Technical Field

The present invention is in the field of 3D printers for the manufacture of objects.

Background Art

Although three-dimensional (3D) printing does currently exist, much of this technology is expensive to use, and the range of materials that are useable in a particular printer are usually quite limited. This creates an encumbrance, especially for those wishing to produce metal parts through 3D printing.

Summary

In a first separate aspect, the present invention may take the form of a method for forming an object having a three-dimensional target shape, that makes use of a build powder, a support powder and a binder. The build powder is more strongly bound by the binder than is the support powder. The build powder and the support powder are dispensed in a sequence of layers of build powder patterned with support powder that collectively form the three-dimensional shape in build powder, and the binder is applied to layers of build and support powder and permitted to cure, thereby forming the object of build powder and binder. Finally, the support powder is removed from the formed object.

In a second separate aspect, the present invention may take the form of an apparatus for making three-dimensional physical objects, that includes a frame and a pan. A build powder pourer is at least partially filled with build powder and a support powder pourer is at least partially filled with support powder, each of the pourers having a dispensing opening and a dispensing plug, controllably covering the dispensing opening. A pourer-movement and dispensing plug-actuating assembly is supported by the frame over the pan, and includes a movement element that is selectively attachable to the build powder pourer and alternately to the support powder pourer and is also capable to controllably move an attached pourer in three orthogonal dimensions and to control the dispensing plug. A computer assembly, including an input for receiving a target three-dimensional shape, controls the pourer-movement and dispensing plug-actuating assembly to move the pourers and selectively open the plugs, thereby causing powder to be poured into the pan, and to thereby create in the pan a sequence of layers of build powder patterned with support powder that collectively forms the target shape in build powder.

Brief Description of the Drawings

FIGS. 1 .1 , 1 .2 and 1 .3 are perspective views of a 3D printer according to one embodiment of the present invention, as viewed from three different angles.

FIGS. 2.1 , 2.2 and 2.3 are detail views of a 3D printer fork, which is a component of the 3D printer of FIG. 1 .1 .

FIGS. 3.1 , 3.2, and 3.3 are detail views of a 3D printer pourer, which is a component of the printer of FIG. 1 .1 , as viewed from three different angles.

FIGS. 3.4 and 3.5 are cross-sectional detail views of the 3D printer pourer of FIG.

3.1 .

FIGS. 4.1 , 4.2 and 4.3 are detail views of the 3D printer fork assembly of FIG. 2.1 holding the pourer of FIG. 3.1 .

FIG. 5.1 is a cross-sectional view of the 3D printer pourer of FIG. 3.1 , showing the plug rod in a raised position.

FIG. 5.2 is a cross-sectional view of a 3D printer pourer of FIG. 3.1 , showing the plug rod in a raised position.

FIGS. 6.1 and 6.2 are detail views of a 3D printer refill assembly, that forms a part of the 3D printer of FIG. 1 .1 , as viewed from two different angles.

FIG. 7.1 is a cross-sectional detail view of the 3D printer refill assembly of FIG.

6.1 , without a pourer present.

FIG. 7.2 is a cross-sectional detail view of the 3D printer refill assembly of FIG. 6.1 , with a pourer present.

FIG. 8A-8D show the pan in the process of being filled and covered, prior to being placed into a kiln. FIG. 9A is a front-top-side isometric view of an alternative embodiment of a 3D printer.

FIG. 9B is a front-bottom-side isometric view of the 3D printer of FIG. 9A.

FIG. 10A is a front-top-side isometric view of the printer of FIG. 9A, with frame elements removed to provide a clearer view of the inner workings.

FIG. 10B is front-top-side isometric view of the printer portions of FIG. 10A, at a less steep angle of view.

FIG. 1 1 A is a front-top-side isometric view of a fork assembly, which forms a part of the printer of FIG. 9A.

FIG. 1 1 B rear-top-side isometric view of the fork assembly of FIG. 1 1 A.

FIG. 1 1 C is a side view of the fork assembly of FIG. 1 1 A.

