Patent Application
20230234280
This disclosure relates to producing dies for use in presses to reshape malleable sheet stock and, more particularly, to using an additive manufacturing process in conjunction with an adapted thermoplastic composition to efficiently create press dies featuring low density and high compressive properties.
High pressure presses with shaped dies have long been used to form sheet metals or other malleable sheet stock materials into final parts, such as body parts for motor vehicles and aircraft. A fixed-shape die, once formed, can be used for mass production of identical sheet metal parts that have complex shapes and curvatures, such as shapes that involve double curvatures.
The formation of a sizable die or pair of complementary dies from a sufficiently sturdy solid metal may be extremely costly and result in very heavy tooling that is difficult to change. The time and cost associated with creating large-format tooling, such as that for forming a door or quarter panel of an automotive body, makes short run tooling or designing by iterative refinements cumbersome and infeasible. Whereas traditional techniques such as CNC machining and electrical discharge machining (EDM) are usually applied to carve out a die from a solid block, metal additive manufacturing techniques may also be used to form press die tooling to some advantage but still require surface machining in many instances and yield a tool having considerable mass and significant cost. Thus, there remains a need for improvements in the field of producing large-format press dies for pressing and stamping of malleable sheet stocks.
The present teachings disclose processes and material compositions that enable large-format press dies to be produced by extrusion of a thermoplastic with enhanced mechanical characteristics. In accordance with some embodiments, a thermoplastic employing a mixture of fillers having different aspect ratios is shown to exhibit strength, modulus and other characteristics that render it suitable for making press dies. In accordance with some embodiments, the use of the extrudable filled thermoplastic extends an achievable linear dimension size, area or volume of a press die beyond the limitations of non-filled plastics. In some embodiments, the filled thermoplastic may be used as a feedstock material for an extrusion additive manufacturing process and, with proper design and slicing, allow for passages, interior frameworks, truss structures, internal voids or inclusions that lighten the die without undermining strength.
Various exemplary embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which:
The following detailed description explains the preparation of a variety of polymeric composite materials according to the present teachings and then describes how to apply composite material as a feedstock an additive manufacturing process to, in turn, produce durable press die tooling for forming materials such as sheets of aluminum, stainless steel or soft iron. As will be shown, the particular novel composition of polymer matrix and a mixture of fillers having the prescribed attributes greatly facilitates the use of additive and subtractive processes in forming cost-effective and rapidly implemented forming tools which exhibit favorable physical properties such as strength, stiffness and durability.
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of illustrative and preferred embodiments of the invention. It is apparent, however, that some embodiments may be practiced without these specific details or with alternative, equivalent arrangements. In some instances, more common structures and devices are excluded from view or shown in block diagram form in order to avoid unnecessarily obscuring components that are more essential for illustrating embodiments of the invention and its operating principles.
At the outset, it is important establish that, unless the context indicates otherwise, the following terms shall have the following meaning as used herein and shall be applicable to both singular and plural forms:
The terms “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably. Thus, for example, a high-performance composite composition containing “a” an amorphous polymer and a reinforcing fiber means that the composite composition may include “one or more” amorphous polymers and reinforcing fibers.
The terms “additive manufacturing”, “three-dimensional printing”, or “3D printing” refer to any process used to create a three-dimensional object in which successive layers of material are formed under computer control (e.g., electron beam melting (EBM), fused deposition modeling (FDM), direct pellet extrusion, ink jetting, laminated object manufacturing (LOM), selective laser sintering (SLS), and stereolithography (SL)).
The term “feedstock” refers to the form of a material that can be utilized in an additive manufacturing process (e.g., as a build material or soluble support). Non-limiting feedstock examples include, but are not limited to, pellets, powders, filaments, billets, liquids, sheets, shaped profiles, etc.
The term “melt processing technique” means a technique for applying thermal and mechanical energy to reshape, blend, mix, or otherwise reform a polymer or composition, such as compounding, extrusion, injection molding, blow molding, roto molding, or batch mixing. For the purpose of clarity, 3D printing processes that are useful in printing thermoplastic and elastomeric melt processable materials are examples of a melt processing technique.
The terms “polymer” and “polymeric” mean a molecule of high relative molecular mass, the structure of which essentially comprises repeating units, derived actually or conceptually from molecules of low relative molecular mass, covalently bonded together.
The term “amorphous polymeric matrix” generally means a polymer that has less than 50% crystallinity as measured by differential scanning calorimetry (DSC). In the context of the present teachings, it is preferred to use an amorphous polymeric matrix exhibiting a flexural modulus (as determined by ASTM D790) that is greater than 2,000 MPa.
The term “reinforcing fiber” means a plurality of fibers having an average diameter less than 20 microns and average aspect ratio (Fiber Length/Fiber Diameter) greater than 10.
The term “polymer composite” means a melt processible composition of an amorphous polymer matrix and a reinforcing fiber.
The terms “preferred” and “preferably” refer to embodiments that may afford certain benefits, under certain circumstances. Other embodiments, however, may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the claimed scope.
The recitation of numerical ranges using endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 3, 3.95, 4.2, 5, etc.) and any subset ranges encompassed within the range.
