Related U.S. Application Data

U.S. Provisional Application No 61/961,936, filed on October 28, 2013 and U.S. Provisional Application No. 61/963,732, filed on December 13, 2013.

Field of the Invention

[0001] Present inventions relate to methods and apparatus for forming thin fused layers by fusing powder materials comprising particles. Present inventions have applications in the fabrication of three-dimensional (3D) objects by forming a plurality of thin fused layers on top of each other wherein at least a portion of the particles within each fused layer may be fused together and wherein a section of each fused layer formed may also be fused to a section of a previously formed fused layer.

Background of the Invention

[0002] 3D printing is a general term often used to define the general class of additive manufacturing approaches that sometimes may also be called solid free-form manufacturing techniques, among other names. The terms "3D printing" and "additive manufacturing" are used interchangeably herein and they refer to techniques that form a solid 3D object from a digital model using 3D printers or materials printers. 3D printing technologies are used for prototyping and distributed manufacturing in a variety of fields such as automotive, health, military, food, art and fashion.

[0003] In additive manufacturing, virtual blueprints of designs of objects are provided to the materials printers and cross sections of these designs are printed successively in layers using materials that may be in the form of liquid, powder, paper or sheet metal. As the printed cross sectional layers join and merge, a final 3D shape or object emerges. Depending on the material used and the nature of the 3D shape, the printing process may take several hours or even days.

[0004] Additive manufacturing techniques differ from each other in the ways the printed cross sectional layers are formed. Some methods deposit polymeric materials in molten phase to form the cross sectional layers on top of each other. Some others, expose a liquid photopolymer material to UV radiation in the shape of a cross sectional layer to be formed, and thus harden the exposed portion of the liquid photopolymer material in the shape of the desired cross sectional layer. As for metal parts fabrication, there are techniques that melt and fuse metal powders using lasers as described in US 5,017,753, or electron beams as disclosed in US 7,454,262, to form the desired cross sectional layers in a successive manner on top of each other. There are also methods that spray hot molten materials through narrow and directional nozzles to form the desired cross sectional layers. In US patent 5,389,408 and patent application publication US 2012/0329659, a powder sintering method based on induction heating has been disclosed wherein an alternating magnetic field is generated within an applicator tip and directed from the applicator tip onto the surface of a powder layer. The alternating magnetic field inductively heats and melts the particles within the powder layer. There is a need to develop low cost and fast approaches to fabricate 3D shapes for various applications.

Brief Description of the Drawin2S

[0005] FIG. 1 is an exemplary 3D object comprising three fused layers formed on a platform.

[0006] FIG. 2 shows an apparatus to fabricate a 3D object.

[0007] FIG. 3 shows an uncured film between a platform and an electrode assembly of the apparatus of FIG.2. [0008] FIG. 3A depicts formation of a first fused layer.

[0009] FIG. 3B depicts formation of a second fused layer over the first fused layer.

[0010] FIG. 3C depicts formation of a third fused layer over the second fused layer.

[0011] FIG. 4 shows an exemplary electrode assembly configuration.

[0012] FIG. 4A shows a powder coating sandwiched between a platform and an electrode assembly plate comprising a large conductive pad and a small conductive pad.

[0013] FIG. 5A shows a cross sectional view of a section of an uncured coating disposed between a section of a platform and a section of an electrode assembly with two conductive pads.

[0014] FIG. 5B shows a fused layer segment formed by passing an electric current between the two conductive pads shown in FIG. 5A.

[0015] Fig. 6A shows a powder film and a round electrode assembly pressed against it.

[0016] Fig. 6B shows a portion of the powder film solidified when the round electrode assembly is moved across the powder film.

[0017] Fig. 7A shows a powder layer and a fused section of the powder layer formed under a small electrode assembly.

[0018] Fig. 7B shows another section of the powder layer of FIG. 7A being fused by moving the small electrode assembly across the surface of the powder layer and applying an electric current.

[0019] FIG. 8 shows exemplary conductive pads of an electrode assembly.

