Abstract:
3D Fused Filament Fabrication (FFF) is improved by heating the deposition nozzle with one or more non-contact heat sources. 3D FFF is also improved by cooling the deposition nozzle with one or more active cooling elements. Temperature control of the deposition nozzle is improved due to the reduction in mass of the nozzle by eliminating conductive heat elements and their associated devices, such as thermal transfer blocks. Responsiveness of the nozzle is improved by using lasers as non-contact heating sources, allow for rapid changes in temperature when necessary.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present invention relates to additive 3D fabrication, and, more particularly, to a fused filament fabrication extruder. 
         [0003]    2. Description of the Related Art 
         [0004]    The extrusion point of a Fused Filament Fabrication (FFF) 3D printer is commonly referred to as a hot end. In these printers, the hot end heats the material being extruded to create a 3D object. The hot end is typically connected to a 3 axis carriage which is typically a Cartesian or polar coordinate arrangement, and allow movement of a FFF deposition head freely in 3D space. Typically, the source of heat used to melt the extruded material is a conductive heater in contact with a heater block connected with the nozzle or liquefier tube feeding the nozzle. Heat is then spread primarily via conduction from the heat source to the nozzle. This process results in high thermal capacitance, due to the heat conducting through the entire heater block and nozzle mass. It also results in high thermal radiation waste heat, due to the relatively large surface area of the assembly. This means a relatively large amount of heat is lost to the ambient environment or significant mass and size from thermal insulation must be added to retain this heat. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
         [0005]    The following detailed description, is better understood when read in conjunction with the accompanying drawings. The accompanying drawings, which are incorporated herein and form part of the specification, illustrate a plurality of embodiments and, together with the description, further serve to explain the principles involved and to enable a person skilled in the relevant art(s) to make and use the disclosed technologies. However, embodiments are not limited to the specific implementations disclosed herein. 
           [0006]      FIG. 1  shows a block diagram of an exemplary system in which embodiments of a fused filament fabrication extruder are shown. 
           [0007]      FIG. 2  shows a block diagram of an exemplary system in which embodiments of a fused filament fabrication extruder with multiple material feedstock inputs is shown. 
       
    
    
       [0008]    Exemplary embodiments will now be described with reference to the accompanying figures. 
       DETAILED DESCRIPTION 
       [0009]      FIG. 1  illustrates a FFF hot end  100  of a FFF 3D printer according to embodiments of the present invention. In this embodiment, one or more non-contact heat sources  110  heat the FFF deposition nozzle  101 . In an example embodiment non-contact heat sources  110  may be a laser. In this example embodiment, heat is generated directly by the laser excitation of the nozzle  101 . The use of a laser heat source in this manner eliminates the need for heat transfer elements attached to the nozzle  101 , such as a metal block or resistive heater. 
         [0010]    The nozzle  101  extrudes a narrow strand of melted material  103 . The material feedstock  120  is shown as a cylinder however it can be of any shape or size. In an embodiment the shape could be a ribbon or other thin profile to allow for faster heating of the material feedstock  120 . Pressure is required to force the melted material through the nozzle  101 . 
         [0011]    Melt zone  130  is where the material feedstock  120  is liquefied by the heat of the nozzle  101 . There is a temperature gradient along the nozzle  101 . Sections of nozzle  101  farther from where non-contact heat sources  110  apply energy will be cooler. Sections of nozzle  101  far enough from the non-contact heat sources  110  energy may not be hot enough to melt the material feedstock  120 . Therefore the size of the melt zone  130  may be smaller than the size of the nozzle if high enough temperature gradients are present. It may be desirable to minimize the size of the melt zone  130  behind the nozzle  101  when it is necessary to frequently stop and start the flow of the material. 
         [0012]    Larger flows of melted material  103  may be desirable. A longer melt zone  130  increases potential melted material  103  flow volume. In this scenario any portion of the nozzle  101  that is not hot enough to melt the material feedstock  120  can be heated with addition non-contact heat sources  120 . These additional non-contact heat sources  110  can operate independently to extend the length of the melt zone, allowing for faster printing. If the non-contact heat sources  110  are lasers the high energy density allows quick response to changing print conditions by heating nozzle  101  to extend melt zone  130 . 
         [0013]    Minimizing the size of the nozzle  101  and associated heating elements is also desirable. In an embodiment, multiple nozzles  101  are incorporated into a 3D FFF printer. Smaller nozzles  101  allow for higher density nozzle placement. Higher density nozzle placement helps improve speed and accuracy of prints, particularly in systems with multiple nozzles  101 . 
