The excuse that we need the part this week is going away. just put it on a Space X cargo ship and its there in a week.
I am not talking about the ISS today but the next station in a few years. Space X will be sending up cargo and people weekly.
To make a part in space with additive tech you still need to design it and convert it make a file for it before you print it. Just send the file down to Earth and they can print it faster and cheaper.

Its not just the printing problems in space its always the power problems. Will the next stations and moon bases have enough extra power to basically run a welder constantly in order to print large metal parts? Plastic parts take far far less power.
Its also the material problem in LEO. You have to send up the raw materials to build something with. So for any large parts just have then pre made and send up the same weight with the next cargo run.

And as always anything mined and built on the Moon will need to stay on the Moon for its own base needs first. There is no rocket fuel on the Moon and any water that is found will need to stay on the Moon for its own needs. Like food and drinking. Its a waste to mine it and throw it away on launches alone.

Once mining is done in large quantities on Mars any metals will need to be processed for use in either the new additive machines or in the old ways.
Once we have pure aluminum its cheaper power wise to just use conventional ways to role it out into sheets or extrude it into long parts.
Until you find a way to additive manufacture something at the same speed its still cheaper to use the old ways. We are talking tons at a time and feet in minutes, not ounces and millimeters.

I think that additive manufacturing will be the preferred method from early on in manufacturing in space. 3D manufacturing is often called “additive manufacturing.” More conventional forms of manufacturing often require the removal of material, which leaves quite a bit of scrap behind, and the material that ends up as scrap would be cost ineffective to send up from Earth. The white paper makes clear that NASA has invested quite a bit of money “to raise the technological readiness level” of various manufacturing methods for use in space. Much of it researched on the ISS in free-fall.

From the white paper:

3-D printing is rapidly transforming the aerospace industry, emerging as a game-changer for space travel. Researchers are pioneering applications for this technology that extend beyond Earth.

Quite a bit of this game-changing technology has been used on Earth, proving that it really does change the game. Many rocket engine parts are being made using additive manufacturing, SpaceX’s Raptors being very heavily made that way. It reduces the number of flanges, the welding, and the necessary assembling, also reducing the cost as well as the weight. As Robert noted, Relativity Space has already built an entire rocket using additive manufacturing, and it successfully launched. It is versatile.

As of spring 2023, NASA has invested more than $60 million in more than 20 In Space Production Applications (InSPA) awards to U.S. entities seeking to demonstrate the production of advanced materials and products on the ISS.

The advanced materials, formed in free-fall, perhaps stronger or otherwise superior, is one of the expected benefits to manufacturing in space. It may take some time before the cost of mining and refining raw materials from the Moon and taking it to low Earth orbit becomes less expensive than taking it up from Earth. These advanced space-created materials will necessarily be expensive, but some of these materials will be well worth the extra price.

The aim is to build housing, infrastructure, tools, or spare parts that are needed to advance space exploration, potentially using space dust or rock as a raw material.

A good goal, but building housing and other structures with lunar or martian dust or rock as raw material may be a decade away. I think that some initial tools and machinery will be sent up from Earth, but once material becomes readily available, I think that additive manufacturing will permit additional tools, tooling, and machinery to be produced in space, especially at and for lunar and martian bases. The processes for stripping various materials out of lunar and martian soil and rock may be expensive by our earthbound standards, but it may prove less expensive than launching material even on a Starship.

The white paper notes several advantages to additive manufacturing. Costs are reduced by bringing up only some raw materials that can be used for made-on-demad spare parts rather than sending up large amounts of spare parts that may never be needed. Costs are further reduced by using In-Situ Resource Utilization, the use of the regolith and soil of the Moon and Mars to create raw materials, allowing for larger and more complex structures on the Moon and on Mars than we could take with us from Earth. As the white paper says, the ability to produce what is needed, when it is needed (including spare parts), giving the possibility for increased mission flexibility and autonomy, reducing the risks associated with supply chain failures. On-the-fly innovation, customization, and rapid prototyping are possible. Additive manufacturing is already used for these three things here on Earth.

Additive manufacturing provides:

… a solution for effective waste management through a process called closed-loop manufacturing. Astronauts no longer throw away broken tools or used plastic packaging. Instead, these waste materials are fed into a special 3-D printing recycler. This machine breaks down the waste, transforming it into usable filament for the 3-D printer.

The first recycling printer sent to the ISS, the Refabricator, has been on board for more than three years. It was designed to recycle 3-D-printed plastic into parts and tools that are then sent back to Earth for analysis to see how the recycling process affects the basic structure of the plastic.

This reduces the amount of mass we have to take to space, also reducing costs.

… the potential of additive technology extends to creating satellite structures directly in orbit.

Imagine not having to beef-up satellites just to survive the vibration of launch. The size of satellites can increase to larger than the largest fairing, yet their structures can be lighter than Earth-launched ones. Space telescopes need not fold up to fit within fairings. The maximum size of space station modules stops being the size of the largest fairing and they don’t need to be expandable so as to fit within a fairing.

Since the various companies currently leading this industry seem to have different focuses, we may not have to bet on which will come out in the lead. They each may lead within their own niche.