Patent Publication Number: US-2020302025-A1

Title: Automated Method for Support Material Placement in Additive Manufacturing for Improved Finish Machining Performance

Description:
STATEMENT OF GOVERNMENT RIGHTS 
     This invention was made with Government support under FA8650-17-2-5246 awarded by the Department of Defense. The government has certain rights in this invention. 
    
    
     BACKGROUND 
     Additive manufacturing is utilized to fabricate 3-dimensional (3D) parts by adding layer-upon-layer of material. Additive manufacturing may utilize 3D-modeling (Computer-Aided Design or CAD) software to design and form a part. Additive manufacturing encompasses a wide variety of technologies and incorporates a wide variety of techniques, such as, but not limited to, laser freeform manufacturing (LFM), laser deposition (LD), direct metal deposition (DMD), laser metal deposition, laser additive manufacturing, laser engineered net shaping (LENS), stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), multi jet modeling (MJM), 3D printing, rapid prototyping, direct digital manufacturing, layered manufacturing, and additive fabrication. Moreover, a variety of raw materials may be used in additive manufacturing to create the part. Examples include but are not limited to plastics, metals, concrete, and glass. 
     To improve the surface finish of a part fabricated with additive-manufacturing equipment, separate post-processing steps may be implemented using conventional surface-finishing equipment and techniques. The AM part should be constructed to withstand the forces applied during the post-processing steps 
     SUMMARY 
     One aspect is directed to a method of designing a manufactured part. The method includes performing frequency analysis on a computer-generated design of the manufactured part and calculating mode shapes at natural frequencies of the computer-generated design. The method includes calculating a static compliance at a plurality of points on the computer-generated design using the mode shapes. The method includes generating a total compliance map of the computer generated design that includes the static compliance at the plurality of points, the total compliance map with an expected displacement at the plurality of points when the computer generated design is exposed to a predetermined non-dynamic load. The method includes outputting the total compliance map. 
     In another aspect, the method includes determining that the expected displacement at one or more of the plurality of points exceeds an allowable amount, and modifying the computer-generated design by adding material that forms one or more structural supports. 
     In another aspect, the method includes using the modified computer-generated design and manufacturing an actual part made from a material. 
     In another aspect, the method includes removing the material that forms the one or more structural supports while manufacturing the actual part. 
     In another aspect, the method includes manufacturing the actual part with an additive manufacturing process. 
     In another aspect, the method includes calculating the static compliance at the plurality of points on the computer-generated design according to: 
     
       
         
           
             StaticCompliance 
             = 
             
               
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             Where j is the number of mode shapes calculated for points, k, on the model 
             Φ i =mass-normalized mode shape displacement at the point 
             f n,i =natural frequency in units of Hertz. 
           
         
       
