DE102015214690A1 - Method and device for producing a three-dimensional object by means of a generative layer construction method - Google Patents

Abstract

A method for layering at least one three-dimensional object (2) comprises the steps of: a material applying step of providing a layer of building material (13) on a previously provided layer of the building material, a solidifying step of solidifying the applied layer by electromagnetic radiation or particle radiation, wherein the material application step and the solidification step are repeated until all cross sections of the at least one three-dimensional object are solidified, wherein at least a portion of an applied layer of the building material is heated by a heater (16), the temperature of an applied layer of the building material a temperature measuring device (17) in a measuring range (17 a) is measured and in dependence on the determined temperature, the heating power of the heating device (16) is controlled, it being determined whether it is z u solidifying points of the layer, which are in the measuring range (17a), and if so, it is ensured that the radiation is supplied to these points only after the lapse of a predetermined delay time.

Description

The present invention is directed to a method for the generative layer-wise construction of three-dimensional objects by means of a generative layer construction device as well as to a control device which controls the generative layer construction device for carrying out the method.

The European patent EP 0 764 079 B1 describes a laser sintering apparatus in which a powdery building material is applied in layers to a support defining a construction field, wherein after a layer application that part of the layer which corresponds to a cross section of the object to be produced is selectively solidified by means of laser irradiation. During solidification of the material by means of laser radiation, so much energy is introduced into the material by the laser beam that at least superficial melting of the powder grains takes place, so that after cooling, the powder grains have joined to form a solid. So that the entire heat energy does not have to be entered by the laser beam alone, a pre-heating of a powder layer applied by means of radiant heaters takes place before the selective irradiation with the laser.

Since the radiant heat emitted by the radiant heaters heats a newly applied layer of powder material only at the surface, it takes a certain time until the entire layer is brought to the desired temperature by heat transport within the layer. Furthermore, the temperature of the layer also changes during the selective exposure of the layer with the laser, on the one hand by heat energy input through the laser, on the other hand by heat emissions. Therefore, in EP 0 764 079 B1 the temperature of the powder layer is measured by means of a pyrometer and the radiant heaters are controlled in dependence on the measured values of the pyrometer by means of a PID controller or PI controller.

EP 0 764 079 B1 mentions that when exposure of the layer in the measuring spot of the pyrometer the latter registers a large excess of the setpoint temperature and this is intercepted by the control of the heating power. Although a PID controller or PI controller is capable of intercepting temporal, even large, variations in the reference variable to some extent, the problem is to distinguish laser-induced temperature changes in the pyrometer's measurement range from temperature changes due to other causes. While the temperature changes caused by the laser in the measuring range of the pyrometer disturb the regulation of the heating power (at other locations of the powder layer than where the laser impinges on it, there is no strong increase in temperature, so there is no need for a change in the heating power), the temperature changes with other causes as well as possible be compensated by the heating power.

One way to overcome this problem is simply to avoid powder compaction by exposure to the laser in the spot of the pyrometer. If one does not choose a complicated pyrometer with a variable measuring range from layer to layer in the construction field, then the measuring range lies in the same place in each layer. In such a case one must then accept that in a part of the construction field, namely where the measuring range of the pyrometer is located, no components to be produced can be arranged. This limits the use of a generative layer construction device.

It is, therefore, an object of the present invention to provide a method and apparatus for the generative layered production of objects which eliminates manufacturing constraints due to the arrangement of the objects to be manufactured.

The object is achieved by a method for the layered construction of at least one three-dimensional object according to claim 1, by a control device according to claim 11, by a generative layer construction device according to claim 12 and a computer program according to claim 15.

Further developments of the invention are specified in the subclaims. Features of the subclaims and the following description, which relate to the method according to the invention, can also be used for the further development of the inventive control device or inventive generative layer construction device or vice versa, unless this is explicitly excluded.

A method according to the invention for layering at least one three-dimensional object from a building material by sequentially consolidating layers of the building material respectively at those locations of a layer corresponding to the cross-section of the at least one object, solidification being accomplished by introducing thermal energy comprises the following steps :
a material application step of providing a layer of a building material on a building substrate or a previously provided layer of the building material,
a solidification step of solidifying the coated layer by means of electromagnetic radiation or particle radiation, in which the Radiation acts on sites of the layer to be consolidated, so that the building material is solidified at these points by the heat energy introduced by the radiation,
wherein the material application step and the solidification step are repeated until all cross sections of the at least one three-dimensional object to be produced have solidified,
wherein at least a portion of a deposited layer of the building material is heated by a heater,
wherein the temperature of an applied layer of the building material is measured with a temperature measuring device in a measuring region which comprises a partial region of the layer, and the heating power of the heating device is controlled as a function of the determined temperature,
wherein, in at least one solidification step, it is determined whether there are sites of the layer to be consolidated in the measurement area and, if so, that the radiation is supplied to these sites only after the lapse of a predetermined delay time after the start of the solidification step becomes.

