates to the smoothly varying tensile and compressive moment6induced strains that result due to loading of the cell. he original transduction method used with the structural ring design predates strain gauges entirely where a manually 7pluc*ed7 metal reed and micrometer assem'ly were used to detect e/ceptionally small deflections of the ring. $ hardened 'all 'earing acts as the micrometer6adjusta'le micrometer6adjusta'le target surface against which the reed tip o scillates, where the reed is also provided with a hardened cylindrical tip, the micrometer is adjusted to move the target until the reed just contacts the target, dampening the reed response. he displacement sensitivity of this very mechanical system is impressive. he output of the sensor is viewed directly on the micrometer scale. It should 'e noted that the design of the 'osses communicating load into the ring structure significantly affects the performance of the ring. he optimum proportions and
62
dimensions of these 'osses is as much determined 'y e/per ience and test as it is 'y rigorous mechanical design. (osses are often undercut or modified to 'e made more fle/i'le in the interest of rejecting off6a/is loads trading off performance for off6a/is load rejection. Li*ewise, transduction Eones are provided with stress6 concentrating notches to enhance output, natural frequency and to reduce compliance. In some cases, the e/tent to which these 'oss and fle/ure modifications e/tend are so radical as to almost defy characteriEation characteriEation as a ring6'ased load cell. he single common thread in all of these designs is the fact that transduction Eones must communicate 'oth 'ending and a/ial loads.
FI30R& <. (ending4 he ring4
63
S#)r8 1train gauge6'ased load cell structures, configured to operate 'ased upon the measurement of shear strain, provide high capacity and low compliance in a compact and low profile geometry. 1train gauges measuring shear are oriented at ;< degrees to the neutral a/is in 'ending and are mounted to straddle the neutral a/is. (ending stresses are, 'y definition, equal to Eero at the neutral a/is in 'ending. $lthough the strain gauge must possess some finite physical dimensions, 'y equally straddling the neutral a/is in 'ending, half of each strain gauge will e/perience some 'ending strain while the other half will e/penence the same strain in the opposite direction there'y largely cancelling 'ending 'en ding in the output of the sensor. 2ractically, 2ractically, the shear patterns cannot 'e positioned with a'solute perfection and shear we's cannot 'e fa'ricated with a'solute symmetry resulting in less than perfect cancellation of 'ending strains. 0nli*e 'ending stresses developed in the cantilever 'eam structure, where 'ending stresses are a direct function of moment which itself is a direct function of the moment arm, shear stresses 'y definition are equal only to the load carried 'y the mem'er and the area of the mem'er, independent of the point of loading. (y varying the thic*ness of the load6'earing mem'er, the shear stresses are varied in direct proportion. 0tiliEing this philosophy, load carrying 'eams are often milled out to create shear 7we's7 possessing an area sufficient to produce shear strains in the 5,::: to 5,@:: microstrain range there'y yielding strain gage full6'ridge outputs of 'etween 8 m and 9 m.
1hear strain gauge patterns are often used to strain gauge dual6a/is shear pin structures 'y gauging the inside diameter of a hole drilled in a cylindrical mem'er. he diameter of the internal hole is dimensioned to result in a shear area sufficient to produce the desired strains at rated input he central hole is readily sealed, usually ' y welding of a
64
hermetically sealed connector, rendering the design useful in hostile environments. In physically realiEa'le sensor structures, it it is impossi'le to configure the structure to e/perience pure shear without the presence of some 'ending. he load 'earing mem'ers me m'ers must therefore communicate 'oth forms of material loading. Due to h igher6order effects tending to couple shear and 'ending strains, and in the interest of minimum compliance, it is advisa'le to configure the spring mem'er for minimum 'ending. he reduction of spring mem'er length will have the effect of reducing moments and 'ending strains. he geometry induces dou'le 'ending where the inflection point is centered on the shear we' there'y minimiEing the 'ending that results at the strain gauge locations.
