6,920 research outputs found
Repair of metallic components using hybrid manufacturing
Many high-performance metal parts users extend the service of these damaged parts by employing repair technology. Hybrid manufacturing, which includes additive manufacturing (AM) and subtractive manufacturing, provides greater build capability, better accuracy, and surface finish for component repair. However, most repair processes still rely on manual operations, which are not satisfactory in terms of time, cost, reliability, and accuracy. This dissertation aims to improve the application of hybrid manufacturing for repairing metallic components by addressing the following three research topics. The first research topic is to investigate and develop an efficient best-fit and shape adaption algorithm for automating 3D models\u27 the alignment and defect reconstruction. A multi-feature fitting algorithm and cross-section comparison method are developed. The second research topic is to develop a smooth toolpath generation method for laser metal deposition to improve the deposition quality for metallic component fabrication and repair. Smooth connections or transitions in toolpath planning are achieved to provide a constant feedrate and controllable deposition idle time for each single deposition pass. The third research topic is to develop an automated repair process could efficiently obtain the spatial information of a worn component for defect detection, alignment, and 3D scanning with the integration of stereo vision and laser displacement sensor. This dissertation investigated and developed key technologies to improve the efficiency, repair quality, precision, and automation for the repair of metallic components using hybrid manufacturing. Moreover, the research results of this dissertation can benefit a wide range of industries, such as additive manufacturing, manufacturing and measurement automation, and part inspection --Abstract, page iv
From 3D Models to 3D Prints: an Overview of the Processing Pipeline
Due to the wide diffusion of 3D printing technologies, geometric algorithms
for Additive Manufacturing are being invented at an impressive speed. Each
single step, in particular along the Process Planning pipeline, can now count
on dozens of methods that prepare the 3D model for fabrication, while analysing
and optimizing geometry and machine instructions for various objectives. This
report provides a classification of this huge state of the art, and elicits the
relation between each single algorithm and a list of desirable objectives
during Process Planning. The objectives themselves are listed and discussed,
along with possible needs for tradeoffs. Additive Manufacturing technologies
are broadly categorized to explicitly relate classes of devices and supported
features. Finally, this report offers an analysis of the state of the art while
discussing open and challenging problems from both an academic and an
industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and
Innovation action; Grant agreement N. 68044
Remanufacturing of precision metal components using additive manufacturing technology
Critical metallic components such as jet engine turbine blades and casting die/mold may be damaged after servicing for a period at harsh working environments such as elevated temperature and pressure, impact with foreign objects, wear, corrosion, and fatigue. Additive manufacturing has a promising application for the refurbishment of such high-costly parts by depositing materials at the damaged zone to restore the nominal geometry. However, several issues such as pre-processing of worn parts to assure the repairability, reconstructing the repair volume to generate a repair tool path for material deposition, and inspection of repaired parts are challenging. The current research aims to address crucial issues associated with component repair based on three research topics. The first topic is focusing on the development of pre-repair processing strategies which includes pre-repair machining to guarantee the damaged parts are ready for material deposition and pre-repair heat-treatment to restore the nominal mechanical properties. For this purpose, some damaged parts with varied defects were processed based on the proposed strategies. The second topic presents algorithms for obtaining the repair volume on damaged parts by comparing the damaged 3D models with the nominal models. Titanium compressor blades and die/mold were used as case studies to illustrate the damage detection and reconstructing algorithms. The third topic is the evaluation of repaired components through material inspection and mechanical testing to make sure the repair is successful. The current research contributes to metallic component remanufacturing by providing knowledge to solve key issues coupled with repair. Moreover, the research results could benefit a wide range of industries, such as aerospace, automotive, biomedical, and die casting --Abstract, page iv
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Compensation for Uneven Surfaces When Building Laser Deposited Structures
Direct Laser Deposition (DLD) is a blown-powder laser deposition process that can be
used to quickly produce, modify or repair fully-dense metallic parts by a layered manufacturing
method. However, uneven substrate surfaces often cause variation in the deposited layer which
is magnified by succeeding layers. Research carried out at the University of Liverpool has
resulted in a non-feedback layer height controlling process based on controlling the shape of the
powder streams emitted from a four-port side feed nozzle. This method limits deposited layer
height by causing a sharp reduction of catchment efficiency in the vertical plane at a fixed
distance from the powder feed nozzle, and is therefore capable of depositing a consistent layer
height in spite of power, powder flow or process velocity variation. This paper demonstrates
how this method of layer height control can compensate for irregular substrate surfaces in the
production of accurate DLD parts.Mechanical Engineerin
Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
In the circular economy, products, components, and materials are aimed to be kept at the
utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered
as proper techniques to return the value of the product during its life. Directed Energy Deposition
(DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most
suitable for repairing and remanufacturing automotive and aerospace components. Its application
allows damaged component to be repaired, and material lost in service to be replaced to restore
the part to its original shape. In the past, tungsten inert gas welding was used as the main repair
method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the
conventional welding processes, repair via DED has more advantages, including lower heat input,
warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding
between the deposited layers, high precision, and suitability for full automation. Hence, the proposed
repairing method based on DED appears to be a capable method of repairing. Therefore, the focus of
this study was to present an overview of the DED process and its role in the repairing of metallic
components. The outcomes of this study confirm the significant capability of DED process as a repair
and remanufacturing technolog
VoroCrust: Voronoi Meshing Without Clipping
Polyhedral meshes are increasingly becoming an attractive option with
particular advantages over traditional meshes for certain applications. What
has been missing is a robust polyhedral meshing algorithm that can handle broad
classes of domains exhibiting arbitrarily curved boundaries and sharp features.