As used herein, the term ‘molten’ is loosely applied to any state of a material when it is heated or otherwise softened and is of sufficiently low viscosity to flow through a small nozzle under pressure. It is recognized that for some materials a more precise terminology, such as a ‘plastic’ or ‘amorphous’ state, may be more commonly used and the term ‘molten’ is intended to encompass these situations. When a material is said to be ‘molten’ herein it will generally be at a temperature substantially at or above its glass transition temperature, where applicable.
Polymeric composites have utility in many commercial applications, including what may be termed ‘additive manufacturing’ or ‘three-dimensional printing’ (3D printing.)
A polymeric material may generally be considered to be ‘3D printable’ if it exhibits several important attributes. A 3D printable feedstock is preferably a thermoplastic that can be softened or melted at elevated temperatures, extruded through a relatively small nozzle and then cooled to solidify without significant chemical or structural degradation. Because 3D printing involves building a solid object by successive addition of extruded polymer, a favorable feedstock material will also exhibit substantial cohesion between newly applied material and previously applied material. Another useful attribute in some contexts is the ability of the feedstock material to be supplied and handled in the form of a flexible or semi-rigid filament wound on reels as is used by many types of 3D printers, though certain other types of printers will accept bulk pellets as an alternative to filament. A few of the many other factors that influence suitability as a 3D printing feedstock relate to heat dissipation, avoidance of nozzle clogging and voids, and achieving isotropic material strength characteristics in the finished object.
‘3D-printable’ polymeric composites, typically comprising a thermoplastic binder and some proportion of a fibrous filler for added tensile and shear strength, have been developed to meet application needs in many industries. However, one industry need that has not yet been addressed is a 3D printable polymeric composite that can meet the performance requirements for tooling applications, specifically sheet metal tooling applications. Such tools or forms have a particular shape and a raw sheet metal piece is reshaped by being forced to conform to the shape of the tooling. Under substantial force to cause deformation, the sheet metal is bent or stretched to conform to the tooling and thereafter retains the shape imparted by the tooling. Sheet metal forms are commonly fabricated out of steel or aluminum. Steel and aluminum have extremely high stiffness and compressive properties as are required to forcefully and permanently bend, deform or stretch a sheet metal blank into a finished shape. Unfortunately, despite the availability of some techniques to produce 3D printed metal parts in general, doing so to create metal tools for sheet metal forming is difficult and often prohibitively expensive, especially for large workpiece sizes. Accordingly, a need is recognized for a cost-effective and readily 3D-printable polymeric composite material for creating this type of tooling.
Polymeric composites have found significant industrial utility in many markets and applications. However, the number of polymeric composites that can be effectively 3D printed is limited as a result of requirements that are specific to 3D printing methods (i.e., rheology, adhesion characteristics, particle size, shrinkage/warpage, etc.). According to the teachings set forth herein, polymeric composites have been formulated to be 3D printable and to possess superior properties that make them amenable for certain tooling applications. In one embodiment, high-performance composites introduced herein comprise an amorphous polymeric matrix, reinforcing fibers and preferably a lightweight filler. In one embodiment, composites formulated according to the present teachings exhibit a compressive modulus greater than 3500 MPa and a compressive strength greater than 70 MPa. The high-performance composites of this invention have utility in many applications, including but not limited to, additive manufacturing feedstocks (e.g., fused deposition modeling and direct pellet extrusion). In a preferred embodiment, the amorphous polymer matrix is polycarbonate (PC), polylactic acid (PLA) or polycycloolefin copolymer (COC). In a preferred embodiment, the reinforcing fiber is carbon or glass fiber. In various preferred embodiments, the lightweight filler comprises hollow glass microspheres.
Thermoplastic composites as described herein have application in 3D printable tooling, specifically, sheet metal tooling. Such applications require extreme resistance to permanent deformation under high-speed, high-force loads. If the tool does deform under load, it must be resilient enough such that it recovers to its original shape when the load is removed. The advantage of 3D printed tooling is that it simplifies tool design and prototyping and enables fast iteration of experimental runs. It is also well suited for small lot productions runs as the cost to create tooling in this manner is far lower than that for conventional metal forms.
The present disclosure describes high-performance polymeric composites comprising a substantially amorphous polymeric matrix, reinforcing fibers and optionally hollow glass microspheres.
A variety of amorphous polymers can be ‘melt processed’ (essentially by heating and thorough mixing) with reinforcing fibers to create a range of composites in accordance with the present teachings. Amorphous polymers for use in the conjunction with present teachings preferably exhibit a flexural modulus greater than 2000 MPa and a degree of crystallinity less than 50%. Non-limiting examples of amorphous polymers that can be used to make such a composition of matter include acrylonitrile-butadiene-styrene copolymers (ABS), polyacrylates, polymethacrylates, polyesters, polyvinylchloride (PVC), polycarbonates, polystyrenes, cycloolefin copolymers (COCs) or combinations thereof. Preferred amorphous polymers include polylactic acid, polycarbonate and polycycloolefin copolymers. Additives, such as those disclosed herein to impart other useful attributes, may optionally be included with the polymer composition as well.
