Abstract:
A post processing apparatus for automated removal of support material from a three-dimensional objected formed from a build material by selective deposition modeling is provided. The apparatus includes a heated main chamber into which is placed the three-dimensional object with the support material attached and first and second liquid heat transfer medium storage reservoirs. The storage reservoirs reversibly provide liquid heat transfer medium to the main chamber to immerse the three-dimensional object and the attached support material for desired periods of time to meltingly separate the support material from the object.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to solid deposition modeling, and in particular to an apparatus for post processing three-dimensional objects produced by such a modeling technique to remove a non-curable phase change support material from a three-dimensional object formed from a curable phase change build material. 
     2. Description of the Prior Art 
     During the past two decades several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies are generally called Solid Freeform Fabrication techniques, and are herein referred to as “SFF”. SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. Complex parts are produced using SFF techniques from a modeling material in an additive fashion, as opposed to conventional fabrication techniques that are generally subtractive in nature. For example, in most conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, layer by layer, in order to build a complex part. SFF technologies typically utilize a computer graphic representation of a part and a supply of a building material to fabricate the part in successive layers. SFF technologies have many advantages over conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with conventional subtractive manufacturing methods, including the need to create molds for custom applications. In addition, customized objects can be directly produced from computer graphic data in SFF techniques. 
     Structures are formed in a layer by layer manner by solidifying or curing successive layers of a build material in most SFF techniques. For example, in stereolithography a tightly focused beam of energy, typically in the ultraviolet radiation band, is scanned across a layer of a liquid photopolymer resin to selectively cure the resin to form a structure. In Selective Deposition Modeling, herein referred to as “SDM” a phase change build material is jetted or dropped in discrete droplets, or extruded through a nozzle, to solidify on contact with a build platform or previous layer of solidified material in order to build up a three-dimensional object in a layerwise fashion. Solid object imaging, solid object modeling, deposition modeling, multi-jet modeling, three-dimensional printing and thermal stereolithography have at various time been used synonymously for SDM. Often, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as an extruder or print head. 
     There has developed recently an interest in utilizing curable phase change materials in SDM. One of the first suggestions of using a radiation curable build material in SDM is found in U.S. Pat. No. 5,136,515 to Helinski, in which it is proposed to selectively dispense a UV curable build material in a SDM system. Some of the first UV curable material formulations proposed for use in SDM systems are found in Appendix A of International Patent Publication No. WO 97/11837, where three reactive material compositions are provided. More recent teachings of using curable materials in three-dimensional printing are found in U.S. Pat. No. 6,259,962 to Gothait and in International Publication Number WO 01/26023. 
     However, one of the most fundamental problems associated with SDM processes is the adverse effect resulting from gravitational forces that act on a part during the build process. All SDM processes must deal with gravitational forces. For example, most downward facing surfaces built by SDM processes need special supports in order to stabilize the part during the build process. 
     One method of supporting the three-dimensional object to counter the gravity problem is to utilize dissimilar materials in the build process. For example, two different solidifying materials can be selectively deposited in a layer-by-layer process, one material for building the part, and the other material for building the support structure. There are some generally recognized methods for removing support material from a SDM object. Three of the methods were initially proposed in U.S. Pat. No. 5,136,515 to Helinski. They include removing the support material by physical force, removing the support material by application of heat and removing the support material by chemical means. However, all methods have their drawbacks. 
     Where the support material is removed by physical force from a different build material, the materials can be carefully selected in order to establish a weak bond joint at their juncture such that the application of an applied force separates the support structure from the part along the joint. Where a single material is used, the point of contact between the supports and the build object can be weakened so the supports are more easily removed. However, the application of applied force to crack or crumble away the support material from the object has limitations, such as marring or damaging the three-dimensional object during support removal or breaking off entirely of delicate features. Additionally it is difficult, and sometimes impossible, to remove the support material for certain geometric configurations, such as in deep cavities or pockets. 
     A second separation approach is to select a support material having a lower melting point than the material of the formed object. After forming the object and support structure, the temperature of the composite is raised in order to melt out the support structure. This type of approach is described in, for example, U.S. Pat. No. 5,141,680 to Almquist et al. 
     A third approach uses a support material that is soluble in a solvent, but in which the different build material is not so that the support structure is dissolved away after the completed part and its support structure are submersed in the solvent. However, it is problematic with this approach that the solvent eventually becomes saturated with removed support material and must be disposed of, and then replaced with fresh solvent. Additionally, unpleasant and potentially unhealthful odors are produced by the evaporation of the solvent. Thus, implementing this approach may not be user friendly or cost effective. 
     None of the prior approaches provided a simple and low cost apparatus to effect reliable removal of support structure. Where the build material is an acrylate/wax based curable phase change material, there is a need to develop an apparatus capable of removing a phase change support material dispensed to support a three-dimensional object formed from a curable phase change build material without adversely affecting the three-dimensional object. These and other problems are solved by the design of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an aspect of the present invention that an automated post processing apparatus is provided to remove support material from a three-dimensional object formed by solid deposition modeling using a different build material in a heated main chamber. 