    
     In another aspect, the modified computer-generated design is designed for use on an aircraft. 
     In another aspect, the method includes manufacturing the actual part with the material that forms one or more structural supports with an additive manufacturing process, reducing a roughness of a surface of the actual part while the material is integrated into the actual part, and removing the material that forms the one or more structural supports after reducing the surface roughness of the actual part. 
     One aspect is directed to a method of designing a manufactured part. The method includes calculating mode shapes at natural frequencies of a computer-generated design of the manufactured part. The method includes calculating a total static compliance of points on the computer-generated design using the mode shapes with the total static compliance comprising an expected displacement throughout the computer generated design when the computer generated design is exposed to a predetermined non-dynamic load. The method includes identifying one or more areas of the computer-generated design for additional material for structural support responsive to the total static compliance. 
     In another aspect, the method includes generating a total compliance map of the computer generated design comprising the static compliance at points on the design, and outputting the total compliance map. 
     In another aspect, the method includes using a mass normalized mode shape displacement for the natural frequencies and calculating the total static compliance. 
     In another aspect, the method includes determining that the expected displacement exceeds an allowable amount at the one or more areas on the computer generated design, and modifying the computer-generated design by adding material for one or more structural supports at the one or more areas. 
     In another aspect, the method includes manufacturing an actual part from a material using the computer-generated design. 
     In another aspect, the method includes manufacturing an actual part from a material using the computer-generated design and including the material that forms the one or more structural supports, performing a surfacing process on the actual part while the part includes the material that forms the one or more structural supports, and removing the material that forms the one or more structural supports after performing the surfacing process. 
     In another aspect, the method includes manufacturing the actual part using an additive manufacturing process. 
     In another aspect, identifying the one or more of the areas of the computer-generated design for the additional material for structural support responsive to the total static compliance comprises determining that the one or more areas have a total static compliance value above a predetermined threshold. 
     Another aspect is directed to a computer-readable storage medium comprising instructions that, when executed by a processing circuit of a computing device, cause the processing circuit to perform operations comprising: performing frequency analysis on a computer-generated design of a manufactured part and calculating mode shapes at natural frequencies of the computer-generated design; calculating a static compliance at a plurality of points on the computer-generated design using each of the mode shapes; and generating a total compliance map of the computer generated part comprising the static compliance at each of the plurality of points with the total compliance map comprising an expected displacement at each of the plurality of points when the computer generated design is exposed to a predetermined non-dynamic load. 
     In another aspect, the computer-readable storage medium is configured for the processing circuit to output the total compliance map. 
     In another aspect, the computer-readable storage medium is configured for the processing circuit to determine that the expected displacement at one or more of the plurality of points exceeds an allowable amount; and modify the computer-generated design by adding material forming one or more structural supports. 
     In another aspect, the computer-generated design is designed for use on an aircraft. 
     The features, functions and advantages that have been discussed can be achieved independently in various aspects or may be combined in yet other aspects, further details of which can be seen with reference to the following description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic diagram of a computing device. 
         FIG. 2  is perspective view of a graphic depiction of a computer-generated design for an AM part. 
         FIG. 3  is a flowchart diagram of a method of analyzing an AM part using a computer-generated design. 
         FIG. 4  is a perspective view of a graphic depiction of a first mode shape. 
         FIG. 5  is a perspective view of a graphic depiction of a second mode shape. 
         FIG. 6  is a perspective view of a graphic depiction of a third mode shape. 
         FIG. 7  is a flowchart diagram of a method of calculating a total static compliance map. 
         FIG. 8  is a perspective view of a total static compliance map. 
         FIG. 9  is a flowchart diagram of a method of designing an AM part using a computer-generated model. 
         FIG. 10  is perspective view of a graphic depiction of a computer-generated design that includes additional material for structural support. 
         FIG. 11  is a flowchart diagram of a method of manufacturing an AM part. 
         FIG. 12  is a perspective view of an AM part that includes additional materials that provide structural support. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a computing device  20  configured to support computer-implemented methods and computer-executable program instructions (or code) during the testing, analysis, and design of a part. For example, the computing device  20 , or portions thereof, can execute instructions to perform the operations described herein with respect to the various methods for designing and analyzing the part. The computing device  20 , or portions thereof, can further execute instructions according to any of the methods described herein. 
     The computing device  20  can include a processing circuit  21 . The processing circuit  21  can include one or more microprocessors, microcontrollers, Application Specific Integrated Circuits (ASICs), or other programmable devices. The processing circuit  21  can be configured to execute program code stored within a memory circuit  22 . The memory circuit  22  can include volatile memory devices (e.g., random access memory (RAM) devices), nonvolatile memory devices (e.g., read-only memory (ROM) devices, programmable read-only memory, and flash memory), or both. The memory circuit  22  can include an operating system that can include a basic/input output system for booting the computing device  20  as well as a full operating system to enable the computing device  20  to interact with users, other programs, and other devices. 
