Metrology and Quality Control

Transcription

1 T.Y. Diploma : Sem. V [ME/PG/PT/MH/MI] Metrology ad Quality Cotrol Time: 3 Hrs.] Prelim Questio Paper [Marks : 100 Q.1(a) Attempt ay THREE of the followig: [12] Q.1(a) (i) State the various eeds of the ispectio. [4] (A) Needs of the ispectio: To esure that the part, material or a compoet cofirms to the established stadard. To meet the iterchageability of maufacturer. To maitai the customer relatio by esurig that o faulty product reaches the customer. Provide the meas of fidig out shortcomigs i maufacture. It helps to purchase good quality of raw material, tools, equipmet which govers the quality of the fiished product. It helps to coordiate the fuctios of quality cotrol, productio, purchasig ad other other departmets of the orgaizatio. To take decisio o the defective parts. Q.1(a) (ii) If legth of sie bar is 100 mm, fid the legth of slip gauges required to build a agle of 14 by usig M45 slip gauge set. (A) Give data : Legth of sie bar (I) = 100 mm Agle () = 14 Height of slop required (h) =? Si = h/i Si 14 = h/100 h = mm For mm, slips are as follows usig M45 set Slips Remaiig size slop s [4] Q.1(a) (iii) Explai why sie bar is ot used for measuremet of agle greater tha 45, [4] if accuracy i agle measuremet is required. (A) Sie bar is ot used for measuremet of agle greater tha 45 : We kow that agle is measured by usig sie bar is based o sie priciple, si = h/l Where, h = Required slip gauge combiatio l = ceter distace of rollers. The relatioship betwee the agular settig accuracy (d) ad ay error which may be preset i the slip gauge combiatio (dh) or the ceter distace betwee roller (dl) ca be determied by differetiatig the equatio si = h/l. Or h = I si The effect of error i specig of roller cetres (dl) or error i combiatio of slip gauges dh o agular settig accuracy ca be obtaied by partial differetiatio of the above equatio h = L si dh dl = si. d d + L cos dh = si, dl + L cos. d 1

2 Vidyalakar : T.Y. Diploma MQC dh si dl = L cos. d d = d = dh si dl Lcos Lcos dh dl Lcos L. ta dh dh = ta Lsi L But L si = h dh dl Therefore, d = ta h L From above it is clear that error is the fuctio of ta. Below 45 errors is smaller which icreases rapidly above 45, as ta 45 is equal to oe. Thus i geeral it is preferable ot to use the si bar for measurig agles greater tha 45 if high accuracy is required. Q.1(a) (iv) Defie lie stadard ad ed stadard. Give oe applicatio of each. [4] (A) Lie stadard is the stadard i which distace is measured betwee two parallel lies. Applicatio : Steel rule, measurig tape Whe the distace is measured betwee two parallel surfaces it is called as ed stadard Applicatio : Slip gauges, Ed bars Q.1(b) Attempt ay ONE of the followig: [6] Q.1(b) (i) Write the procedure for measurig effective diameter of screw thread usig [6] two wire method. (A) Procedure for measurig effective diameter of screw thread usig tow wire method. First the micrometer readig is oted o a stadard cylider (gauge). Let the readig as R1. The takig the micrometer readig with wires over the stadard cylider (gauge). Let the readig as R2. The puttig the work piece whose effective diameter is to be foud. 2

3 Prelim Paper Solutio Micrometer readig is take by placig two wires over the work piece. Let readig over the wire as M. The the effective diameter is calculated as, E = T + P where E = Effective Diameter. T = Dimesio uder the wires = S (R1 R2) or T = M 2d P = Wire costat. S = stadard cylider (gauge) diameter d = Wire Diameter Q.1(b) (ii) What is legal metrology? State ay two fuctios of legal metrology. [6] (A) Legal metrology is cocered with the uits of measuremet, methods of measuremet ad the measurig istrumets, i relatio to the statutory techical ad legal requiremets. The legal metrology is directed by a atioal orgaizatio which is also called Natioal service of Legal Metrology. It icludes a umber of iteratioal orgaizatios whose ultimate object if to maitai uiformity of measuremet throughout the world. The fuctios of legal metrology: 1) To esure coservatio of atioal stadards. 2) To guaratee their accuracy by compariso with iteratioal stadard. 3) To carry out scietific ad techical work i all fields of metrology ad methods of measuremets. 4) To regulate, advice, supervise ad cotrol the maufacture ad repair of measurig istrumets. 5) To ispect the use of these istrumets ad the measuremet operatios whe covered uder public guaratee. 6) To detect fraud of measuremets. 7) To orgaize traiig i legal metrology. 8) To take the part i the work of other atioal orgaizatios iterested i metrology. Q.2 Attempt ay FOUR the followig : [16] Q.2(a) Explai the (LVDT) Electrical comparator with eat sketch. [4] (A) The (LVDT) Electrical Explaatio: LVDT works o mutual iductace priciple. It is a trasformer cosistig of three symmetrically spaced coils carefully woud o a isulated bobbi. It cosists of a primary coil woud o a isulated bobbi ad two idetical secodaries symmetrically spaced from the primary. AC carried excitatio is applied to the primary ad two secodaries are coected exterally i a series oppositio circuit. There is o-cotactig magetic core which moves i the ceter of these coils. Motio of this core varies the mutual iductace of each secodary to the primary, which determies the voltage iduced from the primary to each secodary. 3

