SPC is a quality control tool used to isolate or identify assignable causes so that a process can be restored to its normal state. It involves taking a sample from a process to detect abnormalities (assignable causes) within the process. When the sample indicates that the abnormalities exist,the process is investigated to find the nature of the cause.
Once established,the cause is corrected and the system is restored to its normal state.
A typical product has subassemblies and thus takes a variety of processes to make a single product. Each process works on a particular quality characteristic or variable
For a product to come together and work as intended, all processes have to meet the design specifications for the particular quality variable they are working on. Montgomery (2005) explains that SPC philosophy integrates an array of quality tools designed to solve the problems that result in process variation and states that,"SPC can be applied to any process".
The seven major technical tools available to sustain an SPC program
Flow Chart:A pictorial representation of a process to identify where problems are likely to occur.
Ishikawa Diagram:Identify root causes of problems.
Control Charts:Determines if process is "in-control".
Histogram:Analyzes frequency of occurrence of items.
Scatter Plot:Find the correlations among variables.
Pareto Diagram:Helps in determining which problems to work on first.
Check Sheet:Helps in organizing information in an efficient way.
Let us assume processes A and C are suspected to be the culprits,then SPC tools should be used in processes A and C to detect the presence of abnormalities.
There are two widely used methods for detecting abnormalities within the process and estimating the number of defects the process is likely to produce;these are control charts and process capability study,respectively.
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