2Meaning of Quality Control The word ‘quality control’ comprises of two words i.e.‘Quality’ & ‘Control’Quality is the reflection of your commitment to your customer. It is the sum of various characteristics of the product such as:ShapeDimensionCompositionStrength and durabilityFinish and colour etc.Meaning of Quality Control
3ControlIt is the process of ensuring that everything happens in conformity of:Plan adoptedInstructions issued andPrinciples establishedThe aim is to detect any error or deviation from the set standards, take corrective actions and prevent recurrence.It applies on everything-MenThingsActions
4“Quality control means the recognition and removal of identifiable causes and defects and variables from the set standards.”- J.A. Shubin“Quality control includes techniques and systems for the achievement of the required quality in the articles produced and for the elimination of the sub-standard goods”- Tome, Simen, and H.C.GillDefinitions
5Objects of Quality Control Establishing Quality StandardsSmooth Production ProcessDetecting Deviations in Production ProcessAscertaining Reasons for Low QualitySegregation of Defective Products
6Principles of Quality Control System Clear-cut standards should be fixed.Responsibility for quality of product manufactured be fixed.Routine checks on uniform application of measures.Control should be applied at every stage.Unanimity among workers and managementMaintaining proper records of quality.Principles of Quality Control System
7How to Exercise Quality Control Fixing Standards of QualityControl over Raw MaterialControl over Production OperationsInspection of Machinery and EquipmentPromptness in Inspecting QualityQuality ConsciousnessApplication of Statistical Methods of Quality Control
8Factors Affecting Quality Control Cost of ProductionRequirements of CustomersEquipment and Tools UsedUtility of ProductAttitude of WorkersScale of Operations
9MEANINGQuality control is a system of inspection ,analysis , and action applied to a manufacturing process so that, by inspecting a small portion of the product currently produced, an analysis of its quality can be made to determine what action is required on the operation in order to achieve and maintain the desired level of quality. - JOSEPH MANUEB According to Manueb , quality control is the system whereby it is determined by inspection whether the product conform to the quality standards or not.If the desired quality standard is not achieved then corrective action is also taken in this system.
10FUNCTIONS OF QUALITY CONTROL DETERMINING STANDARDS: Every firm has its own requirements for quality standards. Neither high quality nor low quality is good for a firm’s product. Standards can be set up so that the requirements of the product can be discussed properly through quality control. KEEPING RECORD: All the records of various quality standards and inspection reports should be kept so that proper controls can be maintained and improved when required. DETERMINING SAMPLING LIMITS: Because its at times difficult for the firm to maintain the usual standard, thus, certain quality limits are fixed and goods complying to those limits are accepted and others are rejected. DEVELOPMENT OF BETTER QUALITY DEVICES: Through quality control, management gets to develop better quality control systems so that there is product efficiency and product economy.
11ADVANTAGES OF QUALITY CONTROL PRODUCERSQUALITYCONTROLHELPSCONSUMERS
12(i) Reductions in costs: Since only a fraction of output is inspected ,costs of inspection are greatly reduced. Also, it minimizes the wastage leading to better utilization of resources. (ii) Greater efficiency: Not only there is reduction in costs but the efficiency also goes up because much of the boredom is avoided, the work of inspection being considerably reduced. (iii) Easy to apply: An excellent feature of quality control is that it is easy to apply. Once the system is established, it can be operated by persons who have not had extensive specialized training or a highly mathematical background. It may appear difficult only because the statistical principle on which it is based is unrecognized or unknown, however, as these principles are actually based on common sense, the quality control method finds wide application. (iv) Early detection of faults: Quality control ensures an early detection of faults and hence a minimum waste of reject production. The moment a sample point falls outside the control limits, it is taken to be a danger signal and necessary corrective action is taken. On the other hand with 100 per cent inspection unwanted variations in quality may be detected at a stage when a large amount of faulty products have already been produced. Thus there would be a big wastage. Control chart, on the other hand provides a graphic picture of how the production is proceeding and to tell management where to look for trouble.
