RU2564604C1 - Method of three-dimensional printing of products - Google Patents

Abstract

FIELD: printing industry.

SUBSTANCE: method of three-dimensional printing of products comprises creation of 3D-model of the product, division of the product model into layers in cross-section, applying a layer of powder material by plasma spraying, sequential reproduction of the respective layers in the cross section before formation of the product. Each layer is formed in the following sequence: a) application of the powder material by continuous plasma spraying, b) application of the powder material discretely in the form of a matrix of coarse grains, and the coarse grains of each subsequent layer are applied offset with respect to the previous one, along the contour of the cross section of each layer the powder material is applied by microplasma spraying, the last layer is completed by the continuous plasma spraying of powder material to form a flat and smooth outer surface.

EFFECT: creation of products with high strength by the method of three-dimensional printing using plasma spraying of powder materials, as well as with the ability to manufacture products of compound geometric shape.

4 cl, 5 dwg

Description

The invention relates to methods for three-dimensional printing by plasma spraying of products for various purposes.

The technology of plasma spraying is widely known from the prior art, in particular for the production of new materials, coatings, for the restoration of worn parts, as well as for three-dimensional printing of products.

A known method of three-dimensional printing of products, in which the product can be formed by sequentially applying many separate layers using plasma spraying of a powdery material. The material used is metal or ceramic powders, as well as mixtures thereof. Moreover, the formation of individual layers is carried out by two different methods: layers of a greater thickness - by means of plasma spraying, layers of a smaller thickness - by welding with a laser beam. All layers are formed one on top of the other (US 6744005, IPC B23K 10/00, 10/11/1999).

There is also a method of three-dimensional printing of products, including creating a three-dimensional model on a computer, dividing the model into two-dimensional layers, applying two-dimensional layers of powder material to form the product. One of the methods of applying layers of powder material is a plasma spraying method. The well-known technical solution involves the use of a whole technological complex for the production of products: plasma spraying, laser cladding for areas with increased requirements for geometric accuracy, a milling unit for machining products, tools for threading, automatic optical control of the process, and also means for three-dimensional scanning of an object prototype for its subsequent replication. (US 7020539, IPC G06F 19/00, 03/28/2006).

There is a known method in which plasma particles are applied to a substrate by a plasma flow so that individual particles of the material are welded to the substrate or to each other without full fusion. The plasma torch is controlled so that a three-dimensional article or coating is formed. The material may be in the form of a powder or wire (metal, ceramics, alloys). After applying the first layer, the following layers of particles are applied, and thermal parameters, the temperature of the plasma torch, the duration of heating, the feed rate of the material are adjusted to obtain the product of the desired shape, microstructure, physico-mechanical properties and with the required ratio of pore and solid matter. (US 20090047439, IPC B05D 1/08, 08/16/2007).

The essence of the known methods is that particles of a powdery material are introduced into the plasma jet, which is heated to the melting temperature. Powder particles due to their high speed and their partial penetration are fixed on the substrate, and then on the previously deposited layers.

The disadvantages of the known methods include the absence in the description of specific sequential steps of forming product layers, which implies the use of the traditional method, namely, continuous plasma spraying of the material, i.e. continuous, in some cases at an angle to the spraying surface. As a result, it is extremely difficult, and sometimes impossible, to obtain complete products with increased strength with the required properties, since with a large number of layers applied by the traditional method, mechanical stresses arise, leading to separation from the substrate or cracking. Another disadvantage is the complexity and high cost of designs, the use of a high-power laser, which is an increased danger for maintenance personnel.

The technical result consists in the creation of products of increased strength by three-dimensional printing using plasma spraying of powdered materials, as well as with the ability to perform products of complex geometric shapes.

