Method for solving powder collapse in electron beam printing process

Abstract

The invention discloses a method for solving powder collapse in the electron beam printing process, and relates to the technical field of additive manufacturing. Comprising the following steps that firstly, a vacuum bin is vacuumized; step 2, repeatedly preheating the substrate in the forming area by using an electronic gun; step 3, spreading the powder on the heated substrate; 4, continuously heating the graphite plate; fifthly, the powder layer is subjected to secondary preheating through the electron gun; and sixthly, selective forming is conducted on the powder layer in the false sintering state through the focused beam till printing of the current layer is finished, and then the actions of powder laying, graphite plate heating, preheating and selective forming are conducted after one layer descends. According to the method for solving powder collapse in the electron beam printing process, the vacuum heat radiation principle is used for indirectly heating the powder layer, the risk that cold powder particles make direct contact with electron beams in the printing process is completely avoided, and the powder blowing defect is completely eradicated.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a method for solving powder disintegration in an electron beam printing process. Background Art

[0002] Electron beam selective melting additive manufacturing has the processing characteristics of high vacuum and low stress, which makes it possible to manufacture refractory metals, high-reaction metals, high-temperature alloys, high-entropy alloys, metal-based composites and titanium-aluminum intermetallic compounds. This is mainly because the process is a hot forming process, which reduces thermal stress; the sequence is preheating-melting-post-insulation. However, due to the complex interaction between the electron beam powder bed process and the powder particles after the continuous negative electrons form a focused beam during the preheating process, the powder particles are negatively charged under the action of the electron beam, causing Coulomb interaction, which is easy to cause powder collapse (powder blowing) phenomenon, resulting in large-scale powder lifting. The generation of powder collapse has a serious impact on the entire forming process, and the chain reaction is very serious. It will cause high-voltage discharge, unstable beam, uneven powder spreading and other problems, and then cause the printing to be forced to stop. This phenomenon has become one of the main problems affecting the stability and processing quality of the electron beam printing process, and has become a common problem in the industry. It affects the technical development of this forming manufacturing method from the side.

[0003] It is generally believed that the main measure to prevent powder collapse is to optimize the process parameters, including: preheating current, preheating time, line scanning speed, melting beam current, melting speed, scanning method and substrate base temperature. The current mainstream view is that the main reasons for powder collapse in the electron beam powder bed printing process are the following three points: first, the shape and medium of the metal powder particles; the roughness of the metal powder surface and the electrically insulating oxide film can act as a capacitor to inhibit the redistribution of charge on the particles; second, the preheating temperature; the charge of the powder bed depends on the resistance between the particles, and the resistivity decreases with increasing temperature; third, the vacuum degree (pressure) of the forming chamber. In order to avoid the occurrence of this phenomenon in the electron beam forming process, the present invention provides a method for solving the powder collapse in the electron beam printing process. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for solving the problem of powder collapse in the electron beam printing process, namely: a plate (needs to be grounded) with good thermal conductivity, electrical conductivity and thermal fatigue performance is designed above the forming chamber, and during the preheating process, the plate is heated by an electron beam, and the preformed powder is continuously irradiated and heated (thermal radiation) by the plate, thereby avoiding the phenomenon of powder collapse caused by direct contact between electrons and powder particles, and solving the existing problems.

[0005] To achieve the above objectives, the present invention is implemented by the following technical solutions: A method for solving powder disintegration in an electron beam printing process, comprising the following steps:

[0006] Step 1: Evacuate the vacuum chamber. When the vacuum degree reaches 5.0×10-3Pa, start the high-voltage power supply and fill it with inert gas.

[0007] Step 2: Use an electron gun to repeatedly preheat the substrate in the forming area, and stop heating when the substrate temperature is 500°C-1100°C;

[0008] Step 3: The powder spreading device (scraper) takes out the powder required for the current layer from the powder cylinder and spreads the powder evenly and flatly on the heated substrate in the forming area;

[0009] Step 4: Start the rotating heating plate to the top of the powder layer for continuous heating until the graphite plate turns red and then raise the heating plate;

[0010] Step 5: Preheat the heated powder layer again by an electron gun until the powder particles reach a pseudo-sintering state;

[0011] Step 6: The focused beam performs selective forming on the powder layer that has reached the pseudo-sintering state until the current layer is printed, and then descends one layer to perform powder spreading - heating the heating plate - preheating - selective forming.

[0012] Preferably, the heating plate is made of a graphite plate having good strength, good temperature resistance and good electrical conductivity.

[0013] Preferably, the spacing between the powder layers of the heating plate is 3-8 mm.

