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Quality planning and control Chapter -17

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Summary What is quality How to diagnose quality planning and control? What are the steps to conformance to specification? Importance of statistical process control in quality planning and control. Acceptance of sampling in quality planning and control

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What's quality ?

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Whats quality?

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Quality means: Meeting specification No errors or mistakes Good performance Value for money Why quality is important? Many organizations got a dedicated dept. for quality management, which underlines the importance for quality. For example Mecedez Benz.

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Why quality is important? Good quality reduces: Cost Complaints Waste Good quality increases: Revenue Satisfaction Customers

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Quality up Profits up Processing time down Inventory down Capital costs down Complaint and warranty costs down Rework and scrap costs down Inspection and test costs down Productivity up Service costs down Image up Scale economies up Price competition down Sales volume up Revenue up High quality puts costs down and revenue up Operation costs down

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What is quality in operations? quality is consistent conformance to customers expectations Quality in customers view Customers expectations are based on: Past experiences Individual knowledge History Customers expectations are based on the way they perceive it. For example, one person regard car as a status symbol or luxury, where another considers as means of transport for a family.

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The various definitions of quality or quality is the total of five approaches. The transcendent approach views quality as synonymous with innate excellence. The manufacturing-based approach assumes quality is all about making or providing error-free products or services. The user-based approach assumes quality is all about providing products or services that are fit for their purpose. The product-based approach views quality as a precise and measurable set of characteristics. The value-based approach defines quality in terms of value.

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Reconciling operations & customers view Operations view- meet customers expectations Customers view- what customer perceives So, quality is a fit between customer expectations and customer perceptions. For example yahoo chat and face-to-face encounter.

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Customers expectations for the product or service Customers perceptions of the product or service Gap Perceived quality is poorPerceived quality is good Expectations > perceptions Expectations = perceptions Expectations < perceptions Perceived quality is governed by the gap between customers expectations and their perceptions of the product or service Gap Perceived quality is acceptable Customers expectations for the product or service Customers perceptions of the product or service Customers expectations for the product or service Customers perceptions of the product or service

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The operations domain Managements concept of the product or service The customers domain Previous experience Word-of-mouth communications Image of product or service Customers own specification of quality Organizations specification of quality The actual product or service Customers expectations concerning a product or service Customers perceptions concerning the product or service Gap 1 Gap 2 Gap 3 Gap 4 A gap model of quality Gap ?

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How to diagnose or identify quality problems? 1.Customer specification VS operation specification Gap 2.The concept vs Specification Gap 3.The quality specification gap Vs actual quality gap 4.The actual quality Vs communicated image gap

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The perceptionexpectation gap Action required to ensure high perceived quality Main organizational responsibility Gap 1 Gap 2 Gap 3Operations Gap 4 Marketing Ensure consistency between internal quality specification and the expectations of customers Ensure internal specification meets its intended concept of design Ensure actual product or service conforms to internally specified quality level Ensure that promises made to customers concerning the product or service can really be delivered Marketing, operations, product/service development

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Conformance to specification Conformance to specification means producing a product or providing a service to its design specifications.

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Quality planning and control Quality planning and control activities can be divided into six steps: 1.Define the quality characteristics of the product or service. 2.Decide how to measure each quality characteristic. 3.Set quality standards for each quality characteristic. 4.Control against these standards. 5.Find and correct causes of poor quality. 6.Continue to make improvements.

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I.Define Quality characteristics There are six quality characteristics as follows:

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Quality characteristics of goods and services Functionality how well the product or service does the job for which it was intended Appearance the aesthetic appeal, look, feel, sound and smell of the product or service Reliability the consistency of performance of the product or service over time Durability the total useful life of the product or service Recovery the ease with which problems with the product or service can be rectified or resolved Contact the nature of the person-to-person contacts that take place

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II.Decide how to measure each characteristic. Each characteristic must be taken separately, and broken down into individual parts for measuring. For example Appearance- An appearance characteristic of a car can be spited into the color, finishing and scratches. There are two types of measures to use: Variables something that can be measured by variable scale such as length, diameter, weight, time. Attributes measure by judgments, such as right or wrong, ok or not ok.

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Attribute and variable measures of quality AttributesVariables Defective or not defective? Measured on a continuous scale Light bulb works or does not work Diameter of bulb Number of defects in a turbine blade Length of bar

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Variables things you can measure Attributes things you can assess and accept or reject Quality fitness for purpose Reliability ability to continue working at accepted quality level Quality Quality of design degree to which design achieves purpose Quality of conformance faithfulness with which the operation agrees with design

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III.Step -03 Set of quality standards When quality characteristics are measured, a quality standard is needed to check the performance. For example one customer out of 10000 complains. So? Good. Because 9999 are happy. Bad. Because many others had problem, but didnt complaint. Satisfactory. Because same with other companies. In this situation, we can say quality standard is that level of quality which defines the boundary between acceptable and unacceptable.

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IV.Control quality against standards After setting up appropriate standards, the operation will need to check the products or services to conform to those standards. There are three decisions to be made: 1.Where in the operation should they check, that is conforming to the standards? 2.Should they check every single product and service or a sample. 3.How should the checks be performed?

