Technical Review & Discussion
Methodology for Assessing Measurement Error for Casting Surface Inspection G. Daricilar, F. Peters, Iowa State University, Ames, IA
Reviewer: This is a subject in continued demand and a prob- lem between casting manufacturers and casting users. Visual inspection at best is about 85% reliable, so this also needs to be discussed.
Authors: The authors have heard about the notion of an upper limit on the effectiveness of visual inspection. How- ever, the source for this number, nor the scientific evidence to support it has not been found. The authors do not want to propagate this premise without being able to support it. Cur- rent efforts may help quantify this number for casting oper- ations, but several conditions will still be required because of the variability of operators and inspection requirements.
Reviewer: For some metalcasters, the solution is to fire in- spectors when a bad part is shipped to a customer. I am not sure this solves the problem.
Authors: This study showed that significant variability exists
in the visual inspection process. Firing workers because a bad casting is received by the customer is not going to solve the problem. A comprehensive improvement of the system needs to be implemented including control of environmen- tal conditions that degrade operator performance, selection of operators based on their skill set not on their seniority or other factors, providing adequate training and tools to make comparisons, and providing ongoing retraining to ‘re- calibrate’ the human measurement system. After this is ac- complished, then it may be most appropriate to reassign an operator that allows castings to be shipped to the customer.
Reviewer: The best foundries do not inspect quality into their casting. They establish the right process controls to as- sure things are made correctly without defects.
Authors: For many castings, especially larger and shorter run castings, it is not always feasible (or economically fea- sible) to have them acceptable as they come out of the mold. We believe that visual inspectors still perform a vital need. This goal of this experiment was to capture the variability of the current measurement methods, using their standard inspection techniques and requirements. The authors are fo- cused on providing the metalcasting industry with tools that can lead to improvements.
International Journal of Metalcasting/Summer 2011
15
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