GB2589933A

GB2589933A - Infrared lamp assembly for apparatus for the layer-by-layer formation of three-dimensional objects

Info

Publication number: GB2589933A
Application number: GB1918434.0A
Authority: GB
Inventors: Dorini Gianluca; Hartmann Anders; Garrido Barrabes Marcel; Kongensbjerg Larsen Steffen
Original assignee: Xaar 3D Ltd
Current assignee: Stratasys Powder Production Ltd
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2021-06-16
Anticipated expiration: 2039-12-13
Also published as: GB2589933B; GB201918434D0

Abstract

An infrared lamp assembly 100 for an apparatus 1 for the formation of three-dimensional objects 2 by consolidation of particulate material, the assembly comprising: an elongate infrared lamp 110 extending along a lamp axis, at least one elongate shield 120_1 extending parallel to and along one side of the axis of the lamp, and a support structure holding at least one of the ends of the lamp and of the shield, wherein the elongate shield at least partially bounds the space to one side of the lamp, and wherein the assembly provides a lower opening 150 below the lamp and an upper opening 140 above the lamp, such that radiation generated by the lamp is able to radiate through the openings and away from the lamp in directions not bounded by the shield.

Description

INFRARED LAMP ASSEMBLY FOR APPARATUS FOR THE LAYER-BY-LAYER

FORMATION OF THREE-DIMENSIONAL OBJECTS

The present disclosure relates to an infrared lamp assembly for an apparatus for the layer-bylayer formation of three-dimensional (3D) objects, and to apparatus for the layer-by-layer formation of 3D objects comprising such a lamp assembly. The lamp assembly may be particularly suitable for powder bed applications that require infrared radiation that causes thermal pre-heating and/or consolidation of the particulate material by sintering.

BACKGROUND

Applications such as laser sintering, or so-called "print and sinter" techniques such as high speed sintering, for forming three-dimensional objects from particulate material are receiving increased interest as they are moving towards faster throughput times and become industrially viable. In these processes, the object is formed layer-by-layer from particulate material that is spread in successive layers across a build surface. Each layer of particulate matter is fused, or sintered, over defined regions to form a 'slice' or cross section of the three-dimensional object.

High speed sintering processes, for example, use a high power infrared lamp to sinter areas of particulate material, such as polymer powder, that have been printed with radiation absorptive material (RAM). The RAM enables the printed powder to absorb lamp energy over a wavelength band that is different to the absorption band of the unprinted powder, thus providing selectivity.

One problem that the sintering lamp may cause is that its radiation may excessively heat nearby components, such as the lamp housing. Excessive temperatures can cause ink fumes and airborne particulate matter to stick to and accumulate on surfaces at or near the build bed, causing process issues such as melting and dripping polymer onto the build bed and contaminating the layer. It may also adversely affect the quality and functionality of other parts within the nearby environment; this is because sufficiently hot surfaces turn into secondary radiation sources that may radiate at wavelengths within the absorption band of the unprinted powder. This reduces selectivity of sintering by partially consolidating the unprinted powder, preventing efficient reuse of the unprinted powder, and causing issues with recovering the object from the powder cake. Therefore, the management of heat from the infrared lamps is of importance to provide a reliable process in which accurate consolidation of particulate material, depowdering of the object and recovery of unprinted material may be achieved.

SUMMARY

Aspects of the invention are set out in the appended independent claims, while particular embodiments of the invention are set out in the appended dependent claims.

The following disclosure describes, in one aspect, an infrared lamp assembly for an apparatus for the formation of three-dimensional objects by consolidation of particulate material, the assembly comprising: an elongate infrared lamp extending along a lamp axis, an elongate shield extending parallel to and along one side of the axis of the lamp, and a support structure holding at least one of the ends of the lamp and of the shield, wherein the elongate shield at least partially bounds the space to one side of the lamp, and wherein the assembly provides a lower opening below the lamp and an upper opening above the lamp, such that radiation generated by the lamp is able to radiate through the openings and away from the lamp in directions not bounded by the shield.

According to a second aspect there is provided an apparatus for the formation of three-dimensional objects by consolidation of particulate material comprising a working space, the working space comprising: a build bed surface of particulate material arranged at a lower surface bounding the working space, and a ceiling arranged at an upper surface bounding the working space; and a carriage to which the lamp assembly of the first aspect is mounted and for passing the lamp assembly across the build bed surface, wherein the shield is located between the lamp and surfaces of the carriage facing the lamp, and the at least two openings of the lamp assembly are arranged so that the lower opening allows radiation to pass towards the build bed surface and the upper opening allows radiation to pass away from the build bed surface into the working space and towards the ceiling.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now directed to the drawings, in which.

Figure 1 is a schematic cross-sectional diagram of an apparatus for the layer-by-layer formation of three-dimensional objects, and having a lamp assembly according to an embodiment of the present invention; Figure 2A is a schematic cross section view of a lamp assembly according to an embodiment; Figure 2B is a schematic side view of the lamp assembly of Figure 2A; Figure 2C is a schematic plan view of the lamp assembly of Figure 2A; Figures 3A-3B are schematic cross section views of alternative arrangements of the shield of 10 the lamp assembly; Figures 4A-4B are schematic cross section views of arrangements of lamp assembly having two shields; Figure 5A is a schematic cross section view of a lamp assembly in which the shield comprises a flange along the lower edge; Figure 5B is a three-dimensional illustration of an implementation of the arrangement of Figure 5A; Figure 6 is a schematic cross section view of a lamp assembly in which the shield comprises a lip along the upper edge; Figure 7 is a schematic cross section view of a lamp assembly in wh ch the upper opening is partially restricted; Figure 8 is a schematic three-dimensional illustration of a lamp assembly n which the upper opening has a group of sub openings defined by crosswise struts; Figure 9A is a schematic three-dimensional illustration of a carriage comprising two lamp assemblies in which the upper sub openings are defined by guards; Figure 9B is a plan view from below of the carriage of Figure 9A; and Figure 10 is a schematic cross-sectional diagram of an apparatus for the layer-by-layer formation of three-dimensional objects provided with several lamp assemblies.

In the Figures, like elements are indicated by like reference numerals throughout. It should be noted that the illustrations in the Figures are not necessarily to scale and that certain features may be shown with exaggerated sizes so that these are more clearly visible.

DETAILED DESCRIPTION

Infrared (IR) lamps are conventionally operated as part of an assembly comprising a lamp housing having inner reflective walls and housing the lamp, and a lower opening through which radiation may reach the build bed surface of particulate material in which the object is to be built. The housing conventionally redirects any radiation not directly emitted through the lower opening towards the lower opening by use of downward internal reflectors. The temperature of infrared lamps in a high speed sintering apparatus tends to be well in excess of 1000 °C so that the housing can reach very high temperatures and starts to act as a source of secondary radiation of wavelengths able to be absorbed by the unprinted particulate matter.

To prevent excessive heating, such housings may have active cooling, for example fluid cooling units, attached to them, or the housing body may be a hollow body that is fluid cooled. However, such approaches add complexity and weight to the housing. The printer comprises a working space bounded from below by a work surface comprising the build bed surface. Since the housing may be supported on a carriage that is moveable across the work surface and build bed surface, this also adds weight to a moveable component and complexity in integrating a robust fluid supply.

The present inventors have surprisingly found that, by removing the lamp housing and allowing radiation to dissipate freely into the working space above, selectivity can be well maintained during the printing process. A significant amount of secondary radiation reaching the build bed from the housing may reduce and compromise selectivity. It is thus thought that by reducing or minimising the thermal mass of a housing (i.e. a housing that is able to store heat) and any significant surface area of surfaces adjacent the lamp and directly facing the build bed surface can preserve or enhance selectivity.

