Abstract:
An additive manufacturing process performed by an additive manufacturing machine includes strain gauges that detect stress within a part during fabrication within a defined workspace. When the detected stress is exceeds a desired level the fabrication steps are paused and a stress relieving process is performed within the chamber without moving the part. The additive manufacturing machine includes heaters and coolers for changing the temperature within the chamber to perform the desired stress relieving process in the same space as fabrication is performed. Once it is confirmed that stresses within the part are within acceptable limits the part fabrication process is resumed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/549,883 which was filed on Oct. 21, 2011. 
     
    
     BACKGROUND 
       [0002]    This disclosure generally relates to an LASER configuration for an additive manufacturing machine and process. More particularly, this disclosure relates to a configuration for relieving stress within a part during creation within the additive manufacturing assembly. 
         [0003]    Typical manufacturing methods include various methods of removing material from a starting blank of material to form a desired completed part shape. Such methods utilize cutting tools to remove material to form holes, surfaces, overall shapes and more by subtracting material from the starting material. Such subtractive manufacturing methods impart physical limits on the final shape of a completed part. Additive manufacturing methods form desired part shapes by adding one layer at a time and therefore provide for the formation of part shapes and geometries that would not be feasible in part constructed utilizing traditional subtractive manufacturing methods. 
         [0004]    Additive manufacturing utilizes a heat source such as a laser beam to melt layers of powdered metal to form the desired part configuration layer upon layer. The laser forms a melt pool in the powdered metal that solidifies. Another layer of powdered material is then spread over the formerly solidified part and melted to the previous melted layer to build a desired part geometry layer upon layer. Repeated localized heating by the laser beam coupled with relatively fast cooling across the surface of the part generates stresses in the part that can limit size and part configuration. 
         [0005]    The stresses may be relieved through traditional heat-treating methods but require removal of the part from the additive manufacturing workspace. 
       SUMMARY 
       [0006]    An additive manufacturing process according to an exemplary embodiment of this disclosure, among other possible things includes detecting stress within a part during fabrication within a defined workspace, pausing fabrication steps responsive to a detected stress being within a predetermined range, performing a stress relieving process on the part within the same workspace in which fabrication is performed, and restarting part fabrication on the part within the defined work space once the stress relieving process is complete. 
         [0007]    In a further embodiment of the foregoing additive manufacturing process including heating the part within the workspace to a temperature determined to relieve built in stresses. 
         [0008]    In a further embodiment of any of the foregoing processes including a resistant heater surrounding the workspace for heating the part. 
         [0009]    In a further embodiment of any of the foregoing processes including the step of monitoring stress within the part during the stress relieving process. 
         [0010]    In a further embodiment of any of the foregoing processes including generating an atmosphere within the workspace and surrounding the part that prevents oxidation. 
         [0011]    In a further embodiment of any of the foregoing processes including an atmosphere comprises an argon gas. 
         [0012]    In a further embodiment of any of the foregoing processes including covering an energy directing device to prevent exposure to the workspace during the stress relieving process. 
         [0013]    In a further embodiment of any of the foregoing processes including cooling the workspace to a temperature desired for performing fabrication of the part. 
         [0014]    An additive manufacturing device according to an exemplary embodiment of this disclosure, among other possible things including a workspace defining an area for part fabrication, a powder application device for spreading a powder within the workspace, an energy transmitting device for generating a molten area of powder for forming a layer of a part, a sensor mounted within the workspace that detects stresses within a part during fabrication, and a stress relieving appliance supported proximate the workspace for relieving stress built up in the part during fabrication within the workspace. 
         [0015]    In a further embodiment of the foregoing additive manufacturing device a resistance heater is disposed proximate the workspace for heating the workspace to a temperature determined to reduce stresses built up in the part. 
         [0016]    In a further embodiment of any of the foregoing additive manufacturing devices the workspace includes walls and the resistant heater is supported within the walls of the workspace. 