Detailed Description of the Invention

[0020] Present inventions provide methods and apparatus for fabricating a 3D object in a layer-by-layer fashion by first laying down and then fusing each of a plurality of uncured (i.e., unfused) films comprising a source material. The source material can comprise particles. Fusing is achieved by passing an electric current between an electrode assembly and a predetermined portion of each of the plurality of thin uncured films comprising the source material. The electric current fuses the particles within the predetermined portion of each of the plurality of thin uncured films thus forming a fused layer comprising the predetermined portion, and at the same time may fuse or attach at least a section of each fused layer to at least a segment of a base, the base either comprising a platform on which the 3D object will be fabricated, or comprising a previously formed fused layer. Application of an electrical current to the predetermined portion of each of the plurality of thin uncured films may be achieved through various means including but not limited to: i) rendering the predetermined portion of the uncured film more electrically conductive than the rest of the uncured film so that when a electrical current is applied to the uncured film by the electrode assembly, it preferentially flows through the predetermined portion, and ii) applying the electrical current to the predetermined portion of each uncured film selectively through use of a computer controlled "area selective fusing method" (ASFM). These methods and apparatus may be used for any application that requires formation of fused layers with thicknesses ranging from a few microns to a few millimeters, preferably from about 50 microns to about 5 mm, more preferably from about 100 microns to about 2 mm. The inventions will now be described as they may be applied to the fabrication of a 3D object by selectively fusing predetermined portions of uncured films comprising a source material. The source material may be a powder comprising particles. The powder may further comprise chemicals or materials to assist or enhance fusing of the particles. After successive uncured film fusing steps, the 3D object thus obtained may be additionally treated to increase its strength and/or density.

[0021] Figure 1 shows an exemplary 3D object 100 formed on a surface 102A of a platform 104A using the processes of the present invention. After the 3D object is formed it may be removed from the platform 104 A and may be further treated by additional processes such as cleaning, heating, surface treatment, etc. As will be explained below, the 3D object 100 may be formed by successively forming a plurality of fused layers on top of one another.

[0022] The 3D object 100 may, for example, include a first layer 100A, a second layer 100B formed over the first layer 100A, and a third layer lOOC formed over the second layer 100B. The first layer 100A, the second layer 100B and the third layer lOOC may all be fused together to form the 3D object 100.

[0023] The 3D object 100 may be formed by individually forming the first layer

100A, the second layer 100B and the third layer lOOC separately using at least one source material. It is possible that any one or two of the first layer 100 A, the second layer 100B and the third layer lOOC may be formed using a first source material, and the remaining layer or layers may be formed using a second or a third source material. Now, various embodiments to form the first layer 100A will be discussed in detail. It should be noted that the second layer 100B and the third layer lOOC may be formed using any one of these various embodiments.

[0024] Figure 2 shows an exemplary apparatus 200 that may be used to carry out the processes of the present invention. The apparatus 200 may comprise a process chamber 201 with a platform 104 over which a 3D object such as the one shown in Figure 1 would be formed. The platform 104 may be movable up and down between a position Zl and Z2 so that consecutive layers of the 3D object may be formed on top of each other as the platform 104 is moved down. It is understood that other components of apparatus 200 may additionally or alternatively be movable in such a way as to make platform 104 effectively (i.e., relatively) movable up and down. For example, process chamber 201 may be movable up and down, which can result in platform 104 being moveable up and down relative to the process chamber and/or other components of apparatus 200 (e.g., electrode assembly 113). There may be a powder material dispensing attachment 221 which may be movable at least laterally but optionally also vertically. The powder material dispensing attachment 221 may dispense a dry powder, a slurry, or an ink/dispersion of particles and it may be in the form of a roller, a doctor blade, a spray head, etc. There may also be a nozzle (not shown) to spray a mist of a solvent over the particles to clean and compact them.

[0025] The apparatus 200 is equipped with an electrode assembly 113 which may be connected to at least one power supply 202. Although the electrode assembly 113 is illustrated as being above the platform 104, in some examples, the platform may be above the electrode assembly (i.e., the electrode assembly and the platform may be switched). Further, in some examples, the platform may additionally or alternatively comprise an electrode assembly (i.e., one or more of the configurations/functionalities of the electrode assembly described in this disclosure may be part of the platform), and the electrode assembly may additionally or alternatively comprise a platform (i.e., one or more of the

