RU2423203C2 - Method of sintering solid parts in laser layer-by-layer powder synthesis - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to production of articles laser layer-by-layer synthesis. It may be used in machine and aircraft building. Proposed method comprises metered feed of powder on working table to prepare preset thickness layer. Powder layer is leveled by adjustable-height blade and compacted by free rolling roller. Excess amount of powder is removed to sinter formed layer by laser beam.

EFFECT: higher quality of layer-by-layer sintering due to optimum thickness of layer that allows surface activity of microparticles.

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Description

Technical field

The method relates to technological processes, the field of powder metallurgy, the production of metal, ceramic powders with the sintering process, and in particular to the technology of manufacturing complex parts from fine powder using the technology of laser layer-by-layer synthesis, and can be used in various branches of machine and aircraft industry.

State of the art

Known RF patent No. 2217266 C2, class B22F 3/105, D22P 7/100, 08/11/2000, which includes sequential layer-by-layer placement of the powder mixture on the desktop, processing each layer of the powder mixture with a cylinder to level it and subsequent layer-by-layer laser sintering.

Known installations (for example, the Pnenix-250 machine according to the source www1.pomori.ru) that implement the sintering method for laser layered powder synthesis of bulk parts. Sintering (alloying) parts made of powders and consisting mainly of a laser-optical system, a working chamber with a vertically movable working table equipped with a dosed powder supply mechanism and an alignment mechanism made in the form of a roller, its layer, with vacuum, cleaning and protection of the gaseous medium, as well as with control systems for the temperature of the sinter layer, cooling of the part, with a control system and software, etc., with metal powders with a dispersion of 6-16 microns).

A known method of leveling a layer of powder including with the help of rotating countercurrents - drums with notches that move a portion of the powder poured near the working table and level the formed layer (RF patent 2021881 C1 B22F 3/22 1994), and the distances from the (gaps) of the rollers to the working planes of the table are constant.

A known method of layer-by-layer laser sintering using devices for leveling powder layers in the form of knives installed with constant gaps to the working plane of the tables of sintering chambers (for example, a machine Conzept M2 (Germany) information source http://www.mcp.by/equipment?id = 49 2009) with applied metal powders with a fineness of 23-60 microns).

The disadvantages of all the above methods is the use of layers of powder materials with constant bulk densities, which is caused by the use of mechanisms with knives or rollers (drums) with constant gaps between them, on the one hand, and the working planes of the camera tables, on the other, which does not provide the required quality of the manufactured products due to the heterogeneity of the sintered powder.

SUMMARY OF THE INVENTION

The objective of this method is to develop such a technology that would improve the quality of sintering of the part by leveling each layer of powder with achieving its optimum density with increased accuracy, providing sufficient surface activity of microparticles during sintering.

The problem is solved due to the fact that in the method of sintering during laser layer-by-layer powder synthesis of volumetric parts, including dosed layer-by-layer feeding of powder to the working table, leveling the powder layer, removing excess powder, after leveling the powder layer, it is densified, and then sintering with a laser beam is performed . The list of drawings.

The method is illustrated by drawings, in which:

Figure 1 shows the device mechanism for leveling and compaction of the layer;

Figure 2 shows the alignment scheme of the powder layer, followed by compaction with high accuracy.

The implementation of the invention

It is necessary to manufacture parts by the method of layer-by-layer synthesis using a device (in the form of an experimental stand for working out the sintering regimes of new powder materials) with a laser-optical system with the ability to move the optical head vertically, equipped with a working chamber and a working table (for direct sintering), a container with powder and the mechanism of its metered supply and leveling of the powder layer, with vacuum systems and protective gas supply, heating of the powder layer and removal of unused eyes working chamber drains.

The method in accordance with the invention is as follows:

1. Dosed dispensing of the powder 13 to the working table 3 is carried out, necessary for sintering one layer.

2. Level the poured powder layer.

3. Seal the poured powder layer.

4. Remove excess powder

5. The protective gas is supplied to the working chamber.

6. Carry out the process of sintering the powder layer with a laser beam in accordance with the software

The indicated steps for the preparation of other powder layers are repeated as many cycles as necessary, until the entire part is manufactured, followed by cooling, cleaning and removal from the working chamber.

A device for manufacturing parts by layer-by-layer synthesis technology (in the form of an experimental bench for testing the sintering regimes of new powder materials) consists of a rigid frame 1, on which containers with powder sprinkled in it and a mechanism for its metered feeding, a device for leveling and compaction of the powder layer are placed, as well as a mechanism vertical movement of the laser optical head and carriage 2 with horizontal displacement drives. The stand also contains a fiber optic ytterbium laser, a control cabinet, a working chamber (with vacuum systems, pressurization of a protective gas, cleaning, cooling the chamber, monitoring the actual temperature of the sintered powder), a working table 3 with the possibility of its vertical movement, a control panel with both manual and and automatic control of the stand with software, a protective casing, and a hopper for collecting excess powder 12.

