Note: Descriptions are shown in the official language in which they were submitted.
THREE-DIMENSIONAL SHAPING METHOD
[Technical Field]
[0001]
The present invention relates to a method for producing
a shaped body with a three-dimensional form, by repetition
of a powder layer forming step and a sintering step of the
powder layer by a laser beam or electron beam.
[Background Art]
[0002]
In the aforementioned three-dimensional shaping method,
it is currently impossible to completely prevent sintering
defects, due to the following reasons:
A. ,A problem with the control system involved in
irradiating the laser beam or electron beam onto the powder
layer may result in an excess or insufficiency of the supplied
beam, forming a non-flat sintering surface with a generally
regular uneven condition, compared to when each beam is
supplied normally,
B. Due to formation of the uneven condition of above A
or infiltration of chips, during formation of the powder
layer, squeegee movement is hampered and it becomes difficult
to achieve a uniform flat surface, or joining between the
previously sintered layer and the newly sintered layer by
melting may be incomplete, causing abnormalities in the
powder layer surface that result in a non-flat powder layer
surface with an irregular uneven condition.
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[0003]
However, since in a three-dimensional shaping method
the laminating and sintering steps are repeated in a sealed
apparatus, it is unavoidable that such sintering defects as
mentioned in above A and B will be overlooked and only noticed
after completion of all of the laminating steps and all of
the sintering steps that have been repeated.
[0004]
When a laser beam or electron beam has been irradiated
onto the powder layer surface, sparks are constantly
generated as the powder flies off (sputtering), as shown in
Fig. 7.
When a sintering defect has occurred according to above
A or B, the sparks are known to exhibit a pattern different
from normal sintering, as an empirical rule.
[0005]
In the prior art, however, the technical concept of
focusing on the sparks generated during sintering to detect
sintering defects has not been disclosed in any way.
Incidentally, in Patent Document 1, the sparks that are
generated as powder flies off during three-dimensional
shaping are merely considered to be a cause of abnormal
shaping.
Moreover, no publicly known technical publications
other than Patent Document I can be found that focus on the
sparks generated during irradiation with different beams and
that attempt to actively make use of those sparks in three-
dimensional shaping.
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[Prior Art Documents]
[Patent Documents]
[0006]
Patent Document I: Japanese Published Unexamined Patent
Application No. 2004-277881
[Summary of Invention]
[Technical Problem]
=
[0007]
The present invention provides a three-dimensional
shaping method that focuses on the sparks generated with fly-
off of powder (sputtering) during irradiation of a laser beam
or electron beam onto a powder layer and that rapidly detects
sintering defects, with the aim of preventing generation of
defective three-dimensional shaped products due to inclusion
of sintering defect regions.
[Solution to Problem]
[0008]
In order to solve the aforementioned problems, the
present invention has the following basic configurations.
(1) A three-dimensional shaping method that includes
lamination comprising alternatively repeating a powder layer
forming step and a sintering step in which the powder layer
is sintered by irradiation of a moving laser beam or electron
beam, wherein the following process is adopted during the
sintering step.
a. Measuring the sparks generated with fly-off of powder
caused by irradiation of a laser beam or electron beam over
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the entire periphery of the sintering region are photographed
and the light intensity of the sparks,
b. commanding to continue the sintering step for the
next time unit or the next powder forming step is given, when,
in a time unit within the time necessary for each sintering
step, it has been detected that the width of the spark forming
region photographed according to the process a and the light
intensity of sparks measured according to the process a do
not deviate from the respective ranges of the standard for
the region width and the standard for the light intensity in
which no sintering defect occurs,
c. commanding to cancel the sintering step for the next
time unit or the next powder forming step is given under
judging that a sintering defect has occurred, when, in a time
unit within the time necessary for each sintering step, it
has been detected that the width of the spark forming region
photographed according to the process a or the light
intensity of sparks measured according to the process a
deviates from the respective ranges of the standard for the
region width or the standard for the light intensity in which
no sintering defect occurs,
d. photographing the spark forming regions at the
sintering region in which a sintering defect that resulted
in commanding of the process c was generated, and at the
sintering region within the subsequent time unit,
e. judging that the cause of the sintering defect
resulted in commanding in the process c is a problem with the
control system related to the laser beam or e]ectron beam,
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when each spark forming region width in the process d is
unchanged or changes only gradually, and
judging that the cause of the sintering defect resulted
in commanding in the process c is a problem with the powder
layer surface, when each spark forming region width in the
process d changes rapidly according to comparison of the
spark forming region width in the time unit of the process c
with the spark forming region width in the subsequent time
unit of the process d.
