BR102018015314B1 - ACTIVE COOLING TECHNIQUE FOR ADDITIVE MANUFACTURING - Google Patents

Abstract

ACTIVE COOLING TECHNIQUE FOR ADDITIVE MANUFACTURING The present invention deals with an active cooling technique for additive manufacturing by deposition with directed energy (electric arc, LASER or other compatible material fusion-deposition sources), for the manufacture of metallic parts, based in the continuous and controlled quasi-immersion of the preform in a liquid cooling fluid throughout the entire period of its construction inside a vat. Thus, the cooling rate of the non-immersed part of the preform and the interpass temperature are controlled by the continuous and controlled regulation of the level of the cooling fluid blade and by heat exchange with its immersed part, already in temperature equilibrium with the fluid. . Therefore, by promoting better thermal management of the preform, it is possible to obtain greater manufacturing productivity and parts with better mechanical characteristics.

Description

Field of invention

[01]. The present invention relates to an active cooling technique for additive manufacturing by directed energy deposition with electric arc fusion-deposition of material, but not limited thereto, for the manufacture of metallic parts, based on continuous and controlled quasi-immersion of the preform in a liquid cooling fluid for the entire period of its construction inside a vat. The cooling rate of the non-immersed part of the preform and the interpass temperature are controlled by continuous and controlled regulation of the level of the cooling fluid blade and by heat exchange with its immersed part, in direct contact and already in temperature equilibrium with the fluid. The focus is to act on mitigating problems related to heat accumulation and at the same time preserving or even increasing the productivity of additive manufacturing by fusion-deposition of material using an electric arc, but not limited to it.

[02]. By controlling active/direct and continuous heat dissipation during manufacturing by additive manufacturing, the invention allows, regardless of the geometry to be constructed, to favorably regulate characteristics related to preforms in terms of microstructure and size/type of grain formed, properties resulting mechanics, distortions, residual stresses, deposition irregularities, oxidation and adhesion of splashes, in addition to toxic emissions (metallic fumes). In addition to favorably regulating characteristics related to preforms, the invention allows preserving or increasing the productivity of additive manufacturing by increasing the construction speed, which can occur without or with fewer stops, due to intense and continuous cooling, and/or with greater material fusion-deposition rate, as the corresponding increase in energy input is counterbalanced by a greater heat dissipation capacity provided by the efficient cooling strategy. Therefore, by promoting better thermal management of the preform, it is possible to obtain greater manufacturing productivity and parts with better mechanical characteristics. The active cooling technique for additive manufacturing object of this invention, regardless of the targeted geometry, combines the ability to build larger preforms, typical of processes with directed energy deposition technology, with the ability to build more regular preforms, typical of processes with technology of dust bed.

State of the art

[03]. In recent years, the way products are manufactured, including manufactured goods, has changed. To remain competitive, manufacturers have sought to produce with higher quality, but always seeking to reduce production times and costs. This line includes direct rapid manufacturing routes, which involve subtractive and additive processes. Subtractive, more traditional, are based on the removal of material to reach the final product, and typically consist of computer numerical control (CNC) machining. Additives, which are more recent, are based on the addition of material, and encompass a range of manufacturing processes. Broadly speaking, this technology is called additive manufacturing, in which, by definition, products are built layer by layer, using material addition technologies with a high degree of automation, based on computer-aided design (CAD). The layers are formed by a single pass or multiple passes of material deposition and are then stacked sequentially on a substrate supported on the construction platform to achieve at least an approximate geometry of the product. Additive manufacturing can also be used to modify and, in the event of damage, recover parts. With the demand for additive manufacturing focusing on final product applications, including for extreme situations in terms of performance, and not just for designing prototypes (more conducive to the domain of three-dimensional printing of polymers, known as 3D Printing), the feasibility of Metal parts through this manufacturing route have been the target of enormous research, development and innovation efforts in the mechanical manufacturing sector.

[04]. A major advantage of additive manufacturing lies in saving raw materials. Instead of starting from a volume of material in which parts will be removed and discarded, the material necessary to form the product is basically deposited, that is, the volume of raw material consumed is practically equal to or at least close to the volume of the product. manufactured. Thus, additive manufacturing represents an environmentally friendly manufacturing solution, as material waste in the form of chips can be drastically reduced, as can the expenditure of energy and other inputs with machining operations. Some additive manufacturing processes are capable of manufacturing products for immediate application, generating parts that meet the requirements (geometry and properties) for operation as designed. Other processes build preforms, that is, parts very close to the final shape of the respective parts, but which still need processing to meet the requirements (geometry and properties) for operation. Another advantage of additive manufacturing is the ability to manufacture parts with extremely complex geometries, difficult/impossible to be obtained by traditional means, and designed with a focus on functional performance efficiency and not on limitations of conventional manufacturing processes. Customization represents a strong characteristic of part designs to be manufactured using this direct manufacturing route. Additive manufacturing also allows the production of parts in hybrid materials and formed by metallic alloys produced in-situ (during manufacturing by combining wires and/or powders from different materials). For all these reasons, additive manufacturing has attracted the attention of various industrial sectors and is gaining more and more space.

[05]. Several processes can be used for additive manufacturing. When it comes to manufacturing metal parts, the main ones are those based on powder bed technology, such as sintering or selective melting by LASER and selective melting by electron beam. In these processes, thin layers of metallic powder are spread (deposited) uniformly on a construction platform, inside a chamber with inert gas or vacuum, and processed (sintered or melted) selectively (according to slices/horizontal planes taken of the project in CAD) and sequential, that is, the material is first deposited in one layer and, only then, its sintering/fusion. These material deposition-sintering/fusion processes allow the production of parts with complex geometry and great dimensional precision, with optimized mechanical properties, due to the metallurgical possibilities arising from different powders. However, powder bed technology requires high-cost energy sources, which makes dedicated equipment very expensive and beyond the reach of most companies. Furthermore, in general it is a slow construction technology and for parts of limited dimensions (contained by the chambers) and whose consumables are high in cost.

[06]. As an alternative, there are processes based on directed energy deposition technology, which perform the fusion and, immediately (almost simultaneously), the deposition of the material assisted by an intense and concentrated heat source, generally used for the manufacture of preforms. In this case, typical welding processes are used to deposit layers of molten metal, following trajectories defined by the geometry of the part to be manufactured, until, with constant solidification, a shape very close to the final product is obtained, but with some excess in dimensions, only requiring machining steps, generally for fine grinding and finishing. In the case of these material fusion-deposition processes, special energy sources (LASER or electron beam) can be used, but electric arc processes, considered conventional, and, therefore, already more widespread in industry in general and of lesser cost, such as TIG and MIG/MAG and even Plasma and Tubular Wire, can also be used. Despite not providing a resolution as good as that obtained with LASER or electron beam, especially with powder bed technologies, electric arc additive manufacturing processes allow the highest deposition rates, being ideal for large preforms and when there is no demand for very thin geometries and/or low heat input. However, such processes are always associated with an undesirable transfer and/or accumulation of heat in the preform. Furthermore, with these processes heat dissipation is significantly deteriorated with increasing height of the preform under construction, which makes heat accumulation even more problematic, and then the solidification of the deposited molten metal and its cooling can only be controlled by limited mode.

