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Univ. of Exeter team develops selective laser melting process to produce 3D aluminum composite parts; automotive and aerospace applications
3 July 2012
|A complex SLM part from the University of Exeter. Click to enlarge.|
Engineers at the University Exeter (UK) have developed a new method for making three-dimensional reinforced aluminium composite parts by using Selective Laser Melting (SLM)—a form of additive layer manufacturing (ALM), also sometimes generally called 3D printing. (3D printing is a specific process within the larger ALM domain.) The Exeter method could produce strong, lightweight and complex parts for car manufacturing and the aerospace industry less expensively and more accurately than current methods, according to the team.
SLM builds components up by melting successive layers of powder using a laser source that fuses the material in a pattern corresponding to the final product; the process originated at Fraunhofer ILT in Aachen, Germany some 20 years ago. The specific SLM technique for reinforced aluminum composites is being developed at the University of Exeter’s Centre for Additive Layer Manufacturing. The technique has the potential to manufacture aluminium composite parts such as pistons, drive shafts, suspension components, brake discs and almost any structural components of cars or airplanes.
It also enables the production of lighter structural designs with innovative geometries leading to further reduce of the weight of products.
Parts for cars and airplanes are widely made from aluminium, which is relatively light, with other reinforcement particles to make it stronger. The traditional methods, generally involved casting and mechanical alloying, can be inaccurate and expensive, especially when the part has a complex shape. Over the last decade, new SLM techniques have been developed, which enable parts with more complicated shapes to be produced. The new SLM techniques can be applied to manufacture aluminium composite parts from specific powder mixtures.
The Exeter team’s latest research findings are published in the Journal of Alloys and Compounds. In that paper, they investigated the effects of various Al alloys mixed with 15 wt% Fe2O3 on the selective laser melting (SLM) facilitated in-situ reaction and formation of Al metal matrix composite (MMC) components.
To carry out this new technique, the researchers use a laser to melt a mixture of powders, composed of aluminium and a reactive reinforcing material—e.g., an iron oxide combination as in the new study.
SLM facilitated in-situ reaction and subsequent rapid solidification introduce very fine particles (down to ∼ 50-100 nm), reinforcing the microstructure of all Al (alloy) composites. The particles are Al-Fe intermetallics, Al oxides such as α-Al2O3, plus Si crystals (alone or in combination) depending on the alloy composition...The in-situ particle reinforced Al (alloy) composites are significantly harder than corresponding conventionally manufactured (e.g. casting) Al alloys without Fe2O3, due to superior microstructural characteristics such as featureless or very fine dendritic matrix, ultrafine/nanoscale particles, and also enhanced solid solubility of the SLM products.—Dadbakhsh and Hao (2012A)
This method allows parts with complex shapes to be easily produced. The new materials have very fine particles compared with other composites, making them more robust. The reaction between constituents releases energy, which also means materials can be produced at a higher rate using less power. This technique is significantly cheaper and more sustainable than other SLM methods which directly blend very fine powders to manufacture composites, according to the team.
The Centre for Additive Layer Manufacturing (CALM) is a £2.6-million (US$4-million) investment in innovative manufacturing for the benefit of businesses in the South West and across the rest of the UK. CALM is delivered in collaboration with EADS UK Ltd.
ALM categories, processes, and materials. There are several different categories and processes of additive layer manufacturing available, each appropriate for different materials and requirements, CALM notes.
Powder bed processes—which includes the SLM process used to make the 3D aluminum composites, consolidates thin layers of powder using a laser or electron beam to fuse scans of the sliced Computer Aided Design (CAD) data to create the geometry. A recoater mechanism lays down the powder on top of each scanned area, allowing the build up of the part layer by layer.
Specific process types included within this category are Laser Sintering (LS) for thermoplastics and elastomers; SLM for ferrous and non-ferrous alloys; and electron beam melting for non-ferrous alloys.
Material Deposition/Extrusion processes heat the material through an extrusion nozzle which follows a predefined deposition path, layering on top of a platform, depositing material on top of previous layers to create the 3-dimensional geometry.
For metallics, blown powder and wire extrusion can be used, however the material is melted using a laser or electron beam at source.
Process types within this category include Blown Powder for ferrous and non-ferrous alloys; wire extrusion for ferrous and non-ferrous alloys; and extrusion for thermoplastics and graphite.
3D printing works by laying down thin layers of heated material onto a platform. Either the head or platform will continuously be moving to deposit more material on top of each other to form the 3D object. Binders and powder can also be used to form 3D objects.
This 3D printing process is used with materials such as wax, thermosets, elastomers and graphite.
The liquid vat process solidifies thin layers together, using an ultraviolet (UV) curable thermoset polymer liquid with a solid state crystal laser to create the required geometry layer by layer, using Computer Aided Design (CAD) data. A recoater mechanism is used to cover the previous layer with the material enabling the next layer to be scanned.
This process produces thermoset materials.
S. Dadbakhsh, L. Hao (2012A) Effect of Al alloys on selective laser melting behavior and microstructure of in-situ formed particle reinforced composites, Journal of Alloys and Compounds doi: 10.1016/j.jallcom.2012.06.097
Dadbakhsh, S. and Hao, L. (2012B), In Situ Formation of Particle Reinforced Al Matrix Composite by Selective Laser Melting of Al/Fe2O3 Powder Mixture. Adv. Eng. Mater., 14: 45–48. doi: 10.1002/adem.201100151
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