         [0017]    In a further embodiment of any of the foregoing additive manufacturing devices including a cover movable to a position blocking exposure of the energy-transmitting device to the workspace. 
         [0018]    In a further embodiment of any of the foregoing additive manufacturing devices including an atmosphere within the workspace comprising an argon gas. 
         [0019]    In a further embodiment of any of the foregoing additive manufacturing devices including a cooler for cooling the workspace after performance of a stress relief process. 
         [0020]    In a further embodiment of any of the foregoing additive manufacturing device the sensor comprises a strain gauge mounted within a support holding the part during fabrication. 
         [0021]    Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0022]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic representation of an example additive manufacturing machine during fabrication of a part. 
           [0024]      FIG. 2  is a schematic representation of the additive manufacturing machine during a stress relieving process. 
           [0025]      FIG. 3  is a schematic representation of the example additive manufacturing machine during a cooling process. 
           [0026]      FIGS. 4  is a schematic representation of the example additive manufacturing machine during a measurement process to confirm dimensions of the part. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring to  FIG. 1 , an additive manufacturing machine  10  includes a workspace or chamber  12  that supports an energy transmitting device  18  and a support  14  on which a part  16  is supported during fabrication. In this example, the energy transmitting device  18  emits a laser beam  20  that melts material  24  deposited by a material application device  22 . The example material  24  is a metal powder that is applied in a layer over the support  14  and subsequent layers to produce a desired configuration of the part  16 . The laser beam  20  emits directs energy that melts the powder material in a configuration that forms the desired part dimensions. 
         [0028]    The additive manufacturing process utilizes material  24  that is applied in layers on top of the support  14 . Selective portions of the layers are subsequently melted by the energy emitted from the laser beam  20 . The additive manufacturing process proceeds by melting subsequent layers of powdered material  24  that are applied to the part  16  to form the desired part configuration. As appreciated, the energy focused on the top layer of the part  16  generates the desired heat to melt and then solidify portions of the powdered metal to form the desired part configuration. The repeated localized heating and cooling of the powdered material  24  and the part  16  can result in the buildup of undesired stresses within the part  16 . Stresses within the part  16  may result in undesired cracking or weaknesses within the completed part and therefore are to be avoided. 
         [0029]    The example additive manufacturing machine  10  includes a plurality of sensors  26  that are disposed within the support  14 . In this example, the sensors  26  are strain gauges that measure stress built up within the part  16 . During operating and fabrication of the part  16 , the strain gauges  26  transmit information to a controller  28  that are indicative of the condition and specifically the stress condition of the part  16 . The stress measurements that are provided by the strain gauges  26  are ongoing during the entire fabrication of the part  16 . The ongoing measurement of the stress within the part  16  provides for the detection of undesired rises in stress levels in the part  16 . 
         [0030]    The example additive manufacturing machine  10  further includes heating elements  30  for heating the chamber  12  and a cooler  34  for quickly cooling the workspace  12 . The heating elements  30  and cooler  34  provide for the implementation of a stress relieving heat treat process. 
         [0031]    In response to the controller  28  receiving signals from the strain gauges  26  of a stress built up within the part  16  that are above the desired stress level, the fabrication process can be paused to allow for a stress relieving process to be performed on the part  16 . 
         [0032]    Referring to  FIG. 2 , in response to a detected stress within the part  16  during fabrication, the fabrication process is paused and the chamber  12  is readied for a stress relieving process. In this example, the stress relieving process includes a heat treat process where the part  16  is heated then cooled according to a predetermined temperature and period. 
