However, as more tests are employed, the probability of a false alarm also increases. Statistical quality control SQC is defined as the application of the 14 statistical and analytical tools 7-QC and 7-SUPP to monitor process outputs dependent variables. Statistical process control SPC is the application of the same 14 tools to control process inputs independent variables. In , Dr.
Kaoru Ishikawa brought together a collection of process improvement tools in his text Guide to Quality Control. Known around the world as the seven quality control 7-QC tools , they are:. In addition to the basic 7-QC tools, there are also some additional statistical quality tools known as the seven supplemental 7-SUPP tools:.
A marked increase in the use of control charts occurred during World War II in the United States to ensure the quality of munitions and other strategically important products. The use of SPC methods diminished somewhat after the war, though was subsequently taken up with great effect in Japan and continues to the present day. The use of SPC techniques in America faded following the war.
It was then picked up by the Japanese manufacturing companies where it is still used today. In the s, SPC started to gain acceptance again due to American industry feeling pressure from high quality products being imported from Japan. Today, SPC is a widely used quality tool throughout many industries. SPC is method of measuring and controlling quality by monitoring the manufacturing process.
Quality data is collected in the form of product or process measurements or readings from various machines or instrumentation. The data is collected and used to evaluate, monitor and control a process. SPC is an effective method to drive continuous improvement. By monitoring and controlling a process, we can assure that it operates at its fullest potential. Manufacturing companies today are facing ever increasing competition. At the same time raw material costs continue to increase.
These are factors that companies, for the most part, cannot control. Therefore companies must concentrate on what they can control: their processes. Companies must strive for continuous improvement in quality, efficiency and cost reduction. If process variation e. The type of chart used will be dependent upon the type of data collected as well as the subgroup size, as shown by the table below.
A bar, or line, above a letter denotes the average value for that subgroup. Likewise, a double bar denotes an average of averages. Consider the example of two subgroups, each with 5 observations. Each process charted should have a defined reaction plan to guide the actions to those using the chart in the event of an out-of-control or out-of-specification condition. Read Section 10 below to understand how to detect out-of-control conditions. One simple way to express the reaction plan is to create a flow chart with a reference number, and reference the flow chart on the SPC chart.
Many reaction plans will be similar, or even identical for various processes. Following is an example of a reaction plan flow chart:. A control plan should be maintained that contains all pertinent information on each chart that is maintained, including:.
The control plan can be modified to fit local needs. A template can be accessed through the Control Plan section of the Toolbox. After establishing control limits, the next step is to assess whether or not the process is in control statistically stable over time.
This determination is made by observing the plot point patterns and applying six simple rules to identify an out-of-control condition. When an out-of-control condition occurs, the points should be circled on the chart, and the reaction plan should be followed. When corrective action is successful, make a note on the chart to explain what happened.
If an out-of-control condition is noted, the next step is to collect and analyze data to identify the root cause. Several tools are available through the MoreSteam. You can use MoreSteam.
Remember to review old control charts for the process if they exist - there may be notes from earlier incidents that will illuminate the current condition. After identifying the root cause, you will want to design and implement actions to eliminate special causes and improve the stability of the process. You can use the Corrective Action Matrix to help organize and track the actions by identifying responsibilities and target dates. The ability of a process to meet specifications customer expectations is defined as Process Capability, which is measured by indexes that compare the spread variability and centering of the process to the upper and lower specifications.
The difference between the upper and lower specification is know as the tolerance. Otherwise, it ended up with inaccurate control limits for the data. The selection of control chart depends on the data type: Continuous or Discrete? Measure the output on a continuous scale. It is possible to measure the quality characteristics of a product. The output is a decision or counting. It is not possible to measure the quality characteristics of a product.
In other words, it is based on the visual inspection like good or bad, fail or pass, accept or reject. Question: In the Control Phase of a LSS project a Belt will identify key metrics that can be monitored and analyzed to give an indication that a process may be moving towards an out of spec condition.
A Pareto charts to understand and control a process B inputs to control critical and complex processes C statistical methods to identify and remove manufacturing errors D statistical methods to understand and control a process.
I originally created SixSigmaStudyGuide. Go here to learn how to pass your Six Sigma exam the 1st time through! View all posts. Could you direct me to the AIAG information you mentioned in the control phase quiz? I followed the link provided but do not see the answer. I tried searching in the search bar but no results. By definition out of control could be considered a certain number of points in a row on one side of the X Bar Bar or R in a control chart or a certain number of points in a row that are consistently increasing or decreasing.
The key to the question is knowing that a process shift or trend has begun if you see that behavior emerged.
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