When you machine copper bars on a CNC busbar punching and shearing machine, it causes chips to peel off the material. No matter what material you're machining, dust and debris will break off the metal and travel down under your mold. Even if you are processing copper and aluminum, the copper bar punching will have small scraps that will fall off. Any material coatings, anti-rust chemicals and resins will also peel off during the bending process.