Friday, March 4, 2011

What Its All About

Engineering is about making things. For me, it is incredibly satisfying to conceptualize something and then make it exist and work as intended. I think that is why 3D printing technologies have captured my imagination - they are a step towards a Star Trek style "replicator". They offer the promise of shortening the loop between concept and reality.

I've been dreaming of different projects for the DMLS process for over three years now. A couple weeks ago, I took the plunge and had a chamber printed in 15-5 stainless steel. The first picture is the CAD, the second obviously the manufactured result. It really is a thrill to send electrons across the country and open a box a few days later to find the electrons made metal.

Now, some of you are saying "but you can do that with conventional machining" and you are right. But having a part machined has a certain activation energy - it requires a non-trivial amount of effort and skill. 3D printing is still not effortless - there are rules about what geometries are printable and of course you have to be able to generate a 3D model of your part. But the barriers are much lower. And there is also the fact that it can make geometries which are expensive or even impossible with conventional manufacturing techniques. It is still expensive - my part cost 4 figures even though it is quite small. In fact, it represents the larges single purchase I've made to date on my rocket hobbies. But as with any other process, buying in quantity is cheaper.

Everything in grey in the CAD picture came as is from the DMLS machine. As you may notice it is a regen chamber and instrumentation ports are integral to the DMLS part. Threads for the spark plug and inlet fitting were printed slightly undersized (extra metal) and then I cleaned them up with a tap by hand. The part came out more or less as I drew it, although there were some imperfections that affect the design. I'm talking with the vendor about ways to modify the design to avoid those problems on future builds.

Testing will follow soon. Had this been my "day job" I could have tested the motor the same day that it was delivered. Installing fittings and tapping out the holes took about an hour of slow work. The mounting ears fit directly on my stand as is. Unfortunately, life is a bit busy these days for me. And I still need to get some thermocouples for coolant temp measurements.

Questions welcome!