Reinforcing fibers are melt processed into the amorphous polymeric matrix. The present teachings may be implemented using organic reinforcing fibers or inorganic reinforcing fibers. In accordance with preferred embodiments, the reinforcing fibers have an aspect ratio (length/diameter) of at least 10:1 on average. Non-limiting examples of fibers that may be suitable include carbon fiber, basalt fiber, glass fiber, wollastonite, cellulosic fiber, carbon nanotubes and graphene. Preferred reinforcing fibers are glass fiber and carbon fiber. In one embodiment, the reinforcing fiber comprises between 1 and 50% of the polymeric composite composition. In a preferred embodiment, the reinforcing fiber comprises between 5 and 30% of the composite composition. In a most preferred embodiment, the reinforcing fiber comprises between 10-25% of the composite composition.
In accordance with some compositions made in accordance with the present teachings, the polymeric composite comprises a lightweight filler. Lightweight fillers useful in applying the present teachings are those that can survive the aforementioned melt processing. Non-limiting examples of lightweight fillers useful in implementing variations within the present teachings include hollow glass microspheres, polymeric microspheres, cenospheres, perlite and pumice. Preferred lightweight fillers are hollow glass microspheres with crush strengths greater than 10,000 psi, such as the IM30K hollow glass microspheres commercially available from 3M Company (St. Paul, Minn.). In one embodiment, the lightweight filler comprises between 1 and 30 wt % of the polymeric composite. In a preferred embodiment, the lightweight filler comprises between 5 to 20 wt % of the polymeric composite. In a most preferred embodiment, the lightweight filler comprises between 5-15 wt % of the polymeric composite.
In another embodiment, additional fillers may be added to impart certain performance attributes to the composite material, such as flexural modulus and strength. Non-limiting examples of fillers include mineral and organic fillers including carbonates, silicates, talc, mica, wollastonite, clay, silica, alumina, carbon black, carbon nanotubes, graphite, graphene, solid glass microspheres, ceramics, and conventional cellulosic materials including: wood flour, wood fibers, sawdust, wood shavings, newsprint, paper, flax, hemp, wheat straw, rice hulls, kenaf, jute, sisal, peanut shells, soy hulls, or any cellulose containing material.
The present teachings set forth a polymer composite comprising a novel combination of types of fillers having substantially diverse aspect ratios and maximum dimensions. In accordance with a preferred embodiment of the present teachings, a polymer composite combines both rigid linear fibers and rigid spherical fillers in a polymer to achieve characteristics that favor a specific application, such as creating 3D printed tooling for sheet metal forming presses. The rigid linear fibers may have length-to-width ratios of 10:1 or greater whereas the spherical fillers inherently feature approximately uniform dimension in all directions. The rigid linear fibers may have lengths of, for example, 6 mm and diameters of less than 8 microns whereas the spheres may have an average diameter of, for example, 18 microns.
The mixture of fillers having such diverse morphologies leads to unobvious advantages in various attributes that result from the interaction of the two fillers and go beyond just the superposition of their respective effects. It is contemplated that other combinations of fillers having substantially diverse morphologies may exhibit a similar interaction and improve the physical and mechanical properties of an amorphous polymer, especially in pursuit of the aforementioned feedstock characteristics that make the polymer suited for forming high compressive strength tooling by 3D printing. In accordance with preferred embodiments, the aspect ratios of fillers preferably differ by at least a factor of two, but factors of five, ten or greater are considered preferable. For example, in conjunction with a spherical filler having an aspect ratio of 1:1, a second filler may comprise elongated rigid filaments that have an aspect ratio of 5:1. In this instance, the aspect ratios differ by a factor of five.
TABLE 1 sets forth a complement of specific polymers, reinforcing fibers and lightweight fillers that have been demonstrated to achieve advantages according to the present teachings and principles. It should be underscored that these enumerated species are not to be considered as limiting the scope of the claimed invention.
Topas 6017S-04, polycycloolefin copolymer,
commercially available from Polyplastics USA
(Farmington Hills, MI)
Various formulations of a polymeric composite materials, suitable for use as described herein, may be prepared using procedures and equipment that have been utilized in reduction to practice as outlined below. However, neither the present teachings nor the claimed matter should be construed to be limited in any respect by the complement of equipment, parameters and procedural steps set forth below.
To prepare the material samples, and obtain the data shown in TABLE 2 below, the following procedures were performed: Each of Samples 1-6 was prepared according to the weight ratios in TABLE 2. Samples 1-11 were separately, gravimetrically fed into a 27 mm twin screw extruder (52:1 L:D, commercially available from Entek Extruders of Lebanon, Oreg. as Model QC3. Compounding was completed using the following conditions: For Samples 1-6, the throat was at 100 C and barrels 2-14 and the die were at 220 C. The screw speed was 300 rpm and the output was 10 Kg/hr. For formulations 7-11, the throat was at 100 C and barrels 2-14 and the die were at 180 C. The screw speed was 300 rpm and the output was 10 Kg/hr. For Examples 1-11, The reinforcing fiber and lightweight fillers were separately fed downstream in a side stuffer in zone 5. The melt was extruded through a 3-strand die (3 mm diameter), conveyed onto a continuous cooling belt and pelletized into 3 mm×2 mm pellets. The subsequent pellets were injection molded using an ASTM tool and an Arburg 40-ton press. The barrel temperatures were 220 C for Examples 1-6 and 200 C for Examples 7-11. The resulting specimens were characterized for compression properties following ASTM 1621 and specific gravity following Archimedes Method.
