Patent Application
20190255611
Embodiments are in the field of additive manufacturing. More particularly, embodiments disclosed herein relate to additive manufacturing systems and methods for utilizing metal-based pellet extrusion in an additive manufacturing system.
Additive manufacturing or three-dimensional (3D) printing machines are known. Many such machines use a feedstock provided in filament form. While there are many variants of 3D printers, the three most common technologies are 1) Fused filament fabrication (FFF); 2) Powdered bed additive manufacturing (PAM); and 3) Stereolithography (SL) or Stereolithography apparatus (SLA). Within PAM, laser sintering or jetting technology are dominant techniques. In SL, a liquid pool of material is catalytically polymerized in a liquid material bath to yield a solid part.
There are advantages and disadvantages to all of the 3D printing techniques. However, the one thing they all have in common is the very high cost of the final printed part. The current state-of-the-art in 3D printed parts have a very high cost when measured as a cost per unit ($/unit), or unit cost per pound of material ($/pound) relative to other manufacturing processes. To be succinct, the parts have a high “dollar density”. Of course, if the part cannot be made any other way, then the higher cost might be justified. Dollar dense parts are much more common in specialty markets such as aerospace, biomedical, military, or space exploration.
As mentioned, a common characteristic for specialty market parts is the cost of the material. FFF typically uses a polymer or composite filament as the feedstock. And while the polymer used to manufacture the filament might be common, the market price for well-known and somewhat common polymers in a filament form can be quite high.
Most common polymers are available in the form of a pellet. Additionally, it is common to use a pellet-form to manufacture filaments. A common polymer pelletized material might be $2-$4 per pound. The same material in a filament form might sell for $30-$50 per pound. Similar disparities in material cost exist for PAM and SLA. The material selection of filament feedstock is also relatively limited compared to pellets. While it is expected that filament pricing will decrease over time, it is unlikely that the filament cost will ever be as low as the cost of pellets.
SLA is used with polymer-based materials that can be processed as a liquid. High specific gravity material, like metals, are not compatible with SLA methodologies, manufacturing, or equipment. PAM materials are just that, the material is in a powder form. The polymer powder particle size, shape, and particle size distribution must be closely controlled to allow PAM to work properly. These variables add to the cost.
PAM is more versatile than SLA because PAM can be used to process polymer or metal powders. FFF is widely known primarily for its polymer-based filaments. However, the filaments become increasingly difficult to manufacture when the polymer is a highly filled compound. It is known that an FFF filament can also be made using metal as a filler. However, metal-filled polymer filaments tend to be very brittle and extremely difficult to process. This decreases machine and material yield and slows the 3D printing processing time down considerably.
Finally, in large part, FFF filaments are also a limiting factor to the speed of the machine thus lowering machine throughputs. The filament process, whereby the filament is pulled into the machine before further processing is limited by the material itself. Highly elastic filament materials will stretch and deform causing the machine to not operate properly. Filaments exposed to higher heat will result in a similar failure mode. Conversely, low elastic, highly filled filaments are relatively brittle and break, causing the machine to stop functioning. FFF material cost is high, machine throughputs are low, and highly filled materials are difficult to process. Highly filled metal filaments present similar problems as other highly filled polymers. Thus, it is desirable to provide a 3D printer and method of using same that are able to overcome the above disadvantages.
An example of a metal-based pellet extrusion additive manufacturing system is disclosed. The system may include a printing nozzle system with a turnable screw, an extruder body, and a nozzle end, wherein the turnable screw is configured to transport metal-based pellets from an extruder body towards a nozzle end. A method for fabricating an object using metal-based pellet extrusion system is also disclosed. The method may include feeding metal-based pellets to an printing nozzle system; receiving the metal-based pellets in an extruder body of the printing nozzle system; providing an extruder, such as a turnable screw, in the printing nozzle system to force the pellets through the extruder body; extruding the metal-based pellets and heating the extruded pellets using one or more heaters during transport of the extruded pellets through the extruder body; dispensed the extruded metal-based pellets through a nozzle; and depositing the extruded metal-based pellets onto a printing surface to form a printed object. The method further includes debinding and sintering the printed object.
