WO2022100773A2 - Method for applying particulate building material in a 3d printer - Google Patents

Abstract

The invention, which concerns a method for applying particulate building material (3) in a 3D printer, addresses the problem of providing a solution that permits a more uniform application of the particulate building material (3). This problem is solved by optically monitoring the discharged particulate building material (3) by means of an image-recording device (7) in a working step of smoothing the particulate building material (3) in a region of an accumulation (5) of the particulate building material (3); generating an image of the accumulation (5) and determining at least one dimension of the accumulation (5) from the generated image; comparing the image of the accumulation (5) and/or the at least one determined dimension with an associated reference image and/or a predetermined reference value; and changing at least one application parameter for applying the particulate building material (3) if the image of the accumulation (5) deviates from the reference image and/or if the determined dimension deviates from the associated reference value.

Description

Process for applying particulate building material in a 3D printer

The invention relates to a method for applying particulate building material in a 3D printer, in which particulate building material is discharged onto a building site and smoothed out.

In particular, the uniform smoothing of the particulate building material on a construction site in a 3D printer is to be monitored and irregularities in the smoothing of the particulate building material discharged from an applicator are to be detected. In the event that such irregularities are detected, they are automatically reduced or eliminated using appropriate measures. For this purpose, corresponding parameters for the discharge of the particulate building material are influenced.

It is known to use so-called 3D printing or a so-called 3D printing process to produce individual or serial components, workpieces or molds. In such printing processes, three-dimensional components or workpieces are produced in layers.

The structure is computer-controlled from one or more liquid or solid materials according to specified dimensions and shapes. Specifications for the components or workpieces to be printed can be provided, for example, by so-called computer-aided design systems (CAD).

When printing the 3D structures or 3D components, physical or chemical hardening processes or a melting process take place in a particulate building material, which is also referred to as molding material. Building materials or molding materials such as plastics, synthetic resins, ceramics and metals are used as materials for such 3D printing processes.

Various manufacturing process sequences are known for the implementation of 3D printing processes. However, several of these procedural sequences include the procedural steps shown below by way of example:

• Partial or full-surface application of particulate building material, also referred to as particulate material or powdered building material, on a so-called construction field in order to form a layer of non-solidified particulate material, with the partial or full-surface application of particulate building material removing and smoothing the particulate building material includes;

• Selective solidification of the applied layer of non-solidified particulate building material in predetermined partial areas, for example by selective compacting, printing or application of treatment agent, such as a binder or use of a laser;

• Repetition of the previous process steps in a further layer level to build up the component or workpiece layer by layer. For this purpose, the component or workpiece, which is built up or printed on in layers on the construction area, is lowered with the construction area by one layer level or layer thickness or the 3D printing device is raised by one layer level or layer thickness compared to the construction area before a new one layer is applied over part or all of the surface;

• Subsequent removal of loose, unconsolidated particulate build material surrounding the manufactured component or workpiece.

Various methods for generating a 3D structure or for applying particulate construction material to a construction site to generate a 3D structure are known from the prior art.

A method and a device for applying fluids and their use are known from DE 10117875 C1.

The method for applying fluids relates in particular to particulate material which is applied to an area to be coated, the fluid being applied in front of a blade, as viewed in the direction of advancement of the blade is applied to the area to be coated and then the blade is moved over the applied fluid.

The object is to provide a device, a method and a use of the device with which a distribution of fluid material that is as even as possible can be achieved on an area to be coated.

The solution is that the blade oscillates in the manner of a rotary movement. The fluid applied to the area to be coated is fluidized by the oscillating rotary movement of the blade. As a result, not only can particle material with a strong tendency to agglomerate be applied as evenly and smoothly as possible, but it is also possible to influence the compression of the fluid by the vibration.

In a preferred embodiment, it is provided that the application of the fluid to the area to be coated takes place in excess, so by the constant movement of the blade, which oscillates in the manner of a rotary movement, the excess fluid, seen in the direction of forward movement of the blade, in front of the Blade homogenized in a fluid/particulate roller formed by the advancement of the blade. This allows any cavities between individual clumps of particles to be filled and larger clumps of particulate material are broken up by the roller movement.

