ARTEFACTS FIELD OF THE INVENTION

This invention relates to a method and apparatus for layer manufacturing of three dimensional artefacts.

In this specification, the term "fuse" or "fused" includes within its meaning sintering, partial fusing and complete fusing.

BACKGROUND TO THE INVENTION

A first known process for layer manufacturing of a pre-designed geometric artefact or a three dimensional so-called "near net shape" object, includes the steps of building up the artefact by consecutively fusing fusible particulate material deposited in superimposed layers with a laser beam. A computer controls the deposit of the layers and the fusing by the laser beam, in accordance with a computer-aided design. A wide range of fusible particles such as Polyamide, titanium and its alloys, advanced ceramics, nickel and cobalt and their alloys, aluminium, as well as blends of different powders, to name but a few, could be used.

The particulate material is disposed in a reservoir or hopper having an elongate outlet, positioned in closely spaced relationship relative to a surface or a plane on which the artefact is to be formed or a previously fused layer. The space between the outlet and the surface determines the thickness of the layer to be fused that is deposited on the surface. The hopper is moved relative to the surface in a first direction, whilst depositing the layer on the surface. The laser beam is directed onto the layer in accordance with a pre-programmed pattern, which is determined by the design of the artefact. After depositing the layer, the deposited particles are fused by the laser in accordance with the shape of the artefact to be formed. Subsequently another layer is deposited and fused, so that the artefact is built up layer by layer.

An advantage of the known process over the conventional methods of manufacture is that artefacts having highly complicated shapes, could be manufactured without any or with minimal subsequent machining. Artefacts manufactured with this technology are typically geometrically complex or difficult if not impossible to viably manufacture with another method. In addition, net or near-net shaped artefacts could be formed from materials that are difficult to machine, owing to its hardness or toughness, for example.

A disadvantage of the known process of layer manufacture is that the rate of manufacture is relatively slow, owing to the configuration of the hopper and the fact that the hopper would typically dispense the layer only when moving in one direction over the surface. A further disadvantage is that the manipulation of the prior art laser is electro-mechanical, which is considered restrictive in terms of the speed of the manufacturing process.

Another disadvantage of the known process is that manufacture of relatively larger objects is limited owing to the configuration of the apparatus and limited travel of the hopper arm and limited laser beam adjustment

A further disadvantage suffered by the above method and apparatus is that, owing to the temperature differential or gradient between the artefact being formed and its environment, distortion of the artefact occurs. This is undesirable, as distorted machine components would not be up to specification and would have to be discarded, particularly in precision tooling and machine components having movable parts. A major disadvantage of distortion owing to temperature differentials between the fused particulate material and its environment is that a relatively thin layer of the fused material would curl up and thus interfering with the outlet of the hopper moving over the layer depositing a subsequent layer. Usually the space between the outlet of the hopper and the surface on which the particulate material is deposited and thus the thickness of the layers is 0.1 mm and even the slightest curling or distortion of the artefact would cause an interference with the outlet moving over the layer, whilst depositing a subsequent layer. Moreover, the distortion severely limits the potential of forming relatively complicated artefacts, without providing additional internal support structures not forming part of the original design. These internal support structures, which limit the distortion of the fused layer of particles, have to be machined away afterwards [or otherwise removed], adding to the time and cost of manufacture. In certain instances, the support structures are not accessible after manufacture and cannot be removed easily.

A second known process of direct manufacture utilises an electron beam instead of a laser beam. An advantage of this process is that, owing to the relatively higher energy density, the likelihood of the fusing together of the particles is increased. However, a disadvantage of this process is that the process has to take place in vacuum and the manufacture of relatively larger artefacts are therefore not practical or economically viable, owing the relative size of the vacuum chamber that would be required for manufacturing relatively larger objects.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide a method and apparatus for layer manufacturing of a three dimensional artefact with which the aforesaid disadvantages may be overcome or at least minimised. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method for the layer manufacture of a three dimensional artefact through heat fusion of heat fusible particulate material, in accordance with a computer aided design, including the steps of:

providing a support surface, for supporting the artefact to be formed; providing dispensing means, for depositing a layer of said heat fusible particulate material onto the surface;

dispensing said heat fusible particulate material from the dispensing means onto the support surface to form a layer;

providing a movable deflector member;

directing an energy beam onto the deflector member; and

controlling the movement of the deflector member to deflect the energy beam and move it along the dispensed particulate material to fuse the particulate material along a predetermined fusion path.

The deflector member may comprise a wheel, having a plurality of deflecting and/or reflecting surfaces arranged about its outer circumference, and the step of controlling the movement of the deflector member may include the further step of continuously varying the angle of deflection/reflection of the energy beam onto the surface by rotating the wheel whilst directing the beam onto the deflecting/reflecting surfaces. The step of controlling the movement of the deflector member may include the further step of controlling the motion and speed of the wheel electronically.

