U.S. patent application number 15/041695 was filed with the patent office on 2016-08-18 for device and method for making a three-dimensional object.
This patent application is currently assigned to EOS GmbH Electro Optical Systems. The applicant listed for this patent is EOS GmbH Electro Optical Systems. Invention is credited to Johann Oberhofer.
Application Number | 20160236299 15/041695 |
Document ID | / |
Family ID | 55527242 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160236299 |
Kind Code |
A1 |
Oberhofer; Johann |
August 18, 2016 |
DEVICE AND METHOD FOR MAKING A THREE-DIMENSIONAL OBJECT
Abstract
A device for the making of a three-dimensional object (3) by
means of layer by layer consolidation of a powderlike construction
material (11) by electromagnetic radiation or particle beam has a
height-adjustable carrier (2), on which the object (3) is built,
and whose horizontal dimension defines a construction field (5).
Furthermore, an irradiation device (6, 9) is present for directing
the radiation onto regions of an applied layer of the construction
material within the construction field (5) corresponding to an
object cross section (30). A control unit (10) controls the
irradiation device (6, 9) such that the powder particles of the
construction material (11) are bonded together at the sites where
the radiation impinges on the construction material. A selective
heating device (18a, 18b) is designed so that any given partial
surface (19) of the construction field (5) can be heated before
and/or after to a plateau temperature, which is significantly
higher than the temperature of at least a portion of the
construction field (5) outside the partial surface (19). The
control unit (10) actuates the selective heating device (18a, 18b)
such that the partial surface (19) has a predefined minimum
distance (d) from the edge of the construction field (5).
Inventors: |
Oberhofer; Johann;
(Stockdorf, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EOS GmbH Electro Optical Systems |
Krailling |
|
DE |
|
|
Assignee: |
EOS GmbH Electro Optical
Systems
Krailling
DE
|
Family ID: |
55527242 |
Appl. No.: |
15/041695 |
Filed: |
February 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 35/64 20130101;
B29C 64/188 20170801; B33Y 10/00 20141201; B33Y 30/00 20141201;
B29C 64/295 20170801; B23K 26/0006 20130101; B22F 2999/00 20130101;
B23K 26/342 20151001; C04B 2235/665 20130101; B23K 26/144 20151001;
B29C 64/268 20170801; Y02P 10/25 20151101; Y02P 10/295 20151101;
B22F 2003/1056 20130101; B29C 64/153 20170801; B22F 2003/1057
20130101; B29C 64/393 20170801; B22F 3/1055 20130101; B22F 2999/00
20130101; B22F 3/1055 20130101; B22F 2203/11 20130101 |
International
Class: |
B23K 26/342 20060101
B23K026/342; B23K 26/144 20060101 B23K026/144; B23K 26/00 20060101
B23K026/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2015 |
DE |
102015202964.6 |
Claims
1. Device for the making of a three-dimensional object by means of
layer by layer consolidation of a powderlike construction material
by electromagnetic radiation or particle radiation with: a
height-adjustable carrier, on which the object is built, and whose
horizontal dimension defines a construction field, an irradiation
device for directing the electromagnetic radiation or particle
radiation onto regions of an applied layer of the construction
material within the construction field corresponding to an object
cross section, a control unit for controlling the irradiation
device such that the powder particles of the construction material
are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized by a selective heating device, which is
designed so that any given partial surface of the construction
field can be heated to a plateau temperature, which plateau
temperature is significantly higher than the temperature of at
least a portion of the construction field outside the partial
surface, wherein the control unit is designed so that it actuates
the selective heating device such that the partial surface has a
predefined minimum distance from the edge of the construction
field.
2. Device according to claim 1, wherein the plateau temperature is
at most 200.degree. C. less than an activation temperature of the
construction material.
3. Device according to claim 1, wherein the control unit has a data
storage, in which material parameter values with regard to a
thermal behaviour of at least one construction material, preferably
various construction materials, are stored.
4. Device according to claim 3, wherein the control unit in
operation establishes the minimum distance in dependence on the
material parameter values stored in the data storage for the
construction material being used.
5. Device according to claim 1, wherein the control unit in
operation establishes the shape of the partial surface in
dependence on the shape of the object cross section to be
consolidated.
6. Device according to claim 1, wherein the control unit in
operation establishes the partial surface such that its area extent
is greater than that of the object cross section to be
consolidated.
7. Device according to claim 1, wherein the selective heating
device in operation directs electromagnetic radiation, especially
laser radiation, and/or particle radiation onto the surface of the
construction material.
8. Device according to claim 7, wherein the irradiation device
directs laser radiation onto the surface of the construction
material and the laser radiation of the selective heating device
has the same wavelength as that of the irradiation device.
