U.S. patent application number 10/762449 was filed with the patent office on 2005-06-16 for procedures for rapid build and improved surface characteristics in layered manufacture.
Invention is credited to Gasdaska, Charles J., Jamalabad, Vikram R., Ortiz, Milton.
Application Number | 20050131570 10/762449 |
Document ID | / |
Family ID | 24634485 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050131570 |
Kind Code |
A1 |
Jamalabad, Vikram R. ; et
al. |
June 16, 2005 |
Procedures for rapid build and improved surface characteristics in
layered manufacture
Abstract
Methods for improving layered manufacturing techniques to
improve an objects' surface properties and shorten manufacturing
time for support structures. One aspect of the invention forms
surfaces having reduced or no concavities between layers having
improved crack resistance. One method deposits alternate, surface
improvement material on each layer near the future location of the
main material surface, followed by deposition of the main material,
the edges of which conform to the previously deposited and
solidified alternate material. In this method, the center of the
main material layers can be concave rather than the interlayer
regions. Another aspect of the invention provides removable
structures to support the deposition of main material. The support
structures provide support over main material cavities for
depositing the material to form the cavity ceilings, while
minimizing the time and material required to build the support
structures. Minimized support structures include structures formed
as columns supported by the cavity floor and angle braces to
supported by the cavity walls. Some supports are supported by the
side wall but not the floor, and other by the floor and not the
side walls.
Inventors: |
Jamalabad, Vikram R.;
(Somerville, NJ) ; Gasdaska, Charles J.; (Sparta,
NJ) ; Ortiz, Milton; (Scottsdale, AZ) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
24634485 |
Appl. No.: |
10/762449 |
Filed: |
January 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10762449 |
Jan 20, 2004 |
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09656770 |
Sep 7, 2000 |
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6682684 |
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Current U.S.
Class: |
700/119 ;
264/401 |
Current CPC
Class: |
B28B 3/10 20130101; B29C
64/40 20170801; B29C 64/118 20170801; B29C 64/106 20170801 |
Class at
Publication: |
700/119 ;
264/401 |
International
Class: |
G06F 019/00 |
Goverment Interests
[0002] This invention was made with Government support under ______
contract number N00014-94-C-0115, entitled "______". The Government
has certain rights in the invention.
Claims
1-35. (canceled)
36. A program storage device readable by a machine tangibly
embodying a program of instructions executable by the machine to
perform method steps for improving layer side surfaces of
structural layer areas filled by layered manufacturing, the method
steps comprising: obtaining first curve data defining at least one
layer area to be filled with a first material and to thereby create
said structural layer, including said layer side surfaces; and
generating second curve data defining a second layer area to be
filled with a second material, said second layer area, when filled,
having at least one side surface that has an overall convex shape
and abuts at least a portion of said structural layer side
surfaces.
37. A program storage device as in claim 36, wherein said obtain
and generating steps are executed at least once for each of a
plurality of stacked layers for which said layer side surface
improving is desired.
38. A program storage device readable by a machine tangibly
embodying a program of instructions executable by the machine to
perform method steps for providing support, using first and second
materials by layered manufacturing, underneath a material layer
area having an unsupported portion, the method steps comprising:
obtaining a first data set having a plurality of first layer data
sets representing said layer area to be filled with said first
material by layered manufacturing, along with first support layer
areas underneath said layer area, said first support layer areas to
also be filled with said first material by layered manufacturing;
and generating a second data set having a plurality of second layer
data sets representing second support layer areas underneath said
unsupported portion of said layer area, said second support layer
areas to be filled with said second material by layered
manufacturing, wherein said layer area and said first support layer
areas, when filled with said first material, define a void volume
underneath said unsupported portion of said layer area, wherein
said second support layer areas, when filled with said second
material, define a support structure inside said void volume, the
support structure having a support structure volume that is
substantially less than said void volume.
39. A program storage device as in claim 38, wherein said
generating step includes: (a) selecting a pair of layers having an
upper layer and an immediately lower layer; (b) reducing the area
of said pair upper area by an increment; (c) determining any
portion of said upper layer unsupported by said lower layer; (d)
creating a new support area for said pair lower layer; (e) adding
said new support area to said lower layer; and (f) repeating steps
(a) through (e) for a plurality of said layer pairs by setting said
pair lower layer to be said pair upper layer in the next
iteration.
40. (canceled)
Description
RELATED APPLICATIONS
[0001] The present application is related to co-pending U.S. patent
application Ser. No. ______ [1100.1103101], titled TOOL PATH
PLANING PROCESS FOR COMPONENT BY LAYERED MANUFACTURE, filed on date
even herewith.
FIELD OF THE INVENTION
[0003] 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
[0004] 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.
[0005] 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.
[0006] 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 of 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.
[0007] 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.
[0008] In conventional layered manufacturing techniques, the layers
are formed or deposited in a flowable state which can be in the
form of a series of long beads of extruded material. The beads can
have a rounded, oblong, or circular transverse cross-sectional
profile, where the external side faces of the bead can bulge
outward. The conventional material layers are typically rounded at
the periphery, forming layer surfaces having convex intra-layer
regions and sharp, mechanically weak concave inter-layer regions.
In particular, where the stacked bonded layers form the
manufactured part side surfaces, the concavities can form sharp
crevices having poor properties with respect to crack propagation
and fracture.
[0009] In conventional layered manufacturing, cavities, either
external or internal, are often found in product designs. The
cavities may have upper structures such as ceilings or overhangs.
The upper structures may be cantilevered structures having one end
or edge free or structures only unsupported in the middle, between
supports on either side or edge. The structures are unsupported in
the sense that during deposition or formation of the still flowable
main material, the material will drop down through the cavity
without a structure previously established to support the main
material during hardening. The cavities below have a volume which
can be defined by a downward projection of the unsupported portion
of the main material above.