A method of producing a fan wheel for a fan assembly can include receiving metal-based pellets at a printing assembly including a nozzle and an extruder, the pellets including a metal material and a binder material, extruding and heating the metal-based pellets at the extruder to convert the metal-based pellets to a liquid state material, dispensing the liquid state material from the nozzle to print the fan wheel, the fan wheel being a monolithic object including a base and a plurality of fan blades.
In one example, the dispensing step includes printing the base to have a hollow shape.
In one example, the dispensing step includes printing the base to have a truncated dome-shape or a frustoconical shape and includes printing the fan blades to have an airfoil shape.
In one example, the method further includes debinding the fan wheel to remove a primary binder of the binder material from the fan wheel, and sintering the fan wheel to remove a skeletal binder of the binder material to densify the fan wheel.
In one example, the metal material is a stainless steel material, the primary binder is polyoxymethylene and the skeletal binder is polyethylene.
The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. For the purpose of illustration only, there is shown in the drawings certain embodiments. It's understood, however, that the inventive concepts disclosed herein are not limited to the precise arrangements and instrumentalities shown in the figures.
It is to be understood that the figures and descriptions of the present invention may have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements found in a typical 3D printer or typical method of using/operating a 3D printer. Those of ordinary skill in the art will recognize that other elements may be desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. It is also to be understood that the drawings included herewith only provide diagrammatic representations of the presently preferred structures of the present invention and that structures falling within the scope of the present invention may include structures different than those shown in the drawings. Reference will now be made to the drawings wherein like structures are provided with like reference designations.
Before explaining at least one embodiment in detail, it should be understood that the inventive concepts set forth herein are not limited in their application to the construction details or component arrangements set forth in the following description or illustrated in the drawings. It should also be understood that the phraseology and terminology employed herein are merely for descriptive purposes and should not be considered limiting.
It should further be understood that any one of the described features may be used separately or in combination with other features. Other invented systems, methods, features, and advantages will be or become apparent to one with skill in the art upon examining the drawings and the detailed description herein. It is intended that all such additional systems, methods, features, and advantages be protected by the accompanying claims.
For purposes of this disclosure, the phrases “3D printer” and “additive manufacturing system” may be used interchangeably. Also, the phrases “printing bed”, “printing platform”, and “printing table” may be used interchangeably.
Embodiments of the present disclosure define a fused pellet fabrication (FPF)-style 3D printer system 1000 that, due to the totality of the configuration improvements, achieves improved economic and system capabilities, among other advantages. The resulting printed objects are made without the use of a mold. This is in contrast to using metal-based pellets in an injection molding scenario via employing a hollow container to catch the molten metal-plastic extruded material, which is a widely known technique.
In one example, a printed object 300 is formed from a metal-based pellet feedstock that is fed into the printing nozzle system 100 through a pellet hopper 102 or other equivalent materials feed system. The pellet feedstock can be a mixture of metal powder as a primary material and various binder materials that are integral and homogenous with the primary material. In one aspect, the output of the printing nozzle system 100 yields a three-dimensional “green” object or part 300. The various binder materials are then removed from the primary material in a subsequent phase where the printed part transitions from the “green” printed state, through a de-bind process (“brown” state) and sintering process (material densification), which removes the binder material(s), to allow the primary material to collapse upon itself yielding a three-dimensional solid metal part exhibiting material properties at or near the wrought material strength.
In referring to materials, the use of the term “green” means that the material has been printed but has undergone no further process to remove any binding material. By using the term “brown”, it is understood that the printed material has been printed and undergone a debinding process, but has not received any additional heat treatment or other processing. Referring to a material as “finished” means that the printed material that undergone printing, debinding, and sintering heat treatment (and any other further treatments) to fully densify the printed object.
In a non-limiting example, the material porosity following the debinding process may range from 16% to 17%, while the porosity following the sintering process may range from 1% to 2%. Additional processing may occur after sintering, such as sanding the printed object 300 or polishing the printed object 300. The debinding material is removable by a catalytic process. The catalyst that is used for debinding can be nitric acid and can be used in the CataMIM® debinding method. In one example, nitric acid at a 2 percent (%) concentration is used during the debinding operation. During debinding, nitrogen gas can be used to prevent oxidation of the metal.
Embodiments of the present disclosure also describe a system that is capable of allowing the FPF process to print most common polymer-based pellet-form feedstocks at a significant reduction in material costs. The elimination of the common FFF filament feedstock also allows for a significant reduction in polymer material cost.
