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ROBUST QUALITY AND FOOLPROOFING IN THE DESIGN OF PRODUCTS AND PROCESSES

(AND OTHER QUALITY AT THE SOURCE TECHNIQUES)

by Rene T. Domingo

There are two schools of thought in managing quality. The first is the traditional and most common way known as "quality by inspection" or "quality after the fact" or QAF. The operating principle is that by checking the quality of the product after it is manufactured, assembled, or packed but before it is shipped to the customer, quality is assured. Quality assurance activities like sampling, testing, counter checks, multiple inspection, and even 100% inspection "assure" that there will no external failure in the field or market. Zero defect and zero complaints are expected when the product reaches the hands of the customer. While QAF may assure customer satisfaction, it is costly, time-consuming, labor intensive, and even wasteful. Of course, in many cases it even fails to catch external failures or defects. Its major weakness is that it discovers bad quality after it has happened. QAF assumes and builds mistrust among all parties in the process. It fosters firefighting rather than continuous improvement. It is a reactive approach to quality management and provides little and late feedback to the erring parties or processors.

The other and more effective way to manage quality, without the disadvantages of QAF, is "quality at the source" or QAS. This preventive approach aims to achieve both zero internal and external failure with minimal or no inspection. Internal failures are defects found and fixed before the products are sold to the market. QAS avoids time-consuming inspection activities to catch defects and costly rework processes to repair them. It aims to prevent rather than catch or correct defects. The main principle of QAS is to assure the quality and reliability of the factors affecting quality at the early or upstream stages of production or manufacturing. These stages include raw material and parts purchasing, supplier selection, product design and development, machine and process design. QAS operationalizes the quality definition of "doing it right the first time": designing the product and processes right the first time, buying the right material from the right supplier the first time, choosing the right equipment the first time. QAS is deemed more economical, faster, and more effective in assuring quality than QAF. It confirms the saying that "a ounce of prevention is worth a pound of cure." People operating under QAS work together based on mutual trust and are engaged in continuous improvement of quality and reliability. Companies with QAS can achieve perfect quality with zero inspection in many stages of production.

World class manufacturers are distinguished from traditionally managed companies by the QAS practices they have to manage quality. Let us examine some of the major ones.

The first is Quality Function Deployment of QFD. This technique matches the important customer attributes of a product with its engineering characteristics in a matrix form called "House of Quality". It assures that any improvement in the engineering attributes of a product or its parts result in customer satisfaction. It forces the engineer to have a market orientation and to listen to the "voice of the customer." It prevents costly and wasteful engineering enhancements that does not have end-user utility or value.

The second QAS technique is Design for Manufacturability of DFM. This technique involves the manufacturing and other downstream processes early in the design of the product and its parts. The product designers take into account not only the end-user satisfaction but also the easy manufacturability of the products and its parts. The manufacturing department are consulted along the way as product specifications are changed or enhanced during the development stage. DFM assures that the designed product will not be made with high defects rates or low yields. It is common to see well designed products that meets customer expectation, but are extremely difficult, laborious, and costly to fabricate.

The third QAS practice is Supplier Partnership which includes not only reducing, training and developing one's suppliers but also involving them in the product design phase. Supplier Partnership in product design is like applying DFM with the supplier acting as the manufacturer of the raw materials and subcontracted or purchased parts. Suppliers are advised continuously on the changes in product design and consulted on the manufacturability and cost of the revised parts or raw materials. Supplier Partnership prevents delivery of defective parts from suppliers and high costs due to difficulties in manufacturing the new or revised parts.

The fourth QAS technique is Concurrent Engineering (CE) which embodies the highest and most integrated form of partnership in the product development phase. The basic CE team consists of purchasing, styling (design), engineering, and manufacturing. These four department cast away their functional hats and design the product together as a group in parallel rather than in sequence. CE assures that the product design initiated by the styling department would require materials easy to procure (purchasing), parts easy to design (engineering), and parts easy to make and assemble (manufacturing). The group continuously enhances and refines the product design, and this iteration continues until all parties are satisfied. CE results not only in the highest quality product but also the shortest product development cycle time. The most sophisticated and most effective CE team would include customers and suppliers. This expanded team assures that all design changes and features are immediately validated by the end-user, and changes in part and raw material specifications are understood and accepted by the prospective supplier.

Process capability analysis is a powerful quantitative QAS technique. The process capability of any process - machine, man-machine system, production line, etc. - is measured by the statistical parameters Cp and Cpk. It indicates if the process is capable of meeting or exceeding the required customer specifications and tolerances. The technique prevents the company from accepting a difficult customer order it cannot produce with the current system. Conversely, process capability analysis guides the company on how much it has to upgrade and improve its production systems before accepting such an order, in case it decides to serve the client. A process incapable of producing a specified order will always produce defects even if it is in a state of statistical control. The only remedy in this case is costly inspection at the end of the line to sort the good from the bad parts or products. However, no amount of quality control and inspection activities will stop an incapable process from turning out defects.