9. Device according to claim 1, further comprising a container
surrounding the construction field, wherein the device comprises a
cooling and/or heating device for the cooling and/or heating of the
container.
10. Device according to claim 1, further comprising a temperature
measuring device, wherein the control unit in operation controls
the heat supply by the selective heating device so that a minimum
plateau temperature to which the partial surface of the
construction field is heated in at least one operating state is by
a predetermined amount above a temperature relayed by the
temperature measuring device to the control unit.
11. Device according to claim 10, wherein the control unit controls
the selective heating device so that the partial surface is
preheated to a minimum plateau temperature which lies at least
300.degree. C. above the temperature relayed by the temperature
measuring device to the control unit.
12. Device according to claim 1, wherein the control unit actuates
the selective heating device so that it heats a partial surface of
the construction field after the directing of the electromagnetic
radiation or particle radiation onto the construction material by
the irradiation device such that a cooldown rate in the partial
surface is at least 30% less than without the action of the
selective heating device, wherein the partial surface has a
predefined minimum distance from the edge of the construction
field.
13. Method for making a three-dimensional object by means of a
layer by layer consolidation of a powderlike construction material
by electromagnetic radiation or particle radiation in a device,
according to claim 1, wherein an object is built on a
height-adjustable carrier, whose horizontal dimension defines a
construction field, wherein the electromagnetic radiation or
particle radiation is directed with the aid of an irradiation
device onto regions of a deposited layer of the construction
material within the construction field that correspond to an object
cross section, wherein the irradiation device is controlled with a
control unit such that the powder particles of the construction
material are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized in that, with a selective heating device,
any given partial surface of the construction field is heated to a
plateau temperature, which plateau temperature is significantly
higher than a temperature of at least a portion of the construction
field outside the partial surface, wherein the control unit
actuates the selective heating device so that the partial surface
has a predefined minimum distance from the edge of the construction
field.
14. Method according to claim 13, wherein the minimum distance is
established in dependence on preliminary experiments in which the
heat transmission ability of the construction material used in the
method is determined.
15. Method according to claim 14, wherein the control unit actuates
the selective heating device so that the latter heats the partial
surface of the construction field at least to the plateau
temperature before and/or after the directing of the
electromagnetic radiation or particle radiation onto the
construction material by the irradiation device, wherein the
partial surface has a predefined minimum distance from the edge of
the construction field.
16. Device according to claim 3, with a temperature measuring
device, wherein the control unit in operation controls the heat
supply by the selective heating device so that a minimum plateau
temperature to which the partial surface of the construction field
is heated in at least one operating state is by a predetermined
amount above a temperature relayed by the temperature measuring
device to the control unit.
17. Method for making a three-dimensional object by means of a
layer by layer consolidation of a powder like construction material
by electromagnetic radiation or particle radiation in a device,
especially according to claim 3, wherein an object is built on a
height-adjustable carrier, whose horizontal dimension defines a
construction field, wherein the electromagnetic radiation or
particle radiation is directed with the aid of an irradiation
device onto regions of a deposited layer of the construction
material within the construction field that correspond to an object
cross section, wherein the irradiation device is controlled with a
control unit such that the powder particles of the construction
material are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized in that, with a selective heating device,
any given partial surface of the construction field is heated to a
plateau temperature, which plateau temperature is significantly
higher than a temperature of at least a portion of the construction
field outside the partial surface, wherein the control unit
actuates the selective heating device so that the partial surface
has a predefined minimum distance from the edge of the construction
field.
18. Method for making a three-dimensional object by means of a
layer by layer consolidation of a powder like construction material
by electromagnetic radiation or particle radiation in a device,
especially according to claim 5, wherein an object is built on a
height-adjustable carrier, whose horizontal dimension defines a
construction field, wherein the electromagnetic radiation or
particle radiation is directed with the aid of an irradiation
device onto regions of a deposited layer of the construction
material within the construction field that correspond to an object
cross section, wherein the irradiation device is controlled with a
control unit such that the powder particles of the construction
material are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized in that, with a selective heating device,
any given partial surface of the construction field is heated to a
plateau temperature, which plateau temperature is significantly
higher than a temperature of at least a portion of the construction
field outside the partial surface, wherein the control unit
actuates the selective heating device so that the partial surface
has a predefined minimum distance (d) from the edge of the
construction field.
