Patent Description:
Additive manufacturing techniques and processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though "additive manufacturing" is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer-aided design (CAD) model.

A particular type of additive manufacturing is more commonly known as 3D printing. One such process commonly referred to as Fused Deposition Modeling (FDM) comprises a process of melting a very thin layer of a flowable material (e.g., a thermoplastic material), and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous thin filament of thermoplastic material through a heated nozzle, which melts the thermoplastic material and applies it to the structure being printed. The heated material is applied to the existing structure in thin layers, melting and fusing with the existing material to produce a solid finished product.

The filament used in the aforementioned process is generally produced using an extruder. In some instances, the extruder may include a specially designed screw rotating inside of a barrel. The barrel may be heated. Thermoplastic material in the form of small pellets is introduced into one end of the rotating screw. Friction from the rotating screw, combined with heat from the barrel softens the plastic, which then is forced under pressure through a small opening in a die attached to the front of the extruder barrel. This extrudes a string of material which is cooled and coiled up for use in the 3D printer as the aforementioned filament of thermoplastic material.

Melting a thin filament of material in order to 3D print an item is a slow process, which is generally only suitable for producing relatively small items or limited number of items. As a result, the melted filament approach to 3D printing is too slow for the manufacture of large items or larger number of items. However, 3D printing using molten thermoplastic materials offers many benefits for the manufacture of large items or large numbers of items.

A common method of additive manufacturing, or 3D printing, generally includes forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying the bead of material in a strata of layers to form a facsimile of an article, and machining such facsimile to produce an end product. Such a process is generally achieved by means of an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the X, Y, and Z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber) to enhance the material's strength. The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down or otherwise flattened to some extent, and leveled to a consistent thickness, preferably by means of a tangentially compensated roller mechanism. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness, thus effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that each successive layer of flowable material is deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient enough to allow a new layer of such material to melt and fuse with a previously deposited layer, thus producing a solid part.

In the practice of the aforementioned process, a major disadvantage has been encountered. Material extruders, of the type used in near net shape 3D printing, are designed to operate at a constant steady rate in order to produce a steady, consistent homogeneously melted plastic bead. In most cases, however, the majority of heat energy required to melt the plastic is generated by friction from a screw turning inside a barrel. This steady extrusion rate, however, creates difficulties when 3D printing. Specifically, the computer numeric controlled (CNC) machine used to move the extruder-based print head cannot start and stop instantaneously, and must, by necessity, vary in speed as it traces the path required to print the part.

This combination of a machine moving at variable speeds and an extrusion head outputting material at a constant rate results in a print bead that could vary in size. That is, the bead is thicker when the machine head is moving slowly, and thinner when the machine operates at a relatively higher speed.

A common approach employed in addressing the aforementioned problem is to servo-control the extrusion screw, speeding it up when the machine is moving faster and slowing it down as the machine motion slows. Since much of the energy used to melt the plastic is generated by rotation of the screw in the barrel of the extruder, varying the speed not only varies the rate by which material is pumped through the extruder but it also varies the amount of heat energy generated for melting the flowable material, such as, e.g., thermoplastic. The consequential increased temperature results in the thermoplastic material being less viscous; and, therefore, flowing faster than when it is cooler and thereby more viscous. The effect is that the flow rate from the extruder at any point in time is determined not only by the rotational speed of the extrusion screw, but also by the recent history of rotation, which determines how hot and thus how viscous the melted material is. This means that in a system where the rotation speed of an extruder varies randomly with time, the amount of material flowing from an extruder at a specific rotation speed will not be at a constant rate. Therefore, if the extruder screw is servo-controlled to operate at a specific rotational speed for a specific velocity of the print head, the resulting printed bead will not be consistent. Thus, method and apparatus are needed to produce a consistent print bead size when 3D printing.

Furthermore, the extruder may function to take polymer material in pellet form, heat, soften, and mix the material into a homogenized melt, and then pump the melt under pressure into a die to form the material into a useful extruded shape. This may be accomplished by providing an auger-type screw rotating inside a heated barrel, for example. The geometry, clearances, composition, and functionality of the screw and a barrel of the extruder may be determined as necessary to provide an extruder that operates as desired.

The extruder may be provided with the goal of completely mixing the melted material (e.g., polymer material) into a smooth, consistent form with no unmelted pellet portions or temperature variations in the melted material. One method of achieving this objective includes installing a breaker plate at the exit end of the extruder. A breaker plate may be, for example, a disk or plate that has a series of holes that provide resistance to the flow of the polymer melt. The holes in the breaker plate may be uniform holes approximately <NUM>" inches in diameter, and may be machined through the entire thickness of the breaker plate so as to be aligned with the flow direction of the polymer melt. This breaker plate may restrict the flow of material, increasing pressure inside the extruder barrel which assists in the melting and mixing process. One or more mesh screens or filters may be installed before the breaker plate to further restrict flow and increase pressure to aid mixing.

