Quality Control

Summary

In its broadest sense, the concept of quality control refers to a process that ensures that the physical result of one's work matches the design concept of the work as closely and consistently as possible. As goods began to be produced in large quantities, the importance of standardization, which creates easily interchangeable parts, and quality control, which ensures that goods are produced according to those standards, became apparent. The ideas, concepts, and practices for achieving quality control are readily transferable from one field to another. Thus, quality control as a working concept applies equally well to the preparation of drug compounds in a laboratory and to the manufacture of cast magnesium engine parts in a factory.

Definition and Basic Principles

Quality control can be defined as any process or procedure that maintains an established or stated standard of quality for a product or process. The central aims of quality control are to ensure the consistency of the product or process of interest, reduce costs and losses inherent in the process, and maximize client satisfaction. These are generally embodied in the term “total quality management” (TQM).

TQM is an all-encompassing program designed to manage every aspect of the production of a good or service, from start to finish, and at all levels of a company. Generally, a TQM program includes thorough documentation of every stage through which the good or service passes and implementation of up-to-date processes and procedures designed to ensure quality. A TQM program always has a quality-control function. However, the converse is not always true, as quality-control activities and functions can often be employed on their own and not as an integral part of any TQM program.

Quality-control methods depend on the nature of the process involved. Methods employed, for example, in a manufacturing facility that turns out hundreds of identical machine parts per day will be very different from those used to ensure that teachers are performing to designated standards in their classrooms or that a complicated computer program performs to expectation without difficulty. All methods share the same purpose, however, to ensure that the output of the process meets the conditional criteria placed on its successful production.

In many instances, quality control consists of little more than a visual inspection of a product to check for defects. This is a general and useful starting point for any quality-control function. Quality control is, first and foremost, a feedback process. When quality control is used to detect errors in the output stream, the information it provides is used to adjust how the particular process treats the input stream. Determining the quality of the product (the output stream of the process) requires creating a product-specific system of quality-control testing and unequivocal methods of measuring designated features of the product, which can be compared with the ideal or standard features.

Metrology, the study and application of methods for the measurement of properties, plays an important role in quality control, which depends on measurement to obtain specific information about individual components of an output stream. Also critical in quality-control processes is using statistics, which determines and uses standard methods of obtaining generalized information relevant to specific aspects of the entire output stream. For example, metrology would be used to determine the achievement level of a particular student as a percentage mark on a specific test, while statistics would be used to determine the percentage mark typically achieved by a large number of students of the same age on the same test. In another setting, metrology would be used to accurately measure the distance between two features of individual machined parts in a factory, and statistics would be used to monitor how well, as a group, the parts being manufactured conform to the essential design criteria. The use of such statistical information as the basis for regulating and adjusting how the machine process is carried out is called statistical process control (SPC).

Background and History

People have always sought to create products that are satisfactory to others. Such workmanship generally attracts consumers and generates profits. In ancient times, hunters most likely preferred their arrowheads and spear points to come from the best flintknappers in the village because the best quality objects were the most effective; the efficacy of the goods produced directly correlated with survival. Similarly, farmers who grew the best crops or craftspeople who made the best goods generally were able to sell or trade them more readily, thereby making a better living than those who produced goods of lesser quality.

With the development of skilled trades, the guild system developed. In a guild system, skilled tradespeople became represented in self-governing groups according to their specific type of trade. Each guild ensured that its members could perform the tasks associated with a specific trade to the guild standard. The guild system represents the first systematic approach to quality control. Quality control, in the modern sense, came about through the Industrial Revolution and the development of mass-production methods. In the late eighteenth century, the idea that machine components that were nominally the same should be interchangeable was put forward by American inventor Eli Whitney. Production methods, however, relied more on the machinist's art than anything else, and true interchangeability of parts was difficult to attain.