(2) A three-dimensional shaping method that includes
lamination comprising alternatively repeating a powder layer
forming step and a sintering step in which the powder layer
is sintered by irradiation of a moving laser beam or electron
beam, wherein the following process is adopted during the
sintering step.
a. Measuring the sparks generated with fly-off of powder
caused by irradiation of the laser beam or electron beam over
the entire periphery of the sintering region are photographed
and the light intensity of the sparks.
b. commanding to continue the sintering step for the
next time unit or the next powder forming step is given, when,
in a time unit within the time necessary for each sintering
step, it has been detected that the width of the spark forming
region photographed according to the process a and the light
intensity of sparks measured according to the process a do
not deviate from the respective ranges of the standard for
the region width and the standard for the light intensity in
which no sintering defect occurs,
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c. commanding to cancel the sintering step for the next
time unit or the next powder forming step is given under
judging that a sintering defect has occurred, when, in a time
unit within the time necessary for each sintering step, it
has been detected that the width of the spark forming region
photographed according to the process a or the light
intensity of sparks measured according to the process a
deviates from the respective ranges of the standard for the
region width or the standard for the light intensity in which
no sintering defect occurs,
d. recording the light intensities of sparks at the
sintering region where the sintering defect that was the
cause of commanding in the process c has occurred, and at the
sintering region within the subsequent time unit, and further,
e. judging that the cause of the sintering defect
resulted in commanding in the process c is a problem with the
control system related to the laser beam or electron beam,
when each light intensity in the process d is unchanged or
changes only gradually, and
judging that the cause of the sintering defect is a
problem with the powder layer surface, when each light
intensity in the process d changes rapidly according to
comparison of the light intensity width in the time unit of
the process c with the light intensity width in the subsequent
time unit of the process d.
[Advantageous Effects of Invention]
[0009]
With the basic configurations (1) and (2), the sintering
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step in the next time unit, or the next powder forming step,
can be canceled by detection of a sintering defect with
commanding of the process c, making it possible to prevent
unnecessary steps of further lamination and sintering after
a sintering defect has occurred, and to thus avoid generation
of defective three-dimensional shaped products that include
sintering defect regions.
[0010]
Moreover, when the cause of a sintering defect has been
identified and corrected, and the entire sintering region in
which the sintering defect has occurred, or that entire
region and the already laminated sintering regions, are
removed by melting or softening, or all of the entire
sintering regions are removed with a cutting tool, and a new
laminating step and sintering step are repeated, it is
possible to efficiently carry out production of a three-
dimensional shaped product despite generation of the
sintering defects.
[Brief Description of Drawings]
[0011]
Fig. 1 is a schematic diagram of an apparatus for
carrying out the three-dimensional shaping method of the
invention, (a) is a lateral cross-sectional view and (b) is
a plan view showing the configuration of an apparatus that
photographs the region in which sparks are generated and
measures the light intensity of the sparks.
Fig. 2 is a flow chart representing processes a, b and
c of basic configurations (1) and (2).
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Fig. 3 is a pair of graphs showing time-dependent
transition of the spark forming region width, (a) shows the
state of change in the region width due to a problem with
control according to A under Background Art, and (b) shows
the state of change in the region width due to a problem with
the powder layer surface according to B under Background Art.
Fig. 4 is a flow chart relating to carrying out
processes d and e of basic configuration (1), based on
differences in the state of change as shown in Fig. 3.
Fig. 5 is a pair of graphs showing time-dependent
transition of the light intensity of sparks, (a) shows the
state of change in the light intensity in the case of a
problem with the control system according to A under
Background Art, and (b) shows the state of change in the
light intensity in the case of a problem with the powder
layer surface according to B under Background Art.
