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|United States Patent Application
GREEN; Gordon Robert
December 8, 2011
ROTATING BUILD PLATE
A powder bed additive layer manufacturing system includes a linear
traversing re-coater and a build plate. The build plate is mounted for
rotation relative to the re-coater on an axis extending through the build
GREEN; Gordon Robert; (Bristol, GB)
August 17, 2011|
|Current U.S. Class:
||118/641; 118/107 |
|Class at Publication:
||118/641; 118/107 |
||B05C 19/00 20060101 B05C019/00; B05C 19/06 20060101 B05C019/06|
Foreign Application Data
|Jun 21, 2007||GB||0712027.2|
1. A powder bed additive layer manufacturing system, comprising: a
recoater system comprising a linear traversing re-coater and a powder
dispenser for dispensing particulate material; and a build plate having
an upper surface positioned to receive powder dispensed by the powder
dispenser and spread by a linear traverse of the re-coater, the build
plate rotatable relative to the recoater system about an axis extending
through the build plate.
2. The system as claimed in claim 1, further comprising a motor for
incrementally rotating the build plate.
3. The system as claimed in claim 1, wherein the axis is vertical
relative a horizontal linear traversing direction of the re-coater.
4. The system as claimed in claim 1, wherein the build plate is circular,
and the axis extends through a center of the build plate.
5. The system as claimed in claim 3, wherein the build plate is circular,
and the axis extends through a center of the build plate.
6. The system as claimed in claim 1, further comprising scanning optics
for directing a fusing beam towards a center region of the build plate.
7. The system as claimed in claim 1, further comprising a motor for
progressively rotating the build plate relative to the re-coater between
8. The system as claimed in claim 7, further comprising an elevator
mechanism for progressively lowering the build plate relative to the
re-coater between the layer depositions.
9. The system of claim 7, wherein the axis remains fixed between the
10. The system as claimed in claim 1, wherein the powder dispenser is a
hopper disposed adjacent the periphery of the build plate.
11. The system as claimed in claim 1, wherein the re-coater comprises a
blade having an edge oriented substantially orthogonally to the axis, and
the blade is supported such that the edge thereof remains substantially
orthogonal to the axis as the build plate is rotated.
CROSS-REFERENCE TO RELATED APPLICATION
 This is a continuation of U.S. non-provisional application Ser. No.
12/142,834, filed Jun. 20, 2008, which is incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
 This invention relates to powder additive layer manufacturing
STATE OF THE ART
 Additive Layer Manufacturing (ALM) is a newly-emerging method for
making metal parts. A commonly used approach is the so-called "powder
bed" system. This is illustrated schematically in FIG. 1.
 An infra-red laser 1 is directed by scanning optics 2 such that the
beam 3 defines a 2-dimensional pattern in a thin bed of metal powder 4.
Where the laser impinges upon the bed of powder, the powder is fused to
form a solid layer 5 bonded to a base plate 6. When the first layer is
completed, the build plate is indexed down by the elevator mechanism 7.
The powder bed is then replenished to the original level by the re-coater
8 which scans horizontally so as to scrape powder from supply hopper 9
and deposit a uniform layer above the previously scanned layer. The
second layer of powder is then scanned so as to fuse the required areas
of powder onto the previously fused layer 5. By repeating this process, a
3-dimensional form is progressively build up, being composed of multiple
2-dimensional layers 5. The thickness of the individual layers is
typically 20-50 .mu.m.
 The powder bed 4 typically measures 250 mm.times.250 mm in plan
view and the build plate 6 can be lowered by typically 200 mm. Thus parts
up to 250 mm.times.250 mm.times.200 mm can be manufactured in such
equipment. It should be understood that these are not fundamental limits
however. It is entirely conceivable that scanning optics could be
designed to cover a larger powder bed area and also that the elevator
mechanism could be designed to extend the maximum build height.
 In some powder bed systems, the re-coater 8 has a precision ground
ceramic blade on its lower edge. During the re-coating process, this
translates across the powder bed area, nominally clearing the previously
fused layer 5 by the layer thickness dimension. However there are in
practice a number of factors which contribute to there being considerable
frictional forces between the recoater blade and the previously fused
layer. Firstly, the surface roughness of the previously fused layer is
comparable to the layer thickness, resulting in a degree of interference
between it and the blade. Secondly, the powder generally contains a
proportion of particles whose size is similar to or larger than the layer
thickness which again results in a degree of interference as the
re-coater blade scans. Thirdly, the re-coater blade pushes a "wave" of
powder before it which can cause dynamic pressures against the leading
edge of the developing fused part. Likewise, thermally induced stresses
within the part can cause slight geometric distortions which contribute
additional interference-related forces.
 For parts which possess intrinsic stiffness imparted by their
geometry, the above frictional forces may not be of particular
significance. However a desirable feature of the powder bed technology is
its ability to accurately resolve sub-millimetre features and many parts
which could take advantage of this characteristic can suffer from
mechanical distortion during manufacture due to the above frictional
forces. High aspect ratio (tall or wide compared to thickness) wall-like
features are particularly prone to damage. Problems can be minimized by
advantageously orientating the part with respect to the direction of
travel of the re-coater. However this is not always possible.