4 Vidyalakar : T.Y. Diploma MQC If the core is cetered i the middle of the two secodary widigs, the the voltage iduced i each secodary widig will be idetical ad 1800 out of phase ad the et output will be zero. If the core is moved off middle positio, the the mutual iductace of the primary with secodary will be greater tha the other, ad a differetial voltage will appear across the secodaries i series which ca be directly calibrated i terms of liear movemet of core. Q.2(b) Explai Parkiso s gear tester with eat sketch. [4] (A) Parkiso's Gear Tester : Costructio : 1) Oe fixed spidle ad other movable spidle is mouted o a flat base. 2) The movable spidle moves alog with base by rollig actio o the mai base plate. 3) A Master gear is mouted o the fixed spidle ad gear to be tested is mouted o movable spidle. 4) The dial gauge is set to ote the errors. Workig: whe master gear is rotated slowly, a gear to be tested will also get rotatio movemet because of their meshig. Errors i the maufactured gear cause the gear to move away from the ceterlie of spidle. Whe gear to be tested moves the floatig body also moves by the same distace. Because of displacemet of floatig body dial gauge gives displacemet. The variatio i the readigs ca be observed ad plotted i the graphical format. 100% Ispectio is ot preferred i the idustry for mass productio due to followig reasos. Q.2(c) What is Iterchageability? State its eed ad relevace i mass productio [4] idustries. (A) Iterchagability: Whe a system of such kid is used ay oe compoet selected at radom will assemble correctly with ay other matig compoet that too, selected at radom, the system is called iterchagability. The maufacture of compoets uder such coditios is called iterchable maufacture. Need ad relevace i mass productio idustry. It facilitates productio of matig compoets at differet places, by differet operator, hece outsourcig ca be possible. Productio o a iterchagable basis results i icreased output with a correspodig reductio i maufacturig. The replacemet of wor out or defective parts ad repairs become very easy. There is a divisio of labour, the operator has to perform same limited operatio agai ad agai thus he becomes specialized i that particular work which helps to improve quality ad reduce the time for operatio. The products ca be categorised o the basis of specific operatios required which ehaces the quality ad reduces the cost. 4

5 Prelim Paper Solutio Q.2(d) Explai Taylor-Hobso-Talysurf with eat sketch. [4] (A) Taylor-Hobso Talysurf : Explaatio: The Taylor- Hobso Talysurf is a electroic istrumet workig o carrier modulatig priciple. The measurig head of this istrumet cosists of a diamod stylus ad skid or shoe which is draw across the surface by meas of a motorized drivig uit. I this case the arm carryig the stylus forms a armature which pivots about the ceter piece of E- shaped stampig. O two legs of (outer pole pieces) the E shaped stampig there are coils carryig a AC curret. These two coils with other two resistaces form a oscillator. As the armature is pivoted about the cetral leg, ay movemet of the stylus causes the air gap to vary ad thus the amplitude of the origial AC curret flowig i the coil is modulated. The output of the bridge thus cosists of modulatio oly. This is further demodulated so that the curret ow is directly proportioal to the vertical displacemet of the stylus oly. The demodulated output is caused to operate a pe recorder to produce a permaet record ad a meter to give a umerical value directly. Q.2(e) State the advatages ad limitatios of mechaical comparator. [4] (A) Advatages of mechaical comparators (i) Cheaper i cost. (ii) No eed of exteral power source. (iii) Geerally liear scales are adopted (iv) Robust ad compact desigs. (v) Easy to sue ad uderstad. Limitatios of mechaical comparators (i) Due to movig parts more wear ad tear. (ii) Sesitive to shocks ad vibratios. (iii) Parallax errors are possible. (iv) Rage of applicatios is limited. Q.3 Attempt ay FOUR of the followig : [16] Q.3(a) Defie ay four factors affectig accuracy of measuremets. [4] (A) Factors affectig accuracy of measuremets Measurig Istrumet : The accuracy of the measuremet depeds upo the various static ad dyamic characteristics of measurig istrumets. (like rage, readability, sesitivity, repeatability etc.) 5