he popular 7panca*e7 style load cell, as shown in Figure =c, is configured to operate in shear, offering offering a very low profile in a design that is easily environmentally sealed and is largely insensitive to off6a/is loads. 3enerally, panca*e style shear we' load cells are availa'le in the 5,::: l'f and higher load ranges. he panca*e style load cell also easily accommodates dual electrically 6separate strain 'ridges for high relia'ility applications. he he high stiffness 7tension76'ase 7tension76'ase serves to allow
65
the measurement of tensile forces, acts to stiffen the load cell structure in compression and to allow the incorporation of overrange limiting stops for compression applications. Low profile panca*e load cells are not availa'le in the under <:: l'f force range since the shear we' thic*ness 'ecomes e/ceedingly thin and difficult to manufacture. It should 'e noted that the strain gage clamping fi/tures for the panca*e style sensor either pinch the shear we's to avoid overstressing them during manufacturing o r all cylindrical gaging holes shown are filled with teflon plugs which provide clamping pressure due to volumetric e/pansion at elevated epo/y cure temperatures. he teflon plugs used are closely6toleranced to the diameter of the gauging holes and tend to e/trude into the hole6 to6hole slots reducing the clamping pressure as a function o f he num'er of cure cycles they have 'een e/posed to. $ strain strain gauge is a device used to measure the strain of strain of an o'ject. Invented 'y &dward &. 1immons and 1immons and $rthur +. Ruge in Ruge in 5C9A, the most common type of strain gauge consists of an insulating an insulating fle/i'le fle/i'le 'ac*ing which supports a metallic foil pattern. he gauge is attached to the o'ject 'y a suita'le adhesive, such as cyanoacrylate. cyanoacrylate.W5X $s the o'ject is deformed, the foil is deformed, causing its electrical resistance to resistance to change. his resistance change, usually measured using a )heatstone 'ridge, 'ridge, is related to the strain 'y the quantity *nown as the gauge factor.
-h'sial operation $ strain gauge ta*es advantage of the physical property of electrical conductance and conductance and its dependence on not merely the electrical conductivity of conductivity of a conductor, which is a property of its material, 'ut also the conductorMs geometry. )hen an electrical conductor is is stretched within the limits of its elasticity such elasticity such that it does not 'rea* or permanently deform, it will 'ecome narrower and longer, changes that increase its electrical resistance end6to6end. +onversely, when a conductor is compressed such that it does not 'uc*le, it will 'roaden and shorten, changes that decrease its electrical resistance end6to6 end. From the measured electrical resistance of the strain gauge, the amount of applied
66
stress may stress may 'e inferred. $ typical typical strain gauge arranges a long, thin conductive strip in a Eig6Eag pattern of parallel lines such that a small amount of stress in the direction of the orientation of the parallel lines results in a multiplicatively larger strain over strain over the effective length of the conductor\and hence a multiplicatively larger change in resistance\than would 'e o'served with a single straight6line conductive wire.
/auge fator he gauge factor 3F 3F is defined as4
where
67
R 3 is the resistance of the undeformed gauge, ]R is the change in resistance caused 'y strain, and ^ is strain. For metallic foil gauges, the gauge factor is usually a little over 8. W8X For a single active gauge and three dummy resistors, the output v from the 'ridge is4
)here ( is the 'ridge e/citation voltage. Foil gauges typically have active areas of a'out 865: mm8 in siEe. )ith careful installation, the correct gauge, and the correct adhesive, strains adhesive, strains up to at least 5:Y can 'e measured.