[0010] In conventional layered manufacturing, a support structure
of secondary material is built, layer by layer, to provide a
support structure for the material to be formed or deposited in the
layer above. The secondary material forms layers which also require
support from the layer below for their deposition. Using
conventional methods, an unsupported structure is supported by
secondary material, layer under layer, from top to bottom, until
the bottom of the cavity is reached, or until the workpiece
platform being used to build the article is reached. The secondary
material is later removed by mechanical, chemical, or thermal
means, leaving the main material article. A large amount of
secondary material can be required to build the removable
structure, as well as a large build time required to form the
secondary material layers.
[0011] What would be desirable are methods suitable for making
parts using layered manufacturing which provide superior crack
resistant surfaces. Methods which require less time to build
support structures would also be advantageous.
SUMMARY OF THE INVENTION
[0012] The present invention includes improved methods for making
objects using layered manufacturing techniques, as well as the
objects made possible through use of these methods. One group of
methods forms objects having improved surface properties made
possible by forming a mold layer of a second material prior to
forming a main part layer of a first material. Another group of
methods forms objects requiring less time and material to build.
This group of methods includes methods for building minimized
secondary material support structures having less volume than
conventional support structures.
[0013] More particularly, the present invention includes methods
for forming a mold layer of a second material along the periphery
of the object surfaces to be improved. The second material layers
can be convexly rounded at the periphery, forming a rounded mold
layer to receive the later formed first material. The first
material layer can thus form an impression of the second material
layer along the periphery of the first material layer. The
impression formed along the first layer side face can have a
rounded, concave, middle intra-layer region and a convex,
inter-layer region where the multiple layers stack together. The
inter-layer convexities have superior mechanical strength and
superior crack resistance relative to the concave inter-layer
regions of the conventionally made parts.
[0014] In one method, a data file containing representations of a
three-dimensional object is accepted as input. The data file can be
a three-dimensional CAD file, for example, a stereo lithographic
(STL) file. The three-dimensional data can be partitioned into
horizontal slices or layers, which can be represented by
two-dimensional closed curves or poly-line segments having an
associated layer thickness. The curves can define the outside
and/or inside of areas to be filled with the main material. The
curves can later be filled with raster tool paths generated to fill
the area with material. The user can identify surfaces of the
three-dimensional object to receive surface improvement and,
directly or indirectly, identify the curves or curve portions
corresponding to the surfaces to be improved.
[0015] A set of secondary curves can then be generated, the
secondary curves corresponding to secondary material areas to abut
the main material areas. The secondary curves thus formed
preferably correspond to layer areas having at least two bead
widths of secondary material. Some embodiments form secondary
material layers with no voids, while other embodiments form
secondary material layers having voids to reduce material usage and
build time. The secondary material curves can then be used to
generate tool paths for the secondary material. The secondary and
main material tool paths can be checked for consistency and lack of
interference before being integrated and the processing
completed.
[0016] In the manufacturing phase, the part can be built up, bottom
to top, by depositing the secondary and main materials, layer by
layer. If secondary material is called for in the current layer, a
secondary material nozzle can deposit a bead of secondary material
of the desired bead width along the previously calculated path. A
main material nozzle can then deposit a bead of main material of
the desired bead width and along the previously calculated tool
path. The flowable main material, formed along the previously
formed secondary mold layers, can form an impression of the mold
layers convex edge shape, thereby attaining a concave intra-layer
shape and a convex inter-layer shape, where the stacked layers join
each other. The secondary material can be later removed, exploiting
differential mechanical, chemical, or thermal properties. In a
preferred embodiment, the main and secondary materials are not the
same, but are the same material in other embodiments. Improved
surfaces provided by the present invention can have improved
mechanical properties due to the lack of sharp, inter-layer
convexities.
[0017] The present invention also includes methods for building
removable support structures that form the secondary structures
using substantially less volume than the cavity volume. The support
structures can have at least one sloping side surface having a
substantial deviation from vertical. In one group of structures,
the support forms an angle or corner brace, supporting the cavity
ceiling from a side wall. The angle piece can have a width
decreasing with depth, indenting or offsetting until the support
piece has no width. In another group of structures, the support
forms a column or interior wall having a wide topmost layer and
less wide middle and bottom layers. The wide top layers support the
main material layer above, with the lower layers decreasing in
width. The lower layers can be indented or offset inward by a small
amount at each layer. The indent amount is preferably less than
about one-half of the bead width of the layer above.
[0018] One method for generating the minimized support structures
accepts two-dimensional curves for each layer as input. The
two-dimensional curves represent the inner and outer perimeters of
the main material layers for the part to be built. The unsupported
or overhanging structures can be identified by processing the
layers of the main structure from top to bottom, beginning with the
second to top layer. The layers can be processed as pairs having an
upper and lower layer. The upper layer can be reduced in one or
more dimensions by an indent or offset amount ultimately
corresponding to the slope of the side surface of the minimized
support structure. In some embodiments, certain dimensions are
automatically or manually selected as not to be reduced in extent.
The difference of the reduced projected upper layer and the lower
layer corresponds to an unsupported upper area, which will require
support prior to formation. New secondary support material curves
can be generated at the current lower level to provide the missing
support, and these newly added secondary support material curves
added to the main material curves for the current, lower layer. The
newly added curves will also require support from below during
formation, and are added to the set of main material curves, but
are identified as secondary material curves.
[0019] The current layer can be set to be the next lower layer,
making the previous lower layer of the pair the upper layer, and
the process repeated. The new calculation will now take into
account any curves representing either unsupported main material or
secondary support material. The process can be repeated for all
layers of the part to be made.
