What Does A Cp Of 1.5 Mean?

What does a PPK of 1.0 mean?

Capability indicesPpk is an index of process performance which tells how well a system is meeting specifications .

If Ppk is 1.0, the system is producing 99.73% of its output within specifications.

The larger the Ppk, the less the variation between process output and specifications..

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

A Process Capability Index. The ratio of the tolerance (specification, or permitted amount of variation) to the process variation. A value of 1 indicates the process variation exactly equals the tolerance. Values of less than 1 indicate the allowable variation (the tolerance) is less than the process variation.

What is a good Cp and Cpk value?

When Cpk is negative it means that a process will produce output that is outside the customer specification limits. 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.

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. … Specifications are normally defined in terms of nominal (+/-) tolerances or ranges (low to high.

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.

Can CP CPK be negative?

Both Cpk and Ppk can be a negative numbers. It means that, on average, the process is not meeting customer requirements.

What is the minimum acceptable value for CP?

A value of less than 1 is unacceptable, with values greater than 1.33 (1.25 for one-sided specification limits) widely accepted as the minimum acceptable value, and values greater than 1.50 (1.45 for one-sided specification limits) for critical parameters (Montgomery, 2012) .

What does a CP value mean?

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 an acceptable CP value?

By convention, when a process has a Cp value less than 1.0, it is considered potentially incapable of meeting specification requirements. Conversely, when a process Cp is greater than or equal to 1.0, the process has the potential of being capable. Ideally, the Cp should be as high as possible.

How do you read CP and CPK?

If the overall average is in the center of the specification, the Cp and Cpk values will be the same. 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.

What does a CP of 1 mean?

A Cp of one indicates that the width of the process and the width of the specification are the same. 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.

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.