[0014] Preferably, the heating plate is only kept in close parallel with the powder layer for heat radiation in the preheating stage, and is rotated to a position perpendicular to the powder layer in the powder spreading stage and the melting stage.

[0015] Preferably, the control device of the heating plate is a rotating shaft with strong temperature resistance and fatigue resistance, the rotating shaft is located in the vacuum chamber, and the motor is located outside.

[0016] Preferably, the connecting rod between the graphite plate and the rotating shaft is made of a material with poor thermal conductivity to prevent the rotating shaft behind the graphite plate from being affected by prolonged heating.

[0017] The present invention also discloses a mechanism for solving the problem of powder collapse in the electron beam printing process, comprising a vacuum bin, a forming cylinder is arranged at the lower end of one side of the inner cavity of the vacuum bin, a powder feeding cylinder is arranged at the lower end of the other side of the inner cavity of the vacuum bin, an electron gun is arranged on one side of the top of the vacuum bin, metal powder is arranged on the top of the forming cylinder, a heating plate is arranged above the metal powder, the heating plate is connected to the motor on the back of the vacuum bin through a rotating shaft, a powder dropping bucket is arranged on one side of the powder feeding cylinder, and a scraper system is arranged on the top of the powder feeding cylinder.

[0018] Preferably, a heat insulation cover is provided above the forming cylinder, and the heat insulation cover is provided on the inner walls of the upper, left, right and front four surfaces of the vacuum chamber, as well as the top end of the forming cylinder.

[0019] Beneficial Effects

[0020] The present invention provides a method for solving the problem of powder disintegration in the electron beam printing process. Compared with the prior art, it has the following beneficial effects:

[0021] 1. This method of solving the powder collapse in the electron beam printing process uses the principle of vacuum thermal radiation to indirectly heat the powder layer, completely avoiding the risk of direct contact between cold powder particles and the electron beam during the printing process, and completely eliminating the occurrence of powder blowing defects.

[0022] 2. The method for solving the powder collapse in the electron beam printing process is to heat the graphite plate first, and use the graphite plate to radiate heat to the powder layer below, so as to achieve a state of preliminary pseudo-sintering of the powder layer. After completing the operation of the first step, when the electron beam directly preheats the powder again, the powder collapse phenomenon will not occur at all. The reason for selecting the graphite plate in the present invention is mainly its excellent thermal conductivity, electrical conductivity, and fatigue resistance. Secondly, the price is relatively cheap, so the purpose of reducing costs and increasing efficiency is achieved. Therefore, it is beneficial from the technical and cost aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the method flow of the present invention;

[0024] Figure 2 It is a schematic diagram of the structural cross-section of the present invention.

[0025] In the figure: forming cylinder 1, powder feeding cylinder 2, scraper system 3, metal powder 4, powder dropping barrel 5, heating plate 6, electron gun 7, vacuum chamber 8. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See Figure 1-2 , the present invention provides the following two technical solutions:

[0028] The first embodiment: A method for solving powder collapse in an electron beam printing process, comprising the following steps:

[0029] Step 1: Evacuate the vacuum chamber 8. When the vacuum degree reaches 5.0×10-3Pa, start the high-voltage power supply and fill it with inert gas.

[0030] Step 2: repeatedly preheating the substrate in the forming area using the electron gun 7, and stopping heating when the substrate temperature is 500° C.-1100° C.;

[0031] Step 3: The powder spreading device (scraper) takes out the powder required for the current layer from the powder cylinder and spreads the powder evenly and flatly on the heated substrate in the forming area;

[0032] Step 4: Start the rotating heating plate 6 to the top of the powder layer for continuous heating. The spacing between the heating plate 6 and the powder layer is 3-8mm. Raise the heating plate 6 until the graphite plate turns red.

[0033] Step 5: preheating the heated powder layer again by the electron gun 7 until the powder particles reach a pseudo-sintering state;

[0034] Step 6: The focused beam performs selective forming on the powder layer that has reached the pseudo-sintering state until the current layer is printed, and then descends one layer to perform powder spreading - heating the heating plate 6 - preheating - selective forming.

[0035] The material of the heating plate 6 is a graphite plate with good strength, good temperature resistance and good conductivity;

[0036] The heating plate 6 is only kept parallel to the powder layer at a close distance to radiate heat during the preheating stage, and is rotated to a position perpendicular to the powder layer during the powder spreading stage and the melting stage;

[0037] The control device of the heating plate 6 is a rotating shaft with strong temperature resistance and fatigue resistance. The rotating shaft is located in the vacuum chamber and the motor is located outside. The connecting rod between the graphite plate and the rotating shaft is made of a material with poor thermal conductivity to prevent long-term heating from affecting the rotating shaft behind the graphite plate.

