GB2422344A - Rapid prototyping using infrared sintering - Google Patents

Rapid prototyping using infrared sintering Download PDF

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Publication number
GB2422344A
GB2422344A GB0501380A GB0501380A GB2422344A GB 2422344 A GB2422344 A GB 2422344A GB 0501380 A GB0501380 A GB 0501380A GB 0501380 A GB0501380 A GB 0501380A GB 2422344 A GB2422344 A GB 2422344A
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Prior art keywords
infrared
powder
layer
sintering
built
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GB0501380D0 (en
GB2422344A8 (en
GB2422344B (en
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David Ian Wimpenney
Soumya Banerjee
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De Montfort University
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De Montfort University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/141—Processes of additive manufacturing using only solid materials
    • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/10—Formation of a green body
    • B22F10/14—Formation of a green body by jetting of binder onto a bed of metal powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/22—Driving means
    • B22F12/224—Driving means for motion along a direction within the plane of a layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/40—Radiation means
    • B22F12/41—Radiation means characterised by the type, e.g. laser or electron beam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/90—Means for process control, e.g. cameras or sensors
    • B22F3/008—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
    • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
    • B29C39/02—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor for making articles of definite length, i.e. discrete articles
    • B29C39/12—Making multilayered or multicoloured articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
    • B29C39/02—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor for making articles of definite length, i.e. discrete articles
    • B29C39/12—Making multilayered or multicoloured articles
    • B29C39/123—Making multilayered articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/165—Processes of additive manufacturing using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
    • B29C67/02—Moulding by agglomerating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
    • B29C67/02—Moulding by agglomerating
    • B29C67/04—Sintering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/70—Recycling
    • B22F10/73—Recycling of powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/10—Auxiliary heating means
    • B22F12/13—Auxiliary heating means to preheat the material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • B22F2003/1052—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding assisted by energy absorption enhanced by the coating or powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
    • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
    • B29C2035/0822—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using IR radiation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

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Abstract

The method provides a rapid prototyping method for constructing freeform three-dimensional objects by successive layer-by-layer deposition of powder material. Each layer is created by the successive steps of: (a) providing a layer of powder material that is intrinsically transparent to infrared radiation of a particular wavelength; (b) selectively depositing an infrared-sensitive agent over selected areas of the surface of the powder layer; (c) exposing the layer of the powder material to infrared radiation of a wavelength absorbed by the infrared-sensitive material; and (d) controlling the duration of the infrared exposure to establish sintering or the commencement of sintering of the powder material over which the infrared-sensitive material has been deposited. The unsintered powder may be removed. The infrared sintering may if desired be augmented by further microwave sintering or exposure of the built object to induction heating. Better definition of the shape of the object can be established by using a laser beam to traverse the edge or edges of each layer as the object is built, to improve the resolution of that edge or those edges. Preferably each layer is compressed before sintering.

