# 3D-printing with robots - Savonia AMK

> Small desktop 3D printers are already a familiar sight to industry and consumers alike. The increasing proliferation of different additive manufacturing technologies has also awakened interest in larger-scale printing possibilities.

## Large-Scale Additive Manufacturing
Defining the largest 3D-printed piece is challenging because many structures are made up of several separate parts. For example, 3D-printed bridges and houses often consist of modules manufactured at a factory and connected on-site. 

Notable examples include:
* **3D-printed building (2019):** Considered the largest 3D-printed structure by volume.
* **“3Dirigo” boat (2019):** Manufactured by the University of Maine, considered the largest solid 3D-printed object.
* **U.S. Marine Corps boats (2022):** The University of Maine reportedly printed two new large-scale boats, though technical details remain restricted due to national security.

## Technical Challenges of Large-Scale Printing
Scaling up 3D printing is not as simple as increasing the print area, as this would lead to prohibitively long print times. To maintain efficiency, manufacturers must increase both the material deposition rate and the layer height. 

* **Nozzle size:** While desktop printers typically use 0.2–1 mm nozzles, large-scale systems use nozzles around 5–12 mm.
* **Build rates:** Large-scale projects require high speed; for instance, a 9.5-meter-tall concrete building in Dubai was printed in three weeks, and the 7.62-meter-long 3Dirigo boat was printed in 72 hours.

## Equipment and Systems
There are two primary approaches to large-scale 3D printing:

1. **Fixed Large-Scale Equipment:** Systems like **Thermwood’s LSAM** (Large-Scale Additive Manufacturing) and **Cincinnati Inc.’s BAAM** (Big Area Additive Manufacturing) offer controlled environments. BAAM is often installed on a high-speed laser cutting base, while LSAM systems can reach work areas up to 3 x 6 x 3 meters.
2. **Robotic Tool Heads:** Attaching a 3D-printing tool head to an industrial robot is a cost-efficient alternative. This allows the robot cell to be repurposed for other tasks, making it an ideal solution for universities and R&D institutions.

## Savonia’s Robotic 3D-Printing Workcell
Savonia University of Applied Sciences invested in robotic 3D-printing systems for metal, plastic, and concrete in 2021. The plastic and composite workcell includes:
* **CEAD robotextruder:** A print head that feeds granular material into a heated screw.
* **Granulate dryer:** Essential for preventing moisture absorption, particularly in wood fiber composites.
* **KUKA KR-120 robot:** The articulated arm used to maneuver the print head.

## The Printing Workflow
The process at Savonia involves several key software and mechanical steps:

* **RoboDK:** Used to place and orient the 3D model within a virtual robot cell and simulate the print path.
* **Slic3r:** An open-source program used for slicing the 3D model into layers and defining printing parameters.
* **G-code and Postprocessing:** RoboDK translates the G-code into instructions for the KUKA robot. A Python-based postprocessor converts these into a format the robot understands, adding comments for troubleshooting.
* **Continuous Printing:** Because granulate extrusion systems cannot perform "retraction" (to stop material flow), Savonia often uses "continuous print" or "vase mode" to avoid drips between layers.

## Case Study: Helsinki Fashion Show 2021
In 2021, Savonia collaborated with Glasshouse Helsinki, UPM, and Tampere University of Applied Sciences to print custom mannequins for the Helsinki Fashion Show. 
* **Material:** UPM Formi wood-cellulose composite.
* **Design:** The mannequins were split into parts to allow for assembly and printed in continuous mode to ensure structural integrity without the need for support structures.
* **Collaborators:** Florencia Colombo and Ville Kokkonen.