Rmore:
Maybe you need a new supplier if they don’t have a reasonable QC dept. or set of stds. Have your QC dept. pick a bunch of boxes, and the like, which you have been getting, and really go over them with a fine-toothed comb, for any problems. List these and see if they don’t fit into a number of similar type problem groups. Then, define those issues and your limits of acceptability. That groupings list might include nice tight fitted joints and corners, square, not buckled all over the place, etc.; waterproof or not; no sharp edges so people can’t be cut on them every time they work on the box; properly located and sized internal bracketry and mounting surfaces, and stiffeners on large flat surfaces; limits on size and depth of spot welding markings. Everything you’ve had trouble with over the years on these types of boxes starts out on the basic listing. Is that problem your fault or theirs? All of these things need finer, measurable definitions which anyone can see and measure, without too much arguement. As for sharp edges cutting people, you get to drag their fingers along and over the edges for proof of satisfactory quality. Some Tech. Ed. Sheet Metal text books probably have a QC chapter which might be worth your reading. I suspect that some of the electrical component manufacturer’s groups have some basic stds. lists and limits.