Thus the removal of the lamp housing to allow lamp radiation to dissipate freely into the space above and providing only minimal heat shielding to nearby components from direct lamp radiation may lead to a significant improvement in the management of secondary radiation reaching the build bed surface. The radiation released upwards, away from the build bed surface, may more easily be managed via the comparatively large ceiling area of the apparatus.

Aspects relating to the infrared lamp assembly and an apparatus for layer-by-layer formation of three-dimensional objects by the aggregation of particulate matter comprising the infrared lamp assembly will now be described with respect to Figures Ito 10.

Figure 1 shows an apparatus 1 for layer-by-layer formation of three-dimensional objects by the aggregation of particulate matter by high speed sintering, and having a lamp assembly 100 according to an embodiment of the present invention.

The apparatus 1 has a working space 4 bounded from below by a working surface 13 and from the top by a ceiling 60. One or more carriages 30 (in this case two) are arranged to be movable across a build bed surface 12 that is comprised within the working surface 13. The build bed surface 12 is the surface over which successive layers of particulate material, such as powder, are distributed and processed to form cross sections of an object 2. The apparatus 1 further comprises a powder container system 10 with a build bed 16 within which the object 2 is formed, layer by layer, from a build bed surface 12. A powder dosing module 40 is arranged to dose fresh powder to the working surface. The first and second carriages 30 1, 302 respectively support a distribution device 36, and a printing module 38 and a lamp assembly 100. The carriages are movable on at least one rail 34 back and forth across the build bed surface 12.

In an illustrative process sequence, the floor 18 of the powder container system 10, and which bounds the bottom surface of the build bed 16, lowers the build bed 16 by a layer thickness. With the first carriage 30_1 supporting the distribution device 36 located to the far side of the dosing module with respect to the build bed surface 12, and the second carriage 302 located on the opposite side of the build bed surface 12 with respect to the first carriage, the dosing module 40 doses an amount of powder to the work surface 13, adjacent the build bed surface 12. The first carriage is moved across the build bed surface 12 so that the distribution device 38 distributes the dosed powder so as to form a thin layer across the build bed surface 12. Next, the first carriage 30_i moves back to its starting position, followed by the second carriage 30_2. Starting from the dosing module side, the second carriage moves across the build bed surface to the opposite side and the one or more droplet deposition heads of the printing module 38 deposit fluid containing RAM over selected areas of the build bed surface 12 corresponding to the cross section of the object to be formed, and the infrared lamp 110 of the lamp assembly 100 is operated to sinter the printed powder. The process then may start again to proceed layer by layer until the object is fully built.

The infrared lamp 110 achieves very high temperatures in excess of 1000 °C, and nearby components require shielding from this heat to ensure they continue to operate reliably. One such component is the carriage to which the lamp assembly 100 is mounted. In some implementations this will be the carriage that also supports the printing module, although a lamp may also be mounted to the carriage supporting the powder distribution device 36. For example, an infrared lamp 110 of a similar assembly 100 could be mounted to the first carriage downstream of the distribution device 38 and operate as a pre-heat lamp. As the distribution device 38 distributes the powder layer, the pre-heat lamp 100 is operated to heat the freshly distributed powder layer to near sintering temperature before the second sled is moved across the build bed surface to deposit the RAM and to operate the infrared lamp to sinter the printed powder areas.

In some implementations of the apparatus 1, two lamps may be provided on each carriage, one upstream and one downstream of the printhead module, or one upstream and one downstream of the powder distribution device. These two lamps may be used for sintering on both the forward and backward strokes of the carriage, and/or one may be used to pre-heat and the other to sinter. Since both the preheat function and the sintering function causes the lamp to operate at high temperature, their thermal impact on other components needs to be managed. This may be achieved by providing the preheat and/or sinter lamp within the lamp assembly 100.

An embodiment of the lamp assembly 100 and some variants thereof comprising the infrared lamp 110 will now be illustrated in detail by way of example with reference to Figures 2A to 9B.

Figures 2A to 2C show an infrared lamp assembly 100 according to an embodiment for an apparatus for the formation of three-dimensional objects by consolidation of particulate material, and which may be particularly useful in a sintering apparatus using a laser or an infrared lamp to sinter the material. While the laser sintering process generally does not require a printing module, and a laser source is used to selectively sinter the powder material, a preheat lamp as part of an assembly 100 may be provided for example to the carriage supporting the powder distribution device 38.

Accordingly, the infrared lamp assembly 100 comprises an elongate infrared lamp 110 extending along a lamp axis 114, an elongate shield 120 extending parallel to and along one side of the axis of the lamp 110, and a support structure (e.g. frame) HO holding at least one (and preferably both) of the ends of the lamp 110 and of the shield 120. The elongate shield at least partially bounds the space to one side of the lamp. The assembly provides a lower opening 150 below the lamp and an upper opening 140 above the lamp, such that there is no significant obstruction in the space above and below the lamp within the assembly. In this way, radiation generated by the lamp is able to radiate through the openings 140, 150 and away from the lamp in directions not bounded by the shield 120.

In the present disclosure, radiation may mean direct, primary radiation, reflected upwards by the shield; primary radiation reflected back from the powder bed surface 12 into the lower opening, and secondary radiation emitted from the surface of the hot lamp 110.

As illustrated, the support structure 130 may hold both the ends of the lamp 110 and both the ends of the shield 120. Advantageously, this gives improved structural rigidity to the assembled components, including the lamp HO and the shield 120. However, alternative embodiments may employ a support structure that holds only one end of the lamp 110 and/or only one end of the shield 120, provided the lamp 110 and/or shield 120 are securely supported from that one end, and the lamp is of a type that is powered from only one end.

Figures 2A to 2C show the lamp assembly 100 in greater detail. The infrared lamp 110 may be an elongate lamp such as a tube emitter, such as a 3000W, 400V reflector-type Victory lamp, but not limited to such, supported at one or both of its ends by the support structure (e.g. frame) 130. Alongside the lamp, an elongate shield 120 is mounted to the support structure so that its direction of elongation extends parallel to the lamp axis 114. This is illustrated in a schematic plan view of the assembly in Figure 2C. When mounted to a carriage 30 above a build bed surface 12 within the apparatus 1, the shield surface may be further oriented so that it extends substantially vertically upwards, along a direction perpendicular to the lamp axis (the z-direction in Figure 2A), as also indicated in the cross sectional schematic in Figure 2A, where it is shown how the lamp assembly 100 may be positioned above a build bed surface 12. The lamp axis 114 and elongate direction of the shield 120 meanwhile extend parallel to the build bed surface 12, as is illustrated in a schematic side view of the assembly in Figure 2B. In this way, the assembly 100 provides a shield 120 mounted to one side of and parallel to the lamp axis 114, and an upper opening 140 above and a lower opening 150 below the lamp, such that the lamp can radiate through the lower opening and through the upper opening of the assembly. When the assembly is mounted in the apparatus 1, radiation is able to radiate towards the build bed surface 12 through the lower opening 150, and unimpeded upwards into the working space 4 through the upper opening 140, where the working space 4 is bounded above by ceiling 60. At the same time, there is minimal shield surface directly facing the powder bed surface 12, so that any secondary radiation emitted from the shield 120 cannot significantly affect the temperature of the unprinted (white) powder and thus compromise the selectivity of consolidating the printed and unprinted powder.

