Patent Publication Number: US-10782673-B2

Title: System and method for additive manufacturing with layer-by-layer curing

Description:
STATEMENT OF RELATED CASES 
     This case claims priority of U.S. Patent Application Ser. No. 62/133,237 filed Mar. 13, 2015 and which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to additive manufacturing, also known as 3D printing. 
     BACKGROUND OF THE INVENTION 
     The additive manufacturing process is widely known as the three-dimensional (“3D”) printing of objects. Numerous methodologies for 3D printing have been described in prior art, the most common of which include solid-laser-sintering (SLS), stereolithography (SLA), and extrusion-based 3D printing or FFF (fused filament fabrication). All of these methods involve the deposition of thin layer of thermoplastic or thermoset materials. 
     Prototyping is the most common application for additive manufacturing, using materials such as ABS (acrylonitrile butadiene styrene), Nylon (Polyamide), and PLA (polylactic acid). More recently, 3D printing has been utilizing high performance polymers such as PEI, PPSU, PEEK, etc., as well as metals and ceramics with greater mechanical, chemical, thermal and electrical properties. 
     PAI is a specialty thermosetting polymer that has the highest strength and stiffness of any thermoplastic polymer. PAI is characterized by good wear, low creep, and excellent chemical and heat resistance; it maintains its mechanical properties up to 275° C. Given its exceptional high-temperature performance, PAI is used in extreme environments for aerospace, defense, and other applications. 
     The main drawback of PAI is the very lengthy post-curing cycle requiring a complex, programmable oven. According to Solvay&#39;s Torlon® processing guide, a portion of which is reproduced as Table 1 below, objects or parts (hereinafter simply “objects”) with thicknesses up to and including 7.6 millimeters (mm) require a 17-day cure schedule involving eight temperature cycles. For larger objects up to 15.9 mm thick, a 23-day cure schedule with ten temperature cycles is required. There are no recommended guidelines for objects thicker than 15.9 mm. If a PAI-based object is machined after curing, then it must undergo a re-curing cycle. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Time and Temperature as a function 
               
               
                 of Thickness For a PAI-based Object 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Maximum X- 
                 Days 
                   
                 Cure 
               
               
                   
                 sectional thickness 
                 at 
                 Cumulative 
                 Temperature 
               
               
                   
                 of object &lt;mm&gt; 
                 Temp. 
                 Days 
                 &lt;° C.&gt; 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 7.6 
                 1 
                 1 
                 149 
               
               
                   
                   
                 1 
                 2 
                 191 
               
               
                   
                   
                 1 
                 3 
                 204 
               
               
                   
                   
                 1 
                 4 
                 218 
               
               
                   
                   
                 1 
                 5 
                 232 
               
               
                   
                   
                 1 
                 6 
                 243 
               
               
                   
                   
                 1 
                 7 
                 252 
               
               
                   
                   
                 10 
                 8-17 
                 260 
               
               
                   
                 7.6 &lt; X sect  ≤ 15.9 
                 1 
                 1 
                 149 
               
               
                   
                   
                 1 
                 2 
                 177 
               
               
                   
                   
                 1 
                 3 
                 191 
               
               
                   
                   
                 1 
                 4 
                 204 
               
               
                   
                   
                 1 
                 5 
                 218 
               
               
                   
                   
                 2 
                 7 
                 232 
               
               
                   
                   
                 3 
                 10 
                 243 
               
               
                   
                   
                 2 
                 12 
                 249 
               
               
                   
                   
                 1 
                 13 
                 254 
               
               
                   
