GB2410714A

GB2410714A - Manufacturing three-dimensional products using build-up electron beam welding

Info

Publication number: GB2410714A
Application number: GB0402674A
Authority: GB
Inventors: Paul Nigel Plumb; Conrad Frederick Dumont
Original assignee: Aquasium Technology Ltd
Current assignee: Aquasium Technology Ltd
Priority date: 2004-02-07
Filing date: 2004-02-07
Publication date: 2005-08-10
Also published as: WO2005077586A1; GB0402674D0

Abstract

In this method for manufacture of three-dimensional products out of metal, an electron beam 14 is directed into a vacuum chamber 10, to meet the tip of a wire feedstock 20. Metal will be continuously melted from the tip of the wire and deposited on a table 16 which moves relative to the point where the beam impinges on the wire tip, so that the metal melted from the wire is deposited in a desired pattern 18 on the table where it solidifies. Once a layer of a desired area has been deposited, the table is lowered away from the wire feed by a distance equal to the thickness of the layers being deposited, and successive layers are deposited to build up a three-dimensional shape.

Description

Manufacturing Three-Dimensional Products This invention relates to a

method of manufacturing three dimensional products, preferably metal products.

Three dimensional metal products of complex shape are conventionally manufactured either by casting, or by machining from solid. Casting requires the preparation of an appropriate mould, and produces a product which has a non-uniform internal structure, and machining from solid is time consuming and wasteful of material.

It is known, for example from EP 0 714 333, to manufacture three dimensional bodies from a particulate medium by fusing together particles in successive layers to build up a three dimensional object. The use of particles to from the object, like known wintering techniques, can lead to undesired porosity in the finished product which can affect the physical properties of the product.

The manufacturing process described in EP 0 714 333 produces a product with rough surfaces. In most cases, a further machining operation (to remove a relatively small volume of material) will be carried out to take the product to its final finished state. Thus, the process of building up the product is often referred to as a 'near net shape' process. 2

Near Net Shape means that a product is produced which is close to, but not exactly in, the final desired shape. A subsequent machining step is likely to be necessary to complete the product, but the quantity of material to be removed by machining is minimal, especially in comparison with a comparable product machined from a solid billet or other body.

Other Near Net Shape process are known, for example, from W088/02677 (University of Texas) and from International Application WO 01/81031 (ARCAM). In all these cases, a feed material in a form of powder is spread on a base surface, and then a laser or an electron beam is directed to the layer of particles to fuse and/or melt the particles in a predetermined pattern to form a layer of a predetermined shape. This process is repeated by spreading further layers of particles above the previous layer, and using the laser/electron beam to fuse each layer (which can be a different shape from the preceding layer) so that in this way a three-dimensional object is built up.

A disadvantage with the process described in EP O 714 333 is that porosity in the finished product cannot be avoided, and the process is relatively slow because the fusing action of the electron beam has to be interrupted each time a new layer of particles has to be laid down. - 3 -

According to the invention there is provided a method for manufacture of three-dimensional products out of metal, the method comprising generating an electron beam, generating a vacuum and directing the beam into the vacuum, feeding a wire made of the same metal as that of the product to be made to the focus point of the electron beam within the vacuum, so that the beam melts metal from the tip of the wire, directing the molten metal to a support surface and moving the surface in accordance with a pre-programmed schedule so that metal is deposited from the melting wire onto the surface in a predetermined pattern, and then lowering the surface before repeating the process to build up a product in layers.

The vacuum to be generated may be any sub-atmospheric pressure. Although best results will be obtained with substantial vacuums, an only slightly sub-atmospheric pressure may be adequate for some applications.

The invention also provides apparatus for manufacturing three-dimensional products out of metal, the apparatus comprising a chamber, an electron beam gun, means for generating a vacuum in the chamber, a support surface in the chamber on which the product is to be formed, and means for feeding a wire to a point adjacent the support surface so that metal can be melted from the tip of the wire by the electron beam gun and can be deposited on the support surface, wherein the support 4 - surface can be moved relative to the gun and the wire feed means so that metal is deposited on a predetermined area of the support surface.

The electron beam is directed to the tip of the wire and melts metal from the tip, the molten metal being deposited on a support surface located under the position where the beam and the metal wire meet. All this takes place under vacuum. The wire is continuously advanced as metal is melted from its end.

Gravity and surface tension determine where the molten metal lies as it cools and resolidifies. The process can operate continuously as deposition of a second layer can start immediately a first layer has been completed and the support surface has dropped the requisite distance.

The invention is particularly suitable for use with refractory metals, especially those with a melting point in the range 2400 C - 3400 C. Further optional features of the invention are set out below and are the subject of Claims 2 to 22.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic sketch of apparatus in accordance with the invention; and Figure 2 is a schematic section through part of the apparatus of Figure 1.