[07]. Due to the high melting temperatures, after which solidification of materials occurs, and from which neighboring regions within the preform are heated, the microstructure formed in electric arc additive manufacturing is significantly different from those found in mechanically formed materials ( rolled, forged, etc.) and even cast. The final microstructures and integrity of the material define the resulting mechanical properties. The exacerbated increase in temperature and a unidirectional heat flow can also cause an undesirable growth in the grain size of the preform, deteriorating its mechanical performance in general applications. Current literature (Henckell, P., Günther, K., Ali, Y., Bergmann, J.P., Scholz, J., Forêt, P., The influence of gas cooling in context of wire arc additive manufacturing - a novel strategy of affecting grain structure and size. TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. 2017. https://doi.org/10.1007/978-3-319-51493-2_15) corroborates this aspect, citing that preforms can suffer from grain coarse and constantly growing throughout the construction process. Thus, excessive heat can lead to the formation of large columnar grains that grow towards the height of the preform; Fine and equiaxial grains provide greater mechanical resistance in an isotropic way (with equal properties in all directions) in operations close to room temperature, the working situation of most metallic components.

[08]. Furthermore, the generation of very high temperatures in the preform under construction can cause excessive oxidation, resulting in mechanical fragility due to the inclusion of oxides (loss of ductility, fatigue resistance, etc.) and/or difficulties in the machining stage. due to the possible high hardness of the oxides formed. The literature (Wu, B., Ding, D., Pan, Z., Cuiuri, C., Li, H., Han, J., Fei, Z., Effects of heat accumulation on the arc characteristics and metal transfer behavior in wire arc additive manufacturing of Ti6Al4V. Journal of Materials Processing Technology. 2017. https://doi.org/10.1016/j.jmatprotec.2017.07.037), evaluating additive manufacturing with the TIG process, reports that oxidation increases due to heat accumulation with increasing construction height in the preform. According to the same source, the interpass temperature, i.e., the minimum temperature of the previous layer (single or multiple deposition) before the new passage of the source of energy input and material deposition, is a key factor in determining heat accumulation . In successive depositions of material with this process, it is observed that the average temperature of the substrate experiences a rapid increase during the first passes of the heat source and then reaches an equilibrium value. In contrast, the interpass temperature continues to rise throughout the remaining layers (less heat loss). Thus, during construction, the difference in subsequent interpass temperatures determines the accumulation of heat in the preform, which increases almost linearly with the number of deposition passes. Heat accumulation is attested as a critical factor that influences the stability of the construction process in terms of geometry, deposition defects, microstructural evolution and mechanical properties of the preforms obtained. Naturally, the interpass temperature could be ambient, but this would require a long waiting time between the execution of each of the deposition passes to form the layers and, thus, the preform (lower productivity).

[09]. The literature (Lei, Y., Xiong, J., Li, R., Effect of inter layer idle time on thermal behavior for multi-layer single-pass thin-walled parts in GMAW-based additive manufacturing. The International Journal of Advanced Manufacturing Technology. 2018. https://doi.org/10.1007/s00170-018-1699-1) also mentions that components manufactured via additive manufacturing by electric arc fusion-deposition of material typically go through many reheating cycles, resulting in a complex thermal interaction behavior between the current deposition pass and the previous ones (with consequences on the microstructure formed). Furthermore, the same source highlights that this thermal behavior can be significantly affected by many parameters of the manufacturing process. Substrate preheating temperature, deposition sequence and interpass time (time interval between each layer or single deposition pass), for example, are listed as they greatly affect thermal cycles and interfere with the temperature distribution and microstructure formed. Furthermore, especially in additive manufacturing with the MIG/MAG process, it is highlighted that high energy input and high material deposition rates often degrade the surface quality of the preforms, in addition to causing high stresses and thermal distortions. The literature (Suryakumar, S., Karunakaran, K.P., Chandrasekhar, U., Somashekara, M.A., A study of the mechanical properties of objects built through weld-deposition, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture . 2013. https://doi.org/10.1177/0954405413482122) also shows that during additive manufacturing with the MIG/MAG process, periodic thermal load produces non-homogeneous hardness values with increasing preform height.

[010]. Uncontrolled heat accumulation/dissipation also leads to varied thermal gradients, which, in turn, generate thermal stress fields, which can culminate in distortions of the preform and/or remain there as residual stresses. The first can obviously lead to loss of shape and dimensional quality and make it difficult to finish the part by machining. The latter, depending on the nature and external requests, may result in compromised performance, for example fatigue. These internal stresses occur due to non-uniform thermal contractions and expansions that are experienced by the preform as it heats and cools. They can result in distortion or collapse of the structure, if locally greater than the elastic limit of the material used. Otherwise, in residual stresses concentrated in regions of greater restriction to deformation. And even in cracks, if internal stress levels exceed the local rupture limit of the material. According to the literature (Soul, F., Hamdy, N., Numerical simulation of residual stress and strain behavior after temperature modification. Welding Processes. 2012. https://dx.doi.org/10.5772/47745), in addition to occurring in macroscopic level, as a consequence of non-uniform heating and cooling, thermally generated residual stresses can also be microscopic due to the mismatch of the coefficients of thermal expansion and contraction between different phases formed. In addition to distortions that may occur during additive manufacturing, they may also arise during heat treatment cycles necessary after the construction of the preform or completion of the part to correct other drawbacks of heat accumulation, such as, for example, the formation of undesirable microstructure.

[011]. In additive manufacturing, there is also the problem of irregular shape of the deposited layers, something directly determining the degree of need for machining passes before the part is put into use. A broad term, derived from the aerospace industry's buy-to-fly, called buy-to-apply, which measures the ratio of mass of raw materials required to build the preform and final mass of the part applied after machining, sums up the importance of obtaining preforms with good regularity; the more irregular the preforms are built, the more filler material is consumed (purchased) to leave excess for overcutting and the greater the need for machining to reach the final dimensions and finish suitable for the part's application. Preforms with better regularity result in greater effective volume, that is, greater use of the volume of material deposited for the geometry of the parts. Irregularities arise directly from the difficulty of controlling the melt pool in a stable manner on the preform, especially in depositions on tall and narrow preforms and with a high input of energy and/or mass. The literature (Wang, J.F., Sun, Q.J., Wang, H., Liu, J.P., Feng, J.C., Effect of location on microstructure and mechanical properties of additive layer manufactured Inconel 625 using gas tungsten arc welding. Materials Science and Engineering: A . 2016. https://doi.org/10.1016/j.msea.2016.09.015) even highlights that the molten pool grows as the number of deposition passes (layers) increases, which is justified by the accumulation of heat with increasing preform height (restriction of heat flow towards the substrate). The difference between the phases formed between different layers is also attested, which results in heterogeneity of the preform in terms of mechanical properties. But generally, to obtain greater productivity, it is necessary to operate with a greater input of energy and/or mass, which can further aggravate problems with heat accumulation. The literature (Henckell, P., Günther, K., Ali, Y., Bergmann, J.P., Scholz, J., Forêt, P., The influence of gas cooling in context of wire arc additive manufacturing - a novel strategy of affecting grain structure and size. TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. 2017. https://doi.org/10.1007/978-3-319-51493-2_15) mentions that the increase in energy from the fusion-deposition source affects negatively the width of the preform and increases the following work in the machining stage, and that homogeneous mechanical properties, including high tensile strength, can only be achieved with low energy inputs. Furthermore, according to the same reference, energy sources for additive manufacturing operating at high material deposition rates generate very high temperatures and vaporize part of the molten material, forming metallic vapors and fumes, generally toxic, which are released into the work environment.