The specified technical result is achieved by the fact that by the method of three-dimensional printing of products, including creating a 3D model of the product, dividing the product model into layers in cross section, applying a layer of powder material by plasma spraying, sequential reproduction of the corresponding layers in cross section until the product is formed,

ACCORDING TO THE INVENTION, each layer is formed in the following sequence: a) applying a powdery material by continuous plasma spraying, b) applying a powdery material discretely in the form of a matrix of large grains;

moreover, the grains of each subsequent layer are applied with an offset relative to the previous one; along the contour of the cross section of each layer, the powdery material is applied by microplasma spraying; the last layer is completed by continuous plasma spraying of the powdered material until a smooth and smooth outer surface is formed.

Powdered material consists of both a single component and a mixture of two or more components selected from the groups: refractory oxides (including magnesium oxide, aluminum oxide, calcium oxide, zirconium dioxide, chromium oxide, silicon oxide); oxygen-free compounds (including carbides, borides, nitrides); carbon, ferrous and non-ferrous metals, including refractory metals, organic polymers. Use a powdery material with a particle size of 0.02-0.04 mm, or 0.04-0.08 mm, or 0.063-0 mm.

The choice of powdered material is limited by mutual compatibility and is determined by the operating conditions and the necessary physical and mechanical properties of the product. It is possible to adjust the required properties of the resulting products due to the fact that the method is implemented in several stages, which allows you to alternate powdery material within a single layer, or alternate layers of different materials, or use only one specific powdery material in the volume of the entire product. In the case of using materials with different temperature coefficients of linear expansion, a micro-cracked structure is formed, which allows the product to have high heat resistance. In the case of plasma spraying of a mixture of powdered materials with high and low hardness, a structure is formed that is resistant to variable and impact mechanical loads. If necessary, you can use oxide powder materials with a purity of 97-99% and even more than 99%.

In accordance with the present invention, the proportion of powdered material with a particle size of less than 0.1 mm is at least 95%. The preferred particle size of the powdered material is in the range of 0.02-0.04 mm, or 0.04-0.08 mm, or 0.063-0 mm.

The product is formed by three-dimensional printing, applying layers of powder materials by plasma spraying using a plasma torch. The application of the layer is carried out in the following sequence: the application of powder material by continuous plasma spraying, then the application of the powder material is discrete in the form of a matrix of large grains having a shape close to the sphere. Large grains are obtained as a result of the instantaneous shutdown of the plasma torch, while the temperature of the material has time to rise up to the melting point and a fused large grain is obtained. Due to the fact that the powdery material is applied discretely, the accumulation of mechanical stresses in one direction does not occur due to shrinkage during crystallization of the melt and narrowing with further cooling of the material, since the total stress vectors are small and oriented against each other. Heating and subsequent slow cooling from the application of overlying layers reduce residual stresses to a minimum. As a result of this, strength is achieved with a large thickness of the product, in contrast to traditional methods of plasma spraying.

A distinctive feature of the invention, which consists in applying the material in several stages, first continuously, and then discretely with stops in the form of a matrix of large grains, allows to obtain products of increased strength not only with low but also with high porosity. Low total porosity in coarse grains (less than 10%), in intergranular space (~ 15-20%) and low total porosity of the whole product (~ 10-15%) is ensured by plasma spraying due to the high speed of the powder particles and their partial penetration. The voids between the grains are filled with continuous plasma spraying in motion, which eliminates the open channel porosity of the entire product.

The use of burnable materials and oxidizing plasma-forming gases in a mixture (without the use of a protective gas) is possible to obtain porous products.

The application of each next layer is formed with an offset relative to the previous one in order to ensure the most dense packing of large grains according to the pyramidal method (Fig. 1). Due to this, the strength increases and the anisotropy of the structure of the finished product decreases compared to other packaging methods.

To obtain an exact geometry of the lateral surface, the external contour of each product layer is smoothed by microplasma spraying.

The last layer is completed by continuous plasma spraying to ensure the necessary height of the product, to give a smooth surface.

The essence of the proposed method is illustrated by drawings.

