Quality Digest

I´m working for a Foundy company in Saltillo Coahuila México and due to the type of processes that we have in the plant, most of the characteristics that we need to control are discretes, it means that we perform a visual inspection in order to detect them. My question is WHICH SIX SIGMA TOOL I HAVE TO USE IN ORDER TO FIND A SOLUTION FOR A PROBLEM THAT WE DETECT ON THE FINAL OF THE PROCESS ???