                   
                 10 
                 23 
                 260 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 1  depicts a flow diagram of prior-art additive manufacturing method  100  for producing a polyamide-imide based object. 
     Per task  101  of method  100 , a 3D model of the object is generated. To create a 3D printable model of a new (non-existing) object, a computer aided design (CAD) package is used to create a digital file (mathematical model) of the object. For an existing object (sculpted or otherwise), a 3D scanner or a digital camera with photogrammetry software is typically used. These latter two approaches collect digital data on the shape and appearance of the real object and then use that data to create the digital file of the object in known fashion. 
     The digital file/mathematical model must be further processed prior to printing the object. In particular, in task  102 , “slicing software,” typically executing on a computer physically separate from the 3D printer, is used to “slice” the 3D model into many (typically hundreds or thousands) of horizontal (2D) layers. The slicing software analyzes the 3D model to determine what “G-code” commands (the instruction set used by most 3D printers) can be used to reproduce the model. 
     The slicing software generates the G-code instructions based on rules determined by parameters/values provided by the operator/designer along with algorithms within the slicing software itself. Parameters such as filament size, extrusion width, speed of the print head, among others are used to develop the G-code instructions. Once the complete instruction set (the build instructions) is generated, it is transmitted to the 3D printer. 
     In task  103 , the 3D printer deposits material (PAI), corresponding to each “slice,” in sequential fashion in accordance with the build instructions (G-code instruction set). Query, in task  104 , whether all layers required for building the object have been deposited. If not, processing loops back, via  105 , to task  103  wherein a subsequent layer is deposited per the build instructions. 
     When all layers are deposited the build is complete and, at task  106 , the object is cured. 
     The post-curing process is unique to PAI resins. The resins start at a low molecular weight, which enables the resin to be processed, injection molded, and extruded. After an object is molded but before its cured, it exhibits very poor mechanical, thermal, electrical, and chemical properties due to its short polymer chains. During the post-curing process, the heat supplied to the object causes the end amic acid groups to form imides generating water as a byproduct. This chemical process occurs at the ends of the short chains, chemically bonding them together resulting in chain extension, cross-linking, and branching. 
     The reaction is limited by the diffusion of water from the object. The thicker the object, the further the water must diffuse and the longer the required post-curing time. 
     The art would therefore benefit from a way to reduce the manufacturing lead-time of a PAI-based object. The art would also benefit from a way to build much larger PAI-based objects than is currently practicable given the size limitations that arise from the post-curing process. 
     SUMMARY OF THE DISCLOSURE 
     The present invention provides an apparatus and method that significantly reduces the manufacturing lead-time for objects comprising slow-curing thermoset polymers, such as polyamide-imide, made via additive manufacturing (i.e., 3D printing). Embodiments of the invention also facilitate the manufacture of PAI-based objects that are significantly larger than those made using existing processes. 
     In accordance with the illustrative embodiment, a PAI-based object is cured during the build process. As previously discussed, the time required for post-curing process, as in the prior art, is dictated by the time it takes for water to diffuse out of the printed object during chain extension (curing). A thicker object therefore requires a longer curing time compared to a thinner object because of the longer diffusion length for the water generated at the center of the object. 
     The present inventors realized that if a “growing” PAI-based object could be cured during manufacture, such as on a layer-by-layer basis during the deposition process, the curing process ought to be greatly accelerated relative to the time required to cure a fully formed object. In particular, the thickness or cross-section of material that is extruded from a standard off-the-shelf fused filament fabrication nozzle ranges from about 0.25 mm to 1 mm, which represents a small fraction of the finished object having a thickness of 15.9 mm, for example. In fact, the cure time for a PAI extrudate having a thickness of 0.25 mm to 1 mm is in the range of seconds to minutes, as compared to weeks for a PAI-based finished object 
     The integrated deposition/curing process, as taught herein, might take somewhat longer than the deposition processes of the prior art. This is because in accordance with at least some embodiments, a layer of PAI extrudate must be deposited and cured before the next layer is deposited. However, at the end the process described herein, the PAI-based object is fully cured and ready for use. This is in marked contrast to the prior art wherein, after the deposition process is complete, a several week PAI-curing process begins. Consequently, the processing time to obtain a fully-cured and ready-to-use PAI-based object is greatly reduced using the apparatus and methods disclosed herein. 
     To achieve proper curing of PAI in-situ, specialized software and hardware are required. More particularly, in the illustrative embodiments, the “curing hardware” includes a localized heating system and thermal monitoring system to maintain the appropriate curing temperatures throughout the build process. The heating system includes one or more sources of heat. The thermal monitoring system includes one or more devices that are suitable for monitoring the temperature of the build chamber or the region nearest the deposited layer as well as one or more timing devices that, in conjunction with the software, determine and report the length of time that a deposited layer is exposed to temperature. These systems ensure that the proper curing temperature is achieved and maintained for each layer or segment of material that is deposited and further enables temperature profiles over time to be obtained for each segment or layer throughout the entire build process. 
     In addition to monitoring the cure of each deposited layer by time, the curing hardware also includes one or more devices that are capable of obtaining an analysis of the deposited layer after the curing step. In some embodiments, the data obtained is compared to reference data stored in a curing database to determine whether the layer is fully cured or, if not, to determine the extent (percentage) of curing. Based on the results of the comparison, either the deposited layer is subjected to further curing or, if fully cured, a subsequent layer is deposited in accordance with the build instructions. 