[012]. Thus, in the additive manufacturing of preforms and metallic parts, the lack of control over the solidification and crystallization process of the material makes it difficult to obtain the desired geometry and mechanical properties. And so, generally what is produced falls short of adequately satisfying the requirements for direct and immediate application, making machining and heat treatments more present for the necessary corrections. Therefore, to make additive manufacturing with high energy and/or mass input commercially viable, it is extremely important to promote thermal management of the preform, through control of the application, distribution and removal of heat, before, during and after processing. construction, to control the microstructure and grain size/type formed, the resulting mechanical properties, mitigate distortions and residual stresses, deposition irregularities, oxidation, splash adhesion and even toxic emissions. Perhaps the most obvious way to minimize problems related to overheating of the preform is to wait for it to cool down after each deposition pass to a suitable temperature before executing the next pass, but this can take a long time, especially in depositions with high inputs of energy and/or mass, and would not be productive at all in terms of construction speed.

[013]. Different thermal management approaches for additive manufacturing, whether through cooling and/or heating applied to preforms and parts, and even for related welding processes, have been developed with a focus on mitigating problems related to localized application and heat accumulation. . Thus, problems with microstructure and size/type of grain formed, resulting mechanical properties, distortions, residual stresses, deposition irregularities, oxidation and toxic emissions can be overcome, even partially.

[014]. In general, it is possible to classify thermal management approaches for additive manufacturing as active or passive. In passive thermal management, the cooling and/or heating agent acts only on the construction platform and/or substrate before, during and/or after the construction period, i.e., the temperature control of the preform or part is carried out in a manner indirect through an intermediate element (building platform and/or substrate), which limits the scope of the effects of this approach. Active thermal management, in contrast to passive, consists of acting sharply on the characteristics of the preform or part through direct contact, total or partial, with the cooling and/or heating agent, generally a fluid, during and/or or after the construction period.

[015]. Patent US7326377B2, on a passive/indirect thermal management approach to moderate heat in the preform and its consequences, deals with a system for electric arc additive manufacturing that makes use of a heat extraction or imposition block, with circulation internal fluid around fins, coupled to the build platform. In the case of heat extraction, the cooling fluid used is preferably a liquid substantially colder than the block itself, which can be basically water, but possibly glycol, mixtures of glycol and water and even gases that assume a liquid state at very high temperatures. below that of the environment, such as liquid nitrogen or helium. In the case of heat imposition, heating devices can be incorporated into the block or used to heat the circulating fluid. A fluid circulation control system provides a mechanism for inducing high rates of cooling or heating as molten raw material is deposited onto the substrate. The advantages offered include control of oxidation and grain size of the preform, which allows optimizing the mechanical strength and ductility of the part. However, as the thermal management used is passive/indirect, there is a limitation on the extent of the effects, which are restricted to preforms of reduced height or to layers at levels closer to the temperature control block, therefore to the substrate. The invention presented here performs active/direct, therefore more efficient, and continuous cooling of the preform (in all deposition passes, regardless of the number of layers) always close to the level of energy input and material deposition. , which increases the ability to control the accumulation of heat and its various harmful consequences, including in terms of particle size and oxidation of the part.

[016]. In the same line of passive/indirect action, patent US2010242843A1 deals with a mandrel (support for rotating preforms) used as a construction platform for electric arc, LASER or electron beam additive manufacturing. To cool the preform under construction, this mandrel has a thermal conductivity greater than that of the deposition material and has internal channels for the passage of cooling fluid. The advantages achieved include the speed of manufacturing the preform and the achievement of improved mechanical properties, even if restricted to performances of limited height or layers closer to the mandrel. The invention presented here allows, in addition to improving the mechanical properties, regardless of the dimensions of the preform, to increase productivity even further by increasing the speed of building the preform (without stops and with more intense cooling) and manufacturing the part ( less machining due to better preform regularity) and/or being able to operate with a higher material fusion-deposition rate, which has a corresponding increase in energy input counterbalanced by a greater heat dissipation capacity provided by a more efficient cooling strategy .

[017]. Furthermore, patent CN107498043A deals with the use of cooling of the construction platform in additive manufacturing, but by fusion-deposition of metallic wire by electron beam. The control of indirect and continuous cooling of the preform, through internal fluid circulation on the construction platform, occurs in a closed loop based on monitoring its temperature. Thus, negative effects of low pressure on the melting and solidification of the material (spreading of the melting pool, low heat dissipation, etc.), inherent to the compulsory use of high vacuum in the electron beam construction chamber, are minimized. Although it cannot be used in electron beam additive manufacturing, due to difficulties in interaction between the liquid cooling fluid and the high level of vacuum, the invention presented here can act in a similar way, but to a greater extent, for other processes. operating at or near ambient pressure.

[018]. Patent US20170056975A1 includes, as part of its apparatus, an external heat control mechanism that is positioned next to the lower surface of the construction platform to then form a temperature profile in parts being manufactured by powder bed additive manufacturing. An induction coil below the construction platform allows it to be heated to maintain an adequate temperature profile on the part to prevent the formation of thermomechanical cracks. Therefore, a passive/indirect thermal management approach is also used for the part and applicable only in powder bed additive manufacturing, which does not offer the diversity of control over the various heat build-up effects typical of fusion additive manufacturing. deposition of material, as accomplished by the present invention.

[019]. In a similar vein, patent US2016271732A1 deals with a device for preheating the substrate and/or layers for use in additive manufacturing of metallic preforms by fusion-deposition of powdered material. The preheater, capable of generating heat through the passage of electric current and induction, is mounted in such a way as to accompany the energy source on the deposition trajectory, always close to and heating the substrate and/or previous layer immediately in front of the current deposition region. In this case, it is possible to form the melting pool more easily and thus travel the deposition trajectory more quickly and at the same time obtain a more suitable configuration of the first layer (greater spreading) for the deposition of subsequent layers and so on, since preheating increases the wettability of the melted material on the substrate, previously at room temperature, and/or on the other layers. Similarly, patent US20170355019A1 deals with the use of a heating element for at least part of the preform during additive manufacturing by fusion-deposition of material. The heating element, electric coil or other suitable device, is controlled based on the thermal image of the preform to avoid non-uniform heating of the preform, thus reducing defects related to non-uniform heating and/or cooling during construction. This reduces thermal gradients in the preform, improving distortion control and minimizing the risk of solidification cracks appearing in the preform. Although they can be used for additive manufacturing with material fusion-deposition, these two thermal management approaches do not operate with cooling to mitigate the various negative implications of heat accumulation, as the invention presented here accomplishes.