There may an optimal pressure range within which a particular extruder operates most effectively. Generally, a breaker plate and one or more mesh screens are installed in an effort to generate and maintain this desired pressure during operation of the extruder. While the inclusion of a breaker plate and/or screen may improve some mixing characteristics, they may also introduce drawbacks. For example, the additional restriction to flow may reduce throughput. Additionally, different polymers may require different breaker plate and/or screen configurations to achieve a desired pressure. Thus, the breaker plate and/or screen may need to changed each time the polymer being extruded changes in order to achieve a desired pressure that corresponds to the extruded polymer.

Another approach to achieve enhanced mixing may be to include knobs or other shapes on the extrusion screw, creating a "mixing section" which agitates the melt. This approach may also reduce flow of the melt and, in some cases, the friction caused by the mechanical mixing action can create unwanted heat in the mixing section.

Another purpose of the screen and/or breaker plate may be to create a generally fixed amount of resistance to the material flow in the extruder. This may facilitate generating and maintaining a steady state melt process within the extruder. If the breaker plate and/or screen were not in place in a typical extruder configuration, the amount of resistance to melt flow, and thus the operating pressure inside the extruder may depend solely or nearly primarily on the amount of resistance created by the shape of the forming die through which the melt flows after exiting the extruder. It may then become difficult to achieve consistent operation since the extruder may process material through a variety of different die shapes, each with a different resistance to flow. Some dies may generate insufficient resistance to flow to achieve optimal operating pressure while others may generate significantly higher pressure than is desired. <CIT> discloses an apparatus and a method for additive manufacturing at ambient temperature. <CIT> discloses a 3D printer. <CIT> shows the preamble of claim <NUM>.

Aspects of the present invention relate to a method and apparatus for fabricating components via additive manufacturing as defined by the claims, such as, e.g., 3D printing techniques. Each of the aspects disclosed herein may include one or more of the features described in connection with any of the other disclosed aspects.

In one aspect, a system for additive manufacturing, according to claim <NUM>, includes a nozzle configured to translate along a first axis, a second axis perpendicular to the first axis, and a third axis orthogonal to the first and second axes, wherein the nozzle is operably coupled to: an extruder having an outlet and including a screw disposed within a barrel, and a pump having an inlet and an outlet. The inlet is coupled to the extruder, and the outlet is in fluid communication with the nozzle. The system also includes a pressure sensor for sensing a pressure of the inlet of the pump and a pressure of an outlet of the extruder, and a controller that causes a speed of the pump with respect to a speed of the screw to adjust and thereby apply a target pressure of flowable material at the outlet of the extruder. Further, the controller is programmed to change the target pressure from a first target pressure stored in a memory of the controller to a second target pressure stored in the memory of the controller based on a change of the flowable material from a first flowable material to a second flowable material.

In another aspect, a system for additive manufacturing may include a nozzle configured to translate along a first axis, a second axis perpendicular to the first axis, and a third axis orthogonal to the first and second axes. The nozzle may be operably coupled to: an extruder including a screw disposed within a barrel, and a pump having an inlet and an outlet wherein the inlet may be coupled to the extruder, and the outlet may be in fluid communication with the nozzle. The system may include a controller configured to modify a size of a bead extruded by the nozzle to maintain an approximately constant sized overlap between a plurality of adjacent beads.

In another aspect, an additive manufacturing method, according to claim <NUM>, for delivering a flowable material from a nozzle of a programmable computer numeric control machine (CNC) includes actuating an extruder having an extruder screw to form a flowable material, sensing a pressure of the inlet of a pump and a pressure of an outlet of the extruder with a pressure sensor, delivering the flowable material to a pump, and operating the pump at a speed. The method also includes adjusting at least one of the speed of the pump or a speed of the extruder based on a change from a first flowable material to a second flowable material, to change a target pressure from a first target pressure stored in a memory of the controller to a second target pressure stored in the memory of the controller.

As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus. The term "exemplary" is used in the sense of "example," rather than "ideal.

It may be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, the scope of the invention is defined by the appended claims.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary aspects of the present disclosure and together with the description, serve to explain the principles of the disclosure.

The present disclosure is drawn to a method and apparatus for fabricating multiple components via additive manufacturing techniques, such as, e.g., 3D printing. More particularly, the methods and apparatus described herein comprise a method for eliminating, or otherwise substantially minimizing variations in the flow-rate of a molten flowable material (e.g., a thermoplastic material) in an additive manufacturing process, by, e.g., providing a servo-controlled fixed-displacement pump (e.g., polymer pump) between the output of an extruder and an application nozzle of a CNC additive manufacturing machine. For purposes of brevity, the methods and apparatus described herein will be discussed in connection with fabricating parts from thermoplastic materials. However, those of ordinary skill in the art will readily recognize that the disclosed apparatus and methods may be used with any flowable material suitable for additive manufacturing, such as, e.g., 3D printing.

In one aspect, the present disclosure is directed to an extruder-based 3D printing head that can deposit melted material (e.g., thermoplastic material) when the print head is traveling at a high rate of speed. In another aspect, the present disclosure is directed to depositing material at a consistent controlled rate at any time regardless of melt temperature variations caused by the history of changes in rotational speed of a screw of the extruder.

