The Milling of a Crankshaft - Page 1
Forum section: electronics / general

author: Macbeth
author_rank: Super Contributor
timestamp: July 10, 2015, 04:49:47 pm
content: My head explodes imagining the G-code involved in that! I wonder if it was coded in notepad, hardcore, like I do my HTML?

author: German_EE
author_rank: Super Contributor
timestamp: July 10, 2015, 06:22:48 pm
content: This is the new way of manufacture. The old method was to cast the crankshaft in a sand mold and then grind it down to the right dimensions. Years ago I saw them make a shaft like that in the BMW factory and the tolerance of the finished part was 0.01 mm.I think I prefer the milling machine, I've watched the video above and it's fascinating.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 10, 2015, 07:00:15 pm
content: Neat demo, but I would like to know the cost of this relative to traditional methods. Lots of tooling to capitalize, lots of tool wear, lots of scrap and so on. Certainly makes sense for low volume products, but not as clear for high volume production.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 10, 2015, 07:09:13 pm
content: Quote from: Macbeth on July 10, 2015, 04:49:47 pmAt the thought of the machine cost

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: July 10, 2015, 08:58:44 pm
content: I could watch machining all day.There's a bit in this documentary on the JSF competion :https://www.youtube.com/watch?v=QPvzEr33maM&feature=youtu.be&t=2481(It's at 41:20, if the link indexing doesn't cooperate) where Lockheed spent 5 months machining a single 5 ton slab of titanium billet.Mind boggling.

author: DmitryL
author_rank: Regular Contributor
timestamp: July 10, 2015, 09:18:48 pm
content: Quote from: CatalinaWOW on July 10, 2015, 07:00:15 pmOnce I heard a story of a guy who made 10L bucket from a single billet of titanium, just because he could

author: free_electron
author_rank: Super Contributor
timestamp: July 10, 2015, 10:31:03 pm
content: i always wondered : who machines the parts to make the machine that makes the parts ... (no pun intended, i know this can go on ad infinitum)If this machine can do this precision : it must be constructed of parts that even more precise ...as for G-code : real men write that using Edlin under dos 1.21 running from a single 360k floppy

author: Macbeth
author_rank: Super Contributor
timestamp: July 10, 2015, 10:48:18 pm
content: Edlin? DOS? Luxury!Why, I punch all my G code on paper tape, the proper way.(actually the CNC I used to mess with was from the 70's and used punched tape. We had to hack in a BTR (Behind Tape Reader) to interface it with a long serial cable to our Amiga in the office!)Also, who makes the 9.5 digit meter to calibrate the 8.5 digit meters with?... eh?... and who makes the 10.5 digit one..... etc...

author: Whales
author_rank: Super Contributor
timestamp: July 10, 2015, 11:36:49 pm
content: Quote from: free_electron on July 10, 2015, 10:31:03 pmI believe the idea is the opposite: from less accurate tools you make more accurate tools. It's a bit hard to summarise the total capability of a machine down into one 'accuracy' number however, so it's very situation specific.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 10, 2015, 11:48:25 pm
content: The simplest example of arbitrary machining accuracy is lapping three plates against each other; microinches (optical flats) can be had without much trouble (if time consuming).Another is using a lathe to produce a geometrically perfect circle, perpendicular to the axis of rotation.Seems to me, if you use a given machine to produce parts for another, the distribution of errors (say in how the ways sag more in one part of their range) will be randomized along parts produced, so that the distribution of errors in the 'child' machine will be very much unrelated to the same errors in its parent.Analyzing this properly would take detailed models of the parts and the positions required to machine the steps, but the functional mapping of [set of parent's errors] --> [set of child's errors] would absolutely be computable, and minimizable under control of things like order of operations, positioning offset, etc.Tim

author: IanB
author_rank: Super Contributor
timestamp: July 10, 2015, 11:56:46 pm
content: Quote from: Whales on July 10, 2015, 11:36:49 pmBasically, yes. A moment's thought will realize that today's machine tools are more accurate than Victorian machine tools, which in turn were more accurate than pre-industrial hand tools.An analogy today is that you may buy a cheap lathe from China with all sorts of slack and play in the moving parts, and using that lathe you may machine more precise parts to tighten it up. It is standard practice for a machinist to create new and replacement parts using the very same machine they are destined for.