13(v) Adherence to specifications: Quality control enables a process to be brought into and held in a state of statistical control, a state in which variability is the result of chance causes alone so long as a statistical control continues. Specifications can be accurately predicted for the future, which even 100 per cent inspection cannot guarantee. Consequently, it is possible to assess whether the production processes are capable of turning out precuts which will comply with the given set of specification. (vi) In certain cases 100% inspection cannot be carried out without destroying all the products inspected; for example, while testing breaking strength of chalks, proofing of ammunition, etc. in such cases if 100% inspection methods are followed then all the items inspected will be destroyed. Hence sampling must be resorted to . (vii) To determine the effect of change in process: With the help of control charts one can easily detect whether or not a change in the production process results in a significant change in quality. (viii) Statistical quality control ensures overall coordination. Statistical quality control provides a basis upon which the difference arising among the various interests in an organization can be resolved. In some instances. For example, production engineers may set specifications that are so tight that the operating staff cannot meet them economically and consequently there is an unnecessary high scrapping rate. In other instances the specifications may be too loose and product
14quality will be sacrificed unnecessarily quality will be sacrificed unnecessarily. In either type of case the control recurs provide a valuable lad in solving the problem of getting the standing information on plant capabilities and customer requirements must also be considered in relation to the quality and the sale value of the product. QC has a special role to play in a country like India because of the wide variations encountered in raw materials and in machines. The importance of applying SQC has become greater in our industries in the context of the need for earning foreign exchange by supplying quality goods to successfully compete in the world markets. In fact, one of the most serious problems faced by Indian business community is to supply quality products and services at competitive rates. It is heartening to note that the Government of India is conscious of the quality standard for different products .To the satisfaction of the customers Indian standards institute (ISI) Bahadur Shah Zafar Marg, New Delhi, set up by the Government of India is playing a very important role in maintaining quality standards in the country. After rigorous testing of the quality of the products, the institute grants ISI label to those products which come up to certain prescribed standards and a continuous watch is kept to see that these standards are adhered to and a continuous watch is kept to see that there is another label for standard quality products. Customers are becoming conscious and often insist on buying products bearing ISI or Agmark label.
15Some other advantages are: Consumer satisfactionBetter industrial relations(cordial relations among employees)Better methods of productionIncreased salesjob satisfactionGoodwillFacilitates price fixationEffective advertising
16LIMITATIONS: Despite the great significance of quality control , ‘it should be remembered that it is not a panacea for all quality evils.’ They should be matched to the process being studied. The applications of standard procedures without adequate study of the process is extremely dangerous, and applied on a production process are only an information service, and as such used as part of a general quality awareness, they may only lead to a files with the manager in charge of the process and not with the statistician. The charts do not reduce the manger’s responsibility.
17METHODS OF QUALITY CONTROL INSPECTIONSTATISTICALQUALITYCONTROL
18INSPECTIONInspection is the most common method of attaining standardization, uniformity and quality of workmanship. It is the cost art of controlling the product quality after comparison with the established standards and specifications. It is the function of quality control.If the said item does not fall within the zone of acceptability it will be rejected and corrective measure will be applied to see that the items in future conform to specified standards.Inspection is an indispensable tool of modern manufacturing process. It helps to := control quality,= reduces manufacturing costs,= eliminate scrap losses and assignable causes of defective work.
19OBJECTIVES OF INSPECTION = To collect information regarding the performance of the product with established standards for the use of engineering production, purchasing and quality control etc. = To sort out poor quality of manufactured product and thus to maintain standards. = Detect source of weakness and failure in the finished products and thus check the work of designer. = To establish and increase the reputation by protecting customers from receiving poor quality products by having quality control techniques.
20PURPOSE OF INSPECTION= To distinguish good lots from bad lots = To distinguish good pieces from bad pieces. = To determine if the process is changing. = To determine if the process is approaching the specification limits. = To rate quality of product. = To rate accuracy of inspectors. = To measure the precision of the measuring instrument. = To secure products – design information. = To measure process capability.
21METHODS OF INSPECTIONThe inspection may be undertaken in any of the following ways :Remedial and Preventive InspectionCentralised and Floor Inspection
22Remedial and Preventive Inspection: Inspection allows the separation of good quality products from those of low quality. The goods are compared with the standards set for them.If the goods and services are according to the predecided standards then these are accepted and if they do not confirm to the standards or do not fall within the prescribed limits then they are rejected.This method of inspection is known as remedial inspection.