6 Vidyalakar : T.Y. Diploma MQC Evirometal Coditios : Factors like temperature, pressure ad humidity greatly affects o the accuracy of the measuremet. As per the iteratioal practices temperature i the test laboratories should be maitaied at 20C It is recommeded to maitai positive air pressure (10-20 N/m 2 ) Calibratio of istrumets : It is importat that ay measurig system should be calibrated periodically to get meaigful results. Hadlig of istrumets : Measurig istrumets must be hadled carefully to avoid the errors i measuremet ad also to save the life of istrumet. Proper method of usig a istrumet. Q.3(b) A agle of is to be developed usig agle gauge set of : (1, 3, 9, 27, 41) (1, 3, 9, 27) (3, 6, 18, 30) & a square block. Show the arragemet with eat sketch. (A) Developmet of agle : '27" 1) As 139 is greater tha 90, first use go(square block) = 49 2) 49 = ) 30' = 27' + 3' 4) 27" = 30" 3" [4] Q.3(c) Distiguish betwee accuracy ad precisio with suitable sketch. [4] (A) Accuracy Precisio (i) The closeess to the measured value with true value is called accuracy. Repeatability of measurig process is called precisio. (ii) Costlier to achieve great accuracy Easier ad cheaper to achieve precisio (iii) It is related to true value. It is related to average value. (iv) Example Example 6

7 Prelim Paper Solutio Q.3(d) Defie the terms : [4] (i) CLA (ii) Ra (iii) RMS (iv) Rz (A) (i) CLA : Cetre lie average ( CLA ) is the value of height of the udulatio of the surface. This practice is adapted for obtaiig the umerical evaluatio of the surface texture is to use a parameter base o the cross sectioal profile of the surface uder examiatio. (ii) Ra : Arithmetic mea deviatio from the mea lie of profile is the average value of the ordiates from the mea lie Ra (Roughess average) R = 1 A y dx L 0 (iii) RMS value : It is defied as the square root of the arithmetic meas of values of the squares of ordiates of surface from mea lie. RMS value = y y y... (iv) Rz : The average differece betwee the five highest peaks ad five deepest valleys withi the samplig legth measured form a lie, parallel to the mea lie ad ot crossig the profile are take which are defied as, R z = 1 5 [(R 1 + R 2 + R 3 + R 4 + R 5 ) (R 6 + R 7 + R 8 + R 9 + R 10 )] Q.3(e) Explai how the parallelism betwee two plaes ad parallelism betwee two axes is checked with eat sketch. (A) [4] Parallelism betwee two plae Parallelism betwee two axes Parallelism betwee two plaes: The test for parallelism of two plaes is carried out i two directios (geerally perpedicular to each other). The dial idicator, which is held o a support with a flat base, is moved i oe plae over a give legth, ad the feeler is made to rest agaist the secod plae; ad the deviatio is oted dow. 7

