BACKGROUND

[0001] A three-dimensional (3D) printer may produce a 3D object based on a predetermined set of instructions. For example, the 3D printer may include an extruder assembly to melt a filament (e.g., a polymer filament, a metal filament, a carbon fiber filament, a ceramic filament, a wood composite filament, etc.) by heating the filament. The extruder assembly may deposit the melted filament at predetermined locations on a print bed. For example, the extruder assembly or the print bed may move so the extruder assembly is aligned with the predetermined locations. The filament may cool and solidify at the predetermined locations. Additional layers of filament may be melted and deposited on previous layers to construct the 3D object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1A is a longitudinal cross-section view of an example extruder tip to extrude melted filament at high speed.

[0003] Figure 1 B is a perspective view along the nozzle axis of the example extruder tip to extrude melted filament at high speed.

[0004] Figure 2 is a perspective view along the nozzle axis of an example extruder assembly to extrude melted filament at high speed.

[0005] Figure 3 is a longitudinal cross-section view of another example extruder assembly to extrude melted filament at high speed.

[0006] Figure 4 is a longitudinal cross-section view of another example extruder tip to extrude melted filament at high speed.

[0007] Figure 5 is a longitudinal cross-section view of an example extruder barrel to extrude melted filament at high speed.

[0008] Figure 6 is a longitudinal cross-section view of another example extruder barrel to extrude melted filament at high speed.

DETAILED DESCRIPTION

[0009] An extruder assembly may include a filament gripper to push filament through an extruder tip. The extruder tip may melt the filament so that it can be deposited on the print bed. As used herein, the term "extruder tip" refers to a device that transfers heat to the end of a filament and outputs melted filament. The extruder tip also may be referred to herein as a nozzle, a melt region, a heater barrel, a tapered barrel, or a tapered heated region. The extruder assembly may also include a cooled region (e.g., a heat sink region) that prevents the filament from melting before it enters the extruder tip. In addition, the extruder assembly may include an encoder to measure the position of the filament. As used herein, the term "extruder assembly" refers to a device that takes in solid filament and outputs melted filament at specified rate.

[0010] The extruder tip may include a barrel defining a cavity into which the filament gripper feeds the filament. In an example, the cavity may be wider than the filament until the filament reaches an impingement surface, so there may be a gap between the filament and the barrel walls forming the cavity. Heat may be transferred to the filament as it travels down the cavity towards the impingement surface. At the impingement surface, additional heat may be transferred to the filament, and the cavity may narrow to an output width. In an example, the impingement surface is sloped at a 45-degree angle.

[0011] As used herein, the term "slope" refers to a change in a radial distance from a nozzle axis to a line coplanar with the nozzle axis (e.g., a line on the impingement surface or connecting two points on the impingement surface) between first and second locations on the line divided by the longitudinal distance along the nozzle axis between the first and second locations. As used herein, the term "nozzle axis" refers to an axis of a cylindrical-shaped cavity of an extruder tip or a similarly oriented and positioned line for a non-cylindrical-shaped cavity. As used herein, the term "radial" refers to planes, lines, vectors, etc. normal to the nozzle axis. As used herein, the term "longitudinal" refers to planes, lines, vectors, etc. parallel or coinciding with the nozzle axis. As used herein, the "angle" of a slope or an angle of narrowing or tapering refers to an arctangent of the slope. For example, referring to Figure 1A, the average slope may be AR/ΔΖ, and the angle ø may be the arctangent of AR ΔΖ.

[0012] At higher extrusion speeds, some of the melted filament pushed against the impingement surface can flow back into the gap between the filament and the barrel wall forming the cavity. The thicker backflow reduces the transfer of heat from the barrel to the filament relative to a filament in direct contact with the barrel. The temperature may drop steadily across the backflow from the barrel wall to the edge of the filament, and the temperature gradient at the edge of the filament may be shallow. Little heat may be transferred across the shallow temperature gradient. Accordingly, the filament is still cool when it reaches the impingement surface. The time needed for the filament to melt once it reaches the impingement surface limits how quickly the filament can be extruded. Moreover, the inefficient transfer of heat necessitates additional force be applied to the filament to melt and extrude the filament. There is a limit to how much force can be applied to the filament before the filament gripper starts to slip and strip the surface of the filament. Thus, the extrusion speed is unnecessarily limited by the additional force needed. Filament could be extruded more quickly and with less force if the backflow of melted filament into the cavity was reduced and heat was delivered efficiently to the filament.

