MANUFACTURING METHOD AND APPARATUS

Abstract

The present invention relates to a method of forming a three-dimensional component by additive layer manufacturing. The method comprises scanning a fusing energy beam having a fusing beam focus spot across a layer of powered material in a series of fusing scan lines to fuse the powder material to form a layer of fused material whilst scanning a heating energy beam having a heating beam focus spot in a series of heating scan lines across the material fused by the fusing energy beam. The centre of the fusing beam focus spot and the centre of the heating beam focus spot are off-set from one another and spaced by up to an amount equal to the sum of the radius (y) of the heating beam focus spot and two times the radius (x) of the fusing beam focus spot.

Claims

1. A method of forming a three-dimensional component by additive layer manufacturing, said method comprising: scanning a fusing energy beam having a fusing beam focus spot across a layer of powdered material in a series of fusing scan lines to fuse the powder material to form a layer of fused material whilst scanning a heating energy beam having a heating beam focus spot in a series of heating scan lines across the material fused by the fusing energy beam, wherein the centre of the fusing beam focus spot and the centre of the heating beam focus spot are off-set from one another and spaced by up to an amount equal to the sum of the radius (y) of the heating beam focus spot and two times the radius (x) of the fusing beam focus spot.

2. A method according to claim 1 wherein the centres of the focus spots are spaced by a minimum amount equal to yx (where y and x are as defined above).

3. A method according to claim 1 wherein the centres of the focus spots are spaced by a maximum amount of x+y (where x and y are as described above).

4. A method according to claim 1 further comprising varying the angle of a vector extending between the centre of the fusing beam focus spot and the centre of the heating beam focus spot between two successive scan lines.

5. A method according to claim 4 comprising varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot between zero and 180 degrees in increments, each increment being applied between successive fusing/heating scan lines and/or varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot between 180 and zero degrees in increments, each increment being applied between successive fusing/heating scan lines.

6. A method according to claim 4 wherein, when the vector extending between fusing beam focus spot and the heating beam focus spots is perpendicular (90 degrees) or 45 degrees to the fusing scan line in first fusing/heating scan lines, the method comprises a first step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +90 degrees between first and second scan lines and a second step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 135 degrees between second and third scan lines.

7. A method according to claim 4 wherein, when the vector extending between fusing beam focus spot and the heating beam focus spots is at zero degrees to the fusing scan line in first fusing/heating scan lines, the method comprises: a first step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +90 degrees between first and second scan lines; a second step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +90 degrees between second and third scan lines; a third step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 135 degrees between third and fourth scan lines; a fourth step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +90 degrees between fourth and fifth scan lines; and a fifth step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 135 degrees between fifth and sixth scan lines.

8. A method according to claim 4 wherein, when the vector extending between fusing beam focus spot and the heating beam focus spots is at zero or 45 degrees to the fusing scan line in first fusing/heating scan lines, the method comprises a first step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +135 degrees between first and second scan lines and a second step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 90 degrees between second and third scan lines.

9. A method according to claim 4 wherein, when the vector extending between fusing beam focus spot and the heating beam focus spots is at zero degrees to the fusing scan line in first fusing/heating scan lines, the method comprises: a first step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +135 degrees between first and second scan lines; a second step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 90 degrees between second and third scan lines; a third step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by +135 degrees between third and fourth scan lines; a fourth step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 90 degrees between fourth and fifth scan lines; and a fifth step of varying the angle of the vector extending between the centres of the fusing beam focus spot and heating beam focus spot by 90 degrees between fifth and sixth scan lines.

10. A method according to claim 1 comprising: forming a further layer of fused material by scanning the fusing energy beam across a further layer of fusible powder material in a further series of fusing scan lines whilst scanning the heating energy beam in a further series of heating scan lines across the further material fused by the fusing energy beam; and between forming the layer of fused material and the further layer of fused material, the method comprises varying the angle of a vector extending between the centre of the fusing beam focus spot and the centre of the heating beam focus spot.