Figure 1 shows the device of the mechanism of alignment and compaction of the powder layer, made with a glass 4 with a portion of powder 13 located therein, a movable carriage 2 with a roller 5 that is rigidly fixed to it with a powder compaction layer, and a housing 7 of a vertically positioned differential screw 8 with a step servo drive and a powder leveling knife 9. The carriage 2 is moved by the electric drive 6 along the guides 10 of the device. The knife 9 is rigidly attached to a vertically positioned differential screw with a stepper servo drive, providing vertical movement of the knife with high accuracy.

Proposed by the present invention, the method is as follows:

in a glass 4 pour a portion of the powder with a volume sufficient for one layer.

After which the working table 3 is lowered to a height of h ₀ = 50 μm (figure 2).

The next step is the alignment of the poured powder layer. Pre-determine the required thickness of the layer of powdered powder. The height of the aligned powder layer depends on the set height of the knife 9 relative to the plane of the working table 3. In this case, the estimated thickness of the layer N (μm) of the powder is determined by the formula (1) with the condition of ensuring a relative increase in density:

Where

h ₀ - the required thickness of the sintered layer (μm),

h ₁ - additional layer thickness taking into account the shrinkage of the sintered material (μm),

h ₂ - additional layer thickness, taking into account the increased density (microns). Additional layer density is determined previously experimentally for various powders.

After that, the knife 9 is set to size H (calculated by formula 1), taking into account the necessary relative increase in density.

The relative increase in the bulk density of the powder (P ₁ / P ₀ ) in (%) is determined by the formula (quantitative assessment of the increase in density):

Where

P ₀ - initial bulk density (kg / m ³ ),

P ₁ - final increased density (kg / m ³ ).

Alignment of the poured powder layer is carried out by moving the movable carriage 2 from the extreme right position to the left. In accordance with the software, the electric drive 6 moves the movable carriage 2 from the extreme right position to the left, the knife 9 being rigidly fixed on the carriage and height-adjustable raking a portion of powder and leveling the powder layer. The accuracy of the vertical movement of the knife is illustrated by the differential screw.

The next step is the compaction of the powder as follows. The thickness of the poured layer H, calculated by the formula (1), is compacted by the value of h ₂ , while the density of the powder increases. The seal is performed by horizontal movement of the carriage 2 and the roller 5 fixed on it, in the free rolling mode. Moreover, the gap of the roller to the working plane of the table is less than the similar gap of the knife 9 by the value of h ₂ (Fig. 2). In accordance with the software, the electric drive moves the movable carriage 2 to the left at a speed of 70 mm / s, while the roller 5 compacts the powder layer with the calculated (by formula 2) bulk density on the working plane of the table 3.

After the compaction process, excess powder is removed as follows: the carriage 2 is stopped, the knife 9 is lowered relative to the plane of the working table with a guaranteed gap between it and the plane of the working table of at least 10 microns. After that, the carriage is moved to the leftmost position to the hopper for collecting excess powder 12, while the knife rakes the entire volume of excess powder into the hopper 12. Next, the knife 9 is raised to sizes h ₂ + h ₁ and the carriage 2 is moved to the extreme right position.

The next step is the shielding gas (nitrogen or argon) P = 1.3 × 10 ⁵ MPa.

The prepared densified powder layer is sintered by a laser beam in accordance with the sintering mode software.

When forming the next layer, the cycle of operations is repeated until the entire part is manufactured. After that, the finished product is subjected to cooling, cleaning and removal from the experimental stand.

An experiment was conducted at the experimental bench, confirming the effect of improving the quality of sintering of powder with increased density.

The results of the experimental version of sintering of compacted (P ₁ / P ₀ = 114%) X18H9 powder with a dispersion of 20 μm at low power (N = 70 W) of laser radiation were studied, which were compared with the results of the control version of sintering (at P ₁ / P ₀ = 100 % and N = 80 W).

Experimental sintering.

Parameters of sintered powder: relative density P ₁ / P ₀ - 114%, layer thickness - H = 100 μm, h ₀ = 65 μm, h ₁ = 25 μm, h ₂ = 10 μm.

Sintering modes: beam diameter - 50 microns, beam moving speed - 6000 m / min, power N - 70 watts.

The control version of sintering.

Parameters of sintered powder: relative density P ₁ / P ₀ - 100%, layer thickness - H = 100 μm, h ₀ = 65 μm, h ₁ = 25 μm, h ₂ = 0.

Sintering modes: beam diameter - 50 microns, beam speed - 6000 m / min, power N - 80 watts.

Results: the absence of pore formation of a sintered powder layer with an increased density at a reduced laser radiation power (by 8.75%) indicates an increase in the quality of sintering of the compacted powder by increasing the surface activity of sintered microparticles.

Thus, the application of the proposed method allows you to:

1. To improve the quality of sintering of the powder (with an increase in its density) by increasing the surface activity of sintered microparticles of the powder.

2. Reduce the power of the laser beam during sintering of the powder.

3. To expand the technological universality of equipment for the use of powder mixtures with a wide range of dispersion.

Claims (1)

A method for layer-by-layer laser synthesis of bulk powder parts, including a dosed layer-by-layer powder supply to the desktop, leveling the powder layer, removing excess powder and sintering with a laser beam, characterized in that the dosed powder supply is carried out to ensure the formation of a layer of a given thickness, the powder layer is aligned with using a height-adjustable knife, after which the roller is compacted in free-rolling mode.

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