         [0014]    Nozzle  101  is typically made of metal, for example brass. Nozzle  101  could be made of any material, including metals, ceramics or other materials with appropriate strength, thermal conductivity any other desirable properties. The nozzle orifice can be of any size or shape, but is typically between 200 microns and 1500 microns. The nozzle  101  can be of any length or shape appropriate for extruding liquefied material feedstock  120 . The nozzle  101  may be made up of multiple parts. 
         [0015]    A surface treatment may be required for the nozzle  101  to absorb the energy from the non-contact heat source  110 . In an example embodiment, the nozzle  101  has a black chrome surface treatment. In other example embodiments of nozzle  101  other surface treatments are possible, such as black paints with high temperature capabilities such as are commonly available. Any surface that absorbs the type or frequency of energy generated by the non-contact heat source  110  could be used. The surface treatment size may be limited to the area where the heat source  110  applies energy. Some surface treatments, such as black paints, may have high IR emissivity. If the surface treatment has high IR emissivity reducing the surface treatment size will reduce the radiated heat loss via the nozzle  101 . 
         [0016]    In an example embodiment, a small cavity  111  is made where the heat source  110  energy is incident on the nozzle  101 . The cavity has the effect of trapping reflected energy and to re-radiate the energy back into the nozzle. The cavity  111  would allow for higher retention of applied power, particularly if the nozzle  101  does not have 100% absorption of the heat energy. For example, if the energy absorption of the cavity  111  from non-contact heat sources  110  is 80% any reflections that are absorbed in the cavity will have a minimum of 96% absorption, increasing the energy absorbed by the nozzle  101 . 
         [0017]    When a laser is used as the heat source  110  the laser spot size is maximized so the light energy is spread across the maximum surface area of the nozzle  101 . This minimizes hot spots on the nozzle  101 . In an example embodiment, a plurality of non-contact heat sources  110  are used to distribute the heat more evenly across the surface of the nozzle  101 . In an embodiment with a laser as one or more of the non-contact heat sources  110  a beam splitter may also be used to generate multiple energy distribution locations. The laser is a fiber coupled laser. The fiber guides the light to the nozzle, allowing the laser to be outside the deposition area or build chamber, which frequently has an ambient temperature too hot for lasers. The fiber may have a high temperature sheathing if necessary to withstand the high ambient temperatures in the area of the nozzle, which may be over 300 degrees Celsius. If the emission end of the fiber coupled laser can is close enough to the nozzle  101  no collimating optics are needed to focus the fiber coupled laser. This significantly reduces the complexity and cost of using a laser as the non-contact heat source  110 . 
         [0018]    If significant active cooling is present across the tip of the nozzle  101 , it can be difficult to maintain the temperature of nozzle  101 . The tip of nozzle  101  may become significantly cooler than the area closer to the heat source  110 . In an embodiment, the energy from heat source  110  can be applied very close to the tip of the nozzle  101  so the temperature of the tip can be maintained more easily at a desired target temperature. 
         [0019]    Maintenance of the temperature within a tight band is important in the melt chamber  130 . This is typically accomplished through a feedback loop with a temperature sensor. In an example embodiment, the non-contact heat source  110  has the ability to have its power modulated based on feedback from a temperature sensor  104 . 
         [0020]    Thermally conductive mass increases the thermal capacitance of a system. The larger the mass of the heat block and any other thermally conductive components connected to nozzle  101  the higher the thermal capacitance in the feedback loop. Thermal capacitance in the feedback loop slows temperature response time, reducing the ability to control the system in response to changing conditions. With the system described herein, the thermal capacitance can be minimized to only what is necessary to provide physical support for extrusion of feedstock material  120 , allowing optimal control of thermal conditions. In an embodiment, any materials in contact with nozzle  101  and having at least 25% of the mass of nozzle  101  have a thermal conductivity of 2 W/m*° K or less. 
         [0021]    During high speed printing the amount of energy needed at nozzle  101  to melt feedstock material  120  can change rapidly. Maintaining the temperature accurately can minimize certain undesirable outcomes, such as molten material oozing from the tip of nozzle  101  when the flow of melted material  103  should be stopped or overheating of melt chamber  130 .  FIG. 1  illustrates active cooler  170  cooling the nozzle  101 . In an embodiment, active cooler  170  is activated and non-contact heat sources  110  are de-activated, rapidly reducing the temperature of nozzle  101 . 