Description

TITLE
RAPID PROTOTYPJNG METHOD USING INFRARED SINTERING
DESCRIPTION
Field of the Invention
The invention relates to a rapid prototyping method for constructing freeform three- dimensional objects by successive layer-by-layer deposition of powder material and sintering the powder material of each successive layer using infrared irradiation.
Background Art
A number of methods of rapid prototyping have been proposed, all involving the layer-by- layer build-up of three-dimensional articles. Various technologies have been proposed to produce such objects, including stereolithography (SLA), fused deposition method (FDM), selective laser sintering (SLS) and three- dimensional printing (3DP).
In the 3DP method successive layers of a powder material are applied across the surface of an object being built and droplets of an adhesive bonding agent are applied to selected areas of each powder layer using an inkjet printing device to create bonding of those selected areas of the powder layer to the previously applied layers beneath. Each selected area of each layer of bonded powder is akin to an image of that particular section though the object being created. In the SLS method, the selected areas of the layers of powdered material are sintered and thus bonded to previously applied layers by selectively scanning each successive layer with a laser beam. The main disadvantage of the SLS method is the slow speed, because the laser beam has to scan back and forth across the entire image area of the powder that is being bonded by sintering to the layers beneath.
The use of infrared radiation to sinter and bond selected areas of applied powder layers is also known, and is disclosed for example in US-A653l086. The process uses negative masking. A mask to shield the powder layer from the effects of the infrared radiation is printed using aluminium oxide printed onto a silica plate, using a computer. The silica plate is positioned over the powder layer that has been applied to the surface of the object being created, and the masking prevents the penetration of the infrared radiation through the printed l* e 1 I * * I I II * areas while permitting the sintering of the powder beneath the unmasked areas. The advantage of this process is that the infrared radiation can achieve the sintering of the powdered plastic material in a few seconds, but that is countered by a disadvantage that it can take much longer to form the negative mask and move it into position, resulting in a build time of up to 20 seconds per single layer. The slow time for mask creation is largely due to the time taken to cool the aluminium oxide on the silica masking plate and to dislodge the masking image and clean the silica plate before creating a new masking image. Another disadvantage is caused by reflection and refraction of the infrared radiation as it passes through the silica masking plate, which causes ultimate dimensional inaccuracy of the final object being built. That can be reduced by printing the masking image on the bottom of the masking plate, but the above inaccuracies still cannot completely be avoided.
Another method of rapid prototyping using infrared radiation to selectively sinter image areas of successive powder layers is disclosed in US-B-6589471. In this process an inhibitor, 1 5 which may be a heat reflective material or an anti-sintering agent, is printed selectively on the base powder layer and the unprinted, uninhibited, areas are sintered by direct exposure to infrared radiation. The main disadvantage of this method is that the unsintered powder of each layer, when it is removed from the object being built, is contaminated with the anti- sintering agent so that it cannot be recycled unless it has been cleaned and the anti-sintering agent removed. Moreover the edges of the final built object are generally ill-defined due to edge contamination between the sintered powder areas and the surrounding areas which have been printed with the anti-sintering agent. Moreover the speed can be slow when the area to be sintered and built up into the three-dimensioiial article is small in relation to the total area of the build platform, because the non-sintered area, which is the area printed, is then correspondingly large, which slows down the printing.
Rapid prototyping using microwave radiation to selectively sinter selected areas of successive powder layers has been disclosed for example in US-B-6243616. Each layer is applied as a uniform layer of powdered substrate material, and the selective exposure to microwave radiation is established by moving an arm carrying the microwave source over the powder surface in a scanning movement under computer control. Full directional control of the arm is required, making the process slow and expensive. It is, however, known from for example US-B-6183689 that metal powders including Fe, Ni, Co, Cu, Cr, Al, Mo and W can he sintered using microwave heating, and from WO-A-04/403 7469 that metal, ceramic * I.e I I,. * III * : : * * and metal-ceramic powder mixture can be sintered using microwave heating, although the latter process uses an indirect heating process utilising a high microwave-sensitive material like silicon carbide which is placed in direct contact with the areas to be sintered. The potential for rapid prototyping using microwave heating is therefore very great.
It is an object of the invention to provide a rapid prototyping process which removes the above disadvantages and builds on the above advantages.
THE INVENTION
The invention is as specified in claim 1. The method of the invention is rapid, reliable, and uses inexpensive apparatus. For example the infraredsensitive agent may be a liquid ink, pigmented or unpigmented, coloured or colourless, applied by a conventional ink jet print head such as a piezo-electric or bubble-jet or any other print head. Conventional printer technology can be used, with the print head reciprocally moving in the x direction and the workpiece being reciprocally moved in the y direction. Some z movement of the workpiece is also needed to allow for the increasing thickness of the object being built as successive layers are deposited and sintered. The use of masking plates is totally unnecessary.