The invention thus makes it possible, during the generative layer-by-layer production of objects, to solidify a layer even in the measuring range of a temperature measuring device. According to the invention, this is made possible by solidifying that part of a layer which is to be consolidated in the measuring range of the temperature measuring device only after the lapse of a predetermined delay time after the beginning of the solidification step. The provision of the delay time thereby leads to a simpler and more accurate control of the heating power, that on the one hand possible to collect information about the time course of the temperature of the layer during the delay time. This makes it possible to use this information for the temperature control during the exposure in the measuring range of the temperature measuring device. On the other hand, due to the delay time, an influence of the temperature regulation by the exposure in the measuring range of the temperature measuring device does not occur at the beginning of the solidification of a layer, but only at a later time. As a result, a maladjustment of the heating power of the heating device can only affect the exposed points in the measuring range of the temperature measuring device and the exposed areas of the layer after the exposure of the measuring range. The longer the delay time, the fewer spots of the layer are exposed in the measuring area after exposure. Thus, the longer the delay time, the fewer points of the layer are affected by impaired control of the heating power.

Securing a predetermined delay time can be ensured, for example, by modifying the order in which the locations of the layer corresponding to the at least one object cross-section are determined by radiation input so that the radiation is directed to the measuring range of the temperature measuring device only after the predetermined delay time has elapsed becomes. The term "predetermined" expresses here that the delay time does not change arbitrarily from layer to layer, but deliberately ensures a certain length of the delay time. On the one hand this can be done by setting the delay time before the start of a generative layer construction process to a fixed value, on the other hand, a control device, the length of the delay time for each layer in dependence on other parameters, such. B. the total duration of a solidification step for this layer set.

Preferably, a warning signal or a warning is output to a user if the time necessary for carrying out the solidification step in a shift increases by the insertion of the predetermined delay time by an amount which exceeds a predefined maximum amount. In a further preferred manner, the warning signal or the warning is issued if the time required for carrying out the solidification step in a layer or the predetermined delay time has a greater amount than a time which is necessary for carrying out the solidification step in a layer.

Especially if there are only a few places to be consolidated in a layer, the total duration of a solidification step required for this can be very small. In such a case, the provision of a predetermined delay time could eventually result in the duration actually required by the delay time for the solidification step being significantly longer than the actual total time required for the solidification step, even the delay time itself may be longer than the time duration for the solidification step consolidation step. This is because only the predetermined delay time is awaited before it is solidified within the measuring range of the temperature measuring device.

Alternatively or additionally, a warning is issued to the operator of the generative layer building apparatus if the time required to perform the solidification step in a layer increases by the addition of the delay time by a percentage exceeding a predefined maximum percentage. The maximum percentage is, for example, that percentage by which the duration of the Grouting step may increase without resulting intolerable temperature differences within a layer to be exposed. Furthermore, the maximum percentage may also be determined by a just tolerable fluctuation thereof being determined by means of a simulation of environmental parameters (eg the strength or direction of a protective gas flow) at the location of the measuring range and the maximum percentage being set smaller than the percentage which the just tolerable fluctuation occurs.

Preferably, but not necessarily, the warning is given to the operator right at the beginning of the building process, so that he can decide whether the production process should continue despite any loss of quality or whether the production process should be better stopped.

In a further variant, a maximum delay time is determined and a warning to a user, for. As a warning signal, output when the predetermined delay time has a greater amount than the maximum delay time.

The inclusion of the predetermined delay time could cause the temperature differences within the layer to be exposed to change fundamentally, since heat energy is supplied to the measurement area and its surroundings at a time other than the originally scheduled time. This can be taken into account by calculating a maximum delay time, preferably for each layer. The maximum delay time is, for example, that delay time whose insertion into the exposure process results in barely tolerable temperature differences within a layer to be exposed. Furthermore, the maximum delay time may also be a time within which the simulated environmental parameters (eg the strength or direction of a protective gas flow) at the location of the measuring range show a fluctuation which is still tolerable. In response to a warning signal, an operator of the device could, for example, counteract intolerable temperature inhomogeneities by changes in the exposure order in subsequent layers.

