What is the strength of such a part, compared to a regular cast part? Say I 3-D print a spanner. How well will it hold up against a spanner that was cast and heat treated?
The process in the article is effectively sintering. If [1] is any indication, you can get to within an order of magnitude of strength of cast/forged parts, if sintering variables are controlled for properly. Which may not be the case for a diyer, metallurgy is a complex art.
Yeah and I also worry about shrinkage - they're saying ~15%, which would be a massive issue with some profiles. I don't see how a lot of parts would work very well without distortion.
good spanners are not cast and heat treated. They cast a blank which is roughly the right size, but then they forge it - much like an old fashioned blacksmith, but there are a ton of jigs involved (probably literally 2000 lbs though I first wrote that as an expression).
Heavy use metal parts are often milled/shaped into a blank, then forged.
Forging involves heating the part, then hammering it into shape using specialized jigs (reverse imprint of the part). Most metals have a grain structure, similar to wood. The combination of heat and pressure bends the metal's grain structure around the contours of the part. This imparts a tremendous amount of strength compared to milling or casting. Since milling generally cuts into the grain at arbitrary angles, while casting often creates a disorganized grain structure (there are newer casting techniques which give better results).
The parts are often milled again, to ensure exact dimensions. Then finish/treatments are applied.