The wavelength of the infrared irradiation ought to be carefully selected so that only the printed area aiid not the unprinted area is sintered. That will be a choice based on the transparency of the powder material to the wavelength used, using Fourier Transform Infrared spectroscopy (FTIR), and the absorption characteristics of the infrared-sensitive agent used. It had been found that the majority of suitable polymer powders have a higher infrared absorption sensitivity for the medium wavelength of infrared (between wavelengths of 2 and 6 microns). Suppose the polymer powder is one that has a significant absorption of medium wavelength of infrared but is substantially transparent to infrared in the low band of infrared (wavelengths of about 0.7 to 2 microns), and the infraredsensitive agent is an ink, pigmented for example with carbon black, having a high absorption sensitivity for short wavelength infrared (wavelengths of 0.7 to 2 microns). Then exposure of the entire layer including the unprinted area to short wavelength infrared radiation will result in the sintering effect on only the printed areas, with the unprinted areas being substantially unaffected. The unsintered powder can he removed at the relevant stage in the fabrication cycle either * *, : * * : : *. * manually or as part of an automated process using suction, for example a vacuum pump, and may be re-used since it is uncontaminated by the infrared sensitive agent.
The infrared-sensitive ink is preferably one that does bleed out to a significant extent from the edges of the printed areas, and careful attention is therefore needed to control the viscosity of the ink.
The infrared radiation is preferably under the control of a wavelength controller. This may be a burst fire controller, which chops unwanted wavelengths of infrared to establish a radiation frequency range within the desired range for which the powder material is substantially transparent but the infrared sensitive agent is not. A phase angle controller could conceivably be used but does not have the precision of wavelength control that a burst fire controller offers.
The infrared sintering need not be sufficient to create a built object with the final desired strength. If the infrared radiation creates an object with a green strength which is less than the final build strength but which nevertheless permits further processing and further handling, then further processing can be used to continue the sintering and create a proper compact strength of the final object.
That further processing can be additional sintering using microwave irradiation. That can be layer-by-layer or after the complete threedimensional shape or a significant part of that three-dimensional shape has been built up, in either case after removal of the unsintered powder after the infrared heating step or steps. The infrared-sensitive agent may also be microwave-sensitive.
Alternatively the further processing step of additional sintering can he established after the complete three-dimensional shape or a significant part of that three-dimensional shape has been built up and after removal of the unsintered powder, by induction heating or by oven sintering.
The accuracy, definition and strength of the final prototype is enhanced by creating the fine powder layer (a) as thin as possible. Preferably each layer is compressed before sintering, which reduces it overall thickness.
Preferably the dimensional accuracy of the final product and the edge smoothness of each applied layer can be significantly increased without a severe time penalty by using a laser beam, preferably an infrared laser beam, to traverse the edge or edges only of the image area of each layer immediately prior to, during or after each step (e), to clean up those edges and create a good clean hard edge to the object being built. The use of a laser in this way is significantly faster than conventional SLS technology, since only the edges need to be traversed by the laser beam and there is no requirement for the relatively slow laser scanning of the entire image area as there is with known SLS processes.
After each step (c) of exposing the object layer to infrared radiation, the object being built up is preferably monitored to establish that sufficient natural or forced cooling has taken place before the next process step is commenced. For example images of the irradiated surface may he analysed using an infrared camera or an electron microscope, or a feedback may be monitored from a thermocouple connected to a build platform on which the object is being built. The infrared irradiation may be from a heater such as one or more quartz heater tubes exposing the entire layer of powder to the infrared radiation to the same extent; or it may be from an array of miniature infrared heaters each using a reflector focussing the radiation onto a small surface area, with the heaters of the array being selectively switched on so that the exposure of areas which have not been printed with the infrared-sensitive agent is reduced.
That reduction serves to save power, and also reduces the prospect of unnecessary heating of the build platform on which the object is supported, as the infrared irradiation passes through the layers of infrared-transparent powder and heats the build platform beneath. Such a selective exposure is a power reduction feature only, however, and the sintering of the entire area printed with the infrared-sensitive agent is still defined by the printing of that agent and not by the selective switching OFF of various individual heaters.
It has also been found to be advantageous when using some build powders to preheat the powder before laying the powder layer of step (a). The method of the invention lends itself to the use of a wide variety of powders including thermoplastic polymer powders, metal powders, ceramics or mixtures thereof. Variation of the constitution of the powder and the sintering conditions permits the density and strength of the fabricated object to be controlled as desired.