In TABLE 2, the column labeled ‘Mixture’ is simply an index by which to reference the samples prepared with different amorphous polymers and admixture ingredients that were listed in TABLE 1. The next four columns describe the weight percentages of the polymer matrix and filler materials. The final three columns refer to empirically measured physical properties of the respective mixtures, namely the compressive strength (CS), the compressive modulus (CM) and the specific gravity (SG).
One pattern apparent in TABLE 2 is observed by comparing Mixture 5 to Mixture 2. These represent a consistent proportioning of reinforcing fiber at 15% by weight, yet replacing some of the polymer with 10 wt % of hollow glass microspheres. In the responsive attributes, the compressive strength and specific gravity essentially remain unchanged, yet the compressive modulus is notably increased by about 16%.
Another pattern evident in TABLE2 comes from comparing Mixture 11 to Mixture 8 wherein compressive qualities are similarly increased upon addition of the specified of hollow glass microspheres as the lightweight filler.
Further, in reviewing the trends along mixtures 4-5-6 and 9-10-11 in TABLE 2, wherein the proportion of the spherical filler particles is successively increased, both compressive strength and compressive modulus appear to generally increase as a function of adding low aspect ratio filler material, even as the overall density of the material is reduced. In other words, it is possible to reduce consumption of the amorphous polymer by trading some volume with the spherical particles of the lightweight filler, achieving acceptable strength and stiffness but without also undermining extrudability characteristics as may be the case using only the fibrous filler to replace the polymer.
It should be reiterated that compressive strength and compressive modulus are not the only important response variables when the material is to be applied as a feedstock for additive manufacturing as taught herein. Some tradeoffs of strength and stiffness may be acceptable in favor of enhanced ease of additive manufacture and physical attributes of the object so formed. Some of these attributes may be difficult to quantify. Therefore, some example mixtures shown in TABLE 2, as well as other proportions and other ingredients beyond those listed, may be preferable in a given manufacturing context for reasons that are not evident from just the compressive strength and modulus data alone. Although Mixture 3 indicates that it may be possible to achieve even higher strength and rigidity by the addition of reinforcing fibers alone, other attributes—related to ease of 3D printing, loss of resiliency, lubricity and machinability—may be impacted by adopting this mixture. An exchange of strength and stiffness to yield a better feedstock for additive manufacturing may be well justified given that additive manufacturing enables tooling designs that include interior voids, trabecular structures, ‘where-needed’ interior supports and the like which dramatically improve build times and reduce tool costs and material consumption.
Some important attributes of a finished object formed from the composite are affected by the proportions among the polymer matrix, the substantially elongated fillers and the substantially round fillers. These include, for example, compressive modulus when formed, tensile and compressive strength, resiliency after each load cycle, thermal coefficient of expansion (TCE), surface lubricity, ease of machining, surface durability and isotropic strength characteristics.
Yet other important attributes relate to facilitating 3D printing processes, some of which are different from or go beyond the material requirements in other applications, such as conventional machining or injection molding. Where a filament-fed extruder is used, some crucial properties include the ability to extrude the material into a durable filament for use as feedstock. Where DPE is used, certain qualities may promote the ability to be formed into pellets and to feed reliably into a DPE head. For both extruder types, the extruded material should exhibit good cohesion among printed layers and be stable at extruder temperatures, resistant to nozzle clogging, and able to preserve homogeneity of filler concentrations while going through melting, extrusion, deposition and cooling.
It is postulated that excessive proportions of either type of the fillers described above could be detrimental. A high concentration of elongated (high aspect ratio) or fibrous filler particles may detract from extrudability and inter-layer adhesion during additive manufacturing, as well as finished-part machinability and lubricity. On the other hand, a high concentration of spherical (low aspect ratio) particles, especially if homogeneity is not achieved, can lead to localized brittleness and ‘chip outs’ in the part surface during machining or during cycles of use. The use of spherical additive alone also does not reduce ‘cold flow’ nor improve the tensile or flexural strength of the composite material to the extent that fibers do. The finished part design may well require some members of the part to tolerate tensile and flexural forces with resiliency.
Aside from these concerns with using solely one or the other filler type, a rationale is contemplated for using both types in complement to achieve better overall attributes of the polymeric composite material.
As with the elongated particles of
In addition to the principal constituents mentioned above, various polymeric composite compositions according to the present teachings can also employ a variety of additives that can impart certain attributes and functionality to the resulting polymeric composite. Non-limiting examples of suitable additives include antioxidants, light stabilizers, fibers, blowing agents, foaming additives, anti-blocking agents, heat reflective materials, heat stabilizers, impact modifiers, biocides, antimicrobial additives, compatibilizers, plasticizers, tackifiers, processing aids, lubricants, coupling agents, thermal conductors, electrical conductors, catalysts, flame retardants, oxygen scavengers, fluorescent tags, inert fillers, minerals, and colorants. Additives may be incorporated into a polymeric composite polymer composition as a powder, liquid, pellet, granule, or in any other extrudable form.
