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how did they machine it.

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  • #16
    A little bit about powdered metal technology.

    To begin with, sintered products (as we know them) have been around for several decades. One of the earliest products made from powdered and sintered metal, was the Oilite bearings. If my memory serves me correctly, Oilite bearings were developed in the late 30's, and I think Chrysler was the leader in this field.

    If you use carbide tooling, you are employing a powdered metal product.

    The process is rather simple. Grind your base metal to the required granularity, add a ground filler or matrix metal to bind it, and press hell out of it to hold the mixture together. After molding the part, you simply heat it in an oven (sinter) till the matrix diffuses throughout the base metal structure. In its simplest terms, you are "sweating" the base metal molecules together.

    There are other processes in use now that employ different methods, mostly to obtain greater accuracy of the part, increased strength or other structural qualities, or shorten production time. The basic formula is still pretty much the same though.
    J.D. Leach


    • #17
      Originally posted by Evan
      It's powder metallurgy. Metal powder is compressed under extreme pressure and high temperatures in a mold so it forms a solid mass of metal at net required shape.
      Isn't it more common to press the powder in the mould, extract it from the mould, then sinter it?


      • #18
        No, the process is called Hot Isostatic Pressing (HIP)

        It doesn't use a press but instead compressed inert gas to densify the material at pressures up to 15,000 psi.

        The process to produce these near net shape parts is fairly straightforward. The end user supplies Crucible with a drawing of the finish part with nominal dimensions and machining tolerances. To determine the HIP shape, overstock is added onto finish dimensions to yield a near net shape. The container design is established and drawings are generated in order to fabricate cans, which are usually made from steel tubing, pipe, and/or formed sheet metal. Can components are welded together and fill stems are added for loading of powder into the container. After welding, the container is leaked checked to ensure the can is hermetically sealed. Powder is loaded into the container, and the part is consolidated and brought to full densification by HIP. Because of the void space between particles in the as-loaded container, the compact shrinks during HIP to a smaller size than its original pre-HIP shape. Anisotropic shrinkage often occurs due to the part geometry, heating and pressurization rates prior to the HIP hold cycle, material properties of the powder, and container material, thickness, and position of the welds. Design methodology is critical to ensure dimensional control.
        Last edited by Evan; 10-23-2009, 03:15 PM.
        Free software for calculating bolt circles and similar: Click Here


        • #19
          Powdered Metallurgy is a fascinating, relatively recent development.

          A direct quote from the site below... "In reality, PM comprises several different technologies for fabricating semi-dense and fully dense components."

          I'm guessing semi dense components would be like the oil lite bushings where the permeable void space, once filled with oil makes the bushing self lubricating. Fully dense components might be gears, etc.

          According to this site, there are four sub sets of processes. "Press and sinter", MIM or "metal injection molding", HIP "hot isostatic pressing", and "powder forging"

          Which powdered metal process applied would be dictated by application, economics, access to equipment and the almighty $ as in cost per unit of both capital investment and input materials.

          I've only ever personnally seen the cold process, but a flow chart of alternates is here

          FWIW, the cold process was for shaped charge liners.... Now that was a field trip
          Last edited by camdigger; 10-23-2009, 05:35 PM.
          Design to 0.0001", measure to 1/32", cut with an axe, grind to fit


          • #20
            Originally posted by Evan
            ............. Powder metallurgy can be so accurate as in this example that it is a perfect finger light press fit. ..............
            Correcto-mondo Evan! Triggers and hammers are made from cintered metal process for Smiths and Colts and most others I expect. That the sear is so critical is testament to how accurate they are.
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            • #21
              It could have been hot broaching

              One process I used for making shaped holes in machined parts was hot broaching. An oversize punch is made in the shape of the hole. There is no taper on the body of the hot broach and there is a tapered tip on the punch that expands the part. A part blank is drilled with a smaller hole and then is heated red hot. The punch is then driven through the hole to put in the shape and removed before the part cools. The hot broaching process only takes a few seconds. When the part cools down it shrinks enough to come to the correct size. The part is then put on a shaped mandrel and turned.

              This was a common manufacturing process in the late 1800's and early 1900's when making broaches were relatively much more expensive. I last used it in 1989 to make collets for a hand tool designed in 1902.


              • #22
                Fascinating chaps.

                Hi willmac, yes I'm not far off, I work in garstang and live in preston too, up by the tickled trout.
                If you've seen a worn out camo land rover or a fiat punto with overgrown aerials thats me.

                If you ever visited the fab shop at leyland then you will remember the watkins and mitchell 1200 ton power presses, they made the floor shake too, we took one out, the cushion cylinders went into the floor a good 8 feet.
                Last edited by dr pepper; 10-26-2009, 10:58 AM.
                Build it, bodge it, but dont buy it.