In the preferred embodiment shown in Figure 1, the manufacturing method is performed inside a closed vacuum chamber 10. In the drawing the front face of the chamber is open, so that the chamber contents can be seen but in practice this front face will be closed and the air inside the chamber will be evacuated by a suitable vacuum pump (not shown).

An electron beam gun 12 produces an electron beam 14 which is directed inside the chamber. The gun can be of any known type, but a diode gun is preferred.

The beam is directed to a movable table 16 on which a product 18 is to be produced. The product 18, which will be a solid metal object, is produced from a wire which is fed from a coil 22. The metal of the wire is melted by the beam 14 and is deposited on the table 16, where it solidifies. A suitable guide (not shown) delivers the tip of the wire 20 to the point where the electron beam 14 meets the table 16. The table moves beneath the wire tip so that the metal which is transferred from the wire to the table is deposited on - 6 - the table to cover an area of the table which is determined by the movement of the table.

The metal is deposited on the table in layers. The first layer is deposited directly on the table, and successive layers on the previously laid down layer.

As soon as each layer is completed, the support surface is lowered by the thickness of the layers (which may be between 1 and 5 mm) (ie moved in the Z direction - see Figure 1) so that the next layer can be deposited on the previous layer. The area of each layer may be the same as or different from that of the previous layer, so that a three-dimensional product of any desired shape can be built up. Clearly the material of the wire 20 is consumed as the product 18 is built up and wire is continually fed from the drum 22 to replace the metal which has been melted from the wire tip.

In practice, the product 18 is built up in layers, and the area covered by each layer is determined by taking sections through the desired finished product shape, and laying down a layer of metal covering that area (or a little over).

In order to distribute the metal over the desired area, the table 16 is able to move in the X and Y planes as illustrated in Figure 1. The point at which the metal is melted by the electron beam is, in this embodiment, stationary relative to the chamber 10 and the metal is - 7 - spread over the preceding layer by movement of the table beneath the beam.

Figure 2 illustrates this diagrammatically. The figure shows three completed layers laid down on the table 16, and one partially completed layer 18a. The table will normally be moved relative to the meeting point of the beam 14 and the wire 20 in the direction of the arrow 24, so that that part of the layer 18a on the right hand side of the product is yet to be laid down.

Figure 2 also shows in dotted lines lab, an example of an irregular outlined object which can be produced by this process. The first layer of the product 18 will be applied directly to the surface of the table 16.

Once the manufacturing process is complete, the product will be separated from the table 16 by a mechanical cutting or shearing process.

The product can be produced with internal holes, bores, external undercut areas and virtually any regular or irregular three-dimensional shape.

The support surface is likely to be sacrificial. It could either be machined away during the final stages of product completion, or could remain as a part of the product. - 8 -

The process takes place in a vacuum chamber. The electron beam gun will normally be outside the chamber, with the beam entering the chamber through a suitable aperture. The wire may be fed from a coil located either inside or outside the chamber.

The pattern of movement of the table beneath the wire tip will be determined by suitable computer control, which may be the same in principle as that used to control movement of a workpiece in Electron Beam Welding installations.

The electron beam can be generated from either a diode or a triode gun, but a diode gun is preferred as it has a potentially longer filament life than a triode gun and the beam control available with a triode gun is not needed in this process.

The process can be used to form a new three dimensional shape, on a sacrificial support surface, or can be used to grow material onto an existing component.

In particular, the process could be used to deposit metal onto a surface where there is already a deposit of the same metal or indeed a different material (which could be a metal or a non-metal). The use of an electron beam makes it possible to melt refractory metals with a melting point of between 2400 C and 9 3400 C, which cannot be achieved using lasers or other energy beams.

Parameters which can be varied to control the process are, inter alla, The material of the wire The speed of advance of the wire The cross- sectional area of the wire 10. The energy input from the electron beam The speed of movement of the table More than one wire can be fed simultaneously to the focus point of the electron beam. Where more than one IS wire is fed, the materials of the wires can be the same or different. If they are different, an alloying process can take place when the metals are melted and deposited.

The wire will normally be fed into the electron beam at an angle to the beam and at an angle to the surface on which metal is to be deposited. The table will normally move under the beam in a direction so that the molten metal is dragged away from the wire tip, rather than being pushed under the tip.

It could be possible to use a single electron beam, in a single vacuum chamber, to 'grow' multiple products - 10 and/or to grow additions onto various different parts of one workpiece.

Instead of a stationary electron beam and a moving table, the beam could be moved relative to a stationary table, or both could be movable. Movement of the beam could be by any known methods of beam diversion.

