So we sample 32x and we can calculate the cpk of the dimension from the 32x data. For example , if a dimension is a key characteristic of a product , we have USL and LSL from the drawing. Process Capability (Cp) is a statistical measurement of a process's ability to produce parts within specified limits on a consistent basis. If process spreads as Car B the garage capability will be low, however, if a process is narrowed like C or D we could see that the process is capable to perform as per customer's expectations. I’ve used similar examples when teaching process capability. Take the example of a motorcycle driving in the same lane going in … Measuring the process capability index allows you to see if you have the right combination of materials, equipment, people and methods, by comparing the output of a stable process with the process specifications. Let’s take an example. Cp: Process Capability Index Cpk: Process capability considering location within the upper and lower specification limits or tolerance Cpk is the smaller of the Cpk u or Cpk L C pkU = (USL - X) 3σ C p = (USL - LSL) 6σ C pkL = (X - LSL) 3σ The lower and upper engineering specification limits are 1.90 inches and 2.05 inches. Process Capability Index Example A manufacturing process produces a certain part with a mean diameter of 2 inches and a standard deviation of 0.03 inches. The process of maintaining this temperature has a standard deviation of 2 degrees Celsius. This was well written in entertaining story style. However, I have a real problem with two statements. 0.83 6(0.03) 2.05 1.90 6 = − = − = σ USL LSL Cp Process is not a capable process since Cp<1.0 When a business process meets customer requirements, whether it's manufacturing or service-based, it’s known as process capability. 1. Process Capability Index – Cpk: This is the capability index which accounts for centering of process and is defined as the minimum of Cpk upper and Cpk lower. We want to know the capability of the process . Cp indicates the spread of variation present in a process. how well a process can perform if there is no change in the underlying process conditions. When we talking about the capability of a process , we usually use cpk to show how well the process is. Process capability – Cp: This is defined as the tolerance width divided by the total spread of process. Process capability index (Cpk) is a statistical tool, to measure the ability of a process to produce output within customer’s specification limits. Cpk is the smallest of the Cpu and Cpl. The capability indices Cpk, Ppk, and Cpm are all greater than 1.33, which is a generally accepted minimum value for a capable process. Process Capability analysis Process: - T ake representative sample of process output - Statistical analysis of samples (Ma thematical tools, Scattered Plot, Pareto Chart, Therefore, the engineers conclude that the forging process meets the requirements for the diameters of the piston rings. First, don’t get these guys judging Cp without looking at Cpk also. Cpk uses "s-short-term" to predict the behavior of the process. The Cp and Cpk indices are used to evaluate existing, established processes in statistical control. The above example shows the capability of the garage, the example itself explains what is the process capability. Although SPC control charts can reveal whether a process is stable, they do not indicate whether the process is capable of producing acceptable output—and whether it is performing to capability. 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