Statistical Process Control and Inspection in Footwear Production



Hi all, I am a footwear quality inspector struggling to come up with a proving equation that I can use to determine if a batch produced over an 1 hour period is deemed as conform or non conform.

The footwear industry uses the AQL standard to assess the quality of a product. Within a produced quantity a set amount of samples will be inspected and the defects are categorized as critical, minor or majors. Per each set amount of samples inspected there is a limit of defects in each defect category that will be acceptable in order for the full produced quantity to be deemed as conform.
Critical defects were ignored from example below:

1201 to 3200 pairs - inspect 125 pairs - 7 majors and 10 minors or less = conform
3201 to 10.000 pairs - inspect 200 pairs - 10 majors and 14 minors or less = conform
10.001 to 35.000 pairs - inspect 315 pairs - 14 majors and 21 minors or less = conform

I have started to sit for 1 hour periods at the very end of the production line in order to count the amount of defects that are packed into shoe boxes.
Before the assessment begin I count the number of pairs packed within a 5 minute time period and again at any moment during the 1 hour assessment.
My presence in production line does influence the packing rate as factory quality controllers are more careful with the shoes that they put through packing.

Before assessment: 30 pairs packed in 5 minutes
During assessment: 20 pairs packed in 5 minutes

So, during the assessment I have found 12 defects in 240 pairs, how can I calculate the amount of defects that would be accepted in a 60 minute period based on the quantity produced?
Top Bottom