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An overview of laser metal deposition
This emerging technology is not just for very large manufacturers
- By Melanie Lang
- November 6, 2017
- Article
- Additive Manufacturing
Laser metal deposition (LMD) is an emerging technology being adopted to augment, and in some cases replace, traditional methods for the remanufacturing, laser cladding, and 3-D printing of metallic parts. It holds the potential to save manufacturers time and money when applied in the right situations.
So how does it work? LMD, also known as directed energy deposition (DED), uses a system in which metallic powders contained in one or more hoppers are blown through a deposition nozzle and heated with a laser to produce a metallic bead. The motion system lays the metallic beads down, layer upon layer, to build up a part or to add layers of material to an existing part (see Figure 1).
The process speed, efficiency, and quality can be tailored to the requirements for various applications. Tailoring the process is achieved by varying laser power, bead width, speed of motion, and powder feed rates.
The technology is scalable and can be used to fabricate or repair parts measured in millimeters to meters. Furthermore, building parts or structures with bimetallics and gradient materials, in which multiple materials are used either in a mixture or gradually changed from one material to the next automatically, is being done today. Buildup with nickel, cobalt, iron, and copper-based metals, as well as carbide, magnetic, and other materials, is easily achieved.
Machines and Component Integration
A turnkey LMD machine can be used as a stand-alone device to 3-D print, clad, and remanufacture parts (see Figure 2). Such a system also can include a subtractive feature to finish surfaces. Machines that include an additive and subtractive feature are known as hybrid machines. Key machine components include a powder delivery nozzle, a powder feeder, laser and optics, motion system and controller, process chillers, enclosure for process safety, dust collector, and CAM programming software.
As an alternative to purchasing a turnkey LMD system, a fabricator can integrate deposition heads, powder feeders, and other subassemblies into robot cells (see Figure 3) and production lines to enable LMD capability quickly and at a fraction of the cost of purchasing a turnkey system. For example, an existing robot can be outfitted with an LMD head, powder feeder, and laser to 3-D print, clad, and remanufacture metal parts.
A Look at the Applications
LMD technology is gaining traction in the aerospace, tooling, transportation, and oil and gas sectors because of its scalability and the diverse capabilities that a single system can provide. Fabricators can use the technology’s expanded design envelope to create features with complex geometries, which would be difficult or impossible to fabricate with traditional methods. In addition, parts that are made with traditional manufacturing methods can be repaired or remanufactured (see Figure 4) by adding material to worn or corroded surfaces or new features to accommodate a design change. Castings and forgings can be modified or repaired without having to reproduce the entire part. Figure 5 is an example of laser cladding, and Figure 6 is an example of part creation.
How can this production, repairing, and cladding be so exact? The CAM software takes a CAD model of the part and generates a toolpath that the machine will follow to lay down the material. For the shaft cladding example shown in Figure 7, the shaft is loaded into a fixture in the machine and automated homing takes place. The machine follows the toolpath to lay down the material.
Using LMD for cladding as an alternative to more traditional processes, such as thermal spray, gas metal arc welding, or gas tungsten arc welding (GTAW), provides a better metallurgical bond (not mechanical bond); very low dilution, which leads to enhanced corrosion protection and reduced overlay; finer track resolution and control; a very small heat-affected zone; and localized heat input, which helps to reduce part distortion. The process also is faster than GTAW.
When cladding occurs, the LMD process fuses the material thoroughly with the substrate. Postprocess inspection typically reveals no porosity, no cracking, and no clad-substrate dilution.
Many material properties and hardness ratings can be used for cladding or building with the LMD process. These materials include nickel-based alloys such as INCONEL® and HASTELLOY®, cobalt-based alloys such as Stellite®, carbides, stainless steels, and titanium alloys.
Extreme wear- and impact-resistant coatings have been applied via LMD to parts used in very abusive environments and achieved good results. For example, pre-alloyed carbides deposited via LMD have shown 50 times the impact resistance of tungsten carbide, making it an excellent option for mining, crushing, and similar applications.
Cast iron’s high carbon content can make overlay, hardfacing, and repair challenging and expensive. However, cast iron repair with LMD has been demonstrated with exceptional results, including excellent bonding between the overlay and cast iron substrate with minimal porosity and cracking. This makes repair and feature addition to cast iron parts an economical alternative to buying replacement parts and mold modifications to accommodate design changes.
Industry Impact
Because of the flexibility and benefits of additive manufacturing, experts predict the additive manufacturing industry to grow by more than 30 percent each year, becoming over a $20 billion industry by 2020. According to recent reports published by Gartner, by 2020, 10 percent of industrial applications will integrate robotic 3-D printing technologies into their manufacturing operations. As a result of this technology adaptation, new product release timelines will be reduced by 25 percent, and an estimated 75 percent of all global manufacturers will use some tooling made with additive technology in their production lines.
Additive manufacturing technology such as LMD improves build times, expands build envelopes, improves efficiency and quality, and provides integration flexibility. This technology is available and in operation today and will continue to advance metal manufacturing by expanding the realm of possibility for part creation, cladding, and remanufacturing.
About the Author
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The Fabricator is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The Fabricator has served the industry since 1970.
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