Fig. 6 is a flow chart relating to carrying out
processes f and g of basic configuration (2), based on
differences in the state of change as shown in Fig. 5.
Fig. 7 is a photograph showing generation of sparks on
the powder layer surface, caused by irradiation of a laser
beam or electron beam in a container (vessel) in which three-
dimensional shaping is carried out.
[Description of Embodiments]
[0012]
According to basic configurations (1) and (2), as shown
in Fig. 1, the construction is the same as the prior art in
requiring a table 2 that supports powder to be laminated and
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a sintered product from the powder in a container (vessel)
1, a powder supply device 3 for the container 1, a squeegee
4 used to flatten the provided powder, a laser beam or
electron beam supply source 5 and a scanner device 6 capable
of moving the beams, and a controller 10, but it also
comprises a spark photographing apparatus B and a measuring
apparatus 9 for measurement of light intensity by sparks,
around the entire periphery of the sintering region.
[0013]
As sparks are generated on the sintering surface, the
spark photographing apparatus 8 and the measuring apparatus
9 for measurement of light intensity by sparks are installed
in a region higher than the sintering surface.
Note that the measuring apparatus 9 for measurement of
light intensity may use either luminosity or illuminance of
light by the sparks as standard.
[0014]
In order to evaluate the region width and light
intensity in the processes b and c of basic configurations
(1) and (2), the time unit is set to be within each sintering
step, the reason being for more efficient evaluation, since
it is very cumbersome and also meaningless to perform
evaluation for each measurement.
[0015]
The time unit also includes cases where it is the time
of each sintering step, but it may also be selected as a time
that is 1/10 to 1/2 of that time.
[0016]
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The processes a, b and c of basic configurations (1)
and (2) are shown in the flow chart of Fig. 2, prescribing
that when no sintering defect has occurred and the spark
forming region width and the light intensity of sparks are
within the ranges previously set as standard, then commanding
is given to continue sintering for the next time unit, or the
next powder layer forming step, as is described in the process
b, but when a sintering defect has occurred and the spark
forming region width or light intensity of sparks is outside
of the range previously set as the standard, i.e. it is either
larger than or smaller than the standard range, then
sintering for the next time unit, or the next powder layer
forming step, is canceled, as is described in the process c.
[0017]
The standard range when no sintering defect has occurred
is set beforehand for each sintering step, according to data
based on the maximum width and minimum width for formation
of sparks when it has been confirmed that no sintering defects
have occurred, and the maximum and minimum luminosity or
illuminance of light intensity, for each sintering step.
[0018]
The basis for selecting cancellation as in the process
c when the spark forming region width and the light intensity
of sparks as measured according to the process a deviate from
the aforementioned standard ranges, is as follows.
[0019]
When a problem with control of the laser beam or
electron beam has occurred according to A under Background
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Art and the beams exceed the proper amount to avoid occurrence
of sintering defects, the spark forming region width based
on the photograph in the process a will exceed the prescribed
image range, and likewise the light intensity measured in the
process a will exceed the prescribed numerical range, whereas
when the beams are insufficient, the region width will not
reach the prescribed image range and the light intensity will
by necessity be below the prescribed numerical range.
[0020]
In either case, whether the beams exceed the proper
amount or are insufficient, this means that so long as an
essentially regular uneven condition is formed on the
sintering surface compared to normal sintering, if the region
width deviates from the prescribed image range and the light
intensity deviates from the prescribed numerical range, then
it was appropriate to select the cancellation in the process
c in response to the generation of a sintering defect.
[0021]
On the other hand, in the case of a problem with the
powder layer surface according to B under Background Art, an
irregular uneven condition is formed on the abnormal surface,
thereby increasing the surface area of powder per unit area
in the planar direction (actually the horizontal direction),
and therefore the spark forming region width exhibits a
larger image width than a normal powder layer surface, and
the light intensity of sparks also changes to a larger value
compared to a normal powder layer surface, such that the
selection in the process c was appropriate.
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[0022]
Moreover, a sintering defect that results in commanding
in the process c is due to causes A and B in most cases.
[0023]
Consequently, it is highly appropriate to issue
commanding cancellation for the process c based on the
standard range for the spark forming region width and light
intensity of sparks when no sintering defects occur, and
commanding prevention for the meaningless and futile steps
of further repeated lamination and sintering, so that it
becomes possible to avoid production of a three-dimensional
shaped product with defects.
