This paper provides an overview of quality control principles and practices in manufacturing and engineering. It defines quality in terms of product features and freedom from deficiencies, then surveys the major statistical and graphical tools used to monitor and improve processes, including run charts, Pareto charts, flow charts, cause-and-effect diagrams, histograms, scatter diagrams, and statistical quality control charts. The paper also examines the contributions of key quality theorists—Joseph Juran, who introduced Total Quality Management and the quality trilogy, and Genichi Taguchi, whose methods emphasize deviation from target values and built-in quality. It concludes by noting international standards such as ISO 9000 and the Malcolm Baldrige National Quality Award.
The paper demonstrates effective categorical organization: it groups related content (tools, theorists, standards) into distinct sections and uses numbered lists to present parallel items clearly. This structure allows readers to compare tools and frameworks without losing the thread of the broader argument that quality must be systematically designed and monitored rather than inspected after the fact.
The paper opens with a definition of quality control and its two core dimensions in a manufacturing context. It then proceeds through seven specific QC tools in a numbered sequence. The second half shifts to influential theorists — Juran's quality trilogy and Taguchi's loss-function approach — before closing with a brief survey of global quality standards. The progression moves from practical tools to theoretical frameworks to institutional recognition, forming a logical arc from "how" to "why" to "who certifies."
Dr. W. Edwards Deming (1900–1993) emphasized a clear mission: aim for constant improvement in the product or service you offer your clients. This cannot be achieved without maintaining a high level of motivation and satisfaction among the people who comprise your organization — that, too, must be considered part of the goal.
According to the American Society for Quality, quality control is the constant or periodic inspection at every stage in the manufacture of a product — from raw materials to finished product — in order to ensure that the standards of quality set by the manufacturer, by law, or by customer demand are being met.
In a manufacturing setting, quality has two aspects. First, product features refers to the characteristics of the product that result from design — the functional and aesthetic features of the item intended to appeal to and provide satisfaction to the customer. Second, freedom from deficiencies means that the product does what it is supposed to do, within design limitations, and that it is free of defects and out-of-tolerance conditions.
In the past, quality control pertained to the inspection of goods at the end of the assembly line. In today's engineering organizations, however, it has a much wider application.
Variability exists in any process. Two machined parts, for example, may appear identical yet differ due to variations in the way the parts were made or the materials from which they were produced. There are a number of different tools used to test or control quality in a process.
1. Run charts are used to monitor and analyze processes over time. They display trends, patterns, or shifts according to time. An upward trend, for instance, would contain a section of data points that increased as time passed. A population is the entire data set of the process — if a process produces one thousand parts per day, the population is all one thousand items. A sample is a subgroup or small portion of the population that is examined when the entire population cannot be evaluated.
2. Pareto charts are used to graphically summarize and display the relative importance of differences between groups of data. Eighty percent of problems usually stem from 20% of causes. Pareto charts arrange data so that the few vital factors causing most of the problems reveal themselves. Concentrating improvement efforts on these few factors will have a greater impact and be more cost-effective than undirected efforts.
3. Flow charts are pictorial representations used to describe a process or plan project stages. They tend to provide a common language or reference point. When dealing with a process flow chart, two separate stages should be considered: the finished product and the making of the product.
4. Cause-and-effect diagrams provide a pictorial display in which possible causes of problems, or factors needed to ensure success of an effort, are identified and organized. This is an effective tool that allows people to easily see the relationship between factors, and it is useful for studying processes, analyzing situations, and planning.
5. Histograms, which chart frequency distributions, help engineers portray information on location, spread, and shape to perceive subtleties regarding the functioning of the physical process generating the data. They can also suggest the nature of, and possible improvements for, the physical mechanisms at work.
6. Scatter diagrams are used to study possible relationships between two variables. Although these diagrams cannot prove that one variable causes the other, they indicate the existence of a relationship as well as the strength of that relationship. A scatter diagram is composed of a horizontal axis containing the measured values of one variable and a vertical axis representing the measurements of the other variable.
7. Statistical Quality Control (SQC) charts apply a statistical approach to the study of manufacturing process variation for the purpose of improving the economic effectiveness of the process. These methods are based on continuous monitoring of process variation.
Joseph Juran had an important influence on the development of quality engineering, especially in product and process design. Dr. Juran was the first to incorporate the human aspect of quality management into what is referred to as Total Quality Management (TQM). Central to Juran's message is the belief that quality does not happen by accident — it must be planned.
Juran views quality planning as part of a quality trilogy consisting of quality planning, quality control, and quality improvement. The key elements in implementing company-wide strategic quality planning are: identifying customers and their needs; establishing optimal quality goals; creating measurements of quality; planning processes capable of meeting quality goals under operating conditions; and producing continuing results in improved market share, premium prices, and a reduction of error rates in the office and factory.
You’re 80% through this paper. Sign up to read the remaining 2 sections.
Sign Up Now — Instant Access Already a member? Log inAlways verify citation format against your institution’s current style guide requirements.