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GENER AL AVIATION 32 JANUARY/FEBRUARY 2017 AIRCRAFT MAINTENANCE TECHNOLOGY on the "job box" a vertically moving table. Each layer of sand/resin is then polym- erized - sprayed by a "print head" with a catalyst component - what binds the sand to a solid structure in a required form. When the mold is printed, the loose sand is mechanically removed (air blasted, brushed away) and the different cores are assembled to make the final mold. When using this fully digital, tool-less process, complexity is no more a deter- mining factor. Any part that has been cast can be easily remanufactured. 3-D sand- printing allows a high degree of shape complexity. Sand printing of the mold sand cores is done by additive layer deposit (ALD) or additive manufacturing (AM). It works like a big "jet printer" work- ing over a vertically moving (lowering) flat "job box." A thin layer of sand is spread on the job box. This sand has been previously mixed with one of two components of a special resin. The sand thickness may vary between 0.3 and 1 mm, depending on the accuracy and speed required. The process is very sensitive to the type and amount of resin, and very specific sand is used, which allows a controlled thick- ness and granulometry of the layer. This is a part of Ventana's know-how, that has been developed through a long set up, to be applied to widely used aeronautical magnesium and aluminum based alloys. This thin layer of sand is then sprayed through the printer head with the resin's catalyzer to build up the core where the sand has to remain solid. The loose sand that has not been sprayed is kept in place during the process to support the next layers and allows vaults and arch type geometries to be easily built. This iterative cycle is repeated until the cores are completely built. Multiple imbricated cores can be printed during the same session, permitting the full box volume use and reducing the (expensive) sand losses. The mold is usually printed in several parts to allow a perfect cleaning (loose sand removal) and assembled before pouring. After each layer has been sprayed where it should, the box lowers from the sand layer thickness, and another layer spread- ing and spraying cycle is started. Printing can last from several hours to one or more days depending on multiple factors like requested accuracy, cores volume… CASTING Molten metal is poured into the mold on a low-pressure casting station via a complex feeding network that ensures the integral filling of the mold. Once the mold has cooled down, it is shot blasted to remove the remaining sand from the metal part, and the feeding net- work is cut away. INSPECTION The part then follows an inspection pro- cess that includes geometrical digital scan- ning, radiography, and other checks. The process is similar to the one used for the aeronautical jet engine parts manufactured by Ventana. HEAT TREATMENT To achieve the desired mechanical proper- ties, light alloys are heat treated. Through this process, as it is identi- cal to traditional foundry, the mechani- cal properties and resistance are strictly identical to a casting that would have been obtained through a traditional (not 3-D) pattern casting. TESTING The complete range of NDT (nondestruc- tive testing) is being implemented, from X-ray to automated (PT) fluorescent dye penetrating test - all according to the speci- fications of the contracting parties. Parts are checked for internal defects and correct metallurgical characteristics, all according to the specifications that are part of the reverse engineering process. MECHANICAL MACHINING The cast, if defect-free, is machined on a fully digital, high-precision CNC machines at the Ventana facility with the help of data obtained in the digitization process. If needed, high-precision line boring can be performed, in its own traditional engine machining shop. This can include main and rod bearings boring. COST AND TIME The costs and time exposure are difficult to determine in most reverse engineer- ing processes because those figures are influenced by a number of factors. This depends on the nature and complexity of the part to be restored and the quality of delivered/available original part and blue- prints. This process uses costly equipment and requires considerable design and engi- neering effort. While costs are higher than those of original parts that were manufac- tured in large quantities with a high degree of industrialization, they are much lower than traditional methods for limited quan- tities as no specific tooling is required, and real-life casting testing is dramatically reduced. Traditional, negative forms aren't necessary, which for large series can cost several hundred thousand dollars. Cost level is a function of part complex- VENTANA AND VINTAIR A Renault engine housing is being remanufactured for a Stampe SV4 airplane, with French certification. In this example, the French companies Ventana and Vintair cooperate and manufacture a crankcase using a highly digitalized process. Ventana is a major French aerospace subcontractor. With its four foundr y facilities, high precision machining and sheet metal capabilities, Ventana covers many of the required fields and competences when it comes to remanufacturing. Ventana customers are located worldwide, including Airbus, Rolls Royce, and Pratt & Whitney. Vintair is a small company dedicated to vintage and collection aircraft. It specializes in restoration of vintage engines and has developed reverse engineering skills useful in that field.