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Roschli, Alex

Publications and source records attributed to Roschli, Alex.

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

7. Space-Filling Toolpath Generation

Space-filling toolpaths are used to fill whatever space remains on a layer after closed-loop contours have been planned. They provide structure to the object, both supporting the geometry and creating solid surfaces. As such, there are two main types of space-filling toolpaths: infill and skin. Infill paths are sparse and meant to cover a large area quickly. Infill is typically not visible once a print is complete, because infill is covered by skins. Skins are the solid space-filling toolpaths meant to solidify the top and bottom of the object, which, unlike the sides of the object, are not completely covered by layering contours. Space-filling paths are typically planned by projecting a pattern over the layer, clipping the pattern at the boundary of the object, and then linking the remaining portions of the pattern. A subcategory of skin paths, called gradual infill, can be employed to densify the infill when approaching a top skin layer so that the print path of the top skin is sufficiently supported. Space-filling paths come in a variety of patterns to optimize how the space is filled. This chapter will discuss space-filling path categories, how to find the space for each path type, and how to apply the path type to generate toolpaths.

Roschli, Alex↗
DOE OSTI2023

6. Closed-Loop Toolpath Generation

Closed-loop paths, also known as closed-loop contours, are paths that start and stop at the same point and are typically used to define the perimeter or outermost boundary of the polygon that represents a given layer of an object, referred to as the “layer polygon.” Finding the location of a closed-loop path involves applying two offsetting steps to the edge of the layer polygon. The offsetting steps respectively serve to (1) find the area that contains the toolpath and (2) find the centerline of that area, to define the path itself. After finding the perimeter path, the remaining geometry from the layer polygon can be used for additional path-planning steps. This chapter will discuss how the location for a closed-loop path is found, including various problem scenarios, and the different types of closed-loop paths used in additive manufacturing.

Roschli, Alex↗
DOE OSTI2023

5. Cross-Sectioning

Now that an object has been transformed to an STL representation, the first major step of the slicing process can begin: cross-sectioning. This step converts a 3D object into a stack of polygons. Polygons are closed, 2D shapes composed of straight edges. These polygons are typically the result of intersecting a plane with an object at various heights along the z-axis. These stacked polygons create the “layers” that are characteristic of the 3D-printing process. In addition to the cross-section operation itself, several details need to be addressed. These details include necessary preprocessing and potential stitching, smoothing, and simplification of the cross-sections.

Borish, Michael↗
DOE OSTI2023

4. Geometry Data Storage

3D-printing begins with the design of an object using computer aided design (CAD) software. The geometry of the object must be exported and saved in a data file format that can be used in the slicing process to generate machine instructions for printing. The standard method of saving the data is to tessellate the object as a triangulated mesh stored as a .stl file. Due to the flat triangular faces used to store the data, this mesh is a low-resolution representation of the high-fidelity object designed in CAD. The STL has its limitations with respect to geometrical accuracy, material information, and instances of invalid mesh data, but can still be used for the 3D-printing process. New file variants, such as OBJ, AMF, and 3MF, are being developed to fix some of these issues and increase the capabilities of geometry data storage for 3D-printing.

Roschli, Alex↗
DOE OSTI2023

3. Motion Platforms and Kinematic Arrangements

Within a machine, mechanisms and motion are organized in what is known as a “kinematic arrangement,” which helps classify machines based on how they move. The most common kinematic arrangements for additive manufacturing systems are Cartesian, followed by delta, and then six-degrees-of-freedom robotic arms. However, there are a multitude of less common systems, such as the SCARA, polar robots, cable driven parallel robots, mobile platforms, and multi-agent systems. This chapter surveys these various kinematic arrangements to give a broad understanding of the mechanisms underlying motion within additive manufacturing systems. Understanding these mechanisms and their resulting motion provides a framework for discussing path planning for all scales and families of additive manufacturing.

Wang, Peter↗
DOE OSTI2023

Shifting Layer Heights for Closed-Loop Contours in Additive Manufacturing

Traditional slicing for 3D printing involves a planar cross-sectioning process to create layers. These layers are stacked one on top of the next representing a butt-joint, which is typically the weakest direction for loading a 3D printed part. Because the layers are printed sequentially, no material or reinforcement connects from one layer to the next. This clean layer line between layers is easy to break or separate. To fix this, the authors have implemented a new approach to shift the height of every other closed-loop contour toolpath such that a clean layer line no longer exists. This bead shifting approach involves moving every other contour by half a layer height, after the cross-sectioning step, so that a straight line cannot be drawn between layers. To maintain the original object geometry, a half height layer is printed for the first and last layer to create a flat top and bottom surface. This functionality has been implemented and tested as part of ORNL Slicer 2, an open-source toolpathing software package.

Roschli, Alex↗
DOE OSTI2023

Large Format Composite Additive Manufacturing for Low-Head Hydropower

Hydropower with a small elevation change from inlet to outlet, known as “low-head” hydropower, is a relatively untapped resource for reliable green power generation. One major barrier to entry is the cost of the components needed to generate the power. Each installation site is unique, with various head levels, flow rates, and other unique site characteristics that drive up the cost of development and installation. As a result, custom-made components are necessary because the sites are intrinsically inefficient. However, customized parts are generally more expensive to manufacture than ready-made parts. Often times, the cost of custom-made components is so high that the low-head hydropower installation becomes non-viable. Additive manufacturing offers the ability to make custom components, ideal for one-off applications, at low costs that are well suited for the needs of low-head hydropower. Indirect additive manufacturing, such as making tools or dies rather than end use components, can also be used to make low-cost composite tooling as needed for these custom applications. This paper explores the use of additive manufacturing, both directly and indirectly, to produce the components of a turbine system for a low-head hydropower site. The parts were designed to form a unique modular system, which saves time for future designs and iterations. The system has operated for more than three years without failure at a test site in Wisconsin, USA. This work serves as a basis for future application of AM to low-head systems, in which the modular components can be customized for each unique hydropower installation.

36 MATERIALS SCIENCE↗