Ceramic compositions for additive manufacturing of metal objects

Abstract

The disclosure concerns printable refractory compositions, more particularly ceramic- based pastes for 3D printing of molds for additive metal casting. In particular, the present disclosure concerns composition for forming mold regions having modified thermal conductivity and dissipation and increased release of gaseous products therefrom during heating to mitigate mechanical failure risks in an additive casting process of metal objects.

Description

[0001] Ceramic compositions for additive manufacturing of metal objects

[0002] TECHNOLOGICAL FIELD

[0003] The present disclosure concerns printable refractory compositions, more particularly ceramic -based compositions for 3D printing of molds for additive metal casting.

[0004] BACKGROUND ART

[0005] References considered to be relevant as background to the presently disclosed subject matter are listed below:

[0006] US patent application publication no. 2015 / 0246387

[0007] PCT patent application publication no. WO2019053712

[0008] PCT patent application publication no. WO2022243921

[0009] PCT patent application publication no. W02023002468

[0010] US patent application publication no. 2020 / 269320

[0011] PCT patent application no. PCT / IL2022 / 051191

[0012] European patent publication no. EP2014392

[0013] PCT patent application publication no. WO2021015626

[0014] Chinese patent application publication no. CN 112545066

[0015] Chinese patent application publication no. CN 117923909

[0016] Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

[0017] BACKGROUND

[0018] Casting is one of the oldest material-forming methods still used today. The principal process had not changed since 3200 BC when bronze was melted and poured into a stone mold. Metal casting is defined as the process in which molten metal is poured into a mold that contains a hollow cavity of a desired geometrical shape and allowed to cool down to form a solidified part.

[0019] Most of the world's demand for metal casts is addressed nowadays by traditional casting techniques. While automation solutions are applied, traditional casting involves the global production of molds and the global application of molten metal. For example, additive manufacturing techniques are used for mold fabrication with the implementation of mold curing, sintering, or otherwise mold curing (partially or fully) as a global operation before metal pouring. Molten metal is poured into fully fabricated molds.

[0020] Currently available metal additive manufacturing technologies address complex design and low volume applications of relatively small-size parts. Scaling from small parts to large parts of hundreds and thousands of kilograms is not trivial. In several currently available metal additive manufacturing technologies, size and weight scaling- up involves part deformation, distortion, shrinking, fracture, cracking, and more.

[0021] In some technologies for additive manufacturing of metal object, ultra-thin layers of mold composition are deposited. Due to the small dimensions of the layers, production of large metal object is a lengthy and costly process. Such thin layers prevent casting of large volumes of metal in each casting cycle.

[0022] Despite the advantages of metal additive manufacturing, the associated high cost, low throughput, and scaling-up challenges prevent the adoption of additive techniques for widespread industrial use, especially for manufacturing iron and steel parts.

[0023] Casting is widely used for industrial manufacturing of large production quantities and sizable parts in a one-piece cast. Metal casting can produce complex shapes and features like internal cavities or hollow sections can be easily formed. Materials that are difficult or expensive to manufacture using other manufacturing processes can be cast. Compared to other manufacturing processes, existing casting is cheaper for medium to large metal quantities, especially for iron and steel casting.

[0024] Modem metal casting also has several disadvantages. Patterns and molds are timeconsuming and expensive to manufacture. Additive manufacturing processes, such as binder jetting, are typically used to create patterns and molds. However, the fabrication of patterns and molds extend the lead time and limit design flexibility for modifications and adaptations. Additionally, minor post-processing or significant additional postprocessing operations are needed for certain applications. Furthermore, metal casting is a hazardous activity, as it involves many elements such as furnaces, molds, cooling areas, and additional tooling that are manually operated and exposed, while operating at very high temperatures.

[0025] An example of a system and method for additive metal casting is described in PCT patent applications publication numbers WO2019053712A1, W02023002468 and WO2022243921A1 assigned to the assignee of the present application, which are incorporated herein by reference. The method described therein includes depositing a first portion of a mold (mold region), pouring liquid substance into the first portion of the mold to form a first casted layer (object region), solidifying at least a portion of the first casted layer, depositing a second portion of the mold on top of the first portion of the mold, pouring the liquid substance into the second portion of the mold to form a second casted layer on top of at least a portion of the first casted layer, and solidifying at least a portion of the second casted layer. Thus, in a sequential manner, a stack of production layers is produced on a building table, each production layer is composed of a mold region and an object region. The mold region may be constructed in-situ, by mold paste deposition, or ex-situ, by placing remotely fabricated mold region frames. The object region is produced by depositing molten metal into the mold region, one production layer after the other.

[0026] GENERAL DESCRIPTION

[0027] In the additive casting process, namely in a casting-in-layers process, a metal object region is cast in each production layer by depositing molten metal into a cavity defined by a mold region. A layer of mold composition (typically in paste form) is first deposited according to a pre-defined pattern to form a mold region, at least partially cured, and then molten metal is cast into the cavity defined by the mold region to obtain an object region that is laterally encased by the mold region. The deposited molten metal is then permitted to partially cool and solidify, thereby allowing subsequent deposition of an ensuing layer of mold composition.

[0028] Thus, the casting-in-layers process includes deposition cycles, in each cycle a mold region and a metal object region are formed to define together a production layer, followed by subsequent deposition cycles, until the entire desired object is obtained. In other words, a continuous sequence of deposition cycles is carried out, in each cycle a mold region is deposited first, followed by casting of a metal object region, to obtain a stack of production layers which result in a combined mold-metal layered structure. Typically the subsequent cycles of mold-object deposition involve repeated exposure to heating cycles. The mold regions, which define the cavities into which the molten metal is cast, are exposed to a sequence of thermal shocks at various temperature profiles, resulting from the contact with the molten metal and the dissipation of heat into the mold regions during and subsequent the deposition of the metal object region. Additional thermal shocks may be affected by pre-deposition and post-deposition heating of the deposited metal object regions to define its properties, e.g. metallurgical properties. Further, as the already-cast metal expands and contracts with each deposition of a new metal thereonto, the thermal shock cycles are also accompanied by repeated mechanical stressing of the mold regions due to expansion and contraction of the metal associated with changes in temperatures at the metal object region.

[0029] The heat provided to the metal object region is associated with the deposition of molten metal, the heating of the previously-cast metal (pre-deposition heating) and the heating of the currently-cast metal object region (post deposition heating). A specific metal object region experiences repeated heating cycles associated with its casting, as well as casting of subsequent, upper object regions. The metallurgical properties, mechanical properties and other properties are affected by the above-described heating cycles. In other words, metal properties are affected by heating and reheating, up to melting, of cast residing in the current and previous mold regions. Without wishing to be bound by theory, the dissipation of heat from the metal object region to the mold region does not play a significant part in affecting metal properties. The mold region of the current and previous production layers experience repeated heat cycles, and in order to maintain their mechanical integrity, the mold regions should be designed to withstand heat cycles.

[0030] Hence, the mold region is typically formed out of compositions comprising refractive ceramic materials, special binders that can withstand the high temperatures to which the mold is exposed to, and various additives that increase the thermal and mechanical stability of the mold region to repeated thermal and mechanical shocks. Such compositions are typically expensive, and therefore there is a requirement to reduce the amount of mold composition used for cost-efficiency of the additive casting process.

[0031] The present disclosure provides slurry compositions that can be deposited to form mold regions having controlled gaseous products release rate and improved heat absorbance / conductance, such that once in contact with the metal at various temperatures, can function to provide mechanically stabilized mold regions, heat dissipation through the mold region and reduced risk of mechanical failure when exposed to various heat cycles. In other words, the slurry compositions of this disclosure are characterized by controlled energy absorbance and conduction, as well as controlled gas release during their polymerization and drying, thereby enabling obtaining mold regions that reach thermal and mechanical stability relatively fast with reduced risk of mechanical failure.

[0032] The slurry compositions of this disclosure are designed to have modified energy absorption and dissipation. This permits for effective energy uptake of heat to which the mold region is exposed (e.g. from the surroundings, from the molten metal, etc.), and effective heat dissipation within the voluminous mold region to minimize the thermal shock experienced by the mold region during various stages of casting. In addition, efficient and controllable gas release from the composition during absorption of such heat enables minimizing the mechanical damage to the mold region that can be formed due to uncontrolled and abrupt gas release from the mold region (e.g. due to boiling liquid or gaseous chemical reaction products), hence, maintaining the mechanical integrity of the mold (and particularly the metal-mold interface) during casting.

[0033] While in traditional mold manufacturing techniques, typically based on ceramic compositions, entire molds or mold layers are deposited and then fully sintered before deposition of molten metal, in the presently disclosed additive casting process the mold regions are designed to function in a non-sintered state, typically as a green body (as will be further explained below). Working with green body mold regions enable significant reduction in production time and energy consumption, as full sintering is not required. However, working at a green body state involves significant challenge, as when in the greed body state, the mold region is significantly more sensitive to thermal and mechanical impacts compared to a sintered state. Thus, there is importance to proper designing of compositions that would provide improved mechanical stability of the mold regions during additive manufacturing and exposure to repeated thermal and mechanical shocks.

[0034] Further, unlike other additive processes, in which thin (or even ultra-thin) layers of mold are formed (for example by binder-jetting mold manufacturing, or additive moldmetal manufacturing as described in US2020269320), the additive processes disclosed herein is designed for casting of relatively large metal objects, and are hence designed to enable formation of voluminous mold regions. In other words, the slurry compositions of this disclosure are designed to provide mechanical support for relatively thick and voluminous mold regions, thereby providing sufficient mechanical support for casting- in-layers of large metal objects and minimizing mechanical failure of the mold regions during the additive casting process.

[0035] Working with thick or voluminous mold regions poses several challenges, mostly relating to heat distribution and transfer into the mold region that have detrimental effect on the mechanical stabilization of the mold region (e.g. the rate and extent of polymerization and / or drying), as well as stress loading applied onto the mold region due to repeated expansion of the object region during repeated heating and cooling of the metal therein, making the design of the mold compositions critical.

[0036] The slurry compositions of the present disclosure aim at addressing these challenges. The present disclosure provides slurry compositions suitable for providing voluminous, mechanically stable mold regions, designed for additive casting to form metal objects by the cycled mold-metal regions deposition methods described herein. The compositions are designed to permit effective heat dissipation through the bulk of the mold region, as well as controlled gas release from the compositions during drying and polymerization, as to optimize drying and minimize mechanical damage to the mold region, thereby reducing the risk of mechanical failure of the mold due to the aggressive metal-casting conditions and the risk of leakage of the molten metal during additive casting.