In the event that an exposure takes place in the measuring range of the temperature measuring device during a solidification step of a layer, a sequence of the solidification step is preferably adjusted so that the radiation is supplied to the points in the measuring region essentially only at the end of the solidification step.

If the radiation is supplied to the points in the measuring range substantially only at the end of the solidification step, then it does not matter if the regulation for the heating power is based on excessive temperatures. Even if the heating power is reduced too much, this has no effect since, after the end of the solidification step, a new layer of the building material is applied and the heating power control is then based on the temperature measurement data for the new layer.

In a preferred embodiment of the invention, after the end of the delay time, the heating power of the heating device is controlled until the end of the solidification step as a function of an extrapolated time profile of the heating power or of extrapolated temperature values. The extrapolated temperature values are determined from the time profile of the temperature values measured by the temperature measuring device during the delay time.

According to this preferred embodiment of the invention, the regulation of the heating power is based on a temperature value which would most likely have been determined if the exposure had not taken place in the measuring area but at another point of the layer at that time. This allows a largely realistic control of the heating power.

The extrapolated temperature values preferably form the continuation of the time profile of the temperature values measured by the temperature measuring device during the delay time. Thus, the extrapolation can take place in a simple manner by fitting a curve (for example based on a polynomial) to the time profile of the temperature measured values during the delay time and extending the curve into the period of exposure of the measuring range.

In addition, when determining the extrapolated temperature values, the temporal change of ambient parameters during the solidification step is additionally taken into account. The extrapolation of the temperature values is thereby better adapted to the reality, as more parameters that can change over time are taken into account.

In particular, when determining the extrapolated temperature values, a change in a parameter of an inert gas flow which is conducted over the applied layer can be taken into account. For example, the direction or strength of an inert gas flow, which is passed over the powder layer to be solidified to prevent reactions of the building material with oxygen or else. for elimination vapors that escape the solidified material. In particular, when turbulence occurs in a protective gas flow, the flow can change locally in the short term. When monitoring the flow behavior, such a fluctuation in the extrapolation of temperature values can then be taken into account.

In a preferred variant of the invention substantially no supply of radiation to the applied layer is carried out during a part of the delay time.

In the event that the actual duration of the solidification step is so small that no reasonable extrapolation is possible within such a short period of time, the time duration of a solidification step can be artificially prolonged by inserting a waiting time to obtain a sufficiently long delay time to determine the temperature profile in which no solidification of sites of the applied layer takes place. In this way, despite a short time duration of the solidification step, a reliable temperature value for the duration of the exposure in the measuring range of the temperature measuring device can still be obtained. Likewise, by extending the delay time, an adaptation of the temperature conditions within a layer to the desired temperature distribution can be ensured.

Preferably, the position of the measuring range of the temperature measuring device is not changed during a solidification step, in particular during the entire production process of the at least one object.

Of course, in the case of solidification in the predetermined measuring range of the temperature measuring device, it would be possible simply to have the temperature measuring device carry out a temperature measurement in another region of the layer. However, this would be more expensive, since there would have to be a possibility of being able to direct the temperature measuring device, for example a point pyrometer measuring without contact, to another area of the layer. Here, the invention makes it possible to maintain a simple construction for the temperature measuring device.

A generative layer constructing apparatus according to the invention for stacking at least one three-dimensional object of a building material by successively solidifying layers of the building material respectively at those locations of a layer corresponding to the cross-section of the at least one object, wherein the solidification is accomplished by introducing thermal energy; the generative layer building apparatus comprises at least:
a material application device for providing a layer of a building material in a material application step on a building substrate or a previously provided layer of the building material,
a solidification device, which in operation performs a solidification step of solidifying the applied layer by means of electromagnetic radiation or particle radiation in which the radiation acts on sites of the layer to be solidified, so that the building material is solidified at these locations by the thermal energy introduced by the radiation,
wherein the generative layer building apparatus is configured to repeat the material application step and the solidification step until all cross sections of the at least one three-dimensional object to be produced have solidified,
and wherein the generative layer building apparatus comprises a heating device configured to heat at least a portion of an applied layer of the building material.
and wherein the generative layer building apparatus comprises a temperature measuring device, which in operation measures the temperature of a deposited layer of the building material in a measuring area comprising a portion of the layer,
is designed so that it controls the heating power of the heating device in dependence on the determined temperature and determines in at least one solidification step, if there are sites of the layer to be consolidated, which are within the measuring range, and if this is the case, the radiation only after the lapse of a predetermined delay time after the start of the solidification step.

