Patent Document

BACKGROUND 
       [0001]    The present invention relates to a system and method for surface finishing of rapid-manufactured three-dimensional (3D) objects by vapor smoothing. 
         [0002]    The production and testing of 3D objects is commonly used for developing new products, machines, and processes in a wide range of industries. There are a variety of rapid manufacturing techniques for building 3D objects, each of which develop the objects from geometric computer models under computer control. These techniques generally slice or divide a digital representation of a desired object (e.g., a computer aided design (CAD)) into horizontal layers, then build the object layer-by-layer by repetitive application of materials. The term “rapid manufacturing” herein refers to the building of 3D objects by one or more layer-based additive techniques. Exemplary rapid manufacturing techniques include fused deposition modeling, ink jetting, selective laser sintering, and stereolithographic processes. 
         [0003]    3D objects built by rapid manufacturing techniques generally exhibit “stair-step” appearances, particularly at curved or angled exterior surfaces. The stair stepping effect is caused by the layering of cross-sectional shapes that have square-edge profiles, and is more pronounced as layer thicknesses increase. While the stair stepping effect generally does not affect the strengths of the 3D objects, it may significantly diminish the desired aesthetic qualities. A variety of polishing techniques have been used to improve the surface finish of rapid-manufactured 3D objects. However, there is an ongoing need for surface treatment techniques that provide aesthetically pleasing surfaces to rapid-manufactured 3D objects. 
       SUMMARY 
       [0004]    The present invention is a system and method for vapor smoothing a rapid manufactured three-dimensional object. The system includes a cabinet housing having a sealable interior. A heated vapor chamber in the interior of the cabinet housing contains solvent that is vaporizable to fill the vapor chamber with vapor for smoothing the object when the object is placed in the vapor chamber. A drying chamber is also provided in the interior of the cabinet housing that is separate from the vapor chamber for drying the object when the object is moved from the vapor chamber to the drying chamber. 
         [0005]    The method involves heating a solvent in a vapor chamber to fill the vapor chamber with solvent vapor. The object is placed in the vapor chamber for a time sufficient to at least partially reflow material at a surface of the object. The object is the removed from the vapor chamber and placed in a drying chamber that is separate from the vapor chamber for a time sufficient to dry the surface of the object. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view illustrating a vapor smoothing surface finishing system according to an embodiment of the present invention. 
           [0007]      FIG. 2  is a front view illustrating a vapor smoothing surface finishing system according to an embodiment of the present invention. 
           [0008]      FIG. 3  is a top view illustrating a vapor smoothing surface finishing system according to an embodiment of the present invention. 
           [0009]      FIG. 4  is a flow diagram illustrating an exemplary method of vapor smoothing a rapid manufactured object according to an embodiment of the present invention. 
           [0010]      FIG. 5  is a diagram illustrating the recycling of solvent in the vapor smoothing surface finishing system of the present invention. 
           [0011]      FIG. 6  is a diagram illustrating an exemplary control panel for use by an operator to control the operation of the surface finishing system. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The system and method of the present invention may be employed with respect to objects formed from a polymeric or wax material using layered manufacturing rapid prototyping techniques. An exemplary layered manufacturing technique is the type disclosed in U.S. Pat. No. 5,121,329, wherein an extrusion head deposits “roads” of molten material in layers of predetermined shape, and which material solidifies upon a drop in temperature to form a solid model. The effect of surface finishing of such objects by vapor smoothing is explained in U.S. Patent Publication No. 2005/0173838, the disclosure of which is hereby incorporated by reference in its entirety. 
         [0013]      FIG. 1  is a perspective view,  FIG. 2  is a front view, and  FIG. 3  is a top view, illustrating vapor smoothing surface finishing system  10  according to an embodiment of the present invention. System  10  includes cabinet housing  12 , sliding door  14 , cabinet interior  16 , vapor chamber  18  and drying chamber  20 . Sliding door  21  is provided to selectively cover vapor chamber  18 . Refrigeration compressor  22  is also located in cabinet housing  12 . Solvent storage tank  24  is located in cabinet housing  12  outside vapor chamber  18 , and is connected via a valve (such as a ball valve in one embodiment) to the interior of vapor chamber  18 . Sliding door  14  is operable to selectively open and close over cabinet interior  16 , and may be operated either manually or by an automatic control. 
