The role of your QC team is to understand every aspect of the product from design to shipping. They understand every aspect of the project. How the machines work, what goes into the assembly, and when human hands touch the product.
Their role is to inspect at every level of the production process to control the final outcome. If you are receiving numerous complaints and returns, chances are the problem is in your quality control processes and not necessarily the production line.
If issues are getting past your QC team, they are not operating to the highest standard.