TESTING 1-2-3
Managing Risks in Multiple 100% Inspections
A metalcaster analyzes various factors impacting visual inspection for managers determining the cost/benefit of multiple whole-lot inspections. A MODERN CASTING STAFF REPORT
of keeping returns low. Repeat 100% inspections can incur product dam- age as well as increase the possibility of human error. Managers need to determine the value of multiple qual- ity evaluations. Teodore J. Schorn, vice president,
R Question
What factors must be considered when determining the effectiveness of multiple inspections, and what is the impact of each?
Enkei America Inc., developed a model for analyzing the cost/benefit of multiple whole-lot inspections (see “Determining the Worth of Mul- tiple 100% Inspections,” MODERN CASTING, Nov. 2012). After further study and evaluation, he refined the assumptions made in the initial research to help metalcasters apply the model where ideal conditions cannot be met in practice. Using his quality model for inspec-
tion error, Schorn studied variable factors that affect inspection effective- ness and product quality. Te goal was to establish common-sense guidelines for metalcasters and their customers regarding the practice of conducting multiple whole-lot inspections of cast- ing shipments.
eliance on visual inspection continues unabated, often in response to customer demand or in hope
1 Background
Repeated inspections of the same lot, performed with deliberate care, can mitigate the factors that tend to reduce
the effectiveness of multiple inspec- tions. Te prior theoretical treatment of this issue assumed that such care was taken. In practice, the effectiveness of subsequent inspections rarely equals the initial inspection. Schorn described the reasons and evaluated the impact
ADDING IT ALL UP Breaking down the latest research is as easy as 1-2-3.
“Management Risks in Multiple 100% Inspections” Theodore J. Schorn, Enkei America Inc., Columbus, Ind.
1 2 3
Background—Repeated inspections of the same lot can be performed with deliberate care to ensure inspector effectiveness and minimize handling damage. But, in practice, second and further inspections sel- dom equal the first. Te paper studies the impact of factors affecting
multiple inspections on a quality and cost basis. Procedure—Several influences on inspectors tasked with reinspecting casting lots limit the effectiveness of multiple inspections. Te likely effect is to increase the miss rate while the false alarm rate may be improved or harmed depending on the situation encountered. Schorn recommended
managers apply the model to their own specific operations. Results and Conclusions—Schorn’s model indicates the best one can do with the quality of outgoing lots is to approximate the damage rate. Tis effectively limits inspections to one or two, before the remedia- tion of the lot from continued sorting is smaller than the damage cre- ated by continued handling. When both part damage and decreasing effectiveness are fully accounted for, quality is more effectively built in by process control, capability improvement and other up-front actions than by inspection.
January 2013 MODERN CASTING | 47
of a decline in inspection effectiveness, on a quality and cost basis. Another assumption made in the
earlier treatment of multiple inspec- tions was the freedom from any harm coming to the product by repetitive handling and inspection. Tis simpli- fied Schorn’s theoretical treatment, but it is seldom true in practice unless severe safeguards are put in place. He also evaluated the impact, on a quality and cost basis, of some loss due to damage as inspections continue.
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