[0020] One output of the method can be a set of secondary material
curves to be filled with secondary support material. The secondary
material curves can be further processed by raster filling the
areas within the curves using conventional rasterizing techniques.
The curves and tool paths generated can be checked for consistency
and lack of interference, both within the secondary material and
between the secondary and main materials. The rasters can be used
as tool paths to control the formation or deposition of main and
secondary material.
[0021] In manufacture, the main and secondary material tool paths
can be fed to a layered manufacturing machine for each layer. The
minimized support sloping side faces, which were likely calculated
top down, are built bottom up. The sloping side faces of the
support structures can be built with a slight overhang at each
higher level, the overhang preferably not exceeding one-half (1/2)
a bead width. The secondary material support structures can thus be
built to have large dimensions at the topmost layer. In some
objects, the next layer up will consist of a main material layer
deposited on the now solidified secondary material layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a top, cross-sectional view through a single layer
of a prior art object formed by a bead deposited along a tool
path;
[0023] FIG. 2 is a top, cross-sectional view through a single layer
of a prior art object formed by a bead deposited along a tool path,
including a perimeter contour tool path;
[0024] FIG. 3 is a side view of a prior art object formed by
layered manufacturing techniques having serrated outer surfaces and
interlayer surface concavities;
[0025] FIG. 4 is a detailed view of a surface interlayer of FIG.
3;
[0026] FIG. 5 is a side view of an object formed during layered
manufacture having the main material abutted by a removable
secondary surface improvement material;
[0027] FIG. 6 illustrates the object of FIG. 5 after removal of the
secondary surface improvement material;
[0028] FIG. 7 illustrates in detail the object of FIG. 6, including
an intra-layer surface rounded concavity and an interlayer surface
convexity;
[0029] FIG. 8A is a highly diagrammatic side cross-sectional view
of a design object having a surface curve, the design having been
sliced into layers for layered manufacturing;
[0030] FIG. 8B is a highly diagrammatic side cross-sectional view
of the object of
[0031] FIG. 8A in the process of manufacture, with some main and
secondary material layers having been deposited;
[0032] FIG. 8C is a highly diagrammatic side cross-sectional view
of the object of
[0033] FIG. 8B after all main and secondary material layers have
been deposited;
[0034] FIG. 8D illustrates a highly diagrammatic side
cross-sectional view the object of FIG. 8C after removal of the
secondary material;
[0035] FIG. 9A is a highly diagrammatic top view of a design object
layer to be manufactured by layered manufacturing, the design
having an internal rounded cavity surface and an external perimeter
surface;
[0036] FIG. 9B illustrates the manufacture of the FIG. 9A design
after the secondary surface improvement material layers have been
deposited as a mold for the main material layer;
[0037] FIG. 9C illustrates the manufacture of the FIG. 9B object
after deposition of the main material layer abutting the secondary
surface improvement material;
[0038] FIG. 9D illustrates the manufacture of the FIG. 9C object
after removal of the secondary material;
[0039] FIGS. 10A and 10B illustrate a highly diagrammatic top view
of a secondary material layer, wherein the secondary material layer
has substantial voids within;
[0040] FIGS. 11A and 11B illustrate a highly diagrammatic top view
of a secondary material layer, wherein the secondary material layer
has substantial voids within and no contour bead;
[0041] FIG. 12A illustrates a highly diagrammatic side
cross-sectional view of an object having a cavity defined beneath
an external overhang, the overhang requiring support during
deposition;
[0042] FIG. 12B is a highly diagrammatic side cross-sectional view
of a conventional secondary material support used to support the
overhang of FIG. 12B;
[0043] FIG. 12C is a highly diagrammatic side cross-sectional view
of the composite component formed by the deposition of the main and
secondary material layers of FIGS. 12A and 12B;
[0044] FIG. 13A is a highly diagrammatic side cross-sectional view
of a component having an interior cavity having an unsupported
layer requiring support during deposition;
[0045] FIG. 13B is a highly diagrammatic side cross-sectional view
of a conventional secondary support for supporting the unsupported
layer of FIG. 13A;
[0046] FIG. 13C is a highly diagrammatic side cross-sectional view
of the composite component formed by the deposition of the main and
secondary material layers of FIGS. 13A and 13B;
[0047] FIG. 14A is a highly diagrammatic side cross-sectional view
of a component having an exterior cavity defined by an
overhang;
[0048] FIG. 14B is a highly diagrammatic side cross-sectional view
of a secondary support structure formed according to the present
invention, requiring less material and deposition time;
[0049] FIG. 14C is a highly diagrammatic side cross-sectional view
of the objects of FIGS. 14A and 14B deposited layer by layer;
[0050] FIG. 15A is a highly diagrammatic side cross-sectional view
of an object having an internal cavity requiring support during
manufacture;
[0051] FIG. 15B is a highly diagrammatic side cross-sectional view
of a secondary support structure having two sloping side faces
requiring less material and deposition time;
[0052] FIG. 15C is the object of FIG. 15A deposited over the
secondary support material of FIG. 15B, on a layer-by-layer
basis;
[0053] FIG. 16 is a high level flow chart of a process used to
generate tool paths from a CAD drawing;
[0054] FIG. 17 is a flow chart describing a procedure for
generating curves for all the layers requiring surface improvement
according to the present invention;
[0055] FIG. 18 is a flow chart describing a procedure for
generating a minimized secondary support structure;
[0056] FIG. 19 is flow chart describing a procedure for generating
tool paths for improved surface characteristics; and
[0057] FIG. 20 is a flow chart describing a procedure for tool path
generation for minimized support.
