Automotive Quality Systems Handbook Episode 15 pot

Chapter 20 Statistical techniques Scope of requirements Statistical techniques can be used for a variety of reasons, from sampling product on receipt to market analysis. Any technique that uses statistical theory to reveal information is a statistical technique, but not all applications of statistics are governed by the requirements of this part of the standard. Techniques such as Pareto Analysis and cause and effect diagrams are regarded as statistical techniques in ISO 9000-2 and although numerical data is used, there is no probability theory involved. These techniques are used for problem solving, not for making product acceptance decisions. The only statistical techniques which need control are those used to determine the acceptability of a product or service or the capability of a process that produces the product or service. Any activity where you rely on statistical evidence rather than phys- ical measurement is an activity which should be governed by these requirements. The use of recognized techniques is important to the confidence one has in the result. It is similar to the use of measuring equipment that has been calibrated against known standards of accuracy. Unless you actually check every product, measure every attribute or variable you cannot be 100% certain. But that is costly and you can be 99.99% certain by using statistical techniques; 99.99% may be sufficiently accurate for your needs. The requirement may not apply to all product acceptance decisions. If your acceptance of the end product does not depend upon acceptance decisions being made on its com- ponent parts, any sampling carried out on receipt inspection or in-process is not important to the product acceptance decision and can therefore be ignored in your documented quality system. This is a wise course of action if you can be sure this will always be the case but if you cant, and more often than not you wont know, it is prudent to encompass all sampling activities in your quality system. auto220.qxd 10/04/00 21:43 Page 547 The requirements in element 4.20 are linked with other elements of the standard even when there is no cross reference. This relationship is illustrated in Figure 20.1. Identifying the need for statistical techniques (4.20.1) The standard requires the supplier to identify the need for statistical techniques required for establishing, controlling, and verifying process capability and product characteristics . 548 Statistical techniques Figure 20.1 Clause relationships with the statistical techniques element DESIGN CONTROL (4.4) PARAMETERS TO BE MEASURED IDENTITY NEED FOR STATISTICAL TECHNIQUES (4.20.1) CONTROL PLAN (4.2.4.10) PROCESS CONTROL (4.9) INSPECTION AND TESTING (4.10) MEASURING EQUIPMENT (4.11) APPLY TECHNIQUES (4.20.2) ACTION OR DECISION PROCESS OR PRODUCT PROCESS CAPABILITY STUDIES (4.2.4.5) PROCESS OR PRODUCT SPECIFICATION SELECT TECHNIQUE (4.20.3) TRAINING (4.18) DEVELOP KNOWLEDGE (4.20.4) auto220.qxd 10/07/00 16:55 Page 548 The supplementary requirements require statistical tools to be identified for each process during the advanced quality planning phase and included in the control plan. The standard does not require you to use statistical techniques but identify the need for them. Within your procedures you will therefore need a means of determining when statistical techniques will be needed to determine product characteristics and process capability. One way of doing this is to use checklists when preparing customer specifications, design specifications, and verification specifications and procedures. These checklists need to prompt the user to state whether the product characteristics or process capability will be determined using statistical techniques and if so which techniques are to be used. Techniques for establishing and controlling process capability are essentially the same  the difference lies in what you do with the results. Firstly you need to know if you can make the product or deliver the service in compliance with the agreed specification. For this you need to know if the process is capable of yielding conforming product. Statistical Process Control techniques (SPC) will give you this information. Secondly you need to know if the product or service produced by the process actually meets the requirements. SPC will also provide this information. However, having obtained the results you need the ability to change the process in order that all product or service remains within specified limits and this requires either real-time or off-line process mon- itoring to detect and correct variance. To verify process capability you rerun the analysis periodically using sampling techniques by measuring output product characteristics and establishing that the results demonstrate that the process remains capable. There are many uses for statistical techniques in establishing and controlling product characteristics. l Receipt inspection  a technique for verifying product characteristics where sampling can be used on large quantities to reduce inspection costs and improve throughput. l SPC  a technique for controlling product characteristics as well as controlling processes. l Reliability prediction  a technique for establishing product characteristics where the reliability targets cannot be measured without testing many hundreds of products over many thousands of hours. (On long production runs of low value items, reliability testing is possible but with one-off systems of high value it is not cost effective; hence reliability has to be predicted using statistical techniques.) Statistical techniques 549 auto220.qxd 10/04/00 21:43 Page 549 l Market analysis  a technique for establishing product characteristics where the customer requirements are revealed by market survey and determined by statistical