Hello all!
I am currently setting up a very large timing gear cover, 176 LBS made of grey cast iron. I am not quite sure what the hardness is...I do not believe it has been hardened. I am experiencing problems with the part flexing after milling my 2nd op faces. There is one large face, 1st op. we are taking a total of around .25" of stock off. The inside face, 2nd op. has around .15 that comes off. We have checked a part with only 1st op ran and it is flat, we threw it back on and cut 2nd op and checked it again and it sprung around .01". I am now having to rough both operations and reload the part and finish both operations in order to get the flatness spec we need to hold.
My question is: has anyone experienced this sort of problem machining thin walled cast iron parts? If so, what was the end solution to the correct problem? We are having 10 parts annealed to see if that will rid the casting of unwanted stresses, but I am not holding my breath. Also, we are using a 45 Degree 5" carbide inserted face mill to finish the main,1st op. face. Should we be using coolant on the mill to try and keep heat out of the part? I have also heard suggestions about taking multiple small depth of cut passes at both the 1st op and 2nd op faces. I have been working on this for far too long and it is time to turn to the masses for an opinion....
Thank you,
Rob