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

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, in use, radiation generated by the lamp is able to radiate through the openings and away from the lamp in directions not bounded by the shield.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT Application No. PCT/GB2020/053177, filed on Dec. 11, 2020, which claims priority to GB 1918434.0 filed Dec. 13, 2019 and GB 191835.7 filed Dec. 13, 2019, the disclosures of which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present disclosure relates to an infrared lamp assembly for an apparatus for the layer-by-layer 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 preheating 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 carriage for an apparatus for the formation of three-dimensional objects by consolidation of particulate material, the carriage comprising: an elongate infrared lamp extending along a lamp axis; an elongate shield extending parallel to and along one side of the lamp axis, wherein the shield is mounted so as to at least partially bound the space to one side of the lamp; and a lower opening below the lamp and an upper opening above the lamp, such that in use, radiation generated by the lamp is able to radiate through the lower opening and the upper opening 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, the apparatus 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 according to the first aspect for moving the lamp across the build bed surface, wherein, in use, the lower opening is arranged to pass radiation towards the build bed surface, and the upper opening is arranged to pass radiation away from the build bed surface into the working space and towards the ceiling.

According to a third aspect there is provided 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, in use, 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 fourth 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 third 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, in use, 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.

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 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. In addition, any radiation reflected back from the build bed surface can pass through the open assembly, while the minimal shield surface directly facing the powder bed surface only absorbs a small amount of reflected radiation. Overall, it may be beneficial that the shield is made of a thin sheet of metal, for example 1 mm thin or less, such that it has a low thermal mass and thus is able to cool down quickly when the lamp is switched off.

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 toFIGS.1to13.

FIG.1shows an apparatus1for layer-by-layer formation of three-dimensional objects by the aggregation of particulate matter by high speed sintering, and having a lamp assembly100according to an embodiment of the present invention.

The apparatus1has a working space4bounded from below by a working surface13and from the top by a ceiling60. One or more carriages30(in this case two) are arranged to be movable across a build bed surface12that is comprised within the working surface13. The build bed surface12is the surface over which successive layers of particulate material, such as powder, are distributed and processed to form cross sections of an object2. The apparatus1further comprises a powder container system10with a build bed16within which the object2is formed, layer by layer, from a build bed surface12. A powder dosing module40is arranged to dose fresh powder to the working surface. The first and second carriages30_1,30_2respectively support a distribution device36, and a printing module38and a lamp assembly100. The carriages are movable on at least one rail34back and forth across the build bed surface12.

In an illustrative process sequence, the floor18of the powder container system10, and which bounds the bottom surface of the build bed16, lowers the build bed16by a layer thickness.

With the first carriage30_1supporting the distribution device36located to the far side of the dosing module with respect to the build bed surface12, and the second carriage30_2located on the opposite side of the build bed surface12with respect to the first carriage, the dosing module40doses an amount of powder to the work surface13, adjacent the build bed surface12. The first carriage is moved across the build bed surface12so that the distribution device38distributes the dosed powder so as to form a thin layer across the build bed surface12. Next, the first carriage30_1moves back to its starting position, followed by the second carriage30_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 module38deposit fluid containing RAM over selected areas of the build bed surface12corresponding to the cross section of the object to be formed, and the infrared lamp110of the lamp assembly100is 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 lamp110achieves 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 assembly100is 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 device36. For example, an infrared lamp110of a similar assembly100could be mounted to the first carriage downstream of the distribution device38and operate as a preheat lamp. As the distribution device38distributes the powder layer, the preheat lamp100is 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 apparatus1, two lamps may be provided on each carriage, for example one upstream and one downstream of the printhead module, or one upstream and one downstream of the powder distribution device, or two lamps side by side. 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 preheat 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 assembly100.

An embodiment of the lamp assembly100and some variants thereof comprising the infrared lamp110will now be illustrated in detail by way of example with reference toFIGS.2A to9B.

FIGS.2A to2Cshow an infrared lamp assembly100according 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, in which a laser source is used to selectively sinter the powder material, generally does not require a printing module, a preheat lamp as part of an assembly100may be provided for example to the carriage supporting the powder distribution device38.

Accordingly, the infrared lamp assembly100comprises an elongate infrared lamp110extending along a lamp axis114, an elongate shield120extending parallel to and along one side of the axis of the lamp110, and a support structure (e.g. frame)130holding at least one (and preferably both) of the ends of the lamp110and of the shield120. The elongate shield at least partially bounds the space to one side of the lamp. The assembly provides a lower opening150below the lamp and an upper opening140above 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 openings140,150and away from the lamp in directions not bounded by the shield120.

In the present disclosure, radiation may mean direct, primary radiation emitted by the lamp, lamp radiation reflected upwards by the shield, primary radiation emitted by the lamp and reflected back from the powder bed surface12into the lower opening, and secondary radiation emitted from the surface of the hot lamp110or other hot surfaces, for example surfaces heated by the lamp.

As illustrated, the support structure130may hold both the ends of the lamp110and both the ends of the shield120. Advantageously, this gives improved structural rigidity to the assembled components, including the lamp110and the shield120. However, alternative embodiments of the assembly100may employ a support structure that holds only one end of the lamp110and/or only one end of the shield120, provided the lamp110and/or shield120are securely supported from that one end, and the lamp is of a type that is powered from only one end.

FIGS.2A to2Cshow the lamp assembly100in greater detail. The infrared lamp110may be an elongate lamp such as a tube emitter, such as a 3000 W, 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 shield120is mounted to the support structure so that its direction of elongation extends parallel to the lamp axis114. This is illustrated in a schematic plan view of the assembly inFIG.2C. When mounted to a carriage30above a build bed surface12within the apparatus1, 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 inFIG.2A), as also indicated in the cross sectional schematic inFIG.2A, where it is shown how the lamp assembly100may be positioned above a build bed surface12. The lamp axis114and elongate direction of the shield120meanwhile extend parallel to the build bed surface12, as is illustrated in a schematic side view of the assembly inFIG.2B. In this way, the assembly100provides a shield120mounted to one side of and parallel to the lamp axis114, and an upper opening140above and a lower opening150below 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 apparatus1, radiation is able to radiate towards the build bed surface12through the lower opening150, and unimpeded upwards into the working space4through the upper opening140, where the working space4is bounded above by ceiling60. At the same time, there is minimal shield surface directly facing the powder bed surface12, so that any secondary radiation emitted from the shield120cannot 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 axis114, defined by the lamp power, all or at least a significant amount of 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 front112of the lamp110, as indicated for example inFIG.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 front112is 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 or less from the lamp axis.

