IT202300006870A1 - "Material Jetting Support Structure" - Google Patents

Description

Material Jetting Support Structure

The invention relates to a green body manufactured in layers using the 3D material jetting printing process and connected to a support structure via a separation layer, as well as a process for its manufacture, a sintered part and a process for its manufacture, and the use of a composition containing particles for the manufacture of a separation layer between a green body and a support structure.

In order to produce ceramic components by material jetting, a support material must be used. Only in this way can filigree components with protrusions and undercuts be produced. If such a support material can support the component in the manufacturing process and also in the sintering process, the effort required to produce defect-free ceramic components could be significantly reduced.

The nomenclature in this application refers to DIN EN ISO/ASTM 52900:2022-03.

In material jetting, the construction material is applied using an inkjet print head. The print head can pass through the construction platform lane by lane, printing the layers of the construction element according to the sectioned CAD data. To achieve solidification of the droplets, the printed material is dried using IR radiation, for example, or the photosensitive components of the ink are hardened using a light source. In order to be able to build up protrusions in construction elements, an underlying support structure must be built. Support structures of this type are already used in commercially available 3D printers that work according to the material jetting principle. However, since these printers have so far been used to produce parts made of plastic, water-soluble resins (or low-melting waxes) are used for the support structures, for example.

Even in binder jetting, support structures are already used. The disadvantage of the binder jetting procedure is that in this way one can typically only print layers with a relatively high thickness of more than 100 um, resulting in only green bodies with high porosities of typically more than 40%, which can then shrink very strongly during sintering or become brittle after sintering.

WO2014152798A1 describes a ceramic bearing structure.

WO2018102731A1 describes components manufactured in an additive process with accelerated debinding.

US10800108B2 describes a sinterable separation material.

US2017297100A1 describes the production of a separation layer in a binder jetting procedure.

US2017297097A1 also describes the production of a separation layer in a binder jetting procedure.

US2016229128A1 describes an ink for 3D printing.

EP3612330A2 describes a procedure for the manufacture of print items.

WO2010061394A1 describes a procedure for applying material to a substrate. WO2018193306A2 describes a procedure for manufacturing molded articles.

WO2017180314A1 describes an additive manufacturing with support structures in a binder jetting procedure.

The aim of the present invention is therefore to overcome the disadvantages according to the state

of the art and to develop a technology with which it is possible to manufacture construction elements with protrusions and undercuts by means of material jetting, using support structures during

construction and at the same time also during sintering.

In a first embodiment, the objective underlying the invention is achieved with a green body, manufactured in layers using the 3D material jetting printing process and connected to a support structure via a separation layer,

where green body, separation layer and support structure contain particles,

where the median particle size in the separation layer is in the range

between 200% and 10,000% of the median particle size of the material in the bearing structure, and/or where the median particle size in the layer

separation range is between 200% and 10,000% of the median particle size of the material in the green body,

where the coefficient of thermal expansion of the particle material in the separation layer differs from the coefficient of thermal expansion of the particle material in the supporting structure and/or from the coefficient of thermal expansion of the particle material in the green body by less than 5%, respectively,

where the volume occupied in the green body by air, water and organic substances remains in the range from 5% to 25% by volume.

The green body therefore behaves in such a way that the risk of defects and cracks forming during the drying and/or sintering process is reduced. During

thermal processes, ceramic building elements typically contract, and this process is called shrinkage. As a first approximation, the volume of shrinkage depends on the type of ceramic, the particle size of the raw material and the sintering temperature. To prevent the support material (support structure) from sintering with the building material (green body), a separating layer is applied between the support and the building element.

The patent is based on the concept of manufacturing a support structure, for example using the same material or at least a very similar material to the building element itself (for example Al2O3 with a median grain size of 1?m). In this way, it could sinter and shrink at the same time, so that a support structure that supports the green body during 3D printing can also be used as a base during sintering.

