The ideal manufacturing process is one that produces products that are identical,However,in reality, this is not possible.
Products will always vary from one to another.
As a result, manufacturers have learned to accept variation as part of the manufacturing process [Chase et a1.(1995)],When products are designed, their specifications include tolerances.
This is the amount or the range of variation that can be tolerated. When the product: variation exceeds the tolerance range, problems can result (e.g., parts will be rejected, or parts that are supposed to fit together with another part may not fit, thereby resulting in product defects, etc.)
The aforementioned sources of product variation can be grouped into two categories, assignable and chance causes [Grenier et al. (1997)].
The former refers to causes that can be avoided, such as human error or broken tools, while the latter refers to causes,often random in nature, that are beyond human control, such as the variation in the hardness of steel. When only chance causes are in action, the process is said to be in-control
A process that is in-control is expected to have some variation.
The variation resulting from the presence of chance causes is random and follows no discernible pattern [Delmar and Sheldon (1988)].
While on the other hand, the variation due to assignable causes introduces non-random variation, which follows a pattern.
Much of the effort in quality control is dedicated to isolating assignable causes by detecting the existence of patterns in the data.
The presence of assignable causes leads to an increase in product variation, resulting in the production of defects. Since much of the variation in manufacturing follows the normal probability distribution [Besterfield (1998)], it is used in quality control as a means to detect the existence of assignable causes of non-random variability.
Products will always vary from one to another.
As a result, manufacturers have learned to accept variation as part of the manufacturing process [Chase et a1.(1995)],When products are designed, their specifications include tolerances.
This is the amount or the range of variation that can be tolerated. When the product: variation exceeds the tolerance range, problems can result (e.g., parts will be rejected, or parts that are supposed to fit together with another part may not fit, thereby resulting in product defects, etc.)
The aforementioned sources of product variation can be grouped into two categories, assignable and chance causes [Grenier et al. (1997)].
The former refers to causes that can be avoided, such as human error or broken tools, while the latter refers to causes,often random in nature, that are beyond human control, such as the variation in the hardness of steel. When only chance causes are in action, the process is said to be in-control
A process that is in-control is expected to have some variation.
The variation resulting from the presence of chance causes is random and follows no discernible pattern [Delmar and Sheldon (1988)].
While on the other hand, the variation due to assignable causes introduces non-random variation, which follows a pattern.
Much of the effort in quality control is dedicated to isolating assignable causes by detecting the existence of patterns in the data.
The presence of assignable causes leads to an increase in product variation, resulting in the production of defects. Since much of the variation in manufacturing follows the normal probability distribution [Besterfield (1998)], it is used in quality control as a means to detect the existence of assignable causes of non-random variability.
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