[020]. Other developments utilize both heating and cooling to address thermal management of preforms and parts. In this sense, patent US2016096326A1 deals with a plate-shaped construction base with multiple cooling and/or heating elements, which can be of different nature. This plate is used to selectively cool and/or heat the part being built just above, in order to constantly control the thermal gradient and temperature distribution generated and thus allow mechanical stresses of thermal origin to be reduced. Once again, this is a passive/indirect thermal management approach, as the cooling medium only contacts the base of the part, which restricts the effects to limited heights thereof. In contrast, the invention presented here, by operating a form of active/direct cooling, brings the positive effects of mitigating heat accumulation, such as controlling thermomechanical stresses, to the entire length of the constructed preform.

[021]. In the same vein, patent US6858816B2 proposes carrying out additive manufacturing in a powder bed also with passive/indirect thermal management of the part, in this case inside a heating or cooling jacket. The jacket, formed by heating or cooling rings, is used to heat or cool the surrounding powder and, therefore, the piece as it is constructed, thus acting to conduct subsequent more uniform cooling and thus reducing distortions. Despite acting during construction, this proposition is limited only to powder bed additive manufacturing processes and does not operate a cooling considered active/direct, as in the present invention. In other words, in this case the heat exchanger (jacket) does not come into direct contact with the part, which limits the thermal management capacity in question to optimize its characteristics.

[022]. Patent WO2017097252A1 involves the use of ultrasonic vibration combined with indirect heating or cooling of the part in powder bed additive manufacturing. In this case, the cooling, through fluid circulation, or heating, through the passage of electric current, of the construction platform helps the ultrasonic vibration to continuously affect the microstructure formed in the part and, thus, the resulting mechanical properties. As in other developments already carried out, the extent of the cooling or heating effects of the construction platform is limited to lower levels of the part, which is not true for the invention presented here.

[023]. Still addressing passive/indirect thermal management, patent US20150021815A1 deals with temperature control devices that can be coupled during at least part of the additive manufacturing process. In this case, a device attached to the build platform can indirectly control the cooling rate of the preform to result in the desired microstructure. This device may include a cooling element, such as coils for circulating air, water or oil, and/or fans. This makes it possible to increase the material deposition rate. Furthermore, other temperature control devices can act on the substrate before (preheating) the construction of the preform, to prevent distortions, and/or after (postheating), to provide heat treatment for annealing it. Despite not including heating, the invention presented here uses continuous cooling in an active/direct manner, therefore more efficient to mitigate distortions, residual stresses and the formation of microstructures and undesirable properties, in addition to oxidation, deposition irregularities and toxic emissions.

[024]. The literature (Cao, Y., Li, H., Liang, Z., Wang, D., Effect of Water Cooling on the Microstructure and Mechanical Properties of 6N01 Aluminum Alloy P-MIG- Welded Joints. Journal of Materials Engineering and Performance . 2017. https://doi.org/10.1007/s11665-017-2792-6), in a thermal management approach aimed at fusion welding, addresses the use of passive/indirect cooling through water circulation within a copper base on which the sheets to be welded are supported. In this case, in contrast to natural cooling, water cooling results in a lower peak temperature and a substantially higher cooling rate in the weld bead, leading to a decrease in the partially molten zone and the thermally affected zone. Thus, the total hardness of the welded joint is increased, resulting in the achievement of greater mechanical resistance under tensile loading. Although it works to optimize the characteristics of weld beads close to the passive/indirect cooling level (cooled base), this approach would be limited in additive manufacturing, as well as used in other approaches, as it does not keep the cooling always active close to the cooling level. energy input and material deposition. Unlike what happens with the present invention, in this case the cooling influence power would not act across the entire extension and construction height of the preform.

[025]. Patent DE102007057450A1 deals with an additive manufacturing method by selective irradiation of a liquid or powder bed by an energy beam, in which the part, at the end of construction, is cooled with a gaseous or liquid fluid within the construction space with the objective of improving the resulting microstructure and mechanical properties. Thus, despite employing active/direct thermal management, unlike what is carried out by the present invention, the method does not propose cooling the part concomitantly with its construction to minimize the accumulation of heat and its negative repercussions, which limits the effects achieved in intensity. and type, being more similar to a tempering treatment (rapid cooling) of the part after its construction.

[026]. Other developments use intermittent, albeit active/direct, cooling to promote thermal management of preforms and parts. Along these lines, patent US20170014906A1 deals with an additive manufacturing system using LASER sintering or selective powder bed fusion and includes a device for cooling the part. In this case, a distributor, from a compartment, simultaneously supplies cooling fluid across the entire width of the outermost layer of feed material spread over the entire construction area, after at least a portion of this outermost layer of material is fused. Thus, interspersed melting passes (after spreading the powder) and cooling by the fluid are carried out during the part construction process. In addition to accelerating the cooling of the layer, and thus reducing the waiting time for the formation of the next one, the system reduces spatial temperature fluctuations through and between the layers of spread feed material, thus reducing thermal stresses and improving the mechanical properties of the part. Patent US20170129185A1 also involves cooling interspersed with layer fusion to reduce distortions in the part in powder bed additive manufacturing. In this case, cooling is carried out through a system composed of two heat exchange elements. The first, mobile element, is used to cool the upper layer of the part under construction. The second element, fixed and cooled through internal fluid circulation, is used to cool the first element after it has removed heat from the part. Despite accelerating cooling compared to the conventional approach, which simply consists of waiting for natural cooling intervals, and is therefore time-consuming and unproductive, these two systems do not cool continuously, as in the invention presented here. Furthermore, they are designed only for powder bed additive manufacturing processes and cannot be used in processes with fusion-deposition of material, as in the invention presented here, which, moreover, allows increasing productivity by increasing the speed of preform construction (without stops for cooling).

[027]. In the same vein, the literature (Wu, B., Pan, Z., Ding, D., Cuiuri, D., Li, H., Fei, Z., The effects of forced interpass cooling on the material properties of wire arc additively manufactured Ti6Al4V alloy. Journal of Materials Processing Technology. 2018. https://doi.org/10.1016Zj.jmatprotec.2018.03.024) addresses the application of gas located in the preform for active/direct and intermittent cooling. In this case, CO2 is used applied through a nozzle installed next to a TIG torch used to build titanium preforms. To force rapid cooling of the preform until the temperature (monitored by a pyrometer) reaches the ambient value, the CO2 flow is only started after the deposition of each layer (in a single pass) of material (avoiding disturbance of the arc). When cooling is turned off, a new layer of material is deposited with an interpass temperature equal to that of the environment. As a positive result of this active/direct and intermittent cooling approach, better appearance of the preform is obtained (lower level of visible oxidation), refined microstructure, increased hardness and improved tensile strength (due to less oxidation between layers), in addition to better shape regularity. and a marked reduction in the waiting time between successive depositions (interpass time). However, unlike the invention presented here, in this case it is still necessary to stop deposition for forced cooling to be carried out, which still implies waiting time between material deposition passes, which further restricts productivity in terms of speed. of preform construction.