A disadvantage of this known prior art is that when the particulate building material is discharged onto a building site, the quantity of the particulate building material required to form a layer is insufficiently regulated. This leads to different amounts of the particulate building material in front of a means for smoothing the particulate building material and thus, for example, to different pressure conditions on the layers located below the layer currently to be applied. This leads to disturbances in the uniform structure of the layers and to a deterioration in the quality of the 3D structure to be produced.

DE 10 2015 015 353 A1 describes a method and a device for producing three-dimensional components using an excess quantity sensor. know. The task to be solved is to provide a method and a device that uses the knowledge of the presence of an overfeed, i.e. an excess amount of powder that is pushed along in front of the coater at the end of the construction area during a coating run, in order to ensure a safe process flow to document or regulate.

A system and a corresponding method for the additive manufacturing of a three-dimensional (3D) object are known from US 2019/0 193 150 A1. A system for additively manufacturing a three-dimensional (3D) object includes a metering device configured to meter powder material to generate a metered volume of powder material deposited on a top surface of a powder bed, a volume adjustment device configured to adjust the measured volume to create an adjusted measured volume with a controlled height, a distribution device configured to distribute the adjusted measured volume with the controlled height to create a smooth layer of powder material over the top surface of the powder bed form, a printing device configured to apply a fluid to at least a portion of the slick layer, wherein the fluid causes the slick layer to bond in the at least one portion; and a controller configured to drive the metering device, the volume adjustment device, the dispensing device, and the printing device to create successive smooth layers with the applied fluid to create the 3D object.

A system, a method and a device for supplying powder to a powder bed during an additive manufacturing process are known from US 2019/0 060 998 A1. A recoating apparatus includes a powder hopper and a powder distribution system for delivering powder from the powder hopper to the powder bed. The recoating apparatus further comprises at least two grinding strips, with at least one outlet of the powder distribution system being arranged between the two grinding strips to shield the outlet of the powder distribution system. Some of these solutions from the prior art are not suitable for ensuring continuous monitoring, require special versions of a means for applying particulate building material, or only achieve an insufficient quality of the applied layer of particulate building material.

Thus, there is a need for an improvement in the known art and thus for an improved method for depositing particulate build material in a 3D printer.

The object of the invention is to provide a method for applying particulate building material in a 3D printer, with which the particulate building material is applied more evenly, the application of the particulate building material being both the discharge of the particulate building material onto the surface of a building site and the smoothing of the discharged particulate building material on the construction site.

The method is intended to improve both uniformity in height of the applied layer of particulate build material and uniformity in density within the layer of applied particulate build material. In this way, a better quality of the applied layer of particulate building material is generally achieved.

The object is achieved by a method with the features according to patent claim 1 of the independent patent claims. Further developments are specified in the dependent patent claims.

The use of an optical control system when applying a layer of the particulate building material in a 3D printer according to the present method is provided.

For this purpose, it is provided that the discharged particulate building material is optically monitored by means of an image recording device in a work step of smoothing the particulate building material in an area where the particulate building material has accumulated. This optical Monitoring preferably takes place in an area in front of a means for smoothing the particulate building material.

Such a means for smoothing the particulate building material can be, for example, a scraper blade, an oscillating blade, a knife, a squeegee or comparable means of a 3D printer, by means of which the discharged particulate building material is smoothed.

These means, or means comparable to these means, have the task of arranging the particulate building material carried out or poured onto the construction site in a uniform thickness or thickness of the layer currently to be applied.

For this purpose, the means described above move at a constant distance from the construction site and horizontally across the construction site. During this horizontal movement across the construction site, an accumulation of the excessively discharged particulate construction material occurs in a so-called accumulation in front of the respective means. This accumulation occurs, viewed in the direction of movement of the means above the construction area, in front of the corresponding means.