19. Method for making a three-dimensional object by means of a
layer by layer consolidation of a powder like construction material
by electromagnetic radiation or particle radiation in a device,
especially according to claim 6, wherein an object is built on a
height-adjustable carrier, whose horizontal dimension defines a
construction field, wherein the electromagnetic radiation or
particle radiation is directed with the aid of an irradiation
device onto regions of a deposited layer of the construction
material within the construction field that correspond to an object
cross section, wherein the irradiation device is controlled with a
control unit such that the powder particles of the construction
material are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized in that, with a selective heating device,
any given partial surface of the construction field is heated to a
plateau temperature, which plateau temperature is significantly
higher than a temperature of at least a portion of the construction
field outside the partial surface, wherein the control unit
actuates the selective heating device so that the partial surface
has a predefined minimum distance from the edge of the construction
field.
20. Method for making a three-dimensional object by means of a
layer by layer consolidation of a powder like construction material
by electromagnetic radiation or particle radiation in a device,
especially according to claim 10, wherein an object is built on a
height-adjustable carrier, whose horizontal dimension defines a
construction field, wherein the electromagnetic radiation or
particle radiation is directed with the aid of an irradiation
device onto regions of a deposited layer of the construction
material within the construction field that correspond to an object
cross section, wherein the irradiation device is controlled with a
control unit such that the powder particles of the construction
material are bonded together at the sites where the electromagnetic
radiation or particle radiation impinges on the construction
material, characterized in that, with a selective heating device,
any given partial surface of the construction field is heated to a
plateau temperature, which plateau temperature is significantly
higher than a temperature of at least a portion of the construction
field outside the partial surface, wherein the control unit
actuates the selective heating device so that the partial surface
has a predefined minimum distance from the edge of the construction
field.
Description
[0001] The present invention pertains to an additive manufacturing
device and method, in particular a device and a method for the
making of a three-dimensional object by means of selective layer by
layer consolidation of powder like construction material by means
of the application of energy.
[0002] A method of this kind is used for example for Rapid
Prototyping, Rapid Tooling or Rapid Manufacturing. An example of
such a method is known under the name "selective laser sintering or
laser melting". In this, powder is selectively consolidated by
selective irradiation with a laser beam, in that the thermal energy
introduced into the material by the laser beam is used to melt the
material entirely or superficially so that the powder grains have
joined together after the ensuing cooldown. Besides laser
radiation, other electromagnetic radiation or also an electron beam
for example can be used for the application of energy.
[0003] EP 1 583 626 B1 describes a device and a method by which
objects are made with high precision, despite the rather fast
manufacturing speed sought. In particular, when consolidating a
layer of a powder like construction material in order to generate a
cross section of the object being produced, it is proposed to
alternately aim the energy beam at different regions of the cross
section of the object. In particular, during the manufacturing
process the powder layer to be consolidated is recorded by means of
a thermal imaging camera and after an analysis of the temperature
distribution in the powder layer the temperature is specifically
corrected at individual places in the powder layer. The
computations required for this to determine the nature and manner
of propagation of thermal energy after the energy input by the
energy beam make the method relatively complicated, however.
[0004] Stresses which are supposed to be reduced by the method in
EP 1 583 626 B1 occur in objects manufactured by means of a
generative layered construction method especially when the
temperature of the powder layer, before the energy beam impinges on
it, lies substantially below the temperature at which a
consolidation of the powderlike material takes place by the fusing
thereof. Thus, such stress problems occur in particular, but not
only, with metallic powder materials.
[0005] Therefore the problem which the present invention proposes
to solve is that of providing an improved device and an improved
method for the making of three-dimensional objects. It should be
possible to produce stress-free parts preferably in the simplest
possible manner.
[0006] The problem is solved by a device according to claim 1 and a
method according to claim 13. Further developments of the invention
are indicated in the dependent claims. Here, devices can also be
developed further by the features of the methods indicated below or
in the dependent claims, or vice versa.
[0007] A device according to the invention for the making of a
three-dimensional object by means of layer by layer consolidation
of a powderlike construction material by electromagnetic radiation
or particle beam contains: a height-adjustable carrier, on which
the object is built, and whose horizontal dimension defines a
construction field, an irradiation device for directing the
electromagnetic radiation or particle radiation onto regions of an
applied layer of the construction material within the construction
field corresponding to an object cross section, and a control unit
for controlling the irradiation device such that the powder
particles of the construction material are bonded together at the
sites where the electromagnetic radiation or particle radiation
impinges on the construction material. In particular, a selective
heating device is present, which is designed so that any given
partial surface of the construction field can be heated to a
plateau temperature. The plateau temperature is significantly
higher than the temperature of at least a portion of the
construction field outside the partial surface. The control unit is
further designed so that it controls the selective heating device
such that the partial surface has a predefined minimum distance d
from the edge of the construction field.
[0008] In such a device, it is not the entire construction field
that needs to be brought up to a high temperature in order to
decrease the temperature difference between the fused material and
its surrounding, especially the surrounding unconsolidated powder
material, and consequently reduce stress cracks. Instead, by a
minimum distance from the edge of the construction field the device
is protected against the high temperatures in that the
unconsolidated powderlike construction material surrounding an
object being produced serves as an insulator. Furthermore, a powder
layer in the construction field can be heated selectively, i.e.,
only at selected sites.