[0024]
The image range for the region width when no sintering
defects have occurred, and the standard numerical range for
the light intensity, are set in the following manner.
In a three-dimensional shaping method, an appropriate
laser beam or electron beam intensity range is defined
according to the type of object to be shaped.
Thus, the standard for avoiding a uneven condition
caused by an abnormal beam supply according to above A can
be pre-established by successively increasing and decreasing
the normal supplied amount of a laser beam or electron beam
from the normal state for the prescribed time unit and at the
prescribed measuring position for each type of object to be
shaped, with the supply carried out so as to reach the limits
for the appropriate uneven condition, and measuring the width
of the region in which sparks 7 are formed and the light
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intensity by the sparks 7 at the limit levels, then
determining the maximum just before the supply amount reaches
an excessive level and the minimum just before it reaches an
insufficient level.
[0025]
On the other hand, most types of the shaped body with
the three-dimensional shaping form are common with each other
according to having a normal, i.e. flat powder surface.
With this consideration, the standard for avoiding an
abnormal uneven condition according to above B can be pre-
established, through separate experiments in which by
defining a condition of poor movement of the squeegee 4 that
can interfere with obtaining a flat surface, which is caused
by infiltration of chips, or an incomplete molten state due
to insufficient sintering, during the prescribed time unit
or at the prescribed measuring position, the degree of
irregularity and the degree of incompleteness are gradually
reduced, by confirming the border levels for a normal flat
condition and an abnormal uneven condition, and measuring the
width of the region in which sparks 7 are formed and the
light intensity of the sparks 7 at the confirmed levels, then
determining the minimum just before an irregular condition
is reached.
[0026]
The region width and the light intensity are in a
matching relationship in most cases, such that when the
former is in the standard range the latter will be as well,
and when the former deviates from the standard range the
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latter will be as well.
However, it must be noted that in very exceptional cases,
this matching relationship does not stand, and the latter may
deviate from the standard range even though the former is
within the standard range, or the converse may be true.
Therefore, for a continuing commanding in the process
b, it is a necessary condition for both to be within their
respective standard ranges, while for commanding cancellation
in the process c, it is a necessary condition for at least
one to deviate from its standard range.
Note that in the flow chart in Fig. 2, for
distinguishing between the processes b and c, it is judged
whether or not the region width and the light intensity are
within the standard ranges, but if the judgment is negative
(-No"), so long as at least one of them deviates from the
respective standard range, it is not necessary to judge
whether or not the other one also deviates from its respective
range.
[0027]
When a sintering defect that results in commanding of
the process c has occurred, the cause thereof is usually
diagnosed.
[0028]
In order to diagnose the cause of the sintering defect,
the following process may be adopted according to basic
configuration (1).
d. photographing the spark forming regions at the
sintering region in which a sintering defect that resulted
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in commanding of the process c was generated, and at the
sintering region within the subsequent time unit,
e. judging that the cause of the sintering defect
resulted in commanding in the process c is a problem with the
control system related to the laser beam or electron beam,
when each spark forming region width in the process d is
unchanged or changes only gradually, and
judging that the cause of the sintering defect resulted
in commanding in the process c is a problem with the powder
layer surface, when each spark forming region width in the
process d changes rapidly.
[0029]
The judgment of the process e is based on the following.
[0030]
When above A is a sintering defect caused by a problem
relating to the control system, the laser beam or electron
beam is either in an excessive or a deficient state, and the
state of excess or deficiency continues, such that the region
width will exhibit either no change (also including no change
in approximate terms, i.e. essentially no change), or only a
small change, even with a different sintering region.
[0031]
Consequently, as shown in Fig. 3(a), the region width
for the subsequent sintering region will exhibit either no
change or only a small change compared to the region width
at the region of the sintering defect that resulted in
commanding in the process c, as according to the process d.
[0032]
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In contrast, when a problem with the powder layer
surface is the cause of the sintering defect, as according
to above B, the region of the sintering defect is not
necessarily continuous, and the uneven condition of the
powder layer is irregular.