[0037] It is noted that in the context of the present disclosure, additive metal casting refers to cycles of fabricating production layers. In the context of the present disclosure, the production layer includes one or more mold regions each defining and surrounding a respective metal object region. The mold regions are typically in a closed-loop geometry, each mold region of a production layer defining a cavity into which molten metal is cast to obtain the object region of the production layer. After the stack of production layers is fabricated, a combined mold-metal structure is obtained, following which the mold is removed, e.g. by using known mold removal techniques, and the desired metal object is obtained.

[0038] It is to be noted that, typically, the lowermost, base layer of the mold is made solely out of the mold material, and is typically continuous (z.e. without forming a cavity therein), as to form a uniform, continuous base onto which a sequence of production layers is formed. However, it is to be understood that at times, depending on the desired mold geometry, that no such base layer is needed.

[0039] Thus, in the description below, the term mold region will refer to the mold part / portion within the single production layer. The mold region in each production layer can be a single monolithic layer formed out of a mold composition. Alternatively, the mold region in a production layer can be formed from a stack of sub-layers, together defining a multi-layered mold region. For example, the mold region a production layer can be composed of several (e.g. 2-5) sub-layers (print-lines) of mold compositions that are continuously deposited one on top of the other in order to form the mold region of the production layer before deposition of the into the cavity defined thereby.

[0040] In some configurations, the mold region in each production layer is a single monolithic layer of the paste composition. According to other configurations, the mold region in each production layer comprises at least 2, typically between 2 and 5, sub-layers (print-lines) of the mold composition. According to some other configurations, the mold region in some of the production layers are each a single monolithic layer of the mold composition, while the mold regions in the rest of the production layers are structured from sub-layers of the mold composition.

[0041] For illustration, in a specific non-limiting example, molten metal additive casting of gray iron objects is formed out of a stack of production layers (e.g. 4-100 production layers or more), each of 2-20 mm (millimeters) height. In an exemplary construction, a production layer can be formed from a mold region of 8 mm height, which can be a monolithic deposition of mold composition in the form of solid cylinders with average cross-section of 8 mm; alternatively a mold region of 8 mm height can be constructed by depositing 4 mold sub-layers, each of 2 mm height. The corresponding object region may have the same height - 8 mm (or less), and may be fabricated by a single depositing of 8 mm of metal, by several subsequent depositions within a manufacturing cycle of the fabrication layer, e.g. two consecutive depositions of metal, each 4 mm in height. In other words, the mold region in each production layer can be formed out of one or more print lines, defining the height of the mold region in the production layer. The resultant mold region is therefore voluminous to withstand the thermal and mechanical shock exerted by introduction of molten metal into the cavity defined by the mold region, and designed to receive molten metal of a corresponding height. The terms mold or mold structure will refer to all or part of the stack of mold regions in all or several production layers.

[0042] The geometry of the mold regions is dictated by the geometry of metal object region to be cast, according to the geometry of the final metal object to be manufactured. Therefore, the mold regions of different production layers may or may not be of the same size and geometry.

[0043] The term metal means to denote any metals and / or mellitic alloys which are suitable for melting and casting, for example, ferrous alloys (gray iron, ductile iron, compacted graphite iron (CGI), steel, titanium, etc.), non-ferrous allows (nickelchromium-based superalloys, e.g. Inconel), aluminum alloys, copper alloys, nickel alloys, magnesium alloys, and the like.

[0044] According to one of its aspects, the disclosure provides a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one paste composition, the slurry composition comprising: at least one ceramic material in particulate form; at least one inorganic binder; at least one porosity enhancing additive; at least one thermal modifying additive; and at least one carrier liquid; the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0045] In the context of the present disclosure, the term mass loss will refer to decrease in total mass of the composition when heated to about 220°C for a period of time of no more than about 30 minutes. Unless specifically noted otherwise, the mass loss is measured as the total mass loss from a layer of deposited slurry composition of a sample having a surface area to volume ratio of at least 1.5: 1, typically between 2: 1 and 3: 1 [cm2 / cm3], at an energy flux of about 25 KW. According to some embodiments, the slurry composition has a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 25 minutes.

[0046] According to some embodiments, the slurry composition has a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 20 minutes.

[0047] According to some embodiments, the slurry composition has a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 15 minutes.

[0048] According to some embodiments, the slurry composition has a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 10 minutes.

[0049] The term slurry composition refers to a composition in which solid particles are dispersed in a continuous liquid matrix.

[0050] In the present disclosure, as described herein, each production layer is manufactured by deposition of at least one said slurry composition to form the mold region, drying the mold region, and deposition of molten metal into a cavity defined by the mold region to obtain the metal object region.

[0051] The slurry composition provides effective energy (e.g. heat) transfer through the mold region (for example, heat introduced from the environment when applying heating conditions, from the metal region to the mold region, etc.), and effective heat dissipation therethrough. Further, heating of the mold composition forms gaseous products (e.g. vapors of the carrier liquid, volatile components and / or polymerization reaction gaseous byproducts, etc.). In order to minimize mechanical failure due to uncontrolled release of such gaseous products from the bulk of the mold region, the composition is characterized by providing controlled gas release therefrom, as will be explained below, thereby maintaining mechanical integrity of the mold region, and particularly at the interface between the mold region and the metal region.

[0052] The term porosity enhancing additive refers to one or more components that increase the porosity of the composition. The porosity enhancing additive can be, for example a porous powdery additive, substantially hollow particles, rounded particles, a powdery additive having a large surface area, a sacrificial material, a pore-forming material that decomposes upon heating to form porosity, etc. By increasing the porosity of the composition, control over the release of gaseous products from the bulk of the mold region is obtained. Controllably increasing the porosity of the mold composition results in an interconnected network of spaces or channels within the composition’s bulk, that provide locations for gas expansion and gas evacuation from the bulk towards the surface of the mold region.

[0053] The inventors have found that in slurry compositions of this disclosure, in addition to increasing the overall porosity, the porosity enhancing additives function to provide balance and control over the gaseous products evacuation from the composition during drying from the bulk of the mold region towards its surface. Without wishing to be bound by theory, by forming paths for gaseous products release throughout the bulk of the mold region, the porosity formed prevents internal pressure buildup during drying of the composition (which is carried out by applying heating conditions or in response to heat associated with heating the metal during casting). Further, by temporarily physi-sorb molecules of the carrier liquid, e.g. water, into the pores (or on their surface), a delay in moisture and / or the rate of vaporization of the carrier liquid from the composition may be obtained, thereby assisting in preventing rapid shrinkage and / or capillary collapse. Therefore, the porosity enhancing additives assist in controlling the rate of vaporization of the liquid carrier and other volatile compounds from the composition when exposed to elevated temperatures in the additive casting process. Such controlled release of vapors reduces the risk of cracking or popping effects at the bulk of the mold region as well as at its surface.

[0054] According to some embodiments, the slurry composition comprises between about 0.01 wt% and about 10 wt% of porosity enhancing additive.

[0055] In some embodiments, the at least one porosity enhancing additive is a poreforming material, either as foaming agents or as sacrificial materials, which decomposes when heated to form pores. For example, the pore-forming material can be a foaming surfactant (e.g. sodium dodecyl sulfate), calcium bicarbonate, sodium bicarbonate, an organic compound or composition having a suitable decomposition temperature (e.g. polystyrene beads), etc. Alternatively, the pore-forming material can be a compound that reacts with water (or the carrier liquid) to form gaseous products that can be captured as bubbles in the composition.

[0056] According to some embodiments, the slurry composition comprises between about 0.01 wt% and about 4 wt% of said foaming agents and / or sacrificial material. According to some embodiments, the slurry composition comprises between about 0.05 wt% and about 2 wt% of said foaming agents and / or sacrificial material.

[0057] In some embodiments, the at least one porosity enhancing additive are one or more types of microspheres. Microspheres are highly rounded spherical micronic particles, solid or hollowed (hollow microspheres are sometimes also referred to as microballoons'). When in solid form, the microspheres are typically porous or have a porous (or highly irregular) surface. Further, the round morphology of the microspheres provides some spacing in the packing of the ceramic particles, as a combination of spheres and prismatic particles (and / or dendritic particles) reduces the overall packing density due to geometrical packing constraints. Thus, incorporation of spherical particles may increase the overall porosity of the composition.

[0058] By some embodiments, the microspheres have particle size of no more than about 500 pm (micrometers), typically between about 50 and 500 pm. According to some embodiments, the microspheres have a particle size of no more than about 500 pm, typically between about 100 pm and 300 pm.

[0059] The term particle size refers herein to particle size determined by sieving through sieves with appropriate mesh numbers.

[0060] According to some embodiments, the microspheres are made of glass, ceramic material, polymeric materials (e.g. phenolic microspheres), metallic materials, and mixtures thereof. The microspheres can be at least partially coated with a metal coating (e.g. silver, copper, etc. , for example ceramic microspheres coated by one or more metals. The microspheres can be at least partially coated with one or more hydrophilic coatings to increase their affinity to water molecules, thereby further assisting in controlling the rate of release of water molecules from the paste composition.

[0061] By some embodiments, the microspheres are made of aluminum oxide, aluminum silicate, silicon dioxide, borosilicate glass, yttria- stabilized zirconia, and mixtures thereof.

[0062] By some embodiments, the paste composition comprises between about 4 wt% and about 10 wt% of said micro spheres.

[0063] In order to provide improved and controlled energy absorbance and dissipation in the mold region, the slurry composition comprises at least one thermal modifying additive.

[0064] Within the context of the present disclosure, the term thermal modifying additive means to refer to an additive that modifies the thermal behavior of the slurry composition, more particularly modifies the energy absorbance of the composition and / or the energy conductance through the composition when exposed to an energy source, e.g. heating.

[0065] In some embodiments, the thermal modifying additive is an energy conductive additive. The term energy conductive additive refers to a compound or composition of matter that is capable of transiently absorbing energy, e.g. thermal energy (heat), and transmit (z.e. conduct) such energy therefrom to the surrounding environment. Hence, in the slurry compositions of this disclosure, the energy conductive additive transiently absorbs heat introduced into the mold region, either from the environment (as a result of external heating) or from the metal region, and conduct it away from the metal-mold interface into the bulk of the mold region. Such energy conductive additive effectively transfers the thermal energy from the metal-mold interface and external face of the mold region and direct it into the bulk of the voluminous mold region. This, in turn, permits the heat-driven polymerization reaction of the inorganic binder within the bulk of the mold region, thereby polymerizing the binder and providing the mold region with mechanical stability.