In the work carried out so far, the electron gun has been positioned outside the chamber. It would however be possible to mount the gun inside the chamber and to arrange for the gun to be movable inside the chamber.

This would allow bigger components to be made in the same vacuum chamber.

The table could be moved in any direction, and this movement need not be limited to X, Y and Z axes. A path of movement can be set up for any axis.

The vacuum in the chamber can be set at values below those conventionally used in Electron Beam Welding.

For example the vacuum could be around 5 mb. For poor vacuum of this order, an enclosed vacuum chamber is not required which would have advantages particularly in working with large components.

Thus in the method of the invention it can be possible to melt wire not just in a reduced pressure of 10-3 to - 11 10-6 mb (a normal range) but also all the way up to say 750 mb, or broadly, full atmosphere. - 12

Claims

Claims 1. A method for manufacture of three-dimensional products out of

metal, the method comprising generating an electron beam, generating a vacuum and directing the beam into the vacuum, feeding a wire made of the same metal as that of the product to be made to the focus point of the electron beam within the vacuum, so that the beam melts metal from the tip of the wire, directing the molten metal to a support surface and moving the surface in accordance with a pre-programmed schedule so that metal is deposited from the melting wire onto the surface in a predetermined pattern, and then lowering the surface before repeating the process to build up a product in layers.
2. A method as claimed in Claim 1, wherein wire is continuously advanced as metal is melted from its end.
3. A method as claimed in Claim 1 or Claim 2, wherein gravity and surface tension determine where the molten metal lies as it cools and resolidifies.
4. A method as claimed in any preceding claim, wherein the process operates continuously and deposition of a second layer starts immediately a first layer has been completed and the support surface has been lowered the requisite distance. - 13
5. A method as claimed in any preceding claim, wherein the support surface is sacrificial.
6. A method as claimed in Claim 5, wherein the support surface is machined away during the final stages of product completion.
7. A method as claimed in Claim 5, wherein the support surface remains as a part of the product.
8. A method as claimed in any preceding claim, wherein the support surface is mounted on a table which moves in the X and Y planes beneath the tip of the wire, so that molten metal can be deposited on the surface in a predetermined pattern to form one layer of a three-dimensional product.
9. A method as claimed in any preceding claim, which is carried out in a vacuum chamber.
10. A method as claimed in Claim 9, wherein the electron beam gun is oOutside the chamber, with the beam entering the chamber through a suitable aperture.
11. A method as claimed in Claim 9 or Claim 10, wherein the wire is fed from a coil located inside the chamber.
12. A method as claimed in any preceding claim, wherein the pattern of movement of the table beneath the wire tip is determined by suitable computer control.
13. A method as claimed in any preceding claim, wherein the electron beam is generated from a diode gun.
14 A method as claimed in any preceding claim, wherein two or more wires are fed simultaneously to the focus point of the electron beam.
15. A method as claimed in Claim 14, wherein the materials of the wires are different and an alloying process can take place when the metals are melted and deposited.
16. A method as claimed in any preceding claim, wherein the wire is fed into the electron beam at an angle to the beam and at an angle to the surface on which metal is to be deposited.
17. A method as claimed in Claim 16, wherein the table moves under the beam in a direction so that the molten metal is dragged away from the wire tip, rather than being pushed under the tip.
18. A method as claimed in any preceding claim, wherein the table can be moved in directions not limited to X, Y and Z axes.
19. A method as claimed in any preceding claim, wherein the vacuum is in the range 10-3 to 10-6 mb.
20. A method as claimed in Claim 1, wherein the vacuum is around 5 mb and the method is carried out in an open chamber.
21. A method as claimed in any preceding claim, wherein the metal is a refractory metal.
22. The use of a method as claimed in any preceding claim to form a new three dimensional shape on a sacrificial support surface.
23. The use of a method as claimed in any one of Claims 1 to 13 to grow material onto an existing component.
24. Apparatus for manufacturing three-dimensional products out of metal, the apparatus comprising a chamber, an electron beam gun, means for generating a vacuum in the chamber, a support surface in the chamber on which the product is to be formed, and means for feeding a wire to a point adjacent the support surface so that metal can be melted from the tip of the wire by - 16 the electron beam gun and can be deposited on the support surface, wherein the support surface can be moved relative to the gun and the wire feed means so that metal is deposited on a predetermined area of the support surface.
25. Apparatus for manufacturing a three-dimensional metal product in accordance with the method as claimed in any one of Claims 1 to 22.
26. Apparatus for manufacturing three-dimensional products out of metal substantially as herein described with reference to the accompanying drawings.
27. A method for manufacture of three-dimensional products out of metal substantially as herein described with reference to the accompanying drawings.