In the apparatus shown inFIG.1, the lamp radiation reflected by the shield, or radiation reflected back from the build bed surface onto the inner surface(s) of the shield and reflected upwards, is further able to radiate freely away from the shield surface. Radiation can however not directly reach at least the nearmost surfaces of the carriage30since the shield120blocks direct radiation from the lamp, or radiation reflected from the build bed surface towards the inner surface(s) of the shield(s), 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 surface12and y (into the page inFIG.1andFIG.2A) is the direction of elongation of the lamp and shield, such that the lamp axis114is parallel to the y-axis.

Tilted and Curved Single Shields

It is not essential, when mounted to the carriage30, that the shield surface extends substantially vertically upwards from the build bed surface12. Lamp assemblies100having alternative configurations and arrangements of shields120with respect to the build bed surface12are illustrated inFIGS.3A and3B.

InFIG.3A, the shield120is a planar sheet located within the lamp vaporisation front112. The support structure (e.g. frame)130supporting the shield120and the lamp110is mounted to the carriage30such that the nearmost surfaces of the carriage facing the shield120are located outside of the lamp vaporisation front112. When installed in the apparatus1, the shield120extends upwards at an angle to the vertical to the build bed surface12, so that its upper edge leans away from the lamp axis114and towards the carriage, and its lower edge leans towards the lamp axis114.

In a variant to the shield ofFIG.3A, the shield120may comprise an elongate sheet of a curved, concave cross section, when viewed along the lamp axis114, and arranged within the assembly so that the concave surface faces the lamp110. 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 space4. 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 axis114, or it may be offset from the lamp axis114.

In the implementations shown inFIGS.3A and3B, a normal n to the shield surface facing the lamp110may 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 shield120ofFIG.2A(and for which the vertical component of the normal to the shield surface is zero). This restricts the lower opening150through which radiation can reach the build bed surface12, and through which direct radiation reflected back from the powder may be redirected upwards and out of the upper opening140, which is widened compared to the vertical shield ofFIG.2A. In addition, a higher proportion of lamp radiation compared to the vertical shield120ofFIG.2is reflected upwards into the working space4by the shield120. The arrangements of the shield120inFIGS.3A and3Bdefine an upper opening140that is larger than the lower opening150, so that more radiation is directed upwards and away from the lamp110compared to the radiation emerging from the assembly100ofFIG.2.

Dominant Surface

The shields120of the various embodiments and implementations described herein may be thought of as comprising a dominant surface122, which may comprise more than 50% of the shield surface, and which has the primary function to direct radiation generated by the lamp110out of the upper opening140of the assembly100, so that, in the apparatus, the radiation may radiate unimpeded by obstructions above the upper opening140into the working space4and away from the build bed16to remove heat from the vicinity of the lamp110. The dominant surface122is further arranged to reflect any direct lamp radiation, and any lamp radiation reflected back from the build bed surface12into the lower opening150, towards and out of the upper opening140. Thus unlike conventional downwards focusing reflector housings used with infrared lamps that focus lamp radiation towards the build bed surface12, the assembly100dissipates a substantial amount of radiation upwards and away from the lamp110into the working space4.

The dominant surface122may generally have a lower and upper elongate edge that defines, or contributes to defining, the extent of the upper opening140and the extent of the lower opening150. Furthermore, the dominant surface122may 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 opening140of the lamp assembly100.

With respect to the shields120shown inFIGS.3A and3B, the dominant surface122may be angled with respect to the vertical, or the dominant surface may be curved, such that the dominant surface122has 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 bed16is sufficiently small to avoid significant amounts of secondary radiation being directed at the build bed surface12.

Returning toFIG.2A, the dominant surface of the shield120is 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 lamp110. The upper and lower edges of the dominant surface (here shield120), 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 apparatus1, the sheet does not extend infinitely in a vertical direction away from the powder bed surface12.

In the case of a single shield120having a planar elongate sheet as dominant surface122therefore, the lamp110may be mounted to the support structure (e.g. frame)130so that the planar dominant surface122of the shield forms a tangent plane to the surface of a cylindrical constant power envelope centred about the lamp axis114. Optionally, the planar dominant surface122may extend by different amounts to either side of the contact line between the tangent plane and the constant power envelope. In other words, the lamp110is located closer towards one elongate edge of the planar surface. When the assembly is mounted to the carriage30within the apparatus1, this may mean that the lamp110is located closer to the lower opening150than to the upper opening140.

By mounting the shield120with respect to the lamp axis114so that the lamp axis114is closer to the lower opening150of the shield120than to the upper opening140, the angle over which the lamp can irradiate the build bed surface12is increased.

Two Shields

In some implementations, a second shield120_2may be provided to extend alongside the lamp110, wherein the support structure (e.g. frame)130holds the ends of the second shield120_2, so that the second shield extends parallel to the lamp axis and opposite the first shield so that the lamp110is located between the shields. The infrared lamp assembly100may thus comprise the elongate infrared lamp110having a lamp axis114, two elongate shields120_1,120_2extending parallel to and along the axis114of the lamp110, and a support structure (e.g. frame)130holding at least one (and preferably both) of the ends of the lamp110and of the two shields120_1,120_2. The support structure130locates the first and second shield alongside the lamp110and on opposite sides of the lamp; in other words, the lamp110is located between the shields120_1,120_2. The elongate shields at least partially bound the space to either side of the lamp110. The assembly100thus provides a lower opening150below the lamp110and an upper opening140above the lamp110, such that there is no significant obstruction in the space above and below the lamp110within the assembly100. In this way, radiation generated by the lamp110is able to radiate through the upper and lower openings140,150and away from the lamp110in directions not bounded by the shields120_1,120_2. By providing a second shield, the radiation of the lamp110is 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 carriage30in the apparatus1, this means that the shields120_1,120_2may be arranged so that the inner shield120_1blocks some of the direct lateral radiation from the lamp110reaching near most surfaces of the carriage30, and the outer shield120_2blocks some of the direct lateral radiation from reaching nearby surfaces of components located near the opposite side of the lamp110. For example, as the carriage30moves back and forth across the build bed surface, it may bring the lamp110into close proximity with other components, such as components located near or at extreme positions of its travel. In some implementations of the apparatus1, the carriage30may comprise another module downstream of the lamp assembly100that needs to be protected, for example a thermal sensor module. Where the apparatus1comprises a second carriage30that moves independently of the first carriage30, and located on the other side of the lamp110, such that as the second carriage30moves towards the first carriage30(or vice versa) the lamp110moves 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 assembly100may be mounted between other components on the carriage30, so that the two shields120_1,120_2may be configured to block some of the direct lateral radiation from the lamp110reaching the near most surfaces of the carriage30or the components mounted on it.

Optionally, depending on the configuration of the apparatus, the second shield120_2may further, or instead, be arranged to limit direct lamp radiation reaching a viewer window into the apparatus1.