[0066] By some embodiments, said energy conductive additive is selected from boron nitride, carbon nitride, silicon nitride, silicon carbide, metal particles, metal fibers, metal oxides and mixtures thereof.

[0067] In some embodiments, the said energy conductive additive is metal particles (copper, silver, iron, steel, gold, etc.), metal fibers, metal oxides e.g. iron oxides, copper oxides, silver oxides, etc.) and mixtures thereof.

[0068] By some embodiments, the paste composition comprises between about 0.05 wt% and about 3 wt% of said energy conductive additive.

[0069] In some embodiments, the thermal modifying additive is an energy absorbing additive. The term energy absorbing additive means to denote a compound or composition of matter that is capable of absorbing energy, e.g. thermal energy. The use of energy absorbing additives in a slurry composition of this disclosure permits effective heat absorbance from the environment and the metal-mold interface, thereby promoting heat dissipation within the bulk of the mold region.

[0070] In some embodiments, the energy absorbing additive is selected from carbon black, carbon powder, graphene, graphite, carbon nanotubes, UV-absorbing pigments, visible spectrum absorbing pigments, IR absorbing pigments, magnesium-aluminum oxides e.g. spinel), ceramic fibers, and mixtures thereof. In some embodiments, the energy absorbing additive is selected from carbon black, carbon powder, graphene, graphite, and carbon nanotubes.

[0071] By some embodiments, the slurry composition comprises between about 0.05 wt% and about 3 wt% of said energy absorbing additive.

[0072] In some embodiments, the slurry composition comprises both an energy absorbing additive and an energy conductive additive.

[0073] The combination of thermal modifying additives together with the enhanced porosity of the slurry composition was surprisingly found to strike a balance between the energy absorption that is required for the polymerization processes in the composition (in order to mechanically stabilize it to enable provision of mechanical support for the mold region) and the heat dissipation from the metal-mold interface that is required during the molten metal casting process in order to maintain the mold region’s integrity. Further, this combination strikes another balance of heat conductance into the bulk of the mold region to effectively and quickly polymerize the binder and vaporize the carrier liquid from the mold region (z.e. dry the paste composition), however also maintaining control over the rate of gaseous products release from the slurry composition during these processes in order to minimize abrupt gas / vapor release from the mold region that may hinder its mechanical integrity and have an impact on the integrity of the metal-mold interface.

[0074] The balance between energy absorption and conductivity, together with the increased porosity of the mold region during drying, results in effective utilization and dissipation of the heat introduced into the mold region, however providing minimal stress development in the mold region, thereby minimizing and even preventing mechanical failure of the mold although providing a fast drying rate of the mold region. Such balance enables working at relatively quick fabrication cycles for the production layers utilizing voluminous mold regions, without risking mechanical failure of the mold.

[0075] As noted, the slurry composition comprises at least one inorganic binder. The term inorganic binder refers to a non-organic material or composition (z.e. carbon- free) which functions to bind the particles of the ceramic materials together to form the mold region. In other words, the inorganic binder forms a polymeric chain having an inorganic backbone. The binder acts through a combination of cohesive forces within the binder itself and adhesion to the ceramic material particles at the interface between the binder and the particles. As the additive casting of metal in which the paste compositions of this disclosure are utilized requires exposure of the paste composition to high temperatures, inorganic binders are utilized, that can withstand the process temperatures.

[0076] According to some embodiments, the at least one binder has a polymerization temperature of at least 150°C, typically between about 150°C and about 850°C.

[0077] Unlike existing mold manufacturing processes, in which the entire mold is first produced, and typically sintered in order to obtain a rigid ceramic structure prior to casting of the entire metal object into the mold - in the additive casting processes in which the slurry compositions of this disclosure are used, the mold region is not exposed to sintering conditions (which require a long exposure to high temperatures). It is to be noted that sintering is typically used in known mold manufacturing processes when thick or voluminous mold regions are formed / depo sited in order to provide for a fully sintered mold before introduction of molten metal thereinto. Unlike existing mold manufacturing processes, the slurry composition of this disclosure is designed to provide mechanical support to, and heat conductance from, the external surface of the mold region into its bulk, as to permit thick or voluminous mold regions (typically in the form of cylinders having an average diameter of 2-20 mm), to withstand the mechanical and thermal impacts exerted by the molten metal casting process, without requiring sintering the mold region, namely working with mold regions at a green body state. The term green body (or green body state) means to denote a state in which ceramic particles of the slurry composition are held together by a binder after the binder has gone through at least partial polymerization. Unlike a sintered state, in which the binder is thermally decomposed and the ceramic particles are “fused” to one another to form a continuous, 3 -dimensional ceramic structure, in the green body state the ceramic particles are not fused to one another, and hence the mechanical properties of the mold region are determined by the combination of ceramic material and the binder (at its at least partial polymerized state) and the interactions between them. Working at a green body state of the mold region is accompanied by significant reduction in overall energy consumption of the process, as no energy needs to be invested to first obtain a sintered mold region, while also saving significant process time (as typical sintering spans at least several hours).

[0078] Further, it is at times desired to carry out one or more surface treatments of the mold region before casting the molten metal, e.g. to smoothen the surface or to render the mold region with desired surface features, typically in portions of the mold regions that will be interfacing the molten metal (e.g. inner walls of the mold region). For example, such metal-facing surfaces may undergo surface shaping, material removal (e.g. of ceramic sags), surface smoothening, coating, etc. by a variety of processing techniques, such as milling, grinding, polishing, heating, coating and the like. Such processes are easier to be carried during a green body state, and are preferably carried out before complete polymerization of the mold region to reduce the risk of mechanical damage to the mold region. Therefore, selection of the inorganic binder of the slurry composition to permit at least initial stabilization of the mold region enables the mold region to be sufficiently mechanically stabilized to permit such surface treatments.

[0079] By some embodiments, the composition comprises between about 2 wt% and about 20 wt% of said at least one inorganic binder. According to some other embodiments, the composition comprises between about 5 wt% and about 18 wt% of said at least one inorganic binder. By yet other embodiments, the composition comprises between about 3 wt% and about 10 wt% of said at least one inorganic binder.

[0080] By some embodiments, the at least one inorganic binder is selected from silicate- based binders, phosphate-based binders, aluminosilicate binders, alumino-silico- phosphate binders, colloidal silica, and mixtures thereof.

[0081] According to some embodiments, the at least one inorganic binder is at least one silicate-based binder. In such embodiments, the silicate-based binder can be an alkalisilicate, an earth-alkali silicate, or a combination thereof.

[0082] According to some embodiments, the silicate based binder is selected from sodium silicate, potassium silicate, colloidal silica, and mixtures thereof.

[0083] According to some embodiments, the at least one inorganic binder is at least one phosphate-based binder. In such embodiments, the phosphate -based binder can be selected from alkali metal trimetaphosphate (e.g. sodium trimetaphosphate, STMP), alkali metal monophosphate, aluminum phosphates, sodium tripolyphosphate, silico- aluminophosphate, monoaluminium phosphate, polyphosphates, dihydrogen aluminophosphate, polyphosphazene and mixtures thereof.

[0084] As the slurry composition is typically designed for commercial, mass production additive casting processes, it is important that each manufacturing step will be time efficient. Depending on the heating technology, geometry of the deposited mold region, mass of deposited paste composition, and / or working conditions, the time duration to obtain at least partial polymerization of the paste composition in the mold region to permit it to be sufficiently stable for metal casting is no more than 30 minutes, preferably between about 1 minute and about 20 minutes, e.g. between about 1 minute to 10 minutes.

[0085] The term ceramic material means to denote a material or a composition of matter which is neither metallic nor organic. Preferably, the ceramic material is selected to withstand the high temperatures exerted during the additive casting process, typically over at least 600°C, without undergoing substantive chemical changes or thermal decomposition. The ceramic material is typically in particulate form, i.e. powder. The particles can be crystalline, semi-crystalline, amorphous, or any blend thereof.

[0086] According to some embodiments, the at least one ceramic material is selected from zirconia (ZrCh), alumina (AI2O3), silica (SiCh), zirconium silicate (zircon), quartz, yttria-stabilized zirconia, carbides (silicon carbide, tungsten carbide, etc.), and mixtures thereof.

[0087] According to some embodiments, the at least one ceramic material is selected from zirconia (ZrCh), zirconium silicate (zircon), alumina (AI2O3), silica (SiCh), and any mixture thereof.

[0088] By some embodiments, the refractory ceramic material is a mixture of zirconia (ZrCh) and zirconium silicate (zircon).

[0089] By some other embodiments, the refractory ceramic material is a mixture of zirconia (ZrCh) and alumina (AI2O3).

[0090] By yet other embodiments, the refractory ceramic material is a mixture of zirconium silicate (zircon) and alumina (AI2O3).

[0091] In some embodiments, the refractory ceramic material is zirconia (ZrCh).

[0092] In some other embodiments, the refractory ceramic material is zirconium silicate (zircon).

[0093] In some other embodiments, the refractory ceramic material is silica (SiCh).

[0094] According to some embodiments, the slurry composition comprises at least about between about 60 wt% and about 90 wt% of ceramic materials.

[0095] By some embodiments, in order to further facilitate control over the release of liquid carrier from the slurry composition, at least a portion of particles of said ceramic material are at least partially coated by a hydrophilic coating. Namely, in such embodiments, particles of the ceramic material are at least partially coated by a coating that has affinity to water molecules. Without wishing to be bound by theory, such coating can function as a vaporization inhibitor, reducing and controlling the rate by which gaseous, typically vaporized water molecules, are released from the slurry composition during boiling of the carrier liquid or during polymerization of the inorganic binder once the mold region is exposed to elevated temperatures.

[0096] By some embodiments, the ceramic material particles are porous, and / or have irregular surface. Such porosity or surface irregularity (e.g. high degree of surface roughness) can provide a further means for increasing the porosity in the composition, as well as further vaporization inhibition for the gaseous products from the slurry composition.

[0097] According to some embodiments, the ceramic material has a particle size of no more than about 300 pm. According to some other embodiments, the ceramic material has a particle size of between about 25 pm and about 300 pm.

[0098] Another means of increasing the overall porosity of the composition is tailoring the particle size of the ceramic material(s) to impact the packing of the particles in the composition. According to some embodiments, the at least one ceramic material is a mixture of at least one first ceramic material having a particle size of between about 50 pm and about 300 pm and at least one second ceramic material having a particle size of between about 1 pm and about 15 pm. In some other embodiments, the at least one first ceramic material having a particle size of between about 70 pm and about 200 pm and at least one second ceramic material having a particle size of between about 1 pm and about 50 pm.