The method may include the further step of controlling the switching of the energy beam onto the deflector.

The method may further include the step of elevating the temperature of at least the immediate environment in which the fusion takes place, towards the fusion temperature of the particles, but adequately below the fusion temperature of the particulate material, such that after fusion of the particles, heat energy would dissipate from the material into the said environment sufficiently for the fused material to acquire dimensional stability.

The method may include the further step of extracting fumes from the environment in which fusion takes place.

The step of providing the dispensing means may include the steps of providing a first dispensing outlet for depositing a first layer of the heat fusible particulate material and a second dispensing outlet for depositing a second layer of the heat fusible material whilst moving the support surface in first and second directions respectively.

The reciprocal movement of the support surface may continue in the first and second directions respectively, whilst dispensing the particles and fusing said particles when the surface is moved in both directions, such that subsequent superimposing layers are formed and fused to the previous layer to form the artefact. The first and second outlets and the energy beam may constitute a first modular unit and the method may include the further steps of adding similar modular units in accordance with the relative size of the artefact to be formed.

According to a second aspect of the invention there is provided an apparatus for the layer manufacture of three dimensional artefacts through heat fusion of heat fusible particulate material, in accordance with a computer aided design, including:

a support surface for supporting the artefact to be formed;

dispensing means, for depositing a layer of said heat fusible particulate material onto the surface;

an energy beam;

a movable deflector member onto which the energy beam is directed; and

controlling means for controlling the movement of the deflector member to deflect the energy beam and move it along the dispensed particulate material so as to fuse the particulate material along a predetermined fusion path. The moveable deflector may be a rotating deflector that may rotate on a fixed axis.

The rotating deflector may be in a form adapted to facilitate deflection over the entire width of the bed.

The outward facing sides of the rotating deflector may be made of a reflective material. The path of the energy beam may be altered through a combination of deflective and/or refractive media.

A driving means may drive the rotation of the deflector. The energy beam may be provided by an energy beam source situated in a fixed position relative to the rotating deflector.

The energy beam source may be in the form of a first modular laser beam unit and the apparatus may include additional removable modular laser units that may be added to the first unit, depending on the width of the artefact to be formed.

The apparatus may include a first moving means for moving the dispensing means and the support surface relative to one another in a first plane. Movement in the first plane may be lateral movement.

The apparatus may include a second moving means for moving the dispensing means and the support surface relative to one another in a second plane.

Movement in the second plane may be vertical movement.

The controlling means may be in the form of a computer aided program.

The dispensing means may include first and second spaced apart hoppers each having a dispensing outlet for respectively dispensing the particulate material when the surface is moved in the said first and second directions, to form superimposed layers.

The energy beam source may be disposed between the first and second hoppers such that the particles in the deposited layers are fused to each other and to the previously deposited and fused layer whilst the surface is moving in the said first and in the second directions respectively, thus to form the artefact layer by layer.

The dispensing means may be adapted to depose a second layer of said heat fusible particulate material on top of the first layer whilst the support surface is moved in a second direction relative to the dispensing means opposite to the first direction, to allow the heat fusion by the energy beam of the particles in the second layer to each other and to the first layer whilst the support surface moves in the said second direction. The dispensing means may be in the form of a first modular dispensing unit and the apparatus may include similar additional modular dispensing units that may be added to the first dispensing unit, depending on the width of the artefact to be formed. The apparatus may include heating means and temperature control means for elevating the temperature of at least the immediate environment in which the fusion takes place, towards the fusion temperature of the particles, but adequately below the fusion temperature of the particulate material, such that after fusion of the particles, heat energy would dissipate from the material into the said environment sufficiently for the fused material to acquire dimensional stability.

The heating means may include a heat source such as an electrical element, induction heater, laser or gas burner and may further include a method for monitoring and controlling the temperature inside the chamber.

The apparatus may further include insulating walls defining a chamber at least partially enclosing the support surface and dispensing means. The apparatus may further include a cover plate located between the two hoppers, enclosing the area between the two hoppers, the arm and the surface.

The cover plate may define an aperture in the form of a slot through which the laser beam may pass.

The aperture may be enclosed by an optical window.

The apparatus may further include a fume extractor for extracting fumes from the environment in which fusion takes place.

