RU2386517C1 - Method for sintering in laser layer powder synthesis of volume parts - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to technology of laser layer synthesis of volume parts and may be used to produce parts having complex shapes from finely dispersed powders in various branches of machine building industry. Method includes feeding portion of powder, leveling of layer, sending laser beam to surface of powder layer and sintering each layer as laser beam moves along the area of layer that corresponds to section of part. At the same time point sintering is carried out for selected separate sections in the form of cells with size of 4-6 mm on the area that corresponds to specified section of part. Sequence of separate sections sintering in each layer in process of laser beam traveling is selected provided that point symmetry of heat transfer is maintained from centre of gravity of each section of part in sintered layer to its periphery, as well as maximum area of sintered section contact with neighbouring sections having lower temperature.

EFFECT: improved quality of items as a result of sintered parts deformation (warpage) reduction.

2 cl, 4 dwg

Description

The invention relates to technological processes, powder metallurgy, in particular to the technology of laser layer-by-layer synthesis of bulk parts, and can be used to produce parts of complex shapes from fine powders to improve their quality in various engineering industries.

State of the art

The known method of laser sintering, patent RU 21327161 C1, of thin layers of powder materials using a multi-beam laser optical device in which one or more defocused rays is used to heat the powder zones surrounding the sintering zone to reduce the temperature gradient in order to reduce the sintering warp (warpage) .

The disadvantage of this method is the arbitrary order of sintering with a laser beam of the zones of the powder layer, which can lead to an increase in the temperature gradient between the sintered zone and other zones surrounding it.

A known laser sintering method, US patent 6,215,093 B1 (prototype), which provides for the formation of sintering zones of the powder layer in the form of narrow rectangles adjacent to each other with the greater side with a sequential order of sintering, and in each zone the vector of the laser beam is line-by-line parallel to the narrow side of the rectangle and is consistent with a similar vector of the sintered zone.

The disadvantage of this method is the sequential order of sintering zones with a significant contact area of the sintered zone (on the larger side of the rectangle) with a high-temperature sintered zone, which prevents the maximum local heat removal to neighboring zones with lower temperature.

SUMMARY OF THE INVENTION

The objective of the present invention is to develop such a technology for the production of parts by the method of laser layer-by-layer synthesis, which would improve the quality of products by reducing warpage (leash) of sintered (fused) parts.

The problem is achieved due to the fact that in the sintering method for laser layer-by-layer powder synthesis of volumetric parts, including directing the laser beam onto the powder surface before sintering and moving the laser beam over the entire cross-sectional area of the part, point sintering of selected individual sections of the section of the part is carried out, while the selection of the sintering sequence of individual sections and the movement of the laser beam are made from the condition of providing point symmetry of heat transfer from the center of gravity to the periphery of the section of the part the maximum contact area of the sintered area with the neighboring ones with a lower temperature.

Moreover, during sintering, a contour line is formed on a given section of the part, on the area bounded by the contour line, a grid is formed in the form of transverse and longitudinal lines forming square cells, square zones are allocated on the grid over the entire cross-sectional area of the sintered part, followed by numerical indexation of all cells and zones, choose a sintering center located in the region of the center of gravity of the section of the part, sinter the cells of the central zone, and then sinter the zones surrounding the sintered, moving from the sintering center to the periphery of the section of the part.

This embodiment of the sintering method improves the quality of manufactured parts by reducing their warpage.

List of drawings

The invention is illustrated by drawings, in which:

Figure 1 shows a sintered section of a part with a mesh and a contour in accordance with the invention;

Figure 2 shows a diagram of the diagonal sequence of movement of the laser during sintering of the zone;

Figure 3 shows a diagram of the diagonal and staggered sequence of movement of the laser during sintering of the zone;

Figure 4 shows a sequence diagram of the movement of the laser during sintering of the cell.

Information confirming the feasibility of the invention

The proposed method in accordance with the invention is as follows.

The method is implemented on a laser layer-by-layer synthesis apparatus consisting of a laser device with a working sintering chamber, equipped with a vacuum system, an inert gas system, dosed powder supply and leveling layer mechanisms, a temperature control system both in the sintering zone and in the surrounding zones of the powder layer, lowering working table with the position for cooling the finished part and its cleaning, as well as with a control system with an automatic mode of technological operations and the necessary programs th software.

After performing vacuum operations (P = 3 · 10 ² Pa) of the working chamber, filling it with an inert gas (P = 1.3 · 10 ⁵ Pa), feeding a metered dose of VT-6 powder (dispersion 20 μm), leveling the powder layer ( 50 microns thick), controlled by heating it with shadows to a temperature of 500 ° C and turning on the laser device, the powder is sintered over the entire cross-sectional area of the part.

Sintering of the powder over the entire cross-sectional area is performed by spot sintering of selected individual sections of the section of the part. In this case, the selection of the sintering sequence of individual sections is made from the condition of providing point symmetry of heat transfer from the beginning of sintering to the periphery of the section of the part and the maximum contact area of the sintered section with neighboring ones with lower temperature.

Sintering occurs with constant monitoring of the temperature of both the sintered zone and the temperature of the surrounding zones of the powder layer. After the sintering of the first layer is completed, the chamber table should be lowered to a height of up to 50 μm, followed by the sintering of the following powder layers similar to the first one, taking into account the features of the sections of the part and with the correction of modes (in terms of power and speed of the laser beam) in order to maintain the sintering temperature of the powder (by determining radiation power density) depending on the controlled actual temperature of the sintered zone as a result of the influence and preheating and temperature of the underlying sintered layers. After sintering all layers of the part, it is cooled in a special position, followed by cleaning and removal from the installation of laser layer-by-layer synthesis.