Embodiments of the present disclosure further describe a system 10 that is capable of printing at a much faster rate than FFF-style printers due to the elimination of the filament and the addition of expanded extrusion zones and material feed mechanisms. This is accomplished while maintaining part surface smoothness associated with much slower print speed protocols.
In addition to the ability to 3D print and post-process material to ultimately yield a solid or near-solid metal part, embodiments of the present disclosure are capable of printing 3D parts that are: (1) relatively large (for example, 3×3×2 feet, or more), although smaller parts may be contemplated as well; (2) metal or polymer/composites; (3) at economic levels that are lower than parts currently made using more traditional metal processing techniques; and (4) capable of producing solid metal parts or products that are manufactured (printed) but also takes advantage of FFF 3D printing's promise of mass-customization which is another significant advancement in the state-of-the-art.
Embodiments of the present disclosure achieve at least: Use of metal-based pellets to FPF print 3D shapes. This ultimately results in an ability to use an FPF-style 3D printer to print solid metal parts. The 3D printed part (i.e., the green part—which is a common term in the art)) goes through a post-print process similar to metal injection molding (MIM) to yield the solid part from the 3D printed green part. The metal-based pellets may comprise, for example, stainless steel, copper, aluminum, titanium, cobalt, chromium, magnesium, nickel and many more fusible metal materials such as glass, ceramic or sand. The metal-based (fusible material) pellet will also comprise various binders such as polypropylene, polyethylene, polyoxymethylene (POM), waxes, or other similar materials. The fusible material (metal etc.) may be, for example, of any size, shape, weight, and/or density, as are currently used in state-of-the-art metal injection molding (MIM) processes, although sizes larger than the current MIM process are also possible.
Some benefits of embodiments of the present disclosure are: increased machine throughput from less than 1-2 lbs./hour to 8-10 lbs./hour or more while maintaining a high level of surface smoothness and material strength; increased versatility in the variety of polymers that can be used; and decreased material costs for the polymers and the metals used. Furthermore, the present invention allows 3D printing to be used for more general industrial applications and thereby opens up a much larger portion of the general manufacturing market to 3D printing due to the use of lower material costs and higher machine throughputs.
An additional benefit of the present disclosure is the ability to produce a single printed object design without requiring any welds, rivets, fasteners, or any other attachment means. As such, a monolithic printed object results while having strength properties nearing that of the wrought strength of a typical solid metal part.
In operation, a screw extruder, such as screw 106 illustrated in
Embodiments are directed to a metal-based pellet extrusion additive manufacturing system for fabricating an object. The metal-based pellet extrusion additive manufacturing system comprises: a printing nozzle system 100 (such as that illustrated, in sectional view, in
In an embodiment, the printing nozzle system 100 comprises a turnable screw 106, extruder body 104, and a nozzle 110. The turnable screw 106 is configured to transport the metal-based pellets 112 from an extruder body 104 towards a nozzle 110. The printing nozzle system 100 may further comprise at least one heater 120, 122, or 124 which at least partly surrounds a barrel 108 which houses screw 106. The at least one heater 120, 122, or 124 is configured to heat the metal-based pellets 112 while the metal-based pellets 112 are transported from the extruder body 104 towards the end of nozzle 110.
In the illustrated embodiments, three separate heaters 120, 122, and 124 are provided. However, fewer or more heaters may be utilized in some applications. The heaters 120, 122, and 124 may be electrically-powered.
In an embodiment, the 3D-printed object 300 may be a green part or may be a final part. The 3D-printed object may also be configured to yield a fully densified part after de-binding the binder(s) and sintering of the 3-D printed object, in a secondary post-print operation. A fully-processed part may have 1% to 2% porosity. Printed object 300 may be formed without any welds, rivets, fasteners, or any other attachment means.
In an embodiment, each metal-based pellet comprises (a mixture of) metal powder and binder in a typical ratio of 80% nominal by weight metal to 20% nominal by weight binder and other materials. In another embodiment, there is a primary binder and a secondary or skeletal binder. One example of a primary binder may be POM, and one example of a skeletal binder may be polyethylene. In an example, the printed object has an amount of metal is 60% by volume, the primary binder is 33% by volume, and the skeletal binder is 7% by volume. Other combinations are possible. In one example, the metal pellet is 316L stainless steel, the primary binder is POM, and the skeletal binder is polyethylene at the above-identified percentages. In yet another example, the metal pellet is 17-4 stainless steel, the primary binder is POM, and the skeletal binder is polyethylene at the above-identified percentages.