DETAILED DESCRIPTION OF THE INVENTION
[0058] FIG. 1 illustrates a top view of a single layer of an object
40 made using layered manufacturing techniques. Object 40 is formed
from a single bead 42 laid along a tool path 44, having a zigzag
pattern to substantially fill a rectangular area. Bead 42 has a
diameter or width indicated at D/W and a length indicated at L.
Bead 42 may be seen to flow together at inter-bead region 46 where
adjacent sections of the bead abut one another. Bead 42 and object
40 may be formed using any suitable manufacturing technique, for
example, fused deposition techniques, multi-phase jet
solidification techniques, or laser-engineered net shaping
techniques. Bead 42 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.
Bead 42 can also represent a curable strip of polymer or
pre-polymer with polymerization initiated with UV radiation.
[0059] Referring now to FIG. 2, another object 41 is illustrated,
also formed using layered manufacturing. Object 41 is similar to
object 40 of FIG. 1, but has an outer contour bead 43 formed of a
first bead 45 which surrounds an internal second bead 47. Both
FIGS. 1 and 2 illustrate conventional layered manufacturing
techniques.
[0060] FIG. 3 illustrates a prior art object 50 formed of three
vertical layers 51 abutting one another along interlayer planes 56.
Object 50 includes a sloping surface 52 and a substantially
vertical surface 54. A bead height is indicated at "H" for layer
51. Numerous interlayer serrations may be seen along sloping face
52 at interlayer regions 56. Serrations are formed having concave
regions 58 between layers 51 and convex, rounded regions near the
intralayer regions indicated at convex surface 60. Vertical surface
54 may also be seen to have numerous sharp concave regions 62
disposed along interlayer regions 56. Sloping face 52, in
particular, has sharp serrations along the staircased face.
Concavities 58 and 62 may be seen to have sharp notches which are
stress risers having low mechanical strength.
[0061] Referring now to FIG. 4, prior art concavity 62 of FIG. 3 is
illustrated in greater detail. Concavity 62 may be seen to lie
along interlayer region 56 between two beads or layers 51. Layers
51 extend to an outermost convex and rounded region 60, and come
together along a sharp acute angle 64 formed between the two
layers. In the limiting case, the acute angle 64 approaches zero
degrees (0.degree.) as a limit. Concave region 62 acts as a region
likely to cause crack propagation and weaken the structure.
[0062] Referring now to FIG. 5, an object 90 is illustrated,
showing one method of layered manufacture according to the present
invention. Object 90 is shown to be formed of three vertically
stacked layers 97, 98, and 100. Object 90 includes a sloped
external surface 91 and a substantially vertical external surface
93. Object 90 is formed of a first or main material, which is
abutted in FIG. 5 by a secondary or supporting material 92 and 94.
The structural material of structures 92 and 94 can serve as a
scaffolding or mold for forming the outside of object 90 so as to
have improved surface properties. As will be later discussed,
support structures 92 and 94 are preferably laid down or deposited
prior to the deposition of the main material. For example, a
secondary material layer 95 may be first deposited, followed by a
secondary material layer 96, thereby forming convex regions
inwardly directed. First main material layer 97 may then be
deposited in between support layers 95 and 96, thereby flowing to
assuming the shape of the support layers 95 and 96. This may be
repeated layer by layer, with the main material deposition
following the surface improvement material deposition.
[0063] Referring now to FIG. 6, object 90 is shown after removal of
support structures 92 and 94. Support structures 92 and 94 are
preferably formed of an easy-to-remove material which differs from
the main material. In a preferred method, the structural material
does not mix with the main material, and is easy to separate. In
one embodiment, the alternate material is physically separable,
which can include tearing apart of material and/or use of a
non-sticking material. In another embodiment, the alternate
material has a lower melting point than the main material and can
be separated by heating. In yet another embodiment using chemical
separation methods, the alternate material is soluble in a solvent
that does not dissolve or damage the main material. Sloping side
face 91 and vertical side face 93 may both be seen to lack the
sharp concave features of object 50 illustrated in FIG. 3. In
particular, interlayer regions 108 may be seen to form convex
features 110, while the intra-layer regions form smooth concave
regions 104.
[0064] Referring now to FIG. 7, concave region 104 is illustrated
in greater detail. Concave region 104 may be seen to lie in an
intra-layer region of object 90. In the embodiment illustrated, a
shallow angle 112 may be seen to be formed by concave rounded
regions 104. In the limiting case, a tangent along a semicircular
or concave surface may be seen to approach an angle of 180 degrees
as a limit. In comparing the objects of FIGS. 4 and 7, it may be
seen that object 90 of FIG. 7 lacks the sharp serrations and
crevices present at inter-layer region 56 in the formation of
object 50 of FIG. 4.
[0065] Referring now to FIG. 8A, an object 120, as designed, is
illustrated. Designed object 120 may be the object as modeled in a
CAD drawing or other design tool. Object 120 includes a curved
surface region 124 and a straight surface region 122. Object 120
has been divided into numerous slices 126, denoted by lines in FIG.
8A. In FIG. 8A, slices 126 are demarcated by the center line of
each layer. While FIG. 8A shows all of the slices having the same
thickness, it is contemplated that the slices may have different
thicknesses, if desired. Some embodiments of the invention have
layer thicknesses of between about 0.001 inches and about 0.030
inches. In one embodiment of the invention, the layer thickness is
between about 0.005 inches and about 0.015 inches.
[0066] FIG. 8B illustrates an object being manufactured to form
design object 120. A first surface support material 130 has been
deposited, followed by a first main material layer 132, followed by
a second surface support layer 136, followed by a second main layer
138, followed by a third surface support material layer 140,
followed by a third main material layer 142, followed by a fourth
surface support material layer 144. An interface region 145 between
the structural material and the main material may be seen. FIG. 8C
illustrates a main structure or part 148 abutting a support
structure 146 after completion of the support structure. FIG. 8D
illustrates main structure 148 after removal of support structure
146, thereby exposing side surface 150.