[0009] The plateau temperature can be, e.g., a temperature of the
unconsolidated construction material immediately prior to supplying
the energy for its consolidation. Furthermore, the plateau
temperature can also be a temperature which is adjusted so that an
already consolidated object cross section only cools down slowly.
Preferably, the plateau temperature is at most 200.degree. C.,
especially preferably at most 150.degree. C. and very specially
preferably at most 100.degree. C. less than an activation
temperature of the construction material, i.e., a temperature at
which the powder particles are bonded together by modification of
the chemical and/or physical properties of the powder so that a
solid results after a cooling. Due to the preheating of the
construction material to the plateau temperature as close as
possible to the activation temperature, the energy put in by the
irradiation device is used extensively for the actual consolidation
process and not so much for the preheating of the powder. In this
way, the consolidation process can occur in an overall more
controlled manner.
[0010] Preferably, the control unit has a data storage medium, in
which material parameter values with regard to a thermal behaviour
of at least one construction material, preferably various
construction materials, are stored. This makes it possible in
particular to control the heating process in dependence on the
construction material used in the device. Further preferably, the
control unit in operation, i.e., during the manufacturing process,
establishes the minimum distance d from the edge of the
construction field in dependence on the material parameter values
stored in the data storage medium for the construction material
being used. In this way, it is possible to set the minimum distance
from the edge of the construction field in dependence on the
respective insulating properties of a quantity of the
unconsolidated construction material surrounding the object being
produced.
[0011] Generally in the context of the invention the minimum
distance from the edge of the construction field should be kept as
small as possible so as not to needlessly block space in the
construction field. On the other hand, this minimum distance should
be adequately dimensioned to protect other regions of the device
from damage due to overly high temperature stress.
[0012] Preferably, the control unit in operation establishes the
shape of a partial surface to be selectively heated, inter alia its
shape and/or dimensions, in dependence on the shape of the object
cross section to be consolidated. In this way, the surface of the
powder layer to be heated by means of the selective heating device
can be especially effectively limited to the absolutely necessary
degree, which improves the energy efficiency.
[0013] Moreover, the control unit in operation preferably
establishes a partial surface such that its area extent is greater
than that of the object cross section to be consolidated. In this
way, not only an object cross section to be consolidated, but also
a portion of the powder surrounding it is heated, so that the heat
dissipation from the sites being consolidated at the edge of the
object cross section is lessened. This likewise leads to a
reduction of thermal stresses and/or prevents an inadequate
consolidation of the powder at the edge of the object cross
section.
[0014] In one preferred embodiment of the invention, the selective
heating device in operation directs electromagnetic radiation,
especially laser radiation, and/or particle radiation onto the
surface of the construction material. In this way, a selective
heating of the construction material can occur without the use of
complicated added structures, such as heating hoses or heating
resistors. Furthermore, the heating can occur with high position
selectivity. Especially when laser radiation is used for the
selective heating and this laser radiation has the same wavelength
as that of the irradiation device, if the latter also uses a laser,
one can take the laser radiation for the selective heating from the
same laser source as is used to generate the consolidation
radiation.
[0015] Preferably the construction field is surrounded by a
container, and in addition a cooling and/or heating device is also
present for the cooling and/or heating of the container. Due to a
heating of the container, heat can be supplied additionally to the
powderlike construction material, so that the selective heating
device can be smaller in dimension. By a cooling of the container
surrounding the construction field, heat can be deliberately taken
away and the parts of the device surrounding the container can be
protected against the heat in the construction field. Due to the
cooling, stationary thermal conditions in particular can be
established in the surrounding of the container, by cooling down a
container wall to a given temperature value. Furthermore, due to a
suitable cooling it is possible to reduce the aforementioned
minimum distance from the edge of the construction field. Such a
reduction will be effected preferably in dependence on the
determined (i.e., measured or calculated) cooling parameter values
of the cooling.
[0016] The device for making a three-dimensional object can also
have a temperature measuring device, which performs a temperature
measurement at least in a partial region of the construction field,
preferably near its edge. Preferably, the control unit can then
control the heat supply by the selective heating device during the
manufacturing process such that a minimum plateau temperature to
which a partial surface of the construction field is heated lies in
at least one operating state (i.e., not necessarily during the
entire manufacturing process in one layer, but rather as needed,
even temporarily) above a temperature relayed by the temperature
measuring device to the control unit by a predefined amount.