8 Vidyalakar : T.Y. Diploma MQC Parallelism betwee two axes: I this test, the dial idicatoor is held o a support with a base of suitable shape, so that it slides alog a cylider represetig oe of the two axes; ad the dial idicator is adjusted so that its feeler slides alog the cylider represetig the secod axis. The maximum deviatio betwee the axes at ay poit may be determied by getly rockig the dial idicator i a directio perpedicular to the axes. I the same way the parallelism may be tested i the perpedicular plae. Q.4(a) Attempt ay THREE of the followig: [12] Q.4(a) (i) Explai the various types of quality audit. [4] (A) (1) Iteral Audit : Whe a orgaizatio coducts a audit o its ow quality system usig its ow staff/exteral cosultats, the audit is kow as iteral quality audit. Importat poits are : auditig staff must be traied for coductig this exercise ad should ot bias agaist the fuctioal departmet beig audited. (2) A Exteral Audit : The Exteral quality audit is performed by the purchasig orgaizatio upo the supplier orgaizatio. The idea here is to have a assessmet of the supplier's processes i order to have cofidece that the supplier would be able to supply goods or services of a agreed quality level o a sustaied basis. Importat poits is these audits ca be performed by the traied persoel of the purchasig orgaizatio or a outside agecy hired by them. (3) A Extrisic Audit : This audit is performed by the certificatio bodies (ISO registered bodies) o the applicat orgaizatio seekig such certificatio. If these, auditors, after coductig the quality audit o the orgaizatio with respect to a stadard, fid the orgaizatio to be worthy eough, the certificatio is grated to the orgaizatio. Third party audits ormally results i the disruptio of day-to-day activities of the orgaizatio beig audited durig the duratio of the audit. Apart from the registered certificatio bodies, the third part audit may also be coducted by some govermet departmets dealig with eviromet ad pollutio, health ad safety, atomic eergy etc. Q.4(a) (ii) Defie the terms Rq, CLA, RMS ad R Z values with respect to surface fiish. [4] (A) Rq (Geometric average roughess) : Rq is the geometric average height of roughess compoet irregularities from the mea lie, measured withi the samplig legth. CLA : It is defied as the average height from a mea lie of all ordiates of the surface regardless of the sig. h h h... h 1 2 CLA = Ra = = RMS : It is defied as the square root of the mea of the squares of the ordiates of the surface measured from the mea lie h1 h2 h3... h RMS : selected legth L is divided ito equal parts h1, h2, h3, h4,.., h are the heights of selected poits 1,2,3,4.. Rz : i this the average differece betwee the five highest peaks ad five deepest valleys withi the samplig legth, measured from a cetre lie. Rz = 1/5 [(R1 + R2 + R3 + R4 + R5) (R6 + R7 + R8 + R9 + R10)] 8

9 Prelim Paper Solutio Q.4(a) (iii) Explai cost of quality ad value of quality. [4] (A) Cost of quality ad value of quality : The balace betwee the cost of quality ad value of quality gives optimum quality of desig. From compaies poit of view profit is more importat. It is ot ecessary that the compay should maufacture 100% quality product the study of optimum quality desig ivolves market survey. While carryig out market survey, expected sale for particular quality, profit ad competitio i the market is to be cosidered. The quality of desig should meet the eed of the customer ad at the same time its maufacturig cost should be such which will yield maximum profit. Q.4(a) (iv) State the various factors cotrollig the quality of desig. [4] (A) Factors cotrollig quality of desig are : (1) Desig does ot reflect the customer's requiremets. (2) The product which the producer offers would ot probably satisfy the customer, eve if it does sufficietly coform to the desig. (3) Quality of desig is usually idicated by completeess ad correctess of specificatios. (4) Drawigs, catalogues, etc. Q.4(b) Attempt ay ONE of the followig: [6] Q.4(b) (i) Defie TQM. Describe ay 3 pricipal elemets of TQM. [6] (A) TQM : Defiitio : TQM is the busiess process ad philosophy fouded o customer satisfactio ad eds with the customer. TQM refers to the ivolvemet of staff i a orgaizatio together which icludes suppliers, distributors, ad eve customers i brigig about quality satisfactio. Elemets of TQM (i) Customer satisfactio : It is the ultimate goal i TQM ad thus forms the focal elemet i TQM. TQM aims at satisfyig customer's requiremets which ever remai costat but keep o chagig i times, eviromet, circumstaces, eeds, fashio, stadard of livig etc. (ii) Do it right first : TQM adopts the policy of ZERO defects. There is o scope for rework ad rejectios. The right first time or zero defect is the result of a emphasis o prevetio ad use of SPC (statistical process cotrol). (iii) Cotiuous Improvemet : the orgaizatio has to scope up with the chagig requiremet of customers. The TQM strives for ever better quality, cost reductio to face competitio ad for the survival of the orgaizatio. (iv) Employee Ivolvemet : all the persos workig i the orgaizatio icludig maagers ad workers should be ivolved i TQM operatio. A positive attitude towards customer ad costat ehacemet of quality must be igraied i the mids of the employees. (v) Empowerig the staff (vi) Bechmarkig (vii) Feedback mechaism 9