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a)Where should the checks take place? There are three points where checks can be made: At the start of process ( a placement test in the school) During the process (before the costly part, before series of processes where checking is difficult) After the process.

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b)Check every product and service or take a sample. Here, we decide how many of the products or services to sample. Checking every single product is ideal, but not advisable. For example: Doctor cant check all the blood in a patient. Water cant check the satisfaction of food at every 30 seconds. Why? It is costly Making difficult for employees Sometimes customers give wrong information.(restaurant)

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Checking sample It saves time, but problems are many : Decision may go wrong. Type 1 and Type ii errors These are two incorrect decisions: Type 1 errors Those errors which occur when a decision was made to do something and the situation did not stop it.

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Type 2 error Errors occur when nothing is done yet. How should the checks be performed? In practice most operations will use some sampling. There are two sampling methods: 1.Statistical process control 2.Acceptance sampling

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SPC or statistical process control Sampling during the production of goods or delivery of service. Acceptance Sampling it is a technique of quality sampling that is used to decide whether accept a whole batch of products/services on the basis of sample or not.

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Statistical process control Checking a product or service during the creation. If there is a reason to believe that there is a problem with the process, it can be stopped and problem can be rectified. Methods Control charts It checks the result of many samples over a period of time.

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Process control charting Time Some measure of operations performance Some aspect of the performance of a process is often measured over time Question: Why do we do this?

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Process control charting Time Some measure of operations performance Some aspect of the performance of a process is often measured over time Question: How do we know if the variation in process performance is natural in terms of being a result of random causes, or is indicative of some assignable causes in the process?

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0.8 2.23.6 After the first sample 0.8 2.23.6 After the second sample 0.8 2.23.6 By the end of the first day 0.8 2.23.6 By the end of the second day 0.8 2.23.6 Fitting a normal distribution to the histogram of sampled call times Process control charting

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How can statistical process control help quality planning and control? In theory if you know the specification the characteristics to be measured and the standards to be achieved, delivering products or services to that specification should be easy. Unfortunately this is not the case. The transforming and the transformed resources are never perfect. Consider the problems that a restaurant might face: Transforming resourcesTransformed resources The chef may be suffering from a cold or be untrained in one aspect of preparation or cooking. Material from suppliers may be of varying quality such as interruptions to the electricity supply or bruised and rotten vegetables. The waiting staff may be recently recruited and uncertain about their job, or they all might have been to a party the night before. A customer may be particularly demanding or even unpleasant making it difficult for the restaurant and its staff to satisfy them. The cleaners may not have turned up or have done a thorough job as needed to make the restaurant look clean and smart.

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By checking variables and attributes managers can ensure that the service or products are being deliver to the specification. One important technique in doing this is statistical process control (SPC). Using SPC we can: calculate the likelihood of a process being in or out of control set control limits based on those likelihoods provide control charts to monitor a quality characteristic make decisions about whether a process is in control or not and therefore whether action is needed to find and rectify a problem.

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Variation in the process qualities All processes vary to some extent. No machine gives precisely same result every time. Materials vary a little, the staff also vary in operation, Environment also vary. So quality also varies. These are known as common causes, and these cannot be eliminated.

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A P X X X X Process variability Scatter precision: P On/off target accuracy: A

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Process capability The acceptability of variation in a process. Assignable causes of variation There may be problem with process. 1.Machine damage 2. Inexperienced staff These are known as assignable variations.

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Six Sigma approach An approach for improvement in quality and measurement. The six sigma measuring performances. Page 567 Process control is used to control the quality.

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USL LSL Process variation 3 sigma process variation = 66800 defects per million opportunities 4 sigma process variation = 6200 defects per million opportunities 5 sigma process variation = 230 defects per million opportunities 6 sigma process variation = 3.4 defects per million opportunities Process variation and its effect on process defects per million opportunities (DPMO) USL LSL USL LSL USL LSL

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Acceptance sampling The purpose of acceptance sampling is to decide whether, on the basis of a sample to accept or reject a batch. It uses the proportion of wrongs and rights. In acceptance sampling risks involved, while making judgments. Type 1 risk belongs to the producer, because the operation rejects a batch of good quality Type 2 is consumer risk because the customer accept the poor quality.

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These risks are represented by a curve known as Operating characteristic curve.

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How can acceptance sampling help quality planning and control? you are an employer and you want to recruit 20 graduates it is likely that you will interview each one of them. If the batch size is large or the items of lesser value, we need a simpler, quicker and cheaper means of testing a sample to decide if the whole batch is OK or not = this is acceptance sampling. If you were the quality controller overseeing the manufacture of light bulbs it would be too time consuming to check each of the thousands made each day, and. if the check involved seeing how long they lasted it would destroy the entire output. If you were the quality controller for the marking of an A level examination, it would be impossible to check that every one of the thousands of examiners had correctly marked every one of hundreds of thousands scripts. Using acceptance sampling we can: decide the best size of sample to use judge the acceptable number of defects in a batch which results in the batch being rejected for a specified level of risk decide whether as batch should be accepted or rejected and make decisions about the action needed to find and rectify the problem.

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