Patent Application
20050280189
The present invention relates generally to tooling systems and processes and is more specifically related to the fabrication of tools through selective laser sintering.
Traditional fabrication methods for tools having areas of contour have included fiberglass lay-ups on numerically controlled machined master models or facility details.
A manufacturing master model tool, or “master model”, is a three-dimensional representation of a part or assembly. The master model controls physical features and shapes during the manufacture or “build” of assembly tools, thereby ensuring that parts and assemblies created using the master model fit together.
Traditional tool fabrication methods rely on a physical master model. These master models may be made from many different materials including: steel, aluminum, plaster, clay, and composites; and the selection of a specific material has been application dependent. Master models are usually hand-made and require skilled craftsmen to accurately capture the design intent. Once the master model exists, it may be used to duplicate tools.
The master model becomes the master definition for the contours and edges of a part pattern that the master model represents. The engineering and tool model definitions of those features become reference only.
Root cause analysis of issues within tool families associated with the master has required tool removal from production for tool fabrication coordination with the master. Tools must also be removed from production for master model coordination when repairing or replacing tool details. Further, the master must be stored and maintained for the life of the tool.
Master models are costly in that they require design, modeling and surfacing, programming, machine time, hand work, secondary fabrication operations, and inspection prior to use in tool fabrication.
In summary, although used for years, physical master models have inherent inefficiencies, including: they are costly and difficult to create, use, and maintain; there is a constant risk of damage or loss of the master model; and large master models are difficult and costly to store.
By way of further background, the field of rapid prototyping of parts has, in recent years, made significant improvements in providing high strength, high density parts for use in the design and pilot production of many useful objects. “Rapid prototyping” generally refers to the manufacture of objects directly from computer-aided-design (CAD) databases in an automated fashion, rather than from conventional machining of prototype objects following engineering drawings. As a result, time required to produce prototype parts from engineering designs has been reduced from several weeks to a matter of a few hours.
An example of a rapid prototyping technology is the selective laser sintering process (SLS) in which objects are fabricated from a laser-fusible powder. According to this process, a thin layer of powder is dispensed and then fused, melted, or sintered, by a laser beam directed to those portions of the powder corresponding to a cross-section of the object.
Conventional selective laser sintering systems position the laser beam by way of galvanometer-driven mirrors that deflect the laser beam. The deflection of the laser beam is controlled, in combination with modulation of the laser itself, for directing laser energy to those locations of the fusible powder layer corresponding to the cross-section of the object to be formed in that layer. The laser may be scanned across the powder in a raster fashion or a vector fashion.
In a number of applications, cross-sections of objects are formed in a powder layer by fusing powder along the outline of the cross-section in vector fashion either before or after a raster scan that fills the area within the vector-drawn outline. After the selective fusing of powder in a given layer, an additional layer of powder is then dispensed and the process repeated, with fused portions of later layers fusing to fused portions of previous layers (as appropriate for the object), until the object is completed.
Selective laser sintering has enabled the direct manufacture of three-dimensional objects of high resolution and dimensional accuracy from a variety of materials including polystyrene, NYLON, other plastics, and composite materials, such as polymer coated metals and ceramics. In addition, selective laser sintering may be used for the direct fabrication of molds from a CAD database representation of the object in the fabricated molds. Selective Laser Sintering has, however, not been generally applicable for tool manufacture because of SLS part size limitations, lack if robustness of SLS objects, and inherent limitations in the SLS process.
The disadvantages associated with current tool manufacturing systems have made it apparent that a new and improved tooling system is needed. The new tooling system should reduce need for master models and should reduce time requirements and costs associated with tool manufacture. The new system should also apply SLS technology to tooling applications. The present invention is directed to these ends.
In accordance with one aspect of the present invention, a system for manufacturing a tool within a laser sintering system includes a chamber enclosing a sinter material. The laser sintering system grows or sinters sections of the tool and tool contoured details from the sinter material in response to signals from a controller. The controller generates the signals as a function of a predetermined tool design. The contoured details include attachment holes, which are strengthened by bushings.
In accordance with another aspect of the present invention, a method for laser sintering a tool includes predetermining a position of a contoured detail feature. The method further includes predetermining a configuration for the contoured detail feature such that the contoured detail feature includes securing features for coupling strengthening components thereto. The contoured detail is sintered, and a strengthening component is coupled thereto, thereby reducing stress on the contoured detail feature.
One advantage of the present invention is that use of Selective Laser Sintering can significantly reduce costs and cycle time associated with the tool fabrication process. An additional advantage is that tool features can be “grown” as represented by the three-dimensional computer model, thus eliminating the requirement for a master model or facility detail. The subsequent maintenance or storage of the master/facility is thereby also eliminated.