The control device according to the invention is suitable for carrying out the method according to the invention automatically. As a rule, a generative layer construction device will have a modular design and the control processes will take place in a control device provided specifically for this purpose. In this case, the control device according to the invention can be a separate control device which cooperates with a control module of a generative layer construction device, or it can be a part of the control module of a generative layer construction device.

A generative layer construction device according to the invention has:
a material application device for providing a layer of a building material in a material application step on a building substrate or a previously provided layer of the building material,
a solidification device, which in operation comprises a solidification step of solidifying the coated layer by means of electromagnetic radiation or particle radiation, in which the radiation acts on sites of the layer to be solidified, so that the building material is solidified at these locations by the heat energy introduced by the radiation,
wherein the generative layer building apparatus is configured to repeat the material application step and the solidification step until all cross sections of the at least one three-dimensional object to be produced have solidified,
and wherein the generative layer building apparatus comprises a heating device configured to heat at least a portion of an applied layer of the building material.
and wherein the generative layer building apparatus comprises a temperature measuring device, which in operation measures the temperature of a deposited layer of the building material in a measuring area comprising a portion of the layer,
and wherein the generative layer construction device further comprises the control device according to the invention.

Although it is theoretically possible that the control device according to the invention interacts with a generative layer construction device via a cable or network, ie is arranged outside the generative layer construction device, it will nevertheless be advantageous if the control device according to the invention is arranged directly in the generative layer construction device, in order to keep the signal paths short so that as far as possible a real-time processing of temperature measured values can take place and also in the course of a solidification step by inserting a delay time in real time can be intervened.

Preferably, the temperature measuring device in the generative layer construction device according to the invention comprises a pyrometer. Although it is theoretically possible that the temperature measuring device is a large-area image-providing infrared camera, the method according to the invention and the generative layer construction device according to the invention bring the most benefit if a pyrometer is present as a temperature measuring device that has a fixed measuring range ( Measuring location) within the construction field of the generative layer construction device has.

In particular, a generative layer construction device according to the present invention will be designed so that it can carry out the method according to the invention.

A computer program according to the invention comprises a sequence of instructions by which a method according to the invention is carried out when the computer program is executed in a control device or a generative layer construction device.

Even if it is possible to design a control device according to the invention solely by means of hardware components in such a way that it can carry out a method according to the invention, it will generally be more expedient to use a computer program that runs in a data processing device to determine the individual method steps of the method according to the invention to implement.

1 shows a schematic representation of a generative layer building apparatus using the example of a laser sintering apparatus.

2 and 3 schematically show the procedure according to a first embodiment of the method according to the invention and

4 schematically shows the procedure according to a second embodiment of the method according to the invention.

The following is with reference to 1 An embodiment of a generative layer building apparatus according to the invention 1 described. In the 1 The device shown is a laser sintering or laser melting device 1 , To build an object 2 it contains a process chamber 3 with a chamber wall 4 ,

In the process chamber 3 is an open-topped container 5 with a wall 6 arranged. In the container 5 is a movable in a vertical direction V carrier 7 arranged on which a base plate 8th attached to the container 5 closes down and thus forms its bottom. The base plate 8th can be a separate from the carrier 7 be formed plate attached to the carrier 7 is attached, or it can be integral with the carrier 7 be formed. Depending on the powder and process used may be on the base plate 8th another building platform 9 be attached to the object 2 is built. The object 2 but also on the base plate 8th be built yourself, which then serves as a construction platform. In 1 is that in the container 5 on the build platform 9 object to be formed 2 below a working level 10 presented in an intermediate state with several solidified layers, surrounded by unreinforced building material 11 ,

The laser sintering device 1 also contains a powder container 12 for a solidified by electromagnetic radiation powdery building material 13 and a coater movable in a horizontal direction H. 14 for applying the building material 13 to the working level 10 , At its top contains the wall 4 of the process chamber 3 a coupling window 15 for a radiation serving to solidify the powder. In the process chamber 3 are also a radiant heater 16 and a temperature measuring device 17 arranged.

The radiant heating 16 is designed to heat at least a portion of the construction field, preferably the entire construction field. The construction field is that area of the working level 10 that is inside the upper opening of the container 5 lies. It should be noted in this regard that in place of radiant heating 16 Also, a different type of heater can be used to heat the top layer. In what way is heated is for the invention only of minor importance.

At the temperature measuring device 17 it is preferably a non-contact point pyrometer, although it is also possible to use an IR camera that captures larger, not necessarily contiguous areas of the construction field. The temperature measuring device detects the temperature of the uppermost powder layer in a measuring range 17a which is a portion of the uppermost powder layer and in 2 and 3 is shown. Based on the measured values of the temperature measuring device 17 controls the control module 29 the heating power of the radiant heater 16 ,

The laser sintering or laser melting device 1 also includes an exposure device 20 with a laser 21 , a laser beam 22 generated by a deflection device 23 deflected and by a focusing device 24 via the coupling window 15 focused on the construction field.