In certain sectors of the plastics industry, there are applications in which polymer pumps (also referred to herein as a gear pump) are sometimes utilized, in conjunction with plastic extruders. A polymer pump is a fixed displacement gear pump, which meters a fixed amount of material with each rotation of the pump. Polymer pumps are typically used in operations such as the co-extrusion of two or more materials, where synchronization of the flow rates is critical.

In order for a polymer pump to function properly, the plastic extruder must supply melted material to the input of the polymer pump at a relatively fixed input pressure. The aforementioned method of controlling the rotation of the extruder screw by means of a servo loop (e.g., speeding up the rotation when the pressure drops, or is too low, and slowing down the rotation when the pressure is high) works well in a basic extrusion application because input pressure variations in such a situation are generally slight. As a result, only minor changes to the rotational speed of the extruder screw are necessary to ensure the polymer pump receives melted material at a relatively constant input pressure.

In 3D printing, however, the addition a polymer pump alone to regulate flow-rate does not work satisfactorily. The 3D printing process by nature requires frequent variations in the speed of the print head due to a number of factors. For example, one factor may include speed changes, which are required when applying material in tight arcs or through corners. Speed changes may be necessary when a change in direction of travel for the print head is required. Even with the addition of a polymer pump, variations in the flow rate of such a pump can be dramatic, resulting in servo demands for rapid and substantial changes in extruder rotation speed. A rapid change in extruder screw rotation speed does not immediately translate into a rapid change in flow rate of the melted flowable material. There is a substantial delay between a change in extruder screw speed and a resulting change in flow rate of the melted material. This delay makes the traditional steady state servo approach unworkable when operating with a polymer pump that varies in output rate. For example, if the extruder accelerates quickly, as material is advanced within, the input pressure to the polymer pump will drop, resulting in the servo system quickly increasing the speed of the extruder screw. A delay in the drop in input pressure until after material is moving in the polymer pump, combined with a delay in increased flow rate from the extruder, may allow the input pressure to drop low enough to interrupt a proper flow of material, which results in a deposited bead of inconsistent size and shape.

To address the aforementioned problem, the present disclosure utilizes a modified servo signal approach. Using special algorithms, the control system coordinates the extruder speed with the speed of the polymer pump (gear pump) so that speed increases and/or decreases in both units at the same time. In addition to being simultaneous, the speed changes may be proportional.

With reference now to <FIG> of the drawings, there is illustrated a programmable computer numeric control (CNC) machine <NUM> embodying aspects of the present disclosure. A controller (not shown) may be operatively connected to machine <NUM> for displacing an application nozzle along a longitudinal line of travel or x-axis, a transverse line of travel or a y-axis, and a vertical line of travel or z-axis, in accordance with a program inputted or loaded into the controller for performing an additive manufacturing process to replicate a desired component. CNC machine <NUM> may be configured to print or otherwise build 3D parts from digital representations of the 3D parts (e.g., AMF and STL format files) programmed into the controller. For example, in an extrusion-based additive manufacturing system, a 3D part may be printed from a digital representation of the 3D part in a layer-by-layer manner by extruding a flowable material. The flowable material may be extruded through an extrusion tip carried by a print head of the system, and is deposited as a sequence of beads or layers on a substrate in an x-y plane. The extruded flowable material may fuse to previously deposited material, and may solidify upon a drop in temperature. The position of the print head relative to the substrate is then incrementally advanced along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D part resembling the digital representation.

Machine <NUM> includes a bed <NUM> provided with a pair of transversely spaced side walls <NUM> and <NUM>, a gantry <NUM> supported on side walls <NUM> and <NUM>, carriage <NUM> mounted on gantry <NUM>, a carrier <NUM> mounted on carriage <NUM>, an extruder <NUM>, and an applicator assembly <NUM> mounted on carrier <NUM>. Supported on bed <NUM> between side walls <NUM> and <NUM> is a worktable <NUM> provided with a support surface disposed in an x-y plane, which may be fixed or displaceable along an x-axis. In the displaceable version, the worktable <NUM> may be displaceable along a set of rails mounted on the bed <NUM> by means of servomotors and rails <NUM> and <NUM> mounted on the bed <NUM> and operatively connected to the worktable <NUM>. Gantry <NUM> is disposed along a y-axis, supported at the ends thereof on end walls <NUM> and <NUM>, either fixedly or displaceably along an x-axis on a set of guide rails <NUM> and <NUM> provided on the upper ends of side walls <NUM> and <NUM>. In the displaceable version, the gantry <NUM> may be displaceable by a set of servomotors mounted on the gantry <NUM> and operatively connected to tracks provided on the side walls <NUM> and <NUM> of the bed <NUM>. Carriage <NUM> is supported on gantry <NUM> and is provided with a support member <NUM> mounted on and displaceable along one or more guide rails <NUM>, <NUM> and <NUM> provided on the gantry <NUM>. Carriage <NUM> may be displaceable along a y-axis on one or more guide rails <NUM>, <NUM> and <NUM> by a servomotor mounted on the gantry <NUM> and operatively connected to support member <NUM>. Carrier <NUM> is mounted on a set of spaced, vertically disposed guide rails <NUM> and <NUM> supported on the carriage <NUM> for displacement of the carrier <NUM> relative to carriage <NUM> along a z-axis. Carrier <NUM> may be displaceable along the z-axis by a servomotor mounted on carriage <NUM> and operatively connected to carrier <NUM>.