Having described various polymeric composite materials as examples that embody the present teachings and principles, it is now appropriate to describe an example of manufacturing contexts and processes that influence the formulation of the composite and culminate in the construction of strong, durable components. A clear understanding of the equipment and processing steps affords a better appreciation for how the attributes of the feedstock material are crafted to support the overall production of tooling in this manner.
Extruder head 150 is shown to be attached to a carriage 151 that is controllably moved along the long axis of transverse beam 125 by the rotation of the shaft of an X-axis motor 124. Typically, beam 125 will comprise one or more linear bearings facilitating the smooth movement of carriage 151 parallel to the long axis of beam 125. Furthermore, beam 125 may house a lead screw (not distinctly visible in the diagram) which is coupled to carriage 151 by a precision nut, fixed within the beam 125 by rotary and thrust bearings and coupled to the shaft of X-axis motor 124. The rotation of the shaft of X-axis motor 124 may rotate the lead screw which, in turn, will cause carriage 151 to move closer to or further away from motor 124 in a controlled manner. X-axis motor 124 is often a stepping motor but may also be an AC or DC servo motor with a shaft position encoder and/or tachometer operating in a closed-loop control mode to facilitate moving to very precise positions. Many such arrangements of motors, lead screws, bearings and associated components are possible.
Whereas the arrangement of motor 124 and beam 125 accomplish controlled movement of the extruder head 150 in what may be termed the horizontal X-axis in the print-space coordinate system, motors 122A, 122B and their respective columns 123B, 123A may use a similar arrangement of linear guides, bearings and lead screws such that Z-axis motors 122A, 122B controllably move extruder head 150 in a vertical direction, that is, closer to or further away from build plate 130. More specifically, beam 125 may be attached to carriages (obscured in this view) that couple to lead screws within columns 123A and 123B. As Z-axis motors 122A and 122B rotate their respective lead screws in synchrony, the entirety of beam 125, X-axis motor 124 and extruder head 150 are caused to move upward or downward.
To accomplish yet another motion of build plate 130 relative to extrusion head 150, a third motor, which may be referred to as Y-axis motor 126 may act upon a lead screw 127 to which the build plate 130 is coupled. The rotation of the shaft of motor 126 controls the position of build plate 130. Build plate 130 may be supported by, and may slide or roll along, linear bearing rails such as rail 128.
It should be understood that the arrangement of motors, bearings and such depicted in
In addition, it should be understood that, for simplicity,
Extrusion head 150 is described in further detail below in conjunction with
To orchestrate the moving parts of the system to form a three-dimensional solid object upon the build plate 130 from extruded materials emanating from the tip of nozzle 158, a control box 160 is provided with electronics, such as a microprocessor and motor drive circuitry, which is coupled to the X, Y and Z motors as has been described above, as well as to numerous sensors and heating elements in the system 120. Electronics within control box 160 also control an extruder motor, to be described below, whether the extrusion is of the direct pellet extrusion type (
A wide variety of 3D printer control boards may be used. Some examples of suitable control electronics which may operate within control box 160 are the RAMBo™ control board manufactured by UltiMachine running Marlin firmware and so-called ‘Smoothie boards’ executing open-source Smoothieware firmware.
The primary role of such controller boards is to interpret sequential lists of positional commands, such as so-called G-code files and to output signals that drive the motors to implement the commanded movements. A G-code file, or the like, describing the coordinate movements necessary to form a particular object may be supplied to the controller through connection of the controller to a wired data communications network via, for example, TCP/IP communications through an Ethernet connection or via a wireless network connection, such as ‘WiFi’ or IEEE 802.11 connection. A G-code file (or a data file, such as a file in STL format from which a G-code file may be prepared) may also be supplied on a removable flash memory card, such as an SD card, which may be inserted at SD card slot 165 on control box 160.
For providing a human-accessible control interface, essentially all of the available control boards support an LCD display and user interface 164, as is shown to be a part of control box 160 in
Build plate 130 is preferably heated to a controlled temperature, most commonly using electrical resistance heating elements (not visible in the diagram) which may be mounted under the bed and thermally coupled thereto. For this purpose, it is common to use a heating mat made of high-temperature-rated silicone rubber that has electrically conductive paths embedded within and is adhered to the bottom of the build plate. A temperature sensor, such as a thermistor is typically included to provide feedback to a proportional-integral-derivative (PID) controller which maintains a set build plate temperature by controlling the application of heating current to the heating mat. Such elements for heating the build plate are commonplace and need not be further described here.
The temperature within enclosure 110 may be elevated over typical room ambient temperature by the addition of yet other heating elements (not shown) or simply by the heat incidentally dissipated from build plate 130. With a suitably insulated enclosure 110, heat from build plate 130 may be fully sufficient to heat the interior of the enclosure to beneficial levels by convection alone.