During operation of the apparatus, in a high speed sintering machine for example, the working space is filled with ink fumes and powder dust, which settle on any surfaces and accumulate, turning them dull or even black. Within a cylindrical envelope about the lamp axis 114, defined by the lamp power, all organic matter is pyrolised due to the high temperature of the lamp, preventing it from settling and accumulating on surfaces located within this envelope. This envelope is here referred to as the vaporisation front 112 of the lamp 110, as indicated for example in Figure 2A, within which, in an oxygen containing atmosphere for example (as may typically be the case in a high speed sintering printer), temperatures to achieve pyrolysis of polymer powder may need to be 300 °C or higher. It should be noted that the vaporisation front 112 is a function of lamp power, so that depending on the lamp type and/or operation of the lamp the size of the front may change. During a sintering step at high duty cycle (e.g. 100% for a 3000 W lamp), the vaporisation front may extend radially to 200 mm from the lamp axis.

In the apparatus shown in Figure 1, the lamp radiation is further able to radiate freely away from the shield surface. Radiation can however not directly reach at least the nearmost surfaces of the carriage 30 since the shield 120 blocks direct radiation from the lamp from reaching the nearmost surfaces of the carriage.

In an apparatus for the formation of three-dimensional objects, x is the direction of travel of the carriage, z is vertical height up from the build bed surface 12 and y (into the page in Figure 1 and Figure 2A) is the direction of elongation of the lamp and shield, such that the lamp axis 114 is parallel to the y-axis.

Tilted and curved single shields It is not essential, when mounted to the carriage 30, that the shield surface extends substantially vertically upwards from the build bed surface 12. Lamp assemblies 100 having alternative configurations and arrangements of shields 120 with respect to the build bed surface 12 are illustrated in Figures 3A and 3B In Figure 3A, the shield 120 is a planar sheet located within the lamp vaporisation front 112. The support structure (e.g. frame) 130 supporting the shield 120 and the lamp 110 is mounted to the can-iage 30 such that the nearmost surfaces of the carriage facing the shield 120 are located outside of the lamp vaporisation front 112. When installed in the apparatus 1, the shield 120 extends upwards at an angle to the vertical to the build bed surface 12, so that its upper edge leans away from the lamp axis 114 and towards the carriage, and its lower edge leans towards the lamp axis 114.

In a variant to the shield of Figure 3A, the shield 120 may comprise an elongate sheet of a curved, concave cross section, when viewed along the lamp axis 114, and arranged within the assembly so that the concave surface faces the lamp 110. The cross section of curvature may describe the section of a circle, or it may describe a parabolic curve, or any other concave curvature or shape. The concave surface need not be a smooth surface, but may instead be made up of a series of discrete planar elongate strips attached to one another along their adjacent elongate edges at fixed or varying angle from strip to strip, to form an overall curved, concave cross section. The purpose of the curvature is to guide radiation upwards and away from the lamp into the working space 4. Where a focus may be defined, for e.g. circular or parabolic cross sections, the focus of the curvature may be concentric with the lamp axis 114, or it may be offset from the lamp axis 114.

In the implementations shown in Figures 3A and 3B, a normal n to the shield surface facing the lamp 110 may be defined. Such a normal n generally has a non-zero vertical component. The non-zero vertical component causes lamp radiation to be directed upwards at overall steeper angles compared to radiation reflected by the vertical sheet shield 120 of Figure 2A (and for which the vertical component of the normal to the shield surface is zero). This restricts the lower opening 150 through which radiation can reach the build bed surface 12, and through which direct radiation reflected back from the powder may be redirected upwards and out of the upper opening 140, which is widened compared to the vertical shield of Figure 2A. In addition, a higher proportion of lamp radiation compared to the vertical shield 120 of Figure 2 is reflected upwards into the working space 4 by the shield 120. The arrangements of the shield 120 in Figures 3A and 3B define an upper opening 140 that is larger than the lower opening 150, so that more radiation is directed upwards and away from the lamp 110 compared to the radiation emerging from the assembly 100 of Figure 2.

Dominant surface The shields 120 of the various embodiments and implementations described herein may be thought of as comprising a dominant surface 122, which may comprise more than 50% of the shield surface, and which has the primary function to direct radiation generated by the lamp 110 out of the upper opening 140 of the assembly 100, so that, in the apparatus, the radiation may radiate unimpeded by obstructions above the upper opening 140 into the working space 4 and away from the build bed 16 to remove heat from the vicinity of the lamp 110. The dominant surface 122 is further arranged to reflect any direct lamp radiation, and any lamp radiation reflected back from the build bed surface 12 into the lower opening 150, towards and out of the upper opening 140. Thus unlike conventional downwards focussing reflector housings used with infrared lamps that focus lamp radiation towards the build bed surface 12, the assembly 100 dissipates a substantial amount of radiation upwards and away from the lamp 110 into the working space 4.

The dominant surface 122 may generally have a lower and upper elongate edge that defines, or contributes to defining, the extent of the upper opening 140 and the extent of the lower opening 150. Furthermore, the dominant surface 122 may comprise two or more surfaces of distinct shape or configuration, for example two elongate surfaces adjoint along a respective one of their elongate edges and arranged at an angle towards one another, and where both surfaces in combination have the function to dissipate radiation through the upper opening 140 of the lamp assembly 100.

With respect to the shields 120 shown in Figures 3A and 3B, the dominant surface 122 may be angled with respect to the vertical, or the dominant surface may be curved, such that the dominant surface 122 has a normal with a non-zero vertical component. In the implementations described herein, it is preferable that the area of any angled or curved surface facing the build bed 16 is sufficiently small to avoid significant amounts of secondary radiation being directed at the build bed surface 12.

Returning to Figure 2A, the dominant surface of the shield 120 is simply that of an elongate plane that may be described as being arranged as a tangent plane to a cylindrical envelope of constant power of the lamp 110. The upper and lower edges of the dominant surface (here shield 120), in the length direction of the shield, are arranged parallel to the contact line between the plane of the shield and the envelope. Since the shield only extends a finite amount perpendicularly away from the contact line in either direction, it may be thought of as only partially, and not wholly, bounding the space to one side of the lamp. In other words, when mounted in the apparatus 1, the sheet does not extend infinitely in a vertical direction away from the powder bed surface 12.

In the case of a single shield 120 having a planar elongate sheet as dominant surface 122 therefore, the lamp 110 may be mounted to the support structure (e.g. frame) 130 so that the planar dominant surface 122 of the shield forms a tangent plane to the surface of a cylindrical constant power envelope centred about the lamp axis 114. Optionally, the planar dominant surface 122 may extend by different amounts to either side of the contact line between the tangent plane and the constant power envelope. In other words, the lamp 110 is located closer towards one elongate edge of the planar surface. When the assembly is mounted to the carriage 30 within the apparatus 1, this may mean that the lamp 110 is located closer to the lower opening 150 than to the upper opening 140.

By mounting the shield 120 with respect to the lamp axis 114 so that the lamp axis 114 is closer to the lower opening 150 of the shield 120 than to the upper opening 140, the angle over which the lamp can irradiate the build bed surface 12 is increased.

Two shields In some implementations, a second shield 120 2 may be provided to extend alongside the lamp 110, wherein the support structure (e.g. frame) 130 holds the ends of the second shield 1202, so that the second shield extends parallel to the lamp axis and opposite the first shield so that the lamp 110 is located between the shields. The infrared lamp assembly 100 may thus comprise the elongate infrared lamp 110 having a lamp axis 114, two elongate shields 120_1, 120 2 extending parallel to and along the axis 114 of the lamp 110, and a support structure (e.g. frame) 130 holding at least one (and preferably both) of the ends of the lamp 110 and of the two shields 120 1, 1202. The support structure 130 locates the first and second shield alongside the lamp 110 and on opposite sides of the lamp; in other words, the lamp 110 is located between the shields 1201,_ 1202. The elongate shields at least partially bound the space to either side of the lamp 110. The assembly 100 thus provides a lower opening 150 below the lamp 110 and an upper opening 140 above the lamp 110, such that there is no significant obstruction in the space above and below the lamp 110 within the assembly 100. In this way, radiation generated by the lamp 110 is able to radiate through the upper and lower openings 140, 150 and away from the lamp 110 in directions not bounded by the shields 1201, 1202. By providing a second shield, the radiation of the lamp 110 is partially bound on both sides of the lamp, 'partially' meaning that either shield only finitely extends perpendicular to the direction of elongation and this cannot block all radiation.