[0067] Referring now to FIG. 9A, a single design layer 160 is
illustrated in a top view. Design layer 160 includes a main
material layer or region including an interior cavity 166. Arrow
170 indicates an out direction from main material region 178 on the
external surface, while arrow 172 indicates the out direction from
the interior surface within cavity 166. The term "out" thus refers
to a direction away from the main material and toward the
non-material region or air space near the surface.
[0068] Referring now to FIG. 9B, an object layer being created
according to design layer 160 is illustrated. FIG. 9B illustrates
the object after deposition of the secondary material within a
peripheral region and an interior region. Secondary material may be
seen to have been deposited within an exterior margin 164 and
interior margin 168. Region 178 is indicated as not yet filled by
any main material. FIG. 9C shows the object layer under
construction after deposition of main material within region 178.
The main material within region 178 may be seen to abut secondary
material at regions 164 and 168, thereby being formed between the
two secondary material regions. In this way, interior surfaces may
have the surface characteristics improved as well as the exterior
surfaces. FIG. 9D illustrates the object after removal of the
secondary support material, leaving main material region 178
surrounding cavity 166.
[0069] FIGS. 10A and 10B illustrate a main material layer 180
similar to main material layer 178 of FIG. 9C. The embodiment
illustrated includes secondary material layers using less material.
Secondary material has been deposited as an internal layer 182 and
as an external layer 185, similar to layers 168 and 164 of FIG. 9C.
External secondary material layer 185 is illustrated in greater
detail in FIG. 10B, illustrating a support structure having a large
void contribution. Exterior support layer 185 may be seen to
include a contour bead 186 disposed along the exterior of the
object and a second bead 188 formed in a zigzag or squarewave
pattern, thereby leaving a number of voids 190. External layer 184
thus provides support for forming main material layer 180, while
using less material and requiring less time to form the secondary
support layer.
[0070] Referring now to FIGS. 11A and 11B, a main material layer
180 similar to main material layer 178 of FIG. 9C may be seen to be
surrounded by an external structural support or surface improvement
layer 192 using less secondary material to construct. Support layer
192 is formed of a single bead 194 configured in a zigzag or
squarewave pattern having a number of voids 196. Support region 192
may be seen to have an even larger void contribution than region
185 of FIG. 10B. External support layer 192 may be appropriate
where a less fine external finish in required or allowed for the
main material portion.
[0071] FIG. 12A illustrates a highly diagrammatic side view of a
prior art part 200 having a cantilevered or unsupported ceiling
structure 202 and a side wall, or supported structure 204, thereby
defining a side cavity 206 under the overhang of the cantilevered
portion 202. Cantilevered portion 202 can define a cavity volume by
projecting the cantilevered portion vertically downward. FIG. 12B
illustrates a secondary material support 208 suitable for
supporting cantilevered portion 202. FIG. 12C illustrates support
region 208 supporting cantilevered region 202. Current methods
teach forming support region 208 near, but not touching, side wall
204, leaving a space 201 to ease removal of support structure 208.
FIGS. 12A through 12C illustrate a prior art method for generating
support for a part during manufacture. In particular, it may be
seen that cantilevered region 202, when formed by the deposition of
not-yet-solid bead, would require support during solidification of
the bead over cavity region 206.
[0072] Referring now to FIG. 13A, another part 210 is illustrated
having a supported region 214, a supported region 216, and an
unsupported region 212 suspended therebetween. Unsupported region
212 defines a cavity 218 thereunder. Unsupported region 212, when
formed using many layered manufacturing techniques, requires
support during the solidification of the bead over interior cavity
region 218. FIG. 13B illustrates a secondary support structure 220
suitable for use in manufacturing object 210. FIG. 13C illustrates
object 210, after manufacture, being supported by secondary
supporting material 220. Support material 220 may be seen to
support unsupported region 212 during the solidification of the
bead. Support region 220 may be removed after solidification of the
main material. Current methods teach forming support region 220
near, but not touching, supported regions 214 and 216, leaving
spaces 211 to ease removal of support structure 220. FIGS. 12A
through 12C and 13A through 13C illustrate prior art methods of
providing secondary material support for a part according to
layered manufacturing techniques.
[0073] Referring now to FIG. 14A, structure 200 of FIG. 12A is
again illustrated. FIG. 14B illustrates a minimized support
structure 209 suitable for support of cantilevered region 202. FIG.
14C illustrates minimized support structure 209 disposed within
cavity 206. As may be seen from inspection of FIG. 14C, a
substantial void volume 211 is left within cavity 206. Void volume
211 results in less material being used for formation of support
structure 209, as well as less time required to form support
structure 209. Support structure 209 does not extend to the bottom
of cavity 206, but rather abuts main structure portion 204 along an
interior wall region 207, ending at a base layer 205. FIG. 14C thus
illustrates a support structure that fills less than half of the
cavity volume it is disposed within. Support structure 209 may be
seen to have a sloping side face 215.
[0074] Referring again to FIG. 14B, support structure 209 may be
seen to have a length for each layer indicated at "L" and an indent
or offset for each layer beneath the immediately disposed upper
layer. The indent is indicated at 213. In one embodiment, the
indent varies between about one-tenth ({fraction (1/10)}) of a bead
diameter and about one-half (1/2) of a bead diameter. In a
preferred embodiment, the indent does not exceed one-half (1/2) of
a bead diameter, so as to minimize the unsupported region of the
bead during bead solidification. In another embodiment, not
requiring separate illustration, base layer 205 is repeated
downward to the floor of the cavity, and can be several beads
wide.
