INSTRUCTOR: Statistical Process Control or SPC for short is a method of measuring quality control with statistical methods in order to ensure that the production process is stable and capable. SPC is used in areas of manufacturing that require operation at maximum potential. Maximum potential in many areas of manufacturing could be considered as the minimizing of machine downtime and also the minimizing of part defects.

SPC can also monitor a process and determine how predictable and stable the condition of the output product is. This tool could be regarded as a form of quality control. The application of SPC is done by the use of charts and graphs to measure, record, and analyze results of previous batches of output.

Problems during manufacturing can be fixed much earlier within the stages of production compared to simply having post-production inspection. SPC as a tool allows for the comparison of a parts features to some required specifications. Modern manufacturing focuses on implementing SPC automatically during the processes being done.

To better understand what is going on behind the scenes, we can consider a set of engine heads created on a CNC machine, which have had several holes drilled into their surface. Since we want to see that the process is stable, what we would do is simply collect several sample measures of openings on the part and collect the time at which the measurements are taken and then plot the results on our x-bar chart, also known as a control chart.

On this x-bar chart, we have our upper and lower control limits. These limits are taken from the maximum measurement at which the parts would still be considered within specifications. The center line would be the mean or average value at which the measures of most of the parts fall, which could be considered the ideal line.

From our data, we could also create a histogram. This chart would explain if the process is capable or not. This histogram will also have a lower specification limit and a upper specification limit without any outliers.

With this histogram, we also find the process capability ratio based on the upper specification limit minus the lower specification limit divided by 6 sigma. If the ratio is equal to or greater than 1, the process is capable. If the ratio is greater than 1, the process is also capable.

But if the ratio is smaller than 1, then the process is not capable. If the process is not capable, then we know we are incurring a loss. The goal of SPC is to ultimately have a process fall between certain specification limits so that the profit and material use is optimized and loss among manufacturing is decreased.