     Curing software includes, in addition to any other software or database, the curing database as well as analysis software that: (i) determines the minimum curing time and temperature per layer or segment based on one or more of the extrusion nozzle size, nozzle temperature, extrusion speed, and minimum curing temperature and time per thickness, (ii) and that stores (at least temporarily) the results of analysis of the deposited layer, (iii) stores time and temperature information pertaining to curing for each deposited layer, and (iv) performs the comparison between the analysis and the curing database. It will be appreciated that the analysis software may be one or more separate software applications, running on the same or different processors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a flow diagram of a prior-art polyamide-imide based additive manufacturing method. 
         FIG. 2  depicts a flow diagram of a polyamide-imide based additive manufacturing method in accordance with the illustrative embodiment of the present invention. 
         FIG. 3  depicts a system for printing and rapid curing of PAI-based objects in accordance with the illustrative embodiment of the present invention. 
         FIG. 4  depicts a first embodiment of the localized heating system for use in conjunction with the system of  FIG. 3 . 
         FIG. 5  depicts a second embodiment of the localized heating system for use in conjunction with the system of  FIG. 3 . 
         FIG. 6  depicts a third embodiment of the localized heating system for use in conjunction with the system of  FIG. 3 . 
         FIG. 7  depicts an embodiment of an analysis system for obtaining a measurement of a characteristic of the deposited layer use in conjunction with the system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     As discussed in the Background section, embodiments of the invention significantly reduce manufacturing lead-time for the fabrication, via additive manufacturing, of parts (or, more generally, “objects”) using thermosetting polymers, such as polyamide-imide. Additionally, embodiments of the invention also facilitate the manufacture of parts/objects comprising thermosetting polymer that are significantly larger than those made via existing processes. 
     In the illustrative embodiment, a modified fused filament fabrication (FFF) system and method are used to fabricate (“print”) the thermoset polymer-based objects. However, in light of this disclosure, those skilled in the art will be able to modify, as required, other additive-manufacturing apparatuses and processes, such as SLS or modified SLA, to print PAI-based objects in accordance with the present teachings. 
     Embodiments of the invention are directed to a system and process for the rapid curing of 3D-printed objects made from PAI. However, it will be appreciated by those skilled in the art that the illustrative system and process is equally useful for the fabrication of objects, via additive manufacturing, that are made from other thermoset polymers, such as, without limitation, polyesters, polyurethanes, polyimides, and epoxies, all of which require a lengthy post cure. 
     In some embodiments in accordance with the invention, multiple materials are used to construct a single object, wherein one of the materials is PAI. The inclusion of PAI provides a high level of mechanical strength to the object. Because of the high moisture absorption of PAI, in some embodiments, the outside of the PAI object is covered with a low moisture-absorbing polymer, such as PEEK. By printing PEEK over a PAI object, the moisture absorption is reduced, resulting in a more geometrically consistent object over its lifetime. 
       FIG. 2  depicts a flow diagram of additive manufacturing method  100  for producing a polyamide-imide based object in accordance with the illustrative embodiment of the present invention. 
     The first three tasks of the process—tasks  201 ,  202 , and  203 —are the same as in prior-art method  100  depicted in  FIG. 1  and have been previously discussed. Those tasks include generating a 3D model of the object, slicing the object and generating build instructions, and depositing a layer in accordance with the build instructions. 
     At task  204 , unlike the prior art, the layer of PAI that was deposited in task  203  is cured prior to depositing a subsequent layer. Curing the deposited layer requires time at temperature. To this end, a 3D printer in accordance with the illustrative embodiment (see, e.g.,  FIG. 3 , etc.) includes “fast-cure hardware,” which is defined for use in this disclosure and the appended claims as hardware that facilitates layer-by-layer curing of objects formed from slow curing polymers, such as, without limitation, PAI. 
     In the illustrative embodiment, and as discussed further in conjunction with  FIGS. 4 through 7 , the fast-cure hardware comprises a localized heating system, a thermal monitoring system, and an analysis system. In addition to other functionality discussed below, the curing hardware (in particular the localized heating system and thermal monitoring system) enables the temperature of the nascent PAI-based object to be adjusted to and maintained at the appropriate curing temperature(s) throughout the build process. Task  204  is timed (e.g., via a timer and software, etc.) to meet a minimum curing time and to record the actual curing time of each layer. In the illustrative embodiment, curing temperature is maintained at a single temperature, which is 260° C. 
     The curing of PAI is limited by the rate of diffusion of water out of a PAI-based object, as previously discussed. For the prior art, this diffusion limitation results in a standard minimum cure time of 17 days for an object having a thickness of 7.6 mm (or less). The curing of the material occurs primarily at 260° C. However, to avoid swelling of the object and loss of dimensional accuracy, in the prior art, the object must be heated slowly to curing temperature over a 7-day heating cycle, as shown in Table 1 in the Background section. 
     In method  200  in accordance with the present teaching, each successive layer of PAI is cured immediately after solidification from the melt phase and prior to depositing the next layer. This improvement:
         negates the need for a lengthy (7-day) heat-up cycle;   significantly reduces the curing time at 260° C. relative to the standard cure time for PAI since in method  200 , a single build layer (c.a. 0.05 to 0.3 mm) is being cured rather than a finished object (c.a. 10 mm);   negates the limitation (15.9 mm) on the maximum thickness of the printed object, since, in the illustrative embodiment, water is removed on a layer-by-layer basis.       