In FIG. 1 schematically shows a top view of the displacement of the grains of one layer relative to the grains of another, in FIG. 2. - conventionally shown the sequential application of the powder material discretely in the form of a matrix of large grains - on the example of one layer, in FIG. 3 - shows a 3D printer, in FIG. 4 - construction of a plasma torch, in FIG. 5 is a refractory block for mixing material in a rotary kiln (specific embodiment of the invention). It should be understood that the implementation of the proposed method is not limited to the 3D printer and plasma torch designs described in the present invention, but merely illustrates (explains) the possibility of implementing the inventive three-dimensional printing method. In addition, when implementing this invention, it is possible to use a fairly wide range of settings (flow rate of plasma-forming gas, gas flow rate for powder supply, powder feed rate, angle of incidence of particles to the spraying surface, spraying distance and other parameters), which are determined individually for each specific material .

The essence of the proposed method consists in layer-by-layer application of powder material to the formation of the finished product. In FIG. 2 conventionally shows the sequential reproduction of layers (for example, one layer) of the product. First, a powdery material is applied to the substrate 1 by continuous plasma spraying in the form of a film 2 over the entire surface of the substrate (Fig. 2, a). Further, the powdery material is applied to the film 2 discretely in several stages. At the first stage, the powdery material is applied in the form of a matrix of large grains 3 (Fig. 2, b), then sequentially along the X axis until rows are formed (Fig. 2, c-d). At the next stage, the powdery material is applied in the form of a matrix (displaced along the Y axis by a distance equal to the diameter of the grain) from coarse grains 3 (Fig. 2, e), then sequentially along the X axis until rows are formed (Fig. 2, e-g) , followed by the repetition of this stage until the formation of the product layer (Fig. 2, and-l). To obtain an exact geometry of the lateral surface, the external contour 4 (Fig. 2, m) of the product layer is smoothed by microplasma spraying. Next, the layers are sequentially reproduced until the finished product is formed, and the grains 3 of each subsequent layer are applied with an offset relative to the previous in the direction of the X and Y axes by half the diameter of the large grain. The last layer is completed by continuous plasma spraying of the powdered material to obtain the exact height of the product, the multiple height of the row, and until a smooth and smooth outer surface is formed.

The proposed method is implemented using a 3D printer (Fig. 3).

The source materials are fed from the cuffs 5 to the receiving hopper 6, from which they enter the feeders 7 (in Fig. 3, the cuff, receiving hopper, feeder are shown in the amount of 1 pc.). From where individually using a conveying gas supplied from a cylinder 8 or compressor 9 (if air is selected as one of the gases) through a set of control solenoid valves 10, they are carried away through the pipelines of the dust-gas mixture 11 (in the figure 3 it is shown in the amount of 1 pc.) into the plasma torch 12. Plasma-forming gas is supplied from the cylinder 8 through a set of control solenoid valves 10 to the gas line 13, from where it enters the plasma torch 12, which is moved in the horizontal plane using the carriage device 14.

The chemical carrier gas may be different or identical to the plasma-forming one. Various gases can be used as a plasma-forming one: inert gases (argon, helium), reducing gases (hydrogen) and oxidizing gases (air, nitrogen), as well as ammonia, natural gas, and water vapor.

To form the product 15 in the Z direction (shown in Fig. 3), a table raising and lowering mechanism 16 is provided, which raises a removable one under the trolley 17, rolled up in a sealed noise-proof chamber 18. To power the plasma torch, a step-down transformer 19 with a semiconductor rectifier (diode bridge) is used and an oscillator to obtain a high voltage pulse necessary to obtain a plasma arc when starting the plasma torch 12. To cool the cathode and anode of the plasma torch, water cooling is used, consisting of from the water tank - tank 20, pump 21 and radiator 22.