[0013] Figure 1A is a longitudinal cross-section view of an example extruder tip 100 to extrude melted filament at high speed. The extruder tip 100 may include a barrel 1 10, which may define a cavity 120. The extruder tip 100 may include a heating element 130. The heating element 130 may generate heat and transfer the generated heat to the barrel 1 10. The barrel 1 10 may include an impingement surface 1 12 bounding the cavity 120. The cavity 120 may receive a filament at a first end 122 of the cavity 120, and the impingement surface 1 12 may deliver heat to the filament to melt it. The melted filament may be extruded out of a second end 124 of the cavity 120. The impingement surface 1 12 may cause the cavity 120 to narrow from the first end 122 to the second end 124. The impingement surface 1 12 may force melted filament away from the solid filament. Heat may be transferred to the solid filament more efficiently after the melted filament has been forced away from the solid filament.

[0014] A longitudinal length of the impingement surface 1 12 (e.g., the length ΔΖ in the illustrated example) may be substantially a longitudinal length of the barrel 1 10 (e.g., the length £ in the illustrated example). As used herein, the term "substantially" refers to a value that is at least 50%, 60%, 70%, 75%, 80%, 90%, 95%, 100%, or the like of another value. In the illustrated example, the impingement surface 1 12 may not extend all the way to the first end 122 but may extend the remainder of the barrel 1 10 to the second end 124 (i.e., the impingement surface 1 12 may extend to an exit to the barrel). In alternate examples, the impingement surface 1 12 may extend all the way to the first end 122 but not all the way to the second end 124, may not extend all the way to either end, or the like. The length of the impingement surface 1 12 being substantially that of the entire barrel 1 10 may transfer heat to the filament more efficiently than a short impingement surface with the remainder of the barrel having a gap between the barrel wall and the filament. In some examples the impingement surface 1 12 may narrow at one, two, three, four, five, six, ten, 15, 20 degrees or the like.

[0015] Figure 1 B is a perspective view along a nozzle axis of the example extruder tip 100 to extrude melted filament at high speed. The impingement surface 1 12 may entirely encircle the cavity 120. As a result, the impingement surface 1 12 may narrow the cavity 120 from all directions. The melted filament on all sides of the filament may be forced away from the solid filament as the filament travels down the cavity 120. The impingement surface 1 12 may transfer heat to the solid filament more efficiently when the melted filament has been removed from between the solid filament and the impingement surface 1 12. Removing the hot melted filament may allow the temperature gradient between the impingement surface 1 12 and the cool solid filament to be maximized. More heat may be transferred when the gradient is larger, and the solid filament may melt more quickly.

[0016] Figure 2 is a zoomed, longitudinal cross-section view of an example extruder assembly 200 to extrude melted filament at high speed. In the illustrated example, a filament 220 may arrive at an impingement surface 212 shortly after leaving a cooled region 230 of the extruder assembly 200 and entering a heated region 210 of the extruder assembly 200. The impingement surface 212 may melt the filament 220, which may result in melted backflow 222. The melted backflow 222 may travel back towards the cooled region 230 where it may solidify to form solid backflow 224. The melted backflow 222 may interfere with the transfer of heat from the impingement surface 212 to the filament 220. [0017] However, in the illustrated example, the amount of melted backflow 222 is minimal. The impingement surface 212 may be substantially the length of the heated region 210 and may have a shallow slope. Because of the length and shallow slope, the area that can be occupied by the backflow 222, 224 may be minimal. The distance before the filament 220 arrives at the impingement surface 212 may be small as may be the space between the filament 220 and the impingement surface 212 at the beginning of the heated region 210. Moreover, the filament 220 may be in direct contact with the impingement surface 212 for most of the length of the impingement surface 212 (e.g., including portions of the impingement surface not illustrated). Accordingly, heat may be transferred to the filament 220 efficiently in the heated region 210, and the filament 220 may be extruded quickly and with minimal force.

