What Does Tolerance Limit Mean?
A tolerance limit is a measure used to ensure the uniformity or quality of manufactured products. Any product that falls outside of the specified tolerance limit is deemed unacceptable and is typically discarded or recalled. Manufacturing processes are then adjusted to ensure ensure that future products fall within the limits.
Safeopedia Explains Tolerance Limit
Tolerance limits were introduced in Walter A. Shewhart's 1931 book Economic Control of Quality of Manufactured Product as a way for manufacturers to ensure more reliable production outcomes. These limits can also provide a certain amount of uniformity in the end product.
Statistical Process Control
Statistical process control provides stability and reduces stability when manufacturing a large number of similar items. It signals operators when the process mean has moved away from the target and when item-to-item variability has increased, requiring closer monitoring or corrective action.
The major tools used in statistical process control include the histogram, Pareto chart, cause and defect diagram, defect-concentration diagram, sampling inspection, scatter diagram, check sheet and control chart.
Difference Between Tolerance Limits and Control Limits
Tolerance limits and control limits are both used as part of process control, but they are distinct measures. While tolerance limits apply to individual manufactured components, control limits are used to assess the manufacturing process. It is advisable to make use of both limits, since products that exceed their tolerance limits typically result from processes that have been out of balance for a while.