Since defects are cumulative, as more parts or more operations are added, the chance of producing a defective product goes up. With process drift as a factor, if the number of parts or process steps exceeds 1200, four-sigma processes are virtually incapable of making one good product. On the other hand, a Six Sigma process with 1200 parts or steps would still be producing a yield of 99.593% good products.
The concepts surrounding the drive to Six Sigma quality are essentially those of statistics and probability. In simple language, these concepts boil down to, “How confident can I be that what I planned to happen actually will happen?” Basically, the concept of Six Sigma deals with measuring and improving how close we come to delivering on what we planned to do.
An important aspect of total quality is the identification and control of all the sources of variation so that processes produce essentially the same result again and again. A histogram is a tool that allows you to understand at a glance the variation that exists in a process. Although the histogram is essentially a bar chart, it creates a “lumpy distribution curve” that can be used to help identify and eliminate the causes of process variation. Histograms are especially useful in the measure , analyze and control phases of Six Sigma methodology.
Here’s an example. Consider how your tolerance limits might be structured to respond to customer expectations in these two instructions: “Cut two medium potatoes into quarter-inch cubes.” and “Drill and tap two quarter-inch holes in carbon steel brackets.” What would be your range of acceptability–or tolerances–for the value quarter-inch ? (Hint: a 5/16” potato cube probably would be acceptable; a 5/16” threaded hole probably would not.) Another consideration in your manufacture of potato cubes and holes would be the inherent capability of the way you produce the quarter-inch dimension–the capability of the process. Are you hand-slicing potatoes with a knife or are you using a special slicer with preset blades? Are you drilling holes with a portable drill or are you using a drill press? If we measured enough completed potato cubes and holes, the capabilities of the various processes would speak to us. Their language would be distribution curves. If the range of acceptability, or tolerance limit, for your product is at or outside the four sigma point on the distribution curve for your process, you are virtually assured of producing acceptable material every time–provided, of course, that your process is centered and stays centered on your target value.
Next define Defect Opportunities Look for defects in Products or Services Arrive at DPMO value Convert DPMO to Process Sigma
Define: What is the scope of project? What is the defect? Here the project scope and defects are defined. A business case is made to obtain project approval. Team charter is established with a clear goal statement. A. Identify Project CTQs B. Develop Team Charter C. Define Process Map Measure: What is the frequency of defects? Here we select one or more product characteristics, map the process or processes responsible, and make the necessary measurements to estimate the short and long term process capability. Select CTQ Characteristics Define Performance Standards Validate Measurement System Analyze: When and where do defects occur? Here key product performance metrics are benchmarked. Then a gap analysis is undertaken to identify the common factors of successful performance. Establish Performance Capability Define Performance Objectives Identify Variation Sources These first two phases are referred to as characterization phases. They define and quantify the project, characterizing its objectives. Improve: How can we fix the process? Here product performance characteristics are selected for improvement. They are diagnosed to reveal major sources of variation. Then, key process variables are statistically identified and performance specifications are established for their improvement. Screen Potential Causes Discover Variable Relationships Establish Operating Tolerances
Benefits to Customer Enhanced Product Quality Predictable Delivery Productivity Impact Faster Response Higher customer satisfaction It’s also a practice that ensures that services / products are predictable and meet customer expectations profitably and always lie within a specified tolerance
CS532 Term PaperBandy.ppt
CS532 Term Paper <ul><li>Applying Six Sigma Methodology </li></ul><ul><li>In Software Engineering </li></ul><ul><li>Sourabh Bandyopadhyay </li></ul>
Introduction <ul><li>What exactly do we mean by 6 Sigma? </li></ul><ul><li>Six Sigma is a rigor for measuring and controlling quality in any process. </li></ul><ul><li>Quantitatively, Six Sigma means that the average process generates 3.4 defects per million – from “6 Sigma Quality – The Goal and The Journey” </li></ul><ul><li>“ If we can’t express what we know in the form of numbers, we really don’t know much about it. If we don’t know much about it, we can’t control it. If we can’t control it, we are at the mercy of chance.” </li></ul><ul><li>Mikel J. Harry </li></ul><ul><li>President & CEO </li></ul><ul><li>Six Sigma Academy, Inc. </li></ul>
Why Six Sigma <ul><li>20,000 lost articles of mail per hour </li></ul><ul><li>unsafe drinking water almost 15 minutes each day </li></ul><ul><li>2 short or long landings at most major airports daily </li></ul><ul><li>200,000 wrong drug prescriptions each year </li></ul><ul><li>No electricity for almost 7 hours each month </li></ul><ul><li>7 lost articles of mail per hour </li></ul><ul><li>unsafe drinking water for one minute every seven months </li></ul><ul><li>1 short or long landings every 5 years </li></ul><ul><li>68 wrong drug prescriptions each year </li></ul><ul><li>1 hour without electricity every 34 years </li></ul>99.99966% Good (6 Sigma) 99% Good (3.8 Sigma)
Objective of Six Sigma <ul><li>View processes completely from a customer point of view </li></ul><ul><li>Continual improvement in processes through measurement </li></ul><ul><li>Integration of quality in daily work </li></ul><ul><li>Completely satisfying customer needs profitably </li></ul><ul><li>A statistical measure of a process’s ability to meet customer requirements </li></ul><ul><li>The importance of communicating in financial terms why it makes good business sense to implement selected solutions </li></ul>
Six Sigma Definitions <ul><li>Process : A process is a collection of activities that takes one or more kinds of input and creates output that is of value to the customer. </li></ul><ul><li>CTQ: CTQ is Critical to Quality. A product feature or process step that must be controlled to guarantee that you deliver what the customer wants. </li></ul><ul><li>Defect ( D ): Any non-conformities in a process or product. </li></ul><ul><li>Unit (N): A process step where each unit must be observable and countable with a definite starting and stopping point </li></ul><ul><li>Opportunity (O): An opportunity is a product or process characteristic that adds or subtracts value from the product. To be quantifiable, each opportunity must be independent. Thus opportunity is event which can be measured that provides a chance of not meeting a customer requirement. </li></ul><ul><li>Normal Distribution: A bell-shaped curve showing a frequency distribution which often occurs in nature. </li></ul><ul><li>Standard Deviation: A statistical measure which quantifies the amount of variation in a process. The standard deviation is the average distance, or deviation, that a given point is away from the mean. </li></ul>
Distribution Curves The essence of Six Sigma lies in understanding variations in the process. Distribution curves tell us not only how well our processes have done; they also tell us the probability of what our process will do next. Statisticians group those probabilities in segments of the distribution curve called standard deviations from the mean. The symbol they use for standard deviation is s, the lower-case Greek letter sigma .
