What should machining (turning, milling, grinding) in space look like

Question

As space factories/space colonization gradually move from science fiction to visible reality, one important question is how we can produce the parts we need in space. It is conceivable that if we copy the machining equipment on the ground, we will encounter all kinds of problems, such as the lack of a stable ground with sufficient quality, the lack of sufficient cooling water, the debris will not fall to the ground and float around, and so on.

If we attempted to manufacture parts in space, how would our machining methods and machining equipment differ from the ground, and what are the advantages and disadvantages of space machining.

Answer 1

Traditional subtractive manufacturing (milling, turning, grinding) faces some challenges in space.

Microgravity will make it difficult to deal with cuttings, particularly grinding swarf and grinding grit. If the operations are performed inside a pressurized hull, suction and filtration could be used. Ferrous cuttings can be gathered using a magnet. Depending on the abrasive used, grinding grit and sludge are sometimes magnetic as well.

Aluminum is not magnetic, but eddy currents induced by AC current can generate temporary magnetic fields. Eddy current separators are used to recover aluminum for recycling. This could, in principle, be used to manage aluminum swarf.

The difficulty of dealing with fine particulates would necessitate closed-circuit air supply for humans, if they are present during operations.

One of the potential advantages of manufacturing in space is the ease of access to hard vacuum. This is the ultimate “inert gas” which would prevent oxidation of hot metal surfaces. A downside is the lack of convective cooling. However, during dry cutting operations most heat removal is provided by cuttings, not air. Vacuum would necessitate cutting fluids with low vapor pressure rather than water-based metalworking fluids.

If cooling issues are not dealt with (for example, by reducing cutting speed) accelerated tool wear will occur and thermal expansion may cause measurement errors in high precision machining.

Because vibration and distortion of machine tools are the enemy of precision, machine tools have traditionally been over-built with cast iron being the material of choice. This is why industrial machine tools bear a resemblance to Marvel Comics characters. Such designs do not mesh well with the mass-controlled design of spacecraft. Machine tools would need to be re-designed with rigidity through shape rather than mass.

Raw materials will be significantly more expensive in space-based manufacturing. This will increase the value of recycling off-cuts and swarf. It will also increase the attraction of additive manufacturing over traditional machining.

Answer 2

Additive manufacturing (contrasting Woody's great answer) may actually benefit from being in space.

Being in a hard vacuum would alleviate issues with uneven cooling (since thermal radiation would - in a shadowed environment - be the only heat loss (and far more controlleable) in a hard vacuum, as well as allowing waste-gasses to just vent. Metal-based additive manufacturing would also benefit greatly from operating in a hard vacuum which would allow pausing the printing process (with thermal management) and way cheaper printers due to not requiring an inert gas source / environment and no or lower degradation of stored raw resources.

Some powder or liquid-based techniques would suffer or be unusable but liquid-based ones could also massively expand in capability, especially in regards to not being confined to layers because you can just move and spin the surface-tension-based resource pool as desired.

You'd further loose the necessity for support structures unless you're machining extremely flimsy parts.

The massively reduced weight demand (both in machines* and resources) would further favour additive manufacturing in space over subtractive. The ability for most resources to be recycled on the spot (I think a lot of the liquid-based aren't) makes it even more valuable, since a misprint doesn't mean waiting a month for the next block to cut away from but only an hour or two to shred the waste down.

*=> Since additive machines are subject to far weaker forces than lathes or similar, the required precision can be achieved with far less mass.

Answer 3

In space, machining would face several challenges compared to Earth-based methods. One of the biggest issues is microgravity. Without gravity pulling debris and waste materials like grinding swarf to the ground, these particles would float around and could cause problems for both the machines and the astronauts. This would require special solutions like suction or magnetic collection systems to deal with these particles.

Another major challenge is cooling. On Earth, we can use water or air to cool down tools and machines, but in space, this would be much harder. In the vacuum of space, liquids don’t behave the same way, and it would be difficult to pump cooling fluids in microgravity. To deal with this, manufacturers might have to reduce the cutting speed or use new cooling techniques like heat radiation or solid cooling elements.

The design of the machines would also need to change. On Earth, machine tools are heavy and made of materials like cast iron to prevent vibrations and ensure precision. In space, however, the mass of equipment is more strictly controlled, so machines would need to be lighter but still maintain rigidity. This could mean redesigning the machines to rely more on their shape and structure rather than mass to keep them stable during operation.

Additionally, since raw materials would be much more expensive to transport to space, recycling would become more important. Materials like metal scrap or waste could be recycled and reused to make new parts, reducing the need to bring in new resources from Earth.

Given these factors, it might be worth exploring alternative manufacturing methods in space, such as additive manufacturing (3D printing). This method might benefit from the space environment, especially with the absence of air, which could help prevent material contamination and reduce cooling issues. Also, the lower weight requirements for the machinery could make it a more viable option.

So, the question is: Do you think that additive manufacturing will be the most efficient method for space production, or do you think traditional machining methods can still work with the right adjustments?