     Estimate of Curing Time. 
     Water diffusion through a polymer is generally assumed to be constant as described by Fick&#39;s second law. 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       C 
                     
                     
                       ∂ 
                       t 
                     
                   
                   = 
                   
                     ∇ 
                     
                       · 
                       
                         ( 
                         
                           D 
                           ⁢ 
                           
                             ∇ 
                             C 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   1 
                   ] 
                 
               
             
           
         
       
         
         
           
             where: D (mm 2 /s) is the diffusion constant,
           C (g/mm 3 ) is the moisture concentration, and   t (s) is time.
 
For a one-dimensional case, expression [1] can be solved and integrated to yield the following expression:
   
         
           
         
       
    
     
       
         
           
             
               
                 
                   
                     
                       M 
                       t 
                     
                     
                       M 
                       ∞ 
                     
                   
                   = 
                   
                     1 
                     - 
                     
                       
                         8 
                         
                           π 
                           2 
                         
                       
                       ⁢ 
                       
                         
                           ∑ 
                           
                             n 
                             = 
                             0 
                           
                           ∞ 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             1 
                             
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     n 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                               2 
                             
                           
                           ⁢ 
                           
                             exp 
                             ⁡ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       - 
                                       
                                         
                                           D 
                                           ⁡ 
                                           
                                             ( 
                                             
                                               
                                                 2 
                                                 ⁢ 
                                                 n 
                                               
                                               + 
                                               1 
                                             
                                             ) 
                                           
                                         
                                         2 
                                       
                                     
                                     ⁢ 
                                     
                                       π 
                                       2 
                                     
                                   
                                   
                                     4 
                                     ⁢ 
                                     
                                       l 
                                       2 
                                     
                                   
                                 
                                 ⁢ 
                                 t 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   2 
                   ] 
                 
               
             
           
         
       
         
         
           
             Where: l is the part thickness,
           M t  is the mass of moisture after absorption time t, and   M∞ is the mass of saturated sample.   
         