Sintering of the powder over the entire cross-sectional area of the part is as follows.

A contour line 1 is formed (See Fig. 1.) on a given section of a part by sintering the powder with a laser beam with a ⌀ 50 μm light spot and a power of up to 100 W, moved according to a given program with a speed of up to 150 mm / s.

In the area limited by the contour line 1, a grid 2 is formed by sintering the powder in the form of transverse 4 and longitudinal 3 lines forming square cells 5, for example, with dimensions 5 × 5 mm over the entire cross-sectional area of the part. At the same time, cell sizes can vary between 4-6 mm. A decrease in size of less than 4 mm leads to an increase in labor intensity, and an increase in excess of 6 mm leads to the appearance of warpage of the part and a decrease in the accuracy of the part.

Square grid 6 is distinguished on grid 2, for example, 15 × 15 mm (9 cells 5 × 5 mm) over the entire cross-sectional area of the sintered part, followed by numerical indexing of all cells 5, zones 6 and sections 7, with an area of less than 25 mm ² (Fig. 1). The allocation of zones is carried out according to a given program.

Powder is sintered over the entire cross-sectional area of the part by successively sintering the powder of cells 5, sections 7, zones 6 in accordance with the technology of sintering with a beam of ⌀ 50 μm light spot and power up to 100 watts, with a speed of movement up to 150 mm / s.

Sintering of the zones begins with the selection of the sintering center 8 (the beginning of sintering), which is located in the region of the center of gravity of the section of the part, or in the center of gravity of the section of the part (in the case of a complex section configuration), combining it with the center of the cell of the central zone.

The conditions for ensuring the point symmetry of heat transfer from the beginning of sintering to the periphery of the section of the part and the maximum contact area of the sintered section with neighboring ones with lower temperature are ensured by performing sintering of both cells and zones in a certain sequence.

Such a sintering sequence can be implemented as follows:

1. In the form of a diagonal sequence of the sintering order of both cells and zones, when the beam after filling the previous section is transferred to the next section diagonally, and this next section is in contact with the previous one at one point (the vertices of the corners of the cells or zones). This sequence of sintering cells inside the zone is shown by the numbers in figure 2.

2. In the form of a chessboard and diagonal sequence of the sintering order of both cells and zones. Said sequences are shown in FIG.

Thus, first, using the diagonal or diagonal and staggered sequences, sintering the cells 5 of the central zone 6. After that, sintering of the zones surrounding the central, using the diagonal principle. Subsequently, sintering of the zones surrounding the sintered is carried out, moving from the center of sintering to the periphery of the section of the part.

In the absence of free vertex angles, the contact of each sintered cell or zone with previously sintered cells or zones occurs on the sides of their squares with a maximum time interval read from the completion of sintering of the neighboring cell or zone.

Sintering of the powder in any cell 5 is carried out by sequentially passing the laser beam parallel to one of its sides in the forward 9 and 10 reverse directions in accordance with the scheme of the vectors of the beam paths (see Fig. 4.) until the powder is completely sintered over the entire area of the cell. In this case, when switching to each subsequent direction of travel, the laser is turned off. In addition, the laser beam is moved in the forward and reverse directions with the overlapping of 11 formed tracks by an amount equal to 10% of the beam diameter, and when the beam approaches the cell boundary at a distance of 12 equal to half the beam diameter, the laser is turned off.

As a result of applying both the principle of point symmetry of the direction of heat flow from the sintering center of the section of the part to its periphery, and the maximum contact area of the sintered cell or zone with the neighboring ones with lower temperature, in accordance with the laws of thermal physics, a minimal relatively uniform local temperature gradient is formed over the entire section of the part, which , in turn, leads to a decrease in the leash (warpage) of the sintered parts.

Claims (2)

1. A method of manufacturing volumetric parts by layer-by-layer laser sintering of a powder, comprising feeding a portion of the powder, leveling the layer, directing the laser beam onto the surface of the powder layer and sintering each layer when moving the laser beam over the area of the layer corresponding to the section of the part, characterized in that each layer is produced spot sintering of selected individual sections in the form of square cells with a size of 4-6 mm in an area corresponding to a given section of the part, with the sequence of sintering of individual sections of each layer when moving the laser beam, I choose from the condition of providing point symmetry of heat transfer from the center of gravity of each section of the part in the sintered layer to its periphery and the maximum contact area of the sintered area with neighboring ones with lower temperature. 2. The method of manufacturing parts according to claim 1, characterized in that before sintering the individual sections in each layer, a contour line is formed on the area corresponding to the section of the part by sintering the powder with a laser beam, after which, on the specified area limited by the contour line, sintering with the laser beam is formed the grid in the form of transverse and longitudinal lines forming separate sections in the form of square cells, square zones are selected from the grid from several cells over the entire area corresponding to the section of the sintered part, the center of the joint is selected sintering, located in the center of gravity of the section of the part, and sintering of individual sections in the form of cells in the Central zone, then perform sintering of the sections in the zones surrounding the sintered, moving from the center of sintering to the periphery of the section of the part in the sintered layer.

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