Company I worked at did lots of investigation on this. Once iron cools it's solid, and about as strong as it's going to be. But as you machine it into a usable part, you impose stresses into the casting, and release some stresses from the casting. The part, the casting, will move slightly. What we wanted to know was working with our foundry and outside machining supplier we were assembling machines castings that in some cases were less than a week old. These were BIG castings, weighted a couple thousand pounds, longest time was the wait from pouring molten 2700 degree iron into the mold and waiting for it to cool,solidify, and be able to be cleaned, burned in sand blasted off, ground off, witness points from gates and risers finished off, and parting lines between parts of the mold and cores ground flat.
With the huge variety of castings plants like FARMALL made, lots and lots of machining had to be done, lots of set-ups, back in the 1950's and early 1960's FARMALL was making 300-350 tractors a DAY, lots of parts were set-up, a day's parts ran, and the set-up ripped off and a different part set-up. I worked at FARMALL for 5-6 years, from a sub-assembler, to production scheduler in a gear machining dept, to a material scheduler, chasing parts in from outside suppliers and other IH plants. Actually, other IH plants were THE WORST to get parts out of. True story, my Buddy that replaced me on an inter works desk, His DAD was a production Superintendant at IH East Moline. My buddy called everyone trying to get a badly needed part one day. He then paged his Dad who was in a staff meeting. He paged him as "Dad". After about ten minutes "Dad" called him back, severely scolded him for paging him as "Dad", then hung up on him. My Buddy called his Dad's Boss, and the Boss had a talk with Dad, bottom line told Dad to get my Buddy his parts whatever it took. Dad was still a king-size jerk, but he treated his SON with a little more respect.
Not enough hours in a day, week, or month to waste time making castings that weren't needed right away. Some of the gears I scheduled had heat-treat cycles that took 24 to 36 hours. Our Boss had a "Never Settle for later" attitude, UNTIL somebody told him that the part had to go through heat-treat. Some processes like induction heat-treat for just hardening gear teeth parts ran one at a time thru a fairly quick set-up and a process time of under a minute. Lots of gears had ground surfaces on them, those set-ups also were quick and short cycle times. But on the flip side, lots of transmission gears had hobbled & shaved gear teeth, getting a set-up on a different gear could take up to one to two days. A sample gear had to pass inspection in the gear lab before production could be run. And not every machine had an operator assigned to it, the foreman had to assign the operator to the job he needed the most. I had a group of eight machines, 4 Hobbs and 4 shavers that all 8 machines ran by 2 operators on two shifts, 4 people total. We got a CRAZY amount of work from those machines, and the operators appreciated the good paychecks.
