1. introduction


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1. introduction

  1. 1. Introduction Principles of Reliability • No branch in engineering science, with the exception of computer technology ( including communication Engineering engineering) and environmental engineering, has developed and advanced so phenomenally as Reliability Engineering during last five decades. • In todays technological world, everyone depends upon a wide array of complex equipment, machinery, systems and services to meet one’s everyday needs. And their continued functioning is critical for the well- being and quite often the survival of the humanity. 1 2Need for Product Performance Compulsions for Reliable* Quest of Excellence (better and better Product products) There are basically three main categories of* Economic Implications ( lesser and lesser compulsions to go for reliable product: costs)* Dwindling Resources (for exploding 1. Economic population) 2. Environmental 2 E i t l* Environmental Consequences (Pollution) 3. Performance -” No more than one or few decades remain before the chance to avert the threats we confront, will be lost and the prospects for humanity immeasurably diminished… A new ethics is required – a new These three are however interlinked. attitude towards discharging responsibility for caring for ourselves and for earth … this ethics must motivate a great movement, convincing reluctant leaders, reluctant government and reluctant people themselves to affect the needed changes.” -Warning to humanity given by 102 Noble laureates at Rio Conference in 1992. 3 4 1
  2. 2. Economic Compulsions Environmental Compulsions• For products, the old concept of “use and • Development in the past century has rendered “free throw” does not any more hold good, to resources ( like water, air and soil)” highly polluted. keep the wheels of the industries turning as Further pollution may endanger the existence of humanity on the Earth. Ozone layer depletion and the cost of harnessing material and energy global warming are consequences. goes up with time. • Effective utilizations of World resources is the need• For success in business under the of the hour in the 21st century as exhaustible resources become even more meagre and rare. competitive market, a product must provide • Demand of resources keeps increasing with the trouble-free service and better customer population increasing at an exponential rate. satisfaction. • Sustainable development is the solution to present• Due to tough competition internationally, state of environmental health of Earth. only a company that provides more reliable products at cheaper cost will only survive. 5 6 Performance Compulsions Reliability Definition • Products are becoming more complex, designing for Reliability by IEC is defined as the performance becomes even more challenging as complexity and performance are contradictory capability of a product ( or system or requirements. service) to perform its expected job • Product longevity would imply less world pollution and better utilization of remaining exhaustible under the specific conditions of use resources. over an intended period of time. • Hi h performance also results in l ss botheration Higher p f m n ls sults less b th ti n of after-sales service and thereby less :IEC maintenance costs, reducing overall Life Cycle International Electrotechnical Commission costs. 7 8 2
  3. 3. Expected Job Obviously, now the IEC definition The product or the unit functioning within raises questions, like … the intended bounds of performance and is operating satisfactorily. – Can this capability be quantified ?Conditions of Use (Prob. of Satisfactory Performance) Conditions of use basically refer to the – Can this quantification be used with environmental conditions under which the all kinds of products and system p product of the system has to operate. y p without resorting to any redefinition g y from case to case ?Intended (Mission) Time – Can this capability be used to It is the length of time over which we don’t compare the performance different want the product or system to have any engineering designs and technologies failure at all and desired mission of the for a product or a system and assess system should be carried out successfully their suitability? without being impaired or aborted. – Can this capability be engineered into the products? 9 10 Definition (contd.) Definition of Reliability• And, in reliability engineering, the goal is Reliability implies an aspect of engineering to optimize, in probabilistic sense, the uncertainty, which is often reflected in its performance of the system. probabilistic definition as: It is the probability that a product will perform the intended function without failure under the stated conditions of use over the stated period of time. 11 12 3
  4. 4. Objective of a Reliability Program However one must remember ?The prioritized objectives of a reliability programme are: • Instant of failure is unpredictable. Failure – To apply engineering knowledge and specialized techniques to can occur at any time and random. prevent failures or to reduce the likelihood of the frequency of failures. Example: Failure of 0.9 and 0.6 reliable systems) – To identify and check the cause of failures those do occur, despite the efforts to prevent them. • The importance of reliability lies in relative – To determine ways of coping with the failures which may occur, if terms and not in absolute terms terms. their causes have not been checked. • Failures are inevitable. No matter what you – To apply methods for estimating the reliability of new designs, and for analyzing reliability data with a view to improve future do. One can only minimize but not eliminate designs. altogether their occurrences. • Hundred percent Reliability is impossible. (LIMITATIONS OF RELIABILITY 13 ONCEPTS) 14Failures do occur if: Causes of failures • The design is inherently weak and consumes too much • Failures can be due to inherent weakness. power, suffers resonance at the wrong frequency, etc. The list of possible reasons are endless, every problem • Failures can be caused by wear out. presents the potential for errors, omissions and • Failures can be caused by the time commission. The more complex the design is, the greater is the potential. dependent mechanisms. • The actual strength of any population of components • Failures can also occur on account of varies and there are bound to be some that are errors, such as incorrect specification, , p f , relatively strong, others th t are relatively weak, l ti l t th that l ti l k however most will be of nearly average strength. Failure design or software coding, by faulty will not occur so long as the applied load doesn’t exceed assembly or test, by inadequate or improper the strength. maintenance, or simply by misuse. • Sneaks can cause failures. A sneak is a condition in which the system doesnt work properly even though every part does. 15 16 4
