Quick Answer: How Do You Calculate CP?

What is the CP for a 3 sigma process?

Relationship to measures of process falloutCpkSigma level (σ)Process yield1.00399.73%1.33499.99%1.67599.9999%2.00699.9999998%2 more rows.

What is the formula for CP and CPK?

An estimate for Cpk = Cp(1-k). and since the maximum value for k is 1.0, then the value for Cpk is always equal to or less than Cp. Similar to Ppk, the Cpk capability index is only a function of the standard deviation and mean of the data, not a nominal (target) value that may be historical or provided by the customer.

What is CP CPK?

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.

What is a good CP and CPK?

We generally want a Cpk of at least 1.33 [4 sigma] or higher to satisfy most customers. Cpk can have an upper and lower value reported. If the upper value is 2 and the lower is 1, we say it has been shifted to the left.

What is Cp & Cpk in PPT?

Cpk • Cpk is an process capability index that assesses how close the process mean is from the specification limit. … If the process is stable and in control the estimate of Pp is similar to the estimate of Cp. • If Pp is greater than 1 then the process is meeting the specifications as long as the mean is centered.

How do you read CP and CPK?

If the Cp and Cpk values are different, the overall average is not centrally located. The larger the difference in the values, the more offset the overall average. This concept is shown graphically below. Cpk can never exceed Cp, so Cp can be seen as the potential Cpk if the overall average is centrally set.

What does it mean if capability index CP is less than 1?

The Cp index is a fundamental indication of process capability. … Cpk is calculated using the specification limits, standard deviation or sigma, and the mean value. The Cpk value should be between 1 and 3. If the value is lower than 1 the process is in need of improvement.

What is CP Six Sigma?

Share This. A measure of process capability, calculated as a ratio of tolerance or specification limits (upper limit – lower limit) divided by the process variation (6 standard deviations).

What if CP is higher than CPK?

So this is how Cp and Cpk work together: When the values are similar, the mean is close to the middle of the specification limits. When Cp is greater than Cpk, the mean is nearer to one specification limit or the other.

What is the difference between CP and PP?

Pp vs Cp (Capability Indices) Both Cp and Pp are a monitoring indices for the spread of your process compared to the specification spread. Cp is used when a process is under statistical control. Pp is used when a process is initially starting out.

How many Sigma is 1.67 Cpk?

6 sigmaCp = Cpk = 1.67. The sigma level is now 5 – the specifications are five standard deviations away from the average. The out of specification has decreased to 0.57 ppm. The fourth curve represents that magical 6 sigma level.

What if CP is less than 1?

A Cp of less than one indicates that the process spread is greater than the specification. This means that some of the data lies outside the specification. A Cp of greater than one indicates that the process spread is less than the width of the specification.

What is the minimum sample size for CPK calculation?

approximately 100You need a sample size of approximately 100 to obtain a Cp/Cpk with a reasonable confidence interval. The confidence interval for the mean narrows quickly and at a sample size of 30 – 50 reaches an acceptable level.

What does a Cpk of 1.67 mean?

Excellent, CapableThe outcome of a Process Capability study is a single metric, which provides an indication of the ability of a process to consistently provide output which is within required specifications. CPK <1.00 (Poor, incapable) 1.00< CPK <1.67 (Fair) CPK >1.67 (Excellent, Capable)

What does a 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 a good CP value?

Ideally, the Cp should be as high as possible. The higher the Cp, the lower the variability with respect to the specification limits. In a process qualified as a Six Sigma process (i.e., one that allows plus or minus six standard deviations within the specifications limits), the Cp is greater than or equal to 2.0.

What is CP value?

Cp is a ratio of the specification spread to the process spread. The process spread is often defined as the 6-sigma spread of the process (that is, 6 times the within-subgroup standard deviation). Higher Cp values indicate a more capable process. … When the specification spread is less than the process spread, Cp is low.

What is PP and PPK value?

Process Performance Metrics. Pp is the performance index. It measures how well the data might fit between the spec limits (USL, LSL). It doesn’t care if the process is centered within the limits only if it would fit if it was centered. Ppk is the performance centering index.