[028]. Other developments employ cooling and/or heating means that can be considered active/direct and continuous, that is, that permanently act in contact with at least part of the extension of the preforms or parts for more effective thermal management. Patent EP3069804A2 deals with a method with active/direct and continuous cooling and/or heating of preforms, preferably metallic, for additive manufacturing by selective LASER powder bed fusion or for material fusion-deposition processes. In this case, the preform is built with integrated cooling or heating channels, which can also be on the construction platform, in this case with individually sealable outlets, through which a fluid passes. The temperature and/or flow of the fluid, controlled based on the temperature measurement (thermography) of the preform and through an external cooling and/or heating system, are used to perform thermal management. The fluid used is preferably a liquid with high conductivity and thermal capacity, non-corrosive and non-flammable, and can be used multiple times through filtration. This can partially or completely fill the channels integrated into the preform walls, can overflow between deposition passes to provide protection against corrosion, oxidation and adhesion from splashes from molten material deposition, and even for lubrication and cooling in the case of interspersed machining passes. It can also flow at different temperatures through different channels, with preform temperature changes in time and space, generating a variable thermal gradient. Thus, the method makes it possible to instantly manage the heat coming from the fusion source and emanating from the preform, thus controlling the microstructure formed and resulting mechanical properties as well as residual stresses. Furthermore, it allows heat accumulation to be avoided and, thus, makes it possible to use a higher material deposition rate without deteriorating the resulting mechanical properties. However, to operate, the method requires the substrate to have holes aligned with those on the construction platform, for the fluid to pass through. It also requires that the part be at least partially modified in its three-dimensional CAD design before construction to include internal channels integrated into the preform walls, which requires more machining of the same to remove the volume of material with channels to reach the final geometry of the part. part. The invention presented here allows similar benefits to be achieved, but without the need to modify the three-dimensional CAD design of the part to integrate cooling channels, which require more machining, and eliminates the need for a substrate and construction platform with aligned channels. Furthermore, the invention presented here, by operating with completely exposed refrigeration fluid, also acts to capture toxic particles (vapors and fumes), reducing pollution of the working environment.

[029]. Patent DE102007009273A1 deals with a method for producing parts by additive manufacturing by selective irradiation with an energy beam on a powder bed. In this case, preferably at the end of the construction of the part, the surrounding compacted powder is at least partially crossed by a gaseous or liquid fluid for cooling or heating purposes in order to control distortions. Negative pressure is needed around the part to ensure fluid passage around it. Furthermore, the amount of heat dissipated or diffused strongly depends on the porosity of the powder around the part and it may be necessary to dry it before reusing it. The application is restricted to powder bed additive manufacturing processes and is therefore restricted to the production of parts of limited dimensions. Thus, despite promoting the thermal management of the part and its gains, unlike the invention presented here, the method is not applicable to additive manufacturing by fusion-deposition of material, which are aimed at even large preforms.

[030]. The literature (Yanagida, N., Koide, H., Reduction of residual stress in multilayer welded plates by applying water-shower cooling during welding. Journal of Solid Mechanics and Materials Engineering. 2008. https://doi.org/10.1299/ jmmp.2.943), in another thermal management approach aimed at fusion welding, mentions the use of a water shower behind the molten pool region in order to reduce the incidence of residual stresses in the part. In this case, in an active/direct way, the water quickly cools the high temperature region behind the area of heat entry into the part and is then sucked in, making it possible to even reach residual compression stresses (generally beneficial) in inversion. to tensile stresses generally remaining in this area. The rapid localized cooling induces immediate contraction of the region, causing it to be pulled by the rest of the part and then compressed when cooling continues. A similar approach could be employed for additive manufacturing, but unlike the invention presented here, which can intensely cool the entire preform, the effects would be limited due to only localized cooling.

[031]. There are also developments that employ active/direct and continuous cooling by applying localized gas to the preform. Along these lines, patent CN104959606A deals with a localized temperature control system for additive manufacturing of metallic parts by fusion-deposition of material in the form of wire or powder. In this case, temperature control is carried out during construction through a flow of gas, preferably inert, directed to the already solidified region of the preform, close to the material deposition head, through a cooling nozzle. After draining heat from the preform, the gas flow is sucked through the back of the nozzle and directed to a refrigeration unit to then return to localization. Controlling the flow rate and temperature of the gas flow is used to define the microstructure formed, including dynamically depending on the position in the preform. The literature (Henckell, P., Günther, K., Ali, Y., Bergmann, J.P., Scholz, J., Forêt, P., The influence of gas cooling in context of wire arc additive manufacturing - a novel strategy of affecting grain structure and size. TMS 2017 146th Annual Meeting & Exhibition Supplemental Proceedings. 2017. https://doi.org/10.1007/978-3-319-51493-2_15) also presents the application of additional gas flow as an approach to reduce the temperature of the preform in the deposition pass running in additive manufacturing with the MIG/MAG process. In this case, argon, hydrogen and nitrogen, depending on their thermal capacity and conductivity, are used to influence the microstructure and particle size formed in the preform. With the lower interpass temperature, refined grains are obtained throughout the entire height of the preform with more homogeneity of mechanical properties between layers. Furthermore, there is less need for machining to achieve the geometry of the part. However, the gas flow must preferably be applied to a region relatively distant from the source of energy input and material deposition to avoid disturbances to the source itself and the fusion pool. Thus, despite the advantages, the localized application of gas flow presents limitations in terms of cooling capacity, since a large portion of the heat can propagate in directions other than that of the region where the gas flow is applied. The invention presented here is capable of cooling the entire preform more uniformly and with greater intensity, by using a quasi-immersion approach in a liquid cooling fluid, which also makes it a low-cost solution to control characteristics of the preform. preform, such as formed microstructure and grain size.

[032]. Patent US20030075836A1 deals with an air cooling system for removing heat from polymeric parts built by additive manufacturing. In this case, a duct directs a uniform curtain of airflow over the layers during deposition. In additive manufacturing by fusion-deposition of material using an electric arc, this approach, in addition to having limitations in cooling power, would bring risks of contamination and disturbance of the electric arc and its shielding gas, the molten pool and, thus, the preform itself. In contrast, the invention presented here, by operating with a liquid cooling fluid close to, but never at the level of energy input and material deposition, offers high cooling capacity without risk to the heat source and the molten pool.