The number of standardized parts needed increased tremendously in the mid-twentieth century, largely because of the United States' involvement in World War II. Quality-control methods based on the statistical work of Walter Shewhart—often referred to as the father of statistical quality control—and American statistician W. Edwards Deming were developed as a means of ensuring absolute interchangeability of parts, eliminating waste, minimizing or eliminating liability issues, and maximizing return on investment in materials. Quality-control methods that were developed in the late twentieth century provided ongoing feedback that allowed processes to be adjusted as needed to allow for essentially continuous production of components.

How It Works

Quality-control processes range from the exceedingly simple method of visual inspection and measurement typically used for parts produced in low quantities to the sophisticated automatic inspection and measurement systems employing advanced analytical techniques often used for parts produced in large quantities. All quality-control systems, however, refer to an ideal or design standard. The purpose of any quality-control technique is to determine how well the output item conforms to the ideal or design standard. Acceptable outputs are those that fall within a specific set of limiting values. Depending on the nature of the product, outputs may be subjected to several stages of examination before use and ongoing inspection during use.

For example, in producing cast magnesium rotors, the design standard for acceptable cast parts calls for uniform material distribution. Each part produced must pass a preliminary visual inspection. Those observed to have defects are rejected and recycled. The remaining parts proceed to the next stage, where they are checked for internal defects. Defective parts are sent to recycling, and acceptable parts are sent to the next stage. If a machining stage is required, the machined parts are checked for the correct dimensions. The quality checks continue until the parts are finished and acceptable.

Quality assessments are recorded as statistical data, which are used to maintain or control the specific process from which they were obtained. In the cast magnesium rotor example, if casting flaws frequently occurred in a specific location on the rotor, the casting process would be adjusted to eliminate the flaw or reduce the frequency of its occurrence. In other processes with high throughput (output over an extended period of time), it is not feasible to examine every single unit. In such cases, a random selection of individual outputs is tested, and their conformance to the ideal is extrapolated to the entire output. This method relies on the output history as the basis for comparison, and variances in the output are tracked very closely to ensure that, overall, the individual components of the output stream remain within the parameters set in the design standard.

Applications and Products

The value of quality-control processes and procedures is widely recognized. The quality-control process has been integrated into virtually all aspects of human activity, from the simplest mechanical production operations to the most insubstantial of services. Human activities themselves are subject to the application of quality-control measures.

The quality control process is a feedback control system. The ultimate purpose of determining the quality of any output is to ascertain what aspect of the procedure is not performing adequately so that it can be corrected, and the subsequent output of the process improved or at least maintained within the design standard. This applies equally to physical objects being assembled or manufactured in a factory and to services provided to customers in the retail environment. In essence, quality control ensures that work is being done in an optimal manner that produces the most output with the least waste.

Standardization. Standardization is key to achieving optimal quality control in the international economy. The International Organization for Standardization (ISO) and other organizations provide internationally recognized industrial and commercial standards. For example, the ISO provides standards regarding the magnetic strip on credit cards. The ISO also offers a family of quality management standards, which includes ISO 9000, 9001, and 14000. Other quality-control programs include the Motorola Corporation's Six Sigma and Lean manufacturing (derived from the Toyota Production System). In the medical device industry, corrective and preventive action (CAPA) was considered an essential tool for quality control in the early twenty-first century. Such programs are generally not intended as stand-alone quality-control systems but instead, define an overall management approach in which quality control is an integral component and tool of the project manager.

Quality Management Programs. Quality-control programs determine how standardization is achieved. To obtain certification from any program, a company must first commit to organizing its operations in accordance with the standards specified by the program. These standards govern most aspects of operations, including the documentation of supplies and other inputs, detailed procedures for each step of the manufacturing process, and the storage and internal delivery of materials. The accrediting body rigorously inspects the organization's operations and, if the operations are satisfactory, grants certification to the particular standard. The organization must continue to operate within the specific guidelines of the accreditation standard and undergo periodic checks and assessments to retain the accreditation. Note that certification to an ISO standard means that the company is following formalized business standards created by the ISO; it does not mean that the finished products have been tested. ISO certification represents a significant investment of resources for an organization and can cost tens of thousands of dollars per year to maintain. Much of this money goes to train key personnel and purchase equipment, especially if the certification program is focused on quality control itself. The value of such programs is in the return on this investment. Companies often report that using a quality management program such as Six Sigma has saved the organization hundreds of thousands of dollars per project.