  5. 5. Aging can also lead to Failures • Failures can occur at any point of time in a product’s life. These failures always have a reason. • The failures would occur predominantly in early life of a product if the manufacturer has been t Such failures are called Q lit complacent. S h f il l ll d Quality failures. • Catastrophic or sudden failures can occur any time in the life and are due to accidents. • Wear out failures occur mainly towards the old age. These occur due to deterioration t2 > t1 17 18Three Types of Failures Concern in Reliability Programme • Our concern in Reliability is: – How to extend the useful life of a product? – How to minimize the chance failure of a product? – How to reduce the initial hazard rate and to avoid product failures during its period? • The first two relate to the design and depend on material selection and the choice of safety and derating factors, with an emphasis being on prevention, reduction, or complete elimination of chance f il li i ti f h failures, which considerably affect th hi h id bl ff t the reliability in actual use. • We are also concerned about the overhauling or preventive replacement of the product during its design life. • The third problem of concern is the initial period , which may range from a few minutes to several hundred hours in certain cases. • To eliminate the possibility of failures immediately after the delivery , manufacturers generally conduct test runs or debugging tests before delivery to eliminate quality failures. *Quality Failures *Sudden Failures *Wearout Failures 19 20 5
  6. 6. Various Phases of Reliability • Design phase • Raw Materials, and Parts selection and Vendor Control • Manufacturing phase • Packaging and Transhipment • Storage Reliability Function • Installation • Usage and Consumer Education • Maintenance phase • Reliability Testing, Estimation & Demonstration 21 22 Various Phases of Reliability (cont...)Various Phases of Reliability (cont...) • Design Phase • Raw Material, Parts Selection and Vendor – If any phase in the entire life-cycle of a Control product has maximum impact on its – Once the engineering design of a product is reliability, it is the design phase. Analytical accomplished, the selection of raw material, methods can help only to select an parts and assemblies is taken up as a next step alternative design technology; thereafter where the purchase department has an p p the process is iterative and repetitive till the specified performance goal is achieved. important role to play. A great majority of all Design requires ingenuity and creativeness product failures results from the suppliers and a designer ought to know what has been items. Suppliers/vendor selection, therefore already been tried before and did not work. assumes a crucial role in reliability New prototype is not build because the implementations programme since the quality of designer knows that it will work better that materials, parts, assemblies and components way, but because he has no reasons to supplied by vendors would invariably affect the doubt why it will not work until it has been final quality or reliability of the manufactured tried out. product. 23 24 6
  7. 7. Various Phases of Reliability (cont...) Various Phases of Reliability (cont…) Vendor Control • Manufacturing phase – The extent of supplies made by the vendors for – The human aspects affect the quality and workmanship in any production process. Good workmanship depends considerably manufacturing a product varies from the product upon the team spirit and the skill of a worker. to product and from country to country. In an – The responsibility of quality control is to ensure that all in- automotive industry in U.S.A., purchased plant operations and processes are performed in accordance materials may account for about 50% of the with the specifications laid down. Also all incoming materials and parts conform strictly to the specifications. manufacturing cost, where as Japan, it is about – Reliance on an inspector causes worker to be less concerned 70%. 70% Thus a manufacturer of a final product about quality But recently emphasis has shifted on making quality. recently, depends very heavily for the quality and operators responsible for these attributes as is being done in reliability of the supplies from the vendors. Japan. In Japan, QC is in fact design and process control- oriented instead of inspection-oriented. Vendor relation must involve a systematic – This has been achieved by organizing quality circles with a exchange of technical, economic and managerial company. These circles are voluntary study groups. information, and services. Some reputed manufactures own joint research facilities with their vendors. 25 26Various Phases of Reliability (cont…) Various Phases of Reliability (cont...)• Packaging and Transshipment – It is an established fact that even with the use of • Storage best packaging material, about 10 % of the – Raw materials, components and finished shipment gets damaged in transit. Transportation products are all stored for quite sometime hazards may include temperature, humidity, vibration, road conditions and shocks. before they are used or shipped. It is therefore necessary to minimize deterioration y – In case of integral environment packaging one has packaging, to protect the product from the environment so as or degradation of a product on account of the to preserve metals from rusting, keeping moisture storage. The measures to avoid degradation out, shielding electronic products particularly include specifying the shelf-life of the from electrostatic interferences. The design of product based on the laboratory tests and such a packaging forms an integral part of the field data and by establishing standards design of the original product and as such should thereof. undergo all the design reviews just as is done in case of the product itself. 27 28 7
