Laser-based additive manufacturing (LBAM) processes can be utilized to generate functional parts (or prototypes) from the ground-up via layer-wise cladding – providing an opportunity to generate complex-shaped, functionally graded or custom-tailored parts that can be utilized for a variety of engineering applications. Directed Energy Deposition (DED), utilizes a concentrated heat source, which may be a laser or electron beam, with in situ delivery of powder- or wire-shaped material for subsequent melting to accomplish layer-by-layer part fabrication or single-to-multi layer cladding/repair. Direct Laser Deposition (DLD), a form of DED, has been investigated heavily in the last several years as it provides the potential to (i) rapidly prototype metallic parts, (ii) produce complex and customized parts, (iii) clad/repair precious metallic components and (iv) manufacture/repair in remote or logistically weak locations. DLD and Powder Bed Fusion-Laser (PBF-L) are two common LBAM processes for additive metal part fabrication and are currently demonstrating their ability to revolutionize the manufacturing industry; breaking barriers imposed via traditional, ‘subtractive’ metalworking processes. This article provides an overview of the major advancements, challenges and physical attributes related to DLD, and is one of two Parts focused specifically on DLD. Part I (this article) focuses on describing the thermal/fluidic phenomena during the powder-fed DLD process, while Part II focuses on the mechanical properties and microstructure of parts manufactured via DLD. In this current article, a selection of recent research efforts – including methodology, models and experimental results – will be provided in order to educate the reader of the thermal/fluidic processes that occur during DLD, as well as providing important background information relevant to DLD as a whole. The thermal/fluid phenomena inherent to DLD directly influence the solidification heat transfer which thus impacts the part's microstructure and associated thermo-mechanical properties. A thorough understanding of the thermal/fluid aspects inherent to DLD is vital for optimizing the DLD process and ensuring consistent, high-quality parts.

An overview of Direct Laser Deposition for additive manufacturing; Part I: Transport phenomena, modeling and diagnostics

A method of fabricating a fully dense, three dimensional object by direct laser sintering is disclosed (flow chart). In a chamber (evacuated) with a partial pressure atmosphere, a degased powder layer is dispensed over a target surface and a beam of directed energy melts metallic powder in order to form a solid layer cross section. Another layer of powder is deposited and melted, along with a portion of the previous layer. The energy beam typically is in the form of a laser, scanning along a path resembling a parametric curve or another, arbitrary piecewise parametric curve (vector scan). In another embodiment, the previous layer is not remelted, thus creating an oxide film that acts as a clean stop to prevent unwanted downward growth.

Direct selective laser sintering of metals

Method and apparatus for embedding features and controlling material composition in a three-dimensional structure (130) are disclosed. The apparatus comprises a directed material deposition apparatus having a source (124) of a focused laser beam, a deposition head (11) being coordinated in a plurality of coordinate axes, a controlled atmosphere chamber (128), a control computer (129), a plurality of feedstock (126, 127), a design rendering a solid model including embedded features, and a positioning stage (16) with a substrate (19) disposed on it. Said deposition head (11) can be a multi-axis deposition head, with a volumetric powder feed unit, a rapid acting metering valve for powder feedstock control, a laser delivery system having an optical fiber with heat protection, a laser beam shutter dump assembly and a pluraltity of powder delivery nozzles comprising coaxial gas stream means for reduced powder dispersion. Material properties can be engineered by adjusting laser exposure, material deposition and material constants.

Forming structures from CAD solid models

The present invention relates to methods and an apparatus for the fabrication of solid three-dimensional objects from liquid polymerizable materials.

Method and apparatus for three-dimensional fabrication

An apparatus and method have been developed to exploit the desirable material and process characteristics provided by a low powered laser material deposition system, while overcoming the low material deposition rate imposed by the same process. One application of particular importance for this invention is direct fabrication of functional, solid objects from a CAD solid model. This apparatus uses a software interpreter to electronically slice the CAD model into thin horizontal layers that are subsequently used to drive the deposition apparatus. This apparatus uses a single laser beam to outline the features of the solid object and then uses a series of equally spaced laser beams to quickly fill in the featureless regions. Using the lower powered laser provides the ability to create a part that is very accurate, with material properties that meet or exceed that of a conventionally processed and annealed specimen of similar composition. At the same time, using the multiple laser beams to fill in the featureless areas allows the fabrication process time to be significantly reduced.

Multiple beams and nozzles to increase deposition rate

Method and apparatus for forming articles from materials in particulate form in which the materials are melted by a laser beam and deposited at points along a tool path to form an article of the desired shape and dimensions. Preferably the tool path and other parameters of the deposition process are established using computer-aided design and manufacturing techniques. A controller comprised of a digital computer directs movement of a deposition zone along the tool path and provides control signals to adjust apparatus functions, such as the speed at which a deposition head which delivers the laser beam and powder to the deposition zone moves along the tool path.

Laser production of articles from powders

A deposition head for use as a part of apparatus for forming articles from materials in particulate form in which the materials are melted by a laser beam and deposited at points along a tool path to form an article of the desired shape and dimensions. The deposition head delivers the laser beam and powder to a deposition zone, which is formed at the tip of the deposition head. A controller comprised of a digital computer directs movement of the deposition zone along the tool path and provides control signals to adjust apparatus functions, such as the speed at which the deposition head moves along the tool path.

Deposition head for laser

It has been discovered that wires and small diameter rods can be produced using laser deposition technology in a novel way. An elongated article such as a wire or rod is constructed by melting and depositing particulate material into a deposition zone which has been designed to yield the desired article shape and dimensions. The article is withdrawn from the deposition zone as it is formed, thus enabling formation of the article in a continuous process. Alternatively, the deposition zone is moved along of numerous deposition paths away from the article being formed.

Controlled laser production of elongated articles from particulates

A device for providing uniform powder flow to the nozzles when creating solid structures using a solid fabrication system such as the directed light fabrication (DLF) process. In the DLF process, gas entrained powders are passed through the focal point of a moving high-power laser light which fuses the particles in the powder to a surface being built up in layers. The invention is a device providing uniform flow of gas entrained powders to the nozzles of the DLF system. The device comprises a series of modular splitters which are slidably interconnected and contain an integral flow control mechanism. The device can take the gas entrained powder from between one to four hoppers and split the flow into eight tubular lines which feed the powder delivery nozzles of the DLF system.

Multiple feed powder splitter

A deposition head for the production of articles from metal powder includes an optics package (201) and a delivery nozzle (241) which contains a laser beam passage (242), at least two oppositely disposed powder passages (230), upper, middle, and lower protective windows (202, 207, 209), a coolant channel (234), and upper and lower gas channels (231, 227).

Gary K. Lewis

Papers

Laser production of articles from powders

Deposition head for laser

Controlled laser production of elongated articles from particulates

Multiple feed powder splitter

Deposition head for production of articles from powders