FIG. 12A is a side view of the fork assembly of FIG. 1 1 A and a pourer that forms a part of the printer of FIG. 9A, joined together.

FIG. 12B is a rear-top-side isometric view of the combination of parts shown in FIG. 12A.

FIG. 13A is a top angle isometric view of a pourer, that forms a part of the printer of 9A.

FIG. 13B, is a section view of the pourer of FIG. 13A.

FIG. 13C, is a bottom angle isometric view of the pourer of FIG. 13A.

FIG. 14A is a top angle isometric view of a alternative embodiment of a pourer, that forms a part of the printer of 9A.

FIG. 14B, is a section view of the pourer of FIG. 14A.

FIG. 14C, is a bottom angle isometric view of the pourer of FIG. 14A.

FIG. 15A is an isometric view of a docking station for a pourer, that forms part of the printer of FIG. 9A.

FIG. 15B is a sectional view of the docking station of FIG. 15A.

FIG. 16A is an isometric sectional view of a docking station with a pourer attached, that collectively form part of the printer of FIG. 9A.

FIG. 16B is a side sectional view of the docking station and pourer of FIG. 16A.

FIG. 17 is a block diagram of the printer of FIG. 9A. Best Modes of Carrying Out the Invention

Definition: the term, "metal" is used in this application, encompasses metal alloys.

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.

Note: where there are a set of like elements, labelled N.1 -N.4 (where N is an integer), an arbitrary one of these will be labelled, for example N, where it does not matter which one of N.1 -N.4 is being referred to. For example, if an arbitrary one of pourers 10.1 -10.4 is being referred to, it will be referenced by "10".

FIGS. 1 .1 , 1 .2 and 1 .3 show a 3D printer from various angles. The 3D printer 8 is made up primarily of a pan 4 (also referred as a container), a set of pourers 10.1 -10.4, each of which is associated with a docking station 30.1 -30.4, where the pourer 10 can be refilled by an associated refill tank 1 1 . Also, a rigid frame 3 supports the docking stations 30.1 -30.4 and a pourer movement assembly 1 16 (FIG. 10A). Assembly 1 16 includes a fork assembly 5 (which may also be referred to as a "movement element") that attaches to a selected pourer 10, removes pourer 10 from a docking station 30, and moves pourer 10 through a pattern as fork assembly 5 actuates pourer 10, to selectively dispense powder (by way of pourer plug rod 19, discussed below). When present on assembly 5, pourer 10 rests on fork 6. Accordingly, pourer-movement assembly 1 16, may also be termed a pourer-movement and dispensing plug-actuating assembly 1 16.

The 3D printer uses a build powder and a support powder to build up 3D objects in the pan 4, layer by layer. Each layer consists of a region or multiple regions filled with build powder while the rest of the pan area in that layer is filled with support powder. In one embodiment, some part of a region might be skipped during pouring of a layer and filled later when pouring a layer above it, to increase the speed of the pouring process. After all layers have been poured, the build powder is bound by a binder, resulting in a 3D object, which is then separated from the support powder.

The powders may be made from any appropriate material, provided that the following requirements are met:

1 . Build and support powders are pourable, or at least arrangeable into a desired pattern by an appropriate mechanism.

2. Build powder is strongly bindable by the binder.

3. Support powder is far less strongly bindable by the binder that is the build powder.

4. Build and support powders remain mostly in solid particulate form during the process, to prevent shape distortion.

It is also important that the ambient gas is chosen appropriately to facilitate the above requirements. For example, if oxidation would negatively impact bindability of the build powder by the binder, the ambient gas should be selected to prevent oxidation. For example, in some embodiments the ambient gas is argon. In these embodiments the mechanism is enclosed in an air-tight chamber. In an alternative embodiment a substance that binds with oxygen, such as carbon in the form of coke, is put in the pan 4before it is heated

In a preferred embodiment, iron powder is used as the build powder, silicon dioxide powder is used as the support powder, and molten iron-carbon alloy with high carbon content is used as a binder. Iron-carbon alloys of varying carbon content may be used, although a carbon content of 4.3% has the advantage of having the lowest melting temperature - about 1 147 degrees Celsius. This alloy is commonly available as "Pig Iron," and is henceforth referred to simply as "Pig" in this text. In this embodiment, the powders are poured in such a way that the top layer has exposed build powder.

