Tired Employees Making Tired Mistakes - Technician Connection Employee Review

We have been on mandatory overtime plus Saturdays quite a bit this year (currently) and everyone is getting tired and unable to focus well, morale is low and this is when the mistakes start to escalate and make it out to the customer. There is barley any pushing back on sales when they decide to drop massive orders on us at the last second although this may have more to do with corporate greed wanting to rush everything through so they can make that money instead of trying to have a smart level work load the lab can efficiently handle. We were told by our manager that the reason for the O.T. was because their not sure what was coming... Really? How can we properly function in the dark? We were told back when we got our raises that it was to promote better behavior among the employees meaning better work ethics but what also drives better work ethics is having well rested employees ready to start their shift, I believe with smart work load managing this can be achieved within 8 hour days 5 days a week.