Representative of newer systems,
The operation of both a direct pellet extruder and a filament-fed extruder are briefly described next with reference to how attributes of the composite material may affect suitability for these respective techniques, especially in cases where it may be of practical advantage to accommodate both types of extrusion using a single undifferentiated formulation.
Recently applied to serve as moving 3D printing heads, direct pellet extruder of the type shown in
Another factor in favor of extruding directly from pellets is reduced cost. Plastics in pelletized form are considerably less costly than plastics that have already been formed into precise-diameter filament. Furthermore, because of the direct conversion from bulk pellets to molten form, a pellet extruder can print materials that are not amenable to being intermediately formed, stored and manipulated as solid filament, such as polypropylene, glass-filled polycarbonate, polyethylene and PVC. A direct pellet extruder can also support high throughput and large diameter discharge, such as through a 6 mm nozzle. This is considerably larger than the largest practical filament sizes of around 3 mm which often discharge through a nozzle opening of 1 mm or less. Thus, a direct pellet extruder can print large objects hundreds of times faster than a practical filament-supplied print head.
For explaining the general operating principles of direct pellet extrusion (DPE) head 150,
In
Heating stage 360 also comprises a temperature sensing element 364, such as a thermocouple that provides actual temperature information to a control unit that gate the flow of electrical current to the heating element 362 to maintain a constant desired temperature. This temperature control function may be integrated into or collocated with other control electronic circuitry within control box 160, introduced earlier. Many of the commonly available motor control boards have integrated temperature controller capabilities but this may also be handled by separate, commonly available closed loop controllers.
Heating stages 370 and 380 operate similarly to stage 360, each having respective heating elements 372, 382 and temperature sensors 374, 384 to achieve independent localized temperature control along extruder barrel 310. It is common for each heating element 362, 372, 382 to have an output rating in the hundreds of watts.
The effects of the heat thus applied to barrel 310, along with the compaction and propulsion of material through the barrel by lead screw 312, are apparent in that loose pellets 301, which are depicted as loosely arranged and which tend to settle downward under gravity within pellet hopper 320, are contacted and driven downward by lead screw 312. As the pellets are driven downward and enter transition zone 368, the pellets begin to soften and flow into one another and any interstitial air starts to be driven out due to the rising pressure. As the softened materials move into the more elevated temperature of melt zone 368, the melted plastic becomes homogeneous and free of any voids or air bubbles. In moving downward through the barrel, the materials reach full temperature and are driven down into nozzle 158 and they can be ejected as a continuous bead in the form of an extruded output 390. Even though a continuous outflow can be maintained indefinitely as long as pellets are supplied, it should be noted that, in more typical builds, the expulsion of extruded material can also be abruptly halted and resumed by the control of extruder motor 330, which is within the realm of what is motion-controlled subject to the same G-code scripting just as the X-Y-Z motors. In other words, the extruder can produce continuous streams or short segments of discharged material as needed for a given build process. Control of extruder motor 330 in coordination with the motion effected by the motors 122, 124, 126, results in controlled amounts of material being deposited in specific locations and patterns to construct a three-dimensional solid object on build plate 130.
Pellets 301 are provided to extruder head 150 from a remote location at pellet inlet 325. As mentioned previously, a long pellet feed tube 152 may deliver air-borne pellets using blasts of compressed air. As a burst of air carries pellets into the extruder head 150, the pellets fall into a holding chamber 322 and the air that carried the pellets disperses upward through an air filter 328 which comprises a fine screen or filter medium 327, such as a fluted paper filter. Air filter 328 traps any pellets that are propelled upward by an incoming air blast and allows them to settle into chamber 322 when the blast subsides. Air filter 328, especially filter medium 327, also captures extraneous debris or powder that might arrive with a burst of pellets.
As pellets within feed hopper 320 are consumed by the extrusion process, being pulled into extruder barrel 310 by lead screw 312, pellets in holding chamber 322 drop into feed hopper 320 and the overall level of pellets in chamber 322 slowly diminishes. A pellet level sensor, such as a capacitive proximity sensor 324, detects the presence or absence of pellets above a given level in the holding chamber 322. When sensor 324 senses that the fill level of pellets within chamber 322 is below a threshold, it sends an electrical signal indicating that more pellets are needed and this signal (either directly or through a control circuit in control box 160) causes electrically-actuated air valve 145 (
To support successful operation of a direct pellet extruder as just described, a feedstock composite material must exhibit certain favorable characteristics, such as the ability to be rendered in the form of pellets, spheres or the like. It is highly desirable that pellets of a candidate composite material are light enough to be borne by air bursts and have little tendency to stick to one another or to get hung up in the pathway between the inlet 325 and the transition zone 368 at which the pellets are fully engaged and forcefully driven by extruder screw 312. Surface physics and glass transition dynamics may be important under some circumstances. Surface finish of pellets, such as concavities, flat surfaces and spurs may impact successful feeding, depending on other factors. Finally, some areas of tapering within the extruder, especially near the nozzle, may be prone to clogging as filler particles may become oriented and either coalesce into quasi-organized clumps or into tangles. Selection of fill material and size may affect how well a composite material prints using a DPE. In particular, as it relates to the present teachings, a mixture of filler materials having diverse shapes or aspects ratios may afford some improvement in one or more of these characteristics when a DPE is used.