When mounted to a carriage 30 in the apparatus 1, this means that the shields 1201, 120 2 may be arranged so that the inner shield 120_i blocks some of the direct lateral radiation from the lamp 110 reaching near most surfaces of the carriage 30, and the outer shield 1202 blocks some of the direct lateral radiation from reaching nearby surfaces of components located near the opposite side of the lamp 110. For example, as the carriage 30 moves back and forth across the build bed surface, it may bring the lamp 110 into close proximity with other components, such as components located near or at extreme positions of its travel. In some implementations of the apparatus 1, the carriage 30 may comprise another module downstream of the lamp assembly 100 that needs to be protected, for example a thermal sensor module. Where the apparatus 1 comprises a second carriage 30 that moves independently of the first carriage 30, and located on the other side of the lamp 110, such that as the second carriage 30 moves towards the first carriage 30 (or vice versa) the lamp 110 moves into close proximity of the second carriage and thus the second carriage needs to be shielded from the lamp's direct irradiation to prevent it from heating up excessively. In some apparatus, the lamp assembly 100 may be mounted between other components on the carriage 30, so that the two shields 1201,_ 120_2 may be configured to block some of the direct lateral radiation from the lamp 110 reaching the near most surfaces of the carriage 30 or the components mounted on it.

Optionally, depending on the configuration of the apparatus, the second shield 120 2 may further, or instead, be arranged to limit direct lamp radiation reaching a viewer window into the apparatus 1.

Variants of lamp assemblies 100 comprising two shields are illustrated in Figures 4A and 4B.

Figure 4A illustrates a cross sectional view of a lamp assembly 100 in which the axis 114 of the lamp 110 extends parallel between two planar elongate sheets, forming the dominant surfaces and representing the shields 120_1 and 120_2. The support structure (e.g. frame) 130 locates the shields within the lamp's vaporisation front 112. The lamp 110 is located equidistantly between the dominant surfaces and, in this implementation, also closer to the lower opening 150 (here shown as the opening facing build bed surface 12) compared to the upper opening 140.

In some implementations, at least one of the shields may comprise a dominant surface that is planar. The surfaces of the planar sheets may be arranged parallel to one another. In alternative configurations, each shield may comprise a dominant surface and the dominant surfaces of two shields are non-parallel to one another. The lamp 110 may be located by the support structure 130 with its axis 114 parallel to both sheets, and preferably centrally between the sheets, so that the lamp axis 114 is equidistant from each sheet surface. In some implementations, the lamp axis 114 may be located closer to the lower opening 150 and away from the upper opening 140, or alternatively partially below the lower opening 150. By locating the lamp 110 nearer the lower opening 150, or partially below it, the extreme angles at which radiation may emerge from the lower opening 150, which may also be referred to as

the field of view of the lamp 110, is increased.

In alternative implementations, such as the one shown in Figure 4B, the dominant surfaces of the two planar sheets (shields 120_i and 1202) are angled towards one another such that the lower edges of the sheets are closer to one another than the upper edges of the sheets, and such that the upper opening 140 is larger than the lower opening 150 In other implementations (not shown), the dominant surface may not be planar, but may comprise or consist of a curved cross section having a concave portion facing the lamp 110, similar to the curved sheet described with respect to Figure 3B. The two shields are each comprised at least partially of an elongate sheet of curved, concave cross section, so that the concave surfaces face the lamp 110. The cross section of curvature of each dominant surface may describe the section of a circle or it may describe a parabolic curve, or any other concave curvature or shape. The curve need not be a smooth curve, but may instead be formed from a series of planar elongate strips attached to one another along adjacent elongate edges, at fixed or varying angle from strip to strip.

Where the curvature may be defined in terms of a focal point, the line focus of the curved portion (for e.g. circular or parabolic cross sections) may be coincident with the lamp axis 114, or it may be offset from the lamp axis 114. In these implementations the different arrangements of curvature are intended to achieve an upper opening 140 through which radiation may freely exit the assembly 100 and that may redirect radiation towards and out of the upper opening 140.

For two tilted and/or curved shields arranged to either side of the lamp 110, and in contrast to the two vertical shields described with respect to Figure 4A, the normal n to the shield surface facing the lamp 110 has a non-zero vertical component. For upwards opening shield pairs 120_1, 1202, such as the pair shown in Figure 4B, or for a similarly arranged shield pair with a curved concave portion, lamp radiation not emerging through the lower opening 150 is directed upwards through the upper opening 140 at overall steeper angles compared to radiation reflected by the vertical sheet shields of Figure 4A (and for which the vertical component of the normal to the shield surface facing the lamp is zero) The first shield, i.e. the shield that is to be mounted nearer the carriage (also referred to here as the 'inner shield' when located on the carriage), in these cases comprises a concave or tilted sheet surface facing the lamp that may be defined by one or more normals n1 to the surface for which the x and z components are positive, n1 = (+x, y=0, +z). For the second shield, or 'outer shield' when the assembly is mounted to the carriage, the concave or tilted sheet surface facing the lamp may be defined by one or more normals n2 to the surface for which the x component is negative, 112= (-x, y=0, z).

Lamp location with respect to shields Regardless of whether the shield has a planar or concave portion with respect to the lamp axis 114, the lamp axis 114 may be located nearer the lower edges of the shields and away from the upper edges of the shields. For shields comprising dominant surfaces having upper edges that are further apart than their lower edges, defining a larger upper opening 140 compared to the lower opening 150, the lamp axis 114 may be located near, at, or partially above the plane connecting the divergent, upper edges of the dominant surfaces of the shields.

Alternatively, the lamp axis 114 may be located near, at, or partially below the plane connecting the convergent, lower edges of the dominant surfaces of the shields. In other words, the upper edges of the sheets are further apart from one another compared to the lower two edges, so that that the upper opening 140 is larger compared to the lower opening 150. While the upper opening 140 may be enlarged in this way, the field of view of the lamp 110 with respect to the lower opening 150 may be increased by moving the lamp 110 closer to the lower opening 150 than to the upper opening 140, or even partially below the lower opening 150, so that when the assembly 100 is mounted in the apparatus 1, a sufficient area of the build bed surface 12 may receive direct lamp radiation Outward lower lips Preferably, as discussed above, the shield is made of thin metal sheet or other thin material that dissipates heat easily. Preferably it also has a low coefficient of thermal expansion to prevent material stresses in the shield as it experiences extreme temperature cycles during operation of the lamp 110. In this way, the shield may remain parallel to the lamp 110 during temperature cycling. In addition, the shield preferably has a suitable stiffness to retain its shape during the motion of the carriage 30. Shields made of thin sheet may flex during the process of object build, and it may be beneficial to provide a strengthening lip to one or both of the elongate upper and/or lower edge of the shield. Examples of a strengthening lip are shown in Figures 5 to 7.

