Six Sigma standard

Metrics for this might include number of excursions from statistical process control, but one very useful metric for controllability is process capability, or more accurately, process capability indices. Process capability compares the output of an in-control process to the specification limits by using capability indices. The comparison is made by forming the ratio of the spread between the process specifications (the specification width ) to the spread of the process values. In a six-sigma environment, this is measured by six standard deviation units for the process (the process width ). A process under control is one where almost all the measurements fall inside the specification limits. The general formula for process capability index is ... 

In addition to the standard approaches of knowledge transfer the use of lean six sigma approaches, for instance value stream approaches and process flow charts can facilitate better understanding by the receiving site of both the technical facets of the method and the critical order of the key steps of the method (in an analogous fashion to process understanding assessments). 

A quality management system s process should follow a standard Six Sigma process improvement life cycle that includes the following steps define (process and metrics), measure and control (identify problems and issues), analyze (analyze problems and issues), and improve (implement) circling back to measure and control [11]. An example of a process improvement life cycle can be seen in Figure 9. 

Many people are familiar with work processes, including Bottom Line Innovation, TRIZ, and the various Six Sigma elements. These standardized techniques for work processes have gained a broader use throughout the chemical industry. 

Define the standards against which the audit will be conducted for example, cGMPs, ICH guidelines, and six Sigma. 

Six Sigma focuses on the integration of the human and process aspects of business improvement. By utilizing structured methods that link analytical tools into an overall program framework, there is now a standardized method for resolving work problems. 

Neither lean nor six sigma are standardized in practice. The terms have been used to describe many variants of these programs. No matter what form of lean six sigma program is in place, there are four specific programmatic aspects that are important to a sustainability program ... 

The discussion of sigma (a) given earlier deals with the natural variation in the process.Consequently, we denote the measurement of a as a measure of the voice of the process. This is clearly an internally focused assessment of process capability, i.e., the voice of the process. The probability of a defect in the process, i.e., failure to meet customer expectations, is commonly defined in terms of DPMO. The focus of DFSS is to achieve a minimum of six standard deviations between the mean and the nearest specification ( 6a), corresponding to 3.4 DPMO. Because the specifications are set to meet customer needs, six sigma in this... 

Within the last few decades the automobile industry has undergone a revolution in overall vehicle reliability. With the large number of components and the number of potential failure modes, it has become necessary for a component to provide six-sigma (99.9999%) reliabiUty over its operational life (now assumed to be ten years or 240,000 km/150,000 miles), in order to satisfy customer expectations. Current production automotive batteries do not perform to this standard of course, but it is expected that pressure will come to bear on the industry to perform to this level in years to come. In some respect this may be achievable experience with the first generation Ni-MH traction battery cells in severe electric vehicle (EV) usage has demonstrated less than 25 ppm failures after three years of serviee [2]. In order to achieve this level of performance, however, a close partnership is essential between vehicle sub-systems as the life of the battery is intrinsically entwined with the engine, climate control, and battery charge systems. 

This means that Cpk — 0.42, which is a very poor value. So poor, in fact, that no client would accept it. Some of the most advanced companies in the world, like Motorola and General Electric, have already established a Cpk value of 2 as the minimum quality standard for their own processes and also for those of their suppliers (Bhote, 1996). To satisfy this demand, a process must be perfectly centered on its nominal specification value, while operating with a standard deviation of not more than 1/12 of the tolerance range. In this situation, only two values out of a billion will fall outside the tolerance limits. It is this goal that is the basis of the quality management movement known as Six Sigma ° (Breyfogle, 1998). 

Let s look at right quality the level the customer wants or better if possible. Most customers want zero defects. The traditional method was to use a random sample and develop an acceptable quality level (AQL). A sampling plan was developed and then the sampling standard tables were looked at to determine if the lot should be accepted or rejected. Using the acceptable quality level indicated that the customer was willing to accept some defects. In most cases today this method is not used. With the advent of Six Sigma the levels of acceptability have come way down, approaching zero defects. 

What is Six Sigma It presents an outstanding quality assurance standard. Envision a normal distribution chart, a bell curve. Variability from the mean, the center point of the distribution, is measured in units called sigma, which is defined as the standard deviation. At plus or minus three sigma, three standard deviations, 99.7% of a population would be included. In a manufacturing process using a three-sigma standard, approximately 2700 parts per million could be defective. 

If a quality performance standard of Six Sigma is achieved, at plus or minus six standard deviations from the mean, it can be expected that no more than 3.4 parts per million will be defective. Four-sigma capability is ten times better than three-sigma capability five sigma is 30 times better than four sigma and six sigma is seventy times better than five sigma. One can appreciate the stretch in the quality standard adopted. 

Although Six Sigma had its beginnings as a quality performance standard, some safety professionals have sensed its value and promoted its adoption. As an example of the relevant articles that appeared in the safety literature on Six Sigma, I cite a paper by Tom Rancour and Mike McCracken titled Applying Six Sigma Methods for Breakthrough Safety Performance. This is how the article commences. 

Process control It is important to understand whether the proeess is in control. The number of data points that are more than three standard deviations away from the mean is an indication of the extent to which the process is out of control. What we want is zero data points outside these limits. Companies that have made great strides in process control measure the number of data points thatare outside six sigma limits. This can be used to truly understand variability... 

Six sigma Six sigma is one of the more recent popular approaches to QA that is based on a tight statistical approach to the production of a product. The name arises from a desire to limit the tolerance of a product to plus or minus six standard deviations and thus have only 3.4 defects per million. (This is the fraction outside - - 4.5 standard deviations from the mean the method allows for some measurement uncertainty.) In order for the statistics to hold, the system must be in statistical control and the defects must be random and normally distributed. There is a heavy reliance on control charts and the system is built around what to do if there is evidence for nonconformity. For a nonconforming product six sigma institutes an approach with the acronym DMAIC — define, measure, analyze, improve, control. This has been implemented in some organizations, such as pharmaceutical companies, which produce large volumes of chemicals. However, strict statistical control of chemical products is not always easy, and considerations of the measurement process also needs to be taken into account. 

The Six Sigma program is designed to keep essentially all of a quality-controlled product within half of the variance allowed for each individual unit. This corresponds to one defect in a million possibilities. Thejanuary 28,1986, Challenger space shuttle disaster was caused by defective O-ring seals on the outboard propellant tanks that were not detected during quality checks. Their failure resulted in an explosion that destroyed the vessel and killed all aboard. Quality-control standards developed from mOitary specifications (mil-spec). Anecdotal histories suggest that these standards were established in an attempt to lessen the number of military fatalities caused by defective products. 

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