Still another advantage of the present invention is that the model remains the master definition of the tool, therefore root cause analysis or detail replacement may be done directly from the model definition. Secondary fabrication operations are further eliminated where features are “grown” per the three-dimensional solid model definition.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.
In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:
The present invention is illustrated with respect to a sintering system particularly suited to the aerospace field. The present invention is, however, applicable to various other uses that may require tooling or parts manufacture, as will be understood by one skilled in the art.
The system 100 is further adjusted and controlled through various control features, such as the addition of heat sinks 126, optimal objection orientations, and feature placements, which are detailed herein.
The chamber 102 encloses a powder sinter material that is delivered therein through a powder delivery system. The powder delivery system in system 100 includes feed piston 114, controlled by motor 106, moving upwardly and lifting a volume of powder into the chamber 102. Two powder feed and collection pistons 114 may be provided on either side of part piston 107, for purposes of efficient and flexible powder delivery. Part piston 107 is controlled by motor 108 for moving downwardly below the floor of chamber 102 (part cylinder or part chamber) by small amounts, for example 0.125 mm, thereby defining the thickness of each layer of powder undergoing processing.
The roller 118 is a counter-rotating roller that translates powder from feed piston 114 to target surface 115. Target surface 115, for purposes of the description herein, refers to the top surface of heat-fusible powder (including portions previously sintered, if present) disposed above part piston 107; the sintered and unsintered powder disposed on part piston 107 and enclosed by the chamber will be referred to herein as the part bed 117. Another known powder delivery system feeds powder from above part piston 107, in front of a delivery apparatus such as a roller or scraper.
In the selective laser sintering system 100 of
Referring to
During the sintering process, various features are molded into the large tool section or sections. Such features include steps and thickness variations 158, gussets 160, stiffeners 162, interfaces and coordination features for making interfaces 164, construction ball interfaces and coordination holes 170, trim of pocket and drill inserts 166, hole patterns 172, and holes 168 included in multiple details for interfacing hardware, such as detail 180. Important to note is that a first plurality of features, including a combination of the aforementioned features, may be sintered into the first section 152 and a second plurality of features, including a combination of the aforementioned features, may be sintered into the second section 154.
Individually contoured details, such as detail 180, which may also be considered sections of the tool for the purposes of the present invention, may be sintered separately from the main body of the tool 150, such that they may be easily replaced or replaceable or easily redesigned and incorporated in the tool 150. Alternate embodiments include a plurality of individual contoured details, such as 180, 182, 184, and 186. Each of the contoured details includes holes, e.g. 168, such that a bolt 190 may bolt the detail 180 to a section 152, 154, or 156 of the tool 150. The contoured details 180 further define holes or openings 198 strengthened by bushings 200. The openings 198 reduce friction acting on and strengthen the contoured detail 180 such that other tools, tool components, or devices may be coupled thereto. The contoured detail 180 and the bushings 200 will be discussed further regarding
The features, such as the gusset 160 and the stiffener 162 are, in one embodiment of the present invention, grown on the same side of the SLS tool 150. Growing (i.e. sintering) these features on the same side of the tool takes advantage of the sintering process because a feature grown at the beginning of a sintering operation has different properties than the same feature would when grown at the end of a sintering operation. Therefore, the first side 200 undergoing sintering includes all the tool features.
Alternate embodiments of the present invention include various tool features grown on either side of the tool 150 through various other methods developed in accordance with the present invention. One such method includes adding a heat sink 202, or a plurality of heat sinks 202, 204, 206 to various portions of the bed 117 such that different tool features may be cooled subsequent to sintering on the first section 152 or second section 154, thereby avoiding warping that is otherwise inherent in the sintering process. Alternately, a single large heat sink may be placed on one side such that all features cool at the same rate and immediately following the sintering operation.
A further aspect of the present invention includes separating contoured details and various tool aspects by a proximate amount such that warping between the features is limited and structural integrity of the features is maximized.
An alternate embodiment of the present invention includes designing in access features or buffer features 179 in areas where warping will occur during sintering such that these features may be removed when the sintering process is concluded. These buffer features 179 may be predetermined such that connection between them and the main body of the part facilitates detachment through a twisting off or breaking off procedure for the buffer feature 179.
For embodied contoured details having short edge distances or patterns of openings with thin walls of the sintered material, opening centerlines tend to migrate when bushings are press fit into the sintered material. To prevent this, the present invention includes bushing attachment operations, wherein the bushings 200, 208, 210 are gently slip fit into the openings 198, 202, 206.
The fit between bushing 200 and opening 198 may include a slip fit operation with a bonding agent used between the bushing 200 and the sintered contoured detail 180 to prevent the migration. This slip fit clearance adds to the bushing location tolerance during fabrication.