         [0014]    Vapor chamber  18  includes bottom heater  26  and side heaters  28  and  29 . Primary cooling coils  30  are connected to refrigeration compressor  22 , and are located near the top of vapor chamber  18  to create a vapor ceiling for containing vapor in vapor chamber  18 . In order to operate vapor chamber  18  for vapor smoothing an object, solvent  32  is provided at the bottom of vapor chamber  18 . In an alternative embodiment, solvent  32  may be boiled in an area that is located off to the side of vapor chamber  18 , rather than directly in the bottom of vapor chamber  18 . Solvent  32  has a fluid level that is lower than the elevation of plate  34 , so that any object that may be inadvertently dropped inside vapor chamber  18  does not fall into solvent  32 . Alternatively, plate  34  may be deleted if dropping objects into solvent  32  is not a concern. In a particular embodiment, solvent  32  is maintained at a level between 0.25 and 0.5 inches (0.63 and  1 . 27  centimeters) across the bottom of vapor chamber  18 , as this level is the minimum level of solvent required in such an embodiment to fill the interior of vapor chamber  18  with solvent vapor when boiled. Typical degreasing systems employ a large amount of solvent to fill the exposure chamber with vapor. However, use of the minimum amount of solvent required to fill vapor chamber  18  with vapor (achieved by continually providing solvent from solvent tank  24  to maintain the fluid level of solvent in vapor chamber  18  at this amount) allows surface finishing system  10  to start up and shut down more quickly, and avoids the use of a “boiling cauldron” of solvent that can be unsettling for an operator to work with. As used herein, the term “minimum amount” of solvent needed to fill the chamber with vapor includes some variability, and encompasses a range of solvent volumes that are effective to fill the vapor chamber with vapor without excess solvent in vapor chamber  18 . Heaters  26 ,  28  and  29  are operated to form a vapor from solvent  32  in vapor chamber  18 , which fills vapor chamber  18  below the vapor ceiling formed by primary cooling coils  30 . Solvent  32  is selected to be compatible with the modeling material which forms the object to which surface finishing is to be applied, as is known in the art. For example, suitable solvents may include an n-Propyl bromide solution (e.g., Abzol®), perchloroethylene, trichloroethylene, hydrofluorocarbon fluid (e.g., Vertrel®), methylene chloride, or others. 
         [0015]    Drying chamber  20  is located within cabinet housing interior  16  adjacent to vapor chamber  18 . Drying chamber  20  is provided to allow an object that has been exposed to vapor in vapor chamber  18  to outgas for a period of time until the object is ready for either another exposure in vapor chamber  18  or removal from system  10 . Drying chamber  20  is typically maintained at a temperature below room temperature, such as at or below about 50° F. (10° C.) in one embodiment. The difference between the temperature of the solvent vapor (e.g., about 106° F. (41° C.) for Vertrel® solvent) and the temperature of drying chamber  20  is preferably large, such as a difference of 40° F. (22° C.) or greater, in most embodiments. This ensures that the reaction of the solvent vapor to the material of the object is consistent and controlled. 
         [0016]    In operation, an object to be subjected to surface finishing treatment is suspended in vapor chamber  18  in order to be smoothed by exposure to the vapor therein. An operator opens sliding door  14  to open interior  16  of system  10 , and operates a control to open sliding door  21  to open vapor chamber  18 . The operator then suspends the object, such as from a metal wire or another suspension mechanism, in vapor chamber  18 , and the object is exposed to the vapor in vapor chamber  18  for a period of time sufficient to alter the surface finish of the object. Penetration of the vaporized solvent in vapor chamber  18  of the surface of the object softens the modeling material at the surface of the object, so that the surface material may reflow and thereby smooth the surface of the object. In one embodiment, the exposure time may be selected by observing condensation of solvent vapors on the object, and the object may be removed from vapor chamber  18  when condensation stops, indicating that the temperature of the object surface has reached the temperature of the boiling solvent. In another embodiment, the exposure time may be controlled according to a formula for the type of solvent and modeling material employed. Typical exposure times in vapor chamber are expected to be less than a few minutes, such as about 15-30 seconds in some embodiments. 
