Part 3 of 3: Design for 3D Printing - Design Rules, Complexity, Tolerances and Part Consolidation.

Senior Design Engineer at Ricoh 3D, Richard Minifie, shares his thoughts on the evolution of design for 3D printing, the tools available today and what is still needed to unlock its full potential. Three articles will be published over the course of the next 3 weeks on a Monday morning.

Design rules

So what are the DfAM rules that we need to know? It is difficult to describe what can and cannot be done with AM without referring back to the DFM rules for other technologies. What I don’t want to do is list off a whole plethora of DFM rules for other technologies that do not apply to 3D printing, although only doing this illustrates exactly what the technology is capable of. Instead, I have picked out some of the principles which tend to be the most restrictive below and how they relate to additive manufacturing.

Complexity

Complexity in 3D printing is pretty much free. As there is no associated tooling, we do not have to consider the manufacture of complex tools which can quickly become very expensive. When designing for injection moulding, for instance, it is known best practice to try and avoid undercuts, as this makes the tool complicated and therefore drives up the price. Simple open and close tools are favourable when parts are cost sensitive. Sometimes, however, undercuts cannot be avoided if the feature required is part of the overall function. This can tend to dictate the design process but can simply be disregarded with 3D printing.

Tolerance

One important thing to highlight here is the realistic tolerances we can expect from a 3D printed part today. Typically, an industry standard for Powder Bed Fusion 3D printing technologies is +/- 0.3% with a minimum tolerance of 0.3mm. This must be considered at the start of all projects where 3D printing is the assigned manufacturing process. Sometimes, where this tolerance is not acceptable, the 3D printed part can be post-machined to achieve the required tolerance. 3D printing has a far greater deviation than technologies such as CNC machining and injection moulding, which can often meet the tightest of tolerance requirements.

Some of the DFM considerations for three standard technologies that 3D printing is often benchmarked against are listed below.

Injection Moulding:

Consideration for material shrink rate, sink marks, ejection marks, gate location and gate witness, split lines, draft angles, uniform wall thickness, undercuts, sliding core witness marks, radii to edges, ribs, surface finish texture.

Vacuum Forming:

Draft angle, corner radii, draw ratio, undercuts, reference points, texture, post processing to add cutouts or ribs or join two parts together,

CNC Machining:

3 or 5 axis, work holding, consideration for cutters, pocket depth, rounded pocket corners, warpage when large amounts of material is removed.

Parts Consolidation

It is possible with AM to print parts in place, enabling the consolidation of multiple components into one file with moving features. Here, we have to understand the minimum offset of the intended print technology if parts are to move. Standard hardware fixings, like screws, that would assemble the components together at the end can be designed out of the overall assembly as the part is consolidated into one. This allows us to explore the further inherent benefits that 3D printing offers, such as reduction in assembly time and costs within the supply chain. This example from Fiat Automobile Group shows a welding assembly jig consolidated from at least nine specially manufactured components into one 3D printed part, without any additional fixings required.

Image via: Stephanie Hendrixson of Modern Machine Shop

AM also allows parts to be printed inside other parts, which is particularly interesting for those using the technology for innovative or aesthetic parts.

Customisation

Customisation at scale has always been something of a manufacturing challenge, but this is not the case for 3D printing and is one of its most publicised advantages. Product design is completely opened up, as the number of part variations produced at any one time makes no difference to the printing process. To customise injection moulded components would require a range of different tools or removable inserts, which would be inefficient to run on a part-by-part basis for low volume applications.

Eyewear is one industry already taking full advantage of customisation via 3D printing. Every face shape and visual capability is different so, in what is a highly individualistic market, eyewear tailored to each customer is increasingly expected. Eyewear brand Aoyama Optical France launched their We DDD eyewear collection in 2015 which takes advantage of the limitless design possibilities that 3D printing offers, with 14 frames available in multiple sizes, colour and textures.

“The We DDD collection is designed for the tech-savvy, fashion-oriented consumer of today: aware of what they want and the high quality they deserve. Standardized production and a one-size-fits-all approach are no longer enough. We offer customizable options that speak directly to an individual’s tastes and preferences. Aoyama’s goal with this collection was to bring true mass customization to a luxury consumer-grade product.”

Philippe Beuscart, Aoyama CEO

To manufacture eyewear using injection moulding with all of the options and variants required would simply not be cost effective due to the multiple tool variants that would be necessary. Coupled with the agile nature of 3D printing and its ability to manufacture on demand, customisation on a mass scale is only possible via 3D technology.

Conclusion

In order to fully leverage the true end-to-end benefits of 3D printing it is essential, like most manufacturing technologies, that designers fully understand its capabilities. Design plays the most important role in the product development cycle for parts that are to be manufactured by 3D printing, simply because design influences so many of the other inherent benefits that AM has to offer.

This is not only a case of knowing the DfAM rules, but of having a true understanding of the technology and specific system that is intended for manufacture, whether for a prototype or an end-use part. Having this knowledge of what the technology can and cannot do is essential before the design process starts.

But this in itself does not lead to the unhampered creativity which conceives objects only possible with 3D printing; the ability to translate this understanding into an innovative design is just as important. For this we of course need imagination, but we also need tools that interpret these ideas into CAD format; either via conventional parametric, direct/sub divisional modelling, via a combination or via generative design software.

What is clear is that 3D printing is a technology that is here to stay and that, when fully understood, is an incredibly powerful manufacturing tool to open up new ways of design thinking.

Click here to read the full article on the Ricoh 3D Website which covers part 1 and part 2 of 'Design for 3D Printing'.