  8. 8. Various Phases of Reliability (cont...) Various Phases of Reliability (cont...) • Installation • Usage and Consumer Education – Before a product is put to use , it often – Manufactures usually prepare operating manuals undergoes additional processing during to permit users to use the product properly and distribution, assembly, installation and checkout effectively. For proper usage of a product, etc. In situ installation may sometimes require consumer education is quite essential. special facilities including a controlled – Consumer education is usually imparted by environment,special tools and jigs, instruments l l d providing product i f idi d t information regarding th ti di the and special instructions. Preparation of user’s technical aspects of the product and its site is sometimes required before the performance in the standard popular magazines, installation of the product is carried out. The which are easily available to a user. A user must necessarily know in advance the specifications and instructions for use must accompany a product performance attributes of the product, he or she to avoid its improper installation or use. has selected to purchase amongst the various products of similar types available in the market. 29 30Various Phases of Reliability (cont...) Maintenance Phase (cont...)• Maintenance Phase – Preventive maintenance is advantageous for units whose hazard rate increase with time. Therefore, the chance – Besides one-shot equipments/devices, there are devices failures result into unscheduled maintenance whereas the or products that can be maintained by carrying out scheduled maintenance reduces the occurrence of wear- necessary preventive or corrective maintenance. out failures. The objective of schedule maintenance is to – Preventive maintenance consists of taking preventive replace an item before it wears out. measures at predetermined points of time during the operation phase, to reduce the chances of failures of – To ensure high maintainability, a designer should ensure the device whereas that the components with shorter lives would be easily – corrective maintenance or repairs are carried out only accessible within the equipment and can be removed without difficulty. This would help decreasing repair after a failure has occurred. times and increasing availability of equipment. – Sometimes maintenance or repair is carried out based on the condition of the unit or based on the signature analysis of certain parameters like vibration, noise etc. Such an activity is known as predictive maintenance. 31 32 8
  9. 9. Maintenance Phase (contd.)Maintenance Phase (contd.) – Maintenance has significant influence on the life of a • Maintainability product . – The maintainability is defined as the probability – The supply function is concerned with providing of the of a unit being restored to a functional state necessary personnel, material, parts and equipment to within a specified time interval known as down support operation in the field. Collectively, maintenance time. and supply efforts, facilities and manpower form the logistics support. – Maintainability is related to the total down time, – The logistics cost over the life time of a product often g p which consists of administrative, logistic time considerably exceeds the initial cost of the product. and the actual repair time. d h l i i – In fact, maintenance includes all actions necessary to keep – Actually the preparation time, fault location the product in usable conditions through preventive time, part procurement time, actual repair time measures which includes check-outs, testing, overhaul, repairs, instructions, operational schedules, spares and and testing time after repairs, all add up to last but not the least- personnel. increase the total down time. 33 34Maintenance Phase (cont...) Reliability : A birth to death• Availability – It is defined as the probability that a concern product is working satisfactorily at any given point of time when used under the given conditions of use. Concept and – Up time ( Available Time) is the time definition during which product is working. Down time Design and in which maintenance is done including n wh ch ma ntenance s nclud ng Development logistic and administrative time loss Manufacturing – Free time is the time during which and Installation operational use of a product is not Operation and required. maintenance – Storage time is the time during which the Maintainability product is presumed to be in operable Quality conditions but is being held as spare. Reliability 35 Various phases in a product’s life 36 9
  10. 10. Failure Data Broad Outline for Reliability Prediction• Field failure data Define the system and its conditions. – It constitutes a meaningful data source as they represents experience from the real world. Define systems performance criteria (in terms of either• Service Life data success or failure). – Data on service life is necessary in assessing the Develop System models using either Reliability Logic time characteristic of reliability Diagrams (RLD) or Fault Tree Methodology (FTA).• Data from engineering tests Compile parts list for the system. – V i Various tests Assign failure rates and modify generic failure rates using The problem of acquiring data is not an easy an appropriate procedure for the environment of use. one. Although considerable failures data has been generated and is available for the Select a prediction procedure and perform Parts Count or electronic or electrical component and device, Parts stress method for the system. Comparatively, not much published information is available on the failure of mechanical Combine parts failure rates. components. Estimate system reliability for the specified mission time. 37 38 JournalsReliability Education and Research • IEEE Transactions on Reliability • IIT Kharagpur, Reliability Engineering Center (Est. in 1983) • American Society for Quality Control. • Defence Establishments • Microelectronics Reliability.  • Nuclear Reliability and Safety Establishments • Reliability Engineering and Systems Safety. • Space Programme • The International Journal of Quality and • University of Maryland College park Maryland, Reliability Management R li bilit M m t • The State University of New Jersey, Rutgers • Quality and Reliability Engineering • New Jersey Institute of Technology, Newark • University of Arizona • International J of Performability Eng • Int J of Uncertain System • Int J of Quality Technology and Quantitative management 39 40 10
  11. 11. Thanks 41 11