WeaponsMan by Hognose July 23, 2015
We have mentioned before that the great benefits of 3-D printing include not only the direct printing of parts, but the printing of tooling, models, and patterns. It was inevitable that sooner or later someone was going to 3D print a PLA (polylactic acid, the easiest and most common plastic for 3-D printing) pattern for a firearm receiver, and then make an aluminum alloy casting using the Lost PLA process, essentially identical to the lost wax process used by jewelers and dentists for millennia. And now someone has done it, yielding this receiver, which builds up into a clone of the popular Ruger 10/22.
The 10/22 is a good choice, as a vast quantity of aftermarket parts are available for this rifle, and the original receiver was designed to be produced by investment casting in the first place.
In Lost PLA, the pattern begins as a 3D dimensional file.
The receiver is printed (allowing for a shrinkage percentage), then rods of PLA or wax are attached to form sprues, runners, fillers, and risers (sprues attach multiple parts; runners direct molten metal to parts or to areas of parts; fillers are used to pour the metal in, in most cases there should be only one per sprue; and risers allow air to escape, and signal the completion of the pour).
Then the assembly is invested with high-temperature plaster or plaster and sand mixture. The wax / plastic pattern is then burned out of the mold, and the metal is heated and poured in to the investment.
After the pour has had time to solidify, the casting is removed and any risers and screws are cut off.
Another thermoplastic like ABS can be substituted for PLA, but not a thermosetting (for obvious reasons). We expect PLA to be superior on castability.
In this case, the casting looks like it needed some cleanup (here’s a close-up) before it was built into an actual firearm. That’s not uncommon for investment castings, although industrial investment castings get nearer and nearer to net shape all the time.
More:
http://weaponsman.com/?p=24149
