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.