In custom magnetics the most important aspect of quality assurance is product design, then manufacturing engineering, process control and lastly testing. Quality assurance efforts too often focus on inspection and testing (error-detection) rather than on error-prevention.
Two critical aspects of design are the prevention of voltage and thermal failures. To prevent voltage failure, you must determine the various gradients throughout the design and check each voltage stress, strike and creepage against the safe design limits for the materials used. Similarly, to prevent thermal failure, the various thermal stresses must be evaluated and design changes made until all areas are within reliable limits. Through shape optimization, units can often be made to operate well within thermal limits and still be very cost competitive. Fits and clearances are also managed to assure necessary design features and simplify manufacturing. Manufacturing Engineering and Process Control for quality assurance is all about the details of material selection, equipment and tooling design, and prevention of human error on things not already prevented through design, materials, equipment or tooling.
Lastly, to certify that each product meets it's functional requirements they are 100% tested. Serialized test results can be provided either with the shipment or upon request at a later date.