 There is a class of parts which could advantageously be
manufactured by powder bed ALM technology and which are of high aspect
ratio, but where the optimal build orientation is not constant through
the build height. Aerodynamic blades where a thin aerofoil section twists
along the length of the blade would be an example. This invention
concerns the addition of a rotation axis to the build plate. By this
means, the build plate can be incrementally rotated as the build
progresses such that, layer by layer, the part is orientated to present
any fragile, high aspect ratio features at the optimal angle to the
re-coater travel direction. Thus in the example cited, the build plate
(which could be circular, rather than rectangular) rotates slightly with
each downward step so as to maintain the thin aerofoil section
approximately parallel to the re-coater travel direction. A geometrical
transformation algorithm within the control software adjusts the
laserscanning geometry to match the build plate rotation. Such coordinate
transformations are well known and will not be described here.
 From one aspect the invention includes a powder bed additive layer
manufacturing system including a linear traversing re-coater and a build
plate characterised in that the build plate is mounted for rotation,
relative to the recoater or movement about an axis. A motor may
incrementally rotate the build plate. Additionally or alternatively a
control system may be provided for controlling the rotation. The axis of
rotation is preferably vertical and the build plate may be circular.
 From another aspect the invention includes a powder bed additive
layer manufacturing system including a linear traversing re-coater and a
build plate elevator mechanism where in the build plate elevator
mechanism incorporates a rotation axis.
 From another aspect the invention includes A powder bed additive
layer manufacturing system re-coater mechanism incorporating a rotation
axis and a linear traverse axis.
 Additionally the invention includes a method of forming a body have
parts of different orientations including succesively depositing and
forming layers of powdered material onto a build plate using a transverse
movement re-coater operating along a line of movement characterised in
orientating the uppermost deposited layer so that it lies substantially
orthogonal to the line of movement before the next layer is deposited
 The rotation axis may be vertical and additionally or alternatively
orthogonal to the line of movement of the re-coater. A control system may
progressively rotate the build plate between layers. The control system
may incorporate coordinate transformation algorithms for aligning the
2-dimensional layer geometry to the rotation of the build plate.
 The manufacturing system may include scanning optics for directing
a fusing beam and those optics may be approximately aligned with a centre
line of the build plate.
 Although the invention has been defined above it is to be
understood that the invention includes any inventive combination of the
features set out above or in the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
 The invention may be performed in various ways and specific
embodiment will now be described with reference to the accompanying
drawings, in which:
 FIG. 1 is a prior art arrangement already described;
 FIG. 1A is an arrangement of an inventive variant;
 FIG. 2 is a schematic plan illustrating a problem identified by the
 FIG. 3 is a schematic view of a further embodiment of the
 The in general embodiments would most likely involve a circular
build plate, but might be some other shape. The build plate has a
rotation axis and may be mounted between the elevator mechanism and the
build plate, or have the elevator mounted on an outer rotation axis. Both
would be feasible embodiments of the invention. It is also possible to
rotate the re-coater system rather than the build plate. It should be
understood that this is entirely equivalent to this invention.
 At FIG. 1A the invention is diagrammatically illustrated at 10 in
that the built plate and/or the recoater system rotate with respect to
each other thereby changing the orientation of a part with respect to the
direction of travel of the recoater. In the example illustrated at FIG. 3
the build plate rotates by means of device 12 and the recoater linearly
traverses across the powder bed 4 and upper solid layer 5. An equivalent
system would rotate the recoater with respect to the part built three
dimensional object 11.
 At FIG. 2 is diagrammatically shown a plan view of the problem to
solve. Powder bed 4 lies upon a circular built plate 6 and contains a
part-built object 11 consisting in part of multiple fused layers 5a-5e.
These layers have an orientation and this orientation is not constant. An
example of such an object is a propeller blade or vane perpendicular to
the build plate. Without rotation, as in the prior art one `slice` of the
object may be head onto the recoater and another slice may be
substantially parallel to the recoater.
 At FIG. 3 a device is shown at 12 for rotating the build plate and
thereby the part-build object 11 fused to it, with respect to the linear
traverse of the recoater B.
 In the method of invention more than one layer 5 of the object 11
(consisting of multiple layers 5) is advantageously orientated with
respect to the direction of travel of the recoater. Applicant's may
further provide a drive system to rotate the build plate (or recoater)
and further a control system to progressively rotate the build plate (or
recoater) between layer depositions. Preferably has the centre line of
the scanning optics is at or near to the centre line of the build plate,
which conveniently is the axis of rotation.
 Whilst for any geometry of part a fixed orientation with respect to
the traverse of the recoater system B may be selected, the Applicants
approach allows a new selection of orientation for each layer 5a.about.5e
and the optimal orientation will be that selected for the next powder
layer to be put down by the recoater. By this means the orientation of
the object 11 with respect to a traverse of the recoater may be selected
to avoid distortion or destruction of the uppermost layer 5.
 Whilst fused layer 5e may build satisfactorily, without the ability
to rotate build plate 6, layer 5a may be distorted or damaged thereby
ruining the entire object 11. As the layers 5 may be 20 microns deep and
take .about.1 minute to form there is a clear economic advantage in being
able to assure that complex objects 11 are successfully completed in a
minimal build time.
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