D2 grinding problem
I'm grinding some 6" X 6" .187 plates that are about 56RC. I have to bring these down to .125. I have a surface grinder with a magnetic chuck but it does not have a variable control on the magnet strength. What I have been doing is cleaning up one side then shimming under any low spots and doing the other side. Turn over and repeat. I'm taking about .003 per pass. I am having a devil of a time getting them to come out flat. The last pair I did I had them flat till the last .02 and it sprung on me. Any suggestions on how I might improve the flatness?
First chioce, use CBN wheels. Second chioce,Norton SG blue wheels. Are you using coolant? How flat do you need them? I would anneal them, mill them down soft first, then HT and grind.
You are probably using too hard a wheel.
OR the heat treat may not be so good. On any parts we grind for a customer that are hardened we specify we must heat treat and then grind. That is if they want them flat. Otherwise I guarantee no flatness.
Then we control the entire process.
We grind parts like this all the time with no issue at all.
RJT has the right idea. I would have Blanchard ground down to +.015, heat treated and then finish ground.
D2 is hard to grind, I've made several projects out of it. You have to take very light passes to finish or your wheel will break down. Also a soft, crisp dressed wheel will help. It would also be nice if you only had 0.010" to take off. Grinding so much creates heat and releases stress, both are bad for flatness. How well was it drawn and was it double drawn before grinding. That would help also. Good luck grinding that tough stuff
Yes, double draw EVERY time with D-2. A sub-zero cycle between draws will help stability also.
I have alot of expierence grinding D2. Horrible stuff it is...
if you are doing 6x6 and .003/pass, Im guessing you have a fairly large surface grinder running flood coolant.
D2 will load a wheel faster than you can blink.
I dont think that you can get those plates anywhere near flat with a simple on/off electric or manual magnetic chuck.
If the D2 comes to you for grinding, in a hardened state, look at it on a surface plate with an indicator running over it. It will obviously, be way out of flat. This is the result of the heat treating, and the relative thinness of the part.
The ONLY way to bring a "pringle" shaped piece of hardened metal into "flat" is to either grind it while being held in a mechanical (non magnetic) holder like epoxy or clay (I do not recommend this) or, the right way is to have a well "dressed" variable strength magnetic chuck holding the part at only the strength required to keep the part on the chuck. For safety reasons, you will need to "block in" the part you are grinding. this is a way that you can use minimal magnetic force. minimal magnetic force allows you to let the part be in "pringle" form and take down the high spots, flip, take down the high spots on the other side and repeat ad-neausum until you have brought the part into "flat"
I used to frequently grind D2 to a micron or less (without coolant) on various parts using the above method. I was trained from scratch as a Grinder Hand, and I worked at a shop that did world class grinding. If their were another way to get a thin part flat to a micron or less, we would have figured it out. At least if involved grinding.
I can say with authority, that without a variable strength chuck, you will be chaseing flat forever.
Frankly, grinding the parts you are talking about is one of the most difficult grinding jobs I can think of. Anyone with a half assed machine and a bit of training can grind a solid, stable thick part fairly flat. What you are doing is not easy or slow.
I wish I had more encouraging things to say, but I suspect, its time for a new chuck.
I have had great success super gluing a few graphite pads on to one side and using neodymium magnets to block the part in with the magnetic chuck off. Grind the graphite pads to around .01-.015 high then flip and turn the mag on. Graphite grinds like butter so you dont need much to hold the part on the chuck.