Morphing Based Approach for Process Planning for Fabrication of Geometries and the Control of Material Composition

The inherent limitation of most of the solid freeform fabrication is the deposition in form of layers. Artificial imposition of the process for the desired geometric morphology and the functional gradience of material limits the accuracy of the workpiece. Mathematical morphing of geometry and the material gradience allows a smooth variation across the part geometry and the material composition of the part. The paper describes a framework for process planning and implementation of fabrication of geometries and control of the material composition. Simulation results for the suggested approach are described in the paper.Mechanical Engineerin

Apparatus and Method of High-Pressure Waterjet Assisted Cooling/Lubrication in Machining

An apparatus for high-pressure waterjet assisted machining includes a drive motor, spindle and rotary cutting tool with cutting inserts. The apparatus further includes a high-pressure intensifier pump providing cutting fluid at a pressure greater than 50,000 psi. A cutting fluid conduit system in the rotary cutting tool includes a main flow channel, a distribution manifold, a plurality of radially extending feed channels and a plurality of cooperating nozzles for delivering fluid behind the cutting inserts. The cutting fluid then passes through one or more apertures in the inserts into an interface defined by the inserts of the cutting tool and a chip being cut from the workpiece

Modeling and Verification of Error Propagation in Integrated Additive/Subtractive Multi-Directional Direct Manufacturing

Integrated additive-subtractive manufacturing, when applied in the framework of SolidFreeform-Fabrication (SFF) allows the fabrication of functional parts on single platform, directly from its computer model. Reduction in process complexity and total processing steps is ensured by multi-directional material deposition and machining. However, due to shift in the datum location in reorientation steps and sequential addition of material in the form of layers, the CAD process intent is not exactly replicated. This leads to inclusion of dimensional errors. Machining in order to eliminate the errors as frequent as layer deposition is highly expensive and can be avoided by estimation of errors and varying process parameters, and/or performing machining after a set of layers are deposited. This paper proposes a state space model for modeling the error propagation due to linear as well as angular variation in the datum. The model is based on identification of possible sources of error, mechanism of error inclusion and influence of process parameters. An experiment performed to determine parameters of error modeling has been reported.Mechanical Engineerin

Mechanism for Determination of G-factors for Solid Freeform Fabrication Techniques Based on Large Heat Input

A major class of Solid Freeform Fabrication (SFF) methods for metal deposition are based on large heat input. The geometry and microstructural properties of the deposition depend primarily on the heat input and the subsequent distribution at the substrate. On one hand the insufficient heat may lead to the inadequate melting of the metal, on the other hand overheating and heat accumulation leads to the overmelting, resulting in the deformation of the build up geometry. The heat distribution is governed by the available heat sink . For a better control of the process, the estimation of heat sinks and the subsequent control of the energy input allows a better control of the process. A parameter G-factor that estimates the heat sink based on the local geometry of a part has been introduced. The estimation of G-factor is based on the simulation and the experimental results. Also a mechanism to determine the G-factor for various substrate geometries has been introduced.Mechanical Engineerin

An Investigation of Gas-Powder Flow in Laser-Based Direct Metal Deposition

Laser-Based Direct Metal Deposition (LBDMD) is a blown-powder laser deposition process which can produce fully-dense and metallurgicaly sound parts by a layered manufacturing method. Since a deposition head equipped with discontinuous radially symmetric nozzles has the potential to be tilted without influence of the gravity on the powder stream shape, it can be used for multi-axis deposition. The shape of the gas-powder stream with respect to the shape of laser beam and the size of the molten pool, have a large influence on the size and shape of the buildup. They determine the geometrical accuracy and the surface quality of the buildup. This paper examines gas-powder flow from radially symmetric nozzles using computational fluid dynamics method. For verification purpose the powder flow was investigated by a visualization method and powder concentration distribution was analyzed using image processing technique. The obtained results are in good agreement with numerical model.Mechanical Engineerin

Thermo-structural Finite Element Analysis of Direct Laser Metal Deposited Thin-Walled Structures

Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which particles are injected. During fabrication, a complex thermal history is experienced in different regions of the build, depending on the process parameters and part geometry. The thermal history induces residual stress accumulation in the buildup, which is the main cause of cracking during the fabrication. The management of residual stress and the resulting distortion is a critical factor for the success of the process. A thermostructural finite element model (FEM) of the process is developed, and the analysis reveals different patterns of residual stress in the thin-walled structures depending on the deposition strategy and the geometry of the structures. The residual stress patterns obtained from finite element analysis (FEA) are in good agreement with the experimental results.Mechanical Engineerin

Fabrication of Laser Deposited TiC/Steel Matrix Composite Coatings

The present work investigates the effect of laser scanning beam speeds and the content of TiC in injected powder on morphologies and microstructures of laser deposited beads of a TiC/H13 tool steel composite. The results show that the beam scanning speeds affect the size and morphology of the beads. During laser processing, TiC melts, decomposes, and subsequently, a number of fine TiC precipitates form during cooling that are uniformly distributed in the tool steel matrix. The beam scanning speeds and the amount of injected TiC exert a strong influence on the morphology and size of the fine TiC precipitates. It is believed that the precipitated TiC is the primary phase in hypereutectic Fe-TiC. Rapid cooling develops martensite with retained austenite in a steel matrix. The precipitated TiC can refine grains of the steel matrix as a solidified nucleus. TiC/H13 tool steel composite coatings with various contents of TiC were produced using the laser deposition processing technique.Mechanical Engineerin

Process Planning for Solid Freeform Fabrication Based on Laser-Additive Multi-axis Deposition

This paper describes a new approach for rapid prototyping based on volumetric skeletonization. Contrary to most of the popular techniques for Solid Freeform Fabrication (SSF) based on 2-1/2 -axis layering as planar slices, this approach suggests the growth of the component along all three coordinate axes. While this approach offers many advantages in terms of the elimination of the support structures for the reduction of the staircase effects and the elimination of various post processes for the functional parts, this approach also offers challenges towards process planning. For various complicated shapes it may not be possible to generate the required shape using this approach; however, a hybrid approach which also incorporates the deposition by layers, may offer an optimum solution. Preliminary results are based on the successful laser-based additive deposition along multiple g-vectors. The material properties and the problems of possible porosities are still to be investigated. Advantages, process planning, applications, experimental results, and the challenges of this new method are the subject of this paper.This work was financially supported by THECB (Texas Higher Education Coordinating Board) Grants 003613-0022-1999 and 003613-0016-2001, NSF (National Science Foundation) Grants DMI-9732848 and DMI-9809198 and by the US Department of Education Grant P200A80806-98.Mechanical Engineerin

Laser Welding of Magnesium Alloys: Issues and Remedies

Automotive industry tends to use lightweight alloys to save on mass in order to have more economic and environment friendly automobiles. A variety of alloys have been used in automotive industry such as magnesium, aluminum, and galvanized steel. Magnesium is the lightest structural metal that can significantly help decrease the body structure weight. Laser welding is one of the main joining processes used in automotive industry due to its superior joint properties. In the current study, the main issue that was pore formation during the laser welding of magnesium alloy is investigated. First, the process was performed using different process parameters to study their effect on the weld quality. Then a variety of approaches were used to mitigate pores in the weld. The results showed that these approaches could effectively mitigate pore formation in the weld bead. In addition, the pore formation issue was nondestructively detected using real‐time methods such as spectrometer and high speed charge‐coupled device (CCD) camera. The results showed that there was a good correlation between pore formation and the real‐time‐monitoring detected data