Figure 5A shows a schematic cross section of the lamp assembly 100 of Figure 3A, in which a lip 124 is provided to the lower edge of each planar sheet 122_1, 122_2 of respective shields 120 1 and 1202. Figure 5B shows a three-dimensional illustration of the lamp assembly 100 of Figure 5A. As may be seen, the lip 124 1, 124 2 extending from the lower edges of the respective dominant surface 1221, 122 2 is angled outwards with respect to the lamp 110. The angle and extent of the lip 1241, 124 2 may be chosen to provide stiffness to the sheet forming the dominant surface 122_1, 122_2 that is sufficient to ensure that the dominant surfaces 122_1, 122_2 remain parallel to the lamp axis during temperature changes.

Furthermore, the angle of the lip may also be adjusted to adjust the field of view of the lamp out of the lower opening 150.

It is not necessary that the lip is provided to the lower edge of the shield 120 Instead, it may be provided to the upper edge, as illustrated in Figure 6. This variant shows the lip 124 1, 124 2 extending outward from the upper edge of the dominant surfaces 122_I and 122_2 of the shields.

In Figures 5 and 6, the lip 124 is shown as a planar surface. However, the strengthening lip may instead be a curved extension of the lower and/or upper edges of the sheets 122 1, 122_2, to achieve the same effect.

Accordingly, at least one of the shields comprises a lip 124 angled away from an upper and/or lower edge of a dominant surface of the shield 120 and outwards of the upper opening 140 /and or lower opening 150 respectively. The strengthening lip 124 may be provided to all or part of one or both of the elongate edges of the dominant surface.

It should be noted that the 'dominant surface' may take on a dual purpose of shielding and strengthening. For example, the dominant surface may comprise two elongate sheets, a vertical upper sheet and an angled lower sheet attached to the lower edge of the upper sheet and angled with its lower edge towards the lamp axis 114, both sheets combined representing 100% of the total shield surface.

In other implementations, a horizontal or inwards angled strengthening lip may be provided to the upper edge of the shield, so as to further restrict the radiation emerging from the upper opening 140 to a certain range of angles. This may be useful when the head height above the lamp assembly 100 is limited within the working space. An example of such an implementation is shown in Figure 7. A strengthening lip 124 1, 124 2 is attached to the upper edge of respective sheet 1221, 122 2 and extends laterally inwards over a fraction of the distance of the upper opening defined by the inward edges of the lips 124_1, 124_2.

Therefore, at least one of the shields 120 may comprise a lip 124 angled away from an upper edge of a dominant surface 122 of the shield and into the upper opening 140 above the lamp 110 so as to partially bound the space above the lamp; for example at least one of the shields may comprise a lip 124 in the form of an L-or T-section extending horizontally outwards from the upper edge of the dominant surface of the shield, one section of the lip 124 1, 124 2 extending into the opening above the lamp 110 so as to partially bound the space above the lamp 110. Preferably, the inward facing lip 124 1, 124 2 may be arranged to be located outside of the vaporisation front and has a non-reflective surface so as to prevent direct lamp radiation being reflected back onto the build bed 16 In such implementations, in addition to limiting the angle of radiation emerging from the upper opening, the extent of the lip, similar to the outward angled lips, may be chosen to provide sufficient stiffness to the sheet, while at the same time limiting the surface area presented to the build bed surface that may irradiate the white powder with secondary radiation and partially solidify it.

Preferably, the shield 120 is located at least partially within the vaporisation front 112 of the lamp 110 so as to avoid accumulation of powder and ink mist on the shieldS Preferably, the entire shield 120 is located within the vaporisation front 112. Preferably still further, the lip 124, especially where inward facing, is arranged to be located outside of the vaporisation front 112.

Upper opening -group of sub openings and guards/viewer guards The inward facing lip may be provided in an alternative arrangement and having additional benefit. In some apparatus where frequent access is required that may cause damage to a bare lamp or injury to the user, or where a viewer window would receive a significant amount of the radiation that the assembly allows to radiate upward, it may be beneficial to provide a guard to the upper opening 140. For example, the upper opening 140 may be provided with a series of crosswise upper opening struts 142 spaced apart from one another along the elongated upper edge of the shield 120 and extending across the upper opening 140, thus defining a group of upper sub openings 140_1, 1402,.,..

Figure 8 is a three-dimensional illustration of a lamp assembly 100 having crosswise struts 142 between the upper edges of the shields 120_i and 1202, and defining upper sub openings 140_1, 1402,... . These struts 142, preferably of the same material as the sheet 122 and lip 124 of the shield 120, such as thin metal sheet, are for protective purposes and designed so as to not significantly restrict radiation from passing through the upper opening.

The surface area presented by the lip 124 and the struts 142 only insignificantly restricts the passage of radiation through the upper opening 140. Preferably, the struts are located outside of the vaporisation front and their downward facing surface coated in radiation absorbent material so as to prevent lamp radiation being reflected down towards the build bed surface 12.

In some implementations of the lamp assembly 100, each of the struts 142 of the series of crosswise struts extends upward away from the upper opening to form a series of planar guards 160 extending away from the lamp 110 so as to allow radiation to pass through the upper sub openings. An example of such an implementation is illustrated in Figure 9A by way of a three-dimensional representation of the lamp assembly 100 provided to a carriage 30. In this example, the carriage 30 comprises two identical lamp assemblies 100A, 100B at either side of a printing module 38. The assemblies 100 are similar to that of Figure 8, where the struts 142 are formed by a series of guards 160 mounted parallel to one another down the direction of elongation of the upper edges of the shields 120A 1, 120A2 as indicated for assembly 100A (similarly for assembly 100B). In the Figure, only the outer shield 120A_1 is visible.

The sub openings 140A_1, 140A2 (not labelled but equivalent to those shown in Figure 8) are thus defined by the spacing between the guards 160A. The guards 160A are in the form of planar protrusions extending away from the upper opening 140A along a radial direction, so as to protect a viewer from direct lamp radiation and to prevent a user from being able to access the lamp 110A, or to accidentally touch hot surfaces close to the lamp 110A. The guards 160A are preferably made of thin metal so as to present a negligible obstruction to the upper opening, in this way, the guards do not significantly restrict radiation from passing through the sub openings 140A_1, 140A2,... of the upper opening 140A, and do not to present an obstruction to radiation leaving the upper opening 140A in a direction vertically upwards. The downward facing surface area of the guards (the lower edge defined by the thickness of the sheet of which the guards are made) are preferably arranged to be located outside of the vaporisation front. In addition, the downward facing surface may be coated in radiation absorbent material so as to prevent lamp radiation being reflected down towards the build bed surface 12.

The shields 120A, as shown for the outer shield 120A 1, are comprised of a dominant surface 122A1 and strengthening lips 124A 1, 124A2 (not visible) extending from the lower edges of the respective dominant surface 122A 1, 122A2 and angled outwards with respect to the lamp 110A. The angle and extent of the lips 124A 1, 124A2 may be chosen to provide stiffness to the dominant surface 122A_1, 122A2 that is sufficient to ensure that the dominant surfaces 122A 1, 122A2 remain parallel to the lamp axis during temperature changes. Furthermore, the angle of the lip may also be adjusted to adjust the field of view of the lamp 110A out of the lower opening 150A.

The components of the carriage 30 are further illustrated in a plan view from below in Figure 9B, showing the shields 120A_1, 120A_2 at either side of the lamp 110 in each assembly 100.

The shields 120A_1, 120A2 are identical to one another and arranged as mirror images of one another to either side of the lamp 110A While not essential, the lamp assembly 100B is identical to the lamp assembly 100A, and the shields 120B 1, 120B2 are identical to one another and arranged as mirror images of one another to either side of the lamp 110B. Therefore, equivalent components of each assembly may be identified by replacing 'A' with 'B' Thus, the group of upper sub openings 140 1, 140 2,... may be provided by a series of planar guards 160 mounted to the upper edge of at least one of the shields 120 and across the upper opening 140, creating sub openings 140 1, 1402,,,, wherein the planar surface of the guards 160 extends away from the lamp 110 in a radial direction so as to allow radiation to pass unimpeded upwards through the upper sub openings 140_1, 140_2,.. The guards provide the dual function of strengthening/stiffening struts and viewer guards.