After the 3D pattern of iron powder and S1O2 powder has been created, a separator 1 10, having a through-hole is placed over the powder and a piece of Pig and a piece of carbon, such as coke, are placed on the separator, in such manner to avoid deforming the build powder shape. The pig should cover the hole in the separator 1 10, which should be above a surface of exposed build powder, to avoid S1O2 powder blocking the flow of molten pig. The pan 4 is then filled the rest of the way with S1O2 powder (in some methods, sand). The piece of carbon is needed to convert oxygen into carbon monoxide when heated, to prevent oxidation of the iron. The pan 4 is closed with a lid, transferred to a kiln, and heated. The kiln temperature is chosen to be above the melting temperature of Pig but below the melting temperature of the iron powder. When the temperature gets high enough, the Pig melts and soaks through the iron powder by capillary action, but the Pig does not soak the silicon dioxide powder, which resists wetting by molten iron. The pan is held at that temperature for a certain length of time, referred to as the hold time. During the hold time, the carbon atoms of the molten Pig diffuse into the particles of the iron powder, thus equalizing the carbon content. Longer hold times result in a better diffusion. After the pan is cooled down, the printed object is separated from the support powder and the remains of the Pig are cut off. Preferably, the printed object is designed such that it has an additional narrow neck at the top and a flat pad above it, such that the molten Pig would soak the object through the pad and the neck, making it easier to cut or break the neck separating the object from the pad and the remains of the Pig. The resulting material of the printed object is carbon steel. Further post-processing and heat treatment can be used to achieve desired properties and dimensions.

In another embodiment, the build powder is copper powder, the support powder is silicon dioxide, and the binder is copper-silver alloy.

In additional embodiments, instead of using a molten material as the binder, a chemical process is used to bind the particles of the build powder.

In one embodiment, the build powder is cement, the support powder is silicon dioxide, and the binder is water, which soaks the cement and causes binding.

In another embodiment, an epoxy is used as the binder. The build powder is a polymer such as, for example, Polytetrafluoroethylene (PTFE), Polyether ether ketone (PEEK), Nylon, Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid (PLA),

Polyoxymethylene (POM), Polycarbonate (PC), Polyvinyl Chloride (PVC), Polyethylene terephthalate (PET), Polyethylene (PE), Polypropylene (PP), Polystyrene (PS),

Poly(methyl methacrylate) (PMMA), Polybenzimidazole(PBI), Polyether sulfone (PES), Polyetherimide (PEI), Polyphenylene oxide (PPO), or Polyphenylene sulfide (PPS), and the support powder is another polymer from the same list. The polymer used for support powder is non-wettable by the epoxy; the polymer used for build powder is wettable by the epoxy.

In another embodiment, a glue is used as the binder instead of epoxy. The glue can be either chemical or thermal.

In another embodiment, heat is used to bind the particles of the build powder. The build powder is selected to have a glass transition temperature that is lower than the glass transition temperature of the support powder. The temperature used for binding is chosen to be above the glass transition temperature of the build powder and sufficient to strongly bind the build powder particles together, but not high enough to strongly bind the support powder particles, so that the support can be separated from the object without breaking it. The temperature selected should be below the melting point of either of the two powders to prevent shape distortion.

In another embodiment, multiple build powders of different colors are used to create colorful objects.

Referring again to FIGS. 1 .1 , 1 .2 and 1 .3, a pourer-movement assembly 1 1 6 includes stepper motors 1 .X, 1 Ύ, 1 .Z, which rotate lead screws 2.X, 2.Y, 2.Z to move the fork assembly 5, holding a pourer 10, in three dimensions along the X, Y and Z axes, respectively.

FIGS. 2.1 , 2.2 and 2.3 show details of the fork assembly 5. The fork assembly 5 can hold any one of the four pourers 1 0, which are identical insofar as the portions that contact the fork assembly 5.