[0017] By the monitoring of the temperature, the heating of the
construction material by means of the selective heating device can
be specifically adapted to the particular conditions in the device
at a given time. In particular, the control unit too can control
the selective heating device such that the partial surface is
heated to a minimum plateau temperature which lies at least
300.degree. C., preferably at least 400.degree. C., especially
preferably at least 800.degree. C. above the temperature relayed by
the temperature measuring device to the control unit. In this way,
depending on the construction material used, the plateau
temperature can be set to be as close as possible to the activation
temperature.
[0018] Preferably, the control unit controls the selective heating
device such that the latter heats a partial surface of the
construction field at least to the plateau temperature before
and/or after the directing of the electromagnetic radiation or
particle radiation of the irradiation device onto the construction
material. In this way, the heating process of the construction
material and/or the cooldown process after its consolidation can
occur in a more controlled manner. Without the selective heating,
temperature changes in the powder like construction material as the
irradiation device sweeps over the construction field are more
abrupt and larger.
[0019] In particular, the control unit can control the selective
heating device so that it heats a partial surface of the
construction field after the directing of the electromagnetic
radiation or particle radiation of the irradiation device onto the
construction material such that a cooldown rate in the partial
surface is at least 30%, preferably at least 50%, especially
preferably at least 70% less than without the action of the
selective heating device. By means of a device designed in this way
it is possible to delay the cooldown process after the
consolidation of the powder, which serves in particular to prevent
stress cracks.
[0020] With a device according to the invention, a method for
making a three-dimensional object by means of a layer by layer
consolidation of a powderlike construction material by
electromagnetic radiation or particle radiation is possible,
wherein an object is built on a height-adjustable carrier, whose
horizontal dimension defines a construction field, and
electromagnetic radiation or particle radiation is directed with
the aid of an irradiation device onto regions of a deposited layer
of the construction material within the construction field
corresponding to an object cross section, wherein the irradiation
device is controlled with a control unit such that the powder
particles of the construction material are bonded together at the
sites where the electromagnetic radiation or particle beam impinges
on the construction material. In particular, with a selective
heating device, any given partial surface of the construction field
is heated to a plateau temperature, wherein the plateau temperature
is significantly higher than a temperature of at least a portion of
the construction field present outside the partial surface. Here,
the control unit controls the selective heating device such that
the partial surface has a predefined minimum distance d from the
edge of the construction field.
[0021] In particular, the minimum distance d can be established in
dependence on preliminary experiments in which the heat
transmission ability of the construction material used in the
process is determined. In this way, the heating of the construction
material can be adapted specifically to the construction material
being used with its characteristic thermal properties.
[0022] Further features and purposes of the invention will emerge
from the description of exemplary embodiments with the help of the
appended drawings.
[0023] FIG. 1 is a schematic, partly sectioned view of an exemplary
embodiment of a device according to the invention for the layer by
layer making of a three-dimensional object which is suitable for
carrying out a method according to the invention.
[0024] FIG. 2 is a top view of the construction field of the device
from FIG. 1, showing as an example an object cross section
currently being consolidated.
[0025] FIG. 3 illustrates a preliminary experiment to determine the
heat transmission behaviour of the powder like construction
material.
[0026] In the following, making reference to FIG. 1, an example of
a device 100 according to the invention is described, being suited
to carrying out a method according to the invention. In the device
100, an object 3 is built up in a container 1 open at the top,
having a wall 1a. In the container 1 there is arranged a carrier
which can move in a vertical direction V, whose schematically
depicted carrier plate 2 closes off the container 1 at the bottom
and thus forms its bottom. Not shown in the figure is a
construction platform which may also be present between the
lowermost layer of the object 3 and the carrier plate 2. In FIG. 1,
the object 3 being built in the container 1 is shown in an
intermediate state with several cross sections 30 already
consolidated, wherein the object 3 is surrounded by powderlike
construction material 13 remaining unconsolidated, and represented
as transparent in the figure.
[0027] The device 100 furthermore contains a supply tank 11 for a
powderlike construction material which can be consolidated by
electromagnetic radiation or particle radiation and an applicator
12, able to move in a horizontal direction H, for the application
of a layer of the construction material onto the most recently
consolidated object cross section 30 and the unconsolidated
construction material surrounding it within a construction field 5,
which is bounded by the container wall 1a. The device 100
furthermore contains an irradiation device in the form of a first
radiation source 6, such as a laser, which generates a laser beam
7, which is directed via a deflection device 9 onto a layer of
unconsolidated construction material previously deposited by the
applicator 12. In addition, a selective heating device 18a, 18b is
provided, which is formed for example from a second radiation
source 18a together with another deflection device 18b. The second
radiation source 18a can emit a heating beam 18c, for example,
which can be deflected by means of the deflection device 18b onto
any given partial surfaces 19 of the construction field 5 (see FIG.