According to a third aspect of the invention there is provided a three dimensional artefact manufactured by a method according to the first aspect of the invention; or an apparatus according to the second aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example only, with reference to the accompanying drawings wherein:

figure 1 is a perspective view of an apparatus according to a preferred embodiment of the invention, for layer manufacturing of a three dimensional artefact through the heat fusion of heat fusible particulate material, in accordance with a computer aided design; figure 2 is a semi-transparent view of figure 1 ; figure 3 is a diagrammatical representations of the said apparatus, shown in cross-section along line X-X in figure 1 , the said apparatus being disposed in a thermally insulated heating chamber;

figure 4 is also a diagrammatical representations of the said apparatus, shown in cross-section along line X-X in figure 1 ; figure 5 is a cross-sectional perspective view along line Y-Y' in figure 1 ; figure 6 is a cross-sectional end view along line Y-Y' in figure 1 ;

figure 7 is the same view as that of figure 5, showing successive layers of an artefact being formed with the said apparatus; and

figure 8 is also the same view as that of figure 5, showing successive layers of an artefact being formed with the said apparatus.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawings, an apparatus according to a preferred embodiment of the invention for layer manufacturing of a three dimensional artefact through the heat fusion of heat fusible particulate material, in accordance with a computer aided design, is generally designated by reference numeral 10.

The apparatus 10 includes a support surface 12 for supporting an artefact 14 (figures 3 to 8) to be formed; and dispensing means 16, in the form of elongate spaced apart first and second hoppers 16.1 and 16.2 respectively, for containing and dispensing heat fusible particulate material 18 and for depositing a layer of said material 18 onto the surface 12. The apparatus 10 also includes an energy beam source 20 in the form of a laser and lens unit disposed between the hoppers 16.1 and 16.2, for emitting a laser beam 22. The apparatus 10 further includes a movable deflector member in the form of a rotating wheel 24 for deflecting the laser beam 22 and moving it along the dispensed particulate material 8 so as to fuse the particulate material 18 along a predetermined fusion path.

The hoppers 16.1 and 16.2, with particulate material 18, the laser beam source 20 and the rotating wheel 24 are all mounted on an arm 26, so that they are fixed relative to one another. The supporting surface 12 is adapted to move horizontally in a first and a second direction relative to the arm 26, as indicated by arrows A and B, as well as vertically in a first and second direction, as indicated by arrows C and D in the drawings. The distance of the movement of the support surface 12 in the said directions are variable in accordance with the required length, height and thus size of the artefact to be formed. The artefact to be formed could thus be of any size, since the support surface 12 is movable in the said directions.

Referring to figures 3 to 6, the hoppers 16.1 and 16.2 are provided with elongate dispensing outlets 16.3 and 16.4 respectively, for dispensing the particulate material 18 onto the surface 12 in a relatively thin layer 18. . Layer thickness is governed by the specific material employed. However, depending on the type and size of the artefact to be manufactured, the thickness of the layer 18.1 could be varied. The hoppers 16.1 and 16.2 are positioned on either side of the laser beam 22 to allow for adequate depositing and subsequent fusion of particulate material 18.

The hopper outlets 16.3 and 16.4 are closely spaced from the support surface 12 or from a previously deposited and fused layer 18.1. The distance between the outlets 16.3 and 16.4 and the support surface 12 or previously fused layer 18.1 determining the thickness of the layer to be deposited, as is illustrated in figures 3 and 4. A cover plate 17 is located between the two hoppers 16.1 and 6.2. The cover plate 17 defines an aperture in the form of a slot 17.1 , through which the laser beam 22 passes. The cover plate 17 encloses the area between the two hoppers 16.1 and 16.2, the arm 26 and surface 12. Access for environmental control 19 is provided in the enclosed area to regulate/control the environment in which fusion takes place. The environmental control access 19 is located within the area, which is closed of by the cover plate 17. The addition of the cover plate 17 thus allows easy environmental control to take place, since the area is enclosed.

The rotating wheel 24 includes a plurality of deflecting surfaces 24.1 , as shown in figure 6, arranged about its outer circumference. The surfaces 24.1 are made of a reflective material to adequately deflect the laser beam 22 onto the dispensed particulate material 18. The rotating wheel 24 rotates on an axis that is parallel to the direction A - B. The direction of the laser beam 22 is constant relative to the axis of rotation of the rotating wheel 24. Therefore, directing the laser beam 22 onto the rotating wheel 24 continuously varies the angle of deflection of the laser beam 22 by the deflecting surfaces 24.1.

The rotating action of the wheel 24 deflects the laser beam 22, ensuring maximum coverage by the deflected laser beam 22 of the width of the support surface 12 in a relatively much faster time in relation to prior art apparatus and with limited energy loss. A driving means, in the form of a motor (not shown) rotates the wheel 24. The motion and speed of the wheel 24 is controlled electronically by a controlling means (not shown) by a computer aided program.

The movement of the support surface 12 relative to the arm 26 is controlled by a control means (not shown) typically in the form of a computer aided program. The control means further controls the driving means, and subsequently the speed of rotation of the wheel 24, as well as the switching between on and off conditions and deflection of the laser beam 22 from the laser beam unit 20 in accordance with the dimensions and specifications of the artefact to be manufactured.

