Metal Additive Manufacturing (MAM) can be a great tool for rework. This is more often the case with Direct Energy Deposition (DED) but we found an application for it with Powder Bed Fusion (PBF).
The other day we were building some relatively large parts that took a long time to print. We sent them to a machinist to mill off the critical mounting surfaces and they accidentally milled off a little too much material from one surface. We really didn’t want to tie up the machine and loose schedule to reprint this part for another .020 inches if possible. In this case, the surface that was removed was a parallel plane with the opposite surface; so we decided to try and 3D print a little extra material on the top so the machinist could try again.
We started by locating the part on the center of the build plate as close as we could and tried to quantify the positional error along with the laser error with respect to the plate. Double-sided tape was used to attach the part to the plate as shown below. We were careful to ensure that the damaged surface was sufficiently parallel to the build plate.
We created a new CAD model of an oversized ring, the size of which was large enough to account for the errors we expected in the process (print size, ability to register visually, etc.). That error was small enough that the part could hang off any side slightly without any supports. We placed the new part in the printer and proceeded to fill it up until the top of the part was even with the focus plane.
We exposed the first layer of our new ring onto the damaged surface and found the registration to be off slightly. There was a little more overhang seen on one side than another. We proceeded to shift the position of the part incrementally until we saw approximately equal overhang on all sides and then ran the program to apply another .125″ inches to the top of the part.
After a few of hours, we returned the part to the machinist who milled and ground the surfaces such that the re-work plane was invisible and the final part came within spec.
This was a pretty cool effort that saved us a lot of schedule and budget on the project. The same approach could be followed to mix traditional manufacturing methods with MAM.