/auges in pratie
68
isualiEation isualiEation of the wor*ing concept 'ehind 'e hind the strain gauge on a 'eam a 'eam under e/aggerated 'ending. Foil strain gauges are used in many situations. Different applications place different requirements on the gauge. In most cases the orientation of the strain gauge is significant. 3auges attached to a load cell would normally 'e e/pected to remain sta'le over a period of years, if not decadesV while those used to measure response in a dynamic e/periment may only need to remain attached to the o'ject for a few days, 'e energiEed for less than an hour, and operate for less than a second. 1train gauge 'ased technology is utiliEed commonly in the manufacture of pressure of pressure sensors. sensors. he gauges used in pressure sensors themselves are commonly made from silicon, polysilicon, metal film, thic* film, and 'onded foil.
ariations in temperature
69
ariations ariations in temperature will cause a multitude of effects. he o'ject o'jec t will change in siEe 'y thermal e/pansion, which will 'e detected as a strain 'y the gauge. Resistance of the gauge will change, and resistance of the connecting wires will change. %ost strain gauges are made from a constantan alloy. arious constantan alloys and Tarma alloys have 'een designed so that the temperature effects on the resistance of the strain gauge itself cancel out the resistance change of the gauge due to the thermal e/pansion of the o'ject under test. (ecause (eca use different materials have different amounts of thermal e/pansion, self6temperature compensation -1+ requires selecting a particular alloy matched to the material of the o'ject under test. &ven with strain gauges that are not self6temperature6compensated -such as isoelastic alloy, use of a )heatstone 'ridge arrangement 'ridge arrangement allows compensating for temperature changes in the specimen under test and an d the strain gauge. o do this in a )heatstone 'ridge made of four gauges, two gauges are attached to the specimen, and two are left unattached, unstrained, and at the same temperature as the specimen and the attached gaugesW8X. -%urphyMs -%urphyMs Law was originally coined in response to a set of gauges 'eing incorrectly wired into a )heatstone 'ridge.W;X emperature emperature effects on the lead wires can 'e canc elled 'y using a 796wire 'ridge7W5X or a 7;6wire !hm circuit7W
ther gauge t'pes For measurements of small strain, semiconductor strain strain gauges, so called pieEoresistors called pieEoresistors,, are often preferred over foil gauges. $ semiconductor gauge usually has a larger gauge factor than a foil gauge. 1emiconductor gauges tend to 'e more e/pensive, more sensitive to temperature changes, and are more fragile than foil gauges.
70
In 'iological measurements, especially 'lood especially 'lood flow flow tissue swelling, a variant called mercury6in6ru''er strain gauge is used. his *ind of strain gauge consists of a small amount of liquid mercury enclosed in a small ru''er tu'e, which is applied around e.g. a toe or leg. 1welling of the 'od y part results in stretching of the tu'e, ma*ing it 'oth longer and thinner, which increases electrical resistance. Fi'er optic sensing can sensing can 'e employed to measure strain along an optical an optical fi'er . %easurements can 'e distri'uted along the fi'er, or ta*en at predetermined points on the fi'er. +apacitive strain gauges use a varia'le capacitor to indicate the level of mechanical deformation.
M#+)$i+)' !-p#"
%echanical strain gauge used to measure the growth of a crac* in a masonry foundation. his one is installed on the Hudson6$thens Lighthouse 1imple mechanical types -such as illustrated to the left are used in civil engineering to engineering to measure movement of 'uildings, foundations, and other structures. In the illustrated e/ample, the two halves of the device are rigidly attached to the foundation wall on opposite sides of the crac*. he red reference lines are on the transparent half and the grid is on the opaque white half. (oth vertical and horiEontal movement can 'e monitored over time. In this picture, the crac* can 'e seen to have widened 'y appro/imately :.9 mm -with no vertical movement since the gauge was installed. %ore sophisticated mechanical types incorporate dial indicators and indicators and mechanisms to compensate for temperature changes. hese types can measure movements as small as :.::8 mm.
71
GRAPHS
72
Li*i!)!i,$" , &ri'' !,,' &-$)*,*#!#r 56ma/imum load cali'rated 5<: *g -5;@:# 86weight of the 'ench vice and wor* piece should 'e e/cluded during cali'ration. 96 !pen loop controls hence not a self stopping device.
