Wanted to pass along something that seemed to really work for me. My 50w Fiber was having trouble engraving Copper... no surprise. As I had a large job and not enough time to do it, at the rate it was going I decided to experiment.
Based on a thread here that mentioned a fan blowing on copper had helped. I took it one step further and placed the copper blanks in the freezer for 15-20 minutes and took a few out at a time to laser. Got me much cleaner/deeper results and faster too. It reduced the laser time by at least 25%.
This initial cost estimate put the customer off a bit, but they needed this job done ASAP. This experiment enabled me to reduce my cost enough, I now have a customer that comes back over & over.