ASME B18.18 pdf download Quality Assurance for Fasteners
This Standard places a Cp0 expectation on the sample plans shown herein. However it should be recognized that zero nonconformities (Cp0) in a sampling does not necessarily mean that the population is entirely free of defects. Statistical process control and other variation low- ering measures can significantly reduce the number of defects in the population that may be produced, but it should be noted that statistical indices only imply the quality level produced, and improperly applied statistical treatments will imply the presence of defects that are not present, or miss some deficiencies altogether.
The closest that one can approach zero defects in a population is through 100% part per part examination, but again caution must be exercised.
The goal of zero here can be intractable.
The complexity of resources required, the limitations of the available equipment for each verified characteristic, the stringency of controls required will only be able to demonstrate quality on a parts per million (PPM) basis, and not necessarily any assurance of zero deficiencies.
2.2 In-Process Inspection
2.2.1 Fabricating Operations. General inspection procedures shall be established on the basis of engi- neering and manufacturing experience with regard to the effort of setup, tooling, operator, machine setup, and operation on each characteristic at each processing station. The minimum in-process requirements at each machine or processing station shall be as follows:
(a) Five pieces shall be visually examined for gross defects and surface discontinuities as required by the applicable standards. Three pieces shall be verified for part characteristics imparted to it by that machine or processing station in accordance with Table 1 at the following times:
(1) at the start of each production run
(2) at the start of each new shift
(3) when a tool is changed or when an adjustment in machine setup is made
(4) at the completion of each manufacturing operation NOTE: When tungsten carbide dies are used, it is only necessary to verify a single piece for formed dimensions.
(b) During the production run, on a frequency of not less than one part per every 2 hr, parts shall be inspected for all designated part characteristics imparted to it by that machine or processing station in accordance with Table 1.
2.2.2 Heat Treatment. All heat treating processes and heat treatment equipment shall be regularly moni- tored to ensure process control and proper functioning of equipment.
2.2.3 Finishing Operations. All plating, coating, and post lubrication processes and equipment shall be regu- larly monitored to ensure process control and proper functioning of equipment per applicable standards and specifications.