[0018] Figure 3 is a longitudinal cross-section view of another example extruder assembly 300 to extrude melted filament at high speed. The extruder assembly 300 may include a heated portion of a barrel 310, which may define a cavity 320. The heated portion of the barrel 310 may receive heat from a heating element 330. The heated portion of the barrel 310 may connect to a heat sink 340. The materials of the heated portion of the barrel 310 and the heat sink 340 may be selected to minimize heat transfer from the heated portion of the barrel 310 to the heat sink 340. Similarly, the size of the connection may be selected to minimize heat transfer. The heat sink 340 may maintain the filament at a cool temperature at which the filament remains solid. The heat sink 340 may ensure the filament remains solid until it enters the heated portion of the barrel 310 to be melted and extruded.

[0019] The extruder assembly 300 may also include a filament gripper 350 and an encoder 360. The filament encoder 360 may detect motion of the filament and determine the position, speed, or the like of the filament. For example, the filament encoder 360 may include a rotary encoder, an optical encoder, or the like to detect motion of the filament. The filament gripper 350 may apply a force to the filament to push it through the heat sink 340 and the heated portion of the barrel 310. For example, the filament gripper 350 may be a gear with a plurality of teeth or may include a plurality of gripping members to apply the force to the filament. [0020] The heated portion of the barrel 310 may include an impingement surface 312, which may bound the cavity 320. The impingement surface 312 may be substantially a length of the heated portion of the barrel 310. For example, the impingement surface 312 may not continue all the way to a first end 322 or all the way to a second end 324 of the heated portion of the barrel 310 but may otherwise continue for the remainder of the heated portion of the barrel 310 (e.g., the impingement surface 312 may not extend to an exit to the barrel). In the illustrated example, the impingement surface 312 may narrow by tapering at an angle less than seven degrees. As used herein, the term "tapering" refers to a continuous and constant sloping of the impingement surface between a first location and a second location. The impingement surface 312 may taper smoothly rather than having varying slope or having sections where the impingement surface 312 does not narrow. In examples, the angle at which the impingement surface 312 narrows or tapers may be one, two, three, four, five, six, ten, 15, 20 degrees or the like. In an example, the impingement surface 312 may taper for its entire length.

[0021] The angle less than seven degrees may cause the melted filament to be forced forward when the impingement surface 312 forces the melted filament away from the solid filament. There may be little or no backflow of melted filament in the cavity 320. Accordingly, the filament gripper 350 may need to overcome little additional resistance from solidified backflow. The extruder assembly 300 may be able to extrude filament at a higher speed than printers with backflow for the same amount of force from the filament gripper 350. In addition, the shallow angle may provide minimal resistance to the filament. In some examples, the angle may be between one and five degrees (e.g., one degree, two degrees, three degrees, four degrees, five degrees, or the like). In an example, the angle may be selected based on a rate at which filament melts (e.g., a distance to melt a particular thickness of filament), which may be determined based on the speed at which filament is extruded and the temperature of the heated portion of the barrel 310.

[0022] As the filament melts, the impingement surface 312 may force the melted filament away from the solid filament. The solid filament may be left in contact with the impingement surface 312 or with a thin layer of melted filament between the solid filament and the impingement surface 312. Thus, the impingement surface 312 may maintain a steep temperature gradient at the edge of the solid filament, and heat may be transferred to the solid filament efficiently. The impingement surface 312 may continuously remove the melted filament from the surface of the filament while the filament is being melted by the steep temperature gradient, thereby exposing fresh solid filament to the steep temperature gradient. The impingement surface 312 may efficiently melt the filament at high speeds.

