Hi folks As things seem to sort out for me, it's time to do some thinking on my motorbike cylinder project. 3D printer is back in business, and it looks like i'll get a new job in one or two months. So I had time to make some calls with a german foundryman: Because the sand casting and core making is way to complex for a prototype, we decidet that it's better to use the investment method. A german casting and slurry company offered me a good price for a ceramic investment slurry to make the shell. So the next thing I have to find out, where and how to place the ingate, risers, gates etc... and how to calculate the right intake for the casting. And where do I have to ad more material for the shrinking ? I know I have to ad material on every sealing surface for maschining afterwards, but I do know nothing about shrinking when I pour aluminum. Is it possible, that anybody here can help me? Above the pics from thy cylinder. Thanks allot and greetings
Good news on the job and printer and finding a foundry to help. For the machines surfaces, you could add the 1-2-3-mm into the CAD, perhaps in a way that allows you to see or hide it as needed. For the overall shrink you could add that (1.5 to 3 percent) when making the the gcode file 3D print (scale x-y-z in slicing software) so the main CAD can stay 1:1.
I think he may have been referring to preventing shrink defects, meaning where to place any risers and bobs. The answer to this if needed will be places where the cross section and thickness is large compared to the rest of the casting. I say if needed because it can be feed system dependent too. For aluminum, linear shrinkage from the size change due to cooling is 1.3%. I'm assuming you'll be using lost PLA or some other evaporative/printable material. Looking at the pictures, to me, it's not at all certain you will (immediately) succeed with shell casting. I think block investment with vacuum assist may be the best alternative and maybe even necessary depending upon the features, and it will also require some equipment that you may or may not have. The thickness and spacing of the cylinder fins are the primary drivers but also how the pattern is to be positioned and vented in the mold. The reason I say block investment over shell is I think you will have a very difficult time getting slurry, and then (especially) sand into the spaces between the fins to build the shell. With block investment you can place the entire mold and pattern under vacuum and then when you allow it to repressurize to atmospheric pressue, the investment will have completely filled the spaces down to the root of the fins. You may also need vacuum to evacuate the investment slurry and for the mold during the pour to successfully fill the tips of the fins. Surface tension and air pockets can prevent complete filling. Though investment and shell are porous, not nearly so as and sand molds. Applying vacuum to the entire mold cause the metal to penetrate and fill small features by providing both venting and additional head pressure. In addition to a high temp vacuum apparatus, for either shell or block investment, you will need to fire the mold to vaporize the pattern and cure/vitrify the mold. Do you have a kiln to do that? It can be very difficult to prevent breakage of the fin features during burn out with denser printable materials, and in any case, those areas of the mold are fragile. The molds will also need to be heated prior to the pour, typically 400-600F for aluminum. Is the foundryman suggesting shell casting going to be responsible for all these process for making a casting from the 3D print? Or you? It's not an overly large part, at least by my standards, but certainly larger than most hobbysits are investment casting. I don't mean to discourage but better to make an informed decision than spend all of the effort on a new process only to fail. -Better do some more research before you go too far down this road. Best, Kelly
Thanks Kelly for your respond. Today I had the chance to finaly visit the art foundry nearby and the boss was a really nice man. He will do the casting for me. I only have to print the parts in PLA and he will do the rest. So lost PLA is THE way for this prototype. So I only have to print some cylinders and give them to him. I'm happy
