Practical 3D Printing: Fundamental Knowledge

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Fundamental Knowledge

08.10

00:00	Custom parts are a common sight in many builds, featuring in everything from home -built street cars to top tier dedicated race cars.
00:08	Of those parts that are metal, some are best created with traditional fabrication techniques, while others lend themselves more to being machined on lathes and mills.
00:17	Developing CAD skills does open the door for a lot of opportunities with CNC machining, but creating billet parts can be extremely expensive and also limiting in what we can design.
00:28	These days, we're finding ourselves less and less hamstrung by these methods, as CNC printing of metals becomes a viable alternative.
00:37	That's not to say that metal 3D printing isn't expensive, because it absolutely is, and in many cases it can be more expensive than machining.
00:45	The key benefit though is around the flexibility of the design we can manufacture with additive manufacturing, compared to machining techniques.
00:54	The fact is that many designs that we can produce with 3D printing just aren't possible with machining even on a 5 axis CNC mill.
01:03	For example, hollow sections, internal lattice structures and other small complex geometry.
01:08	Put simply, 3D printing means we don't have to worry about tool access and minimum tool sizes.
01:15	With that said, depending on the project, it can offer advantages in terms of cost as well.
01:21	Particularly for low volume, or large scale and low mass parts, that would typically result in a lot of wasted material from machining.
01:29	This is a factor we mentioned briefly in the SLS section of the course, but it's even more important to reiterate here, as the price increases with selective laser melting services, and that's SLM for short.
01:42	The cost of the manufacturing service is a function of the type of material, the mass of the material used, and the process time among other things.
01:51	For machining, we pay for the price of the billet of material, so this cost is set no matter how much material is left in the final part.
01:59	The more material that's removed, the lighter the part will be, which we generally want for performance, but this often means more machining time and therefore cost.
02:09	Put simply, lighter parts can often end up being more expensive to produce.
02:14	For SLM and most additive manufacturing methods on the other hand, a lighter part means less material is used and this usually has little effect on the process time, in most cases reducing it.
02:27	Lighter parts end up being less expensive.
02:30	Before moving on, it's important to note that while metallic materials can be used in FDM, SLM allows for much more homogenous and isotropic structures, with very comparable properties to parts manufactured through a casting process, but we'll come back to this in more detail in the coming materials module.
02:48	With that covered, let's move on to how this technology works.
02:52	SLM is another form of powder bed fusion and works very similar to SLS.
02:57	The build platform is initially covered in a very thin layer of powder.
03:02	Our high power laser fuses the powder together in the cross section of the part layer by layer on the build platform.
03:09	The build platform is the same material as the powder, so the first layer can be welded to the platform to keep it in place.
03:16	Rather than tracing the cross section profile like SLS, the laser used in SLM printing can usually fuse the entire section at once.
03:25	The build platform, then moves down slightly and more powder is re coated over the top before the laser fuses the next layer.
03:33	You might recall from our SLS discussions that sintering doesn't fully melt the materials into a liquid state.
03:40	Selective laser melting on the other hand, as you might have guessed by the name, does involve melting the materials.
03:46	This can be thought of as welding, and as such the build chamber needs to be flooded with an inert gas like argon or nitrogen to shield the molten metal from atmospheric gases that contanimate and reduce the quality of the fused material.
04:01	There's an extensive range of pure and alloy metals available for this process, like different grades of aluminium, stainless steel, titanium and Inconel to name a few that are commonly used for motorsport applications.
04:15	Another key difference in the process compared to SLS is that SLM requires support for the overhanging structures.
04:22	After printing is complete, the excess powder is typically removed from the part with a special metal powder recovery system, which is kind of like a big vacuum cleaner.
04:33	Alternatively, some machines feature drains for the unfused powder, which can be cleaned and then reused for other prints.
04:40	The parts are welded to the build platform so they need to be cut apart, usually with a wire cutter.
04:46	The supports are also broken off, which can sometimes be done by hand or with hand tools like pliers or even basic power tools.
04:54	The surface of the parts straight out of the printer can be fairly smooth depending on the part and the printer, but it's not uncommon for them to be grainy and matted like SLS produced plastic parts.
05:06	For high quality finishes, we'll often use media blasting with water or sand and usually some form of machining post -processing to finish critical surfaces, like sealing surfaces or threaded holes for example.
05:20	Like MJF is an alternative to SLS, SLM also has alternatives, such as DMLS or EBM.
05:28	Contrary to what the name might suggest, most modern DMLS or direct metal laser sintering machines do melt the material like SLM, rather than sintering like SLS.
05:40	Besides the brands behind the trademarks of the technology, DMLS from the company EOS and SLM from SLM Solutions, they are very similar powder bed fusion methods.
05:53	DMLS will usually have a lower powered laser to SLM, and so prints slower but also more accurately.
06:00	This allows for more complex geometry and finer details.
06:04	DMLS is also often called DMP, which stands for direct metal printing.
06:11	Alternatively, we have EBM, which stands for electron beam melting.
06:16	This is produced by Calibrium Additive, part of the huge General Electric parent company.
06:22	In this process, an electron beam is used instead of a laser beam, and while the results are generally less precise, printing is significantly faster and more suited to large-scale applications.
06:34	The final note I want to make before moving on is around the accessibility of metal 3D printers.
06:40	As you'd expect, these are extremely expensive machines, with the cheapest powder bed fusion options starting from around $100,000, at least at the time of filming this course anyway.
06:51	It's safe to assume that the majority of us taking this course won't have one of these in our workshop.
06:56	As such, we'll be taking a very similar approach to the SLS section of the course, leaning on the many metal additive manufacturing services now available.
07:05	To summarise, SLM is another form of powder bed fusion that uses metal powders, opening the door to much more suitable properties for the demanding motorsport applications.
07:17	The main advantage of SLM over more traditional subtractive methods, like machining, is the design flexibility in what can be manufactured.
07:26	Another key difference is that lighter parts usually lead to a lower cost, unlike those machined from billet.
07:33	The process starts with powder being coated over a build platform, and then a laser fuses the powder in the cross section of the part, building it up layer by layer as the build platform moves down.
07:45	This is much like the technology used for SLS, however the required support structures and inert gases add some complexity to the process.
08:02	EBM is an alternative to SLM and DMLS.
08:07	But while being faster and more efficient for large scale parts, the accuracy is lower, limiting its use for precision automotive parts.