<FIG> shows a machine 1A, which may be a programmable computer numeric control (CNC) machine embodying aspects of the present disclosure. Features of machine 1A that correspond to features of machine <NUM> are indicated with the same numerals and may be provided in the same manner described above with respect to machine <NUM>. Machine 1A may include a carrier 25A that operates in a manner similar to carrier <NUM>.

As best shown in <FIG>, carrier <NUM> is provided with a base platform <NUM>, a gear box <NUM> fixedly mounted on the upper side thereof, and a mounting platform <NUM> rotatably mounted on the underside of base platform <NUM>. Fixedly mounted to the case of gearbox <NUM> is a positive displacement gear pump <NUM>, driven by a servomotor <NUM>, through a gearbox <NUM>. Gear pump <NUM> receives molten plastic from extruder <NUM>, shown in <FIG>, through an input port <NUM>, shown in <FIG>. Platform <NUM> may be provided with openings therethrough disposed along the z-axis of the carrier <NUM>. Gear box <NUM> may be provided with a gear arrangement having an opening therethrough and disposed coaxially with the aligned openings in gear box <NUM> and platforms <NUM> and <NUM>, operatively connected to platform <NUM> for rotation about the z-axis and rotatable about such axis by means of a servomotor <NUM> mounted on base platform <NUM> and operatively connected to such gear arrangement. Applicator assembly <NUM> may include an upper segment <NUM> and a lower segment <NUM>. Upper segment <NUM> includes a transverse portion 41a secured to the underside of mounting platform <NUM> for rotational movement about the z-axis. Upper segment <NUM> may be provided with an opening therethrough along such z-axis, and a depending portion 41b may be disposed substantially parallel relative to such z-axis. Lower segment <NUM> includes a housing 42b disposed on an inner side of depending portion 41b. Housing 42b may be mounted on a shaft journalled in a lower end of depending portion 41b, intersecting and disposed perpendicular to the z-axis of carrier <NUM>, and further housing 42b may be provided with a laterally projecting applicator head <NUM> at a free end thereof. Mounted on a gearbox <NUM> provided on an outer side of depending portion 41b (opposite housing 42b) is a servomotor <NUM> operatively connected through gearbox <NUM> to the shaft journalled in depending portion 41b. Servomotor <NUM> may be configured for pivotally displacing lower segment <NUM> in a y-z plane. A material tamping roller <NUM> (shown in <FIG>), rotatably mounted in carrier bracket <NUM>, provides a means for flattening and leveling a bead of flowable material (e.g., molten thermoplastic), as shown in <FIG>. Carrier bracket <NUM> may be adapted to be rotationally displaced by means of a servomotor <NUM> (shown in <FIG>), through a sprocket <NUM> and drive-chain <NUM> arrangement.

As shown in <FIG>, machine 1A may include a carrier 25A provided with a positive displacement gear pump <NUM>, driven by a servomotor <NUM> through a gearbox <NUM>. Gear pump <NUM> may receive molten plastic from extruder <NUM>, as shown in <FIG>. Material may be pushed out of gear pump <NUM> to an applicator head 43A. The material may proceed from gear pump <NUM> and through nozzle <NUM> to a substrate such as a surface of worktable <NUM> in front of material tamping roller <NUM>. Roller <NUM> may be rotatably mounted in carrier bracket <NUM>, and may provide a means for flattening and leveling a bead of flowable material as shown in <FIG>, for example. Carrier bracket <NUM> may be adapted to be rotationally displaced by means of a servomotor <NUM>, through a sprocket or gear <NUM> and a drive chain or belt <NUM>.

With reference to <FIG>, applicator head <NUM> of machine <NUM> may include a housing <NUM> with a roller bearing <NUM> mounted therein. Carrier bracket <NUM> is fixedly mounted to an adaptor sleeve <NUM>, journalled in bearing <NUM>. As best shown in <FIG>, a conduit <NUM> including an elongated, flexible material for conveying, e.g., a molten bead of a flowable material (e.g., molten thermoplastic) under pressure from a source (e.g., one or more extruder <NUM> and an associated polymer or gear pump) disposed on carrier <NUM>, to applicator head <NUM>, may be fixedly (or removably) connected to, and in communication with nozzle <NUM>. An intermediate portion of conduit <NUM> may be routed through the openings through gear box <NUM>, base platform <NUM> and mounting platform <NUM>, and along the z-axis of carrier <NUM>. In use, the flowable material <NUM> (e.g., melted thermoplastic) may be heated sufficiently to form a molten bead thereof, which is then forced through conduit <NUM> and delivered through applicator nozzle <NUM>, to form multiple rows of deposited material <NUM> in the form of molten beads, as described herein. Such beads of molten material <NUM> may be flattened, leveled, and/or fused to adjoining layers by any suitable means, such as, e.g., bead-shaping roller <NUM>, to form an article. Even though bead-shaping roller <NUM> is depicted as being integral with applicator head <NUM>, bead-shaping roller <NUM> may be separate and discrete from applicator head <NUM>. In some embodiments, the deposited material <NUM> may be provided with a suitable reinforcing material, such as, e.g., fibers that facilitate and enhance the fusion of adjacent layers of extruded flowable material <NUM>.