FIGS 3.1 , 3.2, 3.3, 3.4 and 3.5 show details of a pourer 10.

FIGS 4.1 , 4.2 and 4.3 show the fork assembly 5 (which may also be referred to as a movement element, as it holds and moves a pourer 10).

Referring now to FIGS. 2.1 to 2.3, fork assembly 5 has a pour plug actuating stepper motor 1 P that rotates lead screw 2.P and moves a pourer control carriage 15, vertically. As carriage 15 moves down, referring now to 3.1 , which shows the top of a pourer 10, which for purposes of this discussion is engaged with fork assembly 5, it pushes and tilts seesaw 16 via spring 17 (FIG 2.3). As seesaw 16 tilts it pushes ball bearing 18 up, thus lifting pourer plug rod 19 (FIG. 3.4), so that the end of rod 19 no longer plugs pourer hole 20, thereby permitting powder to flow from hole 20. As the end of plug rod 19 plugs pourer hole 20, this end may be termed a "plug."

Fork assembly 5 also includes plug rod rotating stepper motor 1 .S that rotates a claw 21 . When carriage 15 is lowered, claw 21 engages with and rotates knob 22 (FIG.3.1 ). Referring to FIG. 3.5, knob 22 is connected via axle 23 and coupler 24 to pourer plug rod 19. Axle 23 is held horizontally by another two ball bearings (not shown) inside bridge 26, but can freely rotate and slide vertically. Spring 25 increases closing force of plug rod 19.

FIGS. 5.1 and 5.2 show that plug rod 19 is slightly bent, so when the rod moves up, the bottom end of the rod also moves sideways, such that when rod 19 rotates it stirs the powder, thus increasing the flow rate and consistency. Rod 19 is also flexible, so when it moves down the slope of the bottom guides its tip to slide to the center of the pourer and into hole 20, sealing the opening.

In one embodiment, there are four pourers: two for support powder and two for build powder. Of the two pourers for each type of powder, one has a smaller hole 20 for higher resolution pouring, and one has a larger hole 20 for faster pouring.

FIGS 6.1 , 6.2, 7.1 and 7.2 show the pourer refill mechanism. Each pourer 10.1 - 10.4, is refilled from its own refill tank 1 1 .1 -1 1 .4, respectively. Refill tank 1 1 .1 -1 1 .4 is connected by pipe 12 to injector chamber 13. As shown in detail in FIG. 7.2, the injector chamber has a hole 35 in the bottom, which serves as a refill opening, and which is closed by plug 14, which serves as a refill plug. Geared stepper motor 31 winds and unwinds cable 32 thus tilting refill assembly on hinge 33. As the refill assembly is tilted the injector chamber moves vertically. When a pourer 10.1 -10.4 is engaged with its docking station 30.1 -30.4, and the injector chamber is lowered, rod 34 of the pourer pushes injector plug rod 14 up, thus opening hole 35 and allowing the powder to flow from the refill tank into the pourer. When the injector chamber is lifted, or pourer 10.1 - 10.4 is absent, rod 14 moves down closing hole 35.

Referring to FIG. 1 7A, before the printing process begins, a stereolithography (STL) file 162 is loaded into a computer 160, which executes a computer program that loaded from non-transitory computer readable memory, commonly referred to as a slicer program, that translates the STL file into G-code, a form of motion commands that can be understood by a controller board 161 . Controller board 1 61 creates a set of signals that control motors 1 .x, 1 .y, 1 .z, 1 .p and 151 , through the printing process. At the beginning of this process, fork assembly 5 retrieves a desired pourer 10 from the docking station 30 and positions it in the desired location over pan 4. Stepper motor 1 P opens the through-hole 20 (as described above) allowing the powder to flow into the pan. As the powder pours from through-hole 20, stepper motors 1 .X and 1 Ύ are controlled by controller board 161 to move the fork assembly 5 in and X, Y pattern, creating a desired pattern of either build powder or support powder. Then stepper motor 1 P closes hole 20, shutting off the flow of powder, and returns the pourer to the refill docking station 30. Fork assembly 5 then retrieves a different pourer 10, and so on, until the pan is filled as desired.

