How to automate blueprint building in space engineers?

Depending on how you design your ships and bases, absolutely.

The "standard" way to automate blueprint manufacture in Space Engineers is to use a wall of welders attached to a piston or ship. This is likely to be very laggy, runs the risk of not fully welding up some blocks, and all around is not your friend.

The better way to handle this is to make your ships and bases self-constructing, but this takes quite a bit of thought to pull off, and forces you to design things differently than you might otherwise. Essentially, you build a grid of welders into your ship. All you need to do is weld up the first welder and a cargo container/conveyor connected to a cargo container. That first welder will weld up the nearest welders, which will then weld up other welders.

While this is happening, every block adjacent to the active welders is also welded up to full integrity. This will cause much less lag, because only a fraction of the total number of welders will ever be active at once. It will also guarantee that all blocks end up welded.

This also has the advantage of making any base or ship built this way, fully self-repairing. As long as that first welder remains intact and the object has supplies, it might as well be Wolverine.