Combinations of the various variants of the shields may be used for the two shields in the same assembly. In other words, any variant of the shield as described herein may equally apply to both shields (arranged as mirror images); or in assemblies where two shields are provided, one shield may represent one variant while the other shield represents a different variant.

Variants of lamp assemblies100comprising two shields are illustrated inFIGS.4A and4B.FIG.4Aillustrates a cross sectional view of a lamp assembly100in which the axis114of the lamp110extends parallel between two planar elongate sheets, forming the dominant surfaces and representing the shields120_1and120_2. The support structure (e.g. frame)130locates the shields within the lamp's vaporisation front112. The lamp110is located equidistantly between the dominant surfaces and, in this implementation, also closer to the lower opening150(here shown as the opening facing build bed surface12) compared to the upper opening140.

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 lamp110may be located by the support structure130with its axis114parallel to both sheets, and preferably centrally between the sheets, so that the lamp axis114is equidistant from each sheet surface. In some implementations, the lamp axis114may be located closer to the lower opening150and away from the upper opening140, or alternatively partially below the lower opening150. By locating the lamp110nearer the lower opening150, or partially below it, the extreme angles at which radiation may emerge from the lower opening150, which may also be referred to as the field of view of the lamp110, is increased.

In alternative implementations, such as the one shown inFIG.4B, the dominant surfaces of the two planar sheets (shields120_1and120_2) 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 opening140is larger than the lower opening150.

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 lamp110, similar to the curved sheet described with respect toFIG.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 lamp110. 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 axis114, or it may be offset from the lamp axis114. In these implementations the different arrangements of curvature are intended to achieve an upper opening140through which radiation may freely exit the assembly100and that may redirect radiation towards and out of the upper opening140.

For two tilted and/or curved shields arranged to either side of the lamp110, and in contrast to the two vertical shields described with respect toFIG.4A, the normal n to the shield surface facing the lamp110has a non-zero vertical component. For upwards opening shield pairs120_1,120_2, such as the pair shown inFIG.4B, or for a similarly arranged shield pair with a curved concave portion, lamp radiation not emerging through the lower opening150is directed upwards through the upper opening140at overall steeper angles compared to radiation reflected by the vertical sheet shields ofFIG.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 n1to 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 n2to the surface for which the x component is negative, n2=(−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 axis114, the lamp axis114may 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 opening140compared to the lower opening150, the lamp axis114may be located near, at, or partially above the plane connecting, i.e. defined by, the divergent, upper edges of the dominant surfaces of the shields.

Alternatively, the lamp axis114may be located near, at, or partially below the plane connecting, i.e. defined by, 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 opening140is larger compared to the lower opening150. While the upper opening140may be enlarged in this way, the field of view of the lamp110with respect to the lower opening150may be increased by moving the lamp110closer to the lower opening150than to the upper opening140, or even partially below the lower opening150, so that when the assembly100is mounted in the apparatus1, a sufficient area of the build bed surface12may 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 lamp110. In this way, the shield may remain parallel to the lamp110during temperature cycling. In addition, the shield preferably has a suitable stiffness to retain its shape during the motion of the carriage30. 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 inFIGS.5to7.

FIG.5Ashows a schematic cross section of the lamp assembly100ofFIG.3A, in which a lip124is provided to the lower edge of each planar sheet122_1,122_2of respective shields120_1and120_2.FIG.5Bshows a three-dimensional illustration of the lamp assembly100ofFIG.5A. As may be seen, the lip124_1,124_2extending from the lower edges of the respective dominant surface122_1,122_2is angled outwards with respect to the lamp110. The angle and extent of the lip124_1,124_2may be chosen to provide stiffness to the sheet forming the dominant surface122_1,122_2that is sufficient to ensure that the dominant surfaces122_1,122_2remain 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 opening150.

It is not necessary that the lip is provided to the lower edge of the shield120. Instead, it may be provided to the upper edge, as illustrated inFIG.6. This variant shows the lip124_1,124_2extending outward from the upper edge of the dominant surfaces122_1and122_2of the shields. Other strengthening configurations may equally apply, for example a slightly protruding beam may be formed or applied to the surface of shield so that the beam extends along the shield in the direction of elongation; i.e. the ‘lip’ may not be formed along one of the edges of the shield but instead along one or both of the inner and outer surfaces of the shield.

InFIGS.5and6, the lip124is shown as a planar surface. However, the strengthening lip may instead be a curved extension of the lower and/or upper edges of the sheets122_1,122_2, to achieve the same effect.

Accordingly, at least one of the shields comprises a lip124angled or curving away from an upper and/or lower edge of a dominant surface of the shield120and outwards of the upper opening140/and or lower opening150respectively. The strengthening lip124may 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 axis114, 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 opening140to a certain range of angles. This may be useful when the head height above the lamp assembly100is limited within the working space. An example of such an implementation is shown inFIG.7. A strengthening lip124_1,124_2is attached to the upper edge of respective sheet122_1,122_2and extends laterally inwards over a fraction of the distance of the upper opening defined by the inward edges of the lips124_1,124_2.

Therefore, at least one of the shields120may comprise a lip124angled away from an upper edge of a dominant surface122of the shield and into the upper opening140above the lamp110so as to partially bound the space above the lamp; for example at least one of the shields may comprise a lip124in 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 lip124_1,124_2extending into the opening above the lamp110so as to partially bound the space above the lamp110. Preferably, the inward facing lip124_1,124_2may 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 bed16.

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 shield120is located at least partially within the vaporisation front112of the lamp110so as to avoid accumulation of powder and ink mist on the shield. Preferably, the entire shield120is located within the vaporisation front112. Preferably still further, the lip124, especially where inward facing, is arranged to be located outside of the vaporisation front112.

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 opening140. For example, with reference toFIG.8, the upper opening140may be provided with a series of crosswise upper opening struts142spaced apart from one another along the elongated upper edge of the shield120and extending across the upper opening140, thus defining a group of upper sub openings140_1,140_2, . . . .

In more detail,FIG.8is a three-dimensional illustration of a lamp assembly100having crosswise struts142between the upper edges of the shields120_1and120_2, and defining upper sub openings140_1,140_2, . . . . These struts142, preferably of the same material as the sheet122and lip124of the shield120, 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 lip124and the struts142only insignificantly restricts the passage of radiation through the upper opening140. 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 surface12.

In some implementations of the lamp assembly100, each of the struts142of the series of crosswise struts extends upward away from the upper opening to form a series of planar guards160extending away from the lamp110so as to allow radiation to pass through the upper sub openings. An example of such an implementation is illustrated inFIG.9Aby way of a three-dimensional representation of the lamp assembly100provided to a carriage30. In this example, the carriage30comprises two identical lamp assemblies100A,100B at either side of a printing module38. The assemblies100are similar to that ofFIG.8, where the struts142are formed by a series of guards160mounted parallel to one another down the direction of elongation of the upper edges of the shields120A_1,120A_2as indicated for assembly100A (similarly for assembly100B). In the Figure, only the outer shield120A_1is visible.

