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Why is cold rolled steel so difficult to part?

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  • beanbag
    replied
    I can "machine" cold rolled just great, e.g. turning and milling.

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  • dian
    replied
    interestingly hete it says: better machnability due to the cold drawing process

    http://www.speedymetals.com/information/Material26.html

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  • Evan
    replied
    I/2" should harden well as long as it is kept moving briskly. "Super quench" is the same idea.

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  • beanbag
    replied
    Originally posted by Evan View Post
    Yes, but it depends on the stock size of course. The smaller the piece the better the result. Also, the faster the quench the better it is. Brine is required because it helps prevent the steam jacket from forming and slowing the quench. It also helps to chuck up the part in a drill and swirl it around in the bath while it quenches, if possible. Ice water also helps and LN2 might be even better. The best is a strong lye solution quench but it has been banned in industry because it is somewhat dangerous. Salt is good enough.
    Do you think a 1/2 rod will thru harden?

    This reminds me of the "super quench" recipe I read about, which is basically salt water plus surfactant to help reduce surface tension so the water "wets" better.

    LN2 would be a terrible quenching agent because it is super known for forming a gas layer around everything it touches. I used to get a running start and pour liquid nitrogen down the hallway. The little droplets coast on their air layer and can slide over 100 feet.

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  • Evan
    replied
    A little hard turning with a Kyocera ceramic insert on an outer bearing race:

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  • legendboy
    replied
    I parted the ends off a 2012 R1 swingarm bushing a couple weeks ago. Could see a tight dark HAZ on each end.

    I put my smock on and my tig gloves and with a water based fluid kept sparks to a minimum. I swear i have never
    had to crank my cross slide that hard before. The chips were blue gold ribbons and we eventually did both sides.
    Insert is still good

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  • PixMan
    replied
    OK, so 1117 isn't nearly as bad to machine as 1018 CRS. In that case, here's a video of cutting off 1018 CRS with a 1/8" wide carbide insert parting blade.

    http://www.youtube.com/watch?v=Y52KJ...PMd4fAqCJOzU_g

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  • Evan
    replied
    Is that a through hardening? So you just heat, quench, and don't temper and start machining? This sounds great for making insert toolholders.
    Yes, but it depends on the stock size of course. The smaller the piece the better the result. Also, the faster the quench the better it is. Brine is required because it helps prevent the steam jacket from forming and slowing the quench. It also helps to chuck up the part in a drill and swirl it around in the bath while it quenches, if possible. Ice water also helps and LN2 might be even better. The best is a strong lye solution quench but it has been banned in industry because it is somewhat dangerous. Salt is good enough.

    Leave a comment:


  • gtd63
    replied
    Oh, anytime you can sub 1117/11L17/1213//12L14/1215 for 1018, do it !

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  • beanbag
    replied
    Originally posted by Evan View Post
    Even 1018 can be heat treated and quenched to a significant degree. By using a brine quench it can be hardened to around RC40 or a little more. I have done that many times and it improves surface machinability considerably.
    Is that a through hardening? So you just heat, quench, and don't temper and start machining? This sounds great for making insert toolholders.

    To answer some of the other questions, I don't think I have any problems with my parting setup. I can part hot rolled and even stainless 304 and 316 just fine.

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  • gtd63
    replied
    1018 can be a pain in the butt for turning/partoff, especially with the price of inserts. Alot of the time I'll just settle for plain 'ol HSS and cutting oil for turning and partoff and deal with it. I think it may be due to the remelt situation as was previously mentioned.

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  • Evan
    replied
    @Pixman,

    1117 is screw machine steel. While it has about 1% manganese it also has high sulphur to improve machinability and especially finish.

    John is quite correct about the cooling rate of the bar stock. There is a large difference according to cooling rate in manganese steels. For a full anneal it should be cooled at about 100 degrees F per hour. Any amount of manganese in steel increases toughness which is what makes them difficult to machine. The more manganese, the tougher it becomes. Once it gets in the range of 3 to 5% it is known as AR Steel (Abrasion Resistant). Once in the range of 10% or higher it is practically unmachinable. It work hardens at the touch of a tool or even a stern glance. Even just dropping a piece will tend to harden it from the impact.

    I had a foot square piece I wanted to use as a motor mount. I only needed 4 holes in it. I tried drilling it and that was a total waste of time so I chucked it in the wood stove with a hot fire and let the fire die over night. After cooling until the next evening I was just barely able to drill it, having to resharpen the bit a number of times and using heavy feed rate on my Strands industrial drill press.

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  • BigMike782
    replied
    I parted some 1" 1018 recently using carbide on my SB Fourteen and had no issues at all.......don't ask me speeds and feeds,I just went by the seat of my pants but higher steady feed rate worked way better than slow.

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  • lakeside53
    replied
    Originally posted by Jaakko Fagerlund View Post
    Seems like you haven't used carbide parting off tool, otherwise you would know it cuts even at 20 m/min. And funny thing is, it still cuts even near the center of the workpiece.

    I'll toss all mine in the bin then

    Sure they can cut slower with more feed pressure, but on my machine (heavy) they cut a heck of a lot better fast! I get more chatter issues running too slow than fast. The big problem with running fast is you need a correspondingly fast feed rate. Feed slower and like most carbide it will just want to rub. There's nothing special about the tip of a carbide insert tool - the type I use look like a raised blunt shovel. Apart from machine rigidity issues, I think the want to cut slow is just to overcome slow feed rate, setup deficiencies and reduce the friction on the sides, but with the right setup (dial in your tool for exactly 90 degrees to the work, and have it right on center!) and continous lube, that's hardly an issue. But... whatever works with your setup is good enough.

    Most of mine cut of tools are are "neutral" cut, but I also have left and right biased tooling. Nice for a clean edge on the desired piece. Sometimes these appear to cut easier; maybe it's just the different insert geometry. Even though it cuts at the lower sfm, the cut nearer the center is not the same quality as further out. One day I'll get CSS (contant surface speed) installed.

    One more thing for the OP - keep the tool extention in the holder short as possible (obvious, but..). I adjust mine to the minimum required, and much more so that other tooling.
    Last edited by lakeside53; 03-13-2013, 01:17 PM.

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  • PixMan
    replied
    Most people starting off with carbide insert parting are still in the HSS mindset. The speeds and feed rates that carbide likes are quite a bit higher than HSS, and yes they are still similar once you get closer to center.

    This is a short parting off video I made cutting off 1117 CRS to center. The "thumbs-up" at the end was really just a jokish response to a video Black Forest had made, but the cutting action is perfect and you get the idea.

    http://www.youtube.com/watch?v=Q7_3h...PMd4fAqCJOzU_g

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