Preferably, the linear sintering decrease of the support structure differs by less than 20% from the linear sintering decrease of the green body, very preferably by less than 10%. The sintering decrease can, for example, be determined using a vernier caliper.

To avoid sintering (e.g. at 1600?C) of the green body with the support structure, a layer of coarse-grained material (e.g. with a grain size of 40?m) is preferably applied between the building element and the support structure. Thus, at the sintering temperature, the separating layer material would not be subject to

to sintering in a fixed structure, and after sintering the construction element can be detached from the supporting structure.

In the present invention the term "layer thickness" refers to the thickness of the layers applied on top of each other by the material jetting procedure to obtain the green body.

The layer thickness of the individual printed layers of the support structure is preferably in the range of 1 to 50?m, very preferably in the range of 2 to 30?m, very particularly preferably in the range of 5 to 20?m. Alternatively,

The layer thickness can also be in the range of 2 to 300 um, most preferably in the range of 100 to 250 um, most particularly preferably 150 to 200 um. The layer thickness can be measured, for example, using an optical microscope. For the measurement, for example, 10 measuring points along a given layer can be used, and the average value is then calculated.

Porosity represents the relationship between the volume of the cavities and the total volume. Porosity can be determined in accordance with DIN EN 993-1. The porosity of the bearing structure, determined after sintering, is preferably in the range of 0 to 15% by volume, particularly preferably in the range of 0 to 5% by volume. The porosity of the bearing structure, determined after sintering or even before sintering, preferably differs by less than 5% from the porosity of the green body.

The volume occupied in the green body and/or the support structure by air, water and organic substances (e.g. solvents or binders) preferably remains in the range of 7 to 20% by volume, particularly preferred in the range of 10 to 15% by volume. Sintering causes water and also organic substances to be largely eliminated. In addition, sintering causes a certain reduction. Therefore, the porosity of the resulting sintered object preferably remains in the mentioned preferred range.

The separating layer preferably has a thickness in the range of 10 to 1000 um, with the range of 20 to 200 um being particularly preferred.

The material of the particles in the bearing structure is preferably metallic or ceramic.

The ceramic material can be selected from metal oxides, metal nitrides, metal carbides and/or mixtures of such materials.

The material of the particles in the green body is preferably metallic or ceramic. The ceramic material can be selected from metal oxides, metal nitrides, metal carbides, carbon and/or mixtures of such materials. For example, in the technical book ?Technische keramische Werkstoffe? (Editor: J. Kriegesmann, chapter 4.3.6.0) carbon is described as a ceramic material (ceramics comprising carbon).

The material of the particles in the separation layer is preferably metallic or ceramic.

The ceramic material can be selected from metal oxides, metal nitrides, metal carbides and/or mixtures of such materials. Particularly preferably the particle material in the separation layer is not a carbonate, specifically no iron carbonate, as this can lead to contamination and/or discoloration of the ceramic or metal.

Essentially, the chemical composition of the material of the particles in the support structure and in the green body is preferably identical; in particular, the material has the same sintering temperature.

The material of the particles in the support structure, the green body and the separating layer is preferably identical. This results in fewer defects, such as cracks or deformations due to different thermal expansion of the materials.

If you want to build a support structure that shrinks to the same extent as the actual ceramic during thermal processes, the simplest way would be to use the same material for both the support structure and the sintered part. For this reason, the material of the particles in the support structure and in the green body is identical.

The median of the particle size in the green body is preferably in the range 0.01 to 15?m, particularly preferably in the range 0.05 to 6?m, very particularly preferably in the range 0.1 to 3?m. The median of the particle size in the support structure is preferably in the range 0.01 to 15?m, particularly preferably in the range 0.05 to 6?m, very particularly preferably in the range 0.1 to 3?m. The deviation of the median of the particle size in the green body from the median of the particle size in the support structure is preferably in the range 0 to 5%.