A force for driving filament 401 into and through the passage 410 is provided by extruder drive motor 430 which turns a knurled or ribbed drive gear 431. Gear 431 firmly contacts filament 401 and the knurling or ribs provide traction, with a pinch roller 432 providing opposing force to help grip the filament. Drive motor 430 is typically a computer-controlled servo or stepping motor for providing precise filament advancement in synchrony with other movements of the extruder head relative to the build plate.
As the filament driven by extruder drive motor 430 is pushed within tube 410 towards heater block 414, a particular phenomenon occurs wherein the filament softens just enough to spread and form a perfect seal against the inner walls of tube 410. A localized rigidity gradient is formed within the material and forms a notably stable seal. Were any hotter, softer portion of the material to attempt to seep upward past the ‘seal’, the portion would immediately cool and become integral with the cooler, harder portions above.
In seeming contradiction to the goal of heating and extruding the filament, a cooling block 414 is shown to be thermally coupled to tube 418. Without the benefit of cooling block 414, heating block 412 might heat the entire length of tube 410, especially if the apparatus were to remain idle for a period of time. The uppermost end of tube 410 could then exceed the softening or glass transition temperature of the filament material, at which point the desired seal effect just described would be lost and molten material would exude over the top of the tube. Cooling block 414 is provided to assure that the entirety of tube 410 does not elevate to melt temperatures and, moreover, to control the location where the internal self-sealing phenomenon occurs. A transition region 422 generally designates a small section along tube 410 at which the temperature crosses over between the lower temperature of block 414 and the higher temp of block 412. The actual location of where the seal forms may fall somewhere within section 422 or may be slightly further within block 412 or within block 414, depending upon material flow rates, thermal conductivities, temperature settings, etc.
Selection of a thin-walled tube 410 can reduce the path for thermal conduction in the short segment between heating block 412 and cooling block 414, which reduces the thermal load on each of these members as they strive to maintain their respective temperatures.
Cooling block 414 is equipped to dissipate heat due to conduction or convection from nearby heating block 412. The most common technique is to provide cooling block with heat dissipating fins made from a highly thermally conduction material, such as aluminum, and blowing ambient room air over the fins using a small electric fan 411. Block 414 may alternatively be liquid cooled by circulating a coolant gas or liquid through passages in the block. This approach may be preferred where a heated build enclosure is in use and the nearby ambient temperatures would offer far less cooling efficiency.
In some equipment designs, the extruder motor drive 430 may physically located just above the cooling block 414 and heating block 412 and may be mounted (as upon carriage 251 in
To support successful operation of a filament extruder arrangement as just shown, the feedstock material, provided in the form of filament 401, needs to be capable of being formed into filament and then exhibit sufficient flexibility to be spooled onto reel 402. Temperature-related characteristics such as glass transition rheological properties and thermal stability may render some potential feed stock compositions more suitable than others for filament-fed 3D printing processes. An additional concern when considering filled thermoplastic composite materials is clogging of nozzles due to gathering and clumping of filler material. This is of particular concern if nozzle taper or other prevailing conditions encourage filler particles to align, gather or tangle to form a filler-enriched plug.
In accordance with a preferred embodiment, lightweight filler 506 may comprise particles that, unlike filler 504, are not significantly elongated and may, in fact, be spherical. In particular, lightweight filler 506 may comprise hollow glass spheres to reduce density and provide significant compressive strength and other advantages to be described herein.
Melt process 510 combines these components into a homogenous composite material that may be drawn or extruded into a feedstock in the form of filament 520 or may be calendared, chopped, cast or otherwise pelletized into a feedstock in the form of pellets 530.
Filament 520 may then be provided, such as upon spool 522 to a filament-fed 3D printer 524, that is, one that uses a filament extrusion head similar to that shown in
Alternatively, the composite material in the form of pellets 530, may be provided in bulk form 532 and provided to pellet-fed 3D printer 534 which comprises a direct pellet extrusion head of the type depicted in
Regardless of which type of printer is used, the resulting printed forming tool 550 benefits from the unique ability of additive manufacturing to provide for internal supports 551 in the form of struts, walls, truss structures, waffled fills, interstitial voids and the like, as would be difficult or impossible to form by more traditional means. Large-format tools especially benefit from being additively produced to only place material where needed. At this stage, certain properties of the polymeric composite can facilitate or reduce the burden associated with some of this post-processing. For example, tooling for forming sheet metal into final part shape measuring 1 meter by 0.5 meter and having a relief depth of 0.25 meters may be quickly and efficiently produced from a composite material embodying the present teachings.