With reference to <FIG>, applicator head 43A of machine 1A may include a housing <NUM> with a roller bearings <NUM> mounted therein. A conduit <NUM> for conveying a molten bead of flowable material under pressure from one or more of extruder <NUM> and gear pump <NUM> to applicator head 43A may be fixedly (or removably) connected to, and in communication with, a nozzle <NUM>. Thus, applicator head 43A may operate in a manner similar to applicator head <NUM> of machine <NUM>.

In some embodiments, machines <NUM> and 1A may include a velocimetry assembly (or multiple velocimetry assemblies) configured to determine flow rates (e.g., velocities and/or volumetric flow rates) of material <NUM> being delivered from applicator heads <NUM> and 43A. The velocimetry assembly preferably transmits signals relating to the determined flow rates to the aforementioned controller coupled to machine <NUM>, which may then utilize the received information to compensate for variations in the material flow rates.

In the course of fabricating a component, pursuant to the methods described herein, the control system of the machine <NUM>, in executing the inputted program, may control the several servomotors described above to displace the gantry <NUM> along the x-axis, displace the carriage <NUM> along the y-axis, displace the carrier <NUM> along a z-axis, pivot lower applicator segment <NUM> about an axis disposed in an x-y plane and rotate bracket <NUM> about a z-axis thereof, in accordance with the inputted program, to appropriately deliver material <NUM> and provide the desired end product or a near duplicate thereof. The control system of machine 1A may control the several servomotors to display gantry <NUM>, carriage <NUM>, and carrier 25A in a similar manner to appropriate deliver material <NUM>.

With reference now to <FIG>, there is illustrated, a cross-sectional schematic representation of a thermoplastic extrusion and application system, along with a block diagram of an exemplary servo control circuit, according to aspects of the present disclosure. <FIG> depicts an extruder <NUM>, comprising a heavy duty screw <NUM>, rotatably mounted inside a barrel <NUM>, and driven by a servomotor <NUM> through a gearbox <NUM>. One or both of the screw <NUM> and barrel <NUM> may be made of steel. Pellets of material may be introduced into barrel <NUM> from a hopper <NUM>. Those of ordinary skill will recognize that the pellets may be of any suitable material. For example, in one embodiment, pellets may be made of thermoplastic material. In addition to pellets, the material may be delivered to hopper <NUM> in any suitable size or configuration. The pellets introduced into barrel <NUM> may be heated by the friction generated from the rotation of screw <NUM> and/or one or more barrel heaters <NUM> disposed alone a length of barrel <NUM>. Once the pellets have melted, the molten material may be forced under pressure by screw <NUM>, into a servo-controlled gear pump <NUM>, driven by a servomotor <NUM>, through a gearbox <NUM>. Subsequently, the molten material is delivered from an outlet of gear pump <NUM> to conduit <NUM> (<FIG>, <FIG>, <FIG>, <FIG>) for use in 3D printing activities, as described above.

A stable flow rate into conduit <NUM> and through application nozzle <NUM> may be regulated by providing servo control of the speed of gear pump <NUM>, through an exemplary controller formed by the machine's control computer <NUM> and servo control system, based on the speed of the CNC machine's moving axes. The speed of extruder screw <NUM> likewise may be regulated in proportion with the speed of gear pump <NUM> by a servo control loop. A signal from the gear pump servo loop is processed to control the output of the extruder servo drive in proportion with that of gear pump <NUM>, thus synchronizing the speed of the extruder with that of the gear pump by a predetermined proportion. In other words, the operation speed of gear pump <NUM> and extruder screw <NUM> may be dependent on one another. That is, the speed of extruder screw <NUM> may be determined as a function of the speed of gear pump <NUM>, and vice versa. The speed of extruder screw <NUM> also may be modified by inputs from one or more sensors <NUM> (e.g., a pressure sensor or a flow sensor) operably coupled to the extruder.

As the feed rate of the CNC machine changes, representative servo feedback signals from the moving axes are processed in the machine control computer <NUM> to control the speed of output pump <NUM>, and correspondingly, the speed of extruder screw <NUM>. Stated differently, machine control computer <NUM> serves to increase and/or decrease the speeds of extruder screw <NUM> and gear pump <NUM> based on increases/decreases in movement of CNC machine <NUM> during a 3D printing manufacturing process. In embodiments where sensor <NUM> is a pressure sensor, sensor <NUM> may monitor the pressure at the inlet of gear pump <NUM>, outputting an analog signal into servo controller <NUM> and/or machine control computer <NUM>, which in turn, influences the servo loop controlling the extruder screw <NUM> to bias, adjust, or otherwise fine tune the synchronized speed between extruder screw <NUM> and gear pump <NUM>, in order to compensate for pressure changes at the inlet of gear pump <NUM>. That is, changes in pressure at the inlet of gear pump <NUM> may further be used to modify the speeds of extruder screw <NUM> and/or gear pump <NUM> and the relative speeds thereof. By coordinating the speed of the gear pump <NUM> with the speed of the extruder screw <NUM>, while compensating for pressure variations, a constant output proportional to the feed rate of the CNC machine may be achieved at the output of gear pump <NUM>, and through application nozzle <NUM>. With this approach, input pressure is relatively constant because the extruder screw <NUM> and gear pump <NUM> change speeds at the same time, with minor adjustments being made to compensate for variables resulting from melt-temperature and pressure variations. Thus, the dimensions of a deposited bead of material remains relatively consistent and dimensionally stable throughout the application process.