[0038] The second embodiment: The present invention also discloses a mechanism for solving the powder dispersion in the electron beam printing process, including a vacuum bin 8, a forming cylinder 1 is arranged at the lower end of one side of the inner cavity of the vacuum bin 8, a powder feeding cylinder 2 is arranged at the lower end of the other side of the inner cavity of the vacuum bin 8, an electron gun 7 is arranged on the top side of the vacuum bin 8, metal powder 4 is arranged on the top of the forming cylinder 1, a heating plate 6 is arranged above the metal powder 4, the heating plate 6 is connected to the motor on the back of the vacuum bin 8 through a rotating shaft, a powder dropping bucket 5 is arranged on one side of the powder feeding cylinder 2, and a scraper system 3 is arranged on the top of the powder feeding cylinder 2.

[0039] A heat shield is provided above the forming cylinder 1. The heat shield is provided on the inner walls of the upper, left, right and front four surfaces of the vacuum chamber 8, as well as the top of the forming cylinder 1, to prevent the graphite plate from interfering with the heat shield during movement.

[0040] Meanwhile, the contents not described in detail in this specification belong to the prior art known to those skilled in the art, and the model parameters of each electrical appliance are not specifically limited, and conventional equipment can be used.

[0041] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0042] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for solving powder disintegration in electron beam printing process, characterized in that: The following steps are involved: Step 1: Evacuate the vacuum chamber. When the vacuum degree reaches 5.0×10-3Pa, start the high-voltage power supply and fill it with inert gas. Step 2: Use an electron gun to repeatedly preheat the substrate in the forming area, and stop heating when the substrate temperature is 500°C-1100°C; Step 3: The powder spreading device takes out the powder required for the current layer from the powder cylinder and spreads the powder evenly and flatly on the heated substrate in the forming area; Step 4: Start the rotating heating plate to the top of the powder layer for continuous heating until the graphite plate turns red and then raise the heating plate; Step 5: Preheat the heated powder layer again by an electron gun until the powder particles reach a pseudo-sintering state; Step 6: The focused beam performs selective forming on the powder layer that has reached the pseudo-sintering state until the current layer is printed, and then descends one layer to perform powder spreading - heating the heating plate - preheating - selective forming.

2. A method for solving powder disintegration in electron beam printing process according to claim 1, characterized in that: The heating plate is made of a graphite plate with good strength, good temperature resistance and good electrical conductivity.

3. A method for solving powder disintegration in electron beam printing process according to claim 1, characterized in that: The spacing between the powder layers of the heating plate is 3-8 mm.

4. A method for solving powder disintegration in electron beam printing process according to claim 1, characterized in that: The heating plate is only kept in close parallel with the powder layer for heat radiation in the preheating stage, and is rotated to a position perpendicular to the powder layer in both the powder spreading stage and the melting stage.

5. The method for solving powder disintegration in electron beam printing process according to claim 1, characterized in that: The control device of the heating plate is a rotating shaft with strong temperature resistance and fatigue resistance. The rotating shaft is located in the vacuum chamber and the motor is located outside.

6. A method for solving powder disintegration in electron beam printing process according to claim 1, characterized in that: The connecting rod between the graphite plate and the rotating shaft is made of a material with poor thermal conductivity to prevent the rotating shaft behind the graphite plate from being affected by long-term heating.

7. A mechanism for solving powder disintegration in an electron beam printing process, used for implementing the method for solving powder disintegration in an electron beam printing process according to any one of claims 1 to 6, characterized in that: It includes a vacuum bin, a forming cylinder is provided at the lower end of one side of the inner cavity of the vacuum bin, a powder feeding cylinder is provided at the lower end of the other side of the inner cavity of the vacuum bin, an electron gun is provided on one side of the top of the vacuum bin, metal powder is provided on the top of the forming cylinder, a heating plate is provided above the metal powder, the heating plate is connected to the motor on the back of the vacuum bin through a rotating shaft, a powder dropping bucket is provided on one side of the powder feeding cylinder, and a scraper system is provided on the top of the powder feeding cylinder.

8. The mechanism for solving powder disintegration in the electron beam printing process according to claim 7, characterized in that: A heat insulation cover is arranged above the forming cylinder, and the heat insulation cover is arranged on the inner walls of the upper, left, right and front four surfaces of the vacuum chamber, as well as the top of the forming cylinder.

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