The sub openings140A_1,140A_2(not labelled but equivalent to those shown inFIG.8) are thus defined by the spacing between the guards160A. The guards160A are in the form of planar protrusions extending away from the upper opening140A 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 lamp110A, or to accidentally touch hot surfaces close to the lamp110A. The guards160A 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 openings140A_1,140A_2, . . . of the upper opening140A, and do not to present an obstruction to radiation leaving the upper opening140A 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 surface12.

The shields120A, as shown for the outer shield120A_1, are comprised of a dominant surface122A_1and strengthening lips124A_1,124A_2(not visible) extending from the lower edges of the respective dominant surface122A_1,122A_2and angled outwards with respect to the lamp110A. The angle and extent of the lips124A_1,124A_2may be chosen to provide stiffness to the dominant surface122A_1,122A_2that is sufficient to ensure that the dominant surfaces122A_1,122A_2remain 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 lamp110A out of the lower opening150A.

The components of the carriage30are further illustrated in a plan view from below inFIG.9B, showing the shields120A_1,120A_2at either side of the lamp110in each assembly100.

The shields120A_1,120A_2are identical to one another and arranged as mirror images of one another to either side of the lamp110A. While not essential, the lamp assembly100B is identical to the lamp assembly100A, and the shields120B_1,120B_2are identical to one another and arranged as mirror images of one another to either side of the lamp110B. Therefore, equivalent components of each assembly may be identified by replacing ‘A’ with ‘B’.

Thus, the group of upper sub openings140_1,140_2, . . . may be provided by a series of planar guards160mounted to the upper edge of at least one of the shields120and across the upper opening140, creating sub openings140_1,140_2. . . , wherein the planar surface of the guards160extends away from the lamp110in a radial direction so as to allow radiation to pass unimpeded upwards through the upper sub openings140_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.

FIG.9Aalso illustrates an example of how the lower edge of the guards160may be shaped so as to fall outside of the lamp vaporisation front112—in this design the lower edges describe a segment of a circle outside of the vaporisation front and around the lamp axis114. Additionally, the surfaces outside of the vaporisation front may be IR absorbent, e.g. black.

The struts412or guards160as described herein need not be directly attached to the shield(s). Instead, the struts and/or guards may be attached to the carriage with respect to the shield(s). In this way, the shield(s) may thus be detachable from the carriage, independently from the struts or guards.

The invention disclosed herein is not limited to any particular practical implementation in which the elongate lamp110and elongate shield(s)120are mounted. For example, the elongate lamp110and the one or more shields120may be mounted directly to the carriage30, or to a frame of the carriage. The lamp may be mounted to a different part of the carriage or frame compared to the one or more shields. The specific arrangement between the lamp and the one or more shields may thus be achieved in different practical implementations. The various embodiments and implementations described for the lamp assembly100with respect toFIGS.2A to9Bequally apply to the lamp110and shield(s) when individually and/or directly mounted to the carriage30, where the functionality of the frame130may be readily implemented in alternative ways on the carriage by the skilled person.

Accordingly, an infrared lamp carriage30for an apparatus for the formation of three-dimensional objects by consolidation of particulate material is provided, the carriage comprising:an elongate infrared lamp110extending along a lamp axis114;an elongate shield120extending parallel to and along one side of the lamp axis114, wherein the shield120is such that it at least partially bounds the space to one side of the lamp; anda lower opening below the lamp and an upper opening above the lamp, such that radiation generated by the lamp110is able to radiate through the lower opening140and the upper opening150and away from the lamp in directions not bounded by the shield. The shield120may be mounted between the lamp110and a surface of the carriage30.

The carriage may further comprise a second elongate shield extending alongside the lamp and opposite the first elongate shield so that the lamp is located between the shields.

At least one of the elongate shields120may comprise a dominant surface as described in relation to the lamp assembly100that is planar. Each shield may comprise a dominant surface and the dominant surfaces of the two shields120_1,120_2may be non-parallel to one another. Alternatively, the dominant surfaces of the two shields120_1,120_2may be parallel to one another. As a further alternative, each elongate shield may comprise a dominant planar surface and the dominant planar surfaces may be 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 opening140is larger than the lower opening150. The lamp axis114may be located at or above the plane defining the lower edges of the dominant surfaces of the elongate shields.

The lamp and at least one of the elongate shields120may be is mounted to the carriage such that the planar dominant surface of the elongate shield forms a tangent plane to the surface of a cylindrical constant power envelope centred about the lamp axis.

The planar dominant surface may extend by different amounts to either side of the contact line between the tangent plane and the constant power envelope.

In addition, or instead, at least one of the shields may comprise a lip angled away from an upper and/or lower edge of the or a dominant surface of the shield and outwards of the upper and/or lower opening respectively. The lip may be angled away from an upper edge of the dominant surface of the shield and into the opening above the lamp so as to partially bound the space above the lamp.

The upper opening may comprise a series of crosswise struts142extending from the upper edge of the at least one shield120, or between the upper edges of the two shields120_1,120_2, across the upper opening140and defining a group of upper sub-openings.

Each of the struts142of the series of crosswise struts may extend upward away from the upper opening140to form a series of planar guards or protrusions160extending away from the lamp so as to allow radiation to pass through the upper sub-openings.

In addition to the above lamp110(which may be considered to be a “first” lamp110A extending along a “first” lamp axis), the carriage30may further comprise a second elongate infrared lamp110B, for example as illustrated inFIG.9B, the second lamp110B extending along a second lamp axis parallel to the first lamp axis; a second lamp elongate shield120B_1extending parallel to and along one side of the second lamp axis, wherein the second lamp elongate shield120B_1at least partially bounds the space to one side of the second lamp110B; and a second lower opening below the second lamp110B and a second upper opening above the second lamp110B, such that radiation generated by the second lamp110B is able to radiate through the second lower opening and the second upper opening140B and away from the second lamp110B in directions not bounded by the second lamp elongate shield. Such a carriage is exemplified inFIGS.9A and9B.

The second lamp elongate shield120B_1may be mounted between the second lamp110B and a second surface of the carriage as shown inFIG.9B, or it may be mounted between the second lamp110B and a shield of another lamp. In the variant shown inFIGS.9A and9B, each lamp110A,110B is mounted between respective two elongate shields120_1,120_2, where one of the shields (in theFIG.9Bshields120A_2and120B_1) is located between a respective lamp110and a surface of the carriage. Furthermore, the second shield of respective lamps (in theFIG.9Bshields120A_1and120B_2) is located so as present part of an outward side of the carriage30.