configurations/functionalities of the platform described in this disclosure may be part of the electrode assembly). The electrode assembly 113 has a capability to apply electrical power to various layers that it may be brought in close proximity to or in contact with. The power supply 202 or other power supplies (not shown) may also be connected to the face 102 of the platform 104. The power supplies may be DC or AC power supplies, or they may provide pulsed electrical power comprising pulses of various magnitudes and durations. It is also possible to use voltage or current shapes comprising at least two of DC, AC and pulsed components. Pulse durations may be in the range of 0.1-1000 msec, preferably in the range of 1-100 msec. DC or AC currents and/or voltages, when applied, may be applied for durations similar to the pulse durations above. During processing, the local current densities within the layers to be fused may be in the range of 1-10000 A/cm ² or higher depending upon the nature of the powder materials to be fused. Although the fusing process may be carried out with no applied pressure, the electrode assembly 113 may optionally comprise a mechanism to push its process surface or bottom surface 112 or each of the electrodes against the various layers to be formed at predetermined pressure values which may range from a few psi to a few thousand psi. There may be one or more fluid inlets 203 to carry a fluid such as an inert gas, a reducing gas, or a reactive gas into a confined gap (not shown) formed when the electrode assembly 113 and the platform 104 are brought towards each other. There may be an inline heater (not shown) to heat the fluid before it is delivered to the confined gap to provide heat to the fusing process. Although the fluid inlet 203 in Figure 2 is shown to be placed in the electrode assembly 113, it is possible to have such inlets in the platform 104 or on the walls 204 of the process chamber 201 as long as they are strategically placed to bring the fluid into the confined gap (not shown) formed when the electrode assembly 113 and the platform 104 are brought towards each other. The apparatus 200 may additionally comprise one or more fluid outlets 205 to remove any byproducts of the process and/or the fluid brought in by one or more fluid inlets 203. Although the fluid outlet 205 in Figure 2 is shown to be placed in the electrode assembly 113, it is possible to have such outlets in the platform 104 or on the walls 204 of the process chamber 201. Alternately, vacuum may be pulled through any one of the inlets 203 or outlets 205 to create a vacuum environment within the confined gap. The apparatus 200 may further comprise heating units that may heat at least one of the bottom surface 112 of the electrode assembly 113, the walls 204 and the face 102 of the platform 104.

[0026] In a first embodiment, to form the first layer 100A, a first source material comprising a powder may be used. The powder may comprise conductive particles and it may be deposited or dispensed by the powder material dispensing attachment 221 over the face 102 of the platform 104 in the form of an uncured film 105 as shown in Figure 3. The electrode assembly 113 is then lowered towards the exposed or top surface of the uncured film 105 forming a gap 300. As discussed above, the platform 104 may additionally or alternatively be moved up towards the electrode assembly 113 to form the gap 300. As the electrode assembly 113 is further moved down, the gap 300 gets smaller and eventually the process surface or bottom surface 112 of the electrode assembly 113 either comes to close proximity of or touches the exposed or top surface of the uncured film 105. During this period it is possible to bring a process fluid into the gap 300 through the fluid inlet 203. The process fluid may be a gas, such as an inert gas or a reducing gas such as hydrogen, and it can form a mini environment within which the particle fusing would be carried out. The process fluid may also be heated to provide heat to the mini environment. It is also possible to form a vacuum environment within the gap 300. Use of such a mini environment has many benefits including, but not limited to avoiding excessive oxidation of the powder during processing, and reduction of any oxide that may be present within the powder itself, either as a surface film on the particles or as an ingredient that may be intentionally added to the source material formulation so that upon chemical reduction it may serve as an effective binding agent. For example, if the powder comprises copper and if there is also copper oxide between the copper containing particles of the powder, during the fusing process under a reducing environment, such as a hydrogen-containing gas environment, the copper oxide may be reduced to copper phase and help fuse the copper particles of the powder together. It is also possible to provide chemical ingredients through the inlet 203 that may assist any reaction that may take place during the fusing step. Such ingredients may or may not stay in the fused layer after the process. In an embodiment reactive chemicals may be provided through the inlet 203 to change the composition of the powder during the fusing process. For example by providing a nitrogen containing agent through the inlet, a nitride phase may be formed in a fused layer. An example of this is fusing of a powder comprising titanium in the presence of a nitriding gas and forming a fused layer comprising titanium nitride phase(s). Similarly, fused layers comprising carbide phases may be formed by providing a carbon containing atmosphere during fusing. Such processes may increase the strength and hardness of the fused layers and thus the 3D objects that may be constructed from them. It should be noted that the process fluid may be flown into the gap before the fusing process and/or it may be delivered throughout the fusing process in which case the fluid outlet 205 may exhaust the excess and/or used process fluid as well as any byproducts of heating such as water vapor. Because of the fact that the uncured film 105 is sandwiched between the electrode assembly 113 and the platform 104 within a very small volume, any heat generated within the uncured film 105 by the electrical current and heat provided by a process fluid may be contained in this mini environment, especially if the materials of the electrode assembly 113 and the platform 104 are selected to include poor thermal conductors.