[0075] Referring now to FIG. 15A, object 210 of FIG. 13A is once
again shown. FIG. 15B illustrates a minimized support structure 221
having two sloping or curved side faces 219. FIG. 15C illustrates
support structure 221 disposed within cavity 218, thereby
supporting overhanging region 212. Support structure 221 may be
seen to have a base portion 217 much smaller than top portion 229.
Base 217 may be supported by a workpiece platform or the cavity
floor. Sloping faces 219 may be seen to provide void areas 223 and
225 within cavity 218. Minimized support structure 221 thus
provides support while requiring substantially less material and
deposition time for the support structure.
[0076] Qualitatively, the structures of FIGS. 14A-C and 15A-C are
generated using methods which plan the layers from top to bottom
and which build the layers from bottom to top. Each layer to be
minimized can be indented at each level, not more than the bead
width, otherwise the bead would drop down. The indent is preferably
not more than one-half (1/2) of a bead width. The indenting can
continue at each level until no more support material is required,
or until the minimum allowable support layer dimension is reached.
Some embodiments continue forming the minimum allowable support
layer dimension all the way to the bottom.
[0077] The indents form a local slope which can be defined as the
change in local height per the change in local width. In one
embodiment, the local slope is less than about ten (10). In another
embodiment, the local slope is less than about two (2). One
embodiment has a side face having a deviation from vertical of at
least forty degrees (40.degree.). The resulting support structures
occupy less than about twenty percent (20%), forty percent (40%),
and fifty percent (50%) of the main material cavities in various
embodiments of the invention.
[0078] The methods used to create the structures of FIGS. 14A-C and
15A-C preferably operate on curves generated by slice programs
which slice 3D CAD objects into two-dimensional curves having a
thickness. The two-dimensional curves can be approximated as
poly-lines or a series of ordered points. The curves define the
outer perimeters to be filled, as well as the inner void perimeters
to be left unfilled, for each layer of the part to be made. For
each curve, the curve immediately above that curve can be projected
downward onto the curve, and the difference taken to determine any
unsupported areas that would allow deposited beads to fall through.
The upper curves should first be reduced by the indent amount to
allow for the support structure sloping side faces and reduced
secondary material usage previously described. Any unsupported
areas can be handled by creating new curves to form support areas,
and the new curves added to the current level curves, as the new
curves in turn require support from the level below. This process
can continue until the bottom most layer is reached. The result is
a set of additional curves defining areas to be filled with
secondary support material for each layer.
[0079] The secondary material curves and the main material curves
can be used as input by a rasterizing program which generates
rasters to be used as tool paths to fill the areas within the
curves with material. The tool paths can be followed for each layer
by a layered manufacturing tool head, such as an extruder nozzle,
in generating the support structures from the bottom up. In one
embodiment, two nozzles are used, one for the alternate material
and one for the main material.
[0080] Referring now to FIG. 16, a high level method or algorithm
300 is illustrated. Method 300 and the subsequent methods can be
implemented on a computer using any suitable programming language.
Suitable languages include, without limitation, Fortran, C, C++,
Java, BASIC, and Pascal. Method 300 can operate on a CAD file
containing a representation of an object to be manufactured, and
can output data files describing curves to be filled in, and tool
paths to be followed to fill in the curves. The present invention
explicitly includes computer programs inputting and outputting
data, where the output data will ultimately be used to drive
layered manufacturing tools. The computer programs can exist as
human readable source code and/or as compiled and ready to execute
machine code. The computer programs can reside on machine readable
media, including magnetic and optical discs.
[0081] Method 300 can begin with a CAD drawing input step 302,
which can include input of a 3D CAD drawing file, for example a 3D
Auto-CAD.RTM. drawing file. The 3D CAD file can include primitives
such as solid polygons with holes and extruded two-dimensional
solids. The 3D file can also include a 3D model which has been
converted into a set of triangles, such as is found in a stereo
lithographic (STL) file. In some embodiments, surfaces have been
marked or tagged by a human or machine user to indicate that
selected surfaces are to be improved or used to abut support
structures. The curved surfaces of the 3D object may be represented
or approximated by a surface formed of the straight line segments
of triangles.
[0082] Proceeding to step 304, the 3D CAD model can be sliced into
numerous equal thickness slices along the X-Y or horizontal plane.
One example of slicing technology is the QuickSlice program,
available from Stratasys, Incorporated (Eden Prairie, Minn.). The
X-Y plane is typically horizontal due to the importance of gravity
in determining the placement of flowable, semi-solid beads
requiring solidification. The slices typically correspond to the
layers formed in layered technology and may be one bead thickness
in height. In an illustrative example, in a vertically disposed
cylindrical solid having a vertically disposed interior cylindrical
cavity or annulus, a slice could be modeled as a large circle
having a smaller circle within, where the solid material portion
corresponds to the area between the two circles. The two circles,
along with a depth or height, could represent the slice. In one
embodiment, the cylinder and interior cavity is modeled using an
STL format, and the circles are actually represented by poly-lines
or series of points approximating the circles.
[0083] In one method, the slice thicknesses are not equal, and step
306 is executed in place of step 304. Step 304 utilizes adaptive
slicing, which can vary the slice thickness according to the
geometry and desired surface properties of the part being made. In
the example of the vertically disposed cylinder having a vertical
cavity, the slice could have a large thickness, as the vertical
cross section may not vary with height. Tata et al. discuss an
adaptive slicing technique in U.S. Pat. No. 5,596,504.
