We are having trouble getting a reasonable finish on this 1018 part we are running on an Acme. The Bar stock is 15/16 diameter 1018 steel. The part is 3/4 long with profiles as deep as 1/4 inch on the fully turned OD. We have only 10 days to deliver these parts and the delivery for carbide is two to three weeks. Even if we could get the carbide sooner it would not be economical since this is only a 1500 piece job. With the high speed tool we are using, the micro is as high as 250. A 12 degree rake improved the finish slightly but we are still having problems with the material welding to the tool. We also tried a higher rake which gave us dimensional problems with our part. This high micro does not give the part a very crisp appearance and we don't feel the customer will accept this.
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Trouble getting good finish on 1018 part running on Acme
(5 posts) (5 voices)-
Posted 1 year ago #
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Again, no experience with acme bar machines, but just thinking of good machining practices. Steeper back rake, side rake, and front clearance angles are going to remove mass from the tool. You don't want that. With less mass to wick away the heat buildup there will be more welding of the stock to the tool, causing dimensional changes. You can shallower angles, but you have to control your feed rate accordingly. I don't know what profile you're cutting, but you probably need a bigger radius on the tip of the cutter, or you get that "sewing needle" effect. With HSS I see lots of improvement in finish when I stone in a little radius on the cutter (without dulling the edge0. I'd check the rigidity of your setup (part holder, tool holder, and gibs). And are you using a water soluble cutting fluid? I'd try some heavier stuff. Can you use a sulfurated cutting fluid without running into trouble with the OSHA people? Tends to smoke a bit. Finally, some time in the heat treat oven might make that stuff cut better. 1018 CRS can have a lot of built in stresses.
Posted 1 year ago # -
I agree with Engineeringtech except with regard to the rake angle. I use an air grinder to angle the cutting edge so as to direct the chip away from the work. The finished chip curler is usually conical with the large end away from the work.
Careful attention to the cutting edge, as mentioned before, is critical. Use a fine stone to finish all edges, and hone by hand.
TomPosted 1 year ago # -
1018 is a tough bird, I know you can't do this on an Acme, but we use cermet tools from Iscar, run it at 1000 SF, and the finish comes out like a mirror. 1500 pieces on an Acme seems a little short to me.
Posted 1 year ago # -
I've machined a lot of 1018 over the years. This material is gummy and likes to tear rather than cut. I've found that using a high chlorinated and sulfinated oil helps quite a bit.
To get a nicer finish, use a sizing tool that takes .005-.010 finish cut on diameters and .003-.004 per side. This will clean up the galling left by the form tool. You should also be machining this at 100-110 SFM if you are using any type of high speed cutting tools. For high speed tools, I recommend using Rex 76.
If you are using carbide tooling, then I can't imagine having a problem getting a good finish unless you are feeding too hard....carbide does very well in 1018.
BTW, if you are looking to maintain a 62 RMS finish or better on this, then best of luck to you. It can be done, but it requires a lot of tool sharpening. I machine 1018 and get it to look as good as 12L14 once in a while, but it doesn't stay there long.
Posted 1 year ago #
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