[0099] In such embodiments, each of said first and second ceramic materials is independently selected from zirconia, alumina, silica, zirconium silicate, quartz, yttria- stabilized zirconia, silicon carbide, and tungsten carbide.

[0100] According to some embodiments, the weight ratio between the ceramic material and the inorganic binder in the slurry composition is between about 4: 1 and about 20: 1, e.g. between about 8: 1 and 16: 1.

[0101] According to some embodiments, the weight ratio between the inorganic binder and the thermal modifying additives in the slurry composition is between about 2: 1 and about 100: 1, e.g. between about 2: 1 and about 50: 1, or even between about 2: 1 and about 20: 1.

[0102] According to some embodiments, the weight ratio between the inorganic binder and the porosity enhancing additive in the slurry composition is between about 1:4 and about 2: 1, e.g. between about 1:2 and about 2: 1. As noted, the slurry composition comprises at least one carrier liquid, in which the other components of the composition are dispersed in order to obtain a flowable consistency and homogeneity.

[0103] The liquid carrier is a liquid or a mixture of liquids that permits at least partial wetting and / or at least partial dispersion of the ceramic material, and typically has a boiling temperature of at most about 300°C.

[0104] According to some embodiments, the carrier liquid can be selected from water, Ci-C6alcohols, Ci-C6polyols, C5-C12 alkanes, mineral oils, natural oil, synthetic oils, and any mixture thereof.

[0105] According to some embodiments, the carrier liquid is water. The water can be, for example, tap water, filtered water, distilled water, ionized water, deionized water, sterile water, etc.

[0106] According to some embodiments, the slurry composition comprises between about 6 wt% and about 40 wt% of said liquid carrier. According to some other embodiments, the composition comprises between about 10 wt% and about 30 wt% of said liquid carrier, e.g. between about 10 wt% and 20 wt% of said liquid carrier.

[0107] In some embodiments, the composition is configured to be printable; namely, to be deposited from a bulk container through a suitable nozzle. Hence the composition should have a viscosity suitable for such dispensing. By some embodiments, the slurry composition is in the form of a pourable, self-leveling paste, having a viscosity of at most 5,000 cps (centipois, or mPa-s), e.g. between about 1,000 cps and about 5,000 cps. The term pourable, self-leveling paste means to denote a flowable paste, that due to its fluidity, can form a substantially flat top surface when deposited into a confined space without application of significant pressure (or without application of pressure or external shear forces). In other words, the pourable self-leveling paste, once deployed, forms a substantially flat and level surface, i.e. substantially parallel surface relative to the surface onto which the paste is deposited, upon deposition or within a relatively short period of time (a few seconds to a few minutes). This permits the paste to substantively homogenously fill receiving spaces into which it is disposed, without application of force.

[0108] In other embodiments, the composition needs to substantially maintain its deposited (printed) shape until sufficient polymerization is obtained. In such embodiments, the slurry composition is in the form of a self-supporting paste - namely a viscous paste that is sufficiently fluid to be printable through a nozzle under application of pressure, however also sufficiently viscous and mechanically stable in order to maintain the printed shape without substantive additional support.

[0109] In such embodiments, the composition has a viscosity of at least about 10,000 cps, e.g. between about 10,000 cps and about 1,00,000,000 cps. In some embodiments, the composition has a viscosity of between about 12,000 cps and about 500,000 cps, between about 15,000 cps and about 250,000 cps, between about 15,000 cps and about 100,000 cps, or even between about 15,000 cps and about 50,000 cps.

[0110] According to some embodiments, one or more flow modifiers can be added to the slurry composition to obtain the desired viscosity and / or rheological properties. For example, plasticizers, surfactants, thixotropic flow modifiers, non-Newtonic flow modifiers, temperature-dependent rheology modifiers, etc.

[0111] The slurry composition may comprise one or more additional components, rendering the slurry composition with one or more functional features or improved properties.

[0112] Depending on the carrier liquid and the properties of the ceramic material and / or other components of the composition, surface active components can be used to maintain the solid components of the composition stably dispersed in the carrier liquid, at least for a pre-defined period of time (e.g. for pre-defined storage or during the additive casting process of a complete metal object). Thus, according to some embodiments, the slurry composition further comprises at least one dispersant or surfactant. A surfactant (or a dispersant) is an agent that is capable of lowering the surface tension of a liquid, allowing for the formation of a homogeneous mixture of at least one type of liquid with at least one other type of liquid, or between at least one liquid and at least one solid.

[0113] According to some embodiments, the slurry composition comprises between about 0.01 wt% and 3 wt% of at least one surfactant or dispersant.

[0114] In some pastes, control over the mechanical properties or other properties of the paste composition can be obtained by addition of one or more co-binders. A co-binder is a material or a composition that co-acts with the main binder in the paste to modify one or more properties of the binder, such as polymerization rate, mechanical properties, etc. Exemplary co-binders are, inter alia, magnesium mono-phosphate (MgPCU), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyolefins, polypropylene carbonate, polydimethyl siloxanes (PDMS), and others. According to some embodiments, the paste composition comprises at most about 15 wt% of said co-binder, e.g. between about 0.05 wt% and about 15 wt%, between about 0.05 wt% and about 10 wt%, between about 0.05 wt% and about 5 wt%, or even between about 0.05 wt% and about 2 wt%.

[0115] In order to further increase the strength, i.e. directional strength, of the mold region, mechanical reinforcing agents can be added to the slurry composition. The mechanical reinforcing agent can be in any suitable form, e.g. particles, flakes, discs, rods, short or long fibers, tubular particles, nanotubes, etc.

[0116] According to some embodiments, the slurry composition can include one or more additional functional additives, such as releasing agents, polymerization activating / initiating agents i.e. catalysts), UV absorbing agents, crosslinking agents, drying agents, etc.

[0117] By another aspect, there is provided a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one slurry composition, the slurry composition comprising: between about 60 wt% and about 80 wt% of at least one ceramic material in particulate form; between about 2 wt% and about 20 wt% of at least one inorganic binder; between about 0.01 wt% and about 10 wt% of at least one porosity enhancing additive; between about 0.05 wt% and about 3 wt% of at least one thermal modifying additive; and between about 6 wt% and about 40 wt% of at least one carrier liquid; the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0118] By another aspect, there is provided a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one slurry composition, the slurry composition comprising: between about 60 wt% and about 80 wt% of at least one ceramic material in particulate form; between about 3 wt% and about 8 wt% of at least one inorganic binder; between about 0.01 wt% and about 10 wt% of at least one porosity enhancing additive; between about 0.05 wt% and about 3 wt% of at least one thermal modifying additive; and between about 10 wt% and about 20 wt% of at least one carrier liquid; the slurry composition being in the form of a self-supporting paste having a viscosity of at least 10,000 cps, and the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0119] By yet another aspect, there is provided a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one slurry composition, the slurry composition comprising: between about 60 wt% and about 80 wt% of at least one ceramic material in particulate form; between about 5 wt% and about 18 wt% of at least one inorganic binder; between about 0.01 wt% and about 4 wt% of at least one porosity enhancing additive; between about 0.05 wt% and about 3 wt% of at least one thermal modifying additive; and between about 10 wt% and about 30 wt% of at least one carrier liquid; the slurry composition being in the form of a pourable, self-leveling paste having a viscosity of at most 5,000 cps, and the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0120] By another aspect, the disclosure provides a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, the mold region comprising at least one slurry composition, the slurry composition comprising: between about 60 wt% and about 80 wt% of at least one ceramic material in particulate form; between about 2 wt% and about 20 wt% of at least one silicate-based binder; between about 0.01 wt% and about 10 wt% of at least one porosity enhancing additive; between about 0.05 wt% and about 3 wt% of a thermal modifying additive selected from carbon black, carbon powder, silicon carbide, aluminum nitride, boron nitride, silicon nitride, metal particles, metal oxide particles, and mixtures thereof; and between about 6 wt% and about 40 wt% of at least one carrier liquid; the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0121] By yet another aspect, there is provided a slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one slurry composition, the slurry composition comprising: between about 65 wt% and about 75 wt% of at least one ceramic material in particulate form; between about 3 wt% and about 8 wt% of at least one phosphate -based binder; between about 4 wt% and about 10 wt% of ceramic microspheres; between about 0.05 wt% and about 3 wt% of a thermal modifying additive selected from carbon black, carbon powder, silicon carbide, aluminum nitride, boron nitride and silicon nitride, and mixtures thereof; and between about 10 wt% and about 20 wt% of at least one carrier liquid; the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

[0122] According to another aspect of this disclosure, there is provided a method of preparing a slurry composition as disclosed herein, the method comprising mixing said at least one refractory ceramic material with a mixture that comprises said carrier liquid, said at least one inorganic binder, said at least one porosity enhancing additive, and said at least one thermal modifying additive to obtain said slurry composition.

[0123] According to another aspect of this disclosure, there is provided a method of preparing a slurry composition as disclosed herein, the method comprising providing a first mixture that comprises said carrier liquid and said at least one inorganic binder; preparing a second mixture of said at least one refractory ceramic material, said at least one porosity enhancing additive, and said at least one thermal modifying additive; and mixing said first and second mixtures to obtain said slurry composition.

[0124] According to yet another aspect of this disclosure, there is provided a method of preparing a slurry composition as disclosed herein, the method comprising providing a first mixture that comprises said carrier liquid, said at least one thermal modifying additive, and said at least one inorganic binder; preparing a second mixture of said at least one refractory ceramic material and said at least one porosity enhancing additive; and mixing said first and second mixtures to obtain said slurry composition.

[0125] According to some embodiments, one or more pre-treatments can be applied to the refractory ceramic material. Thus, any one of the following pre-treatments can be applied to the refractory ceramic material prior to mixing with the components of the paste composition: modifying the moisture content of the ceramic particles (e.g. drying or hydrating the ceramic particles), modifying the particles’ morphology (e.g. rounding, forming jagged shape, etc.), modifying the size of the particles (e.g. milling, sieving, crushing, agglomerating, fracturing, etc.), modifying the surface texture of the particles (e.g. smoothing or roughening), modifying the surface properties or composition of the particles (e.g. coating, absorbing binding moieties, activating), or any other suitable pretreatment. By another aspect, this disclosure provides a cartridge for holding and dispensing the slurry composition as disclosed herein, the cartridge comprises a container for holding the slurry composition, one or more dispensing nozzles configured to permit dispensing of the slurry composition from the container, and one or more mixing means disposed within the container for mixing the slurry composition.