Next contains the device 1 a control module 29 , about which the individual components of the device 1 be controlled in a coordinated manner to carry out the construction process. The control module may include 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, in particular into the control module.

In operation, the carrier is first applied to apply a powder layer 7 lowered by a height corresponding to the desired layer thickness. By method of the coater 14 over the working level 10 then becomes a layer of the powdery building material 13 applied. The application takes place at least over the entire cross section of the object to be produced 2 , preferably over the entire construction field. The applied powder layer is heated by the radiant heating 16 preheated. Subsequently, the cross section of the object to be produced 2 with the laser beam 22 scanned so that the powdered building material 13 is solidified at the points that the cross-section of the object to be produced 2 correspond. These steps are repeated until the object 2 is completed and the installation space can be removed.

The inventive method can by means of in 1 shown generative layer building apparatus are performed. For this purpose, the generative layer construction device in 1 a control device 100 on, by means of which the method according to the invention can be implemented. This control device 100 can either, as in 1 shown, part of the generative layer building apparatus, in particular of the control module 29 , or be separate from the generative layer building apparatus and connected to the latter via a network or a cable or bus system.

A first embodiment of the invention will now be described with reference to FIG 2 and 3 described.

2 and 3 each show a plan view of the construction field of the laser sintering device of 1 ie the area of the working level 10 that is inside the upper opening of the container 5 lies. In the example described here, in a construction process, not a single object 2 but six objects are produced in parallel. However, this does not mean that the invention is not also applicable to the production of a different number of objects (ie, for example, only one object).

2 and 3 show a view of the top powder layer during the building process at a certain time during the solidification step. The sake of clarity are in the 2 and 3 the cross sections to be consolidated in this layer 2a to 2f the objects to be produced completely, that is shown in already solidified state. Furthermore, in the two figures, the measuring range 17a the temperature measuring device, such as a non-contact measuring point pyrometer, shown hatched. The order in which the individual object sections 2a to 2f is solidified by specifying the capital letters A to F. As you can see, at first, ie before the end of the method according to the invention, the object cross-section is intended 2e according to the object cross section 2d and in front of the object cross section 2f to solidify.

According to the method according to the invention, the control device checks before starting the solidification step of a layer 100 from whether one of the cross-sections to be consolidated at least partially in the measuring range 17a of the dot pyrometer. For this test, the control device 100 For example, access the input data set of the generative layer building apparatus, in which it is specified at which points in a layer a solidification by means of the laser beam is to take place and in which order the laser beam is directed to the points to be solidified of the layer. The location of the measuring range 17a of the Punktpyrometers in the construction field, the controller 100 For example, be entered via an operator input or this information is the controller 100 from the control module 29 passed the laser sintering device. Once the controller 100 an overlap of the measuring range 17a discovered with a cross-section to be consolidated, engages the controller 100 in the course of the solidification step (for example, by direct access to the input data of the control module 29 or but. through communication with the control module 29 ).

The result of this intervention in the course of the solidification step is in the 3 shown. As you can see, now the cross section 2e that with the measuring range 17a of the point pyrometer overlaps, solidified within the layer last. Within this cross section 2e in turn, that range is preferred which coincides with the measuring range 17a overlapped, last solidified. In other words, the controller sees 100 for the cross section 2e a predetermined delay time after the start of the solidification step, so that this cross section 2e is solidified after the expiration of this predetermined delay time. The in the 2 and 3 illustrated reordering of the order in which the cross sections are solidified with the laser beam is nothing else than the insertion of a delay time for the cross section 2e , as a result of the resorting according to the invention, the cross section 2e that with the measuring range 17a overlaps the point pyrometer, will always be solidified at a later date than originally provided. The purpose of this automatic ensuring a predetermined delay time in the exposure for locations that are in the range of the pyrometer, is the following:
An automatic shutdown of the heating power due to high temperature readings of the pyrometer by an exposure in the measuring range 17a of the pyrometer is less harmful towards the end of the solidification process for a powder layer than at the beginning of the solidification step. Finds the solidification in the measuring range 17a Only at the end of the solidification step instead, there are only a few places to be consolidated in the layer, where a solidification at too low powder material temperature due to low heat output of the radiant heater 16 during the previous exposure in the measuring range 17a takes place of the pyrometer. Even if the solidification of the measuring range 17a overlapping cross-section or the overlap area with the measuring range 17a does not take place towards the end of the solidification step, but nevertheless takes place with a certain delay time since the start of the solidification step, a positive effect can be observed.