I n use, the hopper outlets 16.3 and 16.4 are positioned in close proximity to the support surface 12, the space between them being automatically selected by the control means in accordance with the thickness of a layer 18.1 of particulate material 18 to be deposited onto the surface 12. Further in use, the support surface 12 is moved in the first direction A relative to the dispensing outlets 16.1 and 16.2 whilst the heat fusible particulate material 18 is dispensed from the elongate outlet opening 16.3 of hopper 16.1 to form a first layer 18.1 of particulate material 18 on the surface 12. The layer 18.1 itself would limit deposit of particulate material 18 from outlet 16.3 of hopper 16.1 whilst the support surface 12 is moving in the direction of arrow A.

Simultaneously the control means activates the energy beam 22, and the rotating wheel 24, and the laser beam 22 is directed onto the rotating wheel 24. The rotating wheel 24 continuously varies the angle of deflection of the laser beam 22 by the deflecting surfaces 24.1.

The rotating wheel 24 then continuously deflects and moves the laser beam 22 along the dispensed particulate material 18, in accordance with the particular design of the artefact, to heat fuse the particles 18 in a first layer 18.1 to one another.

The size and dimension of wheel 24 ensures that the rotation of the wheel 24 causes the deflecting surfaces 24.1 to deflect and move the laser beam 22 from one side of the support surface 12 to the other side, across the support 12 and instantaneously thereafter, bring the laser beam 22 back to its starting point. This occurs while the support surface 12 is in moving in the direction of A. This movement of the support surface 12 in conjunction with the movement of the deflected laser beam 22 creates a multitude of obliquely fused paths that are not entirely perpendicular to the direction A - B, but that are parallel to one another. The slower the movement of the support surface 12 in a direction, the less oblique the fused paths will be. However, the obliqueness of the fused paths is not a problem and could be compensated for electronically, if necessary.

The deflected laser beam 22 adequately elevates the temperature of the dispensed particulate material 18 on the predetermined fusion path, above the fusing temperature thereof, so as to optimally fuse the dispensed particles 18, and therefore obtain maximum material strength of the artefact.

At the completion of the layer in the direction of A, the control means moves the support surface 12 in a third direction indicated by arrow C in increments, away from the outlet openings 16.3 and 16.4, the increments being equal to the thickness of the layers to be sequentially deposited on top of the first layer 18.1. The arrangement is such that, in use, after deposition and fusion of the first layer 18.1 , the support surface 12 is moved one increment in the third direction, and subsequently in the second direction B. A second layer is deposited on top of the first layer 18.1 and the particles 18 in the second layer are heat fused to one another, and to the first layer 18.1 to form an integral and coherent unitary body therewith. Movement in these three directions allow for a plurality of superimposed layers of equal thickness to be deposited and fused together, and therefore for the manufacturing of a three dimensional artefact 14 layer by layer. Referring to figures 3 and 4, the apparatus 0 could be located in a pre-heating chamber for elevating the temperature of the particulate material towards its fusing temperature, but adequately below the fusion temperature of the particulate material, such that after fusion of the particles, heat energy would dissipate from the material into the said environment sufficiently for the fused material to acquire dimensional stability. Temperature may also be elevated locally by means of a second laser. It is foreseen that such elevation of the temperature, prior to the fusion of the particles, reduces the amount of energy required to obtain fusion and minimises stresses and distortion in the artefact being formed, owing to a relatively lower temperature differential between the formed artefact and its environment.

A major advantage of the apparatus 10 and method according to the present invention is that the artefact production time, in comparison with that of prior art methods and apparatus, is shortened substantially owing to rapid laser manipulation, and thus accelerated movement, of laser beam 22 across the support surface 12. Further, the electronic control of the switch on and off and deflection of the laser beam 22 is relatively much faster than the mechanical control of prior art apparatus. It is foreseen that the apparatus for layer manufacturing of a three dimensional artefact according to the present invention effectively overcomes the size constraints through variable length, made possible by linear scanning in one plane with the other plane being controlled by the relative motion of the bed. Furthermore, the size of the artefact being manufactured is unlimited since the size of the support surface 12 can be made as big or small as is practically possible. The apparatus could also include similar additional modular dispensing units and additional modular laser units that could be added, depending on the width of the artefact to be formed. It is foreseen that any of the heat fusible particulate material previously used with prior art apparatus could be used with the apparatus 10.

It will be appreciated that variations in detail are possible with a method and apparatus according to the invention without departing from the scope of the appended claims. For example, instead of a hexagonal deflector, the deflector may have various numbers of sides. Further, the control means may move the arm 26 and outlets 16.3 and 16.4, gradually away from the surface 12, after each layer of fusion.