<FIG> illustrates a cross-sectional schematic representation of a thermoplastic extrusion and application system, along with a block diagram of an exemplary servo control circuit. Extruder <NUM> may be driven by servomotor <NUM> through gearbox <NUM>, as discussed above with respect to machine <NUM> and <FIG>. A stable flow rate to conduit <NUM> and through nozzle <NUM> may similarly be regulated by providing servo control of the speed of gear pump <NUM>, through an exemplary controller formed by the control computer <NUM> and servo control system, based on the speed of the moving axes of machine 1A. Thus, machine 1A may be configured to provide a consistent and dimensionally stable bead of material in a manner described above with respect to machine <NUM>.

In addition to providing a consistent and dimensionally stable bead of material, CNC machines <NUM>, 1A may also include a gear pump control switch <NUM> that provides a user the ability to modify a size of the deposited bead of material. Control switch <NUM> may be a hardware switch connected to machine control computer <NUM> and may control a speed (e.g., revolutions per minute) of gear pump <NUM>, for example. By manipulating (e.g., rotating) control switch <NUM>, an operator may cause machine control computer <NUM> to increase or decrease the size of the deposited bead, as described below. After this manipulation, the modified size may be deposited in a consistent and dimensionally stable manner. Control switch <NUM> may be a knob, button(s), lever, or other physical switch. When physical, control switch <NUM> may be provided on a cabinet of machine control computer <NUM>, or may be provided at a location separate from machine control computer <NUM>. Control switch <NUM> may also be implemented as a "soft" switch (e.g., a switch, button, lever, or other feature) displayed on a touch-screen that may be operated by a user.

The ability to achieve a target pressure at an input of the melt pump by controlling the relative speeds of the extruder and gears of gear pump <NUM> may also create the ability to further refine a CNC machine such as CNC machine 1A, improving throughput while generating a properly mixed and thermally homogenized melt. For example, in an exemplary configuration shown in <FIG>, the target pressure may be achieved without the need to include a breaker plate or a screen. In one aspect, this may be achieved by control of gear pump <NUM> by a controller such as machine control computer <NUM>, which may output commands to servo controller <NUM> and/or servo drive output <NUM>. While the machine control computer <NUM>, servo controller <NUM>, and servo drive output <NUM> may be provided separately, one or more of these components may be combined. In one aspect, machine control computer <NUM> may form a single control device or controller that includes one or more servo controllers <NUM> for receiving feedback from servomotor <NUM> and servomotor <NUM>, and one or more servo drive outputs <NUM> that generate signals to drive servomotors <NUM> and <NUM>.

CNC machines <NUM>, 1A may be configured to generate and maintain a controlled target pressure at the input end of the gear pump <NUM>. As the input end of the gear pump <NUM> may also be an exit end of the extruder <NUM>, it may not be necessary to install a breaker plate or screen at the exit of the extruder to generate the pressure required for proper mixing in the extruder. The pressure at the inlet end of gear pump <NUM> may be determined or measured by one or more sensors <NUM>, which may include a pressure sensor as described above. As shown in <FIG>, an outlet end of the extruder <NUM> may also form an inlet end of the gear pump <NUM>. Thus, sensor <NUM> may include a single pressure sensor that is configured to sense both a pressure of the inlet of gear pump <NUM> and a pressure of the outlet of the extruder <NUM>.

In an exemplary embodiment, the CNC machines <NUM>, 1A may generate the required pressure by controlling gear pump <NUM> via machine control computer <NUM>. Machine control computer <NUM> is configured (e.g., programmed with software) to allow a target pressure to be adjusted. Thus, extruder <NUM> and gear pump <NUM> is able to accommodate different requirements that may be necessary for different materials (e.g., different polymers). In one aspect, machine control computer <NUM> controls extruder <NUM> and gear pump <NUM> to generate required pressure and/or adjust the pressure for a plurality of different polymers or flowable materials. For example, target pressures for a corresponding plurality of thermoplastic materials is stored in a memory of machine control computer <NUM>. Thus, when a first material having a first target pressure is extruded, machine control computer <NUM> controls the relative speeds of extruder <NUM> (e.g., screw <NUM>) and gear pump <NUM> to reach and maintain this target pressure. When the extruded material changes to a second material, machine control computer <NUM> changes these relative speeds to reach and maintain a second target pressure, allowing the CNC machines <NUM>, 1A to extrude multiple materials at different respective pressures. In one example, changing the relative speeds of the gear pump <NUM> and the extruder <NUM> is performed by maintaining the speed of the extruder <NUM> constant while changing the speed of gear pump <NUM>, or instead by maintaining the speed of gear pump <NUM> constant while changing the speed of extruder <NUM>. The relative speeds is also be changed by modifying both of these speeds by differing amounts.