2), which is bounded by the container wall 1a.
[0028] The second radiation source 18a can either generate
electromagnetic radiation, i.e., it can be a laser in particular,
or it can generate particle radiation (such as electrons). In the
latter case, the deflection device 18b would be an ion optics. If
the heating beam 18c is a laser beam, the second radiation source
18a can optionally be omitted and in its place the first radiation
source 6 can be used to generate the heating beam 18c. For this,
the light intensity is then expediently reduced by means of a
supplemental optics not shown in FIG. 1 as compared to the light
intensity of the consolidation beam 7. Alternatively or in
addition, the quantity of heat introduced with the heating beam 18c
can also be adjusted via the speed with which it is moved across
the deposited layer of the construction material.
[0029] Furthermore, the device 100 contains a control unit 10, by
which the individual components of the device 100 are controlled in
coordinated fashion to carry out the construction process. The
control unit can contain a CPU, whose operation is controlled by a
computer program (software). The computer program can be stored
separately from the device on a storage medium, from which it can
be loaded into the device, especially into the control unit 10.
[0030] The deflection device 18b is designed so that the heating
beam 18c of the second radiation source 18a can be deflected onto
any given regions of the construction field 5, in particular can be
directed only onto one or more partial surfaces 19 thereof, wherein
the total area of all partial surfaces 19 and in particular the
area of a partial surface 19 is less than the area of the
construction field 5. In particular, the control device 10 can be
used to adjust the introduced thermal energy by altering the power
density at the point of impingement of the heating beam 18c on the
construction field 5 and/or by altering the scanning speed of the
heating beam 18c. The heating device 18a is dimensioned such that,
possibly by sufficient focusing of the heating beam 18c and/or a
sufficiently slow movement of the heating beam 18c across the
construction field 5, at least so much energy can be introduced
into the uppermost powder layer possibly consolidated already in
portions thereof that the temperature at the point of impingement
of the heating beam 18c is significantly higher than in other
regions of the construction field 5. By "significantly higher" it
is preferably meant that the temperature of the powderlike
construction material at the point of impingement of the heating
beam 18c is at least 300.degree. C., preferably at least
400.degree. C. and in some cases at least 800.degree. C. above the
temperature of the construction material in regions of the
construction field 5 where no object cross section of the object to
be made is situated, as a rule in a margin region of the
construction field 5.
[0031] Activation temperature here means a temperature at which the
powder particles bond together as a result of a chemical and/or
physical change in their properties, for example in that the powder
particles fuse entirely or only fuse superficially and sinter
together. The activation temperature is thus a limit temperature at
which the construction material is substantially modified in its
chemical and/or physical structure.
[0032] Furthermore, the control software in the control device 10
controls the heating beam 18c such that the point of impingement of
the heating beam onto the construction field 5 always has a minimum
distance d from the edge of the construction field 5. This
situation is shown in FIG. 2. Here, within the construction field 5
there is shown an object cross section 30 being consolidated, which
is covered by a partial surface 19, in which a heating of the
construction material by means of the heating beam 18c occurs. As
can be seen, the edge of the partial surface 19 has a minimum
distance d from the edge of the construction field 5.
[0033] In order to reduce stresses in the object being made, a
heating of a partial surface to a plateau temperature as close as
possible to the activation temperature is preferably sought, i.e.
for example to a plateau temperature which is at most 200.degree.
C., more preferably at most 150.degree. C. and especially
preferably at most 100.degree. C. lower than an activation
temperature of the construction material (11). However, the
following points speak against a heating to too high a temperature:
[0034] The temperature should not be so high that a consolidation
of the powder material takes place. [0035] The higher the
temperature, the more energy-consuming the heating process is.
[0036] The higher the temperature, the greater is the heat
dissipation to the edges of the construction field 5 and a possible
harmful impact on the other parts of the device for layer by layer
generative manufacturing, in FIG. 1 the laser sintering or melting
device.
[0037] By taking account of the heat dissipating properties of the
particular construction material used, one can specifically
establish the plateau temperature to which the powderlike
construction material needs to be preheated. This is because the
better the heat supplied by the consolidation beam 7 is dissipated
by the construction material, the harder it is to bring about a
consolidation with the consolidation beam 7. Thus, the better the
heat dissipation properties of the construction material, the
closer the plateau temperature should be to the activation
temperature.
[0038] The minimum distance d to the edge of the construction field
5 is also influenced by the heat transmission properties of the
powder. As already mentioned above, the powder within this distance
shall ensure an insulation toward the outside of the construction
field 50. Thus, the better the heat transmission properties of the
unconsolidated powderlike construction material, the greater the
minimum distance d should be chosen.