Of course, no adjustment of the exposure order is necessary if it has already been established prior to carrying out the method according to the invention that the pyrometer measuring area is only exposed to a late time during the solidification step, ie in particular only after the delay time determined according to the invention. However, in such a case, the purpose of the method according to the invention is that it is explicitly checked whether the predetermined delay time for the exposure of the measuring range is maintained. The inventive method thus guarantees compliance with the predetermined delay time. The predetermined delay time is preferably defined by how much time is necessary to ensure sufficiently accurate extrapolation (see below).

Also in the case that only a single large component is manufactured and an exposure to the laser beam in the measuring range 17a the point pyrometer is required, according to the invention the area of the object cross-section which is in the measuring range 17a of the pyrometer, only after a certain delay time from the beginning of the solidification step, preferably until the end of the solidification step, solidified. This can be done, for example, by the control device 100 a division of the cross-section to be solidified of the single large object into segments, wherein the segment that the measuring range 17a cuts or completely in this measuring range 17a is solidified until the earliest possible date. In other words, a re-sorting of the segments of the cross-section takes place in such a way that those segments which cover the measuring range 17a cut, only at a late time during the solidification step, preferably only towards the end of the solidification step, solidified.

According to a second embodiment of the invention is during solidification in the measuring range 17a the temperature measuring device, the normal control of the heating power of the heater overridden and replaced by a special regulation, hereinafter referred to as "exception" replaced. An exemplary procedure will be described below with reference to FIG 4 described. In 4 the heating power P as well as the temperature T provided by the temperature measuring device for the control are shown as a function of time. As one recognizes, rises first with Beginning of the solidification process at time t _0, the temperature T detected by the temperature measuring means gradually, and accordingly, the heating power P is gradually controlled down by the control.

If at time t _1, the solidification in the measuring range 17a the temperature measuring device starts, so the temperature measuring device delivers from this point higher temperature values to the control. In the 4 this is only schematically shown, the exact curve may be different. Due to the higher temperature values, the control regulates the heating power P during the period between t ₁ and t ₂ , within which a solidification in the measuring range 17a takes place and the temperature values that the temperature measuring device outputs are increased sharply. After completion of solidification in the measuring range 17a after the time t ₂ , the temperature T outputted from the temperature measuring means gradually decreases, and the heating power P gradually rises again.

The course described so far, in the 4 is represented by solid curves, reflects the normal case, in which not yet the procedure according to the invention is applied. According to the second embodiment, the too low heating power during solidification in the measuring range of the temperature measuring device (the heating power is so low that they are in the schematic 4 during this period is completely absent), as follows:
During the period between t ₁ and t ₂ , the regulation for the heating power is not supplied to the temperature input values by the temperature measuring device but by the control device 100 or from the control module 29 , The control device delivers 100 or the control module 29 the control temperature values corresponding to the in 4 represented dashed curve of the temperature curve, as it would result if solidification in the measuring range of the temperature measuring device would be omitted. The corresponding dashed curve shown the heating power P is also shown. To be able to perform adequate temperature values during the period between t ₁ and t ₂ of the scheme, detects the control means 100 after it has determined that in a solidification step a solidification in the measuring range of the temperature measuring device will occur, at least during a part of the period between t ₀ and t _1, the time profile of the temperature values output by the temperature measuring device to the control Temperature course, the temperature profile is extrapolated in the period between t ₁ and t ₂ . Between the times t ₁ and t ₂ then supplies the controller 100 the controller, the extrapolated temperature values instead of the output from the temperature measuring device temperature values.

For the detection of the temperature profile between t ₀ and t ₁ , this period must be sufficiently long. In the control device 100 is preferably a minimum detection time T _Erf predetermined. Before the beginning of the solidification step, the control device checks 100 then preferably determines whether the period t ₁ -t _{0 is} greater than T _Erf . If this is not the case, then the controller leads 100 Accordingly, a reordering of the order of the exposures of the individual points, as in the first embodiment, to extend the period t ₁ -t ₀ . In other words, a predetermined delay time is again introduced after the start of the solidification step, so that in the measuring range 17a the temperature measuring device, the solidification takes place only after the expiration of the delay time.

Alternatively, instead of changing the exposure order of the layer to obtain a sufficiently large time t ₁ -t ₀ , in the first and second embodiments, it is also possible to maintain the order in which the locations of the layer are exposed and to insert only one waiting time no exposure takes place to extend the period t ₁ -t ₀ .