After the means has completed its horizontal movement over the construction site, the particulate building material is applied in an even layer, which has a predetermined height or layer thickness at all points.

Such a height or layer thickness of the particulate building material can have a value which is between 0.5 times and 6 times the mean particle diameter of the particulate building material. In order to achieve a height or layer thickness of 0.5 times the average particle diameter of the particulate building material, the particulate building material must be discharged onto the construction site and compacted.

The mean particle diameter of the particulate building material is, for example, at a value of about 0.14 mm. Particulate building material is generally understood to be a collection of individual particles of a substance or a mixture of substances, each particle having a three-dimensional extension having. Since these particles can predominantly be understood as round, oval or elongated particles, it is possible to specify an average diameter for such a particle, which is usually in the range between 0.1 mm and 0.4 mm. Such a particulate building material has fluid properties.

The accumulation of the excessively discharged particulate building material occurring in front of the respective means for smoothing can vary, for example, in its height and quantity. With the change in the amount of particulate building material in the accumulation, for example, the pressure on underlying layers also changes, which may also contain particulate building material or which already have selectively compacted areas for forming the 3D structure. This changing pressure on the underlying layer or layers can result in one or more underlying layers being affected.

With such an influence, the density of the particulate building material of the underlying layers can change, which can lead to a sinking of the particulate building material, at least in places. Such a local sinking or different heights in the currently applied layer of particulate building material leads to deviations or inaccuracies in the generation of the 3D structure, which negatively affect the quality of the 3D structure to be generated and should be prevented.

It is provided that the discharged particulate building material is optically monitored in a work step of smoothing the particulate building material in such a way that the accumulation of the particulate building material is recorded from at least one direction or perspective, for example by means of one or more cameras.

In general, it can be said that an image of the accumulation is generated by an image recording device or a suitable means for optically monitoring the discharged particulate building material in a work step of smoothing the particulate building material, with a such a means is, for example, at least one camera, a laser, a combination of projector and/or laser and/or camera or a comparable image recording device.

In an alternative, it is provided that an image of a sub-area of the accumulation is generated. In one alternative, for the optical monitoring of the discharged particulate building material according to the method, it is sufficient to generate an image of only a part or a partial area of the accumulation and to process it according to the method.

Such an image of the cluster can show, for example, a side view or a front view of the cluster. Alternatively, a perspective view or perspective view of the accumulation can also be generated as an image.

A 3D recording device consisting of a number of cameras or 3D cameras, for example using strip light projection, can also be used.

The resolution and recording rate of the image recording device used or the camera used must be correspondingly high in order to generate a sufficiently precise image of the accumulation at any speed at which, for example, a smoothing device moves over the construction area. Sufficiently precise is understood to mean an image of the cluster that can be further processed according to the present method, ie is suitable, for example, for an image comparison or a determination of dimensions of the cluster, such as a height and/or a width of the cluster.

Depending on the mounting position, the camera can be equipped with a wide-angle lens or provide a suitable perspective in order to record or image the entire area of the accumulation in front of the smoothing agent.

It is also planned to use suitable software with the help of which the recordings or images can be normalized or post-processing with regard to contrast or filtering is made possible. In any case, the aim is to ensure that the images of the accumulation are of sufficient quality for the subsequent process steps.

It is also provided that geometric dimensions of the accumulation of the particulate building material are determined, for example on the basis of the images of the accumulation generated during the optical monitoring, such as individual images or a video from one or more views of the accumulation.

Here, for example, basic dimensions of the accumulation or information about the outer contour of the accumulation can be determined.

The basic dimensions of the cluster include dimensions such as a length, a width or a height of the cluster, in particular in a side view of the cluster.

With regard to the outer contour of the accumulation, radii or angles of the accumulation can be determined, which, for example, describe the rising outer contours of the accumulation.

In addition to such dimensions, which describe the side view, dimensions along the accumulation, ie in its longitudinal extent, can be recorded. Here, for example, heights of the accumulation can be determined at different points along the length of the accumulation. For example, this can be a current height at a specific location. In addition, a maximum and/or minimum height of the accumulation can be determined. In addition, an average height can also be determined.

