Practical 3D Printing: Design for Manufacturing

Back to course

Watch This Course

$199 USD $99.50 USD

-OR-

Or 8 easy payments of only $12.44 USD Instant access. Easy checkout. No fees. Learn more

Enroll Now
8 easy payments of only $12.44 USD

Course Access for Life

60 day money back guarantee

Design for Manufacturing

07.07

00:00	Finally, we've arrived at the last theory module of this course before moving on to finish up with the practical skills around metal 3D printing.
00:07	With that said, the DFM considerations for metal 3D printing, just like any manufacturing process, are of utmost importance in practical applications.
00:17	These are the key to taking our digital designs to reality.
00:21	Let's get into it with the DFM considerations for metal additive manufacturing using SLM or DMLS, remembering that these are also forms of powder bed fusion, so a lot of what we discussed will be similar here to what we covered in the SLS section of the course.
00:38	And again, we've included these in our design guide resource.
00:42	As always, we have the overall part size limitation.
00:46	And just like our discussion with SLS, the service provider will state the build volume for their largest printers that they have available.
00:53	A lot of the machines tend to have a build volume X, Y and Z dimensions in the range of 100mm.
01:00	So, if we get creative with the build orientation, we can squeeze bigger parts into these.
01:06	There's also some specialist industrial equipment out there pushing these up to around 800mm or so, which allows for some relatively big parts, at a higher rate though of course.
01:18	Again, like SLS, we won't dive any deeper into print orientation as this is the service provider's job, and they should have the expertise to get it right.
01:27	In short though, the print orientation can be used to control the heat distribution in the part to prevent warpage, but the geometry of the part does have an impact here as well.
01:37	For the best results, we'll communicate DFM considerations with the supplier, and they should voice any concerns and recommendations for revisions.
01:46	Compared to the likes of FDM prints, SLM parts are more isotropic in their mechanical properties.
01:52	This means that the orientation usually doesn't have a significant impact on the strength.
01:57	However, remember that SLS prints don't require supports.
02:00	So, we didn't need to worry about the surface finish considerations around them.
02:05	Unfortunately though, SLM parts don't have the same benefit.
02:09	There will be witness marks on the surface of the part where the supports connect, and post-processors will be required to remove these.
02:16	Ideally, any critical surfaces will be faced away from the build platform, or supports strategically positioned away from these.
02:24	The other size limitations are around the features of the design.
02:28	And these depend on the machine and the powder used to some degree.
02:32	However, there's still some typical values that we can apply as good design rules.
02:36	An unsupported wall is one that connects to the rest of the part only on one side.
02:41	For SLM, these should generally be at least 0.5mm thick.
02:46	Supported walls can be a little less at 0.4mm.
02:50	Walls under this will likely over-thicken from the heat of the laser, so generally targeting over 1mm is ideal.
02:58	You've likely noticed that these values are the finest of any of the 3D printing methods that we've discussed, which highlights the detailed and precise geometry that's possible with metal 3D printing.
03:10	The minimum hole size, however, should be about 1.5mm, which is about the same size as SLS, so we don't risk powder being stuck inside.
03:20	For accurate small holes, though, it can be worth undersizing slightly and then using a precision drill bit to open them up to the desired size.
03:28	This brings us to printing threads, which will need to be chased with a tap to clean up the inside surfaces as these will naturally be grainy.
03:35	The threads can have great integrity though as we're working with metal.
03:40	Or we can just drill the hole to the correct size and then tap.
03:43	Just remember that while aluminium is easy to work with here, stainless, titanium and inconel are much less so.
03:50	For other fine details, like pin features for example, a minimum diameter of 1mm is suitable for good definition.
03:58	Embossed features, whether details are proud of the face or engraving where they're into the face, only need to be 0 .1mm depth, height and width as there's less risk of wearing them off during media tumbling with metals.
04:11	That's if we're using this as a post process, of course.
04:14	SLM is capable of relatively good accuracy compared to other additive manufacturing methods, coming in at around plus or minus 0.1mm for typical part sizes.
04:25	We still do need to keep this in mind for any critical dimensions, though, and allow for some tolerance to avoid fit and function issues.
04:32	This might be as simple as opening up or slotting some holes, but as always, in extreme cases we may need to reconsider the design.
04:41	Hollowing out the part is a great way to reduce weight and also material usage which as we know lowers surprise, as long as it's considered in relation to the strength of the part.
04:51	However, if the inside forms a complete enclosure, the unfuse powder will be trapped as the walls are filled.
04:58	In this case we need to add an escape hole to allow the powder to be removed.
05:06	The recommended minimum hole size for this is around 5mm, which is fairly large, so depending on the design it may require significant revisions, another reason why it's good to keep these factors in mind from the start of the design phase.
05:21	That covers all the main DFM considerations as far as the limitations go for SLM.
05:26	Some specific and some general to 3D printing.
05:30	What's also important to remember is that we want to design with the advantages of SLM and additive manufacturing in mind so we can make use of the process and justify its use.
05:41	A lot of this comes down to the design flexibility, as we're able to create structures with very free-flowing and natural or organic forms and we don't need to worry about tool axis, tool sizes or other factors like chatter with CNC machining.
05:56	Reducing mass also leads to reduced material usage and a lower cost, so generally it's in our best interest to remove material from the part where possible without compromising the strength.
06:08	Let's wrap up this module by recapping the important points.
06:12	Part size limitations involve the overall size, which is mostly determined by the printer, but also the wall thickness, supported or unsupported, as well as holes or other features.
06:23	SLM is relatively capable of achieving small features compared to other forms of 3D printing, and all the mininum values are included in our design guide resource.
06:33	As we're working with metal, printing threads and chasing them with a tap is possible, but we can also drill the holes to a nominal size and then tap them.
06:42	Hollowing the part out is a great way to save weight, material and money, but we might need to include a relief hole to remove the unfuse powder.
06:51	Lastly it's important that we don't just focus on the limitations, but that we also But also keep in mind how you can get the most out of our 3D printing to justify its use over more traditional metal processing techniques.