23Preventive inspection, on the other hand is concerned mainly to avoid rejections in the future. The causes of low quality are studied properly and then steps are taken so that this is avoided in future.Preventive inspection is very useful because the causes of rejection are found and corrective measures are taken.
24CENTRALISED AND FLOOR INSPECTION Under centralised inspection system all the inspection work is centralised. All goods and materials are taken to Inspection department and then returned to the departments if they conform to the standards.Thus, when materials, parts, products, components etc. are sent to the inspection department for inspection, it is called central inspection. It is so because inspection is carried out at one central place only.
25Central inspection saves time of inspectors, because they don’t need to move out in various departments for their work, but they receive in the inspection department, what they have to inspect. They don’t have to wait for the jobs to inspect. Moreover, the inspectors can work freely without any pressure from the people, whose work they inspect. It makes possible the use of special inspection and testing machines and equipment.The records of the rejected items and their scrap are also kept at the central place. The employing of less inspectors, will be required when the work is undertaken at a centralised place.
26Floor inspection : Inspection at the job place is also used to resolve the problems It is known as floor or patrolling or roving or first piece inspection.Here the inspectors move from one place to another place, or from one department to another department, or from one machine to another machine or from one process to another process etc. to inspect materials, parts, components, tools, equipment, products during the various stages of production and the finished goods.They get the machines set right before production starts and also they catch defective work before a large quantity has been produced.
27Corrective action is immediately taken to set the machines right. This method ensures timely and prompt inspection and avoid delays.Floor inspection keeps the quantity of scrap at the minimum because the inspector can locate the fault and suggest rectification.It also create direct link between the inspectors and the work and this helps in proper communication between the two.
28STATISTICAL QUALITY CONTROL (SQC) Statistical quality control has assumed tremendous importance in industrial technology in recent past. Highly industrialised countries are making maximum use of this device.Walter S. Schewhart and Harold F. Dodge of Bell laboratories U.S.A introduced SQC shortly after world war I.
29This method is based upon the law of probability and may be described as the system for controlling the quality of production within specified limits.The application f these techniques of manufacturing gained momentum during world war II.The armed services in U.S.A. successfully applied these techniques in procurement divisions for establishing quality specification.This technique makes use of statistical methods and principles which aim to assess not only the magnitude of “Chance Cause Variation” but also detect assignable cause variations.
30Since assignable cause variations may be detected, it becomes easy for an individual undertaking to install statistical control at various stages in the production or manufacture of a product.Before the introduction of SQC only inspection method was used to determine the quality of products.Because inspection is possible only when production has already taken place only the quality may be determined.When the goods are already produced then poor quality products will also mean loss.
31In statistical quality control, the quality is checked at every level of production and necessary corrective measures may be taken at the earliest.
32TOOLS OF STATISTICAL QUALITY CONTROL These are two important tools of statistical quality control:Quality Control Charts.Acceptance sampling.
33QUALITY CONTROL CHARTS This is one of the important methods of SQC . A control chart is the graphic representation of expected variations in quality. There are two lines on each graph which indicate the tolerance limits within which the variations of quality will be permitted. In all production processes, we need to monitor the extent to which our products meet specifications. In the most general terms, there are two "enemies" of product quality:deviations from target specificationsexcessive variability around target specificationsDuring the earlier stages of developing the production process, designed experiments are often used to optimize these two quality characteristics; the methods provided in Quality Control are on-line or in-process quality control procedures to monitor an on-going production process.
34Out line known as average line is drawn on chart Out line known as average line is drawn on chart. Two lines, one called upper control limit (UCL) and the other called low control limit, (LCL) are drawn above and below the average line respectively. A sample is selected from every lot. The actual measure merits of the sample are plotted on the chart. If analysis of the control chart indicates that the process is currently under control (i.e., is stable, with variation only coming from sources common to the process), or the dots remain within the two lines i.e., UCL and LCL then no corrections or changes to process control parameters are needed or desired .In addition, data from the process can be used to predict the future performance of the process.If the chart indicates that the monitored process is not in control (i.e., the dots fall outside the tolerance lines) analysis of the chart can help determine the sources of variation, as this will result in degraded process performance.
35If the sample is rejected then assignable cause is determined and immediate action is taken to improve the quality.The causes of production process going out of control may be due to poor materials, negligence of machine operator or defects in machine.A process that is stable but operating outside of desired limits (e.g., scrap rates may be in statistical control but above desired limits) needs to be improved through a deliberate effort to understand the causes of current performance and fundamentally improve the process.
