Stereolithography is one of the oldest and still the most precise forms of additive manufacturing or as we call 3D printing.
A vat of liquid photopolymer resin on a built platform was used in traditional SLA PRINTERS. Precision in this type of printing was achieved by UV laser focus on the surface of raisin which draws each layer curing the liquid into solid.
A blade spreads new resin up on top of the previous layer so that the next can be drawn in between layers when the build platform is lowered.
A drawback includes in this type of printing that the volume of a raisin in the VAT must always be a little more than the maximum build volume.
Today, there are inverted SLA Printers where the laser is directed up through the bottom of the resin tank which has a transparent bottom. Then the build plate rises out of the resin tank one layer at a time. This is only possible with a small volume of resin in the tank.
Below listed are 5 tips and tricks to master SLA printing technique.
1. Design for SLA Printing
- Make sure the supported walls are at least 0.4 mm thick.
- Make a note of supported walls to be at least 6mm thick and should be filleted at the base
- Do not forget to allow 0.5 mm of clearance between moving parts.
- Make sure you allow 0.2 mm of clearance for assembly connections.
- Also do not forget to allow 0.1 mm of clearance for snug fit.
- When creating horizontal breaches always keep in mind to keep wide bridges shorter than narrow bridges.
- Make sure that the embossed details including text should be at least 0.1 mm in height above the surrounding surface.
- Incase your printing without supports, don’t forget that any unsupported overhangs must be kept at least 1 mm in length and at least 19 degrees from level.
- Don't forget that engraved details should be at least 0.4 mm in width and 0.4 mm in depth.
- Also make a note about holes that they should have diameter of at least 0.5 mm.
2. Prepare Your Printer
Just like any other printing technique it is important that you level your build plate.
In case of SLA 3d printing which has a typical higher resolution than FDM printing, it is vital to prepare your build plate as small discrepancy can cause your print to separate from the build plate.
Make sure that you check on the resin tank and if the resin is clean and not expired. Also do not forget to check if the temperature is appropriate.
3. Prepare Your Model
Slicing is different in FDM and resin 3D printing services. One of the issues that include in resin 3D printing is that excess liquid resin generally becomes trapped in hollow areas.
In order to save material and time you need to use the tips and tricks to avoid 100% infill like that of slicing in FDM technique. Incase to avoid the weakening of print the resin must be drained after printing.
You need to manually perform the task in case the slicing software cannot handle the following tasks-
You need to repair your model if it is manifold. Models are non-manifold if they have areas with no thickness or internal faces or disconnected edges are vertices. Slicers such as Cura can handle such models without issue but others cannot. In such cases you need to repair your models using Netfabb or MakePrintable.
Hollow the model’s large solid portion using Autodesk Meshmixer which is available for free for Windows and Mac. Pursue this by leaving weep holes at the bottom for excess resin to drain. Standard proportion of holes is a radius of 1.5 mm.
It is recommended for orienting the part to minimize large z-axis cross sectional areas which in turn minimises the peeling forces on the part is time the platform moves upward to begin a new layer. This process which includes rotating the model to achieve this orientation may require support.
4. Professionally Remove and Clean your Print
Use nitrile gloves to protect your hands from resin while removing and cleaning your model. You can also replace using the spatula by using set of #17 and #18 Acto Knives.
Rings the model using isopropyl alcohol and in case the model is Hollow and has drain holes allowed the alcohol to partially fill the model. Cover the train holes and gently shake the model to rinse the inside of the print.
Make a note of not rinsing the model for more than 10 minutes as the longer you need the model in alcohol the duller it will become.
In case you need a more advanced rinsing solution you might want to look at a magnetic stirrer. A rotating magnetic field is used by this tool to cause magnetic capsules immersed in the isopropyl alcohol to stir the alcohol while rinsing the part.
5. Properly Cure your print
Using 405-nm UV light you need to to cure your print after drying for achieving the best quality. There are some commercial solutions available like the Formlabs Form Cure & the XYZPrinting UV curing chamber.
But on the brighter side you can always build your own curing chamber for far less money.