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Additive Manufacturing and 3D Printing refer to a manufacturing process that creates a three-dimensional object through a series of “addition-material” operations, following the dimensions of a digital 3D model. The digital model is elaborated by a dedicated “3D printer” and it is then realized, printing layer by layer.
Additive printing today represents the new technological frontier in the industrial production sector. Thanks to it, the constructive limits given by traditional processes are overcome, making what was not previously possible.
This article contains excerpts from the paper, “Additive manufacturing and topology optimization applied to impeller to enhance mechanical performance,” by Francesco Cangioli, Giuseppe Lurisci and Simone Corbò of BHGE and Enrico Meli, Andrea Rindi and Enrico Boccini of MDM Laboratory in University of Florence.
The mechanical applications are dominated by the use of a metallic component, and so 3D printing is realized by sintering through a laser beam. 3D laser printers use the light emitted by a laser to melt, one layer at a time, a powder (either monocomponent, usually mineral, or a mixture of different materials).
A slightly different technology uses an electron beam, more energetic than a laser beam, to melt metal materials with greater speed but less accuracy. The advantages of these techniques are linked to the great variety of usable materials, including aluminum, steel, copper, titanium. 3D laser printers can produce geometrically complex objects with precision and speed, less need for support structures to lose during manufacturing and the pieces produced often have excellent mechanical qualities.
On the other hand, laser 3D machines and materials are expensive (for example, metals must be reduced to a very fine powder through a complex grinding process), energy consumption is often prohibitive, the creation of medium and large objects is extremely difficult for now, the surface of the objects is typically porous and most of the time it has to be further refined with traditional methods. The application of additive manufacturing techniques, for Oil & Gas equipment, in particular for the driven machine, as for instance centrifugal compressor or centrifugal pump, needs to consider some additional constraint that are specific for the market.
The choice of the material, for component that enter in contact with process gas/liquid must consider different aspects of the design:
High ductility at different operating temperature (that can go from cryogenic up to 400°C)
Corrosion resistance induced by the presence of water and C02 and/or with presence of H2S
Pitting resistance induced by presence of chlorides - high strength to sustain the working condition (pressure and speed)
Availability of the material in the market to get it in relatively short time and limited cost
Another important aspect to consider is performance. Driven units consume power to operate, so the high efficiency is a fundamental key performance indicator. A new manufacturing technique can’t be successful if it generates some additional constraint on the aerodynamic shapes optimization, on surface roughness or any other geometrical feature that can reduce the efficiency compared to traditional manufacturing methods.
Aside from manufacturing techniques, the mechanical optimization aiming to design lighter components is also of crucial importance. The weight reduction can be of fundamental importance either to improve structural behavior or, when applied to rotating components, to improve rotodynamic behavior. This can allow a more robust dynamic behavior or allow to run at higher speed.
Finally, this weight reduction can be an indirect way to improve thermodynamic performance and deliver lighter equipment, that can be of fundamental importance for off-shore applications. A final important aspect is the time to production and the availability. Whether in new projects or service operation, oil and gas industry is very sensitive to the lead time to procure and produce components and equipment to improve as much as possible the machines availability.
Having a manufacturing method that can reduce significantly the lead time to produce components, is of fundamental importance, to reduce the overall time to put in operation the plant. This is particularly important also for service operation and in particular for remote site, where a 3D printing machine, some metal powder and 3D CAD models, can arrive to substitute a complete chain of forging supplier, manufacturing supplier, workshops, transportations.
Additive Manufacturing release the designers from the traditional constraints, providing advanced means of producing complex mechanical parts. This advantage makes Additive Manufacturing the perfect enabler for topology optimization. In fact, through this methodology it is possible to design innovative concepts, not feasible with standard manufacturing technologies.
Topology optimization improves material distribution within a given design space, for a given set of loads and boundary conditions such that the resulting layout meets a prescribed set of performance targets. Although this approach has never been extensively applied before to centrifugals, the combination of multiple objectives and constraints makes topology optimization suitable for both static and dynamic mechanical performance improvement. This methodology has been applied to rotating components to: reduce the stress level; tune the natural frequencies; reduce the weight of the part.
These objectives can be applied alone or in combination, performing a single analysis or a multiple analysis optimization. This new technique can improve the performance compared to traditional ones for both 2D (low flow coefficient) and 3D (high flow coefficient) closed and open (unshrouded) impellers.
Combining Topology optimization and Additive Manufacturing therefore seems to be a very promising approach for obtaining optimized mechanical parts.