Machining Cast Iron Question
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    Default Machining Cast Iron Question

    First off I do not know how I got cast iron by my name on this forum, it use to be plastic. I cut tons of urethane & aluminum. But I have a question. We are looking at a very large production job machining cast iron wheel blanks. I have cut it maybe once or twice here. We are looking at thousands of castings for wheels and some have thru bores for sleeve bearings and some have stepped I.D. for sealed bearings. I think we will need to hold +/-.0005 on the bores. Diameters will range from about 4 inches by 2 inches wide to 14 inch diameter 6 inches wide. The bearing bores are around 1.5 diameter we will be machining. How is this stuff on tool life? Is coolant needed? We need to paint them after and no coolant will help with the painting. But if coolant is really needed we will use it. How are the chips ( dust) to deal with? It must make a real mess inside the machine. Just looking at this to start quoting it, I hope I gave enough information.
    Thanks

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    You don’t need any coolant but cast iron makes a mess anyway, if you want to paint. Better don’t waste oil or cooling emulsion on carbon. Brushes are my friends with cast iron.

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    Others will weigh-in with more refined answers but I would say (having some but not production-quantity experience) with cast iron:
    - Tool life will be more limited than steel
    - Coolant will likely not be needed
    - Chips and dust are a bitch to deal with. Fine swarf blackens everything it comes in contact with (you'll look like a coal miner). Course swarf is abrasive and if not vacuumed from ways, beds, etc. can do damage to your equipment.

    "Cast Iron" name is a function of your post count and will change as you rise in posts.

    Best.

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    I have done a lot of cast iron automotive machining as well as some cnc industrial work.
    Nasty, dusty stuff from light cuts. Small chips with heavier cuts.
    You will want to invest in some masks or go home with iron nose and lungs.
    Might not hurt to rig up a vacuum in the machines to negate the dust that sticks to everything.
    A vacuum brush around a spindle like the router boys use might be a good thing.
    No coolant used by me. Tried but never found anything that improved the work yet.
    Cuts easy.

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    We machine tons of product out of cast (steel and iron), including wheels. There's variables, but assuming that the castings are made soundly and in good shape, it typically machines nicely.

    Tool life, for us, typically isn't a concern. Just make sure that you have inserts on hand that are graded to work on your particular material. Also, make damn sure your castings are sourced from a reputable place. Poorly made castings can turn the simplest job into a nightmare...in my opinion.

    As far as coolant goes, as long as you're running in the right heat range, you probably won't need it. A lot of our lathes are open, so we like to leave coolant off in a lot of situations. Can't say that not using it has made any sort of substantial difference in tool life or quality of finished product.

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    Cast iron loves a negative top rake, a thicker insert to absorb a lot of heat, running with no coolant.. A very stout machine and fixturing...agree with a good dust mast...

    A chip breaker type insert will not absorb and dissipate as much heat so is more likely to fail faster than a simple flat top with a negative land at top rake position.

    A good edge result is the insert rounding off at the cutting edge not fracturing.

    For milling often roughers and finishers in the same cutter can work well with the finishers taking only a small amount.

    A circle land perhaps .02 at the follow ,with back spinning the grind if possible..or just a small clearance angle on thr follow for a small land perhaps .020 or so.
    Last edited by michiganbuck; 01-10-2019 at 06:55 PM.

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    Using CBN inserts u can use high speeds and feeds. Size of the land plays into durability of insert and i use them dry. A Vacuum cleaner is your friend with cast Iron. Cheap castings will create havoc chipping inserts and larger T land will help durability but increase tool pressure.

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    Quote Originally Posted by Terry Z View Post
    I cut tons of urethane & aluminum. But I have a question. We are looking at a very large production job machining cast iron wheel blanks. I have cut it maybe once or twice here. We are looking at thousands of castings for wheels and some have thru bores for sleeve bearings and some have stepped I.D. for sealed bearings. I think we will need to hold +/-.0005 on the bores. Diameters will range from about 4 inches by 2 inches wide to 14 inch diameter 6 inches wide. The bearing bores are around 1.5 diameter we will be machining. How is this stuff on tool life? Is coolant needed? We need to paint them after and no coolant will help with the painting.
    Cast iron parts are a good opportunity because a lot of shops don't want to touch it. That's how you make money - doing the stuff that nobody else wants to do, as long as you quote appropriately.