11. An apparatus for forming a three-dimensional component by additive layer manufacturing, said apparatus comprising: a fusing energy beam generator adapted to generate a fusing energy beam having a fusing beam focus spot; a heating energy beam generator adapted to generate a heating energy beam having a heating beam focus spot, wherein the fusing energy beam generator is adapted to scan the fusing energy beam across a layer of powdered material in a series of fusing scan lines to fuse the powder material to form a layer of fused material whilst the heating energy beam generator is adapted to scan the heating energy beam in a series of heating scan lines across the material fused by the fusing energy beam such that the centre of the fusing beam focus spot and the centre of the heating beam focus spot are off-set from one another and spaced by up to an amount equal to the sum of the radius (y) of the heating beam focus spot and two times the radius (x) of the fusing beam focus spot.

12. Apparatus according to claim 11 wherein the fusing energy beam generator and heating energy beam generator are adapted to produce the fusing energy beam and heating energy beam such that centres of the focus spots are spaced by a minimum amount equal to yx (where y and x are as defined above).

13. Apparatus according to claim 11 wherein the fusing energy beam generator and heating energy beam generator are adapted to produce the fusing energy beam and heating energy beam such that centres of the focus spots are spaced by a maximum amount equal to x +y (where y and x are as defined above).

14. Apparatus according to claim 11 wherein the heating energy beam generator is adapted to vary the angle of a vector extending between the centre of the fusing beam focus spot and the heating beam focus spot between two successive scan lines or between the formation of successive layers of fused material.

15. An apparatus according to claim 11 wherein the heating beam generator is adapted to modulate the heating energy beam by pulsing the heating energy beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0059] FIG. 1 shows a side view of a standard prior art single beam ALM system;

[0060] FIG. 2 shows a side view of first embodiment of the present invention;

[0061] FIG. 3 shows a top view of the first embodiment of the present invention;

[0062] FIG. 4 shows a second, alternative spacing of the focus spot;

[0063] FIG. 5 shows a third, alternative spacing of the focus spots;

[0064] FIG. 6 shows a fourth, alternative spacing of the focus spots with an elliptical heating beam focus spot; and

[0065] FIG. 7 shows a schematic representation of the angular variation between the fusing energy beam and heating energy beam.

DETAILED DESCRIPTION

[0066] FIGS. 2 and 3 show side and top views of an additive layer manufacturing apparatus/method according to a first embodiment of the present invention with a layer 2 of powder material (such as a powdered nickel based super alloy) deposited on previously fused material 3 which sits on a build plate (not shown).

[0067] A fusing energy beam, such as laser beam 4 is provided and is focussed on the powder layer 2 and melts the powder layer to form a melt pool 5 of melted material which then solidifies to fuse the powder material to form a layer of fused material layer 6 forming part of the component (together with the fused material 3). The fusing energy laser beam 4 is scanned across the powder layer 2 in a series of fusing scan lines.

[0068] A heating energy beam such as laser beam 9 is also provided. The heating energy beam 9 is modulated. This is scanned across the fused material layer 6 simultaneously with the fusing energy beam 4. As shown in FIG. 3, the fusing beam focus spot 10 is smaller in diameter than the heating beam focus spot 11.

[0069] The fusing beam focus spot 10 and the heating beam focus spot 11 are off set from one another and spaced by an amount equal to the sum of the radii of the focus spots 10, 11 such that the circumference of the heating beam focus spot 11 abuts the melt pool 5 of melted material formed by the fusing energy beam 4.

[0070] Alternative embodiments are shown in FIGS. 4-6.

[0071] In FIG. 4, the fusing beam focus spot 10 and the heating beam focus spot 11 are spaced by an amount equal to yx where y is the radius of the heating beam spot and x is the radius of the fusing beam spot. In this embodiment, the fusing beam focus spot is within the heating beam focus spot (but not coincident with it).