The design of the plasma torch 12 (Fig. 4) is proposed with the most dense arrangement of the working cells 23 in the horizontal plane. Cell 23 of the plasma torch consists of a cathode 24 with a replaceable tip and a replaceable anode 25 in the form of a Laval nozzle separated by an insulating material 26 and cooled by water using chambers 27 and 28. The sprayed material passing through the Laval nozzle accelerates to near- or supersonic speeds, heats up a plasma stream 29 and is applied to the substrate 1 in the form of densely sintered coarse grains 3. To cool the grains 3 and to protect them from oxidation in the case of using non-oxide materials, a chamber 30 with supplied protective gas is provided. Inert gas (argon, helium) or carbon dioxide is used as a protective gas.

As a specific example, a refractory block is made (FIG. 5) for mixing the material in a rotary kiln. The example in question does not exclude other variations within the scope of the claims. The block for mixing the material consists of a steel plate 31, anchors 32 made of heat-resistant stainless steel, a lower heat-insulating (reinforcing) part 33 made of chamotte, and an upper working part 34 made of periclase and spinel. For the manufacture of a side recess, a temporary supporting material 35 is required — a composition of a thermoplastic polymer (for example, polypropylene) and graphite, which is then easily separated from the product. The process of forming the product goes from bottom to top in the order of part 33 - part 34 and simultaneously with parts 33 and 34 - anchors 32. The plate 31 is made in advance of sheet metal with thorough cleaning of the working surface.

A 3B model of the product (Fig. 5) in STL format is prepared on the PC of the design engineer and sent to the PC that controls the 3D printer (Fig. 3). The software installed on the control computer conditionally divides the model into n layers and sends control signals. Management of three-dimensional printing is carried out with the electronic control unit 36 (Fig. 3).

The starting materials (chamotte, periclase, spinel and powder from heat-resistant stainless steel) are selected with a particle size of 0.063-0 mm.

The product is formed in the following sequence.

A plate 31 is attached to the substrate 1 (Fig. 5). To obtain part 33 by plasma spraying using a plasma torch 12 (Fig. 3), chamotte powder is applied layer-by-layer to the plate 31 and, at the specified places, the powder is made of heat-resistant stainless steel to obtain anchors 32.

Each layer is applied by plasma spraying as follows. First, fireclay powder is applied by continuous plasma spraying. Then, fireclay powder is applied by the plasma torch with stops to obtain a matrix of densely sintered large grains in several stages. For this, at the first stage, chamotte powder is applied in the form of a matrix of densely sintered grains by moving the plasma torch along the X axis with a step equal to the diameter of the grain until rows are formed. At the next stage, the plasmatron is displaced along the Y axis by a distance equal to the diameter of the grain, and similarly to the first stage, it rows rows of densely sintered grains along the X axis, but in the opposite direction. The step is repeated until the product layer is formed.

The layer is completed by smoothing the outer contour by microplasma spraying of chamotte powder with continuous movement of the plasma torch along the perimeter of the layer.

The densely sintered grains of each subsequent layer are applied with a displacement relative to the previous in the direction of the X and Y axes by half the diameter of the grain with repeating the steps of applying the layer described above, until the formation of part 33.

Part 33 is applied by plasma spraying to obtain part 34 of periclase, spinel and, at the same time, powder of heat-resistant stainless steel in predetermined places in a similar way to obtain layers of part 33 of chamotte powder. The ratio and distribution of periclase and spinel grains in the layer is selected by the computer based on the given chemical composition of the future product. For this specific example, you can use spinel grains in the range of 5-25 wt%, the rest is periclase. It should be noted that the selection of the optimal chemical composition, a preliminary assessment of the properties of products are possible by "printing" (manufacturing) a series of samples of small sizes (for example, 50 × 50 × 50).

Since special recesses in the product pass through part 34, an additional layer of supporting material 35 is applied outside the contour of the product layer (in parallel or after smoothing the contour by microplasma spraying).

