Quality control processes and best practices

¶ … mission/vision/goal -- aim for constant improvement in the product or service you offer your clients. You cannot do this without maintaining a high level of motivation and satisfaction in the people that comprise your organization -- consider that an aspect of your goal.

Dr. W. Edward Deming -- (1900-1993)

According to the American Society of Quality, quality control is the constant or periodic inspection at every stage in the manufacturer 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 to aspects: 1) product features, or the characteristics of the product that result from design. They are the functional and esthetic features of the item intended to appeal to and provide satisfaction to the customer. 2) freedom from deficiencies means that the product does what it is supposed to do, within design limitations and that it is absent 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. However, in today's engineering organizations, is has a much wider application.

Variability exists in any process. Two machined parts, for example, may appear identical but be different due to variations in the way the parts were made or the materials from which they are produced. There are a number of different tools to test or control the quality in a process. These include: 1) Run charts that are used to monitor and analyze processes over time. Run charts contain trends, or 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 a day, the population would be the 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) A Pareto chart is used to graphically summarize and display the relative importance of the 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 that are causing most of the problems reveal themselves. Concentrating improvement efforts on these few will have a greater impact and be more cost-effective than undirected efforts. 3) Flow charts are pictorial representation describing a process or to plan project stages. Flow charts tend to provide a common language or reference point. When dealing with a process flow chart, two separate stages of the process should be considered: the finished product and the making of the product. 4) A cause-and-effect diagram provide a pictorial display of a list in which you identify and organize possible causes of problems, or factors needed to ensure success of some effort. It is an effective tool that allows people to easily see the relationship between factors to study processes, situations, and for planning. 5) A histogram, which allows the charting of frequency, helps engineers portray information on location, spread, and shape to perceive subtleties regarding the functioning of the physical process generating the data. It can also help suggest the nature of, and possible improvements for, 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 do indicate the existance 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 and 7) Statistical Quality Control charts 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 has 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 that is referred to as Total Quality Management. There are many aspects to Juran's message on quality. Intrinsic is the belief that quality does not happen by accident, it must be planned. Juran sees quality planning as part of the quality trilogy of quality planning, quality control and quality improvement. The key elements in implementing company-wide strategic quality planning are in turn seen as 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.