Since the particles of the particulate building material in the accumulation are constantly moving during the movement of the above-described smoothing means over the building area, there are dynamic changes in the height of the accumulation. In addition, the height of the accumulation is different in its longitudinal extension and changes dynamically. It is intended to subdivide the longitudinal extension of the accumulation into partial areas or sections and to determine a maximum and/or a minimum height and/or an average height of the accumulation within these partial areas. In this case, all sub-areas in their sum or their juxtaposition form the entire length of the accumulation in its longitudinal extent.

Provision is also made for a specific dimension to be compared with a predetermined value or reference value for this dimension. If this comparison reveals a deviation between the determined dimension and the specified value or reference value for this dimension, which is above a specified tolerance limit, then at least one parameter for the application of the particulate building material (substrate application parameter), which is referred to below as the application parameter, changes.

As an alternative to a comparison of a specific dimension with a predetermined value or reference value for this dimension, or in addition to this comparison, it is possible to compare the generated image of the cluster with an associated reference image. If such a comparison, such as an image comparison, reveals deviations that are above a predetermined tolerance limit, then at least one parameter for the application of the particulate building material, ie an application parameter, is changed. The aim is for the currently generated images to be brought into agreement with the reference images.

If, for example, a comparison of a specific dimension with its reference value shows that the height of the accumulation falls below the specified reference value for the height of the accumulation, an application parameter that determines the amount of particulate building material to be discharged per unit of time or per area is increased . A larger quantity of the particulate building material is thus poured out or discharged from an applicator. As a result, it can be expected that the height of the build-up before the straightener will increase again, since the height in a directly related to the amount of particulate building material discharged in excess.

When a so-called fluidizer is used to discharge the particulate building material, the application parameters of the quantity of particulate building material to be discharged per unit of time or per area are influenced by controlling a different number of so-called porous gas outlet means in the fluidizer by means of a pressurized gas or be acted upon. Another way to influence these application parameters is to change the pressure of the gas. Another alternative is to change the gas pressure periodically over time, which can be done, for example, with an adjustable frequency.

Provision is also made for several order parameters to be influenced at the same time as a result of the result of one or more deviations determined between one or more dimensions and their correspondingly specified values.

For example, it is possible to change both the application parameter and the speed of movement of the working means of the 3D printer over the surface of the construction field and at the same time to increase the quantity of particulate construction material discharged from an application.

These tools of the 3D printer include in particular an applicator for the particulate building material as well as the means for smoothing the discharged building material such as a scraper blade, an oscillating blade, a knife or a squeegee.

By dividing the optical monitoring of the accumulation into sub-areas, it is possible to change the application parameters for each sub-area according to the deviations of the determined dimensions from the specified values in this sub-area. This presupposes that the means for discharging and/or the means for smoothing the particulate building material are subdivided accordingly or arranged in multiples accordingly. Such a multiple These means can be arranged in such a way that the means are arranged in a row next to one another or in at least two rows and offset from one another. It is clear to a person skilled in the art that with such an arrangement of the means it must always be possible to apply the particulate building material evenly in one layer and in all required areas on the building site.

It is also planned to analyze the accumulation in its longitudinal extent with regard to its dynamic behavior. The particulate build material is in flow during the step of smoothing the particulate build material prior to the means for smoothing the particulate build material. The basic dimensions of the accumulation and/or the outer contour of the accumulation change constantly. These dynamic changes are recorded, for example, over time, for example by means of a video recording or a sequence of images or an image stream. An evaluation of these dimensions that change over time, such as a height of the accumulation, provides information about the range of the height change, ie a minimum and a maximum of the dimension of the height. In addition, such a change in altitude can be analyzed over time. In this way it can be determined, for example, that the change in height occurs periodically, for example between its minimum and its maximum. From this change over time, a mean frequency can be determined, for example, with which the process of changing the altitude is repeated. By means of reference frequencies determined in test series, statements can be made about the influence on the quality of the applied layer of particulate building material as a function of the frequency of the height change by means of a frequency comparison between the frequency of the height change and the determined reference frequencies.