[0027] Figure 4 shows a first embodiment of an exemplary conductive array that may be provided on the bottom surface 112 of the electrode assembly 113. The conductive array can comprise a plurality of conductive pads 400 arranged such that they are substantially electrically isolated from each other. The exemplary conductive array of Figure 4 has sixty four conductive pads 400 arranged along columns 1,2,3,4,5,6,7,8 and rows A,B,C,D,E,F,G, and H. Each of the conductive pads 400 may have electrical connectors and switches (not shown) that may bring electrical power from one or multiple power supplies (not shown) to one or multiple of the conductive pads 400. The process of selecting which pads would be powered may be controlled by a computer that has the information about the shape of the fused layer to be formed. If the face 102 of the platform 104 comprises a conductive material and a selected conductive pad is activated by applying a power between the selected conductive pad and the face 102 of the platform 104, an electric current can flow through a predetermined portion of an uncured layer between the selected conductive pad and the face 102 of the platform 104, causing local activation such as heating and fusing of the particles within the predetermined portion. By activating a series of conductive pads consecutively or at the same time, a predetermined shape of the uncured layer can be fused and a fused layer with the predetermined shape can be obtained. For example, by activating the conductive pads B3, B4, B5, B6, C6, D6, D5, D4, D3, E3, F3, F4, F5, and F6 (conductive pads that are cross hatched in Figure 4) a fused layer with a "S" shape could be obtained. It should be noted that the conductive pads 400 may be of various forms and shapes such as round, rectangular, triangular, square, line, concentric circle, etc. Their size may range from a few microns to several millimeters, preferably from 50 microns to 2 millimeters, more preferably from 100 microns to 1 millimeter. In some examples, the number and size of the conductive pads 400 can be dynamically configurable during processing, and in some examples, the conductive pads 400 may have varying sizes and arrangements that may not be regular. Use of small size conductive pads can be beneficial in many aspects. First of all, an array of small conductive pads allows area selective fusing. As the individual areas of the conductive pads decrease the resolution of the apparatus 200 increases, i.e. a given shape may be formed at better dimensional resolution. Another benefit of using a small area conductive pad may be understood by referring to Figure 4A. Figure 4A shows a cross sectional view of a section of a powder coating 4000 sandwiched between a sheet platform 401 and an electrode assembly plate 402 comprising a large conductive pad 403 with a first connector 450, and a small conductive pad 404 with a second connector 451. The sheet platform 401 may comprise a conductive layer 401A and a third connector 452. In this example, the large conductive pad 403 may have lateral dimensions that may be much larger than the thickness of the powder coating 4000 and the small conductive pad 404 may have lateral dimensions that may be in the order of the thickness of the powder coating 4000. For example, if the thickness of the powder coating 4000 is 0.5mm, the lateral dimension(s) of the large conductive pad may be larger than 5mm and the lateral dimension(s) of the small conductive pad 404 may be equal to or smaller than 1mm, which is two times the thickness of the powder coating 4000. When power is applied between the large conductive pad 403 and the conductive layer 401 A, through the first connector 450 and the third connector 452, an electrical current can pass through the powder coating 4000. If the resistivity and packing of the particles within the powder coating 4000 under the large conductive pad 403 are not uniform, the electrical current may preferentially pass through locations comprising relatively lower resistance paths causing localized fusing rather than fusing of the whole section of the powder coating 4000 under the large conductive pad 403. Figure 4A shows a first localized fused segment 405 A and a second localized fused segment 405B that may be formed due to low resistance paths that may be present within the powder coating 4000 at those locations. This problem can be avoided by employing small area conductive pads such as the small conductive pad 404 of Figure 4A. When power is applied between the small conductive pad 404 and the conductive layer 401 A, through the second connector 451 and the third connector 452, an electrical current can pass through the powder coating 4000 under the small conductive pad 404 forming a uniformly fused segment 405C. It is preferable that a lateral dimension of a conductive pad applying power to a powder layer or coating is less than about five times the thickness of the powder coating, more preferably less than two times the thickness of the powder coating.