           
         
       
    
     In conjunction with the PAI processing guide, etc., expression [2] can be used to provide an estimate of curing time. Using the same mass of moisture after absorption, expression [2] reduces to: 
     
       
         
           
             
               
                 
                   
                     
                       x 
                       1 
                       2 
                     
                     
                       t 
                       1 
                     
                   
                   = 
                   
                     
                       x 
                       2 
                       2 
                     
                     
                       t 
                       2 
                     
                   
                 
               
               
                 
                   [ 
                   3 
                   ] 
                 
               
             
           
         
       
     
     As previously disclosed, in accordance with method  200 , a single layer of extrudate is cured in task  204 . Standard layer height for the deposited layer in additive manufacturing is about 0.1 mm. It is known from the PAI processing guide that a part/object that is no more than 7.6 mm thick requires a curing time of 10 days (after a 7-day heating cycle). 
     The information can be substituted into Expression [3], solving for t 2 , curing time for the 0.1 mm layer, as follows: 
     x 1 =7.6 mm and t 1  (curing time)=10 days. 
     x 2 =0.1 mm and t 2  (curing time) is unknown. 
     
       
         
           
             
               
                 
                   ( 
                   
                     7.6 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     mm 
                   
                   ) 
                 
                 2 
               
               
                 10 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 s 
               
             
             = 
             
               
                 
                   ( 
                   
                     0.1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     mm 
                   
                   ) 
                 
                 2 
               
               
                 t 
                 2 
               
             
           
         
       