Preparing press die tooling by additive manufacturing of the recommended dual-filler composite offers many significant advantages. Large-format tooling can be fabricated relatively quickly and inexpensively compared to all-metal tooling, making even short-run tooling cost effective. Furthermore, because of the increased rigidity and compressive strength imparted by the dual fillers, deep excursion tooling including internal truss structures, struts and lightweighting interior voids are made possible using an extrudable thermoplastic matrix. This large-format tooling may be applied to general purpose flat press jaws and, due to the light weight compared to metal tooling, tool change outs may be carried out more readily and safely than with metal counterparts. In the context of using thermoplastic materials for creating press dies, large format may refer to die dimensions, raw material sheet dimensions or final part dimensions that exceed 0.25 square meters in surface area or have at least one dimension exceeding 0.50 meters. Alternatively, the term ‘large format’ may refer to die dimensions, raw material sheet dimensions or final part dimensions having at least one linear dimension that exceeds one or more values from the set consisting of 0.25 meters, 0.50 meters, 0.75 meters, 1 meter, 1.4 meters, 2.0 meters and 3.0 meters. Additionally or alternatively, the term ‘large format’ may refer to die dimensions, raw material sheet dimensions or final part dimensions wherein the area exceeds one or more values from the set consisting of 0.125 square meters, 0.25 square meters, 0.50 square meters, 0.75 square meters, 1 square meter, 1.4 square meters, 2.0 square meters, 4.0 square meters and 9.0 square meters.
Depth of impression made in the sheet metal may also distinguish ‘large format’ tooling. In proportion to the lateral dimensions discussed above, depth of impression may be 10% or greater, though even some shallow reliefs could be very demanding on tooling if there are significant localized slopes. In absolute measurements, a depth by which a press permanently deforms a flat sheet to form a large format part may be in ranges such as 0.1 meter or greater, 0.2 meter or greater, 0.3 meters or greater, 0.5 meters or greater. While some implementations have sought to use polymers as linings atop shaped metal dies, the present teachings recommend and enable the constructing of press dies completely by additive manufacturing using the particular multiple-filler thermoplastic composition, adapting generic flat press jaws to the desired die cavity shape. This ability for the additively formed tooling to be fully complete and self-contained may in some cases eliminate the need to prepare any part-specific or complementary metal tooling as backing behind the polymeric die face. This practice also facilitates changing out different tooling sets on a given multi-purpose press.
The relative proportions of the amorphous polymer 502, filler 504 and filler 506, along with possible additives 508, may be adjusted to improve the ability to machine, polish or otherwise prepare the surface of forming tool 550. For example, the addition of fillers that stiffen a polymer or alter the thermal conductivity can lead to cleaner, more precise cuts from milling bits with less stringing and collateral melting. However, excessive concentrations or inhomogeneous distribution of some fillers can lead to voids or ‘chip outs’ during machining that causes pits in the surface.
Even though complementary press dies 550 and 555 are shown for illustrative purposes, single-face press dies are equally possible that work in conjunction with rollers or in hydroforming processes. Depending on the design of the final part to be formed, some press dies may be designed to impart only singly curved bends, folds or curvatures and, even with multiple such turns on a single workpiece, if the bends, folds and curvatures do not intersect or overlap within the boundaries of the sheet being formed, there is minimal need to forcefully elongate parts of the sheet stock. In more demanding applications involving doubly curved surfaces, intersecting bends or deeper drawn portions, the press die may be designed to apply significant elongating forces to the sheet stock.
The action of the press with the 3D printed forming tools in place is depicted in
Blank 570 is inserted (stage 572) between the jaws of the press and, in particular, between opposing forming tools 550 and 555 formed in accordance with various aspects of the present teachings.
Compression stage 573 corresponds to pressing the jaws 559 together, trapping blank 570 therebetween and applying sufficient force to displace, deform or reshape the blank according to the design of forming tools 550, 555. In some applications, the compression step may accompanied by heating the blank, the forming tools, or both. The compression process may also include the application of a vacuum, a lubricant or a cover gas. In large presses, the overall force applied to the jaws may be several tons and the overall cycle time may range from fractions of a second to several minutes, depending on the material being formed. In some processes, blank 570 may initially be inserted in a somewhat pliable form but then may undergo hardening, cooling, drying, phase change or a chemical reaction, such as polymerization, to become more permanently shaped in compliance with the cavity defined by the forming tools. After the necessary forming cycle is completed, separation stage 574 is performed wherein jaws 559 are drawn apart and the formed part is removed from the press.
The present teachings as to a polymeric composite and a 3D printing process for creating polymer forming tools is not constrained to the present example involving a sheet metal blank, though this utilization is considered to be particularly challenging and the present teachings are considered particularly advantageous in addressing those challenges. The present teachings may be applicable to vacuum forming and lay up forms as well, depending on compatibility of materials and solvents, where used.
Throughout stages 572-574, compressive strength and modulus, lubricity and abrasion resistance may be at least some useful qualities in considering a material from which to make the tools and in considering the proportions of amorphous polymer, elongated and non-elongated fillers and optional additives from which to make a polymeric composite suitable for the forming tools.
In the preceding description, various exemplary embodiments have been described with reference to the accompanying drawings. It will be evident, however, that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the scope of the invention as set forth in the claims that follow. For example, certain features of one embodiment described herein may be combined with or substituted for features of another embodiment described herein. The description and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.
This application claims the benefit of priority under 35 U.S.C. 119(e) to U.S. provisional patent application No. 63/302,814, which was filed on Jan. 25, 2022 and is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63302814 | Jan 2022 | US |