[0028] Referring back to Figure 3 and Figure 4, the distance between the conductive pads 400 may be in the range of 50 microns to 5 millimeters, preferably in the range of 100 microns to 2 millimeters. The conductive pads 400 may comprise conductive materials such as Cu, Co, Ni, refractory metals such as Mo, Ta, Ti, Cr, W, Zr, Hf and their alloys with at least one of C and N, or other metal alloys such as stainless steel, graphite, conductive compounds, etc. The body of the electrode assembly 113 holding the plurality of the conductive pads 400 may comprise a semiconducting material or an insulating material such as a ceramic or high temperature polymeric material. It should be noted that if a conductive surface of a conductive pad touches an uncured layer, a DC, AC or pulsed current may be flown between the conductive surface and a portion of the uncured layer touching the conductive surface. In this case it is preferable that the conductive surface comprises a low resistivity and high melting point material. Such materials have electrical resistivity values smaller than 0.0001 ohm-cm and melting points above about 2800 C and they include TiN, TaN, ZrN, NbN, HfN, HfC, ZrC, TiC, TaC, WC, NbC, HfC, Carbo-Nitrides or borides of Ti, Ta, Hf, Nb, Zr and W. These materials may be coated on the surface of metallic electrodes using methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) and provide a highly inert, hard, durable and lubricating layer so that the electrode surface does not react with the powder and does not erode during the process. If a conductive surface of a conductive pad is in proximity of an uncured layer, or if there is an insulating film, such as a high permittivity dielectic film, between the conductive surface and the uncured layer, then only an AC or pulsed current may be flown between the conductive surface and a portion of the uncured layer. The frequency of the pulsed or AC current may be in the order of several hundred kHz or several MHz. The high permittivity dielectric films include, but are not limited to films comprising barium titanate with dielectric constants above 3000.

[0029] It is possible to pass an electric current through an uncured layer or coating in a direction substantially parallel to its top surface to achieve fusing. Figure 5A shows a cross sectional view of a section of an uncured coating 500 sandwiched between an exemplary platform 501 and an exemplary electrode assembly 502 comprising a conductive pad CI and another conductive pad C2. Power is applied by a power source 503, between the conductive pad CI and the conductive pad C2. An electric current passes through a segment of the uncured coating 500 between the conductive pad CI and the conductive pad C2 as shown by arrow 504. The electric current facilitates the fusing of at least a portion of the particles within the segment of the uncured coating 500, in some examples yielding a fused segment 505 as shown in Figure 5B.

[0030] Figures 3A, 3B and 3C show a sequence through which a three dimensional shape such as the exemplary 3D object 100 of Figure 1 may be formed. The optional fluid inlet and outlet are not drawn in these figures for simplification. In Figure 3A, the electrode assembly 113 is brought down onto the uncured film 105 of Figure 3 and a series of conductive pads labeled as 400BG2, 400BG3, 400BG4, 400BG5, 400BG6 and 400BG7 are powered or activated to form a first fused layer 310 which may be the first layer 100 A of the 3D object 100 of Figure 1. It should be noted that each one of the above labeled conductive pads can represent more than one of the conductive pads depicted in Figure 4. For example, 400BG2 can represent the conductive pads at locations B2 through G2, i.e. pads B2, C2, D2, E2, F2 and G2. Similarly, 400BG3, 400BG4, 400BG5, 400BG6 and 400BG7 can represent the conductive pads at locations B3 through G3, B4 through G4, B5 through G5, B6 through G6 and B7 through G7, respectively. During the formation of the first fused layer 310, the first fused layer 310 may also be fused or attached to the face 102 of the platform 104 by assuring that an electrical current passes laterally in close proximity to or through an interface 31 OA between the first fused layer 310 and the platform 104.

[0031] After the formation of the first fused layer 310 a second source material comprising a powder may be deposited or dispensed over the first fused layer 310 in the form of a second uncured film 106 by the powder material dispensing attachment 221 shown in Figure 2. The electrode assembly 113 may then be brought down onto the second uncured film 106 and another series of conductive pads denoted as 400CF3, 400CF4, 400CF5, and 400CF6 may be powered or activated to form a second fused layer 320 which may be the second layer 100B of the 3D object 100 of Figure 1. It should be noted that each one of the above labeled conductive pads can represent more than one of the conductive pads depicted in Figure 4. For example, 400CF3 can represent the conductive pads at locations C3 through F3, i.e. pads C3, D3, E3 and F3. Similarly, 400CF4, 400CF5, and 400CF6 can represent the conductive pads at locations C4 through F4, C5 through F5, and C6 through F6, respectively. During the formation of the second fused layer 320, the second fused layer 320 may also be fused or attached to the first fused layer 310 by assuring that an electrical current passes through an interface 320A between a segment of the first fused layer 310 and the second fused layer 320.