[0023] For small angles, manufacturing variances may result in a large region in which the filament may first contact the impingement surface 312. For example, a cavity 320 with a large radius due to a manufacturing variance and a small impingement angle may not be first contacted by the filament until a point far from the first end 322. If the filament first contacts the impingement surface 312 at a point far from the first end 322, the impingement surface 312 may not remove enough melted filament to transfer heat efficiently to the solid filament. If the filament first contacts the impingement surface 312 at a point too near the first end 322, the filament may not be melted when it arrives at the impingement surface 312, which may produce additional resistance. The angle of the impingement surface 312, a cross-sectional area of the cavity 320 at the beginning of the impingement surface 312, etc. may be selected so that the impingement surface 312 initiates contact with the filament in a predetermined region regardless of manufacturing variations in the impingement surface 312. The predetermined region may begin a predetermined length from the first or second end 322, 324, a predetermined length from the beginning or end of the impingement surface 312, or the like. The predetermined region may end a predetermined length from the first or second end 322, 324, a predetermined length from the beginning or end of the impingement surface 312, or the like. In some examples, the impingement surface 312 may narrow at an angle no less than 0.5 degrees, one degree, two degrees, three degrees, four degrees, or the like. The cross-sectional area of the cavity 320 at the beginning of the impingement surface 312 may be selected based on an expected size of a filament, based on the angle, based on a manufacturing tolerance, or the like.

[0024] The heated portion of the barrel 310 may include a tapered region 314 bounding the cavity 320 after the end of the impingement surface 312. The tapered region 314 may taper at angle greater than seven degrees. For example, the tapered region 314 may taper at an angle of at least 30 degrees but no more than 60 degrees. In an example, the tapered region 314 may be included to aid with manufacturing of the cavity 320 and the impingement surface 312 that narrows at a small angle. Including the tapered region 314 may simplify construction of a tool to cut the cavity 320 while leaving the impingement surface 312 that narrows at the proper angle.

[0025] Figure 4 is a longitudinal cross-section view of another example extruder tip 400 to extrude melted filament at high speed. The extruder tip 400 may include a barrel 410 defining a cavity 420 and an impingement surface 412 bounding the cavity 420. The impingement surface 412 may be substantially a length of the barrel 410 and may extend approximately to an exit to the barrel 410. The cavity 420 may receive a filament that travels through the cavity 420 from a first end 422 to a second end 424. The impingement surface 412 may provide heat from a heating element 430 to the filament as it travels through the cavity 420. The filament may be melted as it travels through the cavity 420 and may be extruded out of the cavity 420 at the second end 424.

[0026] The impingement surface 412 may narrow at an angle less than seven degrees. In examples, the impingement surface 412 may narrow at an angle of one, two, three, four, five, six, ten, 15, 20 degrees or the like. The impingement surface 412 may not taper but rather may narrow in a plurality of discrete steps. In the illustrated example, each step may have a slope near 90 degrees. Nonetheless, a line connecting a point on the impingement surface 412 near the first end 422 and a point on the impingement surface 412 near the second end 424 may have a slope angle less than seven degrees. Accordingly, the illustrated impingement surface 412 may narrow overall at an angle less than seven degrees.

[0027] Figure 5 is a longitudinal cross-section view of an example extruder barrel 500 to extrude melted filament at high speed. The extruder barrel 500 may define a cavity 520 to receive a filament. For example, the filament may travel from a first end 522 of the cavity 520 to a second end 524 of the cavity 520 where it may be extruded from the extruder barrel 500. The extruder barrel 500 may include an impingement surface 510, which may bound the cavity 520. In the illustrated example, the impingement surface 510 may be substantially a length of the extruder barrel 500.

[0028] The impingement surface 510 may narrow at an angle less than seven degrees. For example, the impingement surface 510 may taper at a plurality of locations, but the impingement surface 510 may not narrow in between the locations. The instantaneous tapering at the plurality of locations may be at an angle greater than or equal to seven degrees (e.g., at an angle of 15, 30, 45, 60, 75 degrees, etc.). However, a line from a point near the beginning of the impingement surface 510 to a point near the end of the impingement surface 510 may have an average slope less than seven degrees. In examples, the average slope may have an angle of one, two, three, four, five, six, ten, 15, 20 degrees or the like.