As shown in
Printing nozzle system 100 may be used to produce several metallic products by extrusion of metal-based pellets in an additive manufacturing system. Such a metallic product, for example, may be a metallic fan wheel 400 illustrated in
Referring to
With reference to
The emitted heat from heater 120 may result in creating first heat zone having a temperature range between 150° C. and 230° C. The emitted heat from heater 122 may result in creating a second heat zone having a temperature range between 160° C. and 230° C. The emitted heat from heater 124 may result in creating a third heat zone having a temperature range between 180° C. and 230° C. In addition, a fourth heat zone located at nozzle 110 may have a temperature range between 180° C. and 245° C. After passing through heater 124, the extruded pellets pass through nozzle 110. The nozzle 110 may have an orifice size between 0.5 mm and 3 mm.
The extrusion process may result in printing a continuous stream at a speed of 1000 mm/minute to 10,000 mm/minute. These ranges may vary depending upon the MIM material that is extruded. In certain embodiments, printing speeds may also vary from 1500 mm/minute to 3100 mm/minute.
In one example of the method for fabricating an object using metal-based pellet extrusion, and as illustrated in
The process parameters may be controlled to optimize certain features of the printed object 300, such as the smoothness. In one example, surface smoothness for printed object 300 may be enhanced by printing the material with a layer height of about 0.5 mm. In other example, the layer height may be within the range of 0.5 mm to 1.0 mm. In yet other examples, the width of the stream of printed material may be from about 2.5 mm to about 3.2 mm.
Although embodiments are described above with reference to a 3D printer that uses metal-based pellets that includes a plastic binder as part of the pellet material, other material(s) besides (or in addition to metal) may alternatively be employed instead of or in combination with the binder(s) such as glass, ceramic, sand, combinations thereof, or any other fusible material, in any of the configurations and embodiments described above. Other alternatives or additions to the plastic binder such as clay, wax, polymer, combinations thereof, etc., may alternatively or additionally be employed, in any of the configurations and embodiments described above.
Although embodiments are described above with reference to a 3D printer that uses a nozzle system comprising a screw-type extruder, other type of extruders (such as non-screw-type extruders) may alternatively be employed, in any of the configurations and embodiments described above. For example, a ram extruder may be used instead of a screw.
Control System 500
Referring to
The electronic controller 500 typically includes at least some form of memory 500B. Examples of memory 500B include computer readable media. Computer readable media includes any available media that can be accessed by the processor 500A. By way of example, computer readable media include computer readable storage media and computer readable communication media.
Computer readable storage media includes volatile and nonvolatile, removable and non-removable media implemented in any device configured to store information such as computer readable instructions, data structures, program modules or other data. Computer readable storage media includes, but is not limited to, random access memory, read only memory, electrically erasable programmable read only memory, flash memory or other memory technology, compact disc read only memory, digital versatile disks or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by the processor 500A.
Computer readable communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” refers to a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, computer readable communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency, infrared, and other wireless media. Combinations of any of the above are also included within the scope of computer readable media.
The electronic controller 500 is also shown as having a number of inputs/outputs that may be used for operating the printing nozzle system 100. The printing head assembly 150 may include pressure and sensor sensors that provide an input to the controller 500. The printing head assembly 150 can also include inputs and outputs, such as an output to control the operation of the actuator for the screw 106. The controller 500 can also include additional inputs and outputs for desirable operation of the printing nozzle system 100 and related systems, for example motion control servo motors.
It's understood that the above description is intended to be illustrative, and not restrictive. The material has been presented to enable any person skilled in the art to make and use the concepts described herein, and is provided in the context of particular embodiments, variations of which will be readily apparent to those skilled in the art (e.g., some of the disclosed embodiments may be used in combination with each other). Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the embodiments herein therefore should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.”
This application claims priority to U.S. Provisional Application Ser. No. 62/632,951, filed on Feb. 20, 2018, the entirety of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62632951 | Feb 2018 | US |