The first elongate lamp110A may be mounted near or at one of the edges of the carriage30and the second lamp110B may be mounted at another, opposing edge of the carriage. In the apparatus1, these edges of the carriage may represent the leading or trailing edges of the carriage when it is in motion, and the second elongate lamp110B may be mounted near or at the other of the leading or trailing edges of the carriage such that the second lamp elongate shield120B_1is mounted between the second lamp and a second surface of the carriage.

As before, each shield120may preferably be located at least partially within the lamp vaporisation front, and may be formed from a metal sheet of constant thickness of between 0.4 mm and 1 mm thickness.

Apparatus Comprising the Assembly, or the Carriage Comprising the Lamp and Shield(s)

The lamp assembly100and the carriage30comprising at least one elongate lamp110and respective elongate shield120, and the various embodiments and implementations of the assembly or of the lamp in relation to the shield(s), dominant surfaces, lip, struts and protrusions as described with respect toFIGS.2A to9B, are of particular beneficial use in a sintering apparatus, or any apparatus requiring use of an infrared elongate tube lamp that would otherwise excessively heat up nearby components and thus compromise the reliability of the build process. In the following, reference to ‘assembly100’ equally applies to the lamp110and shield(s)120being directly mounted to the carriage, irrespective of how the lamp and shield(s) are mounted to the carriage. Returning toFIG.1, accordingly, an apparatus1for the formation of three-dimensional objects by consolidation of particulate material comprises a working space4, the working space4comprising: a build bed surface12of particulate material arranged at a lower surface bounding the working space4, and a ceiling60arranged at an upper surface bounding the working space4; and a carriage30to which the lamp assembly100is mounted (or to which the lamp and shield(s) and other optional features according to the present disclosure are mounted) and for moving the lamp assembly100(or the lamp and shield(s) and other optional features) across the build bed surface12, wherein the lower opening150is arranged to pass, in use, radiation towards the build bed surface12and the upper opening140is arranged to pass, in use, radiation away from the build bed surface12into the working space4and towards the ceiling60. The shield120may be located between the lamp110and surfaces of the carriage30facing the lamp110.

The lamp may be mounted near the trailing or leading edge of the carriage when in motion. Additionally, or instead, it may be mounted between different components provided on the carriage, for example between a printing module38and a distribution device36.

The lower opening150and the lamp axis114are preferably arranged parallel to the build bed surface12. The upper opening140faces the ceiling60of the apparatus that bounds the working space vertically, and thus the space above the carriages and the build bed surface12. The working space4may 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 lamp110within the apparatus1, the shield120may preferably be located within the vaporisation front112of the lamp110, 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 lamp110is operated as it passes over the build bed surface12, and cools down to below pyrolysis temperature soon after the lamp110is switched off after passing the build bed surface12. 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 shield120and nearby surfaces of the carriage30, the assembly (or lamp and one or two shields) may furthermore be mounted to the carriage30such 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)130may be attached, or it may be the chassis itself for example. By keeping a gap between the carriage30and the shield, a convection flow is allowed to persist through the gap from the hot build bed surface12towards the ceiling60. Thus, the surface of the carriage30facing the lamp110may 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 lamp110, the surface of the carriage30facing the lamp110remains below the melting point of the particulate material.

To remove the heat generated by the radiation that the ceiling60receives from the upper opening140of the lamp assembly100, the ceiling60bounding the working space4may 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 opening140of the lamp assembly100may simply be dissipated sufficiently across and through the ceiling60to the outside of the apparatus1. Otherwise, the ceiling60may furthermore comprise heat fins on its external surface (on the outside of the apparatus1and outside of the working space4), and/or it may comprise liquid or gas cooled pipes that are thermally connected to the working space4. Additionally, or instead, the inner ceiling surface bounding the working 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 may be black. Furthermore, the inner ceiling surface may comprise fins or protrusions reaching into the working space so as to increase the radiation absorbent surface.

Any of the lamp assemblies100described above may be suitable for use in the apparatus1. 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 assembly100is 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 inFIG.1. In this apparatus, with only an ‘inside’ shield120fitted to the lamp assembly100, the lamp radiation may dissipate in a lateral direction away from the carriage30as well as through the upper opening140and the lower opening150. In the implementation ofFIG.1, the shield120comprises a dominant surface that is a planar surface elongate along and parallel to the lamp axis114. The dominant surface extends vertically upward, perpendicular to the build bed surface12, and perpendicular to its direction of elongation. Preferably, the apparatus1comprises an infrared lamp110, and a shield12predominantly comprised of an elongate planar metal sheet that extends vertically upwards from the lower opening150to the upper opening140. The planar metal sheet may be arranged within the lamp assembly100so as to extend vertically upwards from the build bed surface12, to an extent so as to shield the carriage30from direct lamp radiation.

In some variants of the apparatus1, it may further be necessary to protect components on the outer side of the lamp assembly100, requiring an outer shield in addition to the inner shield. For example, the carriage itself may support components on either side of the lamp assembly100such as a printing module and a measuring device module such as a pyrometer. In other variants, a second carriage30may be provided downstream of the first carriage30, so that the lamp assembly100mounted to the first carriage30is adjacent the second carriage30for at least some durations of the build process. As the first carriage30moves the lamp110across the build bed surface12to consolidate the present layer of particulate material, the second carriage30may closely follow behind to spread a fresh layer onto the layer the lamp110has just consolidated. The second carriage30may therefore need protecting by the second shield from the direct irradiation of the lamp110. 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 assembly100may comprise a second elongate shield120_2extending along the side of and parallel to the lamp axis and located opposite the first shield120_1. Optionally the first and the second shield120_1,120_2comprise respective dominant surfaces122_1,122_2that are planar and, optionally, are made of metal.

Additionally, or instead, the planar dominant surfaces122_1,122_2of the two elongate shields120_1,120_2may be arranged within the lamp assembly100so as to extend vertically upwards from the build bed surface12from the lower opening150to the upper opening140.

Alternatively, at least one of the dominant surfaces122_1,122_2may be curved to present a concave surface to the lamp axis114and arranged so as to provide an upper opening140that is larger in area than the lower opening150. The cross section of the curvature, viewed along the lamp axis114, may be circular or elliptical, or another curved shape that directs direct lamp radiation upwards and out of the upper opening140. The specific shape and orientation of the one or more shields120may be determined by the arrangement of components within and the dimensions of the working space4.

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 opening140of the lamp assembly100and into the working space4.

Optionally, at least one of the shields120further 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 lamp110and such that the lower opening150is larger than the upper opening140. 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 axis114.