[0126] In some embodiments, the slurry composition in the cartridge is in the form of a self-supporting paste having a viscosity of at least 10,000 cps.

[0127] In other embodiments, the slurry composition in the cartridge is in the form of a pourable, self-leveling paste, having a viscosity of at most 5,000 cps.

[0128] By some embodiments, the cartridge comprises two separate containers: a first container for holding a first slurry composition in said self-supporting paste form, and a second container for holding a second slurry composition in said pourable, self-leveling paste form. In such embodiments, the cartridge may be configured to deposit slurry compositions from the first and second container concomitantly. In other embodiments, the cartridge may be configured to deposit slurry compositions from the first and second container sequentially.

[0129] The cartridge is typically designed for interfacing with a suitable deposition system, such as that described in PCT patent applications publication numbers WO2019053712, W02023002468 and WO2022243921, and / or in PCT patent applications serial numbers, PCT / IL2022 / 051188, PCT / IL2022 / 051190, and PCT / IL2022 / 051191, all of which assigned to the assignee of the present application, and incorporated herein by reference.

[0130] The cartridge can be designed to be detachably attached to said deposition system. Alternatively, the cartridge can be designed to be an integral part of the deposition system, and configured for filling with said slurry composition upon demand.

[0131] As the composition is a slurry, the cartridge may comprise one or more mixing means to maintain homogeneity of the slurry composition before and during deposition. The term mixing means is meant to denote any suitable mixing or agitation means that can keep the slurry composition under flow to minimize or avoid sedimentation of the solid components out of the slurry. Exemplary mixing means are mechanical stirrers, magnetic stirrers, ultrasonic transducers, circulation loops, etc. The container can also include one or more baffling arrangements or flow diverters to obtain a pre-defined flow profile within the container. According to some embodiments, the mixing means are configured for continuous or intermittent mixing of the slurry in the container.

[0132] The cartridge can also include one or more vents to permit gas discharge from the container, for example of gaseous reaction products or liquid carrier volatile components.

[0133] By another aspect, the disclosure provides a process for additive printing of a mold-metal composite object, the process comprising:

[0134] (a) depositing a slurry composition as disclosed onto a receiving surface to form at least one mold region, the slurry composition being in the form of a self-supporting paste;

[0135] (b) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;

[0136] (c) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0137] (d) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0138] (e) depositing said slurry composition as disclosed herein to form at least one subsequent mold region over the production layer; and

[0139] (f) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;

[0140] (g) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0141] (h) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and

[0142] (i) repeating steps (e)-(h) to form a stack of production layers, constituting together said mold-metal composite object.

[0143] By another aspect of this disclosure, there is provided a process for additive printing of a metal object, the process comprising: (a) depositing a slurry composition as disclosed herein onto a receiving surface to form at least one mold region, the slurry composition being in the form of a self- supporting paste;

[0144] (b) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;

[0145] (c) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0146] (d) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0147] (e) depositing said slurry composition as disclosed herein to form at least one subsequent mold region over the production layer; and

[0148] (f) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;

[0149] (g) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0150] (h) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object;

[0151] (i) repeating steps (e)-(h) to form a stack of production layers, constituting together a mold-metal composite object; and

[0152] (j) removing the mold regions from the mold-metal composite object to obtain said metal object.

[0153] In some configurations, it is desired to have a complex mold region, typically comprising two adjacent sections, laterally arranged within the production layer. Such configurations can provide a mold region having zones of different functionalities, e.g. having different mechanical properties, different drying rates, different polymerization rates, etc. The complex mold region is typically constructed out of a first mold section made of a first slurry composition of this disclosure, which is laterally surrounded by a second mold section of a second slurry composition of this disclosure (which is typically different in its composition from the first slurry composition), in which the metal casting cavity is defined. Together, the first and second mold sections constitute a mold region in production layer.

[0154] Thus, by another aspect, there is provided a process for additive printing of a mold-metal composite object, the process comprising:

[0155] (A) depositing onto a receiving surface a first slurry composition as disclosed herein to form at least one first mold section, the first slurry composition being in the form of a self-supporting paste, and a second slurry composition as disclosed herein to form at least one second mold section, laterally surrounding said first mold section and in contact therewith, said second slurry composition being in the form of a self-supporting paste and different in composition from said first slurry composition, the first and second mold sections defining together at least one mold region;

[0156] (B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0157] (C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0158] (D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0159] (E) depositing said first slurry composition to form a subsequent first mold section, and said second slurry composition to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact therewith, the first and second subsequent mold sections defining together at least one subsequent mold region;

[0160] (F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0161] (G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0162] (H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and (I) repeating steps (E)-(H) to form a stack of production layers, constituting together said mold-metal composite object.

[0163] By yet another aspect, there is provided a process for additive printing of a metal object, the process comprising:

[0164] (A) depositing onto a receiving surface a first slurry composition as disclosed to form at least one first mold section, the first slurry composition being in the form of a self-supporting paste, and a second slurry composition as disclosed herein to form at least one second mold section, laterally surrounding said first mold section and in contact therewith, said second slurry composition being in the form of a self-supporting paste and different in composition from said first slurry composition, the first and second mold sections defining together at least one mold region;

[0165] (B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0166] (C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0167] (D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0168] (E) depositing said first slurry composition to form a subsequent first mold section, and said second slurry composition to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact therewith, the first and second subsequent mold sections defining together at least one subsequent mold region;

[0169] (F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0170] (G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0171] (H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; (I) repeating steps (E)-(H) to form a stack of production layers, constituting together a mold-metal composite object; and

[0172] (J) removing the mold regions from the mold-metal composite object to obtain said metal object.

[0173] The first and second slurry compositions can differ in any one of the ceramic material type, the ceramic material concentration, the inorganic binder type, the inorganic binder concentration, the porosity enhancing additive type, the porosity enhancing additive concentration, the thermal modifying additive type, the thermal modifying additive concentration, the carrier liquid type, the carrier liquid concentration, or any other difference in composition.

[0174] For example, the inorganic binder of the first slurry composition can be selected to have a polymerization rate that is faster than the polymerization rate of the inorganic binder of the second slurry composition at a given temperature. In another example, the inorganic binder of the first slurry composition can be selected to have a polymerization temperature that is lower than the polymerization temperature of the inorganic binder in the second slurry composition. In such examples, the inorganic binder of the first slurry composition reaches a desired degree of polymerization faster at a given temperature, and / or at a lower temperature, than the inorganic binder of the second slurry composition. This permits the first mold section to reach mechanical stability faster than the second mold section, thereby enable the first mold section to provide mechanical support to the second mold section during the various heating processes to which the mold region is exposed during molten metal casting steps.

[0175] In other configurations, the first mold section comprises a slurry composition in the form of a viscous, self-supported paste, while the second mold section comprises a slurry composition which is in the form of a pourable, self-leveling paste. In such embodiments, an additional supporting barrier wall is typically constructed, such that the second slurry composition can be deposited in a receiving space defined between the first mold section and the barrier wall.

[0176] Namely, prior to deposition of the slurry compositions (namely the first and second slurry compositions), a surrounding barrier wall is deposited, with a height that is at least the height of the finished mold-metal composite object, and the fabrication and stacking of production layers is carried out within boundaries defined by the barrier wall. in such configurations, the barrier wall is manufactured in a single preliminary step of production to have the vertical dimension of the final mold-metal object.

[0177] The barrier wall is typically constructed out of a ceramic composition. The term ceramic composition refers to a composition that comprises at least one ceramic material and a liquid carrier, however, is devoid the porosity enhancing additive and / or the thermal additive.

[0178] Thus, by another aspect, there is provided a process for additive printing of a mold-metal composite object, the process comprising:

[0179] (A) depositing onto a receiving surface a closed-loop barrier wall made of a ceramic composition, having at least the height of the mold-metal composite object, and defining mold boundaries a first slurry composition as disclosed herein to form at least one first mold section, the first slurry composition deposited within the mold boundaries and laterally spaced apart from said closed-loop barrier wall to define a receiving space, said first slurry composition being in the form of a self-supporting paste, and a second slurry composition as disclosed herein into said receiving space, to form at least one second mold section, laterally surrounding said first mold section and in contact with the first mold section and the barrier wall, said second slurry composition being in the form of a pourable self-leveling paste and being different from said first slurry composition, the first and second mold sections defining together at least one mold region;

[0180] (B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0181] (C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0182] (D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0183] (E) depositing said first slurry composition to form a subsequent first mold section, and said second slurry composition into said receiving space to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact with the subsequent first mold section and the barrier wall, the first and second subsequent mold sections defining together at least one subsequent mold region;

[0184] (F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0185] (G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0186] (H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and

[0187] (I) repeating steps (E)-(H) to form a stack of production layers, constituting together said mold-metal composite object.

[0188] By yet another aspect, there is provided a process for additive printing of a metal object, the process comprising:

[0189] (A) depositing onto a receiving surface a closed-loop barrier wall made of a ceramic composition, having at least the height of the mold-metal composite object, and defining mold boundaries, a first slurry composition as disclosed herein to form at least one first mold section, the first slurry composition deposited within the mold boundaries and laterally spaced apart from said closed-loop barrier wall to define a receiving space, said first slurry composition being in the form of a self-supporting paste, and a second slurry composition as disclosed herein into the receiving space, to form at least one second mold section, laterally surrounding said first mold section and in contact with the first mold section and the barrier wall, said second slurry composition being in the form of a pourable self-leveling paste and being different in composition from said first slurry composition, the first and second mold sections defining together at least one mold region;

[0190] (B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0191] (C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region; (D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0192] (E) depositing said slurry mold composition to form a subsequent first mold section, and said second slurry composition to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact with the subsequent first mold section and the barrier wall, the first and second subsequent mold sections defining together at least one subsequent mold region;

[0193] (F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0194] (G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0195] (H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object;

[0196] (I) repeating steps (E)-(H) to form a stack of production layers, constituting together a mold-metal composite object; and

[0197] (J) removing the mold regions from the mold-metal composite object to obtain said metal object.

[0198] In some embodiments, the first and second slurry compositions are deposited simultaneously in steps (A) and (E).

[0199] In other embodiments, the first slurry composition is deposited before the second slurry composition in steps (A) and (E).

[0200] According to some embodiments, the mass ratio between said first mold section and said second mold section in a production layer ranges between about 1: 1.5 and about 1: 15, e.g. between about 1:3 and about 1: 15.

[0201] According to some embodiments, said first mold section has a first width and the second mold section has a second width, the ratio between said first width and second width ranges between about 1: 1.5 and about 1:15, e.g. between about 1:3 and about 1: 15.