The median particle size in the separation layer is preferably in the range of 2 to 100?m, very particularly preferred in the range of 6 to 50?m. Preferably, the particle content in the separation layer with a diameter of less

of 6?m is in the range from 0 to 5% relative to all particles in the separation layer.

The particles in the separating layer preferably have a higher sphericity than the particles in the support structure. This has the advantage that the particles in the separating layer are sintered less easily during subsequent sintering. The median of the sphericity of the particles in the separating layer is preferably in the range of 0.6 to 1. The median of the sphericity of the particles in the support structure is preferably in the range of 0 to 0.5.

Sphericity can be determined, for example, by dynamic image analysis.

in accordance with ISO 13322, where the values obtained are the volume-weighted average for the respective sample of the particle mixture of interest. The sphericity of a particle describes the ratio of the surface area of a particle image to the perimeter. A spherical particle would therefore have a sphericity close to 1, while an irregular, serrated particle image would have a roundness close to zero.

In a further embodiment, the objective underlying the invention is achieved by means of a procedure for manufacturing the inventive green body, characterised in that the following steps are performed:

a. manufacturing at least one main suspension, one backing suspension and one separation layer suspension of particles in a solvent, where the median of the particle size in the separation layer suspension is within 200% to 10,000% of the median of the particle size of material in the backing suspension,

and/or where the median particle size in the separation layer suspension is within 200% to 10,000% of the median particle size of material in the main suspension,

b. print at least the main suspension and the suspension for the structure

supported with at least one print head on a substrate to obtain a first layer of the green body and the support structure,

c. repetition of phase b. until the printing of the support structure and the green body is completed, where in all positions where the support structure and the green body meet one or more layers of the suspension for the separation layer are printed, to obtain a separation layer,

where the coefficient of thermal expansion of the particulate material in the suspension for the separation layer differs from the coefficient of thermal expansion of the particulate material in the suspension for the support structure and/or

from the thermal expansion coefficient of the particle material in the main suspension of less than 5%, respectively.

The support structure can be printed from a suspension for the support structure

which is different from the main suspension. Preferably, an additional print head is used for this purpose. The suspension for the support structure can also be identical to the main suspension. In this case, the main suspension is then used as the suspension for the support structure, which is preferably printed with only one print head.

The main suspension and/or the suspension for the support structure may also contain additional components, such as binder, wetting additive, or anti-foaming agent. The suspension for the separation layer may also contain additional components, such as binder, wetting additive, or anti-foaming agent.

The median particle size in the main suspension and/or in the suspension for the support structure is preferably in the range from 0.01 to 6?m, most particularly preferably in the range from 0.1 to 3?m.

The median particle size in the suspension for the separation layer is preferably in the range of 2 to 100 μm, most particularly preferably in the range of 6 to 50 μm.

Preferably, the content of particles with a diameter of less than 6?m in the separation layer suspension is in the range of 0 to 5%, relative to all particles in the separation layer suspension.

The particles in the separation layer suspension preferably have a higher sphericity than the particles in the main suspension and/or the support structure suspension. This has the advantage that the particles in the separation layer are sintered less easily during subsequent sintering. The median of the sphericity of the particles in the separation layer is preferably in the range of 0.6 to 1. The median of the sphericity of the particles in the main suspension and/or the support structure suspension is preferably in the range of 0 to 0.5.

The binder content in the main suspension and/or the suspension for the support structure is preferably in the range of 0.1 to 5% by weight. The binder content in the suspension for the separating layer is preferably in the range of 0.4 to 5% by weight. Preferably, the binder content in the suspension for the separating layer is at least 10%, particularly preferably at least 50% above the binder content in the main suspension and/or the suspension for the support structure. This offers the advantage that, due to the high binder content, the particles sinter with each other less easily. Alternatively, the binder content in the suspension for the separating layer is preferably at least 10%, particularly preferably at least 50% below the binder content in the main suspension and/or the suspension for the support structure. This offers the advantage that a fixed structure could not even be formed in the separating layer.