Of course, it is also possible to combine the first and second embodiments with each other: the exposure order can be changed such that exposure of the layer within the measurement range 17a is moved backwards in time, preferably carried out only at the end of the solidification step, and at the same time during the exposure in the measuring range 17a from the controller 100 the heating power control extrapolated temperature values are provided.

In a modification of the invention which is applicable to both embodiments, a warning signal is output to a user of the generative layer building apparatus in the event that the time period t ₁ -t ₀ , ie the time between the start of the solidification step and the beginning of the solidification in the measuring area of Temperature measuring device, is greater than a predefined maximum delay time. The reason is the following:
If through the control device 100 the period t ₁ -t _{0 is extended} by a reordering of the exposure sequence or the insertion of an exposure pause, then changes the temporal temperature profile at the individual points of the layer. If, for example, a region of the layer in which the measuring range of the temperature measuring device is located, the laser radiation is applied later, then this layer region, under which Assuming that in the immediately underlying layer, a solidification has taken place, cool down longer and therefore there will be a different temperature of the powdered building material than if the laser radiation had already been supplied to this layer region. Such variations in local temperature can lead to changes in the properties of the object at the appropriate locations. It is therefore very helpful for the operator to find out whether there are large temporal shifts or delays with respect to the different solidification areas of a layer. The maximum delay time leading to the issuance of a warning, such as an optical or audible signal or a message issued on a surveillance screen, depends on the particular building process, for example on the building material used, on the fill level of the vessel 5 , ie the percentage of building material in the container that is solidified in the production of objects, etc. Similarly, the maximum delay time can be made dependent on the duration of the solidification step. For example, if the length of the entire solidification step is too small to detect a temperature history within this time as in the second embodiment, the procedure according to the second embodiment can not be selected. In such a case, since the control reacts to solidification in the measuring range of the temperature measuring device as in the prior art, it is important in such a case to notify the user by a warning that for this solidification step only insufficient regulation for the heating power of the heating device present.

In a modification of the second embodiment, when determining the extrapolated temperature values, additional process parameters are additionally used. For example, there may be temperature changes due to changes in a protective gas flow that sweeps over the construction field. Attacks the controller 100 In such a case, for ascertaining the extrapolated temperature values, also for information about changes in the protective gas flow, it is possible to react immediately to changes in the process parameters or environmental parameters without the existence of exact measured values of a temperature measuring device during solidification in the measuring range of the temperature measuring device. In such a case, for example, the temperature values output to the controller in response to changed inert gas parameters during the exposure period in the measuring range 17a (ie between t ₁ and t ₂ ) are adjusted.

Although the present invention has been described with reference to a laser sintering or laser melting apparatus, it is not limited to laser sintering or laser melting. It can be applied to any methods of manufacturing a three-dimensional object by layering and selectively solidifying a powdery building material.

The laser may include, for example, a gas or solid state laser or any other type of laser. In general, any means by which energy can be applied selectively to a layer of building material can be used. Instead of a laser, for example, a plurality of lasers, another light source, an electron beam or any other source of energy or radiation suitable for solidifying the building material may be used. The invention can also be applied to selective mask sintering using an extended light source and a mask, or to absorption sintering.

As powdered building material, all powders or powder mixtures can be used, which are softened by a heat energy input, melted or melted, and have joined after refolding to a solid. Such powders include, for. As plastic powder such as polyamide or polystyrene, PAEK (polyaryl ether ketones), elastomers such as PEBA (polyether block amides), plastic-coated sand, ceramic powder or metal powder, eg. As stainless steel powder or other, adapted to the particular purpose metal powder, in particular alloys.

Depending on the building material used, a suitable gas is a gas which essentially does not undergo any chemical reaction with the building material, for example preferably nitrogen in the case of plastic powder or preferably argon and / or nitrogen in the case of metal powder.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0764079 B1 [0002, 0003, 0004]

Claims (15)

