ADDITIVE MANUFACTURING APPARATUS USING ELECTRON BEAM MELTING

Abstract

In an additive manufacturing apparatus using electron beam melting for manufacturing three-dimensional structures by laminating layers in which metal powder is selectively molten-solidified with electron beam, defect in current apparatus is to be removed such that electrons accelerated with a constant accelerating voltage are irradiated irrespective of filling rate or density of metal powder to be used for additive manufacturing. Voltage of power supply applied between a grid and an anode provided in an electron gun for generating electron beam is varied corresponding to filling rate and/or density of metal powder. With this, velocity of electron such that a position where thermal energy becomes maximum is taken as most suitable can be obtained.

Claims

1. An additive manufacturing apparatus using electron beam melting, comprising: an optical system for an electron beam used as an energy source that scans and converges the electron beam in two-dimensions according to an additive manufacturing data created to have a layout of a three-dimensions CAD data of at least one entity to be additively manufactured, and a start plate, holding a metal powder on an upper face, which is disposed in a face where the electron beam converges, of a raising and lowering mechanism; wherein the additive manufacturing apparatus is configured to form a layer by dispersing the metal powder onto the start plate, smoothing the metal powder to be flat with a rake and scanning the electron beam in two-dimensions to melt the metal powder, and further by laminating the formed layers successively through lowering the raising and lowering mechanism to perform additive manufacturing of the entity, wherein a voltage of a power supply applied between a grid and an anode provided in an electron gun generating the electron beam capable of being varied corresponding to a filling rate and/or a density of the metal powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 is a schematic view showing a situation of heat generation.

[0050] FIG. 2 is a schematic view showing a case where position of maximum heat generation amount is very deep.

[0051] FIG. 3 is a schematic view showing a situation in which melting near surface of metal is insufficient with melting not reaching the surface.

[0052] FIG. 4 is a schematic view showing a situation of metal powder formed to be laminar.

[0053] FIG. 5 is a schematic view showing a main composition of an additive manufacturing apparatus using electron beam according to an embodiment of the present disclosure.

[0054] FIG. 6 is a view showing a rectangular cup for measuring filling rate at the time when metal powder is dispersed.

DESCRIPTION OF EMBODIMENTS

[0055] Embodiments of the present disclosure will be explained in detail referring to figures.

[0056] FIG. 5 is a schematic view showing a main composition of an additive manufacturing apparatus using electron beam according to an embodiment of the present disclosure. With this additive manufacturing apparatus using electron beam, an electron gun comprising a filament 2, a grid 3 and an anode 4 is used as an energy source. The additive manufacturing apparatus comprises: an optical system for electron beam equipped with a scanning coil 6 for scanning electron beam 1 in two-dimensions and a converging coil 7 for converging the electron beam 1 according to an additive manufacturing data created to have a layout of a three-dimensions CAD data of at least one entity to be additively manufactured; and a start plate 12 for holding metal powder on the upper face, which is disposed in the face 11 where the electron beam converges, of an additive manufacturing box 13 placed on a raising and lowering mechanism 14. Thus, the additive manufacturing apparatus is configured such that metal powder 9 supplied from a powder hopper 8 is dispersed onto the start plate 12 and smoothed to be flat with a rake 10, after which irradiated electron beam 1 is scanned in two-dimensions to melt the metal powder. The additive manufacturing apparatus in this basic configuration has a feature such that voltage of a power supply 15 applied between the grid 3 and anode 4 is varied corresponding to density of metal materials used for additive manufacturing in order to set most suitable accelerating voltage corresponding to density of materials with which additive is to be performed.

[0057] FIG. 6 shows a rectangular cup for measuring filling rate of metal powder at the time when it is dispersed to be a layer, with which condition of voids among particles according to size or shape of metal particles can be known.

[0058] With a currently used apparatus having a fixed electron accelerating voltage for a standard metal, accelerating voltage necessary for a novel metal powder can be obtained from reaching depth of a novel metal powder considering density of a standard metal powder (no), density of a novel metal powder (n.sub.1) and reaching depth of a standard metal material.