[033]. Focusing on mitigating problems related to heat accumulation and at the same time aiming to preserve or even increase the productivity of additive manufacturing by fusion-deposition of material using an electric arc, but not limited to the same, this invention deals with a technique for active cooling of the preform based on continuous and controlled quasi-immersion of the preform in a liquid cooling fluid throughout the entire period of its construction inside a vat. Thus, the cooling rate of the non-immersed part of the preform is controlled by the level of the liquid cooling fluid blade and the heat exchange with its immersed part, already in temperature equilibrium with the fluid. Therefore, with better thermal management of the preform, it is possible to obtain greater manufacturing productivity and parts with better mechanical characteristics. The active cooling technique for additive manufacturing object of this invention, regardless of the targeted geometry, combines the ability to build larger preforms, typical of processes with directed energy deposition technology (molten material deposition), with the ability to build more regular preforms , typical of processes with powder bed technology. List of figures Figure 1 - Basic schematic assembly for the operation of the active cooling technique for additive manufacturing Figure 2 - Cross-sectional and longitudinal views of the representation of temperature distribution in simple preforms (walls with single-pass deposition layers) during construction with different cooling approaches with the same number of layers, energy input and material fusion-deposition rate: (a) active/direct cooling; (b) conventional (natural) cooling; (c) passive/indirect cooling Figure 3 - Thermographic images obtained from preforms at the end of construction (soon after extinction of the electric arc) with different cooling approaches: (a) active/direct cooling; (b) conventional (natural) cooling; (c) passive/indirect cooling Figure 4 - Thermal cycle from the central region of the length of the twenty-third layer to the end of preform construction (28 layers of single deposition pass) with different cooling approaches Figure 5 - Height and width profiles (maximum) of preforms built with different cooling approaches Figure 6 - Central cross-sections of preforms built with different cooling approaches: (a) active/direct cooling; (b) conventional (natural) cooling; (c) passive/indirect cooling

Description of the invention

[034]. The present invention, as shown in FIGURE 1, deals with an active cooling technique for additive manufacturing by deposition with directed energy, preferably with an electric arc, but also applicable with LASER or other compatible material fusion-deposition sources, for manufacturing parts metallic materials based on the continuous and controlled quasi-immersion of the preform (A) in a liquid cooling fluid (B) throughout the entire period of its construction inside a vat (C). The liquid cooling fluid (B) used for this active/direct thermal management technique can be reused multiple times through filtration and is preferably water, but other pure liquids or in conjunction with water can be used, as long as they do not pose a risk of fire/explosion, such as, for example, addition of ethylene glycol, to increase the liquid state temperature range of the fluid and/or increase the cooling rate of the preform (A), and/or oil, to supernate the fluid as a way to minimize its evaporation rate and contamination of the preform by hydrogen. The technique includes using a level sensor (D) and inlet (E) and outlet (F) valves for the liquid cooling fluid (B) in the tank (C) activated by the rise of the torch (G) or the temperature of the preform (A) to control the separation distance (H) between the liquid cooling fluid blade (B) and the level of energy input and material deposition on top of the preform (A). It also includes using an external pumping, filtering and cooling system (I) for the liquid cooling fluid (B), whose temperature is controlled based on monitoring the temperature of the preform (A) using a temperature meter (J) , preferably without contact. Both the flow rate and the temperature of the liquid cooling fluid (B) are controlled using a controller (K). The cooling rate of the non-immersed part of the preform (A) is controlled by the separation distance (H) between the heating level, due to energy input and material deposition on its top, and the level of the cooling fluid sheet. (B) and by heat exchange with its immersed part, already in temperature equilibrium with the fluid. This separation distance (H) between the heating level and the upper level of the liquid cooling fluid (B) is previously chosen depending on the desired cooling rate and, thus, the desired characteristics of the preform (A), and has the following minimum limit to excessive vaporization of the liquid cooling fluid (B) that can disturb and/or contaminate the source of energy input and material deposition (L), preferably electric arc, and the molten pool formed. The invention preferably operates with the inlet and outlet of the liquid cooling fluid (B) in the lower part of the construction tank (C). However, for preforms with cavities, it also includes the possibility of using two nozzles for entering the cooling fluid mounted together, but with an adjustable distance, and leveled with the source of energy input and material deposition (L) and always aligned transversely to the direction of the trajectory of the deposition passes. In this case, as material is deposited, it fills with liquid cooling fluid (B), in addition to external regions, also internal regions (cavities) of the preforms, which will always be kept without heat accumulation. In this case, two level sensors are used individually to maintain the levels of liquid cooling fluid (B) equal on both sides, external and internal, by also individually activating two flow valves installed, one on each nozzle. The invention is designed to operate with circulation of liquid cooling fluid (B), but does not exclude the option of just gradually flooding the construction tank (C) to promote active/direct, continuous and rapid cooling of the preform (A) to the measure of increase in height. At the end of the construction of the preform (A), by deposition of the last layer of material, the level of the liquid cooling fluid (B) is raised at a controlled rate until the remainder of the preform (A), that is, the set of last layers hitherto unimmersed, is also immersed for the full effects of active/direct thermal management. The movement system used to operate the invention consists of axes for vertical (Z), longitudinal (X) and transverse (Y) movement of the material fusion-deposition head, that is, the torch (G), and an axis for rotational movement (W) of the vat (C) and, thus, of the construction platform (M), the substrate (N) and the preform (A) built on it, but does not exclude the possibility of using other axes of movement , such as for torch tilt (G).

[035]. The invention operates as if the construction platform (M) and the substrate (N), including intensified heat exchange capabilities (passive/indirect cooling), were always kept close to the level of energy input and material deposition, regardless of the height of the preform (A) and, therefore, the separation distance between the level of energy input and material deposition and the actual level of the construction platform (M) and substrate (N). Thus, the majority of the preform (A) is always below the layer of liquid cooling fluid (B) and at low temperature (in equilibrium with the fluid) and the remaining part is exposed to heating by the heat source and deposition of molten material (L), can be cooled at an accelerated rate by rapid conduction of heat to the cold part, adding to the cooling already obtained by direct contact of this remaining part of the preform (A) with the deposition atmosphere (O), formed by shielding gas and ambient air/gas, and by its emitted thermal radiation. The focus of the invention is to mitigate problems related to heat accumulation and at the same time preserve or even increase the productivity of additive manufacturing by fusion-deposition of material using an electric arc with filler metal in the form of wire and/or powder by the MIG/MAG, Tubular Wire, TIG and Plasma processes, in all their variants and techniques, but does not exclude the application to other energy sources, such as, for example, in additive manufacturing by fusion-deposition of LASER material with the addition of metal in the form of wire and/or powder.

