Tech Briefs

New tool measures quality control system effectivity.

As new technologies are implemented in manufacturing areas, inspection processes will be affected. Often because product quality has increased or automated inspection equipment has been introduced, the inspection activity may be reduced or eliminated. In many cases a disciplined process is needed to evaluate performance data against risk to determine if this change is warranted.

Figure 1. Inspection system and inspector interaction.

A tool has been developed using an Excel® spreadsheet with an imbedded checklist, which will guide users through a series of decision points to make a determination if a change is warranted. The approach attempts to answer the question: How can inspection practices be identified, reviewed, and updated to keep up with technological changes, trend results, facility changes, etc.?

Inspection is often considered a non-value-added expense and therefore subject to budget constraints that usually try to reduce the inspection footprint. If these arguments lead to a reduction in inspection without proper analysis, the organization may be faced with significant risk that will materialize in the future. The inadequacies of inspection can be traced to either improperly applying an inspection system, or the problems with the individual inspection process as shown in Figure 1. Aside from inexperience in designing an inspection system, external forces such as cost and schedule constraints or lack of funding to implement proper inspection processes and tools can increase risks.

The inspection system is the approach for deploying inspectors and the assignment of tasks to these inspectors. Depending on the nature of the process to be inspected and the quality level of the particular process, the inspection system may choose to use 100% inspection, sampled inspection, operator inspection, patrol inspection (inspector moves from station to station), automated inspection, or a combination of multiple types. Inspector capability is dependent upon training to standards, the capability of the inspection tools in use, the time allowed for inspection, and the record keeping provided.

Figure 2. Return on investment (change in inspection resources) vs. investment (effort to perform analyses and capital expenditures).

The inspection result is dependent upon the interaction of the inspection system and the capability of the individual inspector. When either the inspector or the inspection system is poor, then inspection results are erratic as shown in Figure 1. Only when both are good will the inspection result be good. Before significant and potentially expensive changes are made to the manufacturing or inspection processes, it should be determined that the ineffective inspection process isn’t simply the result of a mismatch between inspection system and inspector deployment.

The level of inspection is dependent upon the capability of the underlying manufacturing process, which in turn can be affected by design tolerances and key characteristics. In general, process variability should be independent of the people performing the process. The process should have business or product requirement goals which are met. Ancillary controls should be in place such as adequate worker training, use of calibrated equipment, and appropriate raw materials presented to the process.

When the manufacturing process changes, the inspection approach should be re-evaluated. These changes include introduction of new manufacturing technologies, significant process or facilities changes, and design changes. On the other hand, inspection techniques may improve because of the introduction of inspection technologies or improved inspection techniques. Finally, inspection may be affected by changes in specifications and customer requirements, cost and schedule drivers noted by management, or defect analysis and other anomaly investigations.

Each of these conditions requires an appropriate analysis of the relevant manufacturing, inspection, or stakeholder requirements changes. The tools presented here evaluate the return on investment of an inspection change vs. the investment to implement the change. Investment includes both the effort to conduct the analyses, as well as the effort to modify inspection. As shown in Figure 2, if the return on investment is high and the investment is low, then it is a natural inspection change to make (Just do it). On the other hand, if the return is low and the investment is high, then it’s best to avoid the change (Forget it). When the return on investment is low and the investment is low, most likely these are second in line to tackle and there may be many of these changes to make (Backlog). Finally, when the return on investment is high and the investment is also high, a strategy must be chosen to determine which inspection approach to change (Strategic).

This work was done by Eric S. Richter and Arthur L. McClellan for National Reconnaissance Office. NRO-0001

This Brief includes a Technical Support Package (TSP).

Process Approach to Determining Quality Inspection Deployment (reference NRO-0001) is currently available for download from the TSP library.

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