The idea of embossing metal into a negative space of a pancake die is probably around 30 years old, and I first did it by piercing holes in the die, and having the die lay on a large, thin urethane pad in the press. This is a one-step, cut-and-emboss pressing, where the pressure is cranked up after the part is cut, so that the urethane pushes metal into the holes. This is good for small and medium runs, but it’s less than ideal to press the whole die against anything that isn’t rigid. In fact, a good “rule #1” for pancake dies is to never lay them on anything but a rigid surface in the press. We had dies crack after a few thousand parts because of the repeated stress of flexing without support. One way to avoid that problem is to cut a urethane insert to fit into the design area of the die, and do the embossing step as a second pressing. Much more about that sort of thing as we continue here.
I’m going to skip over most of the pierced version, partly because there’s not a whole lot more to it, but mostly because things get more interesting with the next evolutionary leap. One thing that makes pierced designs hard is the simple fact that you have to saw through steel. Also, the leading edges of the hole that the metal slides over as it gets pushed into the hole needs to be rounded off a little to prevent the metal from tearing. There’s also a detail limit, since piercing and filing small holes becomes very tedious, impractical, or impossible at a certain point. An important note about attempting any of these types of dies is that heat treating (hardening) them is necessary to create any kind of long-lasting tool, with the possible exception of ones only used at the low end of the pressure range. Unhardened steel has a high degree of plasticity under high pressures , and can easily deform, instantly ruining tools. Conventional impression dies are heat treated, and these pancake dies also function as impression dies.
This detail problem was exactly what led my thinking towards other ways of creating a recessed design in the face of a pancake die. I thought of stamping, but didn’t have any stamps that seemed right for it, or looked good. Then I remembered a die project from around 2000, where I etched very low-profile male and female parts of a design into thin steel plates, and incorporated them into a pancake die. A very elaborate, one-time-only die, mind you. Point being, I knew that etching was the way I wanted to go. I won’t go into much detail about the actual etching, because it’s an entire subject itself, so very briefly, I’ll cover the “cheap and easy” way I went about it. Yellow toner transfer paper in a laser jet printer for the mask. A clamping heat press with temperature control (10" x 12" low-end model for about $100) at about 400 F for 90 seconds to 2 minutes for the transfer. Duct tape or vinyl tape to mask the bulk of the die surface. Copper sulphate and salt etching solution, without agitation (so as to disturb the mask as little as possible). Good, but not perfect results. Early transfers without the clamping heat press were iffy. The adhesion of the toner/mask to the steel was not reliable without the heat press, so spots deteriorated too much in the etching process. Using vinyl as a mask is probably “better” because it should hold up better in the etch solution, but I have not tried that yet.
Parallel to the etching experiments were the ones that involved pressing the design into the die plate. One might immediately think of 3-dimensional impression dies, popularized for individuals by Kevin Potter in recent years, and the process used there is the industrial version of what I have tried on a much smaller scale. I don’t have the equipment, experience, or desire to go anywhere near that deeply into it, so I used what I have on hand. Briefly, I used a standard Bonny Doon tool holder to hold either a chopped-off stamp or a stubby die hub (a hub is a hardened steel male punch that’s used to press 3-D designs into another block of steel that will become a (female) impression die)). The stamps and hubs I used are 3/4" diameter, average, and I pressed into steel die plates ranging from .050" to around .090", and so these stamps and hubs are very shallow. The stamps are normal, flat-ended stamps. Pressing with around 20-50 tons, depending on the size and depth of the designs, I was able to get nice impressions. The die plates warped quite a bit around the design, and needed to be pounded flat afterward.
The B-side of this idea was to etch small steel plates so that the design was left as a positive element, harden the plates, and use them to press negative designs into the die plates to achieve the same type of resulting recessed-design die plates. There are many details about both of these approaches that I omit, mostly because I’ve decided not to pursue either one right now, because etching is an easier way to use lots of different designs without having to obtain stamps and/or hubs that are suitable. Of the two, using stamps and hubs is more desirable than pressing with etched plates, because there are fewer technical difficulties to address than making hub plates via etching. Imperfections are passed along, whereas with stamps and hubs, the end results are cleaner. There’s also the possibility of using “regular” (hardened steel) impression dies, with recessed designs that are very shallow, to press against an annealed, but hardenable steel plate, to turn that plate into a flat “hub plate”. Shallow, so that you can use relatively thin steel for the resulting pancake dies, as is my general view of all of these “combo” pancake dies. Other useful approaches would be engraving, CNC milling, and laser etching.