36This will enables the manufacturer to take corrective measures. Control charts are excellent means of determining quality limits which allows immediate rectifying measures.
37OUTLINE OF A CONTROL CHART Quality scaleOut of controlUCLAverageLCLOut of control12345678910Sample number
38As per the information plotted in control chart, one dot is going beyond the upper control limit and one dot is going beyond the lower control limit which shows that the quality of the sample is not under control.If all the dots are between UCL and LCL then the sample’s quality will be under control and variations from average line are only due to chance.
39ACCEPTANCE SAMPLINGAcceptance sampling uses statistical sampling to determine whether to accept or reject a production lot of material. It has been a common quality control technique used in industry and particularly the military for contracts and procurement. It is usually done as products leave the factory, or in some cases even within the factory. Most often a producer supplies a consumer a number of items and decision to accept or reject the lot is made by determining the number of defective items in a sample from the lot. The lot is accepted if the number of defects falls below where the acceptance number or otherwise the lot is rejected.
40This is one of the important techniques of statistical quality control This is one of the important techniques of statistical quality control. This method is used to inspect quality just after the product is manufactured or are in the final stage of production.A sample is taken from the manufactured products and quality of these products is inspected.If the quality of sample conforms to the pre-determined standards then it is presumed that the quality of the whole lot is good.This method is used on the presumption that the sample includes products of varying qualities from the lot and it represents the lot properly.This method is also referred as ‘Sampling Inspection Plan’.
41There is a probability that the sample may not have defective products but the lot may have or vice-versa .The chances are that the sample is accepted but the quality of the lot is good.To avoid this thing we can inspect more than one sample and then take a decision about the acceptance or rejection of a lot.
42There are two limiting levels of quality in an Acceptance Sampling Plan. 1) Acceptable Quality Level (AQL) i.e. the lowest percentage of defectives that the seller expects to supply and the buyer expects to receive,AQL involves producer’s risk or the risk that a lot with an acceptable quality will be rejected on the basis of a sampleLot percentage Tolerance Defective (LPTD) i.e. a limit at which the buyer, or consumer, wants to be quite certain that the lot will not be passed.a) On the other hand, LPTD involves consumers’ risk or the risk that a buyer takes in accepting a lot of the quality which does not conform to the accepted standards.
43Role of Acceptance Sampling Role of Acceptance Sampling. Acceptance sampling is widely used due to the following reasons :Acceptance sampling is much less expensive than 100 per cent inspection.Acceptance sampling also gives good results as compared to 100 per cent inspection. It is generally agreed that 100% inspection will remove only between 85% to 95% of defective material while a very good 100% inspection will remove 99% of defective items. Moreover, 100% inspection involves fatigue also. Acceptance sampling will be much better in controlling quality.Sometimes quality of a product is tested by destroying an item, as in determining the strength of glass containers. In such a case 100% inspection is not possible and acceptance sampling will have to be used.
444) In modern manufacturing concerns acceptance sampling is used for evaluating incoming raw materials, parts at various stages of manufacturing and final inspection of finished goods.
45Advantages of statistical quality control Some of the important advantages of SQC are discussed as follows:This method is based on inspecting a sample instead of the whole lot. This involves lesser cost of inspection and it reduces production costs too.SQC results in increasing profits too. This method minimises rejections which means lesser cost. The rejected products increase cost of other products. So this method helps in increasing profits by keeping control on defective products.It helps in simplifying quality control. The tolerance limits are decided and the products going beyond the tolerance limits are rejected. This method is scientific in nature and allows proper and simple quality control.
464) It helps in creating quality consciousness among employees 4) It helps in creating quality consciousness among employees. The quality of products is tested immediately after their production, so the employees remain conscious about quality. This helps in improving quality of products and rejections are greatly reduced.5) This helps in improving the goodwill of products among consumers. If the consumers regularly get good quality products from a particular business house then the reputation of that concern is enhanced. The consumers will start patronising the products and will help the company in increasing sales.
476) It also helps in smooth and unrestricted production 6) It also helps in smooth and unrestricted production. The defects in products are detected at the earliest and this helps in taking corrective measures.