         [0033]    As is appreciated, the heat treat process utilizes heat to transform material within the part into a more consistent composition. Many heat treatment processes are known and one such process includes the heating of a part to a level to which the material will control the heating and cooling of the part to control the rate of fusion and the rate of the cooling within the microstructure of the material comprising the part  16 . As appreciated, many known heat treating processes may be utilized within the chamber  12  to provide desired properties in the completed part  16 . The example heat treating process includes heating of the part  16  in an inert atmosphere within the same chamber  12  in which part fabrication occurs. Moreover, the example heat process includes heating the chamber  12  to a specific temperature and then cooling the part as is desired within a given period. 
         [0034]    In this example, the chamber  12  includes the electric resistant heaters  30  embedded in the walls of the chamber  12  and a cooler  34  mounted to provide cooling air into the chamber  12 . Alternatively, inductive heaters and other heat sources may be utilized. Before the heat treatment process is begun, the chamber  12  is filled with an inert gas. In this example, Argon gas  44  is utilized to surround the part  16 . A cover  38  is moved to a closed position to protect the energy transmitting device  18  from the heat and environment within the chamber  12  during the heat treat process. The heat treat process then begins by heating the chamber  12 , and thereby the part through the use of the electric resistant heaters  30  to generate heat as indicated by arrow  32 . 
         [0035]    A feature of the example process provides for maintaining the part  16  on the support  14  in the same location as it sits during fabrication. Accordingly, the part  16  remains in place during the heat treatment process such that fabrication is paused only briefly and the part  16  does not need to be removed from its location within the chamber  12 . In this example, the part  16  is heated to a temperature determined to relieve stresses within the part  16 . At all times during the heat treatment process the strain gauges  26  measure stresses within the part  16  and communicate that information to the controller  28 . The controller  28  processes this information and continues with the heat treatment process as it monitors the stresses within the part  16 . The controller  28  may utilize the stress information obtained from the strain gauges  26  to govern operation of the heat treatment process. 
         [0036]    The controller  28  may also implement a heat treatment routine that is defined to heat the part  16  to a desired temperature to cool that part as part of a predefined stress relieving heat treatment process. In each of the instances, the controller  28  may utilize information obtained from the strain gauges  26 . 
         [0037]    Referring to  FIG. 3 , once the part  16  has been heated to a sufficient temperature to provide the desired stress relief, the part  16  is cooled by a cooler  34  that drives cooling air  36  into the chamber  12  to thereby cool the part  16  to a desired temperature required to provide the desired stress relieving function. It should be noted that in all instances, the part  16  remains on the support  14  in the same position in which fabrication had begun. By maintaining the part  16  within the chamber  12 , the specific position is maintained and a secondary set up process is not required. Moreover, overall part fabrication cycle time is reduced. 
         [0038]    Upon completion of the cooling operation, strain and stresses within the part  16  are measured by the strain gauges  26  that remain within the chamber  12  and continually provide information indicative of stresses within the part  16  to the controller  28 . The gauges  26  will indicate that strains and stresses within the part  16  are now within a desired range and fabrication can be restarted. However, if the strain gauges  26  continue to read stress within the part  16  above a desired limit the heat treatment process can be repeated or alternatively, other measures can be instituted to relieve stresses within the part  16 . 
         [0039]    Referring to  FIG. 4 , upon an indication that stresses within the part  16  are now within acceptable ranges a measurement can be made by a measurement device  40  supported within the chamber  12 . This measurement can confirm the parts surface  42  parameters are within those desired for a return to fabrication for the part. The measurement operation can utilize any gauge or system known to provide an indication of the specific part parameters that would be of interest to confirm that re fabrication of the part may begin. In this example, the gauge  40  measures the surface  42 . Upon confirmation that the surface  42  is within the desired range and includes desired attributes, the fabrication process can be restarted on the now stress relieved part  16 . The example stress relieving process can then be repeated as is necessary during the fabrication process to prevent excess stress build up within a part. 
         [0040]    Accordingly, the disclosed advanced manufacturing machine and process of stress relieving a part during fabrication provides for a completed part to be fabricated in a reduced time without removal from the process and fabrication chamber  12 . 
         [0041]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this invention.