techniques for inclusion in specifications. l Design by experiment  a technique where product characteristics are established by conducting experiments on samples or by mathematical modeling to simulate the effects of certain characteristics and hence determine suitable parameters and limits. When carrying out quality planning you will be examining intended product characteristics and it is at this stage that you will need to consider how achievement is to be measured and what tool or technique is to be used to perform the measurement. When you have chosen the tool, you need to describe its use in the control plan. Implementing and controlling the application of statistical techniques (4.20.2) The standard requires that the supplier establish and maintain documented procedures to implement and control the application of statistical techniques . Where statistical techniques are used for establishing, controlling, and verifying process capability and product characteristics, procedures need to be produced for each application. You might for instance need a Process Control Procedure, Process Capability Analysis Procedure, Receipt Inspection Procedure, Reliability Prediction Procedure, Market Analysis Procedure, etc. The procedures need to specify when and under what circumstances the techniques should be used and provide detailed instruction on the sample size, collection, sorting, and validation of input data, the plotting of results and application of limits. Guidance will also need to be provided to enable staff to analyze and interpret data, convert data, and plot the relevant charts as well as make the correct decisions from the evidence they have acquired. Where computer programs are employed, they will need to be validated to demonstrate that the results being plotted are accurate. You may be relying on what the computer tells you rather than on any direct measurement of the product. Knowledge of basic statistical concepts (4.10.4) It is not sufficient to train staff solely in the techniques they need to use  a wider appreciation of the concepts will facilitate improved application. The staff assigned to quality planning need an even wider appreciation of statistical concepts and it is probably use- 550 Statistical techniques auto220.qxd 10/04/00 21:43 Page 550 ful to have an expert in your company upon whom staff can call from time to time. If the primary technique is SPC then you should appoint an SPC coordinator who can act as mentor and coach to the other operators of SPC techniques. All managers need a basic appreciation but those in production ought to be able to apply the techniques their staff use in order to be able to detect when they are not being applied correctly. Auditors need to be able to determine whether the right techniques are being applied and whether the techniques are being applied as directed. Remember that the auditors task is to determine whether the system is effective, so the ability to differ- entiate between the use of inappropriate techniques is essential. Task list 1 Identify product and process acceptance decisions that are based on statistical techniques. 2 Determine and document the statistical theory or national standards used. 3 Provide instructions, charts, and other data to enable staff to use the techniques properly. 4 Review the techniques periodically and revise them (if necessary) to take advantage of new developments in the field. 5 Monitor the effectiveness of the decisions and adjust your rules accordingly. 6 Perform studies in the pre-production period to determine the capability of the man- ufacturing processes. 7 Perform studies to show that the combination of measurement equipment tolerances or variations in the design tolerances cannot result in nonconforming product. 8 Perform studies to prove the soundness of acceptable quality levels. Statistical techniques 551 auto220.qxd 10/04/00 21:43 Page 551 Statistical techniques questionnaire 1 How do you identify the need for statistical techniques required for establishing process capability? 2 How do you identify the need for statistical techniques required for controlling and verifying process capability? 3 How do you identify the need for statistical techniques required for establishing product characteristics? 4 How do you identify the need for statistical techniques required for controlling and verifying product characteristics? 5 How do you control the application of identified statistical techniques and ensure training of personnel using them? 6 What documented procedures exist for implementing the identified statistical techniques? Dos and donts L Dont rely on statistical techniques unless you have evidence that they are valid. L Dont claim emphatically that all products meet the specification if conformance is determined solely by statistical techniques. J Do record the basis on which decisions are made when using statistical techniques. L Dont flinch results on the borderline, take more samples. L Dont derive your sampling plans from unproven statistical methods. J Do locate control charts where they will provide use as a nonconformity prevention tool. 552 Statistical techniques auto220.qxd 10/04/00 21:43 Page 552 Appendix A Glossary of terms This appendix contains a glossary of nearly 200 common and uncommon terms and phrases used in ISO/TS 16949 and the Rules for Achieving IATF Recognition . It contains many terms and phrases not defined in ISO 8402 or ANSI/ASQC A3. Some alternative definitions are provided for clarification. The explanations are given for the context in which the terms are used. Acceptance criteria The standard against which a comparison is made to judge conformance. Activities affecting Any activity which affects the determination of product or service quality features and characteristics, their specification, achievement, or verification, or