Practical 3D Printing: CAD

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CAD

06.59

00:00	This section of the course will be all about taking the theoretical SLM 3D printing knowledge we've learnt and turning it into practical skills.
00:07	Just like our approach to SLS, we'll be using a 3D printing service where a third party manufacturer will produce our part and therefore be responsible for much of the practical work that we discuss for FDM and SLA.
00:21	This will provide a more realistic perspective and more useful skills, as it's unlikely anyone taking this course will have hands-on access to an SLM printer.
00:31	We'll be using a worked example of a real car part to help illustrate how these skills are applied.
00:37	And further worked examples will be added to the course over time so we can take a deeper dive into different materials, applications and considerations.
00:45	The specific part for this example is a merge collector that'll be 3D printed out of 316L stainless steel.
00:53	If you're unfamiliar with this course, this part is responsible for taking the exhaust flow from the primary tubes of the exhaust header or manifold and merging them into the tailpipe.
01:03	This specific example is what's referred to as a 4-to-1, designed to merge four 1-3 quarter inch primaries into one 2.5 inch tailpipe.
01:13	This could be used on a single bank of a V8, but more likely a relatively low capacity 4-cylinder.
01:19	We won't get too deep into the function and design elements of merge collectors, as it's a surprisingly complex topic.
01:27	But the general idea is to merge the airflow in as unrestrictive a way as possible while aiding in a scavenging effect.
01:34	Put simply, this means the pulses from each cylinder will create pressure waves helping to draw exhaust flow from the cylinders.
01:42	We've incorporated something of a vortex structure into the design with the intention that this could help here.
01:48	The primary tubes from each cylinder come into the merge collector in a clockwise order based on the engine's firing order.
01:54	That said, we're well aware that the gains in practice are likely negligible.
01:58	So, let's call this more of an experiment and the chance to create something that looks awesome, as the added complexity of the design has little effect on the printing process.
02:08	A V-Band has been integrated into the outlet, which may need to be machined for a more accurate surface finish, and therefore a better seal.
02:16	This will mean the part won't need to be welded to the rest of the exhaust system at all.
02:21	Although welding to this material is possible.
02:24	The final design element of note is that we've incorporated a slip joint with built -in spring hooks.
02:32	Slip-on collectors are often preferred over a weld-on alternative for the ease of disassembly and to help alleviate stresses as the part grows with heat, which can lead to cracks in the system.
02:44	Webbing between the slip joints will provide some added structure, further strengthening the part.
02:49	Traditionally, merged collectors are fabricated parts, although some are machined.
02:54	It would be impossible or at least extremely difficult to produce this design from any method other than 3D printing, simply because it provides the design flexibility to produce a part without the compromises of more traditional techniques.
03:09	Regarding design flexibility, while modelling this part in Fusion, we leaned heavily on the surface modelling tools for their ability to create complex curves and geometry.
03:19	As always, 3D modelling isn't the focus of this course, so if you're new to CAD, I'd strongly suggest checking out the HPA 3D Modelling and CAD for Motorsport course where you can learn these skills.
03:30	With the design complete, let's review our all-important DFM considerations for the SLM process.
03:37	While there are some detailed areas of the part, nothing is under 2mm in size, so everything should be able to print accurately, and there is no risk for the fine details being worn off in the media test.
03:49	The webbing between the slip joints helps to brace the part to reduce the chance of warpage.
03:55	The holes in the webbing are 3mm, whereas escape holes usually need to be 5mm.
04:01	However, unfuse powder will be able to be removed from the open space between the slip joints, so there is no risk of trapping powder.
04:09	Support structures are something we won't be able to completely avoid with this design, so we'll have to expect areas with some witness marks.
04:16	Although we want the part to look as good as possible, a super fine surface finish is not critical to its function, other than on the sealing surfaces of the V -band and the slip joints, which can be smoothed with machining post-processors if need be.
04:31	The rest of the witness marks will mostly be taken care of with media blasting or tumbling, and the typical satin finish on 3D printed stainless steel parts will be more than adequate for this application.
04:42	There is plenty of access to remove support as the internal structure of the collector is relatively open, so there's no concerns here.
04:50	The accuracy of SLM is around plus or minus 0.1mm.
04:55	With this in mind, we need to consider the slip joints.
04:58	These have been sized at 0.2mm over the primary tube sizes.
05:02	However, the primary tubes won't be anywhere near that accuracy.
05:06	We've measured these anywhere within plus or minus 0.5mm of their nominal size.
05:12	We want the fit to be close to avoid excessive leakage of exhaust flow, but we do need some support.
05:18	We also need some slip to alleviate the stresses as things move with heat.
05:21	Again, if we do run into issues with tight fits, we have plenty of wall thickness here to open up the joints with a light hone.
05:28	The only real concern is the V-band flange, and this is more regarding the surface finish rather than the tolerance.
05:35	The surfaces might need a light machine, or in worst case, we can cut it off and weld on a precision machined V-band flange so the risk is relatively low.
05:45	Once the design was finished, we exported an STL file and printed a prototype using our SLA printer.
05:51	This was a relatively cheap way to provide a physical representation to review and ensure the design is as intended without any oversights before paying for it to be SLN printed.
06:02	Often reviewing a physical part can highlight areas of concern that weren't so obvious in the virtual world.
06:08	Now, that we're happy with the design, let's recap this module before moving on to use a 3D printing service provider to manufacture the part.
06:16	Before any design project, especially those that require considerable investment, it's of utmost importance to have a sound understanding of the function of the part we're creating, as well as the manufacturing process we're going to use to bring it to life.
06:30	Surface modelling techniques are well suited to the design flexibility offered by additive manufacturing, but we still need to create a solid model to be able to print it.
06:39	With the key DFM considerations like minimum feature size limitations, powder removal, support structures, surface finish and expected accuracy in mind, we can design a part that will be efficient to produce while making the most of the production process.