Ebook Industrial engineering foundations - Bridging the gap between engineering and management: Part 2

Part 2 book "Industrial engineering foundations bridging the gap between engineering and management" includes content: Statistical quality control, facility location, system reliability, queueing theory, application of principles.
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Ebook Industrial engineering foundations - Bridging the gap between engineering and management: Part 2 Chapter STATISTICAL QUALITY 7 CONTROL 7.1 INTRODUCTION The importance of quality cannot be underestimated. The least impact resulting from a low-quality product is probably only economical, and this by itself can severely impair the financial health of any enterprise. In the worst case, inferior quality can lead to irreversible consequences, such as loss of life—which can inflict severe financial damages and endanger the existence of the enterprise. A credible enterprise must aim to produce goods and services of the right quantity and value, and also of the right quality. It is important to know the difference between inspection and quality control. Inspection is used to verify the quality of what has already been produced, whereas quality control is a process that is used to foresee, direct, and control the quality of the products yet to be produced. When an item or product fails to meet expectations or perform its intended function, then it is associated with inferior or unacceptable quality. Technically, by “quality” we mean to what degree a measured value of a feature deviates from its stated specifications. The smaller the deviation, the better the quality. To gauge quality, the general public and consumers rely on a company’s reputation for quality and reliability, and the brand name, as they lack any systematic tools to measure quality. The volume of the business, natural desire for profits, and sometimes the regulations in place justify, encourage and force organizations to resort to more scientific and consistent methods of assessment to produce goods of acceptable quality and constantly look for ways of improvement. Statistical quality control (SQC) is an approach that can cost-effectively help any organization to achieve these. We will show that it is not necessary for SQC to screen each and every one of the product items or components. Proven sampling techniques allow only a small part of the output to be examined, yet provide significant insight into the quality and quality trends of the entire production.** It is not even necessary to maintain quality control efforts at all times and for all products. With good measures and a proper combination of factors of production, a process may in time indicate that active quality control is no longer needed. Nonetheless, maintaining some degree of inspection and control provides assurance that the achieved quality levels do not deteriorate. We define factors of production as all elements that play a role in manufacturing a product or when providing a service. In manufacturing, for example, these are primarily equipment, tools, materials, operator skills, and instructions. Other factors may be such things as maintenance and ambient temperature. If proper resources and factors of production are not provided, the expectation for good quality will be unrealistic. Ultimately, quality control efforts are inherently linked to much broader aspects of any production system and running an enterprise. These include design, performance and market indicators, cost analysis and finance, management philosophy and safety. 7.2 DETERMINING QUALITY For small and relatively inexpensive goods, such as consumables and food, for example, personal experience is the primary means of associating a quality rating. For major products and products of high value, customers and consumers actively search various media and seek advice from others. The third, and unfortunate, means of finding out about quality is when a manufacturer or supplier issues a recall of their product as a result of defects, deficiencies, and poor quality and performance. The following is a list of a few common recall scenarios: • Automobiles, practically from all manufacturers • A range of household items, such as strollers, toys, and electronic devices • Processed and packaged food A simple search on the Internet with the keyword recall and any product or automobile brand name will invariably return a list of recalls. This is particularly prevalent in the automobile industry, as every year the manufacturers implement new designs and functionality or introduce new models that accompany new issues in quality. When the deficiencies are significant and affect a broader base of consumers, the companies involved issue public and media announcements. Otherwise, many recalls are handled through the mail and go unnoticed by the general public. A recall can tarnish the reputation and damage the financial health of the manufacturer, and critical defects and deficiencies can lead to catastrophic consequences. 7.2.1 Why Is Quality Inconsistent? When components or products are produced, a set of design, manufacturing, and performance specifications are necessary. It is almost impossible to state and achieve the exact specifications of the product. Even if it were possible, the manufacturing and quality control costs would be prohibitive. In fact, from the cost consideration point of view, it is not even necessary to achieve exact specifications. For example, when a shaft is being machined to support a ball bearing, we commonly state the specification as a desired target diameter plus/minus some acceptable tolerance. If a thousand such shafts are produced, they will hardly be the same. But this is fine because we want shafts to be practically usable and economically justifiable. Inconsistencies and deviations come from numerous sources. They are occasionally random in nature, and most often the result of variations in the factors of production. Taking a machining operation, we can name the following as typical examples: – Tool wear – Slack in machine parts and joints – Error in proper setting of measures and adjustments – Variation in te ...