Quality-Control Processes. A typical quality-control function consists of assessing the output of a process using a representative sample. This quality check can be qualitative (observing employee-customer interactions to gauge customer satisfaction) or based on physical measurements (comparing measurements to evaluate the consistency of a machining operation in a factory). Assessments based on actual physical measurements have spawned an entire industry and science based on metrology.

Simply, if the design standard of a particular piece of work calls for accuracy to be within 0.0001 inch, then devices must be available that can be used by a trained individual to check the measurements of the product pieces. Precision mechanical devices such as micrometers, scales, and gauges have been largely replaced by programmable digital electronic devices that automatically carry out dimensional analyses on specific parts. These devices are capable of far more precise measurement than even the most skilled of human artisans and have much greater consistency and reliability.

Careers and Course Work

Specialization in quality-control procedures is a growing and very viable career option. Careers range from support and maintenance of quality-control programs to advanced project management in practical applications. Academic careers in quality control are available for those who wish to work on statistical procedures and models for the development of quality-control algorithms and procedures. A degree in quality control can lead to a career as a quality control inspector or industrial production manager. Various universities, such as Oakland City University in Indiana, Arden University in England, and the University of Arkansas offer courses in quality management, information quality, data analytics, and operations management. Various distance-learning courses are also available.

Because quality control is a universal concept, it has applications in careers in many fields. Quality-control procedures are used in both simple mechanical production processes and complex computer programming operations. The student who considers a career in quality control will be expected to acquire a sound grounding in mathematics and statistics to understand the basic principles of sampling, variance, and other particular features relevant to quality-control procedures. In postsecondary education, the student will be able to specialize in a particular field of study. Many community colleges offer two-year programs designed to prepare a student to become a quality-control specialist. Following completion of the program, the practicing quality assurance technician would be expected to maintain certification through an appropriate association, such as the American Society for Quality, and to master new and emerging quality-control procedures.

Quality control plays a significant role in many other postsecondary fields of study. Those pursuing a career in one of these fields must acquire a basic understanding of not only quality control but also the specific methodologies used in the particular field. For example, biochemical laboratory procedures require that the practitioner has intimate knowledge of biochemistry and the analytical procedures and sampling methods used in maintaining the quality standard of the tests being carried out. Similarly, a computer science specialist needs intimate knowledge of computer programming as well as the specific methods that are used to ensure the functional quality of software applications.

Social Context and Future Prospects

Quality control is more an application of knowledge than a tangible product. Sound quality-control practices are founded on the basic human desire to access the same goods and services available to others. Suppliers of those goods and services have responded by developing methods to ensure that each unit of a good or service is as uniform as possible. These methods allow sellers to offer virtually identical products to all customers.

The effects and value of quality control are far-reaching, and the absence or failure of quality control has equally far-reaching consequences. One can readily imagine the economic costs if the dependability of products were to decline. The cost per unit produced would rise as the proportion of unusable products increased. In the marketplace, more products would prove defective or fail, resulting in greater repair and replacement costs for the producer and consumer. If quality-control mechanisms affected service, resulting in less effective services, consumer satisfaction would also decline. Quality-control procedures will become an increasingly prominent production component as more effective methods are developed.

Innovations in the twenty-first century have advanced quality control. Artificial intelligence and data analytics have increased the efficiency and problem-solving qualities of the quality control process. Blockchain technology can track products as they move through production, ensuring quality. Quality control processes are also more automated, allowing for less human error. 

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