The extent of direct lamp radiation reaching a viewer window may be adapted by the spacing and/or upwards extent of the guards Figure 9A also illustrates an example of how the lower edge of the guards 160 may be shaped so as to fall outside of the lamp vaporisation front 112 -in this design the lower edges describe a segment of a circle outside of the vaporisation front and around the lamp axis 114. Additionally, the surfaces outside of the vaporisation front may be IR absorbent, e.g. black.

Apparatus comprising the assembly The lamp assembly 100 and its various embodiments and implementations described with respect to Figures 2A to 9B is of particular beneficial use in a sintering apparatus, or any apparatus requiring use of an infrared tube lamp that would otherwise excessively heat up nearby components and thus compromise the reliability of the build process. Returning to Figure 1, accordingly, an apparatus 1 for the formation of three-dimensional objects by consolidation of particulate material comprises a working space 4, the working space 4 comprising a build bed surface 12 of particulate material arranged at a lower surface bounding the working space 4, and a ceiling 60 arranged at an upper surface bounding the working space 4; a carriage 30 to which the lamp assembly 100 is mounted and for passing the lamp assembly 100 across the build bed surface 12, wherein the shield 120 is located between the lamp 110 and surfaces of the carriage 30 facing the lamp 110, and the at least two openings of the lamp assembly 100 are arranged so that a lower opening 150 allows radiation to pass towards the build bed surface 12 and the upper opening 140 allows radiation to pass away from the build bed surface 12 into the working space 4 and towards the ceiling 60.

The lower opening 150 and the lamp axis 114 are preferably arranged parallel to the build bed surface 12. The upper opening 140 faces the ceiling 60 of the apparatus that bounds the working space vertically, and thus the space above the carriages and the build bed surface 12. The working space 4 may be described as the space in which the build process is carried out, and providing the range of motion of the carriages.

As described above, during operation of the lamp 110 within the apparatus 1, the shield 120 may preferably be located within the vaporisation front 112 of the lamp 110, so that, during operation of the lamp, the shield reaches a pyrolysis temperature of 300 °C or more. For example, the pyrolysis temperature may be reached while the lamp 110 is operated as it passes over the build bed surface 12, and cools down to below pyrolysis temperature soon after the lamp 110 is switched off after passing the build bed surface 12. During a build process, the cycle of being above pyrolysis temperature may be a regular cycle, with a constant period between successive intervals during which the shield reaches a temperature above pyrolysis, and a constant duration above the pyrolysis temperature within the period.

To assist with cooling of the shield and nearby carriage 30, the assembly may furthermore be mounted to the carriage 30 such that a gap exists between the (inner) shield and the nearest surface of the carriage facing the shield. For example, this may be the chassis of the carriage to which the support structure (e.g. frame) 130 may be attached. By keeping a gap between the carriage 30 and the shield, a convection flow is allowed to persist through the gap from the hot build bed surface 12 towards the ceiling 60. Thus, the surface of the carriage 30 facing the lamp 110 may be located next to one of the shields so as to create a gap that allows a convection flow, so that, during operation of the lamp 110, the surface of the carriage 30 facing the lamp 110 remains below the melting point of the particulate material.

To remove the heat generated by the radiation that the ceiling 60 receives from the upper opening 140 of the lamp assembly 100, the ceiling 60 bounding the working space 4 may comprise a heat sink. The heat sink may be passive or active. For example, the ceiling may comprise a thermally conductive material and heat received from the upper opening 140 of the lamp assembly 100 may simply be dissipated sufficiently across and through the ceiling 60 to the outside of the apparatus 1. Otherwise, the ceiling 60 may furthermore comprise heat fins on its external surface (on the outside of the apparatus 1 and outside of the working space 4), and/or it may comprise liquid or gas cooled pipes that are thermally connected to the working space 4. Additionally, or instead, the inner ceiling surface bounding the work space may be coated in an IR absorbent material that is able to absorb the radiation from the upper opening of the assembly -for example the inner ceiling surface could be black. Furthermore, the inner ceiling surface may comprise fins or protrusions reaching into the work space so as to increase the radiation absorbent surface.

Any of the lamp assemblies 100 described above may be suitable for use in the apparatus L Lamp assemblies having an inner shield only for mounting between the lamp and the carriage may be useful in an apparatus in which the lamp assembly 100 is located at an extreme end of the carriage and is not bounded by any components on the outer side. An example of such an apparatus is shown in Figure 1. In this apparatus, with only an 'inside' shield 120 fitted to the lamp assembly 100, the lamp radiation may dissipate in a lateral direction away from the carriage 30 as well as through the upper opening 140 and the lower opening 150. In the implementation of Figure 1, the shield 120 comprises a dominant surface that is a planar surface elongate along and parallel to the lamp axis 114. The dominant surface extends vertically upward, perpendicular to the build bed surface 12, and perpendicular to its direction of elongation. Preferably, the apparatus 1 comprises an infrared lamp 110, and a shield 12 predominantly comprised of an elongate planar metal sheet that extends vertically upwards from the lower opening 150 to the upper opening 140. The planar metal sheet may be arranged within the lamp assembly 100 so as to extend vertically upwards from the build bed surface 12, to an extent so as to shield the carriage 30 from direct lamp radiation.

In some variants of the apparatus 1, it may further be necessary to protect components on the outer side of the lamp assembly 100, requiring an outer shield in addition to the inner shield. For example, the carriage itself may support components on either side of the lamp assembly 100 such as a printing module and a measuring device module such as a pyrometer. In other variants, a second carriage 30 may be provided downstream of the first carriage 30, so that the lamp assembly 100 mounted to the first carriage 30 is adjacent the second carriage 30 for at least some durations of the build process. As the first carriage 30 moves the lamp 110 across the build bed surface 12 to consolidate the present layer of particulate material, the second carriage 30 may closely follow behind to spread a fresh layer onto the layer the lamp 110 has just consolidated. The second carriage 30 may therefore need protecting by the second shield from the direct irradiation of the lamp 110. In other implementations of the apparatus, a significant proportion of the lamp radiation may reach the viewer window so that a second shield acts as viewer protection. In some apparatus therefore, the lamp assembly 100 may comprise a second elongate shield 120_2 extending along the side of and parallel to the lamp axis and located opposite the first shield 120 1. Optionally the first and the second shield 1201, 120 2 comprise respective dominant surfaces 1221, 122 2 that are planar and, optionally, are made of metal.

Additionally, or instead, the planar dominant surfaces 1221, i22_2 of the two elongate shields 1201, 120 2 may be arranged within the lamp assembly 100 so as to extend vertically upwards from the build bed surface 12 from the lower opening 150 to the upper opening 140.

Alternatively, at least one of the dominant surfaces 1221, 122 2 may be curved to present a concave surface to the lamp axis 114 and arranged so as to provide an upper opening 140 that is larger in area than the lower opening 150. The cross section of the curvature, viewed along the lamp axis 114, may be circular or elliptical, or another curved shape that directs direct lamp radiation upwards and out of the upper opening 140. The specific shape and orientation of the one or more shields 120 may be determined by the arrangement of components within and the dimensions of the working space 4.

Each of the shields may comprise two or more dominant surfaces of distinct shape or configuration, for example two elongate surfaces adjoint along one of their elongate edges and arranged at an angle towards one another, and where both surfaces in combination have the function to dissipate radiation through the upper opening 140 of the lamp assembly 100 and into the working space 4.