         [0017]    After the object has been exposed in vapor chamber  18 , the object is raised out of vapor chamber  18  and moved to drying chamber  20 . When the object is removed from vapor chamber  18 , it is preferable to cover vapor chamber with sliding door  21 , as a precaution to ensure that no further vapors escape vapor chamber  18 . The object may be suspended in drying chamber for as long as is necessary to dry and re-harden the surface of the object. Secondary cooling coils  36  are connected to refrigeration compressor  22 , and are provided near the top of cabinet housing  12  to cool drying chamber to a desired temperature (typically below room temperature, as discussed above), and to ensure that all vapors are contained within cabinet housing  12 . Exhaust vent  38  is optionally provided to operate when an object is located in drying chamber  20  (that is, when sliding door  21  covers vapor chamber  18 ) to provide ventilation outside of cabinet housing  12 . Control panel  40  allows an operator to control start-up and shutdown of system  10 , and provides system status indicators. 
         [0018]      FIG. 4  is a flow diagram illustrating exemplary method  50  of vapor smoothing a rapid manufactured object according to an embodiment of the present invention. Method  50  includes steps  52 - 66 , and initially involves providing solvent  32  in vapor chamber  18  from solvent tank  24  located outside cabinet housing  12  (step  52 ). In an exemplary embodiment, this is performed under the control of a programmable logic controller (PLC) that operates to provide a precisely measured amount of solvent  32  through a valve (such as a ball valve or another type of valve) into vapor chamber  18 , so as to maintain a fluid level of about 0.25 to 0.5 inches (0.63 to 1.27 centimeters), which in such embodiment is the minimum amount of boiling solvent required to fill-vapor chamber  18  with solvent vapor. This low level of solvent  32  can be used and maintained due to the PLC continually and controllably providing solvent from solvent tank  24  as needed to maintain the desired minimum fluid level that will keep vapor chamber  18  filled with solvent vapor. Heaters  26 ,  28  and  29  are operated to vaporize solvent  32  in vapor chamber  19  (step  54 ). Door  14  is opened to allow access to interior  16  of cabinet housing  12 , and door  21  is opened to allow access to the interior of vapor chamber  18  (step  56 ). In one embodiment, door  21 l is air-powered (although it could be powered electrically or by other means) and is operated by foot-pedal control. The object to be vapor smoothed is then suspended in vapor chamber  18  (step  58 ). For many objects, suspension in vapor chamber  18  for up to about  30  seconds is all that is required for vapor to condense onto the object and reflow the outer surface material of the object to effect smoothing. After exposure of the object in vapor chamber  18 , the object is moved from vapor chamber  18  to drying chamber  20 , and door  21  is closed to reseal vapor chamber  18  (step  60 ). 
         [0019]    During operation of surface finishing system  10 , vapor in vapor chamber  18  is continually condensed onto primary cooling coils  30 , and the distilled solvent is passed through a water separator and returned to solvent tank  24 . The water separator both performs the water removal function and acts as a “plug” to ensure that vapor does not evaporate out of vapor chamber  18  during operation. In an exemplary embodiment, the distilled solvent (with water removed) is returned to the top of solvent tank  24 , and solvent drawn from solvent tank  24  into vapor chamber  18  is taken from the bottom of solvent tank  24 . This cycle of operation allows solvent to be reused and preserved to the extent possible, reducing the burden associated with disposal of solvent or solvent vapors that have been used. 
         [0020]    After a cycle of exposing the object in vapor chamber  18  and drying the object in drying chamber  20 , an operator determines whether smoothing of the object is complete (step  62 ). This determination may be made by observing the appearance of the object, by following a predetermined formula or procedure for a given type of object, or by another method. If smoothing is not complete, another exposure and drying cycle is performed. If smoothing is complete, after sufficient time to fully dry and cure the surface of the object (step  63 ), the object may be subjected to media blasting, such as with baking soda or another abrasive material (step  64 ). In one embodiment, the object is removed from cabinet housing  12  in order to media blast the object. In another embodiment, media blasting capability is provided in drying chamber  20 , such as via a rotary mill, a vibratory process, or by manual blasting by an operator in drying chamber  20 . Media blasting the object removes the sheen that is often present in rapid manufactured objects, providing an aesthetically pleasing satin finish to the object. 