The application of powder from heat-resistant stainless steel for anchors 32 is carried out in the process of obtaining a layer, in predetermined places, corresponding to the nth layer of parts. Before applying each subsequent layer, the substrate 1 with the product is lowered in the Z direction to the thickness of the previous layer.

The last layer of the product is completed by continuous plasma spraying of periclase powder to obtain the exact height of the product, a multiple height of the layer, and until a smooth and smooth outer surface is formed.

The design of the plasma torch provides for the use of one, several or all cells simultaneously, depending on the area and shape of the nth layer. Unused cells are in the mode of maintaining a plasma arc with a small consumption of plasma-forming gas and without feeding sprayed material into them. The use of all involved cells simultaneously increases the productivity of manufacturing products (in particular, large ones).

In the intervals between the application of the product layers, it is possible to use annealing with a plasma stream without spraying material with an increased distance from the product to the plasma torch or penetration with a reduced distance.

The finished product is removed from the workspace of the 3D printer and transported to a place of cooling (storage).

The substrate 1 should be easily detachable from the molded product, aluminum foil, cardboard or a steel sheet with an uncleaned or oiled surface is suitable for these purposes.

The inventive method can be made products of complex geometry and structure from any materials that can melt without decomposition (without restrictions on the melting temperature). For sections of products that are above the voids, if this cannot be eliminated by the appropriate geometric orientation, the use of support materials can be applied, which are then removed. As a supporting material, low-melting substances (including metals such as lead, tin), brittle materials, soluble substances (in water - salts, or organic - in organic solvents), burn-out (plastics, etc.) can be used.

As an example of obtaining products of a porous structure of increased strength, the claimed method of three-dimensional printing due to plasma spraying, it should be noted the use of the finest fraction (0.02-0.04 mm) of technical alumina (to obtain hollow microspheres) as a powder material, the introduction of a special additive (SiO ₂ + TiO ₂ ); or the use of the finest fraction of ZrO ₂ stabilized by the addition of CaO as the powder material, and nitrogen or air as the plasma-forming and transporting gases. Increased porosity is achieved due to the volume of the internal space of the hollow microspheres, and strength due to the low porosity in the intergrain space. The porosity of the product in this case will be predominantly closed. In the case of using powders in a mixture with burnable organic materials and oxidizing plasma-forming gases (without using a protective gas), increased porosity is achieved due to the combustion of organic particles and the formation of voids in their place.

The inventive method of three-dimensional printing by plasma spraying allows to manufacture products for various purposes of increased strength: products of dense microstructure with low porosity, products of a porous structure of increased strength, products with different temperature indicators; complex geometry, using a wide range of materials.

Thus, the claimed technical result is achieved.

Claims (4)

1. The method of three-dimensional printing of products, including creating a 3D model of the product, dividing the product model into layers in cross section, applying a layer of powder material by plasma spraying, sequential reproduction of the corresponding layers in cross section to form the product, characterized in that
each layer is formed in the following sequence: a) applying a powdery material by continuous plasma spraying, b) applying a powdery material discretely in the form of a matrix of large grains,
and large grains of each subsequent layer are applied with an offset relative to the previous one,
along the contour of the cross section of each layer, the powdery material is applied by microplasma spraying,
the last layer is completed by continuous plasma spraying of the powdered material until a smooth and smooth outer surface is formed. 2. The method of three-dimensional printing of products according to claim 1, in which the powdered material consists of both a single component and a mixture of two or more components, including:
refractory oxides (including magnesium oxide, alumina, calcium oxide, zirconia, chromium oxide, silicon oxide),
oxygen-free compounds (including carbides, borides, nitrides),
carbon, ferrous and non-ferrous metals, including refractory metals, organic polymers. 3. The method of three-dimensional printing of products according to claim 1, in which a powdery material with a particle size of 0.02-0.04 mm, or 0.04-0.08 mm, or 0.063-0 mm is used. 4. The method of three-dimensional printing of products according to claim 1, in which the powder material consists of one component, several or a mixture of two or more components within the same layer.

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