26 research outputs found
Dynamic Extruder Control for Polymer Printing in Big Area Additive Manufacturing
Big Area Additive Manufacturing (BAAM) is 3D Printing on a large scale and can be used to create structures on the scale of cars and houses. Scaling up 3D printing to BAAM size meant fundamentally altering the traditional fused deposition modeling process by switching from a filament to a pellet material feed. This meant switching from a stepper motor extruder to a servo driven screw extruder. While increasing the throughput of the system, this new extruder increases the overall complexity. Effective control of the system is paramount to the success of BAAM enabling it to effectively scale in speed in the way it scales in build size. If the extruder can be quickly and accurately controlled, then a dimensionally accurate part can be printed. This paper will focus on the control of a single screw polymer extruder with zone controlled heating. State space control methods will be applied to shape both acceleration and deceleration of the spindle during extrusion so that a consistent bead can be produced at variable speeds
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Level Set Grids for Hybrid Manufacturing
We propose a novel hybrid model, the Level Set Grid, to facilitate parallel additive and
subtractive processes in hybrid manufacturing. The Level Set Grid combines the strengths of
explicit and implicit representations, offering precise modeling of evolving geometries and fast
and efficient collision detection. This research focuses on integrating Level Set Grids into the
additive slicing and subtractive pathing generation processes, laying the groundwork for future
advancements in the parallelization of hybrid manufacturing.Mechanical Engineerin
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Single Path Generation for Closed Contours via Graph Theory and Topological Hierarchy
Slicing converts a 3D object into a set of 2D polygons that are filled with multiple path types. These
paths involve travels where the extruder of the machine must stop building, lift, travel to the next path, lower,
and resume construction. Travels are considered wasted time as construction of the object is not occurring.
Further, the start/stop point, called a seam, causes both reduced aesthetic and weaker material properties. To
address these issues, an algorithmic approach was developed to compute a continuous single path from closed
contours. The algorithm utilizes graph theory and a topological hierarchy to produce a single path for an
individual layer. This approach can be combined with spiralization techniques to compute a single path for
entire objects. The resulting objects can be constructed quicker and have improved material properties as
verified via tensile testing.Mechanical Engineerin
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Transmitting G-Code with Geometry Commands for Extrusion Additive Manufacturing
G-code refers to text-based commands used to instruct a 3D printer how to construct an object. G-code
is generated to represent each toolpath during the slicing process. Each toolpath is represented as a list
of points that define the trajectory of the path to be printed. Additional commands are included to define
the motion velocity and extrusion rate, called the feeds and speeds. These toolpaths and commands must
be generated specific to the machine, material, and calibration settings that will be used during the print.
This paper outlines a new approach for the slicing and g-code creation process that eliminates the need
for outputting feeds and speeds in the slicing process. Instead, the slicer outputs g-code that defines the
desired bead geometry as printed. The 3D printer can then read this geometry data and calculate the
necessary feeds and speeds based on internal calibration data to successfully print the object.Mechanical Engineerin
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ORNL Slicer 2.0: Towards a New Slicing Paradigm
One fundamental step of additive manufacturing is slicing. Slicing is the conversion of a 3D
mesh to a set of layers containing all the necessary pathing to construct the object. The slicing
process is typically viewed as one step in a sequential additive manufacturing workflow: an object is
designed in CAD, sliced, and subsequent G-code is sent to the additive manufacturing system for
construction. While successful, this workflow has limitations such as the utilization of sensor feedback
for pathing alteration. To address limitations and better take advantage of opportunities resulting from
the Industry 4.0 revolution, researchers at Oak Ridge National Laboratory developed a new slicer,
ORNL Slicer 2.0. Slicer 2.0 was developed with the concept of “on-demand” slicing whereby the
slicer takes a more active role in object construction. In this paper, we describe the fundamental
design philosophy of this new approach as well as the Slicer 2.0 framework.Mechanical Engineerin
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Automated Path Planning for Wire Feeding in Large Format Polymer Additive Manufacturing
Polymer-based large format industrial additive manufacturing (AM) technology continues to expand