Preferably, with the inventive procedure, a print head is used for printing the separation layer with the separation layer suspension which is distinct from the print head for printing the main suspension and/or the backing structure suspension. In particular, the print head for printing the separation layer suspension, unlike the print head for printing the main suspension and/or the backing structure suspension, is suitable for printing suspensions with particles having a particle size of more than 5?m. Alternatively, the same print head may, however, be used for printing the main suspension and/or the backing structure suspension and the separation layer suspension. Such a print head will then preferably be suitable for printing suspensions with particles having a particle size of more than 5?m.

Preferably, to obtain the separation layer, in phase c you print from 1 to 50

layers, preferably 1 to 10 layers or 5 to 50 layers with the suspension for the separating layer. The layer thickness of the individual layers printed in the separating layer is preferably in the range of 2 to 200?m, very particularly preferably in the range of 5 to 20?m or in the range of 50 to 180?m.

The solvent is preferably water.

The water content in the main suspension and/or in the suspension for the support structure is preferably in the range of 10% to 40% by weight. The water content in the suspension for the separating layer is preferably in the range of 10% to 40% by weight.

The particle content in the main suspension and/or in the suspension for the support structure is preferably in the range of 60 to 90% by weight. The particle content in the suspension for the separation layer is preferably in the range of 60 to 90% by weight.

The content of the moistening additive in the main suspension and/or in the suspension for the support structure is preferably in the range of 0.1 to 2% by weight, particularly preferably 0.1 to 1. The content of the moistening additive in the suspension for the separating layer is preferably in the range of 0.05 to 2% by weight.

0.5% by weight (up to 1%). Preferably, the content of the moistening additive in the main suspension and/or in the suspension for the support structure is at least 50%, particularly preferably at least 100% above the content of the moistening additive.

of humidification in the suspension for the separation layer.

The content of antifoaming agent in the main suspension and/or in the suspension for the support structure is preferably in the range of 0.01% to 0.2% by weight. The content of antifoaming agent in the suspension for the separation layer is preferably in the range of 0.01% to 0.2% by weight.

In a further embodiment, the objective underlying the invention is achieved by means of a sintered piece, manufactured by sintering the inventive green body, characterised in that the porosity is in the range of 0 to 15% by volume.

Thanks to the separating layer, the sintered part can be easily separated from the support structure. For example, the support structure is sintered together with the green body. Preferably, due to sintering, it may be the case that the separating layer material is sintered in such a way that the green body and the support structure can be easily separated from each other.

Preferably, the porosity of the sintered bearing structure differs less than 5% from the porosity of the sintered workpiece.

The sintered part may exhibit all the characteristics of the aforementioned green body, as long as an expert in the field would not consider them abnormal. In contrast to the green body, for example, no antifoaming agents can be found in the sintered part. On the other hand, the particle materials and particle sizes could, for example, possibly still match.

In a further embodiment, the objective underlying the invention is achieved by means of a procedure for manufacturing the inventive sintered piece, characterised

from the fact that a green body is sintered according to the invention.

In a further embodiment, the objective underlying the invention is achieved by using a liquid composition, containing ceramic or metallic particles, for

the manufacture of a separation layer between a green body and a support structure. The composition may be for example the suspension for the separation layer mentioned above, also with its preferred embodiments.

Example of implementation

In concrete terms, a main suspension was manufactured containing, apart from Al2O3 with a median grain size of 0.7 um (CT3000 SG of ), a wetting additive (Dolapix CE 64 of ), a temporary binder (Optapix AC95 of

) and an antifoaming agent (Contraspum KWE from ). Water was used as the dispersion medium. The composition of such a main suspension is listed in the following table.

This main suspension was used for the manufacture of a green body and a support structure of a construction element by means of material jetting. For the print head, a special print head from the company was used

described in detail in WO2013013983A1. This printhead is very robust against abrasive suspensions, such as ceramic glazes and slip. With this printhead, it is also possible to print suspensions with particles with a diameter of more than 1 mm.

of 45?m. Water-based suspensions with a very low percentage of organic solvents can also be used for printing.