NEED FOR SOCIETY 5. 1imila 1imilarr materia materials ls from from differe different nt sources sources.. 8. Investigat Investigation ion into the machina'ili machina'ility ty of materi materials. als. 9. +ompar +omparing ing and and select selecting ing cutt cutting ing tool tools. s. ;. Determ Determini ining ng optimum optimum machi machinin ning g conditio conditions. ns. <. $nalyE $nalyEing ing causes causes of tool tool fail failure ure . =. Investigat Investigating ing the most suita'le suita'le cutting cutting fluids fluids.. @. Determinin Determining g the conditio conditions ns that yield yield the 'est 'est surface surface quality quality.. A. &sta'lishi &sta'lishing ng the effects effects of fluctua fluctuating ting cutting cutting force force on tool wear wear and tool tool life. C. +an 'e 'e use in all all produc productio tion n indust industrie ries. s. 5:. +an 'e use in +#+ and %anual %anual drill drill machines. machines.
CONCLUSION
73
he completion of our project has 'een a very valua'le e/perience for all the group mem'ers. It has taught us some very important lessons which will prove to 'e invalua'le in the times to come. hrough this project, we got an opportunity to understand the wor*ing of not only various mechanical components co mponents 'ut certain electronic and software coding. It helped us to succeed in today mechanical erne. 0nder the guidance of Mr. i$##! (*)r )"i"!) , Mr. ('&##p G(p!) and )'' ,r",p "!) *#*;#r" "!) *#*;#r" , we
learnt several mechanical and practical s*ills. he project has left us priceless insight into the corporate world and added another dimension to our (achelor of technology Degree. )e were fortunate to design our project in span of si/ months within our college premises. his further further polished our leadership a'ilities and has made us more confident as my leadership a'ilities were put to test while designing the project. In application of the completion of project, we are reminded of the words once said 'y $L(&R +$%016 _"ou _"ou cannot acquire a cquire e/perience 'y ' y ma*ing e/periments. "ou "ou cannot create e/perience. "ou must undergo it>
REFRENCE 5. (ec*with 3 and Lewis (uc* # -5CA8 %echanical measurements.
|
74
;. Ting ( and Foschi R! -5C=C +ross ring dynamometer for direct force resolution into three !rthogonal components. Int. U. %achine oll Design Res. ;, 9;<69<=. <. Levi R -5C@8 %ulti component cali'ration of machine tool dynamometer. U. &ngg. Industry. 55. 55. 5:=@65:@8. %urthy RL and Totiveerachary ( -5CA5 (urnishing of metallic surfaces S a review. 2recision &ngg. 9, 5@8S 5@C. =. 1haw %+ -5C=C %etal cutting principles. 9rd ed. !/ford I(H 2u'l. +o., #ew Delhi. @. 1hneider "u 3 -5C=@ +haracteristics of 'u rnished components. %ech. ooling. ooling. 9A-5, 5C688.
A. hamiEhmnaii 1, (in !mar (, 1aparudin 1 and Hassan 1 -8::A 1urface roughness roug hness investigation and hardness 'y 'urnishing on titanium alloy. U. $chiev. $chiev. %at. %anuf. &ngg. 8A -8, 59CS5;8. C. U.#aga. %alleswara Rao, $. +henna Tesava Reddy and 2. 2.. Rama Rao, -Design and fa'rication of new type of dynamometer to measure radial component of cutting force and e/perimental investigation of optimum 'urnishing force in roller 'urnishing process , Indian 1ociety for &ducation and &nvironment -8:5:, Indian journal of 1cience and echnology. 5:.%achining echnology %achine tools and operations, Helmi a, youssef and Hassan &I6Hofy, +R+ press48::A, page`9@5,e(oo*4I1(#6C@A656;8::6;9;:6 8,Doi45:.58:5C@A5;8::;9;:8.ch5:.
75
76
77