FIGS. 9A through 16B show an alternative embodiment 108 to that of printer 8. Embodiment 108 includes docking stations 140 and a fork assembly 105 that have some significant differences from docking stations 30 and fork assembly 5. In broad overview, docking stations 140 do not include a motor. Rather, the refilling operation is actuated by a sequence of movements of the fork assembly, as will be explained further, below. Also, fork assembly 105 uses a DC motor 151 , rather than the stepper motor 1 .p, to raise and lower the pourer plug rod 19. In one more difference, printer 108 is equipped with adjustable length legs 130, so that it can be placed over a kiln base 131 . In one method of use, printer 108 is lifted away after laying down the build and support powder, and the rest of the kiln is placed on the kiln base 131 , to complete the kiln, so that pan 4 and its contents can be heated in place.

Referring first to FIGS. 15A, 15B and 16A, each docking station 140 defines a powder passageway 142, leading to a powder pour spout 143. Station 140 further includes support balls 163 (only one shown). Additionally, a rocker arm 141 , is hinged to station 140, and has a pair of teeth 145 and a plug 146. A spring urges rocker arm 141 into a powder flow blocking position, where plug 146 is interposed between passageway 142 and pour spout 143. When the computer 160 determines that a pourer 10 will be docked, it commands motors 1 .x, 1 .y and 1 .z to move the pourer 10 to a position in which a portion of the top of pourer 10 is directly beneath the teeth 145, and then pushes pourer 10 upwardly to lift teeth 145 and thereby move rocker arm 141 into a powder dispensing position, where plug 146 is lifted from the top of pour spout 143. Pourer is then moved further into contact with docking station 140 so that the lip 148 of the pourer 10 rests on the support balls 163 and teeth 145 contact the top surface of pourer 10, which thereby maintains teeth in a raised position, which maintains plug 146 in positioned that is not plugging pour spout 143. Finally, a pair of indents 170 (FIG. 13C) on the bottom of lip 148 engaged to a pair of support balls 163 (FIG. 15A) to retain it as it is released by fork assembly 105, by lowering fork assembly 105 and moving it away from pourer 10 when pourer 10 no longer rests on it. This design has the advantage of illuminating four electric motors, thereby reducing cost, complexity and potential maintenance expense.

Referring to FIG. 12A, actuating arm 150, which is hinged to the fork assembly 105 at hinge 149, includes a downwardly extending push panel 156. When arm 150 is lowered, it presses down against pourer rocker arm 16 (FIG. 13 A), which lifts up on ball bearing 18, in turn lifting pourer plug rod 1 9, permitting powder to flow out. When arm 150 returns to its raised position, pourer plug rod 19 is urged downwardly by spring 25, stopping the flow of powder, with hinged arm 16 and ball bearing 1 8 also returning to non-dispensing positions. There are some differences between the pourer 10, shown in FIGS. 13A-13C, and that shown in FIGS. 14A-14C. Hole 20 is smaller in that shown in FIGS. 13A-13C, for laying down a finer line of powder. Similar to the case for printer 8, when pourer 1 0 is on fork assembly 105, it rests on fork 106.

The above noted movement of arm 150 is effected by a DC Motor 151 (FIG. 12B), which turns spool 154, pulling or releasing a steel cable 155 that is engaged with pulley 157 and anchored at a switch 152. Starting with arm 150 in its down position, push panel 156 rests on rocker arm 16, so that there is little tension in cable 155, which has placed switch 1 52, in its cable slack position. When it is required to stop dispensing powder, DC motor 151 turns spool 1 54 to reel in cable 155, thereby causing switch 152 to switch to its cable tense position (a transition that does not affect operation) and for cable to pull up on pulley 157, thereby pulling up on arm 150 which continues to rise until it contacts another switch (not shown) located along the path of arm 150, which creates a signal that stops the process. DC motor 151 maintains its position by the friction of an internal gear assembly and arm 150 stays in the same position until it is time to move arm 1 50 and dispense powder. When this action is required, DC motor 151 , turns spool 1 54 so as to spool out cable 155, causing arm 150 to drop until panel 156 is resting on arm 16. At this point cable 155 goes slack enough so that switch 152 transitions to a cable slack position, which is perceived by computer 160, or in an alternative embodiment, just by controller board 1 61 , causing the process to stop, with the DC motor again stopped in place.

