Manufacturers typically use two different techniques to assess part conformance and process control: either in-process gaging or final inspection. In-process gaging is measuring the part while it is still in the process of being manufactured and using that data to, sometimes, adjust the process, other times for part conformance. Final inspection, on the other hand, requires measuring a finished part after all of the manufacturing processes have been completed. The part is taken to an inspection station, or quality control lab, and measured on a variety of equipment, from calipers to coordinate measuring machines. The accuracy, repeatability and speed of inspection has improved over the years, but final inspection still has a few drawbacks.
One problem with only measuring finished parts is that the determination of conformance of the parts between the machine and the lab is unknown. Some manufacturers continue to add cost to the parts not knowing if the already performed operations were within specification. Others have the machine operators measure the parts within the overall process to ensure that they are in conformance before adding additional manufacturing cost, however, this data is rarely collected, or analyzed.