[0039] In one particular embodiment, the control unit 10 has a data
storage, in which material parameter values regarding the heat
transmission properties of the construction material to be used in
a planned production of one or more objects are stored. Then,
during a manufacturing process, the control unit 10 can carry out
the controlling of the selective heating device 18a, 18b in
consideration of these material parameter values.
[0040] Ideally, material parameters or material parameter values
regarding a plurality of construction materials will be stored in
the data storage, so that prior to the start of a construction
process the control unit 10 only needs to be informed as to the
type of construction material being used.
[0041] In one advantageous embodiment of the invention, prior to a
manufacturing process for objects with the device 100 the heat
transmission ability of the construction material is determined in
pre-tests so that it can be used for determining (establishing) the
plateau temperature and the minimum distance d.
[0042] For the determination of the thermal conductivity of
powderlike materials, first of all one can use the needle probe
method of ASTM D5334-08. Here, a thin, elongated heating source
(the needle probe) is inserted into a powder bed and heated with
constant power. At the same time, the temperature inside the source
is recorded. The slower the rise in the source temperature, the
higher the thermal conductivity of the sample material.
[0043] Alternatively or in addition to the aforementioned method,
the heat transmission ability of the construction material can be
determined with the following preliminary experiment described in
regard to FIG. 3. FIG. 3 shows in magnified view the container 1 of
the device 100 along with the carrier plate 2 arranged in it. On
this carrier plate 2 is placed a heat-insulating base 32, on which
a heating cylinder 33 and a measuring stick 34 having a defined
distance .DELTA. from the heating cylinder 33 are arranged. For the
preliminary experiment, the entire container 1 is filled with
construction material 13 up to a filling height Z, coinciding with
the height of the heating cylinder 33. Next, the heating cylinder
33 is preheated, for example by inductive heating, to a temperature
T.sub.V which is 100.degree. C., for example, below the desired
activation temperature for the construction material 13 in the
actual construction process to follow. Of course, a different
temperature T.sub.V can also be used, but the closer the
temperature T.sub.V to the activation temperature, the more precise
the findings of the preliminary experiment are as to the actual
heat transfer capacity of the construction material that is present
during the actual construction process.
[0044] In the measuring stick 34 there are temperature detection
elements 35 arranged at various heights. In FIG. 3 precisely three
of these elements are shown, but one can also use any given other
number of temperature detection elements. After the end of the
heating process to the temperature T.sub.V of the measuring
cylinder 33, the temperature detection elements 35 are used to
detect the temperature in dependence on the time. The time change
in the temperature is dependent on the heat transmission properties
of the construction material 13 in the space with the distance
.DELTA. between the measuring stick 34 and the heating cylinder
33.
[0045] For an even more precise measurement of the heat
transmission properties of the powder 13, a plurality of measuring
sticks 34 can also be arranged at various distances .DELTA..sub.1 .
. . .DELTA..sub.n from the heating element 33. The heating element
33 for example can be a cylinder, whose height essentially agrees
with the height of the most massive object being made in the
subsequent construction process, or whose diameter essentially
agrees with the maximum diameter parallel to the carrier plate 2 of
the most massive object being made in the subsequent construction
process.
[0046] Alternatively or in addition to the preliminary experiments
just described, the thermal conductivity of the construction
material can also be determined during the manufacturing process of
objects.
[0047] For this, the temperature of the uppermost powder layer is
measured at different sites by means of a thermal imaging camera
(IR camera) or a point pyrometer whose detection surface is moved
across the uppermost powder layer. Since one knows at which points
of the powder layer a consolidation is being carried out with the
consolidation beam 7 and/or a preheating is being carried out with
the heating beam 18c, one can use the distances between the points
of the powder layer where the temperature was determined and the
sites of the powder layer where energy is being supplied to obtain
information about the heat transfer capacity of the powder.
[0048] Otherwise, one can also specifically determine the
temperature at one or more sites in the construction field 5 with
the thermal imaging camera or the point pyrometer and adapt the
heating power to the locally present temperature in the target
region 19 for the selective heating.
[0049] By measuring the temperature at one or more sites at a
reference location in the construction field 5, preferably near the
edge of the construction field 5 at a position where no powder is
being consolidated in any layer, one can also adapt the minimum
distance d from the construction field margin in dependence on the
measured values found. In this way, in particular, the region
outside the construction field 5 can be protected against damage
from too large a temperature rise. But the temperature at the
reference location can also be used alternatively or additionally
for the control of the heat supply to the at least one partial
surface 19 by the selective heating device, so that a minimum
plateau temperature to which the partial surface 19 of the
construction field 5 is heated is a predetermined amount above a
temperature relayed by the temperature measuring device to the
control unit 10. The minimum plateau temperature is preferably at
least 300.degree. C., more preferably at least 400.degree. C.,
especially preferably at least 800.degree. C. above the temperature
relayed by the temperature measuring device to the control unit
10.