     The memory circuit  22  can include one or more applications that can be executable by the processing circuit  21 . As an example, the one or more applications can include instructions executable by the processing circuit  21  to receive a reference design that includes geometrical information associated with a part. The one or more applications can further include instructions executable by the processing circuit  21  that calculates and analyzes the effects of various tests performed at different frequencies. The one or more applications can also include instructions executable by the processing circuit  21  to determine an amount of deflection of one or more points on the part during the testing. 
     The processing circuit  21  can communicate with one or more storage devices  23 . For example, the one or more storage devices  23  can include nonvolatile storage devices, such as magnetic disks, optical disks, or flash memory devices. The storage devices  23  can include both removable and non-removable memory devices. The storage devices  23  can be configured to store an operating system, images of operating systems, applications, and program data. In a particular embodiment, the memory circuit  22 , the storage devices  23 , or both, include tangible computer-readable media. 
     The processing circuit  21  can also communicate with one or more input/output interfaces  24  that enable the computing device  20  to communicate with one or more devices to facilitate user interaction. The processing circuit  21  can detect interaction events based on user input received via the input/output interfaces  24 . 
     In one embodiment, a display  25  provides viewable information for the user. The display  25  can comprise any known electronic display, such as a liquid crystal display. Inputs  26  can include a keyboard, mouse, control buttons, and other like devices. The inputs  26  provide for the user to enter various commands and make menu selections for menus presented on the display  25 . 
     The computing device  20  is configured to analyze a computer-generated design  30 . As illustrated in  FIG. 2 , the design  30  can be processed by the computing device  20  and a graphical depiction can be outputted for viewing on the display  25 . The design  30  can include a complete description of the shape and composition of an AM part, or can include a more basic description of the AM part with design features that are not fully complete. 
     The disclosed methods provide for analyzing the design  30  to determine where additional material is needed for structural support, if any, to accommodate post-processing manufacturing steps. These additional manufacturing steps can include a variety of different steps that can be performed after an initial version of the AM part is formed during the manufacturing process. In one design, the post-processing steps include treating the surface of the AM part to remove roughness along one or more surfaces that result from the layered manufacturing of the AM process. 
       FIG. 3  illustrates a method of analyzing the design  30 . Prior to the analysis, the computing device  20  obtains the design  30 . The design  30  can be a computer-aided design 3D model of the AM part. The design  30  can be received from an outside source through the input/output interface  24  or through the storage device  23 . The computing device  20  can also be configured to generate the design  30 , such as through various computer-aided design programs that can run on the computing device  20 . 
     The method includes performing frequency analysis on the design  30  (block  100 ). The frequency analysis calculates the natural frequency of the design  30  which is the lowest frequency at which the corresponding AM part modeled in the design  30  would vibrate. The analysis also replicates the mode shape that the design  30  would tend to assume when vibrating at the natural frequency. 
     The testing can be performed using finite element analysis software that is stored in the memory circuit  22  or otherwise available to the processing circuit  21 . One example of finite element analysis and computer-aided engineering software is Abaqus/CAE available from Dassault Systemes. The analysis software can take into account aspects that can affect the natural frequency, such as the geometry of the AM part, the material properties and mass, support conditions such as fixtures that are used to secure the AM part, and in-plane loads. 
       FIG. 4  illustrates a graphical depiction of the mode shape  40   a  at the natural frequency (i.e., the normal mode). As illustrated, the mode shape  40   a  illustrates the expected relative displacements of points of the design  30  when the design  30  is vibrated at the natural frequency. As illustrated, many of the points on the design  30  do not experience much if any displacement. However, one or more points  31  on the design  30  experience a larger amount of vibrating movement. 
     The computing device  20  can be configured to output the mode shape  40   a  to the display  25 . The graphic display can include the points  31  illustrated in a manner to emphasize the magnitude of the flexibility. This can include different coloring, shading, surface indicia, or other visual manner of demonstrating relative differences in flexibility. 
     The frequency analysis also includes calculating mode shapes of the design  30  at higher frequencies. This can include frequencies at multiples of the natural frequency. These modes shapes are the shape which the design  30  tends to assume when vibrated at the specific frequencies. These corresponding mode shapes at each of the higher frequencies result in different amounts of flexibility at the different points  31  of the design  30 .  FIG. 5  illustrates a mode shape  40   b  at a second natural frequency, and  FIG. 6  illustrates a mode shape  40   c  at a third natural frequency. As illustrated, the natural frequencies can include different points  31  of the design  30  having relatively high flexibility. 
     The method calculates a static compliance at discrete points of the design  30  (block  104 ). The static compliance is the expected amount of displacement per unit force for the points of the design  30 . The static compliance calculates how the part will displace when under a predetermined non-dynamic load. The static compliance provides an insight into part deformation given a static force estimate. In one example, the static compliance is measured in inches per pound. 
     The static compliance is calculated using the mode shapes for each of the discrete points of the design  30  at each of the analyzed natural frequencies. The static compliance for each point is determined using Equation 1: 
     
