D2 tool steel is a lot like bad tasting medicine that is good for you: you hate it, but you need it. So, how can you grind D2 tool steel on a manual surface grinder, with precision and economy?
How to grind D-2 tool steel without flood coolant
Suppose you are using a typical surface grinder, such as a Mitsui, Brown and Sharpe, Okamoto or Harig 6×12 or 6×18. Your grinder has no flood coolant, and you prefer not to use some kind of spray mist coolant; you are going to be dry grinding the steel. This is a typical injection mold making scenario, one that can be very frustrating.
It is possible to dry grind large workpieces on a manual surface grinder, but it is not easy. Unless you have absolutely no other option, don’t even consider trying to dry grind a large workpiece. Smaller workpieces will work fine, just be patient with the large piece and follow the steps below.
A smaller, typical injection mold or stamping die component could be 2x4x1/2 in, and you might have 4 of them to grind together. They can certainly be ground dry on a manual surface grinder, though flood coolant is obviously preferred.
If you follow these tips you can succeed at grinding this tough steel. If you have any better ideas, please let us know! The surface grinding process is not an exact science.
Secrets to dry grind D2 tool steel
- Use this wheel: RA46-G800-VOS — Radiac Abrasives Ruby Red surface grinding wheel. I have used just about every wheel suggested, including those made especially for tough steels like D2 and this works the best.
- Rough most of the stock in one pass with very little cross-feed. Basically, as long as the corner of the wheel is sharp you can remove .003-.010 in. stock in one pass. A good practice is to start on one side, continue until the wheel is dull, then start on the opposite side, with a sharp corner.
- Dress the wheel often. It is tedious, but absolutely necessary. There is no shortcut.
- Once the steel is cool to the touch you can begin finishing with a newly dressed wheel. The main secret to finishing is to stop the instant the wheel is dull. Stop. The longer you persist in grinding with a dull wheel, the more damage you will do. It will heat up, suck up and warp.
- The final passes might only be .0001 in. or even .00005 in., but this works. You can dry grind a D2 piece that is 12x4x3/8 in flat within .0001 this way. I’ve done it many times, but it took a while to master.
General tips for grinding D2 and other steels
If there is too much stock left for grinding, which seems to often happen, you could try hard milling the excess material off in a manual or CNC milling machine, such as a Bridgeport, Makino or Deckel, using an old solid coated carbide end mill.
Usually there are plenty of good used carbide cutters left over from CNC precision milling jobs in the shop. If you find one with a radius on the corners, it will hold up much longer. A bull nose cutter, with a .010 in. radius will last longer and leave a better finish that a square cornered cutter.
Norton suggests using a 5SG-46 grit grinding wheel
Once you get to the point where you are ready to grind, you can try using a Norton 5SG-46 grit wheel. This is a blue, gel seeded ceramic grinding wheel that is made especially for tough materials, such as D2 and H-13. For the cost, you will get more than your money’s worth. These ceramic grinding wheels work much better than your common aluminum oxide gray wheel. They work best when removing a lot of stock though, not so well at finishing.
Some toolmakers have good results with a hard wheel, such as an H or I from Norton. The softer wheels seem to break down too quickly and waste a lot of your time with constant dressing. Oddly, a 60 I aluminum oxide wheel works well for small pieces of D2.
Try relieving the center of the grinding wheel
One trick is to take a dressing stick, such as a Norbide or carborundum stick, and carve out a groove in the center of the wheel, in order to reduce the heat build-up. This can also be done with a typical single point diamond. The idea is to minimize heat buildup.
You can also dress the wheel with another, thinner grinding wheel to create a segmented wheel. This does wonders to keep the heat from building up. Just mount the thinner wheel on the grinder and press the wheel you will be using to grind against it as it spins. Create 6 gashes in the good wheel, leaving segments. Then remount it and grind as you normally would.
CBN or Diamond wheels work best, if applicable
If you have a lot of grinding of these tough tool steels, A2, D2, H-13, or DC53, you might consider investing in a CBN grinding wheel. These super abrasive grinding wheels work wonders on the toughest hardened tool steels, but cost much more, of course! You will, however, quickly recoup your investment just by saving time dressing the wheel every few passes.
Let the D2 workpiece settle before taking finish passes
D2 also has a tendency to expand and twist after a lot of grinding has been done. It is advisable to let it settle down overnight before taking your finish passes. Once you do get this stubborn material finished, it will be like that nasty tasting medicine and work well in your injection mold or stamping die.
Tips like these are not easily found in most mold making training courses, they only come from the school of hard knocks.