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Punch and die for thin matal (motor laminations)

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  • #16
    Darryl,
    Yes modern transformers are often glassy steel now. I don't how to identify the metal directly, possibly etching it then viewing under a microscope.

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    • #17
      Here is information about silicon steel, showing the grades as well as common thicknesses, and types of coating.

      http://www.protolam.com/page7.html

      There are also other steels that are commonly used:
      http://www.protolam.com/page6.html Cold rolled motor lamination steel - cheapest, least abrasive
      http://www.protolam.com/page8.html Nickel alloys - higher performance, more expensive, fragile
      http://www.protolam.com/page9.html Cobalt alloys - highest performance, most expensive, and magnetic properties are ruined over 1625 F.

      That company specializes in prototype and small production stamping of motor laminations. Some time ago I got a quote from a more local company for a set of laminations for something like a 1 HP motor, about 6" dia and 6" long, and it was about $500. At this point I am just looking at this as a learning experience, but perhaps if it proves successful (especially the SRM or RSM design), I might consider having the laminations professionally made. For most practical applications, it's hard to beat a surplus three phase ACIM. And if size and weight are critical, as in electric cars and bikes, it has already been common procedure to rewind motors for lower voltage and then use a VFD to overclock them and get as much as 4x rated power. Adding liquid cooling can remove heat from the stator to allow higher continuous current, for another 2x or so.
      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

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      • #18
        Not exactly up on the glassy production as it was the annealing bays bit, however when the steel is cast into slabs it must be kept hot, above 750C, if a slab cools it will burst, i have witnessed this many times, the crystalisation forms giant crystals that burst the slab, dramatically, i have some chunks of slab that did this somewhere, ill try and find and photograph them, they are tennis ball size!, fairly easy to see the crystal structure.
        You cannot reheat a cooled silicon slab for rolling, again bursting will occur.
        All GO steels are hot connected from castin through reheat furnace to the roughing mill and coil box that takes the 10" slab down to 1" in about 6 or 7 passes, it then gets uncoiled onto a 7 stand hot mill down to about 1.5 mm and coiled up, thats what stops the stuff bursting, the crustal structure is smaller.
        Its like putty when its hot and you have to get the temp right or it will sag inbetween the bars of the reheat furnace, these are all walking beam these days.
        The lowSils are reasonably tollerant to fatigue and used exclusivly for rotating parts, not as efficient as the higer silicons, but they dont burst!
        The higher silicons are used for transformers and stators as creep isnt an issue.
        Link to the stuff i used to do
        Mark
        http://www.cogent-power.com/unisil-h...ic-properties/
        Last edited by boslab; 01-04-2014, 09:29 PM.

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        • #19
          If you have many to do, punching individual features will be worse than a one-step punch, although they will take a lot less pressure to cut.

          Punching with cruder dies will throw up burrs that can give you big problems later. Then you have the burrs to clean up. Might make it even more tedious.

          I like the stack and WEDM method... should work fine. You can likely de-stack and varnish the pieces, then re-stack in assembly. The WEDM may mess up the edges if they are already varnished for insulation.

          No need to use the greatest steels.... although the stator of SRMs will see a higher frequency input from the inverter.
          CNC machines only go through the motions

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          • #20
            I had no idea of the peculiarities of GOSS. Quite interesting. It seems that such steels are used almost exclusively for large power transformers and perhaps smaller high quality toroidal transformers. Motor laminations generally use non-oriented silicon steel, which is less expensive and easier to use. Because of the geometry of motor laminations, grain-oriented steels would cause variations in magnetic properties and losses. However, the SRM, and RSM designs particularly, may be suited to GOSS because of the way the rotor is constructed. And if the stator were constructed as I proposed, with cut toroid segments, it would also benefit from GOSS. Here is what seems to be a good explanation:
            http://steel.keytometals.com/Articles/Art101.htm

            Their website has a wealth of information on various materials - well worth browsing. The Wiki article also seems to be rather comprehensive:
            http://en.wikipedia.org/wiki/Silicon_steel

            I have also seen transformer cores made from iron wire, which should result in excellent grain orientation and minimal eddy currents if the strands are insulated. It may not achieve the density of flat laminations, unless a hexagonal cross-section could be used and carefully wound with optimal packing. I have searched again more recently for this and have been unable to find anything. This would be ideal for toroids because it would be easier to produce the ideal circular cross-section as opposed to the square that results from tape winding. I have seen tape wound cores that were stepped so as to make a nearly round cross-section, but it is an expensive machining process and probably not worth the extra cost except in high-end military or audio equipment.

            It would be interesting to make a motor using powdered iron or ferrite for the magnetic material. It is best suited to higher frequencies, such as 1 to 10 kHz, and would result in a very high speed motor. A two pole motor is 3600 RPM at 60 Hz, so it would spin at 360,000 RPM at 6 kHz. That may be useful for some applications, such as miniature drills. Otherwise, a higher pole count could reduce the speed, so a 40 pole motor would turn at a more reasonable 18,000 RPM at 6 kHz and 3000 RPM at 1 kHz. It might be possible to make a very small, powerful motor at such high frequencies, as is already done for 400 Hz. But ferrite is very fragile and probably difficult to machine.
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

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            • #21
              A client had 200 kW alternators that ran at 60,000 rpm, gas turbine powered.

              They used a very special type material from Japan, the name of which I forget. It had very good magnetic properties, and exceedingly low losses, but was a bit harder to fab into stator lams than regular steel. The rotors were PM.

              The whole 200kW alternator was about 12" diameter and 18" long. Obviously not directly grid connected, they had a system of rectificatin and boosting and ran 480V grid-tie inverters.

              The alternators worked, their gas turbine was not nearly that good.
              CNC machines only go through the motions

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