Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-09-07
2004-11-23
Paladini, Albert W. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S182000, C264S308000
Reexamination Certificate
active
06823230
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related generally to machine manufacturing of components. In particular, the present invention is related to rapid prototyping manufacturing including layered manufacturing and solid freeform fabrication.
BACKGROUND OF THE INVENTION
Using conventional techniques, a desired article to be made can initially be drawn, either manually or automatically utilizing a computer-aided design (CAD) software package. The article can be formed by removing material from material stock to form the desired shape in a machining operation. The machining operation may be automated with a computer-aided machining (CAM) process. The design and manufacture process may be repeated multiple times to obtain the desired part. A common practice is to mechanically remove material to create three-dimensional objects, which can involve significant machining skills and turn around time.
One process for making three-dimensional objects builds up material in a pattern as required by the article to be formed. Masters, in U.S. Pat. No. 4,665,492, discusses a process in which a stream of particles is ejected and directed to coordinates of the three-dimensional article according to data provided from a CAD system. The particles impinge upon and adhere to each other in a controlled environment so as to build up the desired article.
Processes and apparatus also exist for producing three-dimensional objects through the formation of successive laminae which correspond to adjacent cross-sectional layers of the object to be formed. Some stereo lithography techniques of this type use a vat of liquid photocurable polymer which changes from a liquid to a solid in the presence of light. A beam of ultraviolet light (UV) is directed to the surface of the liquid by a laser beam which is moved across the liquid surface in a single plane, in a predetermined XY pattern, which may be computer generated by a CAD system. In such a process, the successive layers may be formed in a single horizontal plane, with successive layers solidifying together to form the desired object. See, for example, U.S. Pat. No. 4,575,330 to Hull. Arcella et al., in U.S. Pat. No. 4,818,562, discuss a method for forming an article by directing a laser beam on a fusible powder which is melted by the beam, and which solidifies to form the desired shaped object.
Recently, various solid freeform fabrication techniques have been developed for producing three-dimensional articles. One such technique, used by Stratasys, Inc. (Eden Prairie, Minn.), is referred to as Fused Deposition Modeling (FDM). See, for example, U.S. Pat. No. 5,121,329 to Crump, herein incorporated by reference. FDM builds solid objects, layer by layer, from polymer/wax compositions according to instructions from a computer-aided design (CAD) software program. In one FDM technique, a flexible filament of the polymer/wax composition is heated, melted, and extruded from the nozzle, where it is deposited on a workpiece or platform positioned in close proximity to the dispensing head. The CAD software controls the movement of the dispensing head in the horizontal X-Y plane and controls the movement of the build platform in the vertical Z direction. By controlling the processing variables, the extruded bead or “road” can be deposited layer by layer in areas defined by the CAD model, leading to the creation of the desired three-dimensional object.
Other examples of layered manufacturing techniques include multi-phase jet solidification techniques and/or laser-engineered net shaping. The extruded bead can be a ceramic suspension or slurry, a molten plastic, a powder-binder mixture, a polymeric material ready for curing or hardening, a molten metal, or other suitable materials which harden with time and/or exposure to an external stimulus. The bead can also be a curable strip of polymer or pre-polymer with polymerization initiated by radiation.
Conventional machining techniques utilize “subtractive” machining in which material is subtracted from a block of material. An example of subtractive machining is milling. Use of a subtractive computer controlled machine, such as a computer controlled milling machine, requires describing a tool path for the machine cutting element to follow in removing portions of the material stock. A cutting burr typically has a center axis and a known radius. A tool path for the cutting burr to follow is usually a series of line segments, line segment end points, or curves. The tool path may be generated according to a first rule that the innermost tool path stays about one burr radius from the surface perimeter to be formed. In an “additive” manufacturing method, such as solid freeform manufacturing, the first rule from subtractive manufacturing has been informally adapted. The additive first rule is that the outermost tool path should come no closer than about half a bead width from the surface perimeter to be formed.
There are problems caused by a material depositing head following a tool path generated according to this first rule. Surface features that have a width less than a bead width cannot be entered by the depositing head, as the bead would extend outside of the surface perimeter to be formed. As a result, a narrow protrusion or vertex to be formed is not formed at all. This is contrary to the design intent.
A second, related rule for additive tool paths is that the tool path should not come closer than about half a bead width to an inner perimeter defining an interior feature. This rule prevents the path from filling in an interior feature, but can cause interior solid features of less than one bead width to be under-defined. In one example, two holes separated at their perimeters by less than a bead width will be formed as a single oblong hole, as the tool path cannot both follow the second rule and come between the two holes.
A third rule for additive tool paths is that the tool path should not cause the bead to cross the boundary of another bead, already generated from another tool path portion. As a contour, or outer perimeter following tool path may be more important, it is often generated first, to insure a surface closely resembling the design surface. In one case, often found in narrow parts, the inside surfaces of the contour tool path beads may come closer together than one bead width. A void will result at this location, as no tool path following along the contour tool path can enter this narrow region without violating the third rule.
Current processes for generating tool paths may include beginning at the outer perimeter and offsetting that perimeter inward into the material portion by about half the expected bead width. The resulting outer boundary can be used to define a contour tool path to define the limits for a raster tool path. In one situation, a first outer contour tool path may be offset within an outer perimeter vertex to create an outer boundary. If the outer boundary is used to form a contour bead to form the perimeter vertex, the interior of the contour bead may in turn form a second vertex, which may also present a problem in filling.
Another problem with existing technologies includes the creation of weak spots within the filled areas of solid slices made using raster filled layered manufacturing techniques. Yet another problem is the creation of perimeter gaps or sub-perimeter voids where raster tool paths meet perimeters or contour beads, respectively. What would be desirable are methods for generating tool paths that ameliorate some of the above-discussed deficiencies.
SUMMARY OF THE INVENTION
The present invention provides methods for improving the manufacture of objects made by layered manufacturing techniques through improved tool path generation. A vertex improvement aspect improves tool paths used to form vertices. Outer perimeter vertices can be improved by automatically creating an outer boundary reflecting the design intent to have material extending to the outer perimeter vertex. The outer boundary can be used as a contour tool path or as a limit to travel by raster tool pat
Chard Jeffrey A.
Gasdaska Charles J.
Jamalabad Vikram R.
Fredrick Kris T.
Honeywell International , Inc.
Paladini Albert W.
Rao Sheela S
LandOfFree
Tool path planning process for component by layered manufacture does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tool path planning process for component by layered manufacture, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tool path planning process for component by layered manufacture will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3359707