[0084] With the slices completed, step 308 can be executed to form
a tool path within the slice to form that layer of the object by
filling in the solid portion of the slice by traversing the area
with an additive technology tool head, for example, by using a
Fused Deposition Machine. In the vertical cylinder example, a
zigzag pattern may be created to lay down the bead between the
inner and outer circles or poly-lines of the slice. Standard tool
path generation techniques can be used, well known to those skilled
in the art. An improved tool path generation method, discussed in
co-pending U.S. patent application Ser. No. ______, entitled TOOL
PATH PLANING PROCESS FOR COMPONENT BY LAYERED MANUFACTURE
[1100.1103101], herein incorporated by reference, can also be used
in conjunction with the present invention. Step 308 can be executed
before and/or after the generation of additional layers created to
improve the surface properties or provide support for the
deposition of the main material layer.
[0085] In step 310, layers can be created to improve surfaces of
the main material. In the example of the vertical cylinder having
an interior cavity, the inner and/or outer surfaces may be improved
by creating an inner and/or outer annular shell, respectively. The
layers of the shell may be laid down first in the layer, followed
by the deposition of the main material.
[0086] In step 312, the minimized support structures of the present
invention can be created on a layer-by-layer basis. In the example
of the vertical cylinder, if the interior cavity did not extent
entirely through the cylinder, but was a blind cavity having a
ceiling, the deposition of the ceiling would require creation of a
support structure prior to depositing the first beads of the
ceiling. Step 312 allows for creation of a support structure that
does not require filling the entire cavity, to minimize support
formation time and support material usage.
[0087] In step 314, the tool path for the minimized support
structures created in step 312 can be generated. The tool path for
the surface improvement layers created in step 310 can be generated
in step 316. Step 308 can also be executed at this time. In step
318, the tool paths for the main part, the surface improvement
layers, and the support layers can be integrated and checked for
consistency and lack of interference. After execution of step 318,
the layers and tool paths are preferably completely generated.
[0088] Referring now to FIG. 17, a method 350 is illustrated for
improving surfaces of the part being manufactured. In step 352,
layers can be selected for surface improvement either manually or
automatically. In one embodiment, the surface to be improved can be
selected by a human user interacting with a CAD program. In one
example, a human user selects a surface on a CAD program and sets a
property of the surface to indicate that surface improvement is
desired. When the slice generation program operates on the 3D
object in the CAD file, the slicing program can then propagate this
property and mark or tag every slice or slice region with a tag,
indicating that the slice is to be improved. In one embodiment, a
human user acts on the slices in the database only after slice
generation to manually tag every slice to be improved. As the
output of a slice generation program may be a series of poly-lines,
the user may select one or more poly-line segments in each slice
for improvement, typically maintaining consistency vertically
through the slices. This method does not require modification of
the 3D CAD program and can operate on the output of a standard
slice generation program. Intelligence is normally required to
specify which surfaces require improvement, as the intended use may
be known only to a human user. In one example, an internal bore may
call for surface improvement if the intended use is to retain a
load bearing round pin, but may not require surface improvement if
the intended use is to pass cooling fluid.
[0089] In step 354, the current layer being operated on is
initialized to be the topmost layer requiring surface improvement.
The current layer surface curves are copied to a new working set of
curves in step 356. In step 358, the new set of working curves are
offset by the minimum acceptable alternate material shell width,
typically outward from the main material toward the air side. In
one method, the minimum acceptable alternate material shell width
is at least two of the alternate material bead widths. The new set
of offset curves is added to the curve set.
[0090] Interference is checked for in step 360. Interference means
that two curves are intersecting. In one example, an alternate
material curve overlaps a main material curve, which could cause
alternate material, then main material to be deposited in the same
location if the tool paths were generated using the overlapping
curves. In another example, two alternate material curves may
overlap, which would cause two tool paths to be generated for the
same location, causing excess material to be deposited in that
location. If an interference is detected, then step 362 is executed
to clip the curves. In the example where the main material and
alternate material curves intersect, the main material curves will
be used to clip the alternate material curves, as the part
integrity takes precedence of the surface improvement shell
location.
[0091] In step 366, alternate material is assigned to the new
curves, which typically corresponds to a shell of alternate
material being formed near the surface of the main material. The
new set of curves is added to the support set in step 368. If all
layers have been processed, this is detected at step 364, and
method 350 is substantially complete. If all layers have not been
processed, then step 370 is executed to advance the current layer
to the next layer down in step 370, and step 356 is executed
again.
[0092] Method 350 illustrates but one way to form the surface
improvement material layers. The present invention includes the
formation of alternate material layers out a specified distance
from the main material surface. The alternate material provides a
mold at each main material layer surface to be improved. The
distance specified is the offset distance previously referred to,
and will likely be related to the final alternate material shell
thickness. If the offset distance first selected does not interfere
with the main material, it is left unchanged, otherwise it is
clipped so as to not interfere with the main material. If the
resulting alternate material curves do not interfere with other
alternate material curves, they are left unchanged; otherwise, they
are clipped so as to not interfere.
[0093] Referring now to FIG. 18, a method 400 is illustrated,
suitable for generating curves for minimized support structures
such as described in FIGS. 14A-C and 15A-C. In step 402, the
current layer is initialized to be the layer immediately below the
top layer, as there is nothing to support above the top layer. The
current layer is thus the lower layer of a pair and the layer
immediately above is the upper layer of the pair. In step 404, the
upper curve is copied and offset or indented in, thus creating a
new smaller area curve, which is projected onto the lower current
layer. Thus, a curve that may be smaller or larger than the current
layer is projected onto the current layer. In some embodiments, the
upper curve is offset in along some curve perimeters but not
others. In one embodiment, the user can specify certain layer edges
as being anchored, such that when a copy is made of the curve, the
offset is taken only inward from some edges, but not others. In one
example, the top two layers of FIG. 14C could be anchored, such
that the upper layers are never indented in from the right, which
could call for the support material to form a pillar not abutting
the main material portion at the right.