Six Sigma Approach <ul><li>Outside-In Approach </li></ul><ul><li>The essence of Six Sigma methodology lies in understanding the customer requirements and aligning with the larger goals also known as the Big Y or business Y. </li></ul><ul><li>Y = f(X1, X2 ….Xn) where, </li></ul><ul><li>Y is key output metrics that are aligned with the strategic goals/objectives of the business. Big Ys provide a direct measure of business performance </li></ul><ul><li>X is any parameters that influence the Y </li></ul>Traditional View Of Vendor Contribution Customer View ` <ul><ul><li>The Eye Of The Beholder </li></ul></ul>CustomerProcess Vendor Process A B C
Six Sigma Steps <ul><li>The first step of any six sigma project is to come out with the customer issues or problem areas also called as VOC (Voice of Customer) in Six Sigma terms. </li></ul><ul><li>Next these VOCs are mapped to the actual customer CTQs. This is done through a VOC to CTQ translation matrix. </li></ul><ul><li>Finally we should be able to translate this CTQ into a technical requirements document also referred to as the Voice of the Engineer. </li></ul><ul><li>Once we have analyzed the customer problem we need to understand whether its an existing issue or a new issue. </li></ul><ul><li>DMAIC (Used for Process Improvement) </li></ul><ul><li>DMADV (Used for New process or new technology) </li></ul>
DMAIC Approach <ul><li>DMAIC stands for Define, Measure, Analyze, Improve and Control </li></ul><ul><li>Define: Defines the Problem Statement </li></ul><ul><li>Measure: Measure Data regarding your process to find sources variation </li></ul><ul><li>Analyze: Using various statistical tools to analyze the data collected in measure </li></ul><ul><li>Improve: This phase involves screening for potential causes of variation and discovering interrelationships between them. </li></ul><ul><li>Control: Process of validating the measurement system and evaluating capability is repeated to insure that improvement occurred. Steps are then taken to control the improved processes. </li></ul>
Some Six Sigma Tools <ul><li>Define Phase </li></ul><ul><li>Method: Tools: </li></ul><ul><li>Identify Customer CTQ Product Process Tree Bound Project/Benefits Benchmarking Product Tree Formal Approval Histogram Tree Template </li></ul><ul><li>Process Map FMEA Measure Phase Surveys L2 Worksheet </li></ul><ul><li>Method: L1 Worksheet QFD </li></ul><ul><li>Select Lower Level CTQ Define Performance Standard Validate Measurement System </li></ul><ul><li>Analyze Phase </li></ul><ul><li>Method: Tools: </li></ul><ul><li>Establish Performance Capability Events/Causals FMEA Define Performance Objectives F, T, Chi2 Tests Histogram Identify Variation Sources L1 Worksheet L2 Worksheet Pareto Regression Fishbone Hypothesis Test </li></ul>
Some Six Sigma Tools (Contd.) <ul><li>Improve Phase </li></ul><ul><li>Method: Tools: </li></ul><ul><li>Screen Potential ANOVA Residual Discover Variable Relationships Establish Interactions Plot Operating Tolerances Response Surface DOE Level ¾ Main Effects Plot FMEA Ret/Screening DOE Response Equation </li></ul><ul><li>Control Phase </li></ul><ul><li>Method: Tools: </li></ul><ul><li>Validate ‘X’ Measurement System Hypothesis Test Procedures Determine Process Capability SPC Charts Training Implement Process Controls Run Charts </li></ul><ul><li>Project Close-Out </li></ul><ul><li>Method: Tools: </li></ul><ul><li>V – Oper Owner of Control Mechs Audit Plan Financial Audit W – Audit Mechanism Leverage/Best Practices X – Leverage Solution Open Action Tracking Y – Financial Audit Operational Metrics Z – Formal Closure Process Documentation </li></ul>