[0202] In some embodiments, at least a portion of the surface of the cavity (z.e. a metalfacing surface of the cavity defined by the mold region) is coated by a coating formulation, for example a smoothing coating or a refractory coating. In some embodiments, the barrier wall can be manufactured in an additive process, namely, in each production layer another vertical section of the barrier wall is deposited.

[0203] Thus, in another aspect, there is provided a process for additive printing of a moldmetal composite object, the process comprising:

[0204] (A’) depositing onto a receiving surface a closed-loop barrier wall section made of a ceramic composition, defining mold boundaries, a first slurry composition as disclosed herein to form at least one first mold section, the first slurry composition deposited within the mold boundaries and laterally spaced apart from said closed-loop barrier wall to define a receiving space, said first slurry composition being in the form of a self-supporting paste, and a second slurry composition as disclosed herein into said receiving space, to form at least one second mold section, laterally surrounding said first mold section and in contact with the first mold section and the barrier wall, said second slurry composition being in the form of a pourable self-leveling paste and being different from said first slurry composition, the first and second mold sections defining together at least one mold region;

[0205] (B’) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0206] (C’) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;

[0207] (D’) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and

[0208] (E’) depositing a subsequent closed-loop barrier wall section made of said ceramic composition, said first slurry composition to form a subsequent first mold section, and said second slurry composition into said receiving space to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact with the subsequent first mold section and the barrier wall, the first and second subsequent mold sections defining together at least one subsequent mold region; (F’) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;

[0209] (G’) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;

[0210] (H’) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and

[0211] (I’) repeating steps (E’)-(H’) to form a stack of production layers, constituting together said mold-metal composite object.

[0212] As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

[0213] As used herein, the term about is meant to encompass deviation of ±10% from the specifically mentioned value of a parameter, such as temperature, pressure, concentration, etc.

[0214] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0215] Unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any integer or step or group of integers and steps.

[0216] Generally it is noted that the term ...at least one... as applied to any component of a composition of this disclosure should be read to encompass one, two, three, four, five, or even more different occurrences of said component in the composition.

[0217] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0218] BRIEF DESCRIPTION OF THE DRAWINGS

[0219] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0220] Figs. 1A-1B are schematic representation of an additive casting process of a metal object according to an embodiment of this disclosure, in which slurry compositions of this disclosure are used for construction of the mold regions in the production layers of the mold-metal fabricated structure.

[0221] Figs. 1C-1D are schematic top view of production layers: comprising a mold region and a metal object region (Fig. 1C), and a mold region and multiple metal object regions (Fig. ID).

[0222] Figs. 2A-2B are schematic representation of an additive casting process of a metal object, in which a complex mold region is applied in the production layers of the moldmetal fabricated structure, according to another embodiment of this disclosure.

[0223] Fig. 2C is a schematic top view of a production layer of the embodiment of Figs. 1A-1B, comprising a first mold section, a second mold section and a metal object region.

[0224] Figs. 3A-3B are schematic representation of an additive casting process of a metal object, in which a complex mold region is applied in the production layers of the moldmetal fabricated structure, according to another embodiment of this disclosure.

[0225] Figs. 4A-4B are schematic representation of an additive casting process of a metal object, in which a complex mold region is applied in the production layers of the moldmetal fabricated structure, according to another embodiment of this disclosure.

[0226] Fig. 4C is a schematic top view of a production layer of the embodiment of Figs. 2A-2B or Figs. 3A-3B, comprising a barrier wall, a complex mold region (constructed out of first and second sections) and a metal object region.

[0227] Fig. 5 shows small-scale mass loss tests for various slurry compositions. Figs. 6A-6D are images of dried samples of slurry compositions Form. 1-Form 4, respectively, as detailed in Table 1.

[0228] Figs. 7A-7D are optical microscopy pictures of cross-sections of self-supporting paste compositions with various porosity enhancing additives.

[0229] Fig. 8 is an optical microscopy picture of cross-sections of self-leveling paste composition Comp. 10, as detailed in Table 3.

[0230] DETAILED DESCRIPTION OF EMBODIMENTS

[0231] Reference is first being made to Figs. 1A-1C, showing steps of an exemplary additive casting process of a metal object, in which paste compositions of this disclosure are used for the construction of mold-metal structures fabricated from a stack of production layers.

[0232] Process 100 comprises deposition 110 of a slurry composition according to a desired mold contour in a production layer 200i (i being an integer (z>0) defining the number of the production layer). In process 100 the slurry composition is a viscous, self- supporting paste, that can maintain its deposited shape without addition support. The deposited paste is then heated at step 120, continuously or in several heating intervals, to obtain at least partial polymerization of the inorganic binder and a reduction of at least 10 wt% of its total mass of its total mass within no more than 30 minutes, to form the mold region 210 of the production layer 2001.

[0233] At this stage, the mold region 210 is stable enough to carry out one or more postdeposition surface treatments (not shown), if desired, in order to smoothen the surface texture (e.g. the inner walls 212 of mold region 210) or define surface features of the mold region.

[0234] At step 130, molten metal is being cast into the cavity 220 defined by the mold region. The metal 225 then cools at step 140 to at least partially solidify, thereby forming the metal object region 230 and completing the manufacture of the first production layer, before deposition of fresh paste to form the mold region of the ensuing production layer 2002. The cycle of steps 110-140 is repeated, such that a stack of production layers is obtained, by consecutive cycles of production layers fabrication, until the end of the casting of the entire metal object. Step 130 comprises the deposition of molten metal (represented in Fig. IB by molten metal drops 222) into cavity 220. For example, molten metal 222 is deposited while a metal depositor (not shown) is positioned above cavity 220. Step 130 may comprise pre-deposition heating of the previously -cast metal region(s) 225 such that the top surface of metal region 225 - the previously deposited metal - may be in at least partially molten state during molten metal deposition of the subsequent quanta of molten metal. Step 130 may further comprise post-deposition heating of the deposited object region to modify its cooling profile. In some embodiments, step 130 is implemented in a sequential manner on a plurality of working areas (not shown) that constitutes object region 220. For example, a metal head (not shown) composed of molten metal depositor and working area heater, travels over object region 220 during step 130.

[0235] As seen in Figs. 1A-1B, prior to deposition of the first mold region, a base paste layer 200b can be deposited (at optional step 105), as a substantially continuous base layer (z.e. without object regions), thereby functioning as a solid mold base layer.

[0236] As can be seen in Fig. ID, several metal object regions 230 can be formed in a single mold region 210, thereby forming a nested configuration of several, separate metal objects to be produced.

[0237] Figs. 2A-2C show the steps of another exemplary additive casting process of a metal object, in which two slurry compositions of this disclosure are used for manufacturing the mold region in a production layer, both slurry compositions being in the form of self-supporting pastes, however, differ from one another in their composition.

[0238] In process 1000 comprises deposition 1100 of a paste composition according to a desired mold contour in a production layer 2000i (i being an integer (z >0) defining the number of the production layer), to form a first mold section 2100.

[0239] Another paste composition of this disclosure is then deposited, at step 1200, adjacent the first mold section 2100, to form a second mold section 2160 that laterally encloses the first mold section 2100. The second mold section 2160 is deposited such as to form a substantially continuous inter-mold interface 2140 (to ensure physical contact between the first and second mold sections along this interface). The mold region is then heated at step 1300, to permit at least partial polymerization of the inorganic binder, as well as mass loss of at least 10 wt%, to thereby mechanically stabilize of the mold region. As noted above, in such configurations, the first and second mold sections differ in composition or at least one property (e.g. in their drying rate, polymerization temperature, polymerization rate, etc.). Due to this difference, one of the mold sections mechanically stabilizes before the other, hence providing mechanical support to said other mold section until said other mold section is sufficiently stable for the next manufacturing step of the production layer. As can also be seen, the lateral dimension of the second mold section 2160 is typically larger than the lateral dimension of the first mold section 2100 (i.e. the width of the second mold section is larger than that of the first mold section). This permits the second mold section 2160 to effectively function as a mechanical support to the first mold section 2100, which is directly exposed to the extreme mechanical and thermal shocks applied by the molten metal during deposition and cooling cycles.

[0240] The mold region is then optionally further heated, at step 1400, for further mechanical stabilization, followed by deposition of molten metal 2220 into cavity 2200 formed by the mold region 2100, at step 1500. The molten metal is then permitted to cool and at least partially solidify, at step 1600, thereby forming the metal object region 2300. In this manner, a production layer, e.g. layer 20001, that includes the first mold section 2100, the second mold section 2160 and the metal region 2300 is formed. Deposition of the next production layer, e.g. layer 20002, can then commence by repeating the steps 1100-1500 to form a stack of production layers, until the entire object is manufactured in an additive process.

[0241] An optional step 1450 can be carried out between steps 1400 and 1500. After step 1300 (or 1400, if applied), the mold region 2100 is stable enough to carry out one or more post-deposition surface treatments (step 1450), if desired, in order to smoothen the surface texture of metal-facing surface 2120 or define desired surface features of the mold-facing surface.

[0242] Further, step 1500 can comprise pre-deposition heating of the previously-cast metal object region(s) 2250 such that the top surface of metal object region 2250 - the previously deposited metal - may be in at least partially molten state during molten metal deposition of the subsequent quanta of molten metal. Step 1500 may further comprise post-deposition heating of the deposited metal object region to modify its cooling profile. In some embodiments, step 1500 is implemented in a sequential manner on a plurality of working areas (not shown) that constitutes metal object region 2200. For example, a metal head (not shown) composed of molten metal depositor and working area heater, travels over metal object region 2200 during step 1500. As seen in Fig. 2A, prior to deposition of the first mold region, a base mold layer 2000b can be deposited (at step 1050), as a substantially continuous base layer (z.e. without object regions), thereby functioning as a solid mold base layer.

[0243] It is of note that while in this example the first mold section is formed before the second mold section, it will become apparent to any person of skill that the first mold section can also be formed after the second mold section. Further, it will become apparent that in some production layers the first mold section is formed after the second section, and in other production layers of the same mold-metal object the order of deposition can be reversed.

[0244] Alternatively, the first and second paste compositions can be deposited simultaneously, e.g. from adjacent deposition nozzles.

[0245] The embodiment shown in Figs. 1A-2C is exemplary for application of a paste composition according to this disclosure that is self-supporting, namely, sufficiently viscous to maintain its deposited shape without further support. Examples of applications in which the one of the slurry compositions is a pourable, self-leveling slurry that requires initial mechanical support prior to polymerization are provided in Figs. 3A-3B and 4A- 4C.