[0032] After the formation of the second fused layer 320, a third source material comprising a powder may be deposited or dispensed over the second fused layer 320 in the form of a third uncured film 107 by the powder material dispensing attachment 221 shown in Figure 2. The electrode assembly 113 may then be brought down onto the third uncured film 107 and a third series of conductive pads designated as 400DE4 and 400DE5 may be powered or activated to form a third fused layer 330 which may be the third layer lOOC of the 3D object 100 of Figure 1. It should be noted that each one of the above designated conductive pads can represent more than one of the conductive pads depicted in Figure 4. 400DE4 can represent the conductive pads at locations D4 and E4, whereas 400DE5 can represent the conductive pads at locations D5 and E5. During the formation of the third fused layer 330, the second fused layer 320 may also be fused or attached to the third fused layer 330 by assuring that an electrical current passes through an interface 330A between a segment of the second fused layer 320 and the third fused layer 330. After the formation of the third fused layer, the loose powder may be removed from around the fused shape and the fused shape, which may be the 3D object of Figure 1, may optionally be further treated. Such post fusing treatments may include processes such as cleaning, annealing and further densification of the fused shape. In some examples, the loose powder around portions of the fused shape may be removed after processing of each layer, or at other times before completion of the entire shape. In such cases, the removed powder may need to be replaced with additional powder in subsequent fusing steps. In some examples, such intra-process removal and replenishment of powder can be utilized to control one or more aspects of a mini-environment that one or more portions of the fused shape can be subjected to in the processes of this disclosure.

[0033] An electrode assembly may also be used to carry out a powder particle fusing process in a stepwise or continuous manner. Figure 6A shows a cross sectional view of a section of a powder film 600 formed over a base platform 601. The powder film 600 may be formed by depositing a dry powder, a wet powder, a paste or ink comprising the powder, etc. using various different techniques such as doctor blading, screen printing, nozzle dispensing, among other methods. An exemplary electrode assembly 602, which may comprise a conductive surface 602A and may be shaped like a sphere, a wheel or cylinder, may be rolled over the section of the powder film 600 from position "AA" of Figure 6A to position "BB" of Figure 6B while the conductive surface 602 A is pressed against the powder film 600 and an electrical power is applied between the conductive surface 602 A and the base platform 601. Electrical current passing between the conductive surface 602A and the powder film 600 and through the powder film 600, can fuse a portion 603 between the position "AA" and "BB" as shown in Figure 6B. Alternately, as shown in Figure 7 A and Figure 7B, a small electrode assembly 700 may be moved over a powder layer 701 in a stepwise manner to fuse a small portion of the powder layer at a time. In Figure 7A a first small portion 702A of the powder layer 701 may be fused when the small electrode assembly 700 is at a first position. When the small electrode assembly 700 is moved to a second position and the electrical power is applied, a second small portion 702B of the powder layer 701 may be fused or solidified. This way, any desired shape may be fused within the powder layer 701. As may be appreciated from these examples, electrodes shaped in various forms such as spherical, cylindrical, brush, wire, among other shapes may be moved on a powder layer and can fuse sections of the powder layer proximal to them as they move. This way, cross sections of 3D objects may be formed. Such cross sections, when bonded together, form the 3D object.

[0034] Conductive pads in the exemplary electrode assemblies of Figure 3 and Figure

5A are shown to have flat surfaces, which are coplanar with the bottom surface of the electrode assembly. It is, however, possible that the conductive pads have different shape surfaces that protrude from the bottom surface of the electrode assembly. Figure 8 shows an exemplary electrode assembly 800 with three exemplary conductive pads 801 A, 80 IB and 801C, wherein the exposed surfaces of the exemplary conductive pads have different shapes and protrude from the bottom surface 802 of the electrode assembly 800 by a distance which may range from microns to millimeters. When such an electrode assembly is pushed against a powder film, sections of the powder film right underneath the protruding conductive pads can get compacted more and the electrical conductivity of such compacted regions can become higher compared to the other sections, enhancing fusing in those regions. This can be highly desirable.

[0035] Referring back to Figure 3A, 3B and 3C, although a simplified example is given above wherein each fused layer is formed through a single powder dispensing step and a single fusing step, in practice where the thicknesses of the fused layers may be in the order of centimeters or larger, formation of each of the first fused layer 310, the second fused layer 320 and the third fused layer 330 may comprise multiple steps of dispensing a source material forming an uncured film, and multiple steps of fusing a predetermined portion of the dispensed uncured film using an electrode assembly.

[0036] Although the foregoing description has shown, illustrated and described various embodiments of the present invention, it will be apparent that various substitutions, modifications and changes to the embodiments described may be made by those skilled art without departing from the spirit and scope of the present invention.