         [0022]    Nozzle mount  180  attaches the heated nozzle  101  to the FFF printer. The temperature of nozzle  101  can be in excess of 325° C. In an embodiment, nozzle mount  180  is made of material that can withstand the operating temperatures of greater than 325° C. and has a thermal conductance of less than 2 W/m*° K. For example, the type of material that may be used is Macor®, which can withstand temperatures of 800° C., has thermal conductivity of 1.46 W/m*° K and is easily machined. In a further example, the type of material used is Mycalex®, which has a lower thermal conductivity than Macor®. In an example embodiment the nozzle mount  180  is tapped to allow a threaded nozzle  101  to be fitted. Nozzle  101  could also be mounted in nozzle mount  180  with high temperature adhesive instead of threading to better contain the melted material feedstock  120 . A combination of adhesive or other sealing agents and threading or other mounting methods could also be used. The nozzle  101  may have an additional insulating layer  170  between it and the material feedstock inlet  160 . In an embodiment, the insulating layer is created during the machining process for nozzle mount  180  by leaving an insulating layer  170  in between the material feedstock inlet  160  and the nozzle  101 . The hole in nozzle mount  180  may be a through hole and an insulating layer  170  of any material with appropriate thermally insulating and heat resistant properties is placed in between feedstock inlet  160  and nozzle  101 . One or more holes sufficient to allow material feedstock  120  to be fed into the nozzle  101  through the insulating layer  170  exist. 
         [0023]      FIG. 2  illustrates a color blending nozzle  200 . The color blending nozzle  200  has characteristics similar to the nozzle  100  in  FIG. 1  but is optimized for multiple color input material feedstocks  240 . Two or more input colors of material feedstocks  240  are blended in the melt chamber  250  to generate a large number of output colors. For example, with CMYK color inputs, it is possible to generate a large number of color outputs by blending the input colors in correct ratios. One of the challenges with this technique is the size of the melt chamber  250 . Although the ratio of material feedstocks  240  can be varied continuously, as the melted material moves down the melt chamber  240  it will tend to mix along the length of the melt chamber  240 . This causes the color fidelity to be reduced when changing colors. The nozzle  230  shown in  FIG. 2  minimizes the melt chamber  240  using an extremely small melt chamber  240  with one or more non-contact heat sources  220 . With a very small melt chamber  240  and small diameter material feedstock  240  the output color can be tightly controlled and varied quickly. In addition, with a very small melt chamber  240  retraction needed during printing is minimal, thereby further reducing color mixing in the melt chamber  240 . In an embodiment, the melt chamber  240  is less than 5 mm 3  in volume. In an embodiment material feedstocks  240  are smaller than 1.75 mm in diameter. Nozzle mounts  210  are similar in construction and materials to nozzle mounts  180 . Nozzle mounts  210  are smaller in size than nozzle mount  180 . The thermally insulating nature of the nozzle mounts  210  further reduce the amount of melted material feedstock  240  as the temperature outside the melt chamber is decrease quickly. 
         [0024]    The 3D FFF printer will also comprise standard components not pictured, such as a controller, three dimensional carriage, a bed to deposit the object upon and other electrical and mechanical systems as needed to actuate the 3D print nozzle. 
         [0025]    While the technology has been described in conjunction with various embodiments, it will be understood that the embodiments are not intended to limit the present technology. The scope of the subject matter is not limited to the disclosed embodiment(s). On the contrary, the present technology is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope the various embodiments as defined herein, including by the appended claims. In addition, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present technology. However, the present technology may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the embodiments presented. 
         [0026]    References in the specification to “embodiment,” “example” or the like indicate that the subject matter described may include a particular feature, structure, characteristic, or step. However, other embodiments do not necessarily include the particular feature, structure, characteristic or step. Moreover, “embodiment,” “example” or the like do not necessarily refer to the same embodiment. Further, when a particular feature, structure, characteristic or step is described in connection with an embodiment, it is within the knowledge of one skilled in the art to effect it in embodiments. 
         [0027]    Alternative embodiments may use other techniques and/or steps within the spirit and scope of the disclosed technology. The exemplary appended claims encompass embodiments and features described herein, modifications and variations thereto as well as additional embodiments and features that fall within the spirit and scope of the disclosed technologies. Thus, the breadth and scope of the disclosed technologies is not limited by foregoing exemplary embodiments.