     It is another aspect of the present invention that the post-processing apparatus is especially well adapted to remove non-curable support material from a three-dimensional object formed from a curable build material. 
     It is a feature of the present invention that the post-processing apparatus employs a heated main chamber into which a molten heat transfer medium is conveyed to immerse the three-dimensional object for a desired period of time to melt and remove support material from the three-dimensional object without discoloring the object. 
     It is another feature of the present invention that the post-processing apparatus employs a first heated storage reservoir from which and to which molten heat transfer medium is returned from the heated main chamber. 
     It is another feature of the present invention that the post-processing apparatus employs a second heated storage reservoir from which and to which molten heat transfer medium is returned from the heated main chamber to accomplish a final clean melting of the support material. 
     It is an advantage of the present invention that the post processing apparatus is low cost and effective in removing support material from a three-dimensional object formed of a different build material without harming or damaging the object. 
     These and other aspects, features, and advantages are obtained in the post processing apparatus of the present invention to remove support material from an three-dimensional object formed from a different build material by selective deposition modeling by using a heated main chamber into which are pumped molten heat transfer media from separate storage reservoirs. The three-dimensional object is formed from a first heat transfer material, preferably a curable phase change composition, and the support structure is formed from a second heat transfer medium, preferably a non-curable phase change composition. The post processing apparatus stores the heat transfer medium in two heated storage reservoirs. Paraffin is a preferred heat transfer medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aspects, features, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when it is taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a side perspective view of the post processing apparatus of the present invention; 
         FIG. 2  is a top perspective view of the post processing apparatus of the present invention with the external covers removed, the main chamber cover raised and the tops of the storage reservoirs removed; and 
         FIG. 3  is a side elevational view of the post processing apparatus of the present invention with the covers removed. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A post processing apparatus is indicated generally by the numeral  10  in  FIG. 1 . The apparatus  10  has a hinged access cover  11  over a main chamber  16 , see briefly  FIG. 2 , and a removable access panel  16  to the first and second storage reservoirs  19  and  20 , again see briefly  FIG. 2 . A control panel  12  is mounted to panel  14  and provides digital temperature displays and process cycle pads (not shown) to monitor and control the support material removal process from three-dimensional objects positioned within the main chamber  16 . An overflow and waste collection receptacle  15  is removably mounted to the apparatus  10 . Apparatus  10  is mounted on a base frame  26 , best seen in  FIGS. 2 and 3 , and base supports or legs  28 . 
     As seen in  FIG. 2  the main chamber  16  has a hinged cover  18  that serves to retain heat in the chamber  16  during the support material removal process and permit easy access to the chamber. The chamber  16  is formed from aluminum and is heated with blanket type of heaters (not shown). Chamber  16  can have a rack or basket to retain three-dimensional objects being processed for removal of support material. The support material is removed by immersing the objects in chamber  16  in a liquid heat transfer medium, which preferably is molten paraffin wax. 
     The heat transfer medium is fed into the chamber  16  from storage reservoirs  19  and  20  via appropriate feed lines. Storage reservoirs  19  and  20  are also formed from aluminum and heated with blanket type of heaters (also not shown). Each reservoir holds sufficient liquid heat transfer medium to completely fill the chamber  16 . Pipe  21  is the connection from first storage reservoir  19  to chamber  16 . A pressure and vacuum pump  22  forces air into the first reservoir  19  via a solenoid valve (not shown). The pump  22  bubbles air into the closed and sealed reservoir  19  to force the heated liquid heat transfer medium into the chamber  16  to a level that totally immerses any objects within the chamber  16 . A temperature measurement device  24 , such as a resistance thermal device or RTD, is mounted to the storage reservoir  19  and provides sensings of the temperature of the liquid heat transfer medium within the storage reservoir  19 . A controller linked to control panel  12  utilizes a proportional integral derivative function algorithm to control the temperatures in the chamber  16  and the storage reservoirs  19  and  20 . A drain line  25  is shown exiting the bottom of storage reservoir  19  to permit the reservoir to be drained of support material contaminated heat transfer medium that loses its effectiveness after a period of time because of the increase in concentration of support material in it. The drain line is opened by a manually activated valve  29  in the rear of the apparatus  10 , best seen in  FIG. 3 . This arrangement of piping, valving, pump and temperature measurement device is mirrored on second storage reservoir  20 . The tops to first and second storage reservoirs  19  and  20  have been removed in  FIGS. 2 and 3 , but are sealingly secured by appropriate fasteners, such as screws  30 , arrayed about the top of the reservoirs. 
     Build chamber  16  has an overflow tube (not shown) connecting to the overflow and waste receptacle  15  to allow excess liquid in the main chamber  16  to passively drain into receptacle  15 . The level of liquid in the chamber  16  will rise as more parts are immersed and the support material melted off, leading to an increase over time in the liquid level when the first storage reservoir  19  pumps its contents into the chamber  16 . Receptacle  15  optimally has a monitoring device to detect when it is full and needs to be emptied of solidified material, as well as an electromechanical interlock to prevent the drawer from being opened during the support material removal process. 