In some apparatus, the shield may predominantly comprise an elongate planar surface having a lower edge facing the build bed surface12and that is angled inwards of the lamp110such that its lower edge defines a lower opening150that is smaller than the upper opening140. The elongate planar surface may be comprised of metal.

Where the apparatus comprises a second elongate shield120_2extending along the side of the lamp opposite the first shield120_1, the second shield120_2may also comprise a dominant surface122_2having a lower edge facing the build bed surface12and that is angled with its lower edge inwards of the assembly, such that the two lower edges of the two shields120_1,120_2define a lower opening150that is smaller in area than the upper opening140.

The infrared lamp110may comprise a tube having a reflective coating along part of the inner tube surface, for example covering half of the inner tube surface. When mounted in the apparatus1, the reflective coating is on the top portion of the tube to reflect and focus lamp radiation emitted from the upper half of the lamp110to the build bed surface12. The lamp110is mounted in conventional apparatus such that the concave reflector faces the build bed surface12and focusses the lamp radiation along a perpendicular to the build bed surface12, vertically below the lamp110. In an apparatus having a lamp assembly100, the inner shield120_1is bound to one side by the carriage30while the outer shield120_2may not be bound by any fixed components, and thus the inner shield120_1gets hotter than the outer shield.

As described above, the lamp assembly100may equally be useful for the purpose of consolidation as well as, or instead of, for the purpose of preheating the powder layer.

With reference toFIG.10, a schematic cross section through an apparatus1along the direction of travel of the carriages shows various lamp assemblies100, two each mounted to each carriage30_1and30_2.

The distribution module36is provided on a first carriage30_1between two lamp assemblies100_A and100_B, and the printing module38is provided on a second carriage30_2between lamp assemblies100_C and100_D.

During motion of the carriages, for example with respect to the motion of the second carriage in the direction across the build bed surface12indicated by the arrow, the lamp assembly100_D is located downstream, and the lamp assembly100_C is located upstream of the printing module38. The lamp assembly100_D may act as a preheat lamp assembly ahead of the printing module38and the lamp assembly100_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 RAM, the preheat lamp assembly100_D, operating lamp110at a relatively lower power compared to the power required for sintering, is passed over the build bed surface12to preheat the powder to a temperature close to the sintering temperature. The lamp110of lamp assembly100_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 carriage30_1follows the second carriage30_2. The lamp assembly100_A and100_B may both be operated as preheating lamp assemblies. Lamp assembly100_B preheats the layer just processed by the second carriage, followed by the distribution module36spreading a fresh layer over the thus preheated processed layer. This may improve the adhesion between the sintered and fresh layer. The lamp assembly100_A may be operated as a preheat lamp assembly that preheats the freshly distributed layer downstream of the distribution module36.

Alternatively, lamp assembly100_B may be operated as a sintering lamp assembly to provide a second sintering stroke following the first sintering stroke provided by lamp assembly100_C.

Therefore, more than a single lamp assembly100may be mounted to more than one carriage within the apparatus1, and/or more than one lamp assembly100may be mounted to the same carriage to provide a sintering and/or preheat lamp110. Both lamp assemblies have at least an inner shield120_1located between the lamp and the carriage the lamp assembly is mounted to, and optionally, as shown for the assemblies of the apparatus illustrated inFIG.10, also outer shields mounted on the outboard side of the carriage.

General Considerations

The shield120may comprise more than one sub-surface of specific orientation and/or shape, and that together make up the dominant surface122of the shield. One sub-surface contributing to the dominant surface may be angled or shaped differently to the other sub-surfaces contributing to the dominant surface. For example, the sub-surface near the lower opening150may be curved in cross section while a sub-surface near the upper opening140is 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 surface12, 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, where the vertical direction is, in use, a direction substantially vertical to the build bed surface12, such that the upper and lower edges of the two shields (upper and lower with respect to the build bed surface in use, the lower edge being closer to the build bed surface than the upper edge) define an upper opening140that is larger than the lower opening150. Other combinations may be envisaged.

The shields120of the assembly110, once mounted to the carriage in the apparatus1, may extend vertically, i.e. have a height along a direction perpendicular to the build bed surface12, over a distance that is greater than the diameter of the lamp110. Additionally, the lamp, when viewed along a projection direction along the plane parallel to the build bed surface12, 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 carriage30or 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 lamp110is 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 carriage30from 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 PA11 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 PA11, 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 assembly100is mounted to the carriage30such that the shield shields the nearmost parts of the carriage30from direct lamp radiation and so that the nearmost parts of the carriage30may 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 further be controlled.

The location of the shield within the vaporisation front112provides 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 space4above.

For the shield to intercept sufficient radiation and prevent it reaching the carriage, the shield of the assembly100, once mounted to the carriage30in the apparatus1, may extend vertically, i.e. have a height along a direction perpendicular to the build bed surface12, that is greater than the diameter of the lamp, and arranged with respect to the lamp110such that the lamp radiation that would otherwise directly irradiate the carriage30or its components is blocked by the surface of the shield. Optionally, the area covered by the lamp110when projected along a direction parallel to the build bed surface12onto the surface of the shield, at least partially overlaps with a surface of the shield.

In some implementations of the apparatus1when having a plurality of infrared lamps supported on one or more carriages, it may be desirable to provide an alternative lamp assembly in addition to the assembly described above. Such an alternative, second, assembly may comprise a radiation deflector that provides for deflection of radiation energy so as to upwardly release lamp radiation not used for sintering or preheating, and such that the extent and/or the direction of the upward radiated energy may be controlled. As before, the radiation deflector has an upper opening through which radiation unused for sintering may dissipate freely, which reduces or minimises the amount of heat transferred to the radiation deflector, thus preserving or enhancing selectivity. The unused radiation is redirected into the working space above the work surface and away from the build bed surface12, and may more easily be managed via the comparatively large ceiling area of the apparatus.

An example of the infrared radiation deflector of a second assembly200is shown in a schematic cross-section perpendicular to the lamp axis114(i.e. along the y direction) inFIGS.11A to12B. Starting withFIG.11A, the assembly comprises an elongate lamp110similar or identical to the elongate lamp described above, the lamp extending along a lamp axis114. The deflector comprises a first mirror230_1and a second mirror230_2that describe sections of a linear parabolic trough with the lamp axis114located at the focal line f of the trough. The sections of the first mirror230_1and the second mirror230_2are opposing sections to either side of the vertex line V of the parabolic trough. An elongate lower opening250is provided near the vertex line V of the trough such that the lower opening250extends in the direction of the vertex line V.