author: G7PSK
author_rank: Super Contributor
timestamp: July 11, 2015, 08:07:17 am
content: Any crankshaft machined from a billet will be weak due to the way the grain flows or rather doesn't. All high performance crank shafts need to be forged as this makes the grain in the metal flow in the right directions to maximise strength. Production cars use Nodular cast iron sometimes called spherical cast iron for cheapness in production but they have to heavier than is really desirable and run at lower stresses, they will also break sooner, I have seen many broken crank shafts especially on low end diesels.

author: george graves
author_rank: Super Contributor
timestamp: July 11, 2015, 08:26:03 am
content: Quote from: free_electron on July 10, 2015, 10:31:03 pmThat is an interesting question, something I've pondered. It turns out that the reverse is true. You start with a lathe. A lathe will give you accurate rails. Then the rest goes from there. IRRC there is a whole series of web site devoted to "if the world ended, and you had to start over, how would you do it?" kind of thing. Anyone know some links? I don't.

author: German_EE
author_rank: Super Contributor
timestamp: July 11, 2015, 08:29:35 am
content: G7PSK may be right and now I cannot remember if the crankshaft I saw in the grinding machine had been cast or forged. Memories fade.

author: george graves
author_rank: Super Contributor
timestamp: July 11, 2015, 08:39:05 am
content: Aren't all mac book pros milled? I'm guessing that the cost of tolling has hit a break even point. Not surprising.There's nothing special about a CNC machine these days.

author: Lightages
author_rank: Unknown
timestamp: July 11, 2015, 08:40:04 am
content: Billet machining is not the best way to go. It isn't even the cheapest. It is probably the most repeatable. Repeating low quality is the way of now, not the past.The real best way to produce a crankshaft is with open hearth made steel, run through a billet mill, then forged, and then machined. It is not the cheapest way, but it is the best. It produces the least amount of scrap and wasted energy, has the finest metallurgic structure, and the best durability.This "new" way might be faster, more repeatable per part, and cheaper, but it is not going to produce the best end result.Perhaps a sintered metallurgy would be a good start in improving this process.

author: Lightages
author_rank: Unknown
timestamp: July 11, 2015, 08:41:07 am
content: Quote from: george graves on July 11, 2015, 08:39:05 amYes but I believe the Macbook is another metal other than some steel alloy.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2015, 09:00:28 am
content: Quote from: george graves on July 11, 2015, 08:26:03 amThe classic is probably Dave Gingery's machine shop from scrap series (not the exact title).It's not a very good design, it's tiny, and it's in aluminum (which is much lighter, more flexible, and less damped, than a proper gray iron product), but it does work.Quote from: Lightages on July 11, 2015, 08:40:04 amIt's hard to beat forged parts. The grain structure follows the flow lines, almost like having a solid metal version of carbon fiber (which is ironic, because some carbon steels apparently contain sort of fibrous carbon -- nanotubes and such). The anisotropy isn't /that/ pronounced, but every little bit helps when you're talking that last hairy knife-edge of advantage.The best ones are also surface treated (usually carbonitriding, or something like that). A friend works on Jaguar engines, and has serviced engines that have exploded (thrown rods, spun bearings, that sort of thing). Not a scratch on the crank.Powder metallurgy doesn't really get you anything special -- certainly, it'll get you something either isotropic, or somewhat anisotropic in the direction of pressing. That said, there are alloys that you can make in PM that aren't possible to cast or forge, for instance because the grains have vastly different melting points, solubilities*, risk of cracking during casting, or no softening point or plasticity at any temperature (some of these bizarre alloys get harder and stronger with increased temperature!).A11 comes to mind:http://cartech.ides.com/datasheet.aspx?i=103&e=111They can't even quantify its properties in ordinary terms, because it's almost more ceramic than metal; but the typical bending figure is astronomical as iron base alloys go.Common "carbide" (for cutting tools) is a classic case; think of it as tungsten carbide particles (semimetallic, I guess I'd say) "brazed" with cobalt.*Solubility isn't necessary for casting; aluminum and carbide composites apparently exist, and can be cast. They can't be heated too much, or the SiC grains react, the Si dissolving and the C forming Al4C3, a dubious carbide (hard, but not very strong, and not moisture stable).(Ref: I read a lot of metallurgy in a previous life, and did home foundry myself.)Tim

author: G7PSK
author_rank: Super Contributor
timestamp: July 11, 2015, 03:46:03 pm
content: Most car gearboxes are made using powder metallurgy for the gears, you get a much smaller gear box that way than you can with hobbed gears.