**13. Adaptive MAT path**

Traditional contour path always generates gaps or voids as shown in **Figure 19a** and **b**. To avoid internal voids, the MAT path was introduced and its extension for complex geometries was developed. MAT paths are generated by offsetting the medial axis of the geometry from the center toward the boundary. **Figure 19c** shows an example of MAT path with the deposition sequence indicated by numbers. Although void-free deposition is obtained using MAT paths, this is achieved at the cost of creating discontinuity of the path (such as path 3, 4, and 5 in **Figure 19c**) and extra deposition at the boundary as described in **Figure 19d**. Post-process machining must be used to remove the extra materials and improve the accuracy at the cost of material and energy wastage.

Advanced Design for Additive Manufacturing: 3D Slicing and 2D Path Planning http://dx.doi.org/10.5772/63042 19

offsetting is repeated and terminates when the domain is fully covered. Green line loops in

Complete the deposition paths: A complete set of MAT-based deposition paths is obtained by repeating step 3) for all the decomposed domains. The generated paths are a set of closed-loop

From the above description, the MAT path planning algorithm for an arc welding process is able to be automated for any complex geometry; just as the existing commercially available raster and contour path planning strategies have been automatically applied to powder-based AM. MAT path is particularly preferred for void-free AM. Example of MAT path generation

**Figure 18.** Example of a solid structure with holes. (a) Geometry is represented by black lines, MAT represented by

Traditional contour path always generates gaps or voids as shown in **Figure 19a** and **b**. To avoid internal voids, the MAT path was introduced and its extension for complex geometries was developed. MAT paths are generated by offsetting the medial axis of the geometry from the center toward the boundary. **Figure 19c** shows an example of MAT path with the deposition sequence indicated by numbers. Although void-free deposition is obtained using MAT paths, this is achieved at the cost of creating discontinuity of the path (such as path 3, 4, and 5 in **Figure 19c**) and extra deposition at the boundary as described in **Figure 19d**. Post-process machining must be used to remove the extra materials and improve the accuracy at the cost

dotted red lines, and red solid lines stand for branches. (b) Generated trimmed path [26].

**13. Adaptive MAT path**

of material and energy wastage.

lines without start/stop sequences, which is preferred for the arc welding system.

**Figure 17c**, represent the generated deposition paths.

18 New Trends in 3D Printing

for a solid structure with holes is shown in **Figure 18**.

**Figure 19.** Illustrations of different deposition paths. Black lines represent the boundary of the geometry; green lines represent the deposition paths with the numbers representing the order of the deposition paths; grey regions are de‐ posited area by the relevant paths. (a) Contour path patterns; (b) The predicted high accuracy deposition but with in‐ ternal gaps; (c) MAT path patterns; (d) The predicted void-free deposition but with extra material deposited along the boundary; (e) Adaptive MAT path patterns with varying step-over distance; (f) The predicted void-free deposition with high accuracy at the boundary through using adaptive MAT path [28].

Step-over distance, which is defined as the distance between the next deposition path and the previous one, is always constant for both contour path patterns (refer to **Figure 19a**) and MAT path patterns (refer to **Figure 19c**). For certain geometries, it is not possible to achieve both high accuracy (refer to **Figure 19b**) and void-free (refer to **Figure 19d**) components using paths with constant step-over distance. However, some AM processes, such as wire feed AM process, are capable of producing different widths of deposits within a layer through varying travel speed and wire feed rate, while maintaining a constant deposit height. Therefore, we propose an adaptive path planning strategy that uses continuously varying step-over distances by adjusting the process parameters to deposit beads with variable width within any given path [28]. The developed adaptive MAT path planning algorithm is able to automatically generate path patterns with varying step-over distances (refer to **Figure 19e**) by analyzing geometry information to achieve better part quality (void-free deposition), accuracy at the boundary, and material efficiency, as shown in **Figure 19f**. Example of adaptive MAT path generation for a geometry with multiple holes is shown in **Figure 20**. Examples of void-free additive manu‐ facturing using adaptive MAT paths could be found in [27].

**Figure 20.** Example of a geometry with multiple holes. (a) Computed branch loops as represented by red lines; (b) Div‐ ided six domains as represented by different colors; (c) Generated numerous radiations from the branch points and the various decomposed simple shapes; (d) Generated adaptive paths for the geometry.