There’s the background that has resulted in a new-ish mutation in pancake die “technology”. Using these dies is pretty straightforward, but getting to where it was simple has had plenty of twists and turns. The biggest problem I ran into was how destructive 20 tons is when it’s concentrated onto a small area- a square inch or less with most of the ones I’ve made so far. Even when it’s only a small piece of urethane pressing against the contact surface , that material can break if it’s brittle, such as Plexiglas (Acrylic), or steel that’s hardened above about Rockwell 55. If the contact material is soft, it can become indented, and this includes thick mild steel press platens. The bottom contact surface is much more safe, but not invincible, because the die spreads the force out sufficiently, so that can be mild steel or hard steel, or a hard plastic like Nylon, Lexan (Polycarbonate), or G-10 (circuit board stock). The simple solution to spread force out to protect the top contact surface is to use a small steel “interface” plate, which can be thought of as somewhat disposable, because it will become indented from the urethane pads, and from the corners of the pancake die. Basically any steel that isn’t too hard will work for this. I’m trying AR-500 (armor plate) and some generic 304 stainless. Something in the neighborhood of 2.5" across for small dies, and generally, whatever size is enough fully cover the design area with larger shapes.
After etching (or pressing) the design into the die plate, the shape/outline of the part has to be created. One effective method is to use layout fluid or Krylon X Metals spray paint, then use dividers to scribe a line that follows the etched design, one divider point just inside the channel, set so that there’s a minimum of about .030" of undisturbed steel outside the etched area, or however much more of a border you wish to create. You must not saw into the etched area because that eliminates the cutting edge of the die wherever it happens, resulting in messy cuts or metal stuck in dies. I also simply “eyeball it”, sawing without a line to follow, which works with organic shapes, where a little variation in the width of the border doesn’t matter as much, but is too difficult where “perfection” may be called for. Next, the dies are cut and heat treated as usual, and in use, parts are cut flat with them the regular way, as the first pressing stage. (It must be emphasized that dies intended for this process need to be hardened. Using 0-1 tool steel (or, as I’m using now, 4130 alloy steel, a wild animal for heat treating, so I strongly suggest 0-1) and then heat treating it is absolutely essential, because otherwise the die will deform from the intense pressure) Next, inserts of thin cardboard, like shoebox cardboard - thin and dense, or watercolor paper - can also be cut with the die. Using these avoids the trouble of sawing or cutting a fitted urethane piece. Metal pushers or intensifiers can also be cut with the die, and these metal and cardboard inserts are generally a consumable item, with little re-usability. Thin polyurethane sheets (1/16" is thick enough for these shallow-etched dies) can be cut or sawed to fit just smaller than the design, to concentrate the force but it doesn’t have to be, unless that’s the only insert being used. Since forming generally happens easier and better with the cardboard, it’s a lot less trouble to make the fitted piece out of cardboard cut from the die, and have the urethane piece a little oversized.
A sandwich or stack of materials is placed on the die and then the die and stack are pressed again so that the metal is forced into the recesses. Such a stack might go: target metal on the die, then cardboard, then urethane, then metal, then interface plate or: target, cardboard, metal, interface, or: target, urethane, metal, interface. and not all designs work in one pressing, but with the right stack, most small ones will work well at 10-20 tons all in one go. The thinnest stacks (only target and cardboard, for instance), may not need the interface plate, but as I described above, it’s surprising what deformation can be inflicted on unhardened steel by small pieces of seemingly innocent material at high pressures. Sufficiently hard interface plates will stay flat, but most will dish a little right away, so you want to flip the plate over so that the concave side is up, so that the convex side is contacting the material pushing into the die. These dies (the forming of the designs) don’t all behave the same, so it’s best to try different things to find out what works best for a given die. Generally, impressions are easier to get the thinner and softer the metal is, so annealing is recommended, and necessary for some metals as the thickness goes up. Fine details that don’t form with the rest of the design can be dealt with in a subsequent pressing, using a smaller piece of material to concentrate pressure on the target area only. Larger designs in thicker metal may need to be annealed again and pressed again. With 20 tons, this forming process can be so intense that some of the metal of the target piece can squeeze into the saw gap of the die, creating a little extra cleanup of the edges. It doesn’t take quite so much pressure to do sufficient forming on many of these dies.