How to Measure Process Capability ?
The capability indices will be calculated manually, although there are several software packages available which will complete the calculations and supply graphical data illustrating process capability. For the instance during this section, we'll utilize a well-liked statistical software package. For our example, we'll utilize data from randomly collected measurements of a key characteristic of a machined part. to higher represent the population values, the sample data must be randomly collected, preferably over time from an oversized production run. some things to stay in mind:
• Our data is quantitative and variable
• Our data consists of 100 measurements
• The target dimension is 25.4 mm
• USL (Upper Specification Limit) = 25.527 mm
• LSL (Lower Specification Limit) = 25.273 mm
• Range = 0.254 mm
First, we'll examine our data with an easy histogram to work out if it could fit a traditional distribution. additionally, we are able to generate a probability plot evaluating our data’s best suited a line further indicating we are 95% confident that our data fits a traditional distribution
Now allow us to examine the method capability report:
• Cp (Process Capability = 1.68
• Cpk (Process Capability Index) = 1.66
Using the graph, we are able to further evaluate process capability by comparing the spread or range of the merchandise specifications to the spread of the method data, as measured by Six Sigma (process variance units). Through examination of the reports, we are able to determine that our example process is in a very state of statistical control. All the information points fall well within the specification limits with a traditional distribution. A process where most the measurements fall inside the specification limits is deemed a capable process. Process capability studies are valuable tools when used properly. As previously mentioned the data gained is usually wont to reduce waste and improve product quality. additionally, by knowing your process capabilities, the planning team can work with manufacturing to enhance product quality, and processes that are “not in control” could also be targeted for improvement. During a typical Kaizen event or other quality improvement initiatives, Process Capability is calculated at the beginning and end of the study to live the amount of improvement achieved. Accurate knowledge of process capability enables management to form decisions regarding where to use available resources supported data.