[0033]
Consequently, when the sintering region where the
region width was photographed after the sintering region in
which the sintering defect that resulted in commanding in the
process c has occurred still remains as a sintering defect,
the irregular uneven condition will clearly differ from the
uneven condition of the original sintering defect, and the
aforementioned region widths will also differ.
[0034]
On the other hand, when the sintering defect has already
disappeared in the next sintering region, the region width
clearly differs from the original region width corresponding
to commanding in the process c, so long as it is within the
standard range according to the process b.
[0035]
Consequently, as shown in Fig. 3(b), the region width
at the subsequent sintering region changes rapidly with
respect to the region width at the sintering region in which
the sintering defect that resulted in commanding in the
process c has occurred.
[0036]
Thus, due to the distinct difference in transition of
the region width between the case of above A and the case of
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above B, the change in the spectral image also differs, and
a judgment according to the process e can be made.
[0037]
The judgment according to the process e can be made
visually based on the state of change between the region
width corresponding to the sintering defect that resulted in
commanding in the process c and the region width
corresponding to the subsequent sintering region.
[0038]
However, a prescribed numerical control is necessary if
the judgment is to be automated and displayed.
[0039]
Therefore, an embodiment may be adopted as shown in the
flow chart of Fig. 4, such that, among the spark forming
region widths of the process d, if the difference between the
spark forming region width at the sintering region where the
sintering defect that resulted in commanding of the process
c has occurred and the spark forming region width at one
sintering region among the subsequent sintering regions, is
within the prescribed numerical range previously set as the
distinguishing standard, then it is judged and displayed that
the cause of the sintering defect that resulted in commanding
in the process c is a problem with the control system relating
to the laser beam or electron beam,
while if the difference deviates from the prescribed
numerical range previously set as the distinguishing standard,
then it is judged and displayed that the cause of the
sintering defect is a problem with the powder layer surface.
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[0040]
The previous setting of the prescribed numerical range
as a standard can be accomplished by photographing in advance
the width of the region in which sparks are formed with fly-
off of powder, for each sintering step at multiple positions
during each time unit when the problem with the control system
relating to the laser beam or electron beam as according to
A is at its maximum state, and creating the data for the
state of change in the region width in advance, and then for
the actual judgment, using the numerical value for the ratio
or difference between the region widths of the two sintering
regions.
[0041]
This numerical value will also differ depending on the
material of the object to be shaped, the radiation intensity
of each beam and the performance of the measuring apparatus
that measures the region width and light intensity, and it
is impossible to specify the numerical range for the standard
range in a general manner.
[0042]
In order to diagnose the cause of the sintering defect,
the following process may be adopted according to basic
configuration (2).
f. Recording the light intensities of sparks at the
sintering region where the sintering defect that was the
cause of commanding in the process c has occurred, and at the
sintering region within the subsequent time unit, and further,
g. judging that the cause of the sintering defect
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resulted in commanding in the process c is a problem with the
control system related to the laser beam or electron beam,
when each light intensity in the process f is unchanged or
changes only gradually, and
judging that the cause of the sintering defect is a
problem with the powder layer surface, when each light
intensity in the process f changes rapidly.
[0043]
The following is the reasoning under which judging
according to the process g can be made by recording the light
intensity as in the process f.
[0044]
As explained for photographing in the process d and
judging in the process e, when the cause is above A, the
state of generation of sparks accompanying fly-off of powder
is either unchanged (also including unchanged in approximate
terms, i.e. essentially unchanged), or only slightly changed.
[0045]
As a result, the light intensity of sparks also exhibits
either no change or only a small change, as shown in Fig.
5(a).
[0046]
In contrast, when the cause is above B, the uneven
condition of the powder layer surface changes rapidly, and
as a result the light intensity at the sintering region that
was the cause of commanding in the process c and the light
intensity at the subsequent sintering region both change
rapidly as shown in Fig. 5(b).
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[0047]
Thus, the case of above A and B can be judged according
to the process g based on the clear difference in the
transition of the change in light intensity.
[0048]
Judging according to the process g can be made visually
based on the state of change between the light intensity for
the sintering defect that resulted in commanding in the
process c and the light intensity in the subsequent sintering
region.
