3D Printing makes Conventional design rules obsolete

I have observed that when design professionals try their hand at 3D Printing, they struggle to come to realization that most of the design rules governing the conventional processes are obsolete in 3D Printing. Not only does this enthuse and elate them, but this is equally confusing at first and difficult to fathom. When for far too long you have been taught to design things within the purview of what is “manufacturable” and what is not, a sudden disappearance of those boundaries leads to chaos and confusion. The biggest challenge for design professionals, who have previously designed products for conventional technologies, is not their ability to cope with 3D Printing, but to unlearn the design rules of traditional manufacturing.

As easy as it may sound, it is not! I may be crucified by Metal Additive Manufacturing (3D Printing) experts for claiming that there are no design rules in Additive Manufacturing, but I am quite sure that the 3D Printing polymer professionals would second me here. Because quite frankly, when it comes to 3D Printing polymers, there are no design rules apart from a few simple considerations. So today, in this article, I am going to address a couple of considerations.

CNC Machining. Image Courtesy: Smith Industries Ltd.

Some of the major factors to account for, when it comes to designing parts for conventional manufacturing processes are: shrinkage allowances and undercuts. These are every designer’s nightmare. We know that molten Plastic or Metal has a tendency to shrink as it cools down, thus designers have to provide a shrinkage allowance in the design to compensate for the same. This is not the case in 3D Printing, though! Although the material does have a tendency to shrink post sintering/fusion, in 3D Printing processes, this shrinkage is compensated by the 3D Printer itself. While calibrating a 3D Printer, a benchmark part is printed in the test run. Based on the results from this part, values are fed to the printer, which then account for shrinkage, laser diffraction etc. Thus one does not need to give an additional allowance on the part geometry.

Having said that, we have observed one peculiar characteristic working with the 3D Printers. Invariably any hole/cavity comes undersized by almost 200µm (0.2mm). E.g: A hole of, say, 5mm will come out 4.8mm after manufacturing. Thus, we advise the designers to enlarge the holes/cavities by 0.2mm in the 3D CAD file, so that the parts come out as desired.

Undercuts make part fabrication difficult or impossible in conventional technique, because undercuts hinder the tool movement. But since 3D Printing is a tool-less technology, and since the parts are fabricated additively (layer by layer), undercuts or complex geometries, for that matter, don’t pose a limitation. In fact, it is the highlight of 3D printing that, complex parts can be fabricated with utmost ease.

Although that’s true, an important consideration from 3D Printing point of view is the support structure generation. Support structures are to 3D Printing, what undercuts are to conventional manufacturing processes.

Image Courtesy: Chizel

Apart from the laser sintering technologies, almost all the other 3D Printing technologies have support structure generation. And thus it is advised that for parts having complex, intricate geometries it is always better to opt for 3D Printing technologies like Selective Laser Sintering (SLS) that do not yield any supports. As for other technologies, an important aspect from Design for 3D Printing is that, one has to not only optimize the part design with respect to its application, but also with respect to minimizing the support structure generation. Support structures play a pivotal role in Metal 3D Printing than 3D Printing polymers, where apart from supporting the overhanging features they are also used as a medium to dissipate heat. An important consideration is that, at any given point in time, the aim should always be to minimize the amount of support structures generated. More the amount of supports, more will be the material consumption and thus, higher will be the cost. Also, support structures hamper the surface finish which leads to extra post-processing operations, thereby incurring additional costs. Know more about support structures in 3D Printing plastics and how they affect your prints.

These are a couple of considerations that make Design for 3D Printing different from designing for conventional processes. Apart from this, here’s a checklist that talks about the 6 things that you should keep in mind while designing for 3D Printing.

• Gauresh Khanolkar,

Head-Design, Additive Manufacturing (AM)

Chizel

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