raster the entire time. Te third group was provided the same training as the raster group but was also provided green static lines projected onto the part with a projector (overlay group). Once training had been completed,
the participants were asked to inspect 90 parts from five differing casting types ranging from 2 to 55 lbs. (1 to 25 kg). Te laboratory experiment was set up to closely resemble a casting visual inspection process. Tey would inspect the part for surface anomalies. Each anomaly that met the criteria was to be circled using a piece of chalk. Ten, the part was placed back onto the conveyance system and the process repeated for each part. To determine which training
condition was significant from one another, a Tukey-Kramer HSD test was done. Tis showed that the raster training group was superior to the basic training group, and there was no statistically significant difference
between the overlay group and either other group. For false alarm rates, there was
a significant difference between the training approaches. Te basic train- ing group was significantly different from both the overlay and the raster training group. Te lack of search pattern training resulted in more false alarms. But the analysis of variance showed that there was not a signifi- cant difference in hit rates among the different training groups. Te raster training group was superior to the basic training group with regards to overall signal detection, but despite the overlay group’s raster training, they were not superior to the basic overlay group. Te likely reason for the overlay group not performing superior to the others is that the over- lay lines were distracting. Tey are salient and caused the inspectors’ eyes to be drawn to those areas and not to the surface areas to be inspected. Tis
is a common effect. Another factor to consider was that the participants would have to utilize more mental effort to confirm line existence, there- fore slowing the process. Tis time loss had to be compensated by reduc- ing peripheral inspection activities. Tese conclusions were confirmed with the results from the eye tracker used on these subjects. Te raster training group viewed the highest percentage of the part and made the best decisions about what an indication was. Te overlay group had the second highest values, and the basic training group had the lowest percentage of the part viewed. Te participants would view only a certain percentage of the part before making a decision, which would generally be a bad one. However, it was found that both groups with rastering training did adopt a more optimal (rastering) search pattern as opposed to the basic training group, whose search patterns were more random. Te systematic search pattern likely would have helped with both rastering groups, if not for the distract- ing effect of the overlay. Tere are many considerations for
improving the visual inspection process. Te MFFT is effective in identifying the cognitive ability of the inspector and cognitive ability is correlated to performance on a visual inspection task. It can be used to help identify new inspectors and also to recognize the training needs for those of lower cognitive ability. Field studies showed operators are not seeing enough of the casting surface to make a useful judgment. Experiments that provide an overlay on the casting to encourage the operators to inspect the entire part proved to be distracting and therefore ineffective. Rastering training did prove to be effective and can be easily imple- mented to help train operators in a sys- tematic and thorough search pattern. A person’s ability to discriminate between acceptable and unacceptable remains problematic and requires diligence to ensure that inspectors continue to make appropriate decisions.
Tis article is based on a paper (13-1546) presented at the 2013 AFS Metalcasting Congress in St. Louis.
46 | MODERN CASTING January 2014
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