Thus, the first mirror230_1may represent a section along and to one side of the vertex line of a linear parabolic trough, so that the cross section of the first mirror as viewed down the lamp axis114(along they direction) is part of a parabola for redirecting at least a portion of “direct” lamp radiation216in the form of parallel (redirected) radiation through the upper opening240. The first mirror230_1as shown inFIG.11Ahas a cross-section extending linearly along, and to one side of, the vertex line V of the parabolic trough. For example, the section may extend to the lower opening and its lower edge may extend linearly and be aligned with, or define, the edge of the lower opening. The upper edge of the first mirror230_1may extend parallel to the lower edge of the first mirror.

More particularly,FIG.11Ashows the direct lamp radiation216that may be expected to emerge from the lamp110, andFIG.11B, while omitting some of the labels ofFIG.11Afor simplicity but which equally apply, shows the direct lamp radiation216and the redirected lamp radiation218. The second mirror230_2is similarly shaped as the first mirror230_1, and is arranged, almost in mirror image with respect to the plane of symmetry224of the trough, opposite the first mirror. The plane of symmetry224comprises the vertex line V. The radiation deflector represents thus a portion of a linear parabolic trough mirror, where the inner surfaces to either side of the vertex line V are arranged to redirect direct lamp radiation216in the form of parallel radiation218out of the upper opening240as shown inFIG.11B.

In addition, although not essential, radiation absorbing surfaces260may be provided to the radiation deflector to block some of the direct radiation216so as to control the extent of the FOV as defined by the two innermost absorbing surfaces. The absorbing surfaces are non-reflective surfaces. They may for example have a black radiation absorbent finish at least over surfaces that are exposed to receive infrared radiation from the lamp (whether direct or reflected/redirected).

In the example shown, the radiation deflector100is tilted with respect to the build bed surface12such that the plane of symmetry of the parabolic trough is not perpendicular to the build bed surface. The lower opening250is offset from the vertex line such that the plane described by the lower opening250is angled with respect to the build bed surface12. While this is optional, it may be beneficial in cases where the lower opening is to create a uniform field of view FOV(L) that is symmetric about the perpendicular to the build bed surface12.

When viewed in cross section down the lamp axis location (along the y direction), the upper opening240may be arranged symmetrically with respect to the plane of symmetry of the linear parabolic trough of which the first and second mirrors represent sections.

The deflector assembly200may be provided to the carriage30in combination with providing the lamp110and elongate shield(s)120described herein. For example, in addition to at least one set of a lamp110and one or two elongate shields120, the carriage may further comprise a deflector lamp assembly200mounted to the carriage, the deflector lamp assembly comprising a radiation deflector and a deflector elongate infrared lamp110extending along a deflector lamp axis, the radiation deflector comprising:opposing first and second elongate side walls; andan upper deflector opening240and a lower deflector opening250arranged to pass deflector lamp radiation to an exterior of the radiation deflector;wherein the first and second elongate side walls comprise a first elongate mirror230_1and a second elongate mirror230_2extending parallel to the deflector lamp axis and along at least a lower internal portion of the respective first and second side walls;wherein the deflector lamp axis extends along and between the first mirror230_1and the second mirror230_2, the first and second mirror each having a concave surface with respect to the deflector lamp axis; andwherein the first mirror230_1is an upward deflecting mirror and further arranged to be concave with respect to the upper deflector opening240for redirecting at least a portion of direct deflector lamp radiation through the upper deflector opening240; andwherein the radiation deflector is mounted to the carriage30so that, in use, the lower deflector opening250passes radiation towards the build bed surface12and the upper deflector opening240passes radiation into the working space4and, optionally, towards the ceiling60.

The deflector assembly200may be mounted alongside the first lamp110such that the first lamp extends parallel to the deflector infrared lamp110, in other words the two lamps extend side by side. The deflector lamp assembly200may be mounted directly adjacent a set of the lamp110and one or two shields120. Additionally, or instead, the deflector assembly may be mounted to the opposite edge of the carriage, so that for example a printing module38is located between the deflector assembly200and the set of the lamp110and one or two shields120.

The deflector may comprise one or more radiation absorbing surfaces260arranged to block direct radiation from exiting the upper deflector opening240at angles greater than a predetermined upper deflector opening field of view FOV, wherein the radiation absorbing surfaces260are elongate parallel planes extending in a direction parallel to the upper edges of the mirrors and wherein each radiation absorbing surface260has a depth direction chosen so as to block direct radiation from exiting the radiation deflector at angles greater than the predetermined upper deflector opening field of view FOV while allowing radiation to pass at angles equal to or smaller than the predetermined upper deflector opening field of view. Optionally, the first mirror230_1of the deflector may represent a section along and to one side of the vertex line V of a linear parabolic trough so that the cross section of the first mirror230_1as viewed down the deflector lamp axis is part of a parabola for redirecting at least a portion of the deflector lamp radiation in the form of parallel radiation through the upper deflector opening240of the deflector.

End supports not shown may connect the ends of the side walls (the mirrors230_1,230_2in this case) of the deflector. The end supports may be in the form of a plate or of supporting struts, or one or more brackets. Alternatively, the deflector may be mounted directly to a frame on the carriage, by its ends or otherwise, and the lamp110may either be mounted to the deflector or it may be separately mounted to the frame of the carriage or similar structure.

The carriage30as described, comprising one or more sets of an elongate lamp110and one or two shields120, and optionally the deflector lamp assembly200, may be provided to the above-described apparatus1.

It may be preferable to align the absorbing surfaces260such that they are parallel to one another and further parallel to the direction of the redirected radiation218, i.e. parallel to the plane of symmetry of the linear parabolic trough of which the two mirrors230_1,230_2represent sections. Depending on the placement, spacing, and/or extent of the absorbing surfaces260any non-parallel direct lamp radiation216may be substantially blocked from passing through the upper opening240, while any redirected and predominantly parallel radiation218is allowed to pass in-between the absorbing surfaces. The absorbing surfaces260may preferably be located outside of the lamp vaporisation front112so as to ensure they remain absorbent.

Thus using the lamp deflector assembly200, the directionality of the radiation may be controlled and the angular spread that defines the field of view FOV may be equal to or at least close to zero. This may for example be useful where certain locations or features at or near the ceiling60of the working space4are to be protected from receiving radiation from the upper opening, for example the strong radiation emitted from the lamp110when in sintering mode.

Instead of both mirrors representing a section each of a linear parabolic trough, only the first mirror230_1may form a section of a linear parabolic trough. The second mirror230_2may have a linear concave curvature about the lamp axis114, i.e. extending linearly along and parallel to the lamp axis and curving about the lamp axis.FIG.12Ais a schematic cross section of a variant of the radiation deflector, shown perpendicular to the lamp axis114(i.e. along they direction) of the lamp110. The focal line of the parabolic mirror230_1is coincident with the lamp axis114. The second mirror230_2may be a section of a linear cylindrical mirror with its focal line coincident with the lamp axis114. This means that any direct radiation216from the lamp is reflected back by the cylindrical mirror230_2onto the lamp axis114. AsFIG.12Billustrates, any direct lamp radiation216reaching the first (linear parabolic trough) mirror230_1is redirected as parallel infrared radiation out of the upper opening240.