[0050] Optionally, the container, preferably the container wall,
can be provided with a heating and/or cooling device (not shown). A
heating device in this place enables an additional heating of the
construction material, so that not as much heat needs to be
supplied by the heating beam 18c. A cooling device in the wall of
the container 1 means that the temperature outside the container 1
is prevented from rising to excessively high values. If one matches
the heating power of the heating beam 18c, the minimum distance d
and the cooling power of the cooling for the container to each
other, one can achieve a stationary temperature distribution.
[0051] Although in the preceding discussion a laser sintering
device or laser melting device has been described in detail, the
invention can also be applied to other devices for the making of
three-dimensional objects by means of the action of an energy beam
for the consolidation of a powderlike construction material. For
example, the energy for consolidating the powder can also be
introduced by a two-dimensional radiation source, such as an
infrared heater. In addition, it is also possible to use a
plurality of radiation sources for the consolidation. Moreover, one
is not limited to electromagnetic radiation as the radiation for
the consolidation of the construction material. Instead, it is also
possible to use particle radiation, such as an electron beam.
[0052] Even though we have constantly spoken of a heating beam in
the above, it is also possible not to supply the preheating energy
in a partial surface 19 of the construction field 5 by sweeping a
beam across the partial surface 19. Instead the preheating energy
may be supplied by a two-dimensional irradiation of the at least
one partial surface 19 or by sweeping across the at least one
partial surface 19 with a beam action zone that is not pointlike,
but instead has a predetermined lateral dimension and shape. For
example, the partial surface 19 can be scanned with an infrared
radiator. One must distinguish this from the two-dimensional
heating systems known in the prior art, which can be used to heat
the powderlike construction material in the entire construction
field, but can only achieve an insignificant temperature rise in a
freshly applied powder layer.
[0053] The supplying of energy with the heating beam can occur not
only before the beginning of a consolidation process in a deposited
powder layer, but also at the same time as the consolidation
process. Furthermore, it is possible to irradiate such partial
surfaces 19 of a deposited powder layer with the selective heating
device, which are distinguished in that already selectively
consolidated powder material is present in powder layers lying
underneath them. In this way, one avoids too rapid a lowering of
the temperature of the consolidated construction material. This
prevents cracks due to too fast a cooldown of the already
consolidated powder material and thus too rapid a cooldown of parts
of an already consolidated object cross section. Preferably, the
goal of the heating with the selective heating device is to make a
cooldown rate in the partial surface(s) 19 at least 30%, preferably
at least 50%, especially preferably at least 70% less than it would
be without the action of the selective heating device 18a, 18b.
[0054] As in the prior art, the entire powder layer within the
construction field 5 can be preheated additionally with a
nonselective two-dimensional heating to a start temperature of, for
example, 150.degree. C.
[0055] Although this was not explicitly mentioned above in the
description of the exemplary embodiments, it is not only possible
to make one object in a manufacturing process, but also several
objects can be made in parallel in the container 1. Where an object
is mentioned above, such in a selective heating of an object cross
section, such procedure can also be applied to all other objects
being made in the manufacturing process. For example, if several
object cross sections are present in a powder layer, the powder is
selectively heated in the regions of several, preferably all,
object cross sections.
[0056] As emerges from what has been said thus far, a selective
heating makes sense preferably in those partial surfaces 19 which
are almost identical to the object cross section(s) to be
consolidated in a freshly deposited powder layer. Likewise, the
selective heating can be limited to parts of the object cross
section/object cross sections in which the most intense stresses
are expected. One recognizes that the partial surfaces 19 to be
heated with the selective heating device will preferably vary from
one layer to another. Furthermore, it should be noted that
different partial surfaces 19 in a freshly deposited layer (not
necessarily assigned to the cross sections of different objects) do
not necessarily have to be brought to the same plateau
temperature.
[0057] In another possible embodiment, a selective heating of
partial surfaces 19 of a deposited powder layer is effected such
that around each selectively heated partial surface 19 there is a
nonselectively heated powder layer, having at least a lateral
dimension d perpendicular to the edge of the partial surface 19. In
this way, an insulating region of thickness d of nonconsolidated
powder is created around each selectively heated partial surface
19. With this technique, it is possible to lessen the mutual
thermal influencing of partial surfaces 19, for example when
several objects are being made in parallel. As a result, the
manufacturing process can be effected in more controlled
fashion.
[0058] The method according to the invention and the device
according to the invention are especially suited to metallic
construction materials. But in addition to this, the method
according to the invention also brings benefits when other
construction materials are used, such as ceramic or plastic
powders, especially a PAEK powder.
* * * * *