     
     t 2 =0.00173 days=2.5 minutes. 
     Thus, the estimated time it takes to cure a single layer of extrudate is about 2.5 minutes. Ignoring deposition time, and assuming that for 0.1 mm deposited layers, 76 layers are required to build a 7.6 mm object, 2.5 minutes per layer×76 layers or 3.2 hours are required to produce a fully-cured, ready-to-use object. The prior art requires a 17-day curing cycle for an object having a thickness of 7.6 mm (or less). 
     Task  204  is time to provide a minimum cure time. However, to ensure that the layer is cured, in task  205 , the “cured” layer is analyzed to determine, per task  206 , whether the layer is actually fully cured. In the illustrative embodiment, the analysis determines the extent to which the polymer is cured (e.g., percentage cured, etc.). 
     In task  205 , the analysis obtains a measure/value of a characteristic of the deposited layer that has previously been correlated to the extent of cure (or, at a minimum, provides an indication of whether the PAI is cured or not). The measurement is compared to a “curing database.” The curing database relates the extent-of-cure of PAI to values of the characteristic, thus providing a reference for comparison. The comparison of the measured value with the reference information provides an estimate for the extent-of-cure for the deposited layer. Alternatively, an expression can be developed or otherwise obtained that relates the value of the characteristic to the extent of cure of the PAI. If not otherwise available, the curing database can be developed by an operator of the system disclosed herein by performing a simple parametric study. 
     Typically, task  205  will be performed via either visual inspection or via small angle x-ray scattering (SAXS). 
     With respect to visual inspection, as PAI cures, oxidation of its surface causes its color to darken. Visual images of the layer can be obtained and analyzed to determine the extent of curing for a given layer or segment. In some embodiments, a high definition color camera detects the color profile of the surface of the deposited layer (i.e., the polymer). A curing database stores a version of a photo-chart that relates the color profile of the surface to the extent (e.g., percent) to which PAI polymer is cured. The database includes the color profile for a number of stages (about 10 or so) during the curing process. Stage 1, for example, would show a light yellowish-amber colored surface indicating no curing has taken place, while stage 10 would show a dark brown colored surface indicating the surface is fully cured. 
     Relative to visual inspection, small angle x-ray scattering is more accurate in determining the extent of curing of the PAI polymer but is also more costly. In SAXS, a monochromatic beam of X-rays is directed at the sample. (the layer of PAI). Most of the X-rays go through the sample, but some scatter, forming a scattering pattern. The pattern, which is detected at a detector, contains information about the structure of the sample. For this application, SAXS is used to determine the molecular weight of the PAL During the curing process of PAI, polymer chains link together, thereby increasing the molecular weight of the compound. For this embodiment, the curing database contains reference data that relates the molecular weight of the PAI to the extent to which it is cured. 
     Thus, using either approach, the data from the analysis of the layer is stored at least temporarily in processor accessible storage and compared to the database information to determine the extent of cure. These task are performed by analysis software. If the layer is not fully cured, the analysis software can estimate the time remaining for full cure, such as based on based on historical data if available or via quadratic extrapolation (see, e.g., Expression [3]). 
     As used in this disclosure and the appended claims, the phrase “curing data” refers to a value/measure of a characteristic of a deposited polymer layer that correlates to the extent to which the polymer is cured. 
     If the answer to the query at task  206  (is the layer fully cured?) is “no,” processing loops back at  207  to task  204 , for additional curing. If the answer to the query at task  206  is “yes,” then at task  208 , the curing settings (i.e., time at temperature) are stored so that they can be used as the basis for curing the next layer of PAI deposited by the 3D printer. In some embodiments, the full time/temperature history of each layer, including the extent-of-cure information as appropriate, is archived. Such archived data enables further refinements to the timing of the curing step (e.g., it can be used to determine how much additional curing time is required for full cure given a particular extent-of-cure estimate, it can be used to estimate an increase the nominal period of time allotted for curing, etc.). 
     Query, at task  209 , whether all layers of material have been deposited in accordance with the build instructions. If the answer to the query is “yes,” processing ends at task  211 . If the answer to the query at task  209  is “no,” then processing loops back at  210  to task  203 , wherein another layer of PAI is deposited in accordance with the build instructions. 
       FIG. 3  depicts system  300  for printing and rapid curing of PAI-based objects in accordance with an illustrative embodiment of the invention. In the illustrative embodiment, system  300  operates in accordance with method  200 . The salient elements of system  300  depicted in  FIG. 3  include 3D printer  301  and computer  330 , which are in communication with one another via link  319 , which can be wired or wireless utilizing any appropriate telecommunications protocol. 
     Computer  330 , which in some embodiments is a physically distinct device from 3D printer  301 , includes processor  332 , input/output  334 , and processor accessible storage  336 . 