The ability to generate the required pressure may be accomplished with a lower-cost system that reduces mechanical complexity without the need for a breaker plate or a screen (such as a filter) between an end of the screw <NUM> and gear pump <NUM>, as shown in <FIG>, for example. Control of gear pump <NUM> may be performed without unduly restricting throughput, resulting in higher flow rates for extruder <NUM>.

In an exemplary configuration, nozzle <NUM> may have an open round shape (<FIG>) which offers little resistance to material flow. Gear pump <NUM> may restrict flow to the nozzle <NUM>, thereby avoiding the need to provide a nozzle having significant resistance to material flow. A desired or optimal pressure within extruder <NUM> may be created and maintained by controlling the relative speeds of the extruder <NUM> and gear pump <NUM>.

Melt pumps may be used in steady state plastic extrusion processing for two exemplary purposes. First, melt pumps may provide a way of assuring a steady flow of material which overcomes the tendency of extruders to vary the flow rate or "surge" over time. Second, melt pumps may increase the pressure from the extruder to help force material through extrusion dies, which may have significant resistance to flow. Extruders may have a particular pressure range within which they operate optimally. If a die is provided and the pressure required to flow material through the die is higher than the optimal range, a melt pump may be used generate this higher pressure. However, by controlling flow with a gear pump (e.g., by restricting flow when necessary), the need for a breaker plate or a die may be eliminated. An optimal pressure within extruder <NUM> may be maintained, while pressure may be varied in a controllable manner. Thus, a predetermined pressure which is based on the requirements of the particular polymer material being extruded may be provided without changing parts. The configuration may also generate a consistent, controllable flow rate to the print nozzle, resulting in a quality print process.

Controlling flow with a gear pump may also eliminate the need for a mixing section, such as knobs, protrusions, or other shapes on the threading of an extruder screw. Thus, each of the threads of an extruder screw may present a uniform, even thread surface.

When additive manufacturing is performed to form a three-dimensional object, an example of which is shown in <FIG>, several separate beads <NUM> may be printed next to each other, to fuse with adjacent layers and form a solid one-piece object. Each of the two beads <NUM> may tend to form rounded edges. Thus, adjacent beads <NUM> disposed may tend to form a void or hole <NUM> at positions below and above the rounded edges of the beads <NUM>. These holes <NUM> may be undesirable for three-dimensional objects, particularly for objects printed for use in an autoclave. In order to avoid the formation of holes <NUM>, beads <NUM> may be deposited so as to overlap by a certain amount.

With reference to <FIG>, adjacent beads <NUM> may be deposited to have a desired overlap, which may be represented by a particular percent or amount. However, when a nozzle introduces this overlap while also moving by a constant amount throughout the print (e.g., when depositing parallel rows of beads), additional material may be squeezed out by roller <NUM>, forming squeeze-out material <NUM>. Squeeze-out material <NUM> may result in an overlap between two beads by an unintended amount in addition to the desired overlap. Squeeze-out material <NUM> may first occur with the third bead in a row of adjacent beads (resulting from material squeezed out when the second bead <NUM> is applied so as to overlap the first bead <NUM>), and may become larger for each subsequent bead in an exponentially-increasing manner. Thus, the overlap may quickly become significant, and may even result in one bead being deposited on another full bead of squeeze-out material <NUM>, an outcome which would be very undesirable. For example, as shown in the top view in <FIG>, each bead may be deposited by a CNC machine <NUM> programmed for a constant amount or percent of desired (calculated) overlap <NUM>. However, the actual amount the side of bead increases or squeezes out, may compound over time. As more beads <NUM> are printed, the squeeze-out material <NUM> may grow accordingly.

One potential process to counteract the formation of squeeze-out material <NUM> may employ a program that causes the nozzle <NUM> to move over the distance including the desired overlap, plus an estimated amount of squeeze-out material <NUM>, which may continue increasing. The nozzle <NUM> would have to move over different distances when printing subsequent rows, which may make programming difficult.

In order to keep the amount (e.g., percentage) of overlap <NUM> constant for each adjacent bead and keep the nozzle <NUM> moving over the same consistent amount for each row formed by a bead <NUM>, the size (e.g., width) of the third and any subsequent bead <NUM> may be reduced by a particular (e.g., the same) amount to prevent squeeze-out material <NUM> from building up. This reduction may be equal to a calculated amount of squeeze-out material <NUM> that would form if a size of the third bead is not reduced. This reduction may be the same for the third bead <NUM> and for each subsequent bead <NUM> adjacent to the third bead <NUM> in a direction perpendicular to a deposition direction.