means to plan organize, control, assure, or improve them. Adequate Suitable for the purpose. The term adequate appears several times in the standard allowing the assessor to vary the criteria for adequacy and hence not use a finite process to verify that the requirements have been met. Adequacy audit An audit carried out to establish that the quality system documentation adequately addresses the requirements of a prescribed standard; also referred to as a documentation audit . Accreditation A process by which organizations are authorized to conduct certification of conformity to prescribed standards. Appropriate Appropriate means appropriate to the circumstances and requires knowledge of these circumstances. Without criteria, an assessor is left to decide what is or is not appropriate. Approved Confirmed as meeting the requirements. Assessment The act of determining the extent of compliance with requirements. Assurance Evidence (verbal or written) that gives confidence that something will or will not happen or has or has not happened. autoapa.qxd 10/04/00 21:44 Page 553 Audit An examination of records or activities to verify their accuracy, usu- ally by someone other than the person responsible for them. Authority The right to take actions and make decisions. Authorized A permit to do something or use something that may not necessar- ily be approved. Benchmarking A technique for measuring an organizations products, services, and operations against those of its competitors, resulting in a search for best practice that will lead to superior performance. Calibrate To standardize the quantities of a measuring instrument. Capability index C p The capability index for a stable process defined as the quotient of tolerance width and process capability where process capability is the 6σ range of a processs inherent variation. Capability index C pk The capability index which accounts for process centering for a stable process using the minimum upper or lower capability index. Capability index P pk The performance index which accounts for process centering and defined as the minimum of the upper or lower specification limit minus the average value divided by 3σ. Certification A process by which a product, process, person, or organization is deemed to meet specified requirements. Certification body See Registrar. Class A group of entities having at least one attribute in common. A group of entities having the same generic purpose but different functional use. Clause of the standard A numbered paragraph or subsection of the standard containing one or more related requirements, such as 4.10.3. Note that each item in a list is also a clause. (See also Quality system element .) Codes A systematically arranged and comprehensive collection of rules, regulations, or principles. Commitment An obligation a person or organization undertakes to fulfill: i.e. doing what you say you will do. Comparative reference A standard used to determine differences between it and another entity. Compliance audit See Implementation audit . 554 Glossary of terms autoapa.qxd 10/04/00 21:44 Page 554 Concession Permission granted by an acceptance authority to supply product or service that does not meet the prescribed requirements. (Note: the term waiver is used in the USA and has the same meaning.) Concurrent engineering See Simultaneous engineering . Conformance audit See Implementation audit . Conforms to specified Meets the requirements that have been specified by the customer or requirements the market. Contract An agreement formally executed by both customer and supplier (enforceable by law) which requires performance of services or delivery of products at a cost to the customer in accordance with stated terms and conditions. Agreed requirements between a supplier and customer transmitted by any means (ISO 9000-2). Contractual Requirements specified in a contract. requirements Control The act of preventing or regulating change in parameters, situations, or conditions. Control charts A graphical comparison of process performance data to computed control limits drawn as limit lines on the chart. Control methods Particular ways of providing control which do not constrain the sequence of steps in which the methods are carried out. Control procedure A procedure that controls product or information as it passes through an organization. Controlled conditions Arrangements which provide control over all factors that influence the result. Corrective action Action planned or taken to stop something from recurring. Criteria for Acceptance standards based on qualitative measures of performance. workmanship Critical success factors Those factors upon which the achievement of specified objectives depend. For product and service quality they are also referred to as quality characteristics . Cross-functional team See Multidisciplinary team . Customer complaints Any adverse report (verbal or written) received by a supplier from a customer. Glossary of terms 555 autoapa.qxd 10/04/00 21:44 Page 555 Customer supplied Hardware, software, documentation, or information owned by the product customer which is provided to a supplier for use in connection with a contract and which is returned to the customer either incorporat- ed in the supplies or at the end of the contract. Data Information that is organized in a form suitable for manual or computer analysis. Define and document To state in written form, the precise meaning, nature, or characteristics of something. Demonstrate To prove by reasoning, objective evidence, experiment, or practical application. Department A unit of an organization which may perform one or more functions. Units of organization regardless of their names are also referred to as functions (see Functions ). Design A process of originating a conceptual solution to a requirement and expressing it