    You mentioned cutting a lot of aluminum and plastics. How much steel have you machined in the past? It's close enough to 1018 or annealed 4140 that you can use steel cutting parameters as a starting point. Cut dry and use steel-specific cutting tools for facing, profiling, etc. Stay away from iron-specific inserts in the beginning, because IME they're designed for high production environments and are more brittle than steel cutting inserts. We machine cast iron daily and no longer use any iron-specific tooling.

    Once your machines are making good parts, your attention will be directed toward dealing with the dust. Cast iron dust is no joke, as it will make your machine dirty in a heartbeat. While bulk material removal is done dry, we use coolant for all drilling, tapping, threadmilling, brush finishing, and washdown. No part comes out of our machines dry. The benefit of this is that parts are free of dust. The drawback is that all that dust ends up in the coolant. Most of our machines (DMG MORI) have drum-filter chip conveyors, which handles the dust very efficiently. The one machine we have that doesn't have a drum filter has flooding problems if we don't clean out the mesh filters every 1-2 months. This requires lifting up the entire conveyor with a chain hoist in order to get to the filters, which is as much of a PITA as it sounds.

    Some dust gets through the filters and ends up at the bottom of the tank. Every few months, we drain each tank, scoop out the sediment, and then pump the coolant back in. Not a fun task, as it's very dirty and requires wearing a painter's suit, but at least we don't go home with the "coal miner" / "black boogers" problem.

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    I totally agree about getting everywhere. We machine Class 40 cast iron every day. We use coolant for our applications and have had great luck with Perkool 5250-TF-Blue-55 (semi synthetic). We do a lot of deep hole gun drilling so having the coolant is a must. As Dumpster Diving said get ready for things to get dirty though. Best of Luck.

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    Agree with the above posts. CI is a short chipping material & usually likes a tough carbide grade if you’re going hard at it. If you’re planning on a lot of this, a coolant recovery system like the heavy grinders use will make you very happy. Like this one, (option 1 middle of page) → You are being redirected... Barnes in Rockford used to make them, now I dunno...

    Cast iron acts a bit differently than most other metals if you’re doing tight tolerance features like bearing bores though. It doesn’t conduct heat very well so be prepared to learn “this dimension” with the surface at 68°F will be “that dimension" several hours later in a 68° room, using "this recipe" for machining…

    Good luck,
    Matt

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    Shop I worked at 35 years ago cut a lot of cast iron. We always did it wet to keep the dust down and keep chips washed into the conveyor(s). It did make for lots more work in cleaning sumps, but having clean air, a cleaner workplace and clean parts made it worthwhile.

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    We machine a fair amount of cast iron and I would most definitely recommend coolant for the same reasons, mainly dust control.

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    Many type of cast iron out there. Most stuff cuts so way easier than alloy steel. Abrasion wear is normally the failure mode.
    If you are coming from plastics and aluminum it's not as easy as these to cut but the chip control is miles easier.
    It is short chipping so molded chipbreaker tooling is a waste and plus such gives a weaker edge that you most certainly do not want.

    In carbide a cast iron grade is softer and tougher. I find Orange Vise's comment of "because IME they're designed for high production environments and are more brittle than steel cutting inserts" puzzling.
    Perhaps this is from using a CNMG when a CNMA should be in place.
    A cast iron grade should be a "straight carbide" with none of the additives for steel cutting which reduce transverse rupture strength to add the surface harness and thermal resistance alloy steel alloys need.

    Three choices in cutting tool material.
    Carbide, Silicon Nitride, and CBN.
    Carbide should be raw or Al2O3 coated and honed (radiused edge .002-.003)
    Silicon Nitride is the higher speed much less wear tool at a medium cost per edge. In mid volumes where size control is needed this is the ticket.
    You might want to think and explore this option. You need speed to make it work but is not in aluminum cutting speed world so you may be used to higher surface footages.
    CBN is the preferred for high volumes like bake rotors or cast engine bores. Expensive. Crazy great size control and wear.
    The last two choices need a T-land but a hone is not normally applied.

