Method and electron beam equipment for processing powdered materials at high acceleration voltages

Abstract

Methods are provided for processing a powdery material with an electron beam system for additive manufacturing of components, which solve the problem of electrostatic powder expulsion and significantly reduce process times. This effect is achieved by using acceleration voltages of 90 kV or greater in the preheating step and/or in the melting step.

Claims

1. A method for processing a powdery material comprising the following steps: a1) Providing an electron beam system comprising a device for receiving a powder bed of powdery material to be processed, and an electron beam generator configured to direct an electron beam to laterally different locations of the powder bed; b1) Applying a powder layer; c1) Preheating the powdery material of the powder layer with the electron beam; wherein the electron beam in step c1) is operated with an acceleration voltage of greater than 120 kV, and the electron beam system comprises an X-ray shield, which is configured in such a way that despite the acceleration voltage of greater than 120 kV, the X-ray radiation outside the electron beam system stays below a limit.

2. The method according to claim 1, further comprising the step of d1) melting at least part of the powder layer with the electron beam.

3. A method for processing a powdery material comprising the following steps: a2) providing an electron beam system comprising a device for receiving a powder bed of powdery material to be processed, and an electron beam generator configured to direct an electron beam to laterally different locations of the powder bed; b2) applying a powder layer; c2) melting of at least part of the powder layer with the electron beam; wherein the electron beam in step c) is operated with an acceleration voltage of greater than 120 kV, and the electron beam system comprises an X-ray shield, which is configured in such a way that despite the acceleration voltage of greater than 120 kV, the X-ray radiation outside the electron beam system stays below a limit and no preheating of the powder layer takes place between step b2) and step c2).

4. The method of claim 1, wherein the powdery material comprises titanium, copper, nickel, aluminium and/or alloys thereof.

5. The method of claim 1, wherein the powdery material has an average grain size D50 of from 10 m to 150 m.

6. The method according to claim 1, wherein the beam power of the electron beam is at least 100 W and at most 100 kW.

7. An electron beam system for processing a powdery material, comprising: a) a device for receiving a powder bed of the powdery material to be processed, and b) an electron beam generator adapted to direct an electron beam to laterally different locations of the powder bed, wherein c) the electron beam system is adapted to carry out the method according to claim 1.

8. The method of claim 1, wherein the limit is below the limit specified by a Radiation Protection Ordinance.

9. The method of claim 3, wherein the limit is below the limit specified by a Radiation Protection Ordinance.

10. The method of claim 3, wherein the powdery material comprises titanium, copper, nickel, aluminium and/or alloys thereof.

11. The method of claim 3, wherein the powdery material has an average grain size D50 of from 10 m to 150 m.

12. The method of claim 3, wherein the beam power of the electron beam is at least 100 W and at most 100 kW.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, an embodiment of the invention is explained in more detail with reference to the drawing. In this shows:

(2) FIG. 1 perspective view of an electron beam system according to the invention with a powder container.

DESCRIPTION OF PREFERRED EMBODIMENTS

(3) FIG. 1 shows an electron beam system 1 with a vacuum housing 2 in which an electron beam gun 3 for generating an electron beam 4 is arranged. The vacuum housing 2 comprises a viewing window 14, which is provided with a thicker shielding layer 16 as an example of an X-ray shielding.

(4) In the present embodiment, the electron beam gun 3 with an optional magnetoptical unit 5 is arranged above a lifting table 6 with a lifting plate and with a receiving frame, which serves as a spatially limited powder container, which receives a powder bed 7 of a powdery material to be processed.

(5) A powder application device 9 with a squeegee (not shown), which can be moved over the lifting table, is arranged above the receiving frame. The powder application device 9 has a container, not shown, for the powdery material, from which the material can be evenly squeegeed onto the powder bed 7 as the uppermost loose layer 8 by a shifting movement.

(6) The relative movement of the electron beam to the powder bed 7 can be achieved by deflecting the electron beam in the deflection device 5, or by setting the lifting table.

(7) The powder bed contains a base plate 10 on which the component 11 is formed layer by layer.

(8) Components manufactured using the methods according to the invention and the system according to the invention are used, among other things, in the aerospace industry as turbine blades, pump wheels and transmission mounts in helicopters; in the automotive industry as turbocharger wheels and wheel spokes; in medical technology as orthopedic implants and prostheses; as heat exchangers; and in tool and mold making.

(9) The powdery material according to the invention includes all electrically conductive materials suitable for the electron beam process. Preferred examples are metallic or ceramic materials, in particular titanium, copper, nickel, aluminum and alloys thereof such as Ti-6Al-4V, an alloy consisting of titanium, 6 wt % aluminum and 4 wt % vanadium, AlSi10Mg and titanium aluminides (TiAl).

(10) Other exemplary materials according to the invention are nickel-based alloys such as NiCr19NbMo, iron and iron alloys, in particular steels such as tool steel and stainless steel, copper and alloys thereof, refractory metals, in particular niobium, molybdenum, tungsten and alloys thereof, precious metals, in particular gold, magnesium and alloys thereof, cobalt-based alloys such as. CoCrMo, high entropy alloys such as AlCoCrFeNi and CoCrFeNiTi, and shape memory alloys.