[0049]
However, a prescribed numerical control is necessary in
order for the judgment to be automated and displayed.
[0050]
Therefore, an embodiment may be adopted as shown in the
flow chart of Fig. 6, such that, among the light intensities
of the process f, if the difference between the light
intensity at the sintering region where the sintering defect
that resulted in commanding of the process c has occurred and
the light intensity at one sintering region among the
subsequent sintering regions, is within the prescribed
numerical range previously set as the distinguishing standard,
then it is judged and displayed that the cause of the
sintering defect that resulted in commanding in the process
c is a problem with the control system relating to the laser
beam or electron beam,
while if the difference deviates from the prescribed
numerical range previously set as the distinguishing standard,
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then it is judged and displayed that the cause of the
sintering defect is a problem with the powder layer surface.
[0051]
The previous setting of the prescribed numerical range
as a standard can be accomplished by creating the data for
the transition of the light intensity for the time unit of
each sintering step, when the problem with the control system
relating to the laser beam or electron beam as according to
A is at its maximum state, and then for the actual judgment,
using the numerical value standard for the ratio or
difference relating to the sintering intensities for the two
sintering regions.
[0052]
This numerical value will also differ depending on the
material of the object to be shaped, the radiation intensity
of each beam and the performance of the measuring apparatus
that measures the region width and light intensity, such that
it is impossible to specify the numerical range for the
standard range in a general manner.
[0053]
A description will be given as below according to
Examples.
[Example 11
[0054]
For Example 1, the entire sintering region including
the sintering region in which the cause of a sintering defect
has been corrected and commanding in the process c has been
carried out, or that entire sintering region and the entire
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sintering region that has already been laminated below that
region, is melted or softened by a laser beam or electron
beam, and then only the portion of the thickness of the melted
or softened region, or the portion of the thickness of the
sintered and laminated sintering region is removed, or
alternatively the entireties of each of those sintering
regions are removed with a cutting tool, and the laminating
step and sintering step are repeated from the freshly removed
regions.
[0055]
As an explanation in terms of the technical gist of
Example 1, even though the position of the sintering defect
that was the cause of commanding in the process c, and its
proximity, has been melted and removed with the laser beam
or electron beam, new lamination and sintering in that region
requires image analysis of the melted and removed region and
new lamination and sintering based on that analysis.
[0056]
However, it is highly complicated and inefficient to
perform such image analysis, and to carry out the powder
layer forming step and sintering step in a local region based
on the image analysis.
[0057]
Therefore, in Example 1, the entire sintering region
including the position in which the sintering defect has been
produced by each beam, or not only that entire sintering
region, but also the entire sintering region that has already
been formed, are melted, and then based on precise
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dimensional measurement, the portion of the thickness of the
sintering region is removed, or alternatively the portion of
the thickness of that entire region and the entire sintering
region that has already been formed below it, are removed,
then continuously carrying out the new lamination and
sintering.
[0058]
In the case of Example 1, it is possible to effectively
utilize the sintered layer that has already been formed,
except for the region that is melted and removed in this
manner, so that a three-dimensional shaped product without
defects can be produced even when a sintering defect has been
detected.
[Example 2]
[0059]
For Example 2, a light signal and/or an audio signal
indicate the presence of a sintering problem during
commanding in the process c.
[0060]
This configuration allows sintering defects to be
rapidly dealt with.
[0061]
Specifically, if different color light signals are
selected or different audio signals are selected depending
on whether the cause of the sintering defect is above A or
B, it will be possible to rapidly determine and deal with the
cause of the sintering defect.
[Industrial Applicability]
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[0062]
As explained above, in order to make possible production,
the present invention allows sintering defects to be rapidly
detected of three-dimensional shaped products in an efficient
manner, while also preventing production of three-dimensional
shaped products with defects, and therefore the invention is
useful in all three-dimensional shaping methods.
[Reference Signs List]
[0063]
1: Container (vessel)
2: Table
3: Powder supply device
4: Squeegee
5: Laser beam or electron beam supply source
6: Scanner
7: Spark
8: Spark forming region width photographing apparatus
9: Spark light intensity measuring apparatus
10: Controller
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CA 2973456 2018-05-02
