RU2845378C2 - Ssgtu combustion chamber manufacturing method by selective laser fusion technology - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to powder metallurgy, in particular to a method for manufacturing functional blanks of a flame tube of a combustion chamber of a small-sized gas turbine unit (SSGTU) using additive technology. Combustion chamber flame tube workpiece is made from heat-resistant nickel alloy “ВЖ159” by selective laser fusion at laser radiation power from 148 W to 331 W, scanning speed from 480 mm/s to 660 mm/s, layer thickness from 50 mcm to 60 mcm and scanning pitch from 0.11 mm to 0.14 mm. At that, prediction of workpiece deformation and distortions of generative processes is carried out on the basis of finite element method of digital model of selective laser sintering process.

EFFECT: high mechanical characteristics, particularly strength, and geometrical accuracy of the workpiece.

1 cl, 2 dwg, 1 tbl

Description

The invention relates to additive technologies, namely to the production of a flame tube of a combustion chamber of a small-sized gas turbine unit (MGTU) using selective laser melting (SLM) technology of metal powder of heat-resistant alloy VZh159 (KhN58MBYu-ID), and can be used for the production of MGTU parts.

A known method for manufacturing parts by layer-by-layer laser fusion of metal powders of heat-resistant nickel-based alloys is used (RU Patent No. 2623537, IPC B23K 26/342, B23K 26/60, B22F 3/105, C23C 4/12, C23C 4/18, B33Y 10/00, published on 27.06.2017). In this method, the metal powder used is a powder of a chromium-containing heat-resistant nickel-based alloy with an oxygen content of less than 0.01 wt. % of the EP648 brand. A powder layer is applied to a substrate, the first layer of the part is formed by selective fusion of the powder with a laser beam, and the above operations are repeated to form subsequent layers of the part. Hot isostatic pressing in an argon environment and heat treatment of the resulting part are carried out. The metal powder of the chromium-containing heat-resistant nickel-based alloy is preliminarily subjected to gas-dynamic separation followed by degassing. The process of powder fusion with a laser beam is carried out in a protective nitrogen atmosphere. Before hot isostatic pressing, the part is placed in an environment of electrocorundum and titanium or titanium alloy chips so that the part and the said chips do not come into contact.

The disadvantage of this method is the high chromium content in the alloy, which causes low phase stability and insufficiently high long-term strength of the synthesized material. And also the need for hot isostatic pressing (HIP) with subsequent aging of the alloy.

The closest analogue is the method for producing parts from heat-resistant nickel alloys, including the SLS technology and heat treatment (RU Patent No. 2674685, IPC B23K 26/144, B23K 26/70, B33Y 30/00, published on 13.12.2018). In this method, BB751P powder is used as a metal powder. The part is obtained by SLS with a laser radiation power of 280 to 320 W, a scanning speed of 700 to 760 mm / s, a layer thickness of 50 μm and a scanning step of 0.12 mm. The process of manufacturing parts using selective laser melting technology takes place inside a sealed chamber in a protective gas environment. Then heat treatment is carried out at a temperature of 1000 ± 100 ° C for 2 hours. The heating of the part is carried out gradually with holding for 2 hours at temperatures of 200°C, 400°C, 600°C, 800°C. Cooling of the part is carried out together with the furnace.

The disadvantage of this method in the manufacture of blanks of the combustion chamber of an industrial engine, namely burner devices, is: increased roughness, in particular, in the fuel channels of the main and duty zones; instability of flow characteristics; local zones of non-sintering of the grown layers on the body of the burner device; difficulty in extracting metal powder from closed hard-to-reach cavities during growth.

An analogue of the EP648 material for the production of combustion chambers of industrial engines using the SLS method is the VZh159 alloy. This alloy belongs to the first group of alloys used in additive manufacturing, with an aluminum content of up to 2.7% and titanium of up to 3.7%.

The technical result consists in increasing the mechanical characteristics of the blanks due to the use of optimal technological parameters of synthesis, as well as taking into account the level of residual stresses in the thin-walled blank and, as a consequence, high accuracy of the geometric dimensions and the location of the surfaces of the blank of the combustion chamber of the MSTU flame tube.

The technical result is achieved due to the fact that according to the method for producing parts from a heat-resistant nickel alloy, including the technology of selective laser melting of metal powder, the manufacture of parts is carried out using the technology of selective laser melting from a heat-resistant nickel alloy VZh159 at a laser radiation power of 148 to 331 W, a scanning speed of 480 to 660 mm/s, a scanning step of 0.11 to 0.14 mm and a layer thickness of 50 to 60 μm, wherein before manufacturing the parts, a forecast of the deformation of the workpiece and distortions in generative processes is made based on the finite element method of the digital model of the technological process of selective laser melting, which makes it possible to take into account the level of residual stresses in a thin-walled workpiece. This process includes optimization of process parameters according to the criteria for achieving the required mechanical properties, calibration of the properties of the VZh159 metal powder on test samples for subsequent calculation of the occurrence of bias from the action of residual stresses during fusion in the CAE system, clarifying calibration of the CAE system on a structurally similar sample of the part, simulating the conditions of growing a full-scale workpiece of the part according to the technological process, automated calculation of the 3D function of finite element analysis errors when performing correction operations for the STL file of the workpiece in the CAE system by comparing the measurement results of the grown sample and the nominal model, automated correction of the STL file of the full-scale part based on the calculation results in the previously "calibrated" system with subsequent elimination of the finite element analysis error by additional displacement of the nodes of the geometric model of the part based on the previously calculated 3D function of the error.