Optionally, at least one of the shields 120 further comprises two or more elongate sub surfaces forming the dominant surface, wherein the lower or upper elongate edge of the first surface is arranged at an angle to the second surface, such that the dominant surface flares outwards with respect to the lamp 110 and such that the lower opening 150 is larger than the upper opening 140. Such a configuration may provide a dominant surface that has a dual purpose of allowing radiation to pass through the upper and lower openings while being self-stiffening and making the shield robust against warping during cycles of extreme temperatures, and so as to ensure that the elongate surfaces of the shield remain substantially parallel to the lamp axis 114.

In some apparatus, the shield may predominantly comprise an elongate planar surface having a lower edge and that is angled inwards of the lamp 110 such that its lower edge defines a lower opening 150 that is smaller than the upper opening 140 The surface may be comprised of metal Where the apparatus comprises a second elongate shield 120 2 extending along the side of the lamp opposite the first shield 1201, the second shield 120 2 may comprise a dominant surface 122 2 haying a lower edge that is angled with its lower edge inwards of the assembly, such that the lower edges of the two shields define a lower opening 150 that is smaller in area than the upper opening 140.

The infrared lamp 110 may comprise a tube having a reflective coating along part of the inner tube surface, for example covering hall of the inner tube surface. When mounted in the apparatus 1, the reflective coating is on the top portion of the tube to reflect and focus lamp radiation emitted from the upper half of the lamp 110 to the build bed surface 12. The lamp 110 is mounted in conventional apparatus such that the concave reflector faces the build bed surface 12 and focusses the lamp radiation along a perpendicular to the build bed surface 12, vertically below the lamp 110. In an apparatus having a lamp assembly 100, the inner shield 120 1 is bound to one side by the carriage 30 while the outer shield 120_2 may not be bound by any fixed components, and thus the inner shield 120_i gets hotter than the outer shield.

As described above, the lamp assembly 100 may equally be useful for the purpose of consolidation as well as, or instead of, for the purpose of pre heating the powder layer.

With reference to Figure 10, a schematic cross section through an apparatus 1 along the direction of travel of the carriages shows various lamp assemblies 100, two each mounted to each carriage 301 and 302.

The distribution module 36 is provided on a first carriage 30_1 between two lamp assemblies 100_A and 100_B, and the printing module 38 is provided on a second carriage 30_2 20 between lamp assemblies 100_C and 100D.

During motion of the carriages, for example with respect to the motion of the second carriage in the direction across the build bed surface 12 indicated by the arrow, the lamp assembly 100 D is located downstream, and the lamp assembly 100_C is located upstream of the printing module 38. The lamp assembly 100 D may act as a pre-heat lamp assembly ahead of the printing module 38 and the lamp assembly 100_C may act as a sintering lamp assembly following the printing module. This means that, for example, before the printing module is operated across a fresh layer of powder to deposit RANI, the preheat lamp assembly 100 D, operating lamp 110 at a relatively lower power compared to the power required for sintering, is passed over the build bed surface 12 to pre-heat the powder to a temperature close to the sintering temperature. The lamp 110 of lamp assembly 100 C, functioning as a sintering lamp and operating at higher power than the preheat lamp, may thus not have to impart as much power to achieve consolidation of the printed powder as it would if the layer had not been preheated.

Next, the first carriage 301 follows the second carriage 302. The lamp assembly 100_A and 100_B may both be operated as preheating lamp assemblies. Lamp assembly 100_B preheats the layer just processed by the second carriage, followed by the distribution module 36 spreading a fresh layer over the thus pre-heated processed layer. This may improve the adhesion between the sintered and fresh layer. The lamp assembly 100_A may be operated as a pre-heat lamp assembly that preheats the freshly distributed layer downstream of the distribution module 36.

Alternatively, lamp assembly 100_B may be operated as a sintering lamp assembly to provide a second sintering stroke following the first sintering stroke provided by lamp assembly 100_c.

Therefore, the lamp assembly 100 may be mounted to more than one carriage within the apparatus 1, and/or more than one lamp assembly 100 may be mounted to the same carriage to provide a sintering and/or pre heat lamp 110. Both lamp assemblies have at least an inner shield 120_I located between the lamp and the carriage the lamp assembly is mounted to, and optionally, as shown for the assemblies of the apparatus illustrated in Figure 10, also outer shields mounted on the outboard side of the carriage.

General considerations The shield 120 may comprise more than one subsurface of specific orientation and/or shape, and that together make up the dominant surface 122 of the shield. One sub surface contributing to the dominant surface may be angled or shaped differently to the others sub surfaces contributing to the dominant surface For example, the sub surface near the lower opening 150 may be curved in cross section while a subsurface near the upper opening 140 is a planar sub surface.

In some implementations having two shields at either side of the lamp axis, the shields may have different shapes or vertical extents from one another so as to direct the lamp radiation into the working space as required by the design of the apparatus. For example, the inner shield between lamp and carriage may be taller, in the vertical direction away from the build bed surface 12, than the outer shield, and/or the inner shield may have a planar dominant surface extending vertically and the outer shield a planar dominant surface angled away from the vertical such that the upper and lower edges of the two shields define an upper opening that is larger than the lower opening 150. Other combinations may be envisaged.

The shields 120 of the assembly 110, once mounted to the carriage in the apparatus 1, may extend vertically, i.e. have a height along a direction perpendicular to the build bed surface 12, over a distance that is greater than the diameter of the lamp 110. Additionally, the lamp, when viewed along a projection direction along the plane parallel to the build bed surface 12, overlaps at least partially with one of the surfaces of the shield. Furthermore, the height of the shields may have a sufficiently vertical component so that any of the lamp radiation that would directly irradiate the carriage 30 or its components, or that would emerge from the lamp over at least its diameter in the horizontal direction, is blocked by the surface of the shield.

Material and thickness, temperatures The shields according to the various implementations disclosed are preferably made of thin sheet, preferably thin metal sheet, of a thickness between 1 mm and 0.4 mm. This ensures that in one respect, the shield does not present a substantial surface area facing the powder bed and emitting secondary radiation that may be absorbed by the unprinted powder. In another respect, heat is not stored by the shield since its thermal mass is small. This means the metal sheet cools down rapidly as soon as the lamp 110 is turned off. Preferably, the shields have a reflective surface. The shield may remain reflective and clean by mounting it within the vaporisation front.

The thin metal sheet from which the shields may be made may be aluminium or stainless steel, for example, as these materials are both good IR reflectors.

In some implementations of the lamp assemblies, the shield or shields may be mounted to the support structure (e.g, frame) with minimal contact area so as to limit thermal conduction between the shield and the support structure (and thus between the support structure and the carriage, once mounted).

The shield may be made at least partially of thermally non conductive ceramic. Alternatively, the surface of the shield not facing the lamp may be coated with a thermally insulating layer; or the outer surface not facing the lamp may be a non conductive ceramic having an inner surface coated in a thin metal layer. This may further protect the carriage 30 from the extreme temperatures the shield may reach, for example where a gap ensuring sufficient convection flow may not be maintained to sufficiently cool the sheet over certain durations of the build process During operation of the apparatus, the shield intercepts some of the direct lamp radiation so as to prevent adjacent parts of the carriage from heating up excessively. The sintering temperature of a nylon powder such as PAll is around 180 °C or higher depending on the grade of polymer. Therefore the carriage is preferably kept at a temperature lower than the sintering temperature, for example lower than 160 °C for PA I I, and preferably lower than 140 °C or even 120 °C. As the sintering temperature is powder material dependent, the carriage should not reach temperatures close to the melting point of the powder, Tm, which could be as low as 100 °C for thermoplastic polyurethane.