In addition, the power of primal-dual mesh pairs, exemplified by
Voronoi-Delaunay meshes, has been recognized as an important ingredient in
numerous formulations. The VoroCrust algorithm is the first provably-correct
algorithm for conforming polyhedral Voronoi meshing for non-convex and
non-manifold domains with guarantees on the quality of both surface and volume
elements. A robust refinement process estimates a suitable sizing field that
enables the careful placement of Voronoi seeds across the surface circumventing
the need for clipping and avoiding its many drawbacks. The algorithm has the
flexibility of filling the interior by either structured or random samples,
while preserving all sharp features in the output mesh. We demonstrate the
capabilities of the algorithm on a variety of models and compare against
state-of-the-art polyhedral meshing methods based on clipped Voronoi cells
establishing the clear advantage of VoroCrust output.Comment: 18 pages (including appendix), 18 figures. Version without compressed
images available on https://www.dropbox.com/s/qc6sot1gaujundy/VoroCrust.pdf.
Supplemental materials available on
https://www.dropbox.com/s/6p72h1e2ivw6kj3/VoroCrust_supplemental_materials.pd
Algorithms and methods for discrete mesh repair
Computational analysis and design has become a fundamental part of product research, development, and manufacture in aerospace, automotive, and other industries. In general the success of the specific application depends heavily on the accuracy and consistency of the computational model used. The aim of this work is to reduce the time needed to prepare geometry for mesh generation. This will be accomplished by developing tools that semi-automatically repair discrete data. Providing a level of automation to the process of repairing large, complex problems in discrete data will significantly accelerate the grid generation process. The developed algorithms are meant to offer semi-automated solutions to complicated geometrical problems—specifically discrete mesh intersections and isolated boundaries. The intersection-repair strategy presented here focuses on repairing the intersection in-place as opposed to re-discretizing the intersecting geometries. Combining robust, efficient methods of detecting intersections and then repairing intersecting geometries in-place produces a significant improvement over techniques used in current literature. The result of this intersection process is a non-manifold, non-intersecting geometry that is free of duplicate and degenerate geometry. Results are presented showing the accuracy and consistency of the intersection repair tool. Isolated boundaries are a type of gap that current research does not address directly. They are defined by discrete boundary edges that are unable to be paired with nearby discrete boundary edges in order to fill the existing gap. In this research the method of repair seeks to fill the gap by extruding the isolated boundary along a defined vector so that it is topologically adjacent to a nearby surface. The outcome of the repair process is that the isolated boundaries no longer exist because the gap has been filled. Results are presented showing the precision of the edge projection and the advantage of edge splitting in the repair of isolated boundaries
Analysis of rotor vibratory loads using higher harmonic pitch control
Experimental studies of isolated rotors in forward flight have indicated that higher harmonic pitch control can reduce rotor noise. These tests also show that such pitch inputs can generate substantial vibratory loads. The modification is summarized of the RotorCRAFT (Computation of Rotor Aerodynamics in Forward flighT) analysis of isolated rotors to study the vibratory loading generated by high frequency pitch inputs. The original RotorCRAFT code was developed for use in the computation of such loading, and uses a highly refined rotor wake model to facilitate this task. The extended version of RotorCRAFT incorporates a variety of new features including: arbitrary periodic root pitch control; computation of blade stresses and hub loads; improved modeling of near wake unsteady effects; and preliminary implementation of a coupled prediction of rotor airloads and noise. Correlation studies are carried out with existing blade stress and vibratory hub load data to assess the performance of the extended code
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