Muhammad Aslam - Introduction to Statistical Process Control

Most of the emphasis on the execution of the control chart has been seen in the second half of the twentieth century when the monitoring of small shifts in the production process was focused by announcing two methodologies. These methodologies were the cumulative sum introduced by E. S. Page in 1954 and the EWMA by S. W. Roberts in 1965. Another direction was introduced by R. E. Sherman in 1965 when he hovered the idea of repetitive group sampling. The technique of the repetitive sampling was readdressed by S. Balamurali and C. H. Jun in 2006. Currently, a plenty of literature can be seen on the application of repetitive group sampling technique with the major contributions of M. Aslam and L. Ahmad (Ahmad, Aslam, & Jun, 2014; Aslam, Srinivasa Rao, Ahmad, & Jun, 2017).

Quality may be defined as the characteristic of a good or service that can fulfill our desire. In other sense, it is defined as the fitness to use. This quality of product is used as a powerful tool for deciding/selecting from many competing products. This quality plays a vital role in the growth, business success, and to face the competing market. It is a widespread phenomenon as the quality may be an individual, a departmental store, a food chain, a cellular company, a transport company, etc. The quality may be classified as the quality of the design and the quality of the conformance. The quality of design may be described as the goods and the services produced in various designs and levels. The quality of the product like other corporate matters must be reviewed continually in the light of current settings. Two of the most famous authors, Shewhart and Deming, worked for the quality and management of the quality using statistical theories and concepts.

The quality of conformance depends on several factors, such as specifications of the design, selection of manufacturing process, types of process control, etc. Garvin (1987) described eight dimensions of quality. These dimensions are explained as follows:

1 Performance

How much the product is worth for the intended job? The product or services are evaluated for its specific functions. If the desired functions are performed well, then the performance of the product is high.

1 Reliability

How often does the product fail to perform? When the use of the product is fit for a long time, then it is said the product is reliable for a long time. When a product requires repair or change frequently, then it is said to be unreliable. For example, if the use of plug‐in motor car engine lasts for long time, then its reliability is high; otherwise it is said to be unreliable.

1 Durability

How long the product serves? This is the most common property desired by the customers for any product. The customers want to purchase the products which serve them for longer lifetimes. Particularly, this dimension is applicable in automobile, electronics, communication products, etc.

1 Serviceability

How informal is it to get repair? Wear and tear is common in any product. The quality of any product is fit to the consumer if it is easy to get its service. The purchasing decision of the product is directly related to the serviceability of that product. For example, the mobile manufacturing companies normally provide after‐sales service of the mobile. Now if any problem is met to the user, then most of the companies provide the replacement of the mobile and some companies pronounce time for its repair as they send the mobile in the workshop, which may take weeks or even months to deliver it back to the customer.

1 Aesthetic

How beautiful the product looks? The look of the product plays an important role in determining the quality of the product. There are many factors that are directly related to the aesthetic of the product, for instance, the color, design, shape, model, style, packing, and such other sensual features. For example, in automobile industry the color and design of a vehicle play a significant role toward its quality.

1 Features

What extra functions the product can do? The customers have the tendency toward the articles having some extra features which others brands do not have. These added features are provided in addition to the original or main functions for which that article has been given. For example, if a mobile phone manufacturing company introduces a function of converting voice to text form while others do not have this function, then this is quality added function.

1 Perceived Quality

What is the repute of the product? Usually, customers are associated with those companies or products with which their past experience is pleasing and satisfying. Most of the customers attach the experiences of such other products while deciding to purchase or hiring a new one product or service. Normally the brand once selected urges the customers to decide for the next time. For example, consider an electronic company manufacturing a wide range of electronic goods like air conditioner, deep freezer, cooking range, washing machine, television sets, LEDs, mobiles, etc. If a customer uses a mobile phone of that company and he feels zero problem and fully satisfied with its working and after‐sales services or experience of warranty claim, then absolutely he will prefer to purchase such other items like air conditioner, deep freezer, cooking range, washing machine, television sets, and LEDs of that company.

1 Conformance to Standard

How much the product is made according to the set standard? The product quality is very much related to correctness of the designed item with the final product. Any product is designed first based on so many parameters and then sent to the manufacturing unit for production. Any difference between the design and the final shape of the product affects the quality of the product.

In connection with these concepts, the quality may be defined by either the characteristic of fitness for intended purpose or the conformance to specification. To achieve target explained in the chief definition, which is much broader concept, is not so easy task, but a continuous monitoring of manufacturing and management system and the later concept which is related to manufacturing phase is monitored using the SPC technique.

The long‐term effect of the quality is a desirable target for the administration of the business. Only obtaining the quality or service of the product is not enough, but keeping it up is a continuous process, which demands for financial allocation. Now we analyze the cost aspects for maintaining the quality of the product. There are three aspects of cost burden associated with the quality of the product. These cost aspects are the real efforts toward attaining the quality of the product. It is sole responsibility of the management to keep the balance between the quality and the cost incurred for maintaining such quality. A competent analysis of the costs of quality will lead to the objective of the administration.

The quality costs are the same costs as happened other costs like production cost, distribution cost, promotion cost, maintenance cost, sales cost, design cost, etc., which is a significant management tool for monitoring and assessing overall effectiveness of the treated quality.

The quality‐related costs can be divided into three types:

a) Prevention Cost

These are costs incurred before the production or operation. These are associated with the design, implementation, and the maintenance of the quality management system costs (Garvin, 1987):

Design Costs: The setting and determination of the required design and corresponding specifications, the incoming material, etc.

Quality Planning Cost: The cost incurred on the formation of quality, process control, inspection, and supervision.