into new application areas. One area of interest is large scale composite molds and dies. These molds and dies
can be used for out-of-autoclave tooling applications. However, at these sizes, several challenges remain that
prevent the use of AM technology due to cost. One such challenge is the need to heat these molds in large
thermal ovens. To address this challenge, researchers at Oak Ridge National Laboratory developed the
necessary hardware to allow co-extruded wire to be embedded into the material during construction. Using this
hardware, a demonstration mold was successfully constructed and subjected to mechanical testing. The
construction of this object required a unique pathing solution to achieve success. In this paper, we describe the
needed software development in ORNL Slicer 2.0 to allow the automated production of this unique pathing
solution.Mechanical Engineerin
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Modelling of Microstructure Evolution in Wire-Based Laser Direct Energy Deposition with Ti-6Al-4V
Over the past years, wire-based direct energy deposition (DED) has been transitioning from rapid
prototyping to the production of end-use part and mass production. However, a wide market
penetration of the DED has not happened yet. The difficulties for wide-scale market adoption to
critical structural components are related to the development cost for process optimization and for
manufacturing of high-quality parts. For metallic components, the process conditions (e.g., power,
speed, tool path) control the material and mechanical properties/performance of the printed part. The
thermal history strongly determines the phase fraction, morphology, growth pattern, size of
microstructure, and nature of defects. Thus, in this study, we: 1) developed a thermal simulation using
finite element method, 2) experimentally measured thermal histories from a U-shaped part with four
tool paths of horizontal, vertical, raster, and contour to calibrate and validate the thermal model, and 3)
investigated the effect of thermal history on microstructure evolution and quantified the
microstructural variation during the printing process.Mechanical Engineerin
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Using Skeletons for Void Filling in Large-Scale Additive Manufacturing
In additive manufacturing (AM), slicing software is used to generate tool paths that are
then converted to G-Code, which tells the 3D printer how to build a part. Toolpaths are generated
using closed-loop paths. Sometimes the space left for a closed-loop is not sized perfectly. This can
lead to overfill or underfill issues. Therefore, skeletonization of a polygon seeks to resolve this
issue by creating an open-loop path to fill the voids between adjacent toolpaths. A straight skeleton
was used to explore this work. Straight skeletonization represents the topological skeleton of a
shape through line segments. After skeletonization, the extrusion rate can be varied to adjust bead
width more precisely to fill the gap.Mechanical Engineerin
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Creating Toolpaths Without Starts and Stops for Extrusion-Based Systems
Toolpath generation for extrusion-based additive manufacturing systems, called slicing,
involves operations on polygonal contours that are derived from an STL file. Slicing generates
multiple paths per layer (both closed-loop and open-loop) that are designed to optimally fill the
space outlined by the polygon(s). In the course of printing a layer, the extruder must start and stop,
the tip must be wiped, and the extruder must travel between paths without printing. Any amount
of time the printer spends moving without printing is considered wasted time because the part isn’t
being constructed. In addition, the start/stop point, known as the seam, is often a blemish on the
surface of the part that contributes to weaker material properties. Therefore, a single path for
creating multi-bead walled structures is desirable because it would save machine time and create
parts with better surface finish. This paper will cover one method of modifying the CAD file and
slicing engine to allow for parts to be printed without starting and stopping the extruder.Mechanical Engineerin
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ORNL Slicer 2: A Novel Approach for Additive Manufacturing Tool Path Planning
ORNL Slicer is the first software designed to generate machine instructions, or tool paths,
from CAD files for large-scale 3D printing of metals and polymers. The software was
revolutionary because it allowed for slicing of models reaching 20 feet long, generating millions
of lines of G-Code in seconds. The structure of the first ORNL Slicer had limitations in its
framework, which has led to the development of ORNL Slicer 2. In the second version of the
slicer, the process is modularized with individual layers being divided into regions, smarter infill
patterns, and traversals are generated based upon stress, thermal, and other models. The new
software has also been structured to allow for slicing and reslicing based on machine feedback
during the printing process.Mechanical Engineerin