Claims (22)

1. A rapid prototyping method for constructing freeform three-dimensional objects by successive layer-by-layer deposition of powder material, comprising: (a) providing a layer of powder material that is intrinsically transparent to infrared radiation of a particular wavelength of range of wavelengths; (h) selectively depositing an infrared-sensitive agent over selected areas of the surface of the powder layer; (c) exposing the layer of the powder material to infrared radiation of a wavelength absorbed by the infrared-sensitive agent but not significantly absorbed by the powder material; (d) controlling the duration of the infrared exposure to establish sintering or the commencement of sintering of the powder material over which the infrared-sensitive agent has been deposited; and (e) repeating steps (a) to (d) until a three-dimensional object has been formed, with successive layers being fused together by sintering.
2. A method according to claim 1, wherein after each step (d) the unsintered powder is removed and the entire layer is exposed to a specific wavelength of microwave radiation to which the powder material is sensitive, to complete the sintering of the powder material.
3. A method according to claim 2, wherein the infrared-sensitive agent is also microwave-sensitive.
4. A method according to claim 1, wherein after repeating steps (a) to (d) until the three- dimensional shape or a significant part of the three-dimensional shape of the object being built is complete, the unsintered powder is removed and the entire object is exposed to a specific wavelength of microwave radiation to which the powder material is sensitive, to complete the sintering of the powder material.
5. A method according to claim 1, wherein after repeating steps (a) to (d) until the three- dimensional shape or a significant part of the three-dimensional shape of the object being built is complete, the unsintered powder is removed and the entire object is exposed to induction heating or oven sintering, to complete the sintering of the powder material.
6. A method according to any preceding claim, wherein after each step (c) of exposure to infrared radiation, the object being built up is monitored to establish that sufficient cooling has taken place before the next process step is commenced.
7. A method according to claim 5, wherein the monitoring of the object being built after each step (c) of exposure to infrared irradiation to establish that sufficient cooling has taken place comprises analysing images of the irradiated surface using an infrared camera or an electron microscope.
8. A method according to claim 6, wherein the monitoring of the object being built after each step of exposure to irradiation comprises monitoring a feedback from a thermocouple connected to a build platform on which the object is being built.
9. A method according to any preceding claim, wherein immediately prior to, during or after each step (e) the edge or edges only of the sintered area or the area to be sintered are scanned with a laser beam.
10. A method according to any preceding claim, wherein in step (c) the source of infrared radiation comprises infrared heaters coated with an infrared filter material which controls the wavelength of the infrared radiation irradiated onto the powder layer.
11. A method according to any preceding claim, wherein in step (c) the entire surface of the powder layer is exposed to the infrared radiation.
12. A method according to claim 11, wherein the source of infrared radiation is at least one quartz heater tube.
13. A method according to any of claims 1 to 10, wherein in step (c) only selected areas of the surface of the powder layer are exposed to the infrared radiation.
14. A method according to claim 13, wherein the source of infrared radiation is an array of miniature infrared heaters each having a reflector focussing the radiation onto a small area of the powder surface, to reduce the exposure to the radiation of the areas of powder which have not been coated with the infrared-sensitive agent.
15. A method according to any preceding claim, wherein the infraredsensitive agent is liquid, and is selectively deposited in step (b) using an inkjet printer head.
16. A method according to claim 15, wherein the inkjet printer head is a piezo-electrjc printer head.
17. A method according to claim 15 or claim 16, wherein the printer head is reciprocally movable in one direction (the x direction) and the object being built is on a build platform that is reciprocally movable in an orthogonal direction (the y direction) and is also movable in a direction away from the print head (the z direction) to allow for increasing thickness of the object being built as successive layers are deposited and sintered.
18. A method according to any of claims 15 to 17, wherein the infraredsensitive agent is a highly infrared sensitive ink that has a relatively high absorption of infrared radiation of a particular wavelength.
19. A method according to claim 1 8, wherein the infrared-sensitive ink is enriched with one or more suitable pigments.
20. A method according to claim 19, wherein the infrared-sensitive ink is enriched with carbon black.
21. A method according to claim 18, wherein the infrared-sensitive ink is pigment-free and colourless.
22. A method according to any preceding claim, wherein the powder is preheated before being laid in each step (a).
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