Metrology and Quality Control

Transcription

1 T.Y. Diploma : Sem. V [ME/MH/MI/PG/PT/FE/FG] Metrology and Quality Control Time: 3 Hrs.] Prelim Question Paper Solution [Marks : 100 Q.1(a) Attempt any THREE of the following: [12] Q.1(a) (i) ra te sket o Hole asis ystem and gie reason for [4] selecting them. Hole Basis System In this system, the design size of hole, whose lower deviation (fundamental deviation) is zero, is assumed as basic size Sind different clearances or interferences are obtained by varying the limits of the shaft to have different class of fit. In other words, the limits of the hole are kept constant and those of the shaft are varied so as to obtain the necessary essary fit. In this system, the hole has constant high and low limits for all fits of the same accuracy grade and for the same basic size. As it is very easy, convenient and less costly to make holes of correct sizes by using drills, reamers etc., this system is preferred in industries. It is also much easier to vary shaft sizes according to the fit required, by adjustable methods such as grinding and turning. Also, inspection of shafts can be done easily and rapidly with the help of adjustable gauges. Direct external measurement is easier than internal measurement. ement. Fig.: Hole basis system. Q.1(a) (ii) Define the terms scientific metrology and industrial metrology. [4] Scientific Metrology : It deals with the establishment and development of measurement standards along with their maintenance. Industrial Metrology : It has to ensure the adequate functioning of measurement instruments used in industry as well as in production and testing processes. 1114/TY/Pre_Pap/2014/CP/MQC_Soln 1

2 : T.Y. Diploma MQC Q.1(a) (iii) List the four instruments used in angular measurement. [4] The following are the instruments for angular measurements : 1) Universal bevel protractor 2) Spirit level 3) Sine bars 4) Angle dekkor 5) Clinometer 6) Auto-collimetor 7) Angle gauge Q.1(a) (i) State any four characteristics of good comparator. [4] A good quality comparator is expected to have the following essential characteristics : 1) Robust design and construction : The instrument must be robust in design and construction, so that, it will withstand the effects of ordinary usage without affecting its measuring accuracy. 2) Linear scale : Recording or measuring scale should be linear and uniform (straight line characteristic) and its indications should be clear. 3) High magnification : The magnification ication of the instrument should be high as possible as to detect smaller deviation in size of component. 4) Versatility : The comparator should be so designed that it can also be used for several purposes other than thickness or external diameter measurements. 5) The contact plunger should be provided with a hardened steel contact or diamond, to minimize the wear effects. 6) The indicating ing system should be such that the readings are obtained in least possible time. 7) Indicator should be provided with maximum compensation for temperature effects. 8) The pointer should come rapidly to rest and should be free from oscillations. 9) System should be free from backlash and unnecessary friction and it should have minimum inertia. 10) Means should be provided for lifting the plunger for quick insertion of the work and the table of the instrument should preferably be adjusted in the vertical sense. [4] 2

3 Prelim Question Paper Solution Q.1(b) Attempt any ONE of the following: [6] Q.1(b) (i) Draw labeled diagram of showing the working mechanism of dial [6] indicator. Fig.: Working mechanism of dial indicator. Q.1(b) (ii) State the taylors principal of gauge and draw labeled sketch of [6] Go-NOGO plug gauge. Taylors principal of Gauge According to Taylor's principle, 'GO' and 'NO GO' gauges should be designed ed to check maximum and minimum material conditions as below : 'GO' Limit : This designation is applied to 'maximum material conditions' i.e. upper limit of shaft and lower limit of hole. 'NO GO' Limit : This designation is applied to 'minimum material conditions' i.e. lower limit of shaft and upper limit of hole. 'GO' plug gauge is the size of minimum limit of the hole. 'NO GO' plug gauge is the size of the maximum limit of the hole. 'GO' for snap gauge corresponds to maximum limit of the shaft and 'NO GO' to minimum limit of the shaft. Taylor's principle states that, GO gauges should be of full form, such that, 'GO' gauge should check all possible elements of dimension at a time (such as roundness, taper, location etc.), whereas 'NO GO' should check only one dimension at a time. As GO gauge assembles with mating component, it should check number of dimensions, including errors of form such as straightness, roundness, squareness etc. which are outside the maximum metal limit. NO-GO gauge, 3

4 : T.Y. Diploma MQC on the other hand should check only one dimension of part at a time in order to find out any dimensions, which are outside the minimum metal limit. Sketch of Go-NOGO plug gauge : (a) Plug gauge for hole. (b) Snap gauge for shaft. Q.2 Attempt any FOUR of the following in brief [16] Q.2(a) Draw a labeled led sketch of pneumatic comparator and list down its [4] components. Pneumatic Comparator Vidy Q.2(b) State merits and demerits of acceptance sampling. [4] Merits of Acceptance Sampling (a) Since-only a part is inspected, the sample may not represent the exact/true picture of the entire lot; hence risk of making wrong decisions about the lot is involved. (b) The producer will pass on the cost of rejected lot on the consumer. (a) S dyalankar 4