10 Vidyalakar : T.Y. Diploma MQC Q.4(b) (ii) Explai the advatages ad limitatios of ISO [6] (A) Advatages of ISO 9000 : (1) ISO 9000 series of stadards useful to meet the requiremets of a iteratioally uiform quality system (2) It would ehace foreig exchage. So it is importat for the Idia idustry to adopt it (3) It eables the compay to built customer's cofidece (4) It reduces the eed of assessmet by multiple buyers (5) Motivates the employees ad develops pride i them for achievig excellece Limitatios : (1) Formulatio ad documet of the system is complicated ad time cosumig (2) Assessmet ad registratio are also expesive (3) Uless carefully iterpreted ad plaed the system ca become bourdo some. (4) It eed to chage attitude ad accept ew workig practices may strai the maagemet Q.5 Attempt ay TWO of the followig: [16] Q.5(a) Explai the costructio ad workig of sigma comparator with eat sketch. [8] (A) Fig shows the costructio details of the sigma comparator. The vertical beam is mouted o flat steel sprig ad coected to fixed members which i tur are screwed with back plate. The shak at the base of the vertical beam is arraged to take a measurig cotact selected from the available rage. The stop is provided to restrict movemet at lower extremity of the scale. Higed assembly carryig the forked arms. The metal ribbo attached to the forked arms passes roud the spidle causig it to rotate o specially desiged miiature ball bearigs. The dampig actio to the movemet is affected by a metal disc mouted o the spidle rotatig i a magetic field betwee a permaet maget ad a steel plate. The idicatig poiter is secured to a boss o the disc The trigger is used to protect the measurig cotact. At the upper ed of the measurig beam a adjustable screw is provided for fial zero settig o the scale., Q.5(b) With a eat sketch, explai measuremet of tooth thickess by costat chord method. (A) [8] Costat chord of a gear is measured were the tooth fials touch the flak of the basic rack. The teeth of the rack are straight ad iclied to their cetre lies at the pressure agle as show i figure. The gear tooth ad rack space are i cotact i the symmetrical positio at the poit of cotact of the flaks. The chord is costat at this positio irrespective of the gear of the system i mesh with the rack. This is the property utilized i the costat chord method of the gear measuremet. 10

11 Prelim Paper Solutio The measuremet of tooth thickess at costat chord simplified the problem for all umber of teeth. Lie AB is kow as costat chord. The value of C ad its depth from the tip d where it occurs ca be calculated mathematically ad the verified by a istrumet. d = m 1 cossi 4 C = AB = costat chord C = AB /z m.cos 2 Q.5(c) Followig are the ispectio results of soldered PCB boards for 6 days. Draw proper cotrol chart ad coclude. Day No. of PCB checked Defects foud (A) This is the problem related to U chart. Step I calculate the umber of defects per uit i each lot (U) U = c/ = umber of defects i the lot/umber of uits i the lot Sample calculatio for day 1 U = 4/20 = 0.20 Step II Calculate U bar U bar = Total defects i all lots/total uits i all lots U bar = 18/136 = Step III Calculate UCL, LCL for each lot UCL : U bar + 3(sq. Root U bar/) LCL : U bar 3(sq. Root U bar/) UCL / 20 = LCL : / 20 = (if LCL is egative the assume it to 0) Day No. of PCB checked () Defects foud U UCL LCL [8] Q.6 Attempt ay TWO of the followig: [16] Q.6(a) The followig table gives the umbers of missig rivets oted at aircraft fial [8] ispectio: Air Plae No. No. of missig reverts Air Plae No No. of missig reverts Air Plae No No. of missig reverts Fid C compute trial cotrol limits ad plot cotrol chart for C. What values of C would you suggest for the subsequet period? 11

12 Vidyalakar : T.Y. Diploma MQC (A) Step I Calculate C = Sum of total defects/quatity ispected C = 351/25 = Step II Calculate statistical cotrol limits for C chart Step III Plot C chart Step IV Commets o C chart Q.6(b) Explai the terms : [8] (i) Primary texture (ii) Secodary texture (iii) Samplig legth (iv) Lay (A) Studet may have may other factors which affect quality of the product. (i) Primary texture : Irregularities of small wavelegth are called primary texture. These are geerally caused due to cuttig tools, frictio, wear etc., it is also termed as roughess. (ii) Secodary texture : Irregularities of cosiderable wavelegth are called secodary texture, also called as waviess. These are geerally caused due to misaligmets, o liear feed motios, geerally due to problems i machie tools (iii) Samplig legth : It is legth of the profile ecessary for evaluatio surface roughess. Samplig legth is related to the maufacturig process adopted, desired surface roughess value ad the measurig istrumet available. (iv) Lay : Lay is the directio of predomiat surface patter, decided by the maufacturig process adopted or lay is decided depedig o maufacturig process adopted. Q.6(c) Followig are the ispectio results of magets for five observatios. Draw appropriate cotrol chart ad coclude. Week No No. of magets ispected Defectives foud (A) Lot size Defectives Fractio Defectives % defectives [8] 12

13 Prelim Paper Solutio d 329 P = = 3626 = 3626 = = = 9.07% UCL = P + 3 P 1 P = UCL = 12.26% LCL = P 3 P 1 P = LCL = 5.88% = =