     Processor  332  is a general-purpose processor that is capable of, among other tasks, executing an operating system and executing specialized application software used in conjunction with the embodiments of the invention. Processor  310  is also capable of populating, updating, using, and managing data in processor-accessible data storage  336 . In some alternative embodiments of the present invention, processor  332  is a special-purpose processor. It will be clear to those skilled in the art how to make and use processor  332 . 
     Processor-accessible data storage  336  is non-volatile, non-transitory memory technology (e.g., ROM, EPROM, EEPROM, hard drive(s), flash drive(s) or other solid state memory technology, CD-ROM, DVD, etc.) that stores, among any other information, data (such as curing data, curing time and temperature history for each deposited layer, etc.) and specialized application software, which, when executed, enable processor  332  to generate instructions for 3D printer  301  and analyze curing data, among other tasks. It will be clear to those skilled in the art how to make and use processor-accessible data storage  312 . 
     Specialized application software executed by processor  332  and stored in processor accessible storage includes, without limitation, CAD software  340 , slicing software  342 , curing database  344 , and analysis software  346 . CAD software  340  and slicing software  342  have been previously discussed in conjunction with generating build instructions for controller  316 . Curing database  344  and analysis software  346  have been discussed in conjunction with determining the extent-of-cure of a deposited layer of PAI. In some embodiments, analysis software  346  also estimates the minimum curing time and temperature per layer or segment based on one or more of nozzle size, nozzle temperature, extrusion speed, and minimum curing temperature and time per thickness, in known fashion. See, e.g., the previous discussion pertaining to estimating curing time. After determining the minimum layer time and temperature, the deposition and travel rates may be adjusted accordingly to synchronize the curing time with the build time. In such an embodiment, the object construction is timed to finish when the part is fully cured. 
     Input/output  334  enables communications with, for example and without limitation, a human operator, controller  316  of 3D printer  301 , and optionally the Internet. Communications can be via any appropriate medium, including wireline and/or wireless, and via any appropriate protocol (e.g., Bluetooth, Wi-Fi, cellular, optical, ultrasound, etc.). The term “input/output” is meant to include a transceiver or any communications means and, as appropriate, various supporting equipment, such as communications ports, antennas, etc. It will be clear to those skilled in the art, after reading this specification, how to make and use input/output  334 . 
     System  300  “prints” objects utilizing fused filament fabrication processing, wherein filaments of material—in this embodiment PAI—are extruded from an extrusion head. Using this method, a part or object is constructed layer-by-layer through controlled deposition of the extrudate (i.e., the material exiting the nozzle of the extrusion head). The nozzle has an opening with a diameter in the range of about 0.25 to 1 mm, which produces an extrudate having a typically circular cross-section of like or somewhat smaller diameter or layer height (as small as about 0.1 mm). 
     3D printer  301  includes housing  302 , which defines build chamber  303 . Fixture  305 , which is movably supported by gantry  304 , supports extrusion head  306 , which includes nozzle  308 . Gantry  304  enables movement of nozzle  308  in the X direction (left and right in  FIG. 3 ) and Y direction (backward or forward in  FIG. 3 ). Below nozzle  308  is build plate  310 , upon which nozzle  308  deposit successive layers of extrudate to build object  318 . Build plate  310  is movable in the Z direction (i.e., up and down in  FIG. 3 ), providing 3 degrees-of-freedom to the build. 
     3D printer  301  also includes controller  316 . The controller reads and executes commands from the G-code generated from outboard computer  330 . For example, controller  316  orchestrates the build of object  318 , based on build instructions received from computer  330 , by controlling gantry movement and build plate movement, extrusion rate, and build plate and nozzle temperature via control signal(s)  321 . Computer  330  generates the build instructions using, for example, CAD software  340  (for generating a 3D model of the object) and slicing software  342  (for “slicing” the 3D model into planar segments and generating the G-code instruction set). 
     In accordance with the present teachings, 3D printer  301  also includes fast-cure hardware, including localized heating system  312 , thermal monitoring system  313 , and analysis system  314 . In conjunction with curing database  344  and analysis software  346 , which are stored in processor-accessible storage  336 , the fast-cure hardware facilitate the rapid curing of PAI-based objects that are printed by 3D printer  301 . 
     More particularly, localized heating system  312 , in conjunction with thermal monitoring system  313 , maintains the appropriate curing temperature throughout the build process. Localized heating system  312  includes a heat source, such as, without limitation, one or more: infrared heat lamps, lasers, heat guns, heat cartridges, etc. Controller  316  controls localized heating system  312  via control signal  323 . This communications link, and other links between other equipment, can be either wireline or wireless using an appropriate telecommunications protocol. 
     Thermal monitoring system  313  comprises a temperature-measuring device, such as, without limitation, one or more: thermocouples, resistance temperature devices, infrared temperature measurement devices, bimetallic temperature measurement devices, fluid-expansion temperature measurement devices, change-of-state temperature measurement devices, etc. Controller  316  controls thermal monitoring system  313  via control signal  329 . 
     The temperature measured by thermal monitoring system  313  is reported to controller  316  over link  331 . As necessary, controller  316  then adjusts the heat provided by localized heating system  312  to maintain a desired curing temperature in build chamber  303  or at least in the immediate vicinity of the deposited layer on nascent object  318 . 