     The immersion process is selectable for a desired length of time from preset cycles that vary in length from as little as 30 minutes to as long as 2 hours or more. The length of time needed to remove the support material is dependent upon the size and the complexity of the three-dimensional objects being cleaned. After liquid heat transfer medium has been pumped into chamber  16  and the three-dimensional object immersed for the desired period of time, the pump  22  is reversed and a vacuum is drawn in the first reservoir  19 , causing the liquid heat transfer medium with the now melted support material to be forced back into the storage reservoir. Then the liquid heat transfer medium in storage reservoir  20  is pumped into the chamber  16  to immerse the three-dimensional object a second time in what is considered a final cleansing bath or “rinse” with relatively uncontaminated heat transfer medium since the bulk of the support material has been removed in the first immersion by the liquid heat transfer medium from the first storage reservoir  19 . When the preset time has been completed, the pump for second storage reservoir  20  is reversed and the liquid heat transfer medium is forced back into reservoir  20  in the same manner as accomplished with first storage reservoir  19 . The manually activated drain valve  29  at the rear of apparatus  10  is switched from first storage reservoir  19  to second storage reservoir  20  as needed to drain the contaminated liquid heat transfer medium from each and permit replacement with fresh heat transfer medum. 
     A typical build material is described in detail in U.S. Pat. No. 6,841,589 entitled “Ultra-Violet Light Curable Hot Melt Composition”, which is assigned to the assignee of the present invention. A typical support material is described in detail in pending application U.S. Ser. No. 10/186,447 filed Jul. 2, 2002 and published as Publication 2003/0100658 A1 and also assigned to the assignee of the present invention. The materials preferably have a melting point from about 45° C. to about 65° C., a freezing point from about 33° C. to about 60° C., and a jetting viscosity of about 10 to about 16 centipoise at the dispensing temperature. A preferred temperature for the liquid heat transfer medium during the support removal process is about 70° Centigrade. 
     In operation the apparatus  10  is turned on and the heaters begin to heat the storage reservoirs  19  and  20  to raise the temperature of the heat transfer medium to the operating temperature. The controller using the proportional integral derivative function algorithm maintains the temperature in the storage reservoirs  19  and  20  throughout the support material removal process. A prompt alerts the operator to inspect the waste and overflow receptacle to remove any hardened material deposited therein from previous use. An electromechanical interlock can be used to verify this has been performed. Once the storage reservoirs and their liquid heat transfer medium have been heated to the operating temperature, the operator raises cover  11 , places the three-dimensional object or objects within the main chamber  16 , closes the cover  11 , and selects the pre-set cycle according to the size and complexity of the part. The pump  22  is activated and bubbles in air into the first storage reservoir  19 , thereby positively displacing the heated liquid heat transfer medium from the reservoir  19  into the chamber  16  to immerse the part. Chamber  16  has been heated to maintain the correct temperature of the liquid heat transfer medium. The three-dimensional object is immersed for the desired pre-set time. Any excess liquid material in the chamber  16  drains into the overflow and waste collection receptacle  15 . The pump  22  is reversed and the liquid heat transfer medium with the now melted support material is drawn back into the first storage reservoir  19 . The liquid heat transfer medium in the second reservoir is then pumped in the chamber  16  in the same manner and immerses the object for the pre-selected and desired length of time in a final or cleansing immersion of the object. At the conclusion of the selected time, the pump is reversed and the liquid transfer medium is drawn back into the second storage reservoir  20  and the object is ready for removal and final cleaning, as necessary. Optionally, heated air can be directed into the chamber  16  at this time to further remove any residual support material. At the conclusion of the support material removal process, the post processing apparatus  10  is put into a sleep mode by its controller, allowing the temperatures in the chamber  16  and the storage reservoirs  19  and  20  to drop. 
     Although paraffin wax is the preferred liquid heat transfer medium, other media such as organic oil or mineral oil may be employed in the post processing apparatus  10 . One organic oil that has been used with mixed success is peanut oil. Another potentially suitable liquid heat transfer medium is water. 
     While the present invention is applicable to removing support material from any SDM created three-dimensional objects, the invention has been described with respect to three-dimensional objects created utilizing an ink jet print head dispensing a ultraviolet radiation curable phase change material. However, it is to be appreciated that the present invention can be implemented to remove support material from three-dimensional objects created by any SDM technique utilizing a wide variety of curable phase change materials. For example, the curable phase change material can be cured by exposure to actinic radiation having wavelengths other than in the ultraviolet band of the spectrum, or by subjecting the material to thermal heat. 
     While the invention has been described above with references to specific embodiments thereof, it is apparent that many changes, modifications and variations in the materials, arrangements of parts and steps can be made without departing from the inventive concept disclosed herein. For example, although the post processor has been shown and described as using only molten paraffin wax to remove the support material, it is also possible to blow warm air into the main chamber to achieve supplemental melting of any residual wax after the primary immersion, or the secondary immersion. Accordingly, the spirit and broad scope of the appended claims are intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.