BETTER
human casting inspectors. While cog- nitive ability can be identified through a simple test and rastering training improves the percentage of a casting surface that is inspected, discrimina- tion between acceptable and unaccept- able surfaces continues to be problem- atic. Undetected surface defects result in additional rework cycles, or worse, returns from the customer. Marking acceptable anomalies as defects results in excessive processing. Operators must be provided with appropriate training and inspection aids to help reduce measurement errors.
Known Factors Affecting Visual Inspection
Environmental factors: Te work
environment can play a major role in the outcome of visual inspection tasks. Before assumptions can be made
HIT or MISS V
Than
Testing and training improve visual inspection of casting surfaces. FRANK PETERS, R. STONE, K. WATTS, P. ZHONG AND A. CLEMONS, IOWA STATE UNIVERSITY, AMES, IOWA
isual inspection is a critical step in metalcasting, and many factors affect
on individual or task factors, first it must be determined if the environ- ment itself represents a confounding variable. Temperature is an obvious but often overlooked factor in visual inspection environments. Tempera- ture and humidity together affect the ability to achieve optimal thermal exchange with the environment: too hot and the body will focus on cooling; too cold and it must focus on conserv- ing heat. Both of these affect a person’s ability to achieve optimal cognitive performance. It has been found that cooling
sensations (e.g. from a fan) activate the brain and excite the nervous system
Table 1. MFFT Results by Population Population Group
Fast
Students Pipefitters
Metalcasting
Accurate 22 17 9
controlling thermoregulation. Tis activation of the sympathetic nervous system elevates mental alertness, increasing general attention capabilities. Ideally, use work stations that have localized cooling sources to keep an environment near 70F (21C) with a relative humidity between 60% and 70%. Operator factors: Some of these
include visual acuity, color vision and depth perception. As an eye becomes less accurate, so will its ability to accurately interpret defects. Experience on the job can be a very positive individual factor. In fact, inspectors who are experienced in performing a specific visual inspection
Percentage of Population Group in Each Classification Relective
Impulsive
(Slow Accurate) 31 47 25
(Fast Innaccurate) 43 33 28
Slow
Innaccurate 3 3
39 January 2014 MODERN CASTING | 41
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