RECENT DEVELOPMENTS IN WORKPIECE REPAIR USING ADDITIVE MANUFACTURING TECHNOLOGY
Institute for Advanced Studies (IEAv)
An essential part of the concept of the service life of a part or component is its ability to perform a given pre-established function. In today's industry, it is common to discard complex parts, tools and components due to slight geometry deviations, wear, corrosion or fatigue. Many of these defects are superficial and pose no operational or human risk, as long as that material is fit for purpose. Hybrid manufacturing has brought about the possibility of eliminating the defective part while keeping the core intact and adding a new material with properties consistent with operational requirements. Hybrid manufacturing repair studies are already underway in various research groups, with the main feature of being more easily transferable to the productive sector than an integral AM part. Here research is being directed at some particular demands, which are part of the original proposal and demand synergies between project members. The H13 steel die and mould repair part began with simpler PBF experiments at the IEAv facility and then gone into hybrid manufacturing at EESC. At this time, studies on metallurgy and phase transformations are being performed in Ryerson University and have shown low dilution and few defects, with epitaxy as required in these cases. Tube repair of the pneumatic aircraft system is being studied, although we have not yet started the experimental part on the tubes. Preliminary results on prismatic samples indicate substantial corrosion resistance gain when tube repair (AISI 347 steel) is made with 316L stainless steel. Steam turbine blades, grade AISI 420 steel, will be the subject of ITA's thesis study next year. The distortion and residual stress mitigation part are already underway, with the finite element modelling part and initial experiments already carried out at ROMI facilities. Two lines of research using PBF (Biofabrics) are beginning, one with laser shot peening of titanium prostheses and another in the manufacture of satellite elements in titanium, although not fully linked to the subject of repair. As can be seen, there are several collaborative research opportunities in the area of hybrid manufacturing.
Collaboration:
IPT: steel powder developments.
Biofabris: LBF support and expertise.
International collaboration:
Department of Mechanical and Industrial Engineering, Ryerson University (Toronto): microstructure and mechanical behavior of H13 tool steels after AM
Industrial Engineering Department, Padova University: hybrid manufacturing of tubes for hot sections
Centro de Ingeniería y Desarrollo Industrial (Mexico): Laser shot peening of titanium prostheses
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SOFTWARE FOR ADDITIVE MANUFACTURING DEVELOPMENTS
Centro de Tecnologia da Informação Renato Archer
The integration between the Directed Energy Deposition (DED) and the High-Speed Machining/Grinding (HSM/G) processes includes challenges associated with the hardware and software development. In parallel to the physical integration, it is required the development of toolpath strategies for a complete hybridization. Hence, algorithms are being developed through visual scripting, which is widely used for digital fabrication. In an initial stage, a toolpath generator was created for the DED process, taking into account the parameters of the machining center ROMI D800 and the DED printing head. This visual script works with a three-dimensional object as input, which is sliced using constant or adaptive layers. Then, after a sequence of algorithms for the raster calculation, a g-code file is obtained. This latter is simulated using open-source CAM software, aiming to validate the functionality of the toolpaths. In the next steps will be developed algorithms for the HSM/G process and to integrate the two processes. Finally, the g-code files will be validated through simulations and in the machining center in a real fabrication process.
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METALLIC POWDER FOR ADDITIVE MANUFACTURING AND DEVELOPMENTS
Institute for Technological Research
The production of metal powders is a primordial step in the manufacture of parts by AM. The type and configuration of the atomization process by which metal or alloy is processed influences directly particle size and morphology, affecting the quality of manufactured products. This work aims to study the operating parameters of the gas atomizer in order to obtain the desired size distribution and morphology of the H13 and 316L steel particles, which are ideal for the DED and PBD processes. Partial results for 316L show that increasing the atomization pressure results in a finer powder with higher yield in the desired particle size range (44 to 105 µm), but the shape ratio is not affected by the pressure difference. For comparative purposes, the rheological properties of 316L powder produced at different pressures and commercial 316L were analyzed in the same particle size range. According to the analyzes, the powder produced rheological properties compatible with commercial powder, with no “satellites” particles, allowing its application in DED process. In addition, in order to better understand and predict particle size distribution, a study is done to elaborate computational fluid dynamics models related to metal atomization.
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HEAT TREATMENTS IN ADDITIVE MANUFACTURING COMPONENTS
Prof. Éder S. N. Lopes, and MSc. Eduardo B. Fonseca (UNICAMP)
AISI H13 tool steel is widely used as mold and die materials due to its elevated hardness at high temperature and resistance to thermal fatigue. However, tool geometries are limited by conventional fabrication techniques, which can be overcome by additive manufacturing. Nevertheless, thermal cycle of powder bed fusion may cause cracking and other processing defects, which are detrimental for mechanical properties. Thus, it is instrumental to determine adequate processing parameters for powder bed fusion of H13. Powder bed fusion experiments were performed with varying laser power (97 to 216 W) and scan speed (300 to 700 mm/s). Consolidation was evaluated by helium gas pycnometry, optical microscopy and Archimedes' principle. High energy density parameters resulted in gas pores within the tracks and low energy density parameters caused lack of fusion between tracks. Consolidation of up to 99.97% was obtained at appropriate processing parameters. Microstructure of parts produced by different parameters was assessed by optical microscopy, scanning electron microscopy, Vickers hardness, and nanoindentation hardness. Solidification structure was cellular/dendritic, and martensite was formed during processing, along with 16-30% retained austenite. A heat affected zone was formed by deposition of adjacent layers, where martensite tempering partially occurred. Alternating layers were observed to form as a result of the intrinsic thermal cycle during processing. As-built parts were tempered in a thermomechanical simulator coupled to the diffraction beamline of a synchrotron source (XTMS at LNLS/CNPEM). Lattice parameter and peak width were calculated to evaluate the extension of tempering in the temperature range of 550 to 650°C.
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