Quick Answer: What Is Spec Limit?

What is lower specification limit?

Definition of Lower Specification Limit (LSL): Value above which performance of a product or process is acceptable.

This is also known as a lower spec limit or lower specific limit representing the minimum acceptable value of a variable..

What USL Six Sigma?

Six Sigma stands for 6 standard deviations (6σ) between avarage and acceptable limits. LSL and USL stand for “Lower Specification Limit” and “Upper Specification Limit” respectively. Specification Limits are derived from the customer requirements, and they specify the minimum and maximum acceptable limits of a process.

What is the formula for CPK?

The formula for the calculation of Cpk is Cpk = min(USL – μ, μ – LSL) / (3σ) where USL and LSL are the upper and lower specification limits, respectively. A process with a Cpk of 2.0 is considered excellent, while one with a Cpk of 1.33 is considered adequate.

What is the difference between UCL and USL?

The UCL or upper control limit and LCL or lower control limit are limits set by your process based on the actual amount of variation of your process. The USL or upper specification limit and LSL or lower specification limit are limits set by your customers requirements.

What is the difference between control limits and specification limits?

Specification limits are used to determine process capability and sigma value. You can define Upper Specification Limits (USL) and Lower Specification Limits (LSL) for each chart. Control limits are limits or averages that are calculated based on previous history.

How is USL calculated?

To find USL, multiply the process capability index and Process Standard deviation and then multiply the obtained value with 6.

What does CP of 1.33 mean?

Process capability indexProcess capability index (Cpk) is a statistical tool, to measure the ability of a process to produce output within customer’s specification limits. … Cpk = or >1.33 indicates that the process is capable and meets specification limits.

What is natural tolerance limit?

Natural tolerances are the control limits placed at three times the standard deviation from the process average. These limits are some times refered to as three sigma limits.

What is sigma value?

A sigma value is a statistical term otherwise known as a standard deviation. … Sigma is a measurement of variability, which is defined by the Investor Words website as “the range of possible outcomes of a given situation.” Add a set of data and divide by the number of values in the set to find the mean.

Why Six Sigma means 3.4 defects?

A Six Sigma process has a short-term (DPMO) process sigma of 6. … Six Sigma is often wrongly defined as “3.4 defects per million products,” when in fact, Six Sigma is actually defined as 3.4 defects per million opportunities (DPMO). Six Sigma’s goal is to improve all processes to that level or better.

Where do specification limits come from?

Specification limits come from your customer. They are limits on product characteristics that define where the product works and where it does not work. Spec (Specification) limits define the allowable deviation from a target or ideal value.

What is the upper specification limit?

Definition of Upper Specification Limit (USL): An upper specification limit, also known as an upper spec limit, or USL, is a value below which performance of a product or process is acceptable. Upper Specific Limit: representing the maximum acceptable value of a variable (see also LSL).

How do you define USL and LSL?

LSL stands for Lower Specification Limit and USL stands for Upper Specification Limit. Often we describe Cpk as the capability the process is achieving whether or not the mean is centered between the specification limits.

How do you calculate control limits?

Control limits are calculated by:Estimating the standard deviation, σ, of the sample data.Multiplying that number by three.Adding (3 x σ to the average) for the UCL and subtracting (3 x σ from the average) for the LCL.

What is CP process?

Cp and Cpk, commonly referred to as process capability indices, are used to define the ability of a process to produce a product that meets requirements. … Specifications: Specifications define product requirements. In other words, they define what is expected from an item for it to be usable.

Why it is called 6 Sigma?

The name Six Sigma is derived from the bell curve used in statistics where one Sigma represents one standard deviation away from the mean. The defect rate is said to be extremely low when the process exhibits Six Sigma’s, where three are above the mean and three below.

What are 3 sigma limits?

Three-sigma limits (3-sigma limits) is a statistical calculation that refers to data within three standard deviations from a mean. Three-sigma limits are used to set the upper and lower control limits in statistical quality control charts.