Support Structures & Part Orientation
sIn the last article we talked about the process architecture and printer characteristics of a Formlabs SLA printer. In this article we will cover other important aspects like part orientation and support structure generation.
As you all know, although the methodology, in theory, of Formlabs SLA is similar to a traditional SLA process, the actual part fabrication technique is totally different. However, the role of support structures is the same as in case of any other 3D Printing technology — they help support the overhanging features and in this case, support the weight of the part. But there are a few important considerations while orienting the part and designing the supports.
To begin with, Formlabs SLA comes with a Preform software for part orientation and support structure generation. One should note that the part will be oriented upside-down with respect to the part orientation displayed on the Preform software. See the image below for more clarity.
It is recommended that the parts be oriented at an angle because the Formlabs SLA performs a “peel” action after every layer for the new layer of resin to be agitated in place. The peeling action basically detaches the print from the PDMS surface of the resin tank. If a part having a planar surface is oriented flat to the build platform, there is more surface area per cross-sectional layer exposed to the laser. This implies that, there will be more surface area of the part adhering to the PDMS surface of the resin tank, which results in higher peel forces required to detach the same. Such forces can distort the extremely thin layers mounted on support structures; they could detach the print from the build platform or could break the inter-layer bonding between the layers. More the cross-sectional area adhering to the surface of the resin tank, more the peel forces required.
Orienting the part at an angle to the build platform results in less cross-sectional area per layer exposed to the laser. Also, there’s only little overhang for each new layer. As a result, the peel forces required to detach the print from the resin tank are reduced.
Preform comes with a “magic” button that orients the part at an angle based on the default settings. This may not always be the optimal part orientation, and it is advised that, based on the part application and geometry, one should re-design the part orientation and support structure placement.
Even if the part geometry is simple and can be printed without supports, it is highly recommended that support structures are put in place while printing. The reason being that, Formlabs compresses the initial few layers of the print for better adherence between the part and the build platform. Thus, if you are printing the part without a base, the part would be dimensionally smaller in the Z-axis. But when supports are placed, the part dimensions are within tolerance since the initial few layers that get compromised constitute the base of the support structure, whose dimensions are of little of no importance to us.
Preform also comes up with default settings corresponding to base thickness, support structure density, support structure tip diameter etc. All these parameters can be changed at will. But unless you are confident of the changes, it is advised not to tweak these default parameters. For example, to save the cost incurred in material consumption, one may opt for less support structure density than what the default parameter suggests, but this may result in the print falling off the build platform due to its own weight. Whereas, if one were to increase the support structure density, it could result in too much material consumption and resin entrapment. A proper trade-off is necessary. For parts which are unsupported, Preform displays a warning by highlighting the concerned area in red color.
Hope these insights come in handy the next time you are dealing with desktop Stereolithography. In the next article we will talk about part orientation for hollow models on Formlabs SLA, and we will address the impending implications if they aren’t oriented properly. In case you’d like us to cover any other topic in particular, do let us know.