Process for the layered construction of at least one three-dimensional object ( 2 ) from a building material ( 13 ) by successively solidifying layers of the building material ( 13 ) at respective locations of a layer corresponding to the cross-section of the at least one object, the solidification being accomplished by introducing thermal energy, the method comprising the steps of: a material applying step of providing a layer of building material ( 13 ) on a construction document ( 8th . 9 ) or a previously provided layer of the building material, a solidification step of solidifying the applied layer by means of electromagnetic radiation or particle radiation, wherein the radiation acts on sites of the layer to be solidified, so that the building material is solidified at these locations by the thermal energy introduced by the radiation wherein the material applying step and the solidifying step are repeated until all cross sections of the at least one three-dimensional object to be produced are solidified, wherein at least a portion of an applied layer of the building material is heated by means of a heating device. 16 ), wherein the temperature of an applied layer of the building material with a temperature measuring device ( 17 ) in a measuring range ( 17a ), which comprises a portion of the layer, is measured and, depending on the determined temperature, the heating power of the heating device ( 16 ) is determined, wherein in at least one solidification step, it is determined whether there are sites of the layer to be consolidated in the measuring range ( 17a ), and if so, ensuring that the radiation is not supplied to these sites until a predetermined delay time has elapsed after the start of the solidification step. A method according to claim 1, wherein a warning is issued to a user when the time necessary to perform the solidification step in a layer increases by the addition of the predetermined delay time by an amount exceeding a predefined maximum amount. The method of claim 1 or 2, wherein a maximum delay time is determined and a warning is issued to a user when the predetermined delay time has a greater amount than the maximum delay time. Method according to one of the preceding claims, in which a sequence of the solidification step is adapted such that the radiation reaches the points in the measuring range ( 17a ) is supplied essentially only at the end of the solidification step. Method according to one of the preceding claims, in which, after the delay time has elapsed, the heating power of the heating device ( 16 ) is regulated up to the end of the solidification step as a function of an extrapolated chronological progression of the heating power of the heating device and / or of extrapolated temperature values, the extrapolated temperature values being determined by the temperature measuring device ( 17 ) during the delay time measured temperature values are determined. Method according to Claim 5, in which the extrapolated temperature values are the continuation of the time profile of the temperature measurement device ( 17 ) represent measured temperature values during the delay time. The method of claim 5 or 6, wherein in the determination of the extrapolated temperature values additionally the temporal change of environmental parameters during the solidification step, is taken into account. A method according to claim 7, wherein, in determining the extrapolated temperature values, a change in a parameter of a protective gas flow conducted over the applied layer is taken into account. A method according to any one of the preceding claims, wherein substantially no supply of radiation to the applied layer is performed during a portion of the delay time. Method according to one of the preceding claims, in which the position of the measuring range ( 17 ) during a solidification step, in particular during the entire production process of the at least one object ( 3 ), not changed. Control device ( 100 ) for a generative layer building apparatus ( 1 ) for the layered construction of at least one three-dimensional object ( 2 ) from a building material ( 13 by successively solidifying layers of the building material in each case at those points of a layer which correspond to the cross-section of the at least one object ( 2 ), wherein the solidification is accomplished by introducing thermal energy and the generative layer building apparatus ( 1 ) at least comprises: a material application device ( 14 ) for providing a layer of a building material ( 13 ) in a material application step on a construction document ( 8th . 9 ) or a previously provided layer of the building material, a solidification device ( 20 In operation, performing a solidification step of solidifying the coated layer by means of electromagnetic radiation or particle radiation, wherein the radiation acts on solidified sites of the layer, so that the building material is solidified at these locations by the heat energy introduced by the radiation, wherein the Generative layer construction device ( 1 ) is configured to repeat the material application step and the solidification step until all cross sections of the at least one three-dimensional object ( 2 ) and wherein the generative layer building device comprises a heating device ( 16 ), which is formed at least a portion of an applied layer of the building material ( 13 ), and wherein the generative layer building apparatus ( 1 ) a temperature measuring device ( 17 ), which in use, the temperature of a coated layer of the building material ( 13 ) in a measuring range ( 17a ), which comprises a subregion of the layer, wherein the control device ( 100 ) is designed so that it depends on the determined temperature, the heating power of the heating device ( 16 ) and determines, in at least one solidification step, whether there are sites of the layer to be solidified that are in the measuring range ( 17a ), and if so, does not supply the radiation to these sites until a predetermined delay time has elapsed after the start of the solidification step. Generative layer construction device ( 1 ) with the features of the generative layer building apparatus of claim 11, further comprising a control device ( 100 ) according to claim 11. Generative layer construction device ( 1 ) according to claim 12, wherein the temperature measuring device ( 16 ) comprises a pyrometer. Generative layer construction device ( 1 ) according to claim 12 or 13, which is designed to carry out a method according to one of claims 1 to 10. A computer program comprising a sequence of instructions by which a method according to any one of claims 1 to 10 is performed when the computer program is stored in a control device ( 100 ) according to claim 11 or a generative one. Layer construction device ( 1 ) is carried out according to one of claims 12 to 14.

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