in a form from which a product may be produced or a service delivered. Design and Design creates the conceptual solution and development transforms development the solution into a fully working model. Design of experiments A technique for improving the quality of both processes and products by effectively investigating several sources of variation at the same time using statistically planned experiments. Design review A formal documented and systematic critical study of a design by people other than the designer. Disposition The act or manner of disposing of something. Documentation audit See Adequacy audit . Documented Procedures that are formally laid down in a reproducible medium procedures such as paper or magnetic disk. Effectiveness of the The extent to which the (quality) system fulfills its purpose. system Employee An environment in which employees are free (within defined limits) empowerment to take action to operate, maintain, and improve the processes for which they are responsible using their own expertise and judge- ment. Ensure To make certain that something will happen. 556 Glossary of terms autoapa.qxd 10/04/00 21:44 Page 556 [...]... 561 Quality commitment to, 95 meaning of, 561 Quality activities, 512 meaning of, 561 Quality and cost, 22 Quality and price, 22 Quality and reliability, 25 Quality and safety, 25 Quality and the environment, 27 Quality assurance, 5, 6, 8, 17, 28, 33, 37, 38, 44, 45, 90, 106, 113, 158 , 226, 312, 317, 512 Quality assurance meaning of, 561 Quality Assurance Department, 39 Quality auditors, 123, 516 Quality. .. 534 Quality characteristics, 24 meaning of, 561 Quality conformance meaning of, 561 Quality control, 5, 29, 31, 32, 35, 38, 103, 189, 192, 375 meaning of, 561 Quality costs, 23, 515 meaning of, 561 Quality engineer, 437, 440 Quality function deployment meaning of, 561 Quality goals, 40, 42 Quality improvement, 28, 34 meaning of, 562 Quality improvement plan, 164 Quality improvement programs, 42 Quality. .. ISO 10005 Quality management guidelines for quality plans ISO 10007 Quality management guidelines for configuration management ISO 10011-1 Guidelines for auditing quality systems auditing ISO 10011-2 Guidelines for auditing quality systems qualification criteria of quality system auditors ISO 10011-3 Guidelines for auditing quality systems management of audit programs ISO 10012 Quality assurance... 537 Quality management, 28, 29, 86 meaning of, 562 Quality manager, 89, 98 Quality manual, 89, 160 meaning of, 562 Quality objectives, 103 meaning of, 562 Quality of conformance, 26 Quality of design, 26 Quality of use, 26 Quality parameters, 25 autoidx.qxd 10/04/00 21:46 Page 577 Index 577 Quality plan, 321, 378 meaning of, 562 preparing, 188 use of, 173, 195 Quality planning, 186 meaning of, 562 Quality. .. types of, 491 Quality requirements, 25 meaning of, 562 Quality system audits of, 507 development, 157 documents, 161, 281 effectiveness, 134, 182, 500, 514 implementation, 183 maintenance, 157 , 170 meaning of, 42, 562 purpose of, 42, 159 requirements, 157 subcontractors, 324 Quality system assessments meaning of, 562 Quality system characteristics, 42 Quality system documentation, 185 Quality system... programs ISO 10012 Quality assurance requirements for measuring equipment ISO 10013 Guidelines for developing quality manuals ISO 8402 Quality management and quality assurance vocabulary ISO 9000 Quality System Development Handbook, David Hoyle (Butterworth-Heinemann, 1998) ISO 9000 Quality Systems Handbook, 3rd edition, David Hoyle (Butterworth-Heinemann, 1998) ISO 9000-1 Guidelines for selection and... Model for quality assurance in design/development, production, installation, and servicing ISO 9002 Model for quality assurance in production and installation ISO 9003 Model for quality assurance in final inspection and test ISO 9004-1 Quality management and quality system elements guidelines ISO 9004-2 Quality management and quality system elements guidelines for services ISO 9004-3 Quality management... as quality planning, quality control, and quality improvement within the quality system (ISO 8402) Quality manual A document stating the quality policy and describing the quality system of an organization (ISO 8402) Quality objectives Those results which the organization needs to achieve in order to improve its ability to meet current and future customer needs and expectations Quality plans Plans produced... documented quality system is also a quality activity Quality assurance All the planned and systematic activities implemented within the quality system and demonstrated as needed, to provide adequate confidence that an entity will fulfill requirements for quality (ISO 8402) Quality characteristics Any characteristic of a product or service that is needed to satisfy customer needs or achieve fitness for use Quality. .. Industry Association) autoapb.qxd 10/04/00 21:45 Page 568 Appendix C Bibliography Advanced product quality planning and control plan reference manual AQ-002 ANFIA evaluation of quality systems checklist AVSQ ANFIA evaluation of quality systems guidelines for use Benchmarking, Sylvia Coding (Gower, 1998) Business systems engineering, Gregory H Watson (Wiley, 1994) EAQF Evaluation Aptitude Qualité Fournisseur . as quality planning, quality control, and quality improvement within the quality system (ISO 8402). Quality manual A document stating the quality policy and describing the quality system of. those needs. If the quality system defines the activities that need to be executed to achieve quality then any activity specified in the documented quality system is also a quality activity. Quality assurance. for quality (ISO 8402). A process for maintaining standards of quality that prevents and corrects change in such standards so that the resultant output meets customer needs and expectations. Quality