     Analysis system  314  is capable of obtaining curing data of the deposited layer of PAI. Controller  316  controls analysis system  314  via control signal  325 . 
     In some embodiments, the curing data obtained by analysis system  314  is reported to controller  316  over link  327  and then to computer  330  for at least intermediate storage in storage registers designated for processing results. Processor  332  in computer  330  compares, via analysis software  346 , the curing data to information in curing database  344 . The comparison provides an estimate of the extent to which the deposited layer is cured. 
     Based on the outcome of the analysis, analysis software  346 , executing on process  332 , generates additional instructions for 3D printer  301 . For example, the instructions might be to continue localized heating (curing) for a certain period of time to finalize an incomplete cure, or it might be to continue the build by depositing a subsequent layer. The additional time for curing can be estimated based on the determination of extent-of-cure and historical data (which can provide the time required to advance from the present state of cure to a complete cure). The instructions are transmitted from processor  332  via I/O  334  to controller  316 , which then directs the operation of 3D printer  301  pursuant to the instructions. 
     In an alternative embodiment, analysis of the curing data is performed by an analyzer associated with controller  316 , wherein the analyzer determines is the curing step needs to be prolonged or not. 
     It will be appreciated that all of the processing discussed above can take place either in computer  330  or in a processor associated with controller  316  in 3D printer  301  or processing can be distributed so that it is performed partially, to any extent, in both locations. 
       FIGS. 4 through 6  depict several embodiments of localized heating system  312 . Only elements that are germane to the localized heating system are identified in these Figures and discussed. 
       FIG. 4  depicts an embodiment wherein the entire build chamber  303  is heated to the required curing temperature using one or more heating elements  412  (e.g., infrared heat lamp, laser, heat gun, heat cartridges, etc.). Fan  413  is disposed in the immediate vicinity of the heating element(s)  412  to distribute the heat throughout build chamber  303 . Heating element(s)  412  and fan(s)  413  are controlled by separate control signals, which are depicted, for simplicity, as single control signal  423 . 
       FIG. 5  depicts an embodiment wherein one or more heating elements  512  (e.g., infrared heat lamp, laser, heat gun, heat cartridges, etc.) are mounted near nozzle  308  on the same fixture (fixture  305 ) as PAI extrusion head  306  for targeted curing. As the extrusion head lays down PAI, the heating element follows behind, heating and curing the deposited extrudate. In this regard, in some embodiments, the fixture/extrusion head can rotate 360 degrees so that heating element  512  is always following nozzle  308 . Controller  316  controls heating element(s)  512  via control signal  523 . 
     In some other embodiments, the fixture/extrusion head is not rotatable; rather, there are multiple heating elements  512  positioned around nozzle  512 . In some such embodiments, the heating elements are controlled collectively such that all heating elements  512  are active at the same time, thereby heating/curing material ahead of, behind, and to the sides of nozzle  308 . In some other of such embodiments, heating elements  512  are individually controllable such that they can be selectively activated, for example, to heat/cure only the material that is behind nozzle  308 , etc. 
     In some embodiments, if the extrudate cross-section is small enough to enable curing immediately following material deposition, the curing and object construction effectively occur simultaneously. However, if additional curing time is required, the head can move across the same layer or segment any number of times without extruding until that section is fully cured from the exposure to heat. 
       FIG. 6  depicts an embodiment wherein one or more heating elements  512  (e.g., infrared heat lamp, laser, heat gun, heat cartridges, etc.) are mounted on one or more fixtures  650  that are independent from fixture  305  that supports extrusion head  306 . In such embodiments, the one or more heating elements  512  move independently of extrusion head  306 , enabling targeted curing of multiple regions of the object during the build process. This embodiment might result in faster curing rates compared to the embodiment depicted in  FIG. 5  wherein heating element(s)  512  are mounted on the same fixture as extrusion head  306 . 
     System software instructs controller  316  to coordinate the movements of the heating elements  512  (via control signal  623 ) and extrusion head  306  (via controls signal  321 ) to avoid collision and ensure each layer or segment is subject to the calculated minimum curing time. Controller  316  controls the heating operation of heating element(s)  512  via control signal  321 . 
       FIG. 7  depicts an embodiment of analysis system  314 , wherein high definition color camera  714  is disposed on the same fixture (fixture  305 ) as extrusion head  306 . Controller  316  controls the operation of camera  714  by control signal  725 . The curing data obtained by camera  714  is transmitted over link  727  to controller  316  and then to computer  330  (not depicted in  FIG. 7 ) for intermediate storage and processing via software. 
     It is to be understood that although the disclosure teaches many examples of embodiments in accordance with the present teachings, many additional variations of the invention can easily be devised by those skilled in the art after reading this disclosure. As a consequence, the scope of the present invention is to be determined by the following claims.