5 Prelim Question Paper Solution (c) This method may not be suitable for taking decision on acceptance or rejection of very costly items. (d) It is necessary to use random sampling, select proper sample size and acceptance criteria for accurate results. De-merits of Acceptance Sampling (a) Random sampling. (b) Proper sample size and lot size. (c) Acceptance criteria. (d) Quality characteristic to be measured. Q.2(c) What is importance of Quality Audit? [4] Importance of Quality Audit Quality audit is an important management agement ent tool for achieving the objectives in the organization's policy. According to ISO-8402, Quality Audit is defined as, "A systematic and independent examination to determine whether quality activities and related-results comply with planned arrangements and whether these arrangements are implemented effectively and are suitable to achieve objectives". Quality audit is analogous to accounting audit. Accounting audit checks the books and bookkeeper, keeper, whereas, quality audit checks the product, inspectors and inspection devices. Quality audit ensures the adequacy of control system for betterment of quality. In brief, quality audit is the examination of records or activities to verify their accuracy, usually by some one other than responsible for them. Once a system of quality is established, it is needed to measure its effectiveness and its report is to be submitted to management. This is done by quality audit. Quality audit is carried out at periodic schedule or when need arises due to symptoms of bad quality. Quality audit team consists of president as chairman and several other members including the experts from concern department. Quality audit is used in various departments. Effective Quality Audit requires active co-operation of all departments and sections concerned with quality of product. (i) Design Department : To examine whether the design specifications meet to maximum consumer needs. They should be complete and clear cut. 5

6 : T.Y. Diploma MQC (ii) Production Department : To examine whether the manufacturing specifications conform to design specifications or not. They should be complete and clear cut. (iii) Inspection Department : Adequacy of measuring instruments used in the process. Selection of inspection process. (iv) Quality Control : Collection of data from inspection department. Control charts are to be prepared. (v) Field Work / Sales Departments : Processing on the consumer complaints. Necessary action taken by the company for consumer satisfaction. Quality audit is independent of the established inspection and process control. The results of audit are properly rly documented and forwarded to the quality manager as well as the concerned sections of organization. Any discrepancies found in audit are rectified within a reasonable period. Thus, quality audit is a tool to help in improving quality of product. Q.2(d) Draw the labeled ed sketch of Parkinson Gear tester. [4] 6

7 Prelim Question Paper Solution Q.2(e) What are the sources of error in mfg. gears? [4] Sources of error in mfg. gears The gears are manufactured by two methods, gear reproducing method and gear generating method. In gear reproducing method, a formed involute cutter is used to cut gear teeth. The various sources of errors are, (a) Errors in manufacture of cutter. (b) Errors in positioning of cutter relative to work. (c) Errors due to incorrect indexing of gear blank. In gear generating method, the cutting ting tool forms the profile of several teeth simultaneously during constant motion of tool and blank. The various sources of errors rs are, (a) Errors in manufacture of cutting tool and blank. (b) Errors in positioning the tool relative to work. (c) Errors in relative e motion of tool and blank during cutting operation. Q.3 Attempt any FOUR of the following : [16] Q.3(a) State the importance of Six-Sigma Sigm quality programme. [4] Six-Sigma igma quality programme 1) Customer drien : Six-sigma is proactive rather than reactive, as it sets out to determine how improvements can be made even before defects or shortcomings are found. 2) Continuous Improement Enironment : Six-sigma is valuable, because it creates an environment for improving productivity and efficiency in a business environment of continuous improvement. It gives everyone an opportunity to make improvements to traditional processes. Employees, who are trained in Six Sigma processes, are able to identify problem areas that slow down production or the ability to perform assigned tasks. Employees are able to visualize how processes are currently being completed and identify improvement ideas continuously. [4] 7

8 : T.Y. Diploma MQC Continuous improvement helps to improve existing products and processes, develop new products and processes that ultimately provide financial savings through improved efficiency and effectiveness. 3) Customer satisfaction : It helps in increased customer satisfaction due to ability of handling competition, which has increased considerably in today's business world to offer better quality products or services to their customers and that too at competitive rates. 4) Dominance oer other quality control programmes : Six-Sigma is dominant over all other existing quality improvement techniques, because it is flexible and can be altered to suit the requirements of new businesses that might come up in the near future. Q.3(b) Define acceptance sampling and 100% inspection. [4] Q.3(c) Explain the importance of QS standard. [4] Q.3(d) State the meaning of (i) Flow (ii) Wainess (iii) Lay (i) Roughness wrt the surface finish. Q.3(e) Write importance of TQM. [4] Q.4(a) Attempt any THREE of the following: [12] Q.4(a) (i) Find Mean, Mode, Median and Standard deiation for following [4] data : Q.4(a) (ii) Differentiate between precision and accuracy. [4] Q.4(a) (iii) Explain Quality of Conformance and Quality of Performance. [4] Q.4(a) (i) Calculate the Alignment error for the Headstock and Tailstock [4] [4] 8

9 Prelim Question Paper Solution for the following data. Initial reading of dial indicator = 0.1 mm Final reading of dial indicator = 0.2 mm Moement of carriage along longitudinal direction = 100 mm Q.4(b) Attempt any ONE of the following : [6] Q.4(b) (i) Enlist the Sampling plans and Draw the block diagram of Single [6] Sampling Plan. Q.4(b) (ii) What do you understand by Linear measurement? List the arious instruments used for Linear measurement. ent. Q.5 Attempt any TWO of the following: [16] Q.5(a) In the lot of 50 pieces each subgroup up is of 5 pieces and for 10 [8] subgroup X-bar and R-alues for the length of Pieces is as under. X-bar R 1) ) ) ) ) ) ) ) ) ) al (Gien data : A 2 = D 3 = 0 D 4 = 211 D 2 = 2.362) Dla Q.5(b) (i) Define CLA and RMS alue applied to surface roughness measurement? (ii) What is arious techniques of qualitatie analysis? Explain. Q.5(c) List the adantages and limitation of ISO 9000 standard. [8] Q.6 Attempt any TWO of the following: [16] [6] [8] 9

10 : T.Y. Diploma MQC Q.6(a) (i) Define the process capability and state how it is achieed. (ii) State the meaning and importance of SQC. Q.6(b) (i) Describe Taylors principal for design of limit gauge. (ii) State adantages and disadantages of optical comparator. [8] [8] Q.6(c) (i) What is interchangeability and its adantages. (ii) Requirement of good comparator. [8] [8] 10