(11) Preferably, the powdery material has an average grain size D50 of 10 m to 150 m.

(12) According to the invention, the acceleration voltage in the preheating step and/or in the melting step is 90 kV or more. The observed effects are based on the formula for calculating the electrical power P=U.sub.accI, where U.sub.acc stands for the acceleration voltage and I for the beam current.

(13) Consequently, at a constant beam current, a higher acceleration voltage results in a higher energy input and thus a reduction of the process time, since a given temperature can be reached more quickly. Alternatively, higher build temperatures can be realized with the same exposure time.

(14) With constant energy input, i.e. the beam current is reduced proportional to the increased acceleration voltage, a substantial increase in process stability can be observed. According to P=U.sub.accI, the number of charge carriers decreases approximately reciprocally proportional to the increase in acceleration voltage. The lower number of charge carriers introduced leads to lower electrostatic powder expulsion for the same exposure time.

(15) Increasing the acceleration voltage causes a greater penetration depth of the electrons into the powdery material. In addition to the acceleration voltage, the maximum penetration depth of the electrons into the material is influenced by material parameters such as density, atomic mass and nuclear charge number. It is known that the maximum penetration depth in titanium at 60 kV is about 15 m, at 90 kV about 30 m and at 150 kV about 70 m.

(16) Due to the increased acceleration voltage, the energy introduced is distributed over a larger volume in the powder bed and, as a result, the tendency to form local temperature peaks and thus melting is reduced already during the preheating step. This leads to increased quality of the residual powder and effectively higher recycling grades of the material.

(17) The maximum beam power of 100 kW takes into account the fact that in the interaction volume between electrons and the powdery material to be processed, the material can be converted to the molten state at typical beam parameters without undesirable effects caused by overheating, such as vaporization of the material. The calculation is based on the material-specific energy required for heating and melting and the interaction volume, which is a function of the acceleration voltage and the area exposed by the electron beam.

(18) Method at Increased Acceleration Voltages with Preheating:

(19) In the method according to the invention, the top loose layer 8 of powdery material is first applied to a substrate with the powder application device 9. Depending on the process stage, the base plate 10 or the powder bed 7 can be considered as the substrate, as well as the component 11 in later process stages.

(20) In one embodiment of the method according to the invention, a preheating step is carried out. For this purpose, the uppermost loose layer 8 is exposed to the electron beam 4. The acceleration voltage of the electron beam 4 is at least 90 kV. In preferred embodiments of the method according to the invention, the acceleration voltage is between 90 and 150 kV, acceleration voltages of 100 kV and 120 kV are particularly preferred.

(21) The blasting parameters are selected according to the quality of the powdery material. Typically, a beam current between at least 100 W and at most 100 kW is set. The scanning speed is at least 1 m/s and at most 1000 m/s.

(22) In the preheating step, the loose layer 8 is bonded together by diffusion processes at the grain surfaces. This leads to a reduction in the contact resistance between the individual powder particles 12 in the layer 8, and consequently to a higher electrical conductivity at the surface of the powder bed. As a result, the charge introduced by the electron beam can be better dissipated and electrostatic powder expulsion can be avoided.

(23) Subsequently, the melting step takes place. In this step, the electron beam gun 3 creates a solid bond by melting the powder particles 12 at points of the prepared powder bed 7 or its uppermost loose layer 8, which are specified by the 3D structure to be created.

(24) The steps described above are repeated layer by layer until the 3D structure is finished.

(25) Method at Increased Acceleration Voltages without Preheating:

(26) Furthermore, the invention relates to a method for processing a powdery material without an additional preheating step.

(27) In the method according to the invention, the powder application device 8 applies the top loose layer 8 of powdery material to a substrate. Depending on the process stage, the base plate 10 or the powder bed 7 can be considered as the substrate, as well as the component 11 in later process stages.

(28) Subsequently, the electron beam gun 3 is used to create a solid bond by melting the powder particles 12 at locations of the prepared powder bed 12 or its uppermost loose layer 8, which are specified by the 3D structure to be created.

(29) The acceleration voltage of the electron beam 4 is at least 90 kV. In preferred embodiments of the method according to the invention, the acceleration voltage is between 90 and 150 kV. Preferred examples are acceleration voltages of 100 kV and 120 kV.

(30) The steps described above are repeated layer by layer until the 3D structure is finished.

(31) In summary, the idea of the invention therefore manifests preferably in a method for additive manufacturing with an electron beam in which an acceleration voltage between 90 kV to 160 kV, in particular 100 kV or greater, preferably 120 kV or greater, again preferably greater than 120 kV, again preferably between 135 kV and 160 kV, is used during preheating and/or melting.

(32) TABLE-US-00001 Reference numbers 1 Electron beam system 2 Vacuum housing 3 Electron beam gun 4 Electron beam 5 Magnetic optics unit 6 Lifting table 7 Powder bed 8 Top loose layer 9 Powder application device 10 Base plate 11 Component 12 Powder particles, powdery material