The fork assembly 105, rides vertically on a vertical tube 186 (FIG. 10B), which extends through partially enclosed space 188, with a pair of upper ball bearings 182 and lower ball bearings 184 smoothing the ride. Vertical tube 186 rides on a carriage 190, that is moved side-to-side on tubes 192 and forward and backward on tubes 1 94 (FIG. 10B). Tubes 192 and 194 provide a light weight but rigid framework for movement of carriage 190, and thereby fork assembly 1 05, which also moves on tube 186. As noted elsewhere, this movement is powered by motors 1 .X, 1 Ύ and 1 .Z.

Example 1 :

In one example the following parameters were used to produce a high carbon steel 3D printed object.

Build powder: IRON1 00

The specification, and ordering information for I RON100 can be found on the Internet at: http://www.iron-powder.com/wp-content/uploads/2014/03/I RON100_Specifications.pdf

Following is some information concerning I RON100:

Chemical Analysis (by weight)

Fe 99.5%+

O 0.200%

C 0.030%

Si 0.030%

Flow rate 29.00 sec/50g

Particle size <21 2 microns.

Median particle size: 100 microns. Support powder: OK85

The specification for OK85, a product of USSilica, can be found at the following Internet address, and is also reproduced below. http://www.ussilica.com/sites/ussilica.com/uploads/files/pro duct-data- sheets/industry/foundry/OK85.pdf Grain Shape: Round

Melting Point: 3100 Degrees F

Mineral: Quartz

Typical Chemical Analysis: Si02 (Silicon Dioxide) 99.8%

Particle size: <425 microns.

Median particle size: 150 microns.

SORELMETAL GRADE RF1

Carbon Silicon Manganese Phosphorus Sulfur 4.25% 0.15% 0.022% 0.033% 0.013%

Available in an Ingot Size (Approx) :

1 85 x 120 x 55mm (7.25" x 4.7 x 2.5) Weight (Approx.) :

5.54 kb (12 lbs.)

Pourer hole diameter: 1 mm for the smaller hole and 4mm for the bigger hole.

Pourer horizontal moving speed while pouring (in millimeters per second):

Build: 2

Support: 8

Kiln settings:

Ramp: 600 degrees Celsius per hour

Hold temperature: 1250 degrees Celsius Hold time: 4 hours

Example 2:

In another example similar parameters were used, except the following:

The OK85 powder was filtered to remove 25% of the largest and 5% of the smallest particles.

The I RON100 powder was filtered to remove 20% of the smallest particles.

Pourer hole diameter: 1 mm for the smaller hole and 2mm for the bigger hole.

Pourer horizontal moving speed while pouring (in millimeters per second):

Build: 16

Support: 20

Kiln settings:

Ramp: 600 degrees Celsius per hour

Hold temperature: 1 1 80 degrees Celsius

Hold time: 2 hours

Referring, now, to FIGS 8A through 8D, after the process of filling pan 4 with build and support powder by the 3D printer is complete, a shelf 1 10, having an opening and being shaped to encourage liquid flow through the opening, is placed on top of this powder. A piece of pig 1 1 1 and a piece of coke 1 12 are placed on top shelf 1 10, and a lid 1 13 is placed over all of this. An inert particulate material, such as sand is then poured through a hole 1 14 in lid 1 13. This prevents shelf from riding up, and aids shelf in keeping the S1O2 powder tightly packed, thereby preventing the molten pig from lifting

Industrial Applicability

The present invention finds industrial applicability in the manufacture of objects via 3D printing.

While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.