         [0021]    After use of surface finishing system  10  is complete, a shutdown process if performed (step  66 ), in which the vapor present in vapor chamber  18  is condensed, and the solvent may be returned to solvent tank  24 . In an exemplary embodiment, condensing the vapor is achieved via operation of cold finger  42  ( FIG. 2 ), which is connected to refrigeration compressor  22 . In an exemplary shutdown sequence, the valve that connects solvent tank  24  to vapor chamber  18  is first closed, to stop the provision of solvent to vapor chamber  32 . Then, all solvent remaining in vapor chamber  18  is vaporized and condensed onto primary cooling coils  30 . Last, cold finger  42  is activated to attract and condense any remaining solvent vapor to the bottom of vapor chamber  18 , and this solvent is returned to solvent tank  24  via a pump-based or gravity-based transport mechanism. The shutdown procedure is typically initiated by an operator, although the system may be programmed to automatically shut down after an extended period of inactivity under control of the system PLC. 
         [0022]    The process of exposing an object to vapor in vapor chamber  18  and drying the object in drying chamber  20  may be repeated as many times as desired, to obtain a desired surface finish of the object. When the vapor smoothing process is complete, the “stair-step” features that are typically present in rapid manufactured objects will be significantly reduced or eliminated. 
         [0023]    In some embodiments, it is desirable to precool the object to be vapor smoothed by placing it in drying chamber  20  before the initial exposure to solvent vapor in vapor chamber  18 . This ensures that vapor is attracted to the object in vapor chamber  18 , and that the reaction at the surface of the object occurs as desired. 
         [0024]      FIG. 5  is a diagram illustrating the recycling of solvent by surface finishing system  10 . As discuss above, during operation of surface finishing system  10 , vapor in vapor chamber  18  is continually condensed onto primary cooling coils  30 , and the distilled solvent is passed through water separator  68  and returned to solvent tank  24 . Solvent is also continually controlled to be provided from solvent tank  24  to vapor chamber  18  to maintain a desired fluid level in vapor chamber  18 , to ensure that solvent vapor fills vapor chamber  18 . This recycling of solvent continues until surface finishing system  10  is shut down. In a shutdown procedure, as discussed above, all remaining solvent in vapor chamber  18  is vaporized, and the solvent vapor is condensed on primary cooling coils  30  as in normal operation, and in addition cold finger  42  is activated to condense any remaining solvent vapor to the bottom of vapor chamber  18 . This condensed solvent vapor is transported by pump  69  (or some other transport mechanism) through water separator  68  and back to solvent tank  24 . Thus, the solvent may be recycled and reused for future operation of surface finishing system  10 . 
         [0025]      FIG. 6  is a diagram illustrating exemplary control panel  40  for use by an operator to control the operation of surface finishing system  10 . Control panel  40  includes system start button  70 , system shutdown button  72 , and emergency stop button  74 , and also includes indicator lights for low fluid level (light  76 ), system ready status (light  78 ), system shutdown complete status (light  80 ), and system fault status (light  82 ). Pressing system start button  70  results in provision of solvent into vapor chamber  18  from solvent tank  24 , and operating heaters  26 ,  28  and  29  to vaporize solvent  32  in vapor chamber  18 . System ready status light  78  will illuminate when vapor chamber  18  reaches a temperature that is ready for an object to be vapor smoothed. After vapor smoothing is complete, an operator may press system shutdown button  72  to initiate a shutdown sequence, in which all of the vapor in vapor chamber  18  is condensed and returned to solvent tank  24  as described above. 
         [0026]    Vapor smoothing surface finishing system  10  provides separated vapor chamber  18  and drying chamber  20  within the same cabinet housing  12 . Vapor is contained within vapor chamber  18 , and a small amount of solvent is used to form the vapor used for vapor smoothing of a rapid manufactured object. Plate  34  is provided at a higher elevation than the fluid level of solvent  32  in vapor chamber  18 , to hide boiling solvent  32  and to protect against dropping of an object in solvent  32 . These features assure operator safety in operation of vapor smoothing finishing system  10 . Moreover, the small amount of solvent employed in vapor chamber  18  allows system  10  to be rapidly started up and shut down. 
         [0027]    Drying chamber  20  is maintained at a temperature below room temperature, to ensure that the reaction of solvent vapor to the material of the object being smoothed is consistent and controlled. The difference between the temperature of the solvent vapor in vapor chamber  18  and the temperature of drying chamber  20  is preferably greater than 40° F. (22° C.) which may be achieved in some embodiments by maintaining drying chamber  20  at a temperature of no greater than 50° F. (10° C.). 
         [0028]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Technology Category: 7