The support structure was made using the same main solution and the same print head.

In order to prevent sintering of the component with the supporting structure, a suspension for the separating layer was produced using a chemically identical particle material, but with a significantly larger grain size (?separating layer?). A cast corundum of size F600 with an average grain size of approximately 9?m was found to be suitable for this purpose. From this material, a suspension for the separating layer was produced, the composition of which is listed in the following table:

This separation layer suspension was printed with a second printhead that was connected to a second ink supply system.

After sintering at 1600?C and a waiting time of 2 hours the green body was sintered

in a ceramic piece, as well as the support structure. The significantly thicker material between the now sintered piece and the support structure was not sintered, but had instead formed a separating layer, so that the sintered piece could be separated from the support structure.

The generation of the support structure and the green body and the separation layer was assisted by a specific software. In particular, the printing of the separation layer between

the green body and the support structure was controlled by the 3D printer software.

Claims (1)

Claims Green body, manufactured in layers using the 3D printing process ?material jetting? and connected to a support structure by a separation layer, where green body, separation layer and support structure contain particles, where the median particle size in the separation layer is within the range of 200% to 10,000% of the median particle size of material in the support structure, and/or where the median particle size in the separation layer is within the range of 200% to 10,000% of the median particle size of material in the green body, where the coefficient of thermal expansion of the particle material in the layer of separation differs from the coefficient of thermal expansion of the particle material in the support structure and/or from the coefficient of thermal expansion of the particle material in the green body by less than 5%, respectively, where the volume occupied in the green body by air, water and organic substances remains in the range from 5% to 25% by volume. Green body according to claim 1, characterised in that the median of the particle size in the separation layer is in the range from 2 to 100?m. Green body according to claim 1 or 2, characterized in that the linear sintering decrease of the support structure differs by less than 20% from the linear sintering decrease of the green body. Green body according to one of the preceding claims, characterised in that the separating layer has a thickness in the range from 10 to 1000 m. Procedure for manufacturing the green body according to one of claims 1 a 4, characterized by the fact that the following phases are performed: a. manufacturing of at least one main suspension, one suspension for the support structure and one suspension for the particle separation layer in a solvent, where the median particle size in the suspension for the separation layer is in the range 200% to 10,000% of the median particle size of material in the suspension for the backing structure, and/or where the median particle size in the suspension for the separation layer is in the range from 200% up to 10,000% of the median particle size of material in the main suspension, b. print at least the main suspension and the suspension for the structure supported with at least one print head on a substrate to obtain a first layer of the green body and the support structure, c. repetition of phase b. until the printing of the support structure and the green body is completed, where in all positions where the green body and the support structure meet one or more layers of the suspension for the separation layer are printed, to obtain a separation layer, where the coefficient of thermal expansion of the particulate material in the suspension for the separation layer differs by less than 5% from the coefficient of thermal expansion of the particulate material in the suspension for the support structure and/or from the coefficient of thermal expansion of the particulate material in the main suspension, respectively. Process according to claim 5, characterised in that the main suspension and the separation layer suspension contain a wetting additive and that the content of the wetting additive in the main suspension exceeds the content of the wetting additive in the separation layer suspension by at least 50%. Procedure according to claim 5 or 6, characterised in that in phase c 1 to 50 layers are printed, preferably 1 to 10 layers or 5 up to 50 layers, with the suspension for the separation layer, to obtain the separation layer. Sintered piece, manufactured by sintering the green body according to one of claims 1 to 4, characterised in that the porosity is in the range between 0 and 15% by volume. Procedure for manufacturing the sintered piece according to claim 8, characterized in that a green body according to one of claims 1 to 4 is sintered. 10. Use of a liquid composition, containing ceramic or metal particles for the fabrication of a separation layer between a green body and a supporting structure.