    It can be machined dry with all these but what a mess. You are most likely going to want coolant.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    In carbide a cast iron grade is softer and tougher. I find Orange Vise's comment of "because IME they're designed for high production environments and are more brittle than steel cutting inserts" puzzling.
    Perhaps this is from using a CNMG when a CNMA should be in place.
    A cast iron grade should be a "straight carbide" with none of the additives for steel cutting which reduce transverse rupture strength to add the surface harness and thermal resistance alloy steel alloys need.
    Sorry, I was referring to milling cutters.

    Rereading the first post, this is likely a lathe application.

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    Dry or flooded is the drill for machining CI with carbide. Intermittent coolant will destroy the cutter quickly.

    HSS will cut CI but should be limited to only an odd feature because CI destroys HSS.

    Often a big shop will order a special carbide insert for an odd part feature on a production run..

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    Quote Originally Posted by CarbideBob View Post
    In carbide a cast iron grade is softer and tougher. I find Orange Vise's comment of "because IME they're designed for high production environments and are more brittle than steel cutting inserts" puzzling.

    Bob
    I saw that too C’Bob, I just figured he was using one of the jacked up nodular or ADI types of CI. Those increasingly “look like” steel when machining. They also toss up way less free graphite into the air when machining dry.

    Cutting grey iron or the plane jane flake type meehanite dry and looking towards a sunny window the cloud of dust that “just hangs” will make you worry.

    Good luck,
    Matt

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    i have machined easily over 2000 tons of cast iron parts, maybe 200 tons ductile iron parts
    .
    1) for cast iron coolant is usually used to cool as in if using 10hp thats 7457 watts so imagine 4 each room heaters in the cnc, does anybody really think it wont get warm ?? obviously if using more hp you have even more heat. i often get so much steam from the coolant and hot chips i cannot see the end of the part by the milling cutter covered in the cloud of steam. usually coolant is used like a firehose to blast the chips off part, off table/pallet so they go down to chip conveyor. i use a 2000 gallon coolant system with temperature cooling control to +/-1F usually at 70F. obviously if i got a 10 ton part and 1/2 ton of chips is sitting on the top of it. when chips are removed it usually part bows up .0005" from the 1000 lbs of chips removed. if coolant blast the chips off the part it can help automatically remove this weight.
    .
    2) tool life normally 60 to 120 minutes. shorter life only if tool is vibrating. i have seen over 400 minutes tool life on lightly used tooling
    .
    3)most tooling i use is made for cast iron. usually slightly positive rake (been slightly positive rake for decades now), edge prep and coatings on tooling is specialized. roughing inserts typically feed at .010 to .015 ipt so chips fairly big though rarely over 1" chips, only get dust taking light finishing cuts. special finishing inserts often will give a mirror finish
    .
    4) boring tolerance i often have to bore to +/-.0001", obviously need short length and rigid boring bars, they sell expensive anti vibration boring bars for longer length and will vibrate a lot less, can hold much tighter tolerance and bore faster. obviously if boring bar length to dia ratio is too high (over 5x to 10x) you could have trouble holding +/-.0005"
    coolant on boring has advantages and disadvantages, often used to blast chips out of the way, but if coolant acting cold the bottom of a bore can easily be .0003" smaller than front of bore by coolant cooling the boring bar over the time its boring. this effect get bigger with bigger dia boring bars like over 10" dia
    ....if spade drilling i always use coolant literally can drill 200% or more faster with coolant than without coolant. not to mention most big spade drills create heat alot of heat. again if using 10hp to drill thats 7457 watts thats a lot of heat. through the tool coolant that coolant comes out of tip of drill will blast chips out of hole and often allow 300% faster drilling, deeper holes it really helps. basically for every cubic inch per minute turned into chips takes about 1hp. big drills need alot of hp and create alot of heat
    .
    5) dust ? from cast iron machining never noticed any dust though often i use nylon abrasive scouring pad and then rag wipe part and wipe and blow rag dust off before measuring as rag will come off some black dust on it til part is cleaned of machined "fuzz" hard to describe. when blowing out tapped holes you get dust out of holes not long chips more like sand size chips

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