@TOODMR
Aside from what Stos said, there is another point in why he makes them in a low-grade way.
And that is the fact that anything he makes "properly" is way, way, WAY too OP.
So he makes his general model with casting, and his higher-end model also with casting, but with a lot more work done to it afterwards. And then his custom models are made properly with folding and hammering and all that. And yes, there's still some parts of fiction to his superhuman ability as a blacksmith. But who would think there weren't fantasy stuff in an isekai manga.