[0072] In FIG. 5, the fusing beam focus spot 10 and the heating beam focus spot 11 are spaced by an amount equal to y+2x where y is the radius of the heating beam spot and x is the radius of the fusing beam spot. In this embodiment, the heating beam focus spot abuts the melt pool 5 created around the heating beam focus spot.

[0073] In FIG. 6, the heating beam focus spot is elliptical and the fusing beam focus spot 10 and the heating beam focus spot 11 are spaced by an amount greater than yx where y is the major radius of the heating beam spot and x is the radius of the fusing beam spot. In this embodiment, the fusing beam focus spot and the heating beam focus spot overlap.

[0074] By off-setting the centres of the focus spots 10, 11 and spacing them by up to an amount equal to the sum of the radius of the heating beam focus spot 11 and two times the radius of the fusing beam focus spot 10, the heating beam focus spot 11 abuts or overlaps the melt pool 5 formed by the fusing beam 4 (which is typically between 1.5 and 2 times the size of the fusing beam spot size).

[0075] By scanning the heating energy beam 9 over the fused material 6 whilst scanning the fusing energy beam 4 in a series of scan lines over the powder layer 2,it is possible the reduce the thermal gradient between the melted material and the fused material layer 6 and thus reduce the cooling rate of the melted material. This results in a more uniform equiaxed grain structure in the fused material 3 which, in turn reduces residual stresses and cracking in the resulting component. A reduction in the thermal gradient and residual stresses also reduce ductility drop cracking.

[0076] Furthermore, the heating energy beam 9 alters the direction and magnitude of the heat flux vector 7 and the grain growth vector 8. The principle cooling mechanism is still due to conduction through the fused material 3 towards the build plate, but because of heating by the heating energy beam 9 the heat flux vector 7 is not aligned directly away from the fusing energy beam 4 but is instead at an angle (less than 90) to it. In turn, this means that the grain growth vector 8 is also at an angle, anti-parallel to the heat flux vector 7 which reduces high angle columnar grain boundaries in the build component which reduces the likelihood of cracking.

[0077] FIG. 7 shows a schematic representation of the relative positioning of the heating beam focus spot 11A-11E and the fusing beam focus spot 10 during successive scan lines.

[0078] Initially the vector extending between fusing beam focus spot 10 and the heating beam focus spot 11A is at zero degrees to the fusing scan line. Between the first and second scan lines, the angle of the vector is varied by +90 degrees (such that the heating beam focus spot 11C is at 90 degrees to the fusing beam focus spot 10. Next, the angle of the vector is varied by +90 degrees between second and third scan lines (such that the heating beam focus spot 11E is at 180 degrees to the fusing beam focus spot 10). Between the third and fourth scan lines, the angle of the vector is varied by 135 degrees (such that the heating beam focus spot 11B is at 45 degrees to the fusing beam focus spot 10. Next, the angle of the vector is varied by +90 degrees between fourth and fifth scan lines (such that the heating beam focus spot 11D is at 135 degrees to the fusing beam focus spot 10) and, finally, the angle of vector the vector is varied by 135 degrees between fifth and sixth scan lines (such that the heating beam focus spot 11A returns to zero degrees relative to the fusing beam focus spot 10

[0079] These steps may then be repeated.

[0080] By changing the angular relation between the fusing beam focus spot 10 and the heating beam focus spot (11A-11E) between successive scan lines, the heat flux vector 7 can be changed across the layer of used material 6. The grain growth vector 8 is always directed anti-parallel to the heat flux vector 7. Changing the heat flux vector 7 between successive scan lines produces a structure in which grains have a different orientation, disrupting epitaxial grain growth and texture of the microstructure. This, in turn, reduces internal stresses caused by the high angle columnar grain boundaries and thus cracking/fracture in the resulting component.

[0081] In order to build up the component, multiple layers are built as described above one upon another in the build direction Z. The orientation of the fusing scan lines may be changed by 67 degrees between successive layers.

[0082] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the scope of the invention.