Design for manufacturing is the building block for every successful digital manufacturing project. While DFM for 3D printing is not as strenuous as injection molding or CNC machining, pairing the right material with the wrong techniques is a recipe for disaster. The following guidelines are relevant, and should be followed when designing for 3D printing PLA material.
The PLA Resin
PLA stands for poly lactic acid. It is a biodegradable material made from cornstarch. PLA is well suited for hobbyist 3D printing, particularly when working with early stage prototypes that have minimalistic or straightforward geometries.
PLA is used with the Fused deposition modelling (FDM) printers. It has a melting temperature around 54 degrees Celsius, thus limiting its performance in hot environments. It is affordable, but isn’t well suited to projects that require high resolutions. It also uses a rigid support system and has limited mechanical functionality.
Design Guides for 3D Printing PLA
1. At least 1.5mm on the Walls
Because of the fragility and low resolution of PLA, walls that are too thin will often result in a failed print. At Firstpart, we recommend using a minimum wall thickness of 1.5mm. Where possible, you can increase your wall thickness beyond the minimum recommendations to ensure that your prints do not fail and come out firm.
2. Use Ribs for support
The processing technique for printing PLA involves melting and cooling of plastic layer by layer. Because of the heat involved and the nature of PLA, there is always a risk of warping. To mitigate this risk, use ribs to provide support around tall or long walls, pins or columns.
3. Keep angles within 45o
Fused deposition modelling (FDM), the technology used to 3D print PLA has the ability for up to 45-degrees of self-support. Support materials are only needed for angles over 45 degrees. Should your prints feature angles and geometries that span pass this, you will need rigid support to prevent sagging and bending during the print. While support materials are acceptable in 3D printing, it is better avoided as they add cost to the setup, and flaw the surface finish when removed post-print.
4. Use inserts, not threads
The delicate nature of PLA makes it unsuitable for threading unless you will be using high-thread pitches. Rather, the low melting point of PLA means that you can easily fit heated brass inserts.
When using inserts, design the holes to the smallest tapered hole diameter. Also, ensure that the walls surrounding the insert have a minimum wall thickness of 2mm. As a rule of thumb, the length of the column should be proportional to the wall thickness.
5. Engrave, don’t emboss
As earlier noted, PLA cannot deliver high quality resolutions, and thus, isn’t the best for capturing details. Should you need to brand or label your prototype, elect to engrave your part rather than emboss it. This is because embossing is very thin, and will result in poor support layers in your part. Engraving on the other hand is more suitable for capturing your details without affecting or stressing your part.
For engraving, use at least 16 points of a boldface font and ensure that the text sits around 0.2mm into the PLA print.
Bottom Line
PLA 3D printing is the perfect way to start your product prototyping and development process. It is very affordable and well suited to elementary print requirements. However, with its low price point comes a number of compromises. PLA risks print failure, hardly achieves great resolution and has a risk of warping. Sticking to our design guide for 3D printing PLA will help you get the best out of PLA.
Got a bigger-than-hobbyist-project? Firstpart is always ready to help and collaborate. Our rapid prototyping, industrial 3D printing and other low-volume manufacturing operations will help you execute your product development needs from start to finish.