[0246] In the embodiment of Figs. 3A-3B, a process 1000’ similar to process 1000 of Figs. 2A-2B is demonstrated, however including a step 1150 of first forming a barrier wall 2400 prior to deposition of the slurry compositions. Thus, the second slurry composition, which is in the form of a pourable self-leveling paste is deposited to the receiving space formed between barrier wall 2400 and surface 2140 of the first mold section 2100’ (that is in the form of a self-supporting paste). In process shown in Figs. 3A-3B, the barrier wall is constructed in an additive manner - namely, for each production layer 2000’i, another vertical section of barrier wall 2400 is deposited.

[0247] In other words, in the embodiment of Figs. 3A-3B, each production layer is manufactured by first depositing a closed-loop barrier wall section 2400’, that defines the external boundaries of the production layer 2000’i. This barrier wall section is typically made of a ceramic composition, as defined hereinabove. Then, a first slurry composition in the form of a self-supporting paste is deposited without the boundaries defined by the wall barrier section 2400’, however separately and laterally spaced-apart from the wall barrier section - thereby forming a first mold section 2100’ that defines a receiving space between the barrier wall and the first mold section. A second slurry composition in the form of a pourable, self-leveling paste is then deposited into the receiving space to form the section mold section 2160’. The second slurry composition is flowable enough as to fill the receiving space, thereby forming a leveled and substantially homogenous second mold section, that provides mechanical support for the first mold region. Due to its fluidity, a more homogenous and complete contact is provided at the interface between the first mold section and the second mold section, permitting more effective mechanical and thermal shock transport from the first mold section to the second mold section during deposition of the molten metal 2220 to obtain the metal region 2250.

[0248] In the embodiment of Figs. 4A-4B, process 1000” is similar to process 1000’, however in this process a vertically continuous barrier wall 2420 is deposited at step 1030, such that the barrier wall 2420 has a height that is at least the same as the height of the final mold-metal object to be produced.

[0249] As can be seen in Fig. 4C, the processes of Figs. 3A-3B and 4A-4B result in a construction of production layers that are constituted by a barrier wall, a mold region constituted by first and second mold sections, and a metal object region.

[0250] As noted, the slurry compositions of this disclosure are designed to be suitable for such mold-metal additive casting processes, particularly tailored to maintain their mechanical stability and mold integrity during the cycles of extensive heat shocks and applied stresses (e.g. due to volume changes of the melting and solidifying metal in the object region).

[0251] The slurry compositions of the present disclosure are deposited to form mold regions having controlled gaseous products release rate and improved heat absorbance / conductance, such that once exposed to heat e.g. resulting from contact with the molten metal or from external heating), the compositions function to provide mechanically stabilized mold regions, improved heat dissipation through the mold region bulk and reduced risk of mechanical failure. In other words, the compositions of this disclosure are characterized by modified energy absorbance and conduction, as well as improved gas release during their polymerization and drying, thereby enabling obtaining mold regions that reach thermal and mechanical stability relatively fast with reduced risk of mechanical failure.

[0252] The slurry compositions of this disclosure are designed to have efficient energy absorption and dissipation. This permits for effective energy uptake and transfer through the voluminous mold region during casting, to minimize the thermal shock experienced by the mold region during casting and thermal cycling. In addition, efficient and controllable gas release from the compositions during absorption of such heat enables minimizing the mechanical damage that can be formed due to uncontrolled and abrupt gas release from the mold region (e.g. due to boiling liquid or gaseous chemical reaction products), hence, maintaining the mechanical integrity of the mold (and particularly the metal-mold interface) throughout the casting process.

[0253] The inventors have found that in slurry compositions of this disclosure, effective energy (e.g. heat) uptake and effective heat dissipation through the mold region, together with controlled evacuation of gaseous products, can be obtained to permit a relatively quick cycle time in the additive manufacturing process. By increasing overall porosity formed during heating and drying of the slurry compositions, it was found that a balance between energy uptake and dissipation with control over the gaseous products evacuation can be obtained. Without wishing to be bound by theory, by forming paths for gaseous products release, porosity prevents internal pressure buildup during drying of the slurry (which is carried out by applying heating conditions). Further, by temporarily physi-sorb molecules of the carrier liquid, e.g. water, a delay in moisture and / or the rate of vaporization of the carrier liquid from the slurry composition can be obtained, thereby assisting in preventing rapid shrinkage and / or capillary collapse. Addition of a thermal modifying additive improves heat uptake and dissipation through the bulk of the mold region. The balance between the fast energy absorption and dissipation, that cause quick increase in temperature within the bulk of the mold region, together with the careful control over the porosity formed during the drying process, results in optimal rate of drying and / or gaseous products evacuation from the mold region. Such balance permits a significant reduction in the risk of cracking or popping effects at the bulk of the mold region as well as at its surface, while also permitting high resistance of the mold region to thermal shock, thereby permitting relatively short fabrication cycles at elevated temperatures and cost-effective process.

[0254] Example 1

[0255] In order to demonstrate the combined effect of the porosity enhancing additive and the energy absorption / conductivity additive, self-supporting paste compositions were prepared according to Table 1 and 1-2: Table 1-1: Tested compositions (wt%)

[0256] Table 1-2: Tested compositions (wt%)

[0257] Small scale samples were prepared to assess the effect on the mass loss, drying profile and the mechanical stability of the compositions.

[0258] Small scale mass loss and drying profile was assessed using Radwag MA50R halogen lamp moisture scale, using 3-7g samples, at heating to 220-230°C, at ambient atmosphere.

[0259] The results for the small scale mass loss tests are shown in Fig. 5.

[0260] Further, the compositions were deposited in cylindrical forms and dried at 230°C over a hot plate. Development of surface and bulk artifacts were monitored and captured, as shown in Figs. 6A-6D. As can be seen from Fig. 5, addition of the microspheres and / or carbon-based additive significantly shortened the overall drying time, as well as increased the drying rate. While from Fig. 5 it seems that the combination of microspheres and carbon-based additive (Comp. 4) does not provide significant change in drying rate of a sample that contained carbon black without microspheres (Comp. 3), the significance of the combination of Comp. 4 is clearly evident from Figs. 6A-6D.

[0261] As can be seen in Figs. 6A-6D, in all of Comps. 1, 2 and 3, significant mechanical artifacts, such as cracks and voids, are observable, while in Comp. 4 no such artifacts can be seen under the same drying conditions.

[0262] The combination of results of Fig. 5 and Figs. 6A-6D provides evidence of the careful balance obtained by the combination of porosity enhancing additives and thermal modifying additives in compositions of this disclosure. Utilization of thermal additives (Comp. 3) increases the absorbance and dissipation of energy, i.e. thermal energy, through the composition - however due to the fast increase in temperature, the liquid components in the composition boil faster and more violently, causing development of internal stresses in the paste during its drying, resulting in significant cracking of the drying paste. Utilization of porosity enhancing additives (Comp. 2), while accelerating to some extent the drying process due to formation of evacuation paths for the gaseous products, also causes results in cracking, typically due to capillary collapse during heating without sufficient heat dissipation means.

[0263] When combining the microspheres with the thermal modifying additive (Comp. 4), a balance is obtained between the quick uptake and dissipation of energy within the paste during heating, and the control over the porosity which provides means for controlling the gradual release of gaseous products from the paste during heating. Hence, the development of internal stresses and surface stresses is kept to a minimum, preventing formation of cracks, voids or other surface artifacts that reduce the mechanical stability of the mold region produced from the paste.

[0264] It is of note that when the samples were utilized to produce large-scale samples, e.g. of a sample having an area of 100 cm2at a thickness of 4-8mm, Comp. 1 remained moist even following 30 minutes of heating , while Comp. 4 dried within 6-7 minutes (to a moisture degree of <2%). In other words, in large scale, Comp. 1 showed significantly low mass loss, while Comp. 4 showed a mass loss of over 10 wt% within 6-7 minutes.

[0265] The compositions of Table 1-2 have shown similar behavior pattern - namely Comp. 6 that contained both the porosity enhancing additive and the thermal modifying additive performed significantly better compared to Comp. 5 that did not contain a porosity enhancing additive. Example 2

[0266] The effect on porosity utilizing different porosity was assessed for self-supporting paste compositions utilizing various porosity enhancing additives, as detailed in Table 2. No energy absorbance / conductance additives were used for these samples in order to permit better visualization of porosity artifacts. All samples were dried under the same conditions. Optical microscopy images of cross-sections of the samples are shown in Figs. 7A-7D.

[0267] Table 2: Effect of various porosity enhancing additives on porosity formation

[0268] As can be seen, without addition of porosity enhancing additives (Fig. 7A), uneven and uncontrolled macropores form prior to and / or during drying. Such uncontrolled macropores constitute voids in the mold region and are locations for stresses development during drying and thermal cycling, that may eventually cause mechanical failure of the mold.

[0269] Addition of microspheres (Fig. 7B), e.g. alumina microspheres, resulted in evenly distributed fine porosity, mainly due to the utilization of substantially monodisperse hollow microspheres that have relatively high mechanical stability.

[0270] Foaming agents, such as sodium dodecyl sulfate (SDS) and the like (Fig. 7C), resulted in formation of air bubbles trapped in the paste composition, that collapse to form porosity during heating of the paste. This additive resulted in significant increase in overall porosity, however also to the formation of relatively large pores.

[0271] Sacrificial materials undergo at least partial decomposition during heating and drying of the paste. Addition of fine powders of PDAC (Fig. 7D), resulted in finer pores than those obtained with SDS. Example 3

[0272] Similar even porosity was obtained for pourable self-leveling pastes prepared according to the compositions of Table 3:

[0273] Table 3: Tested slurry compositions (wt%)

[0274] As can be seen in Fig. 8, which is an image of a sample of Comp. 11 after drying shows that relatively homogenous, fine porosity was obtained.

[0275] Comp. 10 and Comp. 11 are characterized by low viscosity, typically 2,000-4,000 cps. Once deposited into a receiving cavity (or receiving space), the compositions flow within the cavity to fill it, and quickly (a few seconds or minutes) form a substantially horizontal, even top surface. No external force or vibration needed to be applied. Hence, the composition demonstrates sufficient, non-forced, fluidity to permit fast self-leveling.

[0276] It should be noted that the present disclosure is not limited to the production conditions and operational parameters provided in the above-discussed Examples, and the present disclosure may be implemented in various production conditions and operational parameters. The present disclosure is not limited to the casting of gray iron objects and various metals and / or metallic alloys which are suitable for melting and casting, can be used, for example, other iron types, steel and other ferrous alloys, aluminum alloys, copper alloys, nickel alloys, magnesium alloys, and the like.