[0094] A check is made in step 406 to determine if the offset,
reduced area upper curve even exists after the offsetting, as it
may have been reduced either to nothing or a size below a limit. In
one illustrative example, a {fraction (1/10)}-inch diameter circle
offset in by {fraction (1/10)}th inch will vanish. Step 408 finds
the difference in projection by subtracting the current layer curve
from the projected offset curve. For example, in a solid
cylindrical region, the upper layer will be a circular layer the
same size as the lower layer. The algorithm will make a copy of the
upper layer and offset this upper layer curve inward by the offset
or indent amount. In the cylindrical solid case, the upper offset
circle will have the lower full size circle subtracted from it,
leaving negative area, as there is no unsupported material above
the current layer. In the case of an overhang, such as a
cantilevered region, the overhanging curve, once reduced, will have
the support member subtracted from it, leaving the reduced overhang
area as the difference area.
[0095] Step 410 determines whether a difference exists, that is,
whether any part of the offset upper curve is not supported by the
lower layer. The projection, difference calculation, and check for
a difference thus determines whether the upper layer, once reduced
by the offset, is fully supported by the layer below. An
unsupported portion of an upper curve corresponds to beads that
will fall unless a support has been built immediately beneath those
beads prior to their deposition.
[0096] If a difference exists, step 412 is executed, and the offset
curve is added to the set of curves belonging to the set of support
set curves. The newly added curve is tagged or identified as being
a support layer curve, but will be later treated in many respects
as a main material layer, as the support layer also requires
support during deposition, even though the purpose of the support
layer is different than the purpose of the main material layer.
[0097] Step 416 determines whether all layers have been processed.
If true, this portion of the processing is complete for algorithm
400. If more layers require processing, step 414 is executed to
increment the layer, making the next lower layer the current layer.
Execution proceeds again at step 404.
[0098] If step 406 determines that one or more curves have
disappeared, then step 418 is executed. Step 418 begins iterating
through each missing or vanished curve. In step 420, a check is
made to determine whether the missing curve abuts another layer. If
this is true, then it may be possible to completely eliminate the
support material layer, as illustrated with support base layer 205
in FIG. 14C, as the small support layer portion, for example one
third of a bead width, is adequately supported by the layer below.
In step 424, the projected upper curve is eliminated. If the curve
does not abut, then step 422 is executed, and the original upper
curve or some minimally dimensioned upper curve is projected onto
the current layer. In this way, a minimally dimensioned support
column, as illustrated in FIG. 15C, can be continued downward
without further offsetting to provide support for the higher
layers.
[0099] Method 400 thus operates by taking each layer, determining
whether the layer above, when reduced inward by an offset, would be
unsupported by the current layer, and if so, adding a support
material layer level with the current layer. When the current layer
is abutting another layer, the layer above may be eventually
reduced to nothing. When the current layer is not abutting another
layer, the layer above may be clamped such that it is never reduced
below a minimum dimension, providing a minimum cross section column
for the remainder of the vertical distance to the cavity floor or
the workpiece platform.
[0100] Referring now to FIG. 19, a method 450 for creating support
material layer tool paths is illustrated. Method 450 is only one
example of a method suitable for creating minimized support layer
tool paths. Method 450 can start with the support and main material
layers or slices already calculated. The curves or outlines of the
main material layers and the support layers have been calculated,
but not the raster tool paths within.
[0101] In step 452, the interference distance for the support
material is determined. For example, the interference distance can
be set to the bead width of the alternate material. In step 454,
the current layer is initialized to be the top layer. A decision
step 456 checks whether the current layer requires surface
improvement; if not, a check is made in step 478 as to whether all
layers have been processed. If all layers have been processed, then
the method is essentially finished, and the method proceeds to 479.
If all layers have not been processed, then the next layer is set
to be the current layer at 480, and step 456 is executed again.
[0102] If surface improvement is required for the current layer,
then in step 458 the previously generated curve from the support
set is retrieved. If the retrieved curve does not abut the main
material, checked in step 460, then the curve is copied to the fill
set in step 470, with further processing discussed below. If the
retrieved curve does abut the main material, then the support
material curve is offset in the inward direction by the support
material bead width, toward the support material, in step 462. The
new curve can be used as the contour tool path for the alternate
material. In step 464, the alternate material is assigned to the
curve which is stored in the tool path set in step 466. The curve
is also copied to the fill set in step 468, with execution
proceeding to step 472. If all support curves for this layer have
been processed, checked at step 472, then the rasters are created
in step 474 and stored in the tool path set in step 476. Execution
then proceeds as previously described at step 478.
[0103] Referring now to FIG. 20, a method 500 is illustrated for
generating tool paths for minimized support layers. Beginning at
step 502, the current layer is initialized to be the top layer. If
the current layer is to receive minimized support, checked at step
504, then the curve is selected from the support set at step 506.
In step 508, rasters are created within the curve boundary to fill
the layer with support material. Support material is assigned to
the rasters in step 510, and the rasters stored in the tool path
set in step 512. If all layers have been processed, checked in step
514, then method 500 is essentially finished and execution proceeds
to 515. If all layers have not been processed, then the current
layer is incremented to the next layer down in step 516, and
execution proceeds again to step 504.
[0104] Numerous advantages of the invention covered by this
document have been set forth in the foregoing description. It will
be understood, however, that this disclosure is, in many respects,
only illustrative. Changes may be made in details, particularly in
matters of shape, size, and arrangement of parts without exceeding
the scope of the invention. The invention's scope is, of course,
defined in the language in which the appended claims are
expressed.
* * * * *