Rational properties of the metal powder VZh159 and the operating parameters of the TP SLS, selected according to the criteria for achieving the required mechanical properties, ensure high density of the material. Metal powder of fraction (-50) μm, consisting of at least 70.0% of particles of sizes from 22 to 50 μm, rounded in shape, has no sharp edges and satellites, is uniform in color and quality, dry and free from agglomerated masses.

The specified technological modes allow for the complete fusion of the metal powder VZh159, creating an overlap zone between the scanning vectors at a level of 30...45%, which has a positive effect on the mechanical properties of the material and its density.

Taking into account the level of residual stresses in the workpiece is achieved by predicting the deformation of the workpiece and distortions of the flame tube workpiece in generative processes based on the finite element method (FEM) of the digital model of the selective laser melting process (SLM TP) in the following stages:

- optimization of the operating parameters of the SLS TP according to the criteria for achieving the required mechanical properties;

- calibration of the properties of the metal powder VZh159 on test samples for subsequent calculation of the occurrence of stresses due to the action of residual stresses during fusion in the SAE system;

- refining calibration of the CAE system on a sample structurally similar to the blank of the MSTU combustion chamber flame tube, simulating the conditions of growing a full-scale blank of the combustion chamber according to the TP SLS, with the aim of minimizing the error function of material properties, specially calculated for this class of parts (identification and elimination of systematic errors in determining the properties of the material for specific growing conditions);

- automated calculation of the 3D error function of finite element (FE) analysis when performing correction operations of the STL file of a workpiece in a CAE system by comparing the measurement results of the grown sample and the nominal model (the latter is the identification of a systematic modeling error for the purpose of performing the correction operation in the CAE system);

- automated correction of the STL file of the full-scale blank of the MSTU combustion chamber flame tube based on the calculation results in the previously "calibrated" system with subsequent elimination of the error of the FE analysis by additional displacement of the nodes of the geometric model of the blank of the MSTU combustion chamber flame tube based on the previously calculated 3D error function. The value of the inherited deformations for the manufacture of the blank of the MSTU combustion chamber flame tube was: ε _x = 0.021, ε _y = 0.009, ε _z = 0.091.

After digital modeling of the TP SLS process and correction of the geometric parameters of the blanks of the combustion chamber flame tube of the MSTU, full-scale cylindrical samples were manufactured for uniaxial tensile testing.

To implement the invention, samples were made from heat-resistant nickel alloy VZh159 (KhN58MBYu-ID) with a fraction of up to 50 microns.

The process of manufacturing parts using selective laser melting technology took place inside a sealed chamber in a protective gas environment - argon under the following conditions:

Sample I: laser fusion power - 148 W, scanning speed - 480 mm/s, scanning step - 0.11 mm and layer thickness - 50 µm.

Sample II: laser fusion power - 218 W, scanning speed - 540 mm/s, scanning step - 0.12 mm and layer thickness - 60 µm.

Sample III: laser fusion power - 331 W, scanning speed - 660 mm/s, scanning step - 0.14 mm and layer thickness - 60 µm.

Figure 1 shows samples manufactured according to the above-mentioned technological parameters of the SLS in a total quantity of 9 pieces (3 samples for each technological mode).

The construction platform was also preheated to a temperature of 180°C. The results of testing the mechanical properties of the samples manufactured using the proposed method are presented in Table 1.

Rational modes of the SLS process, namely: laser fusion power - 218 W, scanning speed - 540 mm/s, scanning step - 0.12 mm and layer thickness - 0.06 mm. Thus, the proposed method allows to manufacture functional blanks of the MSTU combustion chamber flame tube with a sufficient level of mechanical properties, as well as to take into account the level of residual stresses in the thin-walled blank and, as a result, to ensure high accuracy of geometric dimensions and surface locations of the MSTU combustion chamber flame tube blank.

Figure 2 shows the flame tube of the MSTU combustion chamber, manufactured using SLS technology under optimal process conditions.

Claims (1)

A method for producing a flame tube for a combustion chamber of a small-sized gas turbine unit (MGTU), including the technology of selective laser melting of metal powder, characterized in that the metal powder is nickel alloy powder VZh159, before selective laser melting, a forecast of the workpiece deformation and distortions in the generative processes of selective laser melting is carried out, which includes optimization of the operating parameters according to the criteria for achieving the required mechanical properties, calibration of the properties of the metal powder on test samples for the subsequent calculation of the occurrence of leashes from the action of residual stresses during melting in the CAE system, a clarifying calibration of the CAE system on a structurally similar part sample simulating the conditions of growing a full-scale workpiece of the part according to the technological process, automated calculation of the 3D function of finite element analysis errors when performing correction operations of the STL file of the workpiece of the part in the CAE system by comparing the measurement results of the grown sample and the nominal model, automated correction of the STL file of a full-scale part based on the results of calculation in a previously calibrated system, followed by the elimination of the error of the finite element analysis by additional displacement of the nodes of the geometric model of the part based on the previously calculated 3D error function, and selective laser melting is carried out at a laser radiation power of 148 to 331 W, a scanning speed of 480 to 660 mm/s, a scanning step of 0.11 to 0.14 mm and a layer thickness of 50 to 60 μm.