The most effective QAS technique is known as "robust quality" which is designing quality into the product or process so that it could withstand the abuse, misuse, and carelessness of customers and workers respectively. Making a process or machine robust is also known as foolproofing or pokayoke in Japanese.

A lot of so called non-factory defects or warranty claims come from the customer's misuse of the product due to ignorance or carelessness. Customer education, training, and product safety instruction and labelling have its limits in preventing these disasters. The proactive QAS principle of robust quality assumes that the customer will always tend to misuse the product one way or another. Robust products are designed such that it is virtually impossible for any customers in any state of mind to misuse or destroy the product and hurt himself or others in the process. A classic example is the round electric plugs of 110 volt appliances that differentiate them from the flat headed plugs of 220 volt appliances. Whether the customer reads instruction or not, or forgets the correct voltage, it is impossible for him to plug the 110 v appliance into a normal 220 v outlet. One of the most foolproofed product is the modern camera with its numerous auto features - auto flash, exposure, load, wind, rewind, etc. - which is designed for worry-free use by ordinary and forgetful users. But there is still room for improvement, as all loaded cameras can still be accidentally opened with its unused film, thereby destroying the used ones. Another example of robust product design is the desiccant in medicine bottles that keep the pills or capsules dry. The present sachet or "tea bag" shape prevents it from being swallowed by the unwary user. The old capsule shaped desiccant, even with its different color and bold warning "Do not eat" could easily be mistaken for the medicine capsule.

Process foolproofing or pokayoke is a fertile ground for engineers, equipment makers and users to explore the application of the robust quality principle. Pokayoke, together with a vigorous TQM program, quality-trained and empowered workforce, and application of statistical process control, enable most Japanese companies, especially the Toyota group, to achieve high internal and external quality, and consequently global competitiveness. Sadly, most equipment manufacturers or suppliers do not design quality into the machine and expect their customers or users to inspect the equipment output before it goes on to the next process or production stage. The principle of pokayoke is that the machine or process would automatically stop or discern by itself if it has produced a defect or there is a malfunction that may cause defective output. A pokayoke compliant equipment is self-inspecting, self-monitoring, self-controlling, and self-managing. It can make the right decisions even without its operator around. The pokayoke can make any machine robust, i.e., capable of producing the right products even when the worker gets careless.

There is a difference between pokayoke and automation. Most automated process and equipment are unintelligent quality wise. They can quickly produce mountains of defects if unattended or unmonitored. Most automated production lines require continuous and costly human monitoring, tending, and inspection at the end of the line. Pokayoke lines and equipment, on the other hand, can be left alone. Operator productivity is high since numerous pokayoke lines can be managed by one worker.

Pokayoke lines require human intervention only in exceptional and abnormal cases during which it will stop by itself to prevent further loss or defects. It will call for human assistance through conspicuous signal lights (usually red lights), and/or loud sound or sirens. These signals are also known as visual control devices, and factories which use these to facilitate management are called "visual factories". Omron Malaysia Sdn. Bhd., a large maker of electronic relays in Kuala Lumpur and a subsidiary Omron Corporation of Japan, employs pokayoke and visual control to sustain its efficient Just-in-Time assembly lines that run with very little inventory. Colored lights, blue, yellow, and red, at the end of each line indicate its production achievement relative to the target. Operators are also empowered to stop any line with a stop button in case of defects or machine malfunction.

Most pokayoke are inexpensive devices and modifications suggested by the workers and operators themselves involved in continuous improvement programs. They are added and incorporated into both general purpose or specialized equipment, automated or manually operated. They often use light, tactile, and air pressure sensors that continuously gauge product specification like diameter and width. Any abnormal product will trigger the sensor which in turn cuts the power and turns on the alarm or light. Instead of the product, a pokayoke may monitor an equipment part like a toolbit. A good example is the automatic drill. Wear and tear may break the drillbit. Without a pokayoke, a drill with a broken bit may come down on the part, spin, without actually boring a hole. The defective part moves on to the next equipment unnoticed where it will be further processed unnecessarily. Many pokayoke are also applied to the material handling or transport devices rather than to the equipment themselves. When a defect is caught by these pokayoke, it can stop the producing machine and/or the receiving one.

A pokayoke equipment will not create its own defects. Moreover, it will not accept defects from the prior stages. Its pokayoke device will not allow the machine to process a defective part or raw material made by earlier processes. The machine will also not be able to pass on defects to the next process or machine. A pokayoke therefore will prevent or minimize wastes and defective products in all stages of the production line. Pokayoke is indeed a most effective technique using the principle of "Quality at the Source" that we can see in world class manufacturers.


 

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