[036]. By controlling active/direct and continuous heat dissipation during manufacturing by additive manufacturing, the invention allows, regardless of the geometry to be constructed, to favorably regulate characteristics related to preforms in terms of microstructure and size/type of grain formed, properties resulting mechanics, distortions, residual stresses, deposition irregularities, oxidation and splash adhesion, in addition to toxic emissions. By controlling the microstructure formed over the entire length of the preforms, it is possible to avoid the formation of undesirable phases and, thus, more easily obtain the expected performance over the entire length of the corresponding parts. The grains formed can be reduced in size and be equiaxed across the entire length of the preform to optimize mechanical properties in a homogeneous and balanced manner in different directions of the part. Residual stresses that are harmful to the mechanical strength of the part can be minimized by rapid, continuous and homogeneous cooling of the preform, which prevents varied thermal gradients and, thus, non-uniform thermal deformations and the formation of heterogeneous phases, eliminating the need for heat treatment to relieve stresses. . By avoiding non-uniform thermal deformations, distortions of the preforms are also minimized, which may, depending on the extent and intensity, require heat treatment for corrections and/or more machining to reach the shape designed for the corresponding parts. Deposition irregularities are minimized by obtaining smaller and more stable melting pools on the preforms under construction, even with high energy input and/or material deposition, and, thus, better shape and dimensional qualities are obtained. preforms, which minimizes the need for machining to reach the final shape and finish of the corresponding parts. The oxidation of the preforms can also be minimized throughout the rapid cooling achieved, which reduces possible embrittlement of the parts, due to the presence of oxides between deposition passes and between formed layers, and facilitates the machining stage by preventing possibly hard oxides from forming. and abrasives, which accelerate the wear of cutting tools, are present in the preforms. The almost total immersion of the preforms throughout the construction period minimizes the adhesion of possible spatter emanating from the melting-deposition of material, which reduces the need for machining for cleaning. Emissions, mainly formed by toxic metallic fumes, originating from vapors released from the deposited molten material and the weld pool, especially at high deposition rates to increase productivity, can be trapped in the cooling liquid always at a level just below the melting point. energy input and material deposition, which minimizes pollution of the working environment. In addition to favorably regulating characteristics related to preforms, the invention presented here allows preserving or increasing the productivity of additive manufacturing by increasing the construction speed, which can occur without or with fewer stops, due to intense and continuous cooling, and/or with a higher material fusion-deposition rate, since the corresponding increase in energy input is counterbalanced by a greater heat dissipation capacity provided by the efficient cooling strategy.

[037]. The technique object of this invention, as shown in FIGURE 2(a), uses an active/direct cooling approach for preforms manufactured by additive manufacturing. This cooling approach is capable of significantly affecting the characteristics of the preform (A) under construction due to the direct contact of the liquid cooling fluid (B) with all its layers inside the tank (C), with the exception of some last ones just below the level of energy input and material deposition (level of heat source and melted material). The liquid cooling fluid (B) removes heat directly from the preform (A), significantly reducing the interpass temperature, i.e., the minimum temperature of the previous layer before the new passage of the source of energy input and material deposition, thus significantly reducing the accumulation of heat, represented by the temperature distribution, in the preform (A) as construction is carried out. It can be said, then, that the heat flow just below the deposition region assumes a three-dimensional and balanced regime, inducing a cooling close to isotropic (equal in all directions), which confers balance of properties in the directions (typically vertical and horizontal) of growth of the preform (A). As the level of the liquid cooling fluid (B) continually rises with the level of the heat source and melt, this effect and its benefits, as well as other favorable effects, are maintained in all deposition passes and layers, not importing the height of the preform (A) built. In addition to being controlled by the temperature and circulation/flow of the liquid cooling fluid (B) and by the separation distance (H) between the blade of this fluid and the level of energy input and material deposition, the preform cooling rate (A) is regulated by its thermal capacity and conductivity. The thermal capacity measures the power of the liquid cooling fluid (B) to store heat removed from the preform (A). Thermal conductivity measures the power of the liquid cooling fluid (B) to dissipate the heat stored in the preform (A).

[038]. For comparison purposes, as shown in FIGURE 2(b), in the conventional (natural) cooling approach, the interpass temperature and, thus, the heat accumulation in the preform (A) can be reduced only by direct contact with the atmosphere of deposition (O), formed by the shielding gas and ambient air/gas, and by the thermal radiation emitted by it, in addition to the heat extraction promoted, at least initially, by the substrate (N) and the construction platform (M) , which, in general, are initially at room temperature. In this case, both the preform (A) and the substrate (N) and the build platform (M) are cooled only by the surrounding gaseous deposition atmosphere (O) and this can require a lot of waiting time between deposition passes to maintaining a certain interpass temperature to control the characteristics of the preform (A), compromising productivity by reducing construction speed. The heat extraction promoted in this approach is precarious, and it can be said that the heat flow has a two-dimensional and unbalanced regime (more in the vertical direction than in the horizontal) in the preform (A), inducing an orthotropic cooling (different depending on the direction) and, therefore, imbalance of mechanical properties resulting in the directions (typically vertical and horizontal) of its growth and other harmful effects.

[039]. Still for comparison purposes, as shown in FIGURE 2(c), in the passive/indirect cooling approach for the preform (A), or active/direct only for the construction platform (M) and/or substrate (N), the temperature of interpass, and thus heat accumulation in the preform (A) can be reduced indirectly by direct contact of the liquid cooling fluid (B) with the build platform (M) and/or substrate (N). The liquid cooling fluid (B) draws heat indirectly from the preform (A) as it directly cools the build platform (M) and/or substrate (N) below. Thus, it can be said that the heat flow below the deposition region also assumes a two-dimensional and unbalanced regime (more in the vertical direction than in the horizontal) in the preform (A), as in the conventional (natural) cooling approach, but slowed down. , inducing still orthotropic cooling (different depending on the direction), but with less imbalance between directions (typically vertical and horizontal) of growth. In this way, even if more restricted to deposition passes and layers closer to the construction platform (M) and/or substrate (N) or to preforms of limited height, it favors the reduction of imbalances in mechanical properties resulting as a function of the direction of their growth. As the level of liquid cooling fluid (B) in this approach does not rise with the level of energy input and material deposition, the effects of passive/indirect cooling are restricted to low-height preforms or deposition passes and initial layers .

Example

[040]. For the purposes of demonstrating the present invention, results are presented from the use of active/direct, continuous and rapid cooling of preforms using water at room temperature as the cooling fluid. Gradual flooding of the construction tank was used without external circulation of fluid, but always at a level just 15 mm below the level of energy input and material deposition throughout the entire construction period. Preforms with conventional (natural) cooling, with only heat exchange with the external environment, and with passive/indirect cooling, by cooling with water in contact only with the construction platform, are taken as a comparison parameter. All preforms constructed consist of walls of approximately 250 mm in length with 28 layers (each with a single deposition pass) stacked in a back-and-forth sequence (zigzag inversion of the direction of the deposition path at each layer) and without stops between the execution of layers (interpass time equal to zero). As a deposition process, the MIG/MAG CMT (electric arc with metal transfer by controlled short circuit) was used, integrated into a six-axis industrial robot, with a torch displacement speed of 60 cm/min, with the addition material being Al 5356 wire with a diameter of 1 mm fed at 8.2 m/min, contact tip distance of 12 mm, argon shielding gas at 15 L/min, with an average power of the heat source (electric arc) of 765 W (average deposition current of 90 A and average arc voltage of 8.5 V). The substrate used in all cases was Al5052 with 300, 40 and 3 mm in length, width and thickness, respectively. Under the same energy input and melt deposition rate, the preforms constructed with the three thermal management approaches were evaluated in terms of thermographic image and thermal cycle (obtained using an infrared camera) and geometry (maximum height and width measured with caliper and cross-section image).

[041]. Figure 3 shows thermographic images obtained from the preforms at the end of construction (soon after the extinction of the electric arc) for the three cooling approaches evaluated. In Figure 3(a) it is clearly noted, even in qualitative terms, that the preform built with active/direct cooling has lower temperature levels throughout almost its entire length, including most of it at room temperature. Only the region close to the final point of incidence of the electric arc is hotter. This reveals that the continuous rise in the water level, closely following the level of energy input and material deposition throughout the construction period, drastically reduces the accumulation of heat in the preform, even without waiting stops between successive passes. deposition (layers). Preforms built with conventional (natural) cooling, as shown in Figure 3(b), or passive/indirect cooling, as shown in Figure 3(c), exhibited high temperature levels throughout. In other words, after construction time, in both cases there was a large accumulation of heat.