Claims

CLAIMS:

1. A slurry composition for manufacturing of a mold for additive casting of a metal object, in a process of subsequent formation of production layers, each production layer comprising at least one mold region and at least one metal object region, the mold region comprising at least one slurry composition, the slurry composition comprising: at least one ceramic material in particulate form; at least one inorganic binder; at least one porosity enhancing additive; at least one thermal modifying additive; and at least one carrier liquid; the slurry composition having a mass loss of at least about 10 wt% out of the total mass of the slurry composition when heated to about 220°C for a period of time of no more than about 30 minutes.

2. The composition of claim 1, wherein each production layer is manufactured by deposition of at least one layer of said composition to form the mold region, drying the mold region, and deposition of molten metal into a cavity defined by the mold region to obtain the metal object region.

3. The composition of claim 1 or 2, wherein said at least one porosity enhancing additive is a pore-forming material or a sacrificial material.

4. The composition of claim 3, wherein said at least one porosity enhancing additive is selected from a foaming agent, calcium bicarbonate, sodium bicarbonate, polystyrene beads, and mixtures thereof.

5. The composition of claim 3 or 4, comprising between about 0.01 wt% and about 4 wt% of said pore-forming material or a sacrificial material.

6. The composition of claim 1 or 2, wherein said at least one porosity enhancing additive is selected from one or more types of microspheres.

7. The composition of claim 6, wherein said microspheres are made of aluminum oxide, aluminum silicate, silicon dioxide, borosilicate glass, yttria- stabilized zirconia, and mixtures thereof.

8. The composition of claim 6 or 7, wherein said microspheres have a particle size of between about 50pm and about 500pm.

9. The composition of any one of claims 6 to 8, wherein said composition comprises between about 5 wt% and about 10 wt% of said microspheres.

10. The composition of any one of claims 1 to 9, wherein said at least one ceramic material is selected from zirconia, alumina, silica, zirconium silicate, quartz, yttria- stabilized zirconia, silicon carbide, tungsten carbide, and mixtures thereof.

11. The composition of claim 10, wherein at least a portion of particles of said ceramic material are at least partially coated by a hydrophilic coating.

12. The composition of any one of claims 1 to 11, wherein said at least one ceramic material has a particle size of no more than about 300pm.

13. The composition of any one of claims 1 to 11, wherein said at least one ceramic material is a mixture of at least one first ceramic material having a particle size of between about 50 pm and about 300 pm and at least one second ceramic material having a particle size of between about 1 pm and about 15 pm.

14. The composition of any one of claims 1 to 11, wherein said at least one ceramic material is a mixture of at least one first ceramic material having a particle size of between about 70 pm and about 200 pm and at least one second ceramic material having a particle size of between about 1 pm and about 50 pm.

15. The composition of claim 13 or 14, wherein each of said first and second ceramic materials is independently selected from zirconia, alumina, silica, zirconium silicate, quartz, yttria- stabilized zirconia, silicon carbide, tungsten carbide, and mixtures thereof.

16. The composition of any one of claims 1 to 15, wherein said at least one inorganic binder has a polymerization temperature of at least 150°C.

17. The composition of any one of claims 1 to 16, wherein said at least one inorganic binder has a polymerization temperature of between about 150°C and about 850°C.

18. The composition of any one of claims 1 to 17, wherein said at least one inorganic binder is selected from silicate-based binders, phosphate-based binders, aluminosilicate binders, alumino-silico-phosphate binders, colloidal silica, and mixtures thereof.

19. The composition of claim 18, wherein said at least one inorganic binder is at least one silicate-based binder.

20. The composition of claim 19, wherein said silicate -based binder is an alkalisilicate, an earth-alkali silicate, or a combination thereof.

21. The composition of claim 20, wherein said silicate based binder is selected from sodium silicate, potassium silicate, colloidal silica, and mixtures thereof.

22. The composition of claim 18, wherein the at least one inorganic binder is at least one phosphate-based binder.

23. The composition of claim 22, wherein said phosphate-based binder is selected from alkali metal trimetaphosphate (e.g. sodium trimetaphosphate, STMP), alkali metal monophosphate, aluminum phosphates, sodium tripolyphosphate, silico- aluminophosphate, monoaluminium phosphate, polyphosphates, dihydrogen aluminophosphate, polyphosphazene and mixtures thereof.

24. The composition of any one of claims 1 to 23, wherein said composition comprises between about 2 wt% and about 20 wt% of said at least one inorganic binder.

25. The composition of any one of claims 1 to 24, wherein said thermal modifying additive is an energy absorbing additive.

26. The composition of claim 25, wherein said energy absorbing additive is selected from carbon powder, carbon black, graphene, graphite, carbon nanotubes, UV-absorbing pigments, visible spectrum absorbing pigments, IR absorbing pigments, magnesiumaluminum oxides, ceramic fibers, and mixtures thereof.

27. The composition of claim 25 or 26, wherein said composition comprises between about 0.05 wt% and about 3 wt% of said energy absorbing additive.

28. The composition of any one of claims 1 to 24, wherein said thermal modifying additive is an energy conductive additive.

29. The composition of claim 28, wherein said energy conductive additive is selected from boron nitride, carbon nitride, silicon nitride, silicon carbide, metal particles, metal fibers, metal oxides and mixtures thereof.

30. The composition of claim 29, wherein said composition comprises between about 0.05 wt% and about 3 wt% of said energy conductive additive.

31. The composition of any one of claims 1 to 24, wherein the thermal modifying additive is a mixture of at least one energy absorbing additive and at least one energy conductive additive.

32. The composition of any one of claims 1 to 31, wherein said at least one liquid carrier is selected from water, Ci-Ce alcohols, Ci-Ce polyols, C5-C12 alkanes, mineral oils, natural oil, synthetic oils, and any mixture thereof.

33. The composition of any one of claims 1 to 32, further comprising at least one surfactant.

34. The composition of any one of claims 1 to 33, further comprising at least one mechanical reinforcing element.

35. The composition of any one of claims 1 to 32, being in the form of a self- supporting paste having a viscosity of at least 10,000 cps.

36. The composition of any one of claims 1 to 32, being in the form of a pourable, self-leveling paste, having a viscosity of at most 5,000 cps.

37. A cartridge for holding and dispensing the slurry composition of any one of claims 1 to 36, the cartridge comprising a container for holding said composition, one or more dispensing nozzles configured to permit dispensing of said composition from said container, and one or more mixing means disposed within the container for mixing said composition.

38. The cartridge of claim 37, wherein said mixing means are configured for continuous or intermittent mixing.

39. The cartridge of claim 37 or 38, comprising one or more gas inlets, configured for introducing gas into the container.

40. The cartridge of any one of claims 37 to 39, comprising one or more vents to permit gas discharge from the container.

41. The cartridge of any one of claims 37 to 40 wherein the container is configured to maintain the slurry composition under pressure.

42. A process for additive printing of a mold-metal composite object, the process comprising:(a) depositing a slurry composition of any one of claims 1 to 34 onto a receiving surface to form at least one mold region, the slurry composition being in the form of a self-supporting paste;(b) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;(c) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;(d) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and(e) depositing said slurry composition to form at least one subsequent mold region over the production layer; and(f) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the slurry composition by at least 10 wt%;(g) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;(h) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and(i) repeating steps (e)-(h) to form a stack of production layers, constituting together said mold-metal composite object.

43. A process for additive printing of a mold-metal composite object, the process comprising:(A) depositing onto a receiving surface a first slurry composition of any one of claims 1 to 34 onto a receiving surface to form at least one first mold section, said first slurry composition being in the form of a self-supporting paste, and a second slurry composition of any one of claims 1 to 34 to form at least one second mold section, laterally surrounding said first mold section and in contact therewith, said second slurry composition being in the form of a self- supporting paste and being different in composition from said first slurry composition, the first and second mold sections defining together at least one mold region;(B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second mold compositions by at least 10 wt%;(C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;(D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and(E) depositing said first slurry composition to form a subsequent first mold section, and said second slurry composition to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact therewith, the first and second subsequent mold sections defining together at least one subsequent mold region;(F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;(G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;(H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and(I) repeating steps (E)-(H) to form a stack of production layers, constituting together said mold-metal composite object.

44. A process for additive printing of a mold-metal composite object, the process comprising:(A) depositing onto a receiving surface a closed-loop barrier wall made of a ceramic composition, having at least the height of the mold-metal composite object, and defining mold boundaries, a first slurry composition of any one of claims 1 to 34, to form at least one first mold section, the first slurry composition deposited within the mold boundaries and laterally spaced apart from said closed-loop barrier wall to define a receiving space, said first slurry composition being in the form of a self- supporting paste, and a second slurry composition of any one of claims 1 to 34 into said receiving space, to form at least one second mold section, laterally surrounding said first mold section and in contact with the first mold section and the barrier wall, said second slurry composition being in the form of a pourable self-leveling paste and being different in composition from said first slurry composition, the first and second mold sections defining together at least one mold region;(B) heating the at least one mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second slurry compositions by at least 10 wt%;(C) depositing molten metal into a cavity defined by the at least one mold region, to obtain at least one metal object region;(D) allowing the molten metal to at least partially solidify, thereby obtaining a production layer of said mold-metal composite object; and(E) depositing said first slurry composition to form a subsequent first mold section, and said second slurry composition into said receiving space to form a subsequent second mold section laterally surrounding said subsequent first mold section and in contact with the subsequent first mold section and the barrier wall, the first and second subsequent mold sections defining together at least one subsequent mold region;(F) heating the at least one subsequent mold region to at least 220°C for no more than 30 minutes to at least partially polymerize said inorganic binder and reduce the overall mass of the first and second mold compositions by at least 10 wt%;(G) depositing molten metal into a cavity defined by the at least one subsequent mold region, to obtain at least subsequent metal object region;(H) allowing the molten metal to at least partially solidify, thereby obtaining a subsequent production layer of said mold-metal composite object; and(I) repeating steps (E)-(H) to form a stack of production layers, constituting together said mold-metal composite object.

45. The process of claim 43 or 44, wherein in steps (A) and (E), the first and second mold sections are formed simultaneously.

46. The process of any one of claims 43 to 45, wherein the mass ratio between said first mold section and said second mold section in a production layer ranges between about 1: 1.5 and about 1: 15.

47. The process of any one of claims 43 to 46, wherein said first mold section has a first width and the second mold section has a second width, the ratio between said first width and second width ranges between aboutl:1.5 and about 1: 15.

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