In this variant, the second mirror230_2further acts as a radiation restrictor similar to the absorbing surfaces, although this is achieved by reflection rather than absorption. The upper edge of the second mirror delimits the angular spread of the FOV to one side of the upper opening240. In addition, some of the reflected radiation may pass from the second mirror to the first mirror, either to be redirected to pass out of the upper opening240, or to be absorbed by the absorbing surfaces260.

The angular spread of the FOV to the other side of the upper opening240may be delimited by radiation absorbent surfaces260arranged parallel to the direction of the redirected radiation, i.e. parallel to the plane of symmetry of the linear parabolic trough of which the first mirror230_1represents a section. The previous description of the radiation absorbent surfaces260may equally apply. The vaporisation front112may extend to the upper edge of the first mirror230_1and encompasses the second mirror230_2.

With the variant ofFIG.12B, it is possible to block all or substantially all non-parallel radiation by extending the upper edge of the second mirror230_2to or beyond the plane of symmetry224. It will be appreciated that where radiation absorbing surfaces are provided, the upper opening240is defined by the combined opening presented by the sub openings defined between the radiation absorbent surfaces260.

The mirrors230_1,230_2of the deflector may be formed from thin metal sheet 0.4 to 1 mm thick. This ensures the mirrors have a low thermal mass and do not store heat, while a high thermal conductivity (for example by being made of metal) ensures ready heat dissipation. For example, the radiation deflector may temporarily pass through cooler air flows within the working space4and is able to cool down quickly, or it may lose heat readily as soon as the lamp is switched off.

In the apparatus, as will be appreciated from the foregoing description, the direction of radiation emerging from the first ‘open’ assembly100via the upper opening140may not be well controlled and may interfere with sensitive measurement equipment, for example an infrared camera monitoring the build bed surface.

FIG.13illustrates how variants of the deflector lamp assembly comprising a radiation deflector and a lamp110(which is referred to herein as a ‘deflector lamp’ to distinguish from the lamp110used in combination with one or two shields, even though these two lamps may be identical), when used for example for sintering, may be beneficial in protecting sensitive components comprised at or within the ceiling of the apparatus1that are affected by the strong radiation of a sinter lamp.FIG.13is a side view of an apparatus1in which a deflector assembly is provided comprising a linear parabolic reflector comprising two opposing mirrors230_1,230_2that are positioned as mirror images of each other, similar to or the same as the deflector illustrated inFIG.11A. While for simplicity a carriage30is not shown, nor the assembly of the first type, the deflector lamp assembly200may be mounted to a carriage30travelling in the direction of the arrow. The deflector lamp assembly200shown is mounted such that the plane of symmetry of the linear parabolic trough, of which the first and second mirrors230_1,230_2form side wall sections, is tilted by an angle α with respect to the perpendicular to the build bed surface12(along the z direction).

The upper opening240(not labelled but similar to the same to the one indicated inFIG.11A) is arranged to emit substantially parallel radiation at an angle α with respect to the perpendicular to the build bed surface12by use of radiation absorbing surfaces260arranged as previously described in relation toFIGS.11A and11B.

A radiation sensitive component70is mounted to the roof of a recess72in the ceiling60. The radiation sensitive component70may be a sensor that requires protection from the lamp radiation emitted from the upper opening240. To protect the component70, the recess72in the ceiling may be designed to have a width w and height h that ensures that, as the lamp assembly200is moved across the build bed surface12, the parallel radiation emerging at an angle α to the vertical (z direction) from the build bed surface12does not reach the top surface of the recess72and thus does not irradiate the component70. This is achieved by setting the width w, height h and angle α such that the angle α is larger than tan−1(w/h).

In the apparatus1, the deflector lamp assembly200may be mounted to the same carriage30to which the first assembly100is mounted.

The deflector assembly200may be mounted alongside the first assembly100such that the infrared lamp110of the first assembly100extends parallel to the deflector infrared lamp110of the deflector assembly200.

Alternatively, the deflector lamp assembly200may be mounted to a second carriage30_2independently moveable from the (first) carriage30_1to which the first assembly100is mounted.

The deflector may further comprise one or more radiation absorbing surfaces260arranged to block direct radiation from exiting the deflector upper opening240at angles greater than a predetermined upper opening field of view, wherein the radiation absorbing surfaces260are elongate parallel planes extending in a direction parallel to the upper edges of the mirrors230and wherein each radiation absorbing surface260has a depth direction chosen so as to block direct radiation from exiting the radiation deflector at angles greater than the predetermined upper opening field of view FOV while allowing radiation to pass at angles equal to or smaller than the predetermined upper opening field of view FOV.

The first mirror230_1of the deflector may represent a section along and to one side of the vertex line V of a linear parabolic trough so that the cross section of the first mirror230_1as viewed down the lamp axis114is part of a parabola for redirecting at least a portion of lamp radiation in the form of parallel radiation through the upper opening240of the deflector.

The deflector may be arranged such that the direction of the parallel radiation emerging from the upper opening240forms an acute angle α to the perpendicular to the ceiling60. Where the radiation emerging from the deflector upper opening240is parallel radiation, the angle of the perpendicular to the ceiling to the ‘FOV’ of the parallel radiation is the angle α as shown.

To remove the heat generated by the radiation that the ceiling60receives from the upper opening140from the lamp(s)110mounted to the first assembly and/or second assembly, the ceiling60bounding the working space4may comprise a heat sink. The heat sink may be passive or active. For example, the ceiling may comprise a thermally conductive material so that heat received from the upper opening140of the lamp assembly100or200may simply be dissipated sufficiently across and through the ceiling60to the outside of the apparatus1. The ceiling may alternatively, or in addition, be cooled by a coolant flowing through coolant pipes in contact with the ceiling. In order for the ceiling to efficiently absorb radiation from the lamp assembly100/200, the inner surface of the ceiling facing the carriage(s) may be radiation absorbent, for example it may be black.

The deflector may take any of the variants described above in relation toFIGS.11A to12Bwhen implemented on the carriage30(or one or both of the carriages31_1,30_2) and/or in the apparatus1.

The function of the various lamp assemblies100may vary during the process of building the object, simply by altering the power of the lamp110. 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 preheat lamp compared to the shield(s) location with respect to a sintering lamp, so as to ensure that the shield(s) of the preheat 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 apparatus1, the purpose of the elongate configuration is to span the width of the build bed surface12so as to provide homogeneous irradiation to all parts along the width of the build bed surface12, and this may be achieved by a single lamp or by multiple lamps spanning the width of the build bed surface12.