In an alternate embodiment of the present invention, assembly features, here embodied as a retaining undercut 218 and applied epoxy 216 at the head 220 of the bushing 200, are included to allow a light press fit between the bushing 200 and the sinter material. The retaining undercut 218, attached through epoxy 216, prevents bushing migration during production usage of the detail 180. The bushing 200 in this embodiment may be easily removed without damage to the detail 180.
The openings 198, 202, 206 include the undercuts 218, 226, 234, which are embodied herein as coaxial with the openings 198, 202, 206 and having greater diameters thereto.
The undercut 218 is grown into the SLS detail in the area of the flange or bushing head 220 attachment. A commercially available epoxy 216 is applied to the undercut 218 overlapping the bushing head 220, the hardened epoxy 216 thereby traps the head 220 of the bushing 200. The undercut 218 includes a flange holding portion or base 223 (bushing flange support ledge), an overhanging portion 225, and a common sidewall 227.
Bushings 200, 208, 210 include heads 220, 221, 228 or flanges such that the bushings 200, 208, 210 may be inserted into the openings 198, 202, 206 and catch on the respective undercuts 218, 226, 234 and attached with epoxy thereto. The bushings 200, 208, 210 further include cylindrical bodies 211, 213, 215, as will be understood by one skilled in the art.
Important to note is that bushings 200, 208, 210 may be attached through a plurality of points through epoxy attached to each bushing head. In other words, the head 220 of bushing 200 is attached at points 216 and 219 to undercut 218; the head 221 of bushing 208 is attached at points 222 and 224 to undercut 226; the head 228 of bushing 210 is attached at points 230 and 232 to undercut 234.
Referring to
In operation block 304, the features, such as thickness variations 158, gussets 160, stiffeners 162, interfaces and coordination features 164, construction ball interface and coordination holes 170, trim of pockets and drill inserts 166 and holes 168 provided in details for interface hardware, such as screws, are all predetermined for the tool.
In operation block 306, optimal orientation of the SLS tool design within the parts cylinder is predetermined. In one embodiment of the present invention, this predetermination involves including all features of the tool 150 on the same side of the tool, thereby limiting warping on tool features in accordance with the present invention.
In operation block 308 heat sinks, such as 202, 204, or 206, are positioned in various parts of the parts cylinder 102 such that tool features may be cooled immediately following the sintering process and while the rest of the tool or tool components are being sintered, thereby minimizing warping of the tool features. Alternate embodiments include activating the heat sinks 202, 204, 206 or alternately inputting them into the parts cylinder 102 prior to sintering. Further alternate embodiments include a single heat sink, or a heat sink activating in various regions corresponding to tool features on the tool being sintered.
In operation block 310 the sintering process is activated, and the controller 105 activates the pistons 114, 117, the roller 118, the laser 120, and the mirrors 124. The pistons force sinter material upwards or in a direction of the powder leveling roller 118, which rolls the sinter powder such that it is evenly distributed as a top layer on the parts cylinder 102. The laser 120 is activated and a beam 126 is directed towards scanning gears, which may be controlled as a function of predetermined requirements made in operation block 302. During the sintering operations, the heat sinks 202, 204, 206 are activated for cooling various sintered portions of the tool 150 as they are sintered, and as other parts of the tool are being sintered such that warping is minimized. In alternate embodiments wherein a plurality of tool sections, such as a first and second tool section, are sintered collectively or successively, heat sinks may be included to cool various features of the second tool section as well.
In operation block 312, post-sintering process adjustments are conducted. These adjustments include removing warped portions that were deliberately warped such that tool features would not undergo typical warping associated with the sintering process. Further, post-process adjustments involve fitting together components or sections of the tool 150.
In operation, a method for laser sintering a tool includes predetermining a position for a first tool feature on a first section of the tool. The method further includes predetermining an orientation of the first section of the tool within the part chamber as a function of minimizing warping of the first tool feature during sintering and activating a heat sink within a part chamber for limiting warping of the first tool feature. The first section of the tool is laser sintered within the part chamber.
The method further includes predetermining a position for a second tool feature on a second section of the tool and predetermining an orientation of the second section of the tool within the part chamber as a function of minimizing warping of the second tool feature during sintering. The second section of the tool is laser sintered and coupled to the first section.
A position and configuration of a contoured detail feature is predetermined such that the contoured detail feature includes securing features for coupling strengthening components thereto. The contoured detail is sintered and a strengthening component is coupled thereto, thereby reducing stress on the contoured detail feature. The contoured detail is coupled to at least one of the sections.
From the foregoing, it can be seen that there has been brought to the art a new and improved tooling system and method. It is to be understood that the preceding description of the preferred embodiment is merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Numerous and other arrangements would be evident to those skilled in the art without departing from the scope of the invention as defined by the following claims.