[042]. In quantitative terms, Figure 4 presents the thermal cycle results from the central region of the length of the twenty-third layer until the end of the preform construction, that is, during the execution of the last five deposition passes (layers), with the different approaches of cooling. It can be clearly seen that the preform built with active/direct cooling has lower interpass temperatures (lower levels of the cycle) (close to the ambient level) and practically unchanged until the end of construction and that the cooling rates (from peak levels for lower temperature levels) are significantly more intense. The preform built with a conventional (natural) cooling approach exhibits successively increasing interpass temperatures and continuously decreasing cooling rates until the end of construction, in clear correspondence to the greater heat accumulation occurring. The preform built with a passive/indirect cooling approach resulted in thermal cycles of intermediate dynamics. The higher cooling rate obtained with the active/direct approach, more easily comparable after the last deposition pass (layer), illustrates the potential for increasing the preform construction speed (productivity gain) due to the non-need for waiting time. cooling between passes (layers) and/or by allowing higher rates of material deposition, generally linked to greater energy inputs. These thermal analysis results prove the effectiveness of the present invention to prevent heat accumulation in the preform regardless of the construction height.

[043]. As graphically presented in Figure 5, in terms of geometry, the preform constructed with active/direct cooling was considerably taller and narrower in relation to the preform obtained with conventional (natural) cooling, with the preform obtained with passive/indirect cooling having the appearance intermediary. These results can be related to the lower and constant interpass temperatures obtained with active/direct cooling, which result in lower and controlled wettability (spreading of melted material) between the deposition passes and, thus, in higher, narrower and more regular layers. . It is also noticed that there is less variation in height and width along the length of the preform built with active/direct cooling. Even at the ends, with the reversal of the deposition direction and immediate rerouting of the heat source and molten material deposition, thermal management according to the present invention is capable of minimizing heat accumulation. This greater shape constancy results in less need for fine grinding of the preform to reach height and width values with uniform geometry in the eventual part.

[044]. From the central cross-sections of the preforms built with the different cooling approaches, shown in Figure 6, one can see, in addition to the greater height and smaller width, the better layer-to-layer form regularity obtained with active/direct cooling. This result is explained by the smaller melting pool obtained, which is maintained throughout all material deposition passes (layers), by the reduction and constant control of heat accumulation. For the other two cooling approaches, even more notably for the conventional (natural) case, the preforms have a gradually increased width, and consequently a smaller final height, even without changes in the energy input and melt deposition rate. , due to the constant increase in interpass temperatures and then heat accumulation. The combination of layer-to-layer width regularity and height uniformity of the constructed preforms is essential in additive manufacturing, as it maximizes the effective volume, that is, that which is deposited and can be used for the final geometry of the part, thus minimizing raw material waste in the next stage of fine roughing and/or finishing machining.

Claims (20)

1. ACTIVE COOLING TECHNIQUE FOR ADDITIVE MANUFACTURING, characterized by employing the continuous and controlled quasi-immersion of metallic preforms (A) in a liquid cooling fluid (B) throughout the construction period inside a vat (C). 2. COOLING TECHNIQUE according to claim 1, characterized by using water as liquid cooling fluid (B), but not excluding the use of other pure liquids or in conjunction with water, such as the addition of ethylene glycol, to increase the interval of liquid state temperature of the fluid and/or increase the cooling rate of preforms (A), and/or oil, to supernate the fluid as a way to minimize its evaporation rate and contamination of the preform by hydrogen. 3. COOLING TECHNIQUE according to claim 2, characterized by controlling the cooling rate and the interpass temperature and, thus, the accumulation of heat in preforms (A), by selecting the separation distance (H) between the blade of liquid cooling fluid (B) and the level of energy input and melt deposition. 4. COOLING TECHNIQUE according to claim 2, characterized by capturing in the liquid cooling fluid (B) a large part of the toxic emissions (vapors and metallic fumes) and spatter that emanate from the melting-deposition of material during the construction of preforms (A), controlling, respectively, the pollution of the work environment and the adhesion of splashes therein. 5. COOLING TECHNIQUE according to claim 3, characterized by automatically maintaining the level of the liquid cooling fluid (B) at a given pre-fixed distance from the level of energy input and melt deposition by means of a flow control driven by the rise of the torch (G) (source of energy and deposition) or by the temperature of the preform (A) throughout the construction time. 6. COOLING TECHNIQUE according to claim 5, characterized by controlling the temperature of the liquid cooling fluid (B) through flow and temperature imposed by a pumping, filtering and external cooling system (I). 7. COOLING TECHNIQUE according to claim 6, characterized by controlling the temperature of the liquid cooling fluid (B) as a function of the temperature measured in the preforms (A) by means of a temperature meter (J). 8. COOLING TECHNIQUE according to any of the previous claims, characterized by controlling the productivity of preform construction (A) by allowing reduction or elimination of waiting time between deposition passes (layers). 9. COOLING TECHNIQUE according to any of the previous claims, characterized by controlling the productivity of preform construction (A) by allowing operation with greater energy input and higher material melting-deposition rate (L). 10. COOLING TECHNIQUE according to any of the previous claims, characterized by controlling the size of the molten pool in preforms (A) and, thus, the flow of deposited molten metal and toxic emissions into the working environment. 11. COOLING TECHNIQUE according to claim 10, characterized by controlling the geometric regularity of preforms (A). 12. COOLING TECHNIQUE, according to claim 11, characterized by controlling the effective volume of deposited material and, thus, minimizing the amount of machining required to transform preforms (A) into parts. 13. COOLING TECHNIQUE according to any one of the previous claims, characterized by controlling and balancing the cooling rates of deposits and layers and, thus, of preforms (A), in all construction directions. 14. COOLING TECHNIQUE according to claim 13, characterized by controlling the microstructure and grain size of preforms (A). 15. COOLING TECHNIQUE according to claim 14, characterized by controlling the mechanical properties of preforms (A). 16. COOLING TECHNIQUE according to any one of the previous claims, characterized by controlling the oxidation of deposited layers and, thus, of preforms (A). 17. COOLING TECHNIQUE according to any one of the previous claims, characterized by controlling distortions in preforms (A). 18. COOLING TECHNIQUE according to any one of the previous claims, characterized by controlling residual stresses in preforms (A). 19. COOLING TECHNIQUE according to any of the previous claims, characterized by not inducing porosity in preforms (A). 20. COOLING TECHNIQUE, according to any of the previous claims, characterized in that it can be applied with directed energy deposition processes with fusion-deposition of electric arc material with filler metal in the form of wire and/or powder by the processes MIG/MAG, Tubular Wire, TIG and Plasma, in all their variants and techniques, but does not exclude the application to other energy sources, such as, for example, in additive manufacturing by fusion-deposition of LASER material with addition of metal in the form of wire and/or powder.