In addition, the lamp assembly 100 is mounted to the carriage 30 such that the shield shields the nearmost parts of the carriage 30 from direct lamp radiation and so that the nearmost parts of the carriage 30 may be inside of the lamp vaporisation front whilst being shielded from excessive temperatures. In addition, a sufficient gap between the shield and the carriage may be provided to ensure convective cooling, so that the temperature of the carriage as well as of the shield may finther be controlled The location of the shield within the vaporisation front 112 provides a reflective surface of the shield throughout operation of the apparatus. Whilst this prevents accumulation of molten material on the shield, a reflective surface further is able to redirect some of the lamp radiation reflected back from the powder surface away from the shield and into the working space 4 above.

For the shield to intercept sufficient radiation and prevent it reaching the carriage, the shield of the assembly 100, once mounted to the carriage 30 in the apparatus 1, may extend vertically, i.e. have a height along a direction perpendicular to the build bed surface 12, that is greater than the diameter of the lamp, and arranged with respect to the lamp 110 such that the lamp radiation that would otherwise directly irradiate the carriage 30 or its components is blocked by the surface of the shield. Optionally, the area covered by the lamp 110 when projected along a direction parallel to the build bed surface 12 onto the surface of the shield, at least partially overlaps with a surface of the shield.

The function of the various lamp assemblies 100 may vary during the process of building the object, simply by altering the power of the lamp 110. The preheat function may result in a smaller vaporisation front than the sintering function. As a result, the shield, or shields, may need to be located closer to a lamp used solely as pre heat lamp compared to the shield(s) location with respect to a sintering lamp, so as to ensure that the shield(s) of the pre heat lamp remain reflective Alternatively, the lamp power of the preheat lamp may temporarily be increased during maintenance so as to pyrolise and clean the shields.

The outer shield may be of the same shape and size as the inner shield, however this is not essential and the relative shape and size will depend on the requirements of the apparatus.

The infrared lamp need not be a tube lamp spanning the direction of elongation of the assembly. Instead, a series of IR lamps may be arranged to form a row representing the elongate infrared lamp. Within the apparatus 1, the purpose of the elongate configuration is to span the width of the build bed surface 12 so as to provide homogeneous irradiation to all parts along the width of the build bed surface 12, and this may be achieved by a single or by multiple lamps spanning the width of the build bed surface 12.

Claims

C LA I NIS1. An infrared lamp assembly for an apparatus for the formation of three-dimensional objects by consolidation of particulate material, the assembly comprising: an elongate infrared lamp extending along a lamp axis, an elongate shield extending parallel to and along one side of the axis of the lamp, and a support structure holding at least one of the ends of the lamp and of the shield, wherein the elongate shield at least partially bounds the space to one side of the lamp, and wherein the assembly provides a lower opening below the lamp and an upper opening above the lamp, such that radiation generated by the lamp is able to radiate through the openings and away from the lamp in directions not bounded by the shield.
2. The infrared lamp assembly of claim 1 further comprising a second shield extending alongside the lamp, wherein the support structure holds at least one of the ends of the second shield to position the second shield alongside the lamp and opposite the first shield so that the lamp is located between the shields.
3. The infrared lamp assembly of claim 1 or claim 2, wherein at least one of the shields comprises a dominant surface that is planar.
4. The infrared lamp assembly of claim 2, wherein each shield comprises a dominant surface and the dominant surfaces of the two shields are non-parallel to one another.
5. The infrared lamp assembly of claim 2, wherein each shield comprises a dominant surface and the dominant surfaces of the two shields are parallel to one another.
6 The infrared lamp assembly of claim 2, wherein each shield comprises a dominant planar surface and wherein the dominant planar surfaces are angled towards one another such that the lower edges of the dominant surfaces are closer to one another than the upper edges of the dominant surfaces, and such that the upper opening is larger than the lower opening.
7. The infrared lamp assembly of claim 2, or of claim 3 when dependent on claim 2, or of claim.5 or claim 6, wherein the lamp axis is located at or above the plane connecting the lower edges of the dominant surfaces of the shields.
8 The infrared lamp assembly of claim 3, wherein the lamp is mounted to the support structure so that the planar dominant surface of the shield forms a tangent plane to the surface of a cylindrical constant power envelope centred about the lamp axis.
9 The infrared lamp assembly of claim 8, wherein the planar dominant surface extends by different amounts to either side of the contact line between the tangent plane and the constant power envelope.
10. The infrared lamp assembly of any preceding claim, wherein at least one of the shields comprises a lip angled away from an upper and/or lower edge of a dominant surface of the shield and outwards of the upper/and or lower opening respectively.
11. The infrared lamp assembly of any preceding claim, wherein at least one of the shields comprises a lip angled away from an upper edge of a dominant surface of the shield and into the opening above the lamp so as to partially bound the space above the lamp.
12. The infrared lamp assembly of any preceding claim, wherein the shield is located at least partially within the lamp vaporisation front.
13. The infrared lamp assembly of any preceding claim, wherein the upper opening comprises a series of crosswise struts extending across the upper opening and defining a group of upper sub openings.
14 The infrared lamp assembly of claim 13, further wherein each of the struts of the series of crosswise struts extends upward away from the upper opening to form a series of planar guards extending away from the lamp so as to allow radiation to pass through the upper sub openings
15. The infrared lamp assembly of any preceding claim, wherein the shield is formed from a metal sheet of constant thickness of between 0.4 mm and 1 mm thickness.
16. An apparatus for the formation of three-dimensional objects by consolidation of particulate material comprising a working space, the working space comprising: a build bed surface of particulate material arranged at a lower surface bounding the working space, and a ceiling arranged at an upper surface bounding the working space; and a carriage to which the lamp assembly of any of claims 1 to 15 is mounted and for passing the lamp assembly across the build bed surface, wherein the shield is located between the lamp and surfaces of the carriage facing the lamp, and the at least two openings of the lamp assembly are arranged so that the lower opening allows radiation to pass towards the build bed surface and the upper opening allows radiation to pass away from the build bed surface into the working space and towards the ceiling.
17 The apparatus according to claim 16, wherein the shield, during operation of the lamp, reaches a pyrolysis temperature of 300 °C or more.
18. The apparatus according to claim 16 or claim 17, wherein the surface of the carriage facing the lamp is located next to one of the shields so as to create a gap that allows a convection flow, so that, during operation of the lamp, the surface of the carriage facing the lamp remains below the melting point of the particulate material.
19. The apparatus according to any one of claims 16 to 18, wherein the ceiling comprises a heat sink.
20. The apparatus according to any one of claims 16 to 19, wherein the shield predominantly comprises an elongate planar metal sheet that extends vertically upwards from the lower opening to the upper opening.
21. The apparatus according to claim 20 comprising a second elongate shield extending along the side of the lamp opposite the first shield, wherein the second shield predominantly comprises an elongate planar dominant surface that extends vertically upwards from the lower opening to the upper opening.
22. The apparatus according to claim 20 or claim 2L wherein at least one of the shields comprises two or more elongate planar sub surfaces forming the dominant surface, wherein the first surface is arranged at an angle to the second surface, such that the dominant surface flares outwards with respect to the lamp and such that the lower opening is larger than the upper opening.
23. The apparatus according to any one of claims 16 to 19, wherein the shield predominantly comprises an elongate planar metal sheet having a lower edge and that is angled inwards of the lamp such that its lower edge defines a lower opening that is smaller than the upper opening.
24. The apparatus of claim 23, further comprising a second elongate shield extending along the side of the lamp opposite the first shield, optionally wherein the second shield predominantly comprises an elongate planar metal sheet haying a lower edge and that is angled inwards of the assembly such that the lower edges of the shields define a lower opening that is smaller than the upper opening.