[0059] Relativistic expression of conservation of energy is as follows.

E=(m.sub.0.sup.2c.sup.4+p.sup.2c.sup.2).sup.1/2=m.sub.0c.sup.2+ev

[0060] Here, c: velocity of light, e: charge of an electron, m.sub.0: rest mass of an electron.

[0061] And, momentum p is expressed in relativistic manner as follows.

p=m.sub.0v/{1(v/c).sup.2}.sup.1/2.

[0062] Here, v is velocity of an electron.

[0063] From the two equations, the following is obtained.

eV=m.sub.0c.sup.2{c.sup.2/(c.sup.2v.sup.2).sup.1/21}

[0064] From this equation, the following can be obtained.

v=c(eV(2m.sub.0c.sup.2+eV)).sup.1/2/(m.sub.0c.sup.2+eV)Eq. (5)

[0065] After filling a rectangular cup for measuring of a volume (abc) as shown in FIG. 6 with metal powder having a density (n.sub.1) used for additive manufacturing, the mass (w) of the metal powder is measured and filling rate (j) of the metal powder is calculated from the following equation.

j=w/(abc)n.sub.1Eq. (6)

[0066] As an electron having penetrated into the metal powder advances repeating collision or interference with atoms of the metal, the reaching depth (D) is proportional to a function F(v) of velocity of the electron and in inverse proportion to a function F(n) and filling rate of the metal powder (j). That is,

D=F(v)/jF(n.sub.1)=abcF(v)/wF(n.sub.1)

[0067] Here, taking reaching depth (D) of the electron as reaching depth (D.sub.0) of a standard metal,

D.sub.0=F(v.sub.0)/j.sub.0F(n.sub.0)

[0068] For making reaching depth of an electron of material with which additive manufacturing is to be performed equal to reaching depth D.sub.0 of a standard metal, the following needs to be satisfied with.

D.sub.0=F(v)/jF(n.sub.1)=F(v.sub.0)/j.sub.0F(n.sub.0)

[0069] From this, the following can be obtained.

F(v)=jF(n.sub.1)F(v.sub.0)/j.sub.0F(n.sub.0)Eq. (7)

[0070] From Eq. (7), velocity v of an electron necessary for additive manufacturing of material used for additive manufacturing with density n.sub.1 and filling rate j so as to have reaching depth of an electron equal to that of a standard material can be calculated.

[0071] According to Eq. (5), velocity of an electron can be obtained from accelerating voltage applied to a standard material. Hence, accelerating voltage of material for additive manufacturing can be obtained by applying the result of Eq. (7) to Eq. (5).

[0072] Melting with most suitable depth can be attained by applying accelerating voltage for novel material obtained here with the power supply (15) shown in FIG. 5.

[0073] Specifically, in a case where 6-4 titanium with particle diameter distribution of 40 m to 120 m is used as a basic material for an actual additive manufacturing apparatus, filling rate measured with a rectangular cup for measuring of a volume 2 cm2 cm2.5 cm is 0.98, density is 4.43 g/cm.sup.3 and used accelerating voltage is 60 kV.

[0074] On the other hand, in a case where aluminum with same particle diameter distribution is used as a novel material, filling rate measured with same rectangular cup is 0.98 and density is 2.70 g/cm.sup.3, so that accelerating voltage of 21 kV is suitable.

[0075] In this, accelerating voltage may be set by selectively changing from preliminarily established values for material such as 60 kV, 21 kV, etc. or accelerating voltage may be arbitrarily variable in certain range.

[0076] The above example has been explained in which accelerating voltage is varied based on both of filling rate and density of metal powder. However, not limited by this, accelerating voltage may be varied based on either one of filling rate and density. For example, if filling rate of a novel material is near to that of a standard material, it may be sufficient to vary accelerating voltage based on density of the novel material. On the other hand, if density of a novel material is near to that of a standard material, it may be sufficient to vary accelerating voltage based on filling rate of the novel material. That is, it may be sufficient to vary accelerating voltage corresponding to filling rate and/or density of metal powder.