In order to print the third bead <NUM> (and a subsequent bead <NUM>) with a reduced size, the print head may provide the ability to both: produce a consistent-sized bead <NUM> at different machine speeds, and change the bead <NUM> to a smaller or larger sized bead as desired, while still producing the bead <NUM> with a consistent (changed) size. This may be performed altering the relationship between the machine speed (e.g., a translation speed of nozzle <NUM>) and the melt pump speed. For example, a ratio of the machine speed to the gear pump <NUM> speed may be altered. Such an alteration of the machine or nozzle translation speed to the melt pump speed may be performed by at least one of a CNC "G" code program, or manually, by operating melt pump control switch <NUM>. In one aspect, the ratio of machine speed to nozzle translation speed may be changed to a first value based on a program stored by machine control computer <NUM>, thereby adjusting the size of the bead <NUM> by a first amount. The ratio of machine speed to nozzle translation speed may be changed to a second value based on the operation of control switch <NUM>, thereby adjusting the size of the bead <NUM> by a second amount. In one aspect, machine control computer <NUM> may increase or decrease the size of the bead <NUM> by a first amount. Manipulation of melt pump control switch <NUM> may increase or decrease the size of the bead <NUM> by a second amount. Thus, melt pump control switch <NUM> may be used to increase or decrease the first amount.

The machine speed to melt pump speed relationship may be altered in the CNC program to cause an increase or decrease in bead <NUM> size by a particular percentage. The bead <NUM> size can be increased or decreased by a lesser amount than the amount specified in the CNC program by operating control switch <NUM>. Thus, the control switch <NUM> may operate separately from the adjustment in the program, allowing manual adjustment of the size of the bead <NUM>.

For example, when first starting to print a three dimensional object, the bead <NUM> may differ by small amount than what was originally specified by the printing program. In one aspect, a slight operation of the control switch <NUM> may bring the bead <NUM> to the exact size that was used to program the production of the three dimensional object.

In one aspect, by providing a program and/or control switch for changing bead size during printing, the formation of holes, which may be present if the bead is smaller than what was specified in the printing program, may be avoided. Additionally, excessive squeeze-out, which may be present if every bead were produced larger than a size was specified in the printing program, may also be avoided. Thus, a part may be printed in a precise manner.

As shown in <FIG>, a plurality of beads <NUM> of flowable material may be deposited in a manner that can form a boundary or fill area <NUM> (e.g., a bounded area in which one or more beads <NUM> may be deposited to provide a fill). By depositing one or more beads <NUM> in a closed path, a periphery may be defined such that boundary or fill area <NUM> is located within the periphery. When a boundary is formed, the boundary or fill area <NUM> may result in the formation of a void <NUM>. In one aspect, control computer <NUM> may determine when void <NUM> would be formed if bead width <NUM> is provided with a value initially specified in a software (e.g., slicing software) program.

In one aspect, machine control computer <NUM> may be programmed to evaluate the boundary or fill area <NUM> and apply a standard size (e.g., width) for bead <NUM>. A standard width may be specified by slicing software. Machine control computer <NUM> may determine when the area <NUM> can be filled without a void by using the standard width, and deposit beads <NUM> accordingly.

In one aspect, control computer <NUM> may determine when void <NUM> would be formed if bead width <NUM> is provided with the standard width (e.g., a value initially specified in a slicing software program). Machine control computer <NUM> may be configured to determine when, by varying a width of a plurality of beads <NUM> by a particular (e.g., the same) amount, a void <NUM> may be filled. This may include modifying a size of a plurality, or all, of the beads <NUM> within boundary or fill area <NUM>. When control computer <NUM> (or a separate controller) determines that a void <NUM> will be formed in area <NUM>, as shown in <FIG>, control computer <NUM> may calculate a modified bead <NUM> size for a single bead that will completely fill void <NUM> in area <NUM>. This modified bead <NUM> size may be larger or smaller than the standard bead size which was used to deposit adjacent beads <NUM>. Thus, a size and/or shape of boundary or fill area <NUM> (and a size or shape of one or more adjacent beads in boundary or fill area <NUM>) may be used to determine a speed of gear pump <NUM> and/or a speed of translation of nozzle <NUM> that forms a plurality of beads <NUM> or a single bead <NUM> with an adjusted size to fill void <NUM>.

Claim 1:
A system for additive manufacturing, comprising:
a nozzle (<NUM>) for delivering a flowable material, the nozzle configured to translate along a first axis, a second axis perpendicular to the first axis, and a third axis orthogonal to the first and second axes, wherein the nozzle (<NUM>) is operably coupled to:
an extruder (<NUM>) having an outlet and including a screw (<NUM>) disposed within a barrel (<NUM>); and
a pump (<NUM>) having an inlet and an outlet, the inlet being coupled to the extruder (<NUM>), and the outlet being in fluid communication with the nozzle (<NUM>);
a pressure sensor (<NUM>) for sensing a pressure of the inlet of the pump (<NUM>) and a pressure of an outlet of the extruder (<NUM>),
and
a controller (<NUM>, <NUM>) that causes a speed of the pump (<NUM>) with respect to a speed of the screw (<NUM>) to adjust and thereby apply a target pressure of flowable material at the outlet of the extruder (<NUM>), characterized in that the controller (<NUM>, <NUM>) is programmed to change the target pressure from a first target pressure stored in a memory of the controller (<NUM>, <NUM>) to a second target pressure stored in the memory of the controller (<NUM>, <NUM>) based on a change of the flowable material from a first flowable material to a second flowable material.