# Design considerations for large scale additive manufacturing, part 1 - Savonia AMK

> We are excited to share some design considerations for large scale additive manufacturing.

## Introduction to Large Scale Additive Manufacturing (LSAM)
In the world of 3D printing, various terms are used to describe the same technology: Large Scale Additive Manufacturing (LSAM), Big Area Additive Manufacturing (BAAM), and Fused Granulate Fabrication (FGF). Regardless of the terminology, these systems utilize a pellet extruder mounted on a large gantry system or a robotic arm to deposit material. They function as larger, more powerful versions of standard desktop 3D printers.

## The 3DROBO Laboratory
Savonia’s 3DROBO laboratory features several advanced tools for research and production:
*   **KUKA robotic arm KR120 2700R** with a **CEAD robot extruder**
*   **Hyperion Robotics concrete extruder**
*   **Flexmill robotic milling toolkit**

The insights shared here are based on six months of experimentation, primarily using **UPM Formi 3D20** pellets. These guidelines are specific to this equipment and material, though they serve as a valuable starting point for understanding LSAM technology.

## LSAM Wisdom Nuggets: Design Guidelines

### 1. Wall Angles
While desktop printers often struggle with angles greater than 45 degrees, LSAM requires even more caution. For vertical printing, it is recommended to stay below 30 degrees, though this varies based on material, layer height, and width.

### 2. Minimizing Segmented Toolpaths
FGF systems face challenges with material leakage and pressure, making it difficult to stop and start extrusion cleanly. This leads to blobs and gaps at seams. Designers should minimize "islands" (segmented toolpaths) within a single layer. If they cannot be avoided, air movement between segments must be kept as brief as possible.

### 3. Connecting Islands
When islands are unavoidable, they can be connected using a "double wall" integrated into the design. This bridge-like structure, roughly twice the width of the printing path, ensures continuity and can be machined away after printing.

### 4. Layer Width and Nozzle Size
In LSAM, we utilize large nozzles ranging from 3 mm to 10 mm, with deposition rates reaching up to 12 kg/h. We have found that the optimal layer width is **120% to 180% of the nozzle diameter**. 
*   **Below 120%:** Results in a rough, "shark-skin" texture.
*   **Above 180%:** Results in a bumpy, uneven bead.

### 5. Layer Height
For UPM Formi 3D20, we have observed the following:
*   Layer heights below 1 mm result in poor surface quality.
*   Layer height should not exceed the nozzle size, especially for angled walls.
*   The ideal range is **1/4 to 2/3 of the layer width**.
*   Currently, most parts are printed within a layer height range of **2 mm to 4 mm**.

### 6. Material Preparation
Always dry the material before printing. Moisture negatively impacts both print quality and the mechanical strength of the final part.

### 7. Double Wall Overlap
To prevent porosity and improve mechanical properties in double walls, beads should overlap. Our experiments determined that an **overlap of 15%** (meaning the wall thickness should be 5–20% less than twice the bead width) produces the highest quality results.

## Future Perspectives: Robotic Printing Strategies
The freedom of movement provided by robotic arms allows for advanced printing strategies beyond traditional vertical slicing. We utilize **Adaxis Adaone** software, which supports seven distinct strategies:
1.  Planner printing (vertical printing)
2.  Angled printing
3.  Radial printing
4.  Cladding
5.  Printing on non-planar surfaces
6.  Variable printing orientation
7.  Revolving surfaces

Designers must evaluate the geometry of their part to select the appropriate strategy, as each carries unique design considerations. Future articles will explore angled slicing and other advanced techniques in greater detail.

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**Alireza Badiee**
Testing Engineer
Savonia University of Applied Sciences