[0029] In some examples, the impingement surface 510 may initiate contact with the filament in a predetermined region regardless of manufacturing variations in the impingement surface 510. For example, the overall angle of the impingement surface 510, a cross-sectional area at the beginning of the impingement surface 510, or the like may be selected to ensure the impingement surface 510 initiates contact with the filament in the predetermined region. In an example, the angle or length of the tapering at the first or second taper locations may be selected to ensure that contact is initiated in the predetermined region. The overall angle of the impingement surface 510 may also, or instead, be selected to ensure contact is initiated in the predetermined region. The impingement surface 510 may be in contact with the filament for substantially a length of the extruder barrel 500. In an example, the predetermined region where contact is initiated may be selected to ensure that the impingement surface 510 is in contact with the filament for substantially a length of the extruder barrel 500. The length of the impingement surface 510 may also be selected to ensure that the impingement surface 510 is in contact with the filament for substantially the length of the extruder barrel 500. For example, the impingement surface may be substantially the length of the extruder barrel 500.

[0030] The impingement surface 510 may reduce backflow of filament in the cavity 520. Any gap between the impingement surface 510 and a filament may disappear after the initial taper locations (e.g., first, second, etc. taper locations). The melted filament arriving at later taper locations may have nowhere to flow but forward. There may not be a gap into which the melted filament can flow, and solid filament behind the melted filament may push the melted filament forward. In addition, the long, shallow overall shape of the impingement surface 510 may cause little force to be applied opposing the direction of travel of the filament. As a result, there may be little or no backflow in the cavity 520.

[0031] The impingement surface 510 may maintain a steep temperature gradient at a boundary of the unmelted filament. The impingement surface 510 may maintain the steep temperature gradient for an entire distance the impingement surface is in contact with the filament. The narrowing of the cavity 520 may force melted filament on the edges of the filament forward. After the melted filament has been forced forward, little melted filament may remain between the impingement surface 510 and cool solid filament towards the center of the filament. There may be no material to moderate the temperature difference between the boundary of the unmelted filament and the impingement surface 510. Accordingly, the forcing of melted filament away from the boundary of the unmelted filament may maintain the steep temperature gradient. The impingement surface 510 may narrow for the entire distance it is in contact with the filament. As a result, the melted filament may be forced away for the entire distance, and the steep temperature gradient may be maintained for the entire distance. In some examples, the steep temperature gradient may also or instead be maintained by increasing the temperature from the beginning of the extruder barrel 500 to the end. Because the impingement surface 510 reduces backflow and maintains a steep temperature gradient, the force applied to the filament may be mostly or entirely dedicated to extruding melted filament out of the second end 524 of the cavity 520. The filament may be extruded at higher speeds with less applied force relative to an impingement surface that does not maintain a steep temperature gradient.

[0032] Figure 6 is a longitudinal cross-section view of another example extruder barrel 600 to extrude melted filament at high speed. The extruder barrel 600 may define a cavity 620. The cavity 620 may receive filament that is pushed from a first end 622 of the cavity 620 to a second end 624 of the cavity 620. The extruder barrel 600 may include an impingement surface 610 bounding the cavity 620. The impingement surface 610 may reduce backflow of filament in the cavity 620. The impingement surface 610 may also maintain a steep temperature gradient at a boundary of unmelted filament for an entire distance the impingement surface 610 is in contact with the filament.

[0033] The impingement surface 610 may narrow at an average angle less than seven degrees. In examples, the average angle may be one, two, three, four, five, six, ten, 15, 20 degrees or the like. In the illustrated example, the impingement surface 610 may not taper at a constant slope. Rather, the instantaneous slope may change across the impingement surface 610. For example, a longitudinal cross-section of the impingement surface 610 may produce a polynomial curve, an exponential curve, or the like. However, the overall slope from a point near the beginning of the impingement surface 610 to a point near the end of the impingement surface 610 may be less than seven degrees. The melt depth into the filament at the beginning of the impingement surface 610 may be minimal, so the impingement surface 610 may narrow gradually. As the area of the filament decreases, the melt depth may be deeper for the same volume of filament depth. To compensate, the impingement surface 610 may narrow more rapidly towards the end of the impingement surface 610 to remove more melted filament. Moreover, the beginning of the impingement surface 610 may be more susceptible to backflow, so the changing slope may also adjust according to the susceptibility to backflow. Thus, the impingement surface 610 may reduce backflow while maintaining a steep temperature gradient at the boundary of the unmelted filament for the entire distance the impingement surface is in contact with the filament.

[0034] The above description is illustrative of various principles and implementations of the present disclosure. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. Accordingly, the scope of the present application should be determined only by the following claims.