3D printing

There are many technologies in 3D printing, and this article on All3DP discuss them in detail. At our Laboratory, we have two different printing techniques available to us, and they have different purposes. Most prints are made with fused deposition modeling or FDM, with filaments of various types. These filaments are cheap and easy to use, and we have seven FDM printers at the Lab. 3D printing courses are primarily run on FDM machines.

For detailed work we have one SLA, or resin, printer, which is capable of amazing resolution in prints. This resin is rather more expensive than the filaments, and therefore we use SLA for prints that need to show fine details or have intricate internal structures.

All 3D printing works with layers: when an object is prepared for printing, it is sliced into layers of a selected thickness, and the slicing software produces the code needed for printers to work. The layer thickness is typically 0.1mm to 0.3mm for FDM machines. Layer speed is directly proportional to print speed: a print is three times slower at 0.1mm as compared to 0.3mm. Typical print times for Arduino parts range from 30 minutes to 4 hours.

In SLA printers, layer thickness can be set between 0.05mm to 0.16mm. SLA printing is usually slower than FDM.

Modeling for printing

Regardless of the print method, designing for printing is the same. While in normal 3D modeling, virtual objects need not be structurally sound (nobody can see whether the model has loose vertices or edges), in printing all loose parts cause the slicer software to halt and demand for the mesh to be fixed first. This is called making the mesh manifold.

Sequence of modeling a small plastic piece shown on top left

All holes and other special features of the print must be designed in the 3D software, and they must be made structurally valid in order for the object to be manifold. Protrusions from the sides of object must be supported during printing, if the angle from the horizontal is less than 60 degrees. Slicing software is able to create the supports during the slicing, and after printing, the lightweight supports can just be broken off the piece.

Filament printing

All filament printers share a common structure, with a roll of filament at one end, a hotend in the middle, and a print table or bed to receive the molten plastic, forming into a print. Filament diameter is either 1.75mm, or 3mm. Most of our printers are thin wire machines, but our BCN3D Sigmax has two rolls of 3mm wire. Generally speaking thicker wire can apply more material into the printed piece per second, but we have found that the speed is on a par with the thin wire machines.

Filament print with designed holes

Filament types are more numerous than can be listed here, but we mostly use PLA (polylactic acid) filament for its easy printing, cheap price, and adequate structural strength. Another common material is ABS, commonly found in plastic buckets. It is structurally tougher, but is not as tolerant to air drafts during printing, which often results in cracks as the printed item cools unevenly. We also have nylon for tough parts, and TPU for soft prints (one innovation course used TPU to print acupuncture inner soles for shoes).

Filament printed scale model of the Dubai World Expo pavilion

SLA Resin printing

In resin printing, the machine has a pool of resin that hardens in ultraviolet light. That is why all resin printers have a transparent, but UV blocking, case. The underside of the pool is a mesh that allows ultraviolet laser light to enter the resin pool. From above, the print table is immersed in the resin, and when laser light is directed into the resin by a system of mirrors, it hardens the resin at the boundary layer of air and resin. The form of the mesh to be printed is then traced with the laser, after which the table is retracted from the pool by one layer height, and the next layer is then traced on the print.

Resin printer with cover open

Resin printers can print in much higher detail, and resins are available in many colors and mechanical properties. At Haaga-Helia we only use a resin called Basic Grey IV, because our prints do not need specific qualities. Grey IV can be painted over with spray paint or paints used for scale modeling.

Resin printed cube with supports removed

When the client tells us the intended use of the piece, we decide what printer and material we will use.