       
         
           
             StaticCompliance 
             = 
             
               
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                   = 
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                 2 
               
             
           
         
       
         
         
           
             Where j is the number of mode shapes calculated for points, k, on the model 
             Φ i =mass-normalized mode shape displacement at the point 
             f n,i =natural frequency in units of Hertz. 
           
         
       
    
     In one design, k is calculated for a predetermined number of discrete points on the computer-generated design. In one specific design, k is calculated for all points on the computer-generated design. 
     The method then calculates a total static compliance for the design  30  (block  106 ). The total static compliance is the overall expected amount of displacement for the discrete points of the design  30 . The total static compliance for the design can be output (block  108 ). The output can then be used for additional testing and analysis of the design  30 . 
     Another method can include calculating a total static compliance map of the design  30 .  FIG. 7  illustrates a method that includes performing frequency analysis on the design  30  (block  100 ), calculating a static compliance at discrete points of the design  30  (block  104 ) and calculating a total static compliance of the design  30  (block  106 ) as explained above. 
     The method also includes generating a total static compliance map of the design  30  (block  110 ). The total static compliance map  50  includes a graphical depiction of the design  30  with an expected displacement at each of the discrete points  31  when the design  30  is exposed to a predetermined non-dynamic load.  FIG. 8  illustrates a graphical display of a total static compliance map  50  of the design  30 . As illustrated in  FIG. 8 , the design  30  can be displayed in a manner that highlights the relative flexibilities of the different points. This can include coloring, shading, surface indicia, or other visual manner of demonstrating relative differences in flexibility. The total static compliance map  50  can be output for use and further analysis (block  111 ). 
     The total static compliance of the design  30  can be used to determine if the design needs additional material for structural support to perform one or more post-processing steps. One example includes whether the design can withstand forces applied during surface finishing that occurs during post-processing. In the event one or more points exceed an expected displacement when exposed to a predetermined non-dynamic load, additional material for structural support can be added to the design  30  to prevent and/or reduce the amount of displacement. 
       FIG. 9  includes a method of designing an AM part using a design  30 . Steps  100 - 106  are performed as explained above. The design is further analyzed to determine whether any points exceed a predetermined displacement (block  120 ). This calculation compares the total static compliance of the points of the design  30  relative to a predetermined displacement amount. The design remains without requiring additional material if no points exceed the predetermined displacement amount (block  122 ). Thus, the design  30  can withstand the expected amount of force applied to the AM part without deforming to an amount that prevents or reduces the effectiveness of subsequent post-processing step(s). 
     If any points exceed the predetermined displacement amount, additional material for structural support is added to the design  30  (block  124 ). The additional material prevents or reduces the displacement thus providing for the design  30  to withstand the subsequent manufacturing processes. 
       FIG. 8  illustrates a total static compliance map  50  that illustrates this issue. The total static compliance map  50  indicates that points  41 ,  42  have a flexibility in excess of a predetermined amount of displacement. Subsequent manufacturing steps would not be effective when performed on these points  41 ,  42  due to the high flexibility. 
     Additional material is added to the design  30  at the points  41 ,  42  to address the issue.  FIG. 10  illustrates a graphical depiction of the design  30  that now includes the material for structural supports  32  at the high flexibility areas. The size and shape of the structural supports  32  can vary depending upon the specific design criteria. 
     The updated design is then used to manufacture an AM part  60 .  FIG. 11  illustrates a method of using the updated design  30  to manufacture an AM part  60 . The method includes manufacturing an initial phase of the AM part  60  that includes the additional material for structural supports  61  (block  200 ).  FIG. 12  illustrates this initial phase of the AM part  60  that includes material for structural supports  61  at the areas of high flexibility. 
     The method then includes performing one or more additional processing steps on the AM part  60  (block  202 ). In one design, the additional processing steps include finishing the surface of the AM part  60  to remove roughness using conventional surface-finishing equipment and techniques. These techniques provide a more desirable AM part  60  and can prevent undesirable effects such as limited applicability of the AM part  60  due to stress risers typically associated with high surface roughness, and difficultly in use with non-destructive inspection systems because rough surface finishes generate high levels of noise in such systems. 
     Once the one or more post-processing steps are completed, the additional material that formed the structural supports  61  are removed from the AM part  60  (block  204 ). Thus, the additional material provides support just during the time that post-processing steps are being performed on the AM part  60 . Once finished, the material is removed. 
     The finished AM part  60  can be used in a variety of different environments. One specific use is for a vehicle. Vehicles can include but are not limited to manned aircraft, unmanned aircraft, manned spacecraft, unmanned spacecraft, manned rotorcraft, unmanned rotorcraft, satellites, rockets, missiles, manned terrestrial vehicles, unmanned terrestrial vehicles, manned surface water borne vehicles—unmanned surface water borne vehicles, manned sub-surface water borne vehicles, unmanned sub-surface water borne vehicles, and combinations thereof. 
     The methods disclosed above can be used for designing and manufacturing an additively manufactured part. The methods can also be used for designing and manufacturing parts made from other manufacturing processes. 
     The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.