For example, values about such changes in height determined in test runs and the associated reference frequencies can be related to the quality to be achieved of the layer of particulate building material to be produced. It is thus possible, given certain changes in height or frequencies of such changes in height, to influence application parameters in such a way that the change in height becomes smaller or the frequency of the changes in height changed so as to improve the quality of the current layer of particulate build material to be applied.

For example, an angle or setting angle of the means for smoothing or the blade can be mentioned as a changeable application parameter. Furthermore, it is possible to change the quantity or discharge quantity of the particulate building material per unit of time and/or per area. In addition, such a change in the discharge quantity per unit of time and/or per area can be changed over time, with this change being able to take place at a specific or variable frequency. It is provided, for example, to counteract the temporal change in height of the accumulation by means of a temporal change in the discharge quantity of the particulate building material and to at least reduce or eliminate the temporal change in height.

The particle movement of the particulate building material or the kinematics can thus be changed in a targeted manner in order to prevent quality disruptions when the particulate building material is applied. This influencing of the particle movement of the particulate building material can take place differently both for the entire accumulation and for its sub-areas if the optical monitoring is already carried out separately in these sub-areas.

Furthermore, the dynamics of the accumulation can be further analyzed when using correspondingly fast sensors for optical monitoring of the discharged particulate building material or for image acquisition.

The accumulation of particulate matter can behave like a water wave. As with a water wave, there can be an increase in the height of the accumulation. Such a mountain of water can become unstable, and this process of overcoming the surface tension at the crest of the wave leads to the so-called breaking of the wave. This process of breaking the wave is transferable to the accumulation. If the wave of the accumulation breaks in this way, particulate material is thrown out of the accumulation or the wave crest. Since there- If the quality of the applied layer of particulate building material or an underlying layer deteriorates, it is important to recognize this breaking process in good time and to prevent it. To prevent this, application parameters such as the angle of attack of the smoothing agent or the amount of particulate building material discharged per unit of time can be changed or reduced.

Furthermore, it is also possible to detect the formation of a plurality of accumulations during a work step of smoothing the particulate building material. In this case, too, the quality of the applied layer of the particulate building material or an underlying layer is influenced. In this case too, application parameters such as the angle of attack of the smoothing agent or the quantity of particulate building material discharged per unit of time are changed in order to ensure high-quality application of the layer of particulate building material.

The foregoing features and advantages of this invention will be better understood and appreciated after a careful study of the following detailed description of preferred non-limiting example embodiments of the invention herein, with the accompanying drawings, which show:

1: a virtual representation of a side view of an accumulation of the particulate building material on a building site in a 3D printer,

2: a virtual representation of a perspective view of an accumulation of the particulate building material on a building site in a 3D printer,

Fig. 3: an arrangement for discharging the particulate building material and a means for smoothing the particulate building material over a construction field and

Fig. 4: an exemplary arrangement for discharging the particulate

building material in a 3D printer. 1 shows a virtual representation of a side view of an accumulation 5 of the particulate building material 3 on a building site 1 in a 3D printer.

A means for smoothing 2 the discharged particulate building material 3 is shown above a construction field 1 of a 3D printer, which is only partially shown. A discharge of the particulate building material 3 is not shown in FIG. 1 .

This means 2 for smoothing the discharged particulate building material 3 is shown as a blade, for example, and is moved across the building field 1 in the direction of movement shown by the arrow 4 .

An accumulation 5 of the particulate building material 3 forms in front of the means 2 for smoothing the discharged particulate building material 3 . This area of the accumulation 5 is shown in FIG. 1 surrounded by a dash-dash line.

If the means 2 for smoothing the discharged particulate building material 3 is moved over the building field 1, a layer of the particulate building material 3 with a layer thickness 6 is applied.

A means 7 for optically monitoring the accumulation 5 or an image recording device 7 is shown in FIG. 1 as an example. Such a means 7 for optically monitoring the accumulation 5 can be, for example, a camera 7 which is arranged and aligned with its recording area 8 in such a way that this camera 7 generates a side view of the accumulation 5 . Such a side view of the cluster 5 is shown in FIG.

In an alternative, an image recording device 7 or the means 7 can be arranged and aligned in such a way that it generates a front view of the accumulation 5 . Such a frontal view of the cluster 5 can be generated with the position and orientation of the means 7 shown in FIG.

In a further alternative, the means 7 can be arranged and oriented in such a way that it creates a perspective view along the cluster 5 partially or completely. Both when generating the front view of the cluster 5 and when generating the perspective view along the cluster 5, a plurality of means 7 can be arranged, the partial images of which are combined to form an overall representation. The sub-images can be combined in this way, for example, using suitable software from the prior art.

One or more recordings of the image recording device 7 such as images or videos are analyzed using suitable image analysis software in such a way that the dimensions of the accumulation 5 are determined. These dimensions of the accumulation 5 include, for example, the width 9, a length 10 and a height 11. The length 10 of the accumulation, which is not shown in FIG. 1, extends, so to speak, into the depth of the illustration in FIG.

These dimensions of the accumulation 5 also include an angle 12 and a radius 13. The angle 12 is, for example, the angle that results between the surface of the building field 1 and the inclination of the means 2 for smoothing the particulate building material 3, as shown in Fig 1 shown. This angle 12 also corresponds to a so-called angle of attack of the means 4.

The radius 13 forms, for example, on the front side of the accumulation 5, viewed in the direction of movement 4 shown in Fig. 1.

According to the present method for applying particulate building material 3 in a 3D printer, it is provided that at least one dimension 9,10,11, 12,13 of the accumulation 5 is determined. Provision is also made for this specific dimension 9, 10, 11, 12, 13 of the accumulation 5 to be compared with a predetermined value or a reference value. Such predetermined values for the dimensions 9,10,11, 12,13 can be empirical values. These specified values can also be determined experimentally in test series and correspondingly stored for the present method. In any case, a dependency of the quality to be achieved when applying a layer of the particulate building material 3 as a function of these dimensions 9,10,11,12,13 is known. It is also provided that at least one of these specific dimensions 9, 10, 11, 12, 13 is compared with its associated specified value or its reference value and that if the dimension deviates from the specified value or its reference value, at least one application parameter for the application of the particulate building material 3 is changed.

For example, in the event that the height 11 exceeds a maximum permissible value, the quality of the layer to be applied can be reduced by the increasing pressure on the underlying layers caused by the accumulation 5 . An impermissibly high pressure leads, for example, to sagging of individual areas in one or more layers of the applied particulate building material 3. Alternatively, the impermissibly high pressure can affect the density of partial areas of one or more underlying layers. In addition to influencing the particulate building material 3, areas that are already solidified and are intended to form the 3D structure can also be affected. Such an influence leads to deviations in the dimensional accuracy of the 3D structure to be produced, for example due to a compression or displacement of such an already solidified area.

In order to avoid such influences on the 3D structure to be generated and to ensure consistent quality when the particulate building material 3 is applied, the present method changes at least one application parameter in such a way that the dimension returns to the specified value.

In this case, two or more specific dimensions can also be compared with their associated predefined stored values or reference values. In addition, when at least one deviation of at least one specific dimension from its associated value is determined, two or more application parameters can also be changed in such a way that the deviation is reduced or eliminated. 2 shows a virtual representation of a perspective view of an accumulation 5 of the particulate building material 3 on a building site 1 in a 3D printer.

For better clarification, FIG. 2 shows the accumulation 5 consisting of particulate building material 3 over the building site 1 in a perspective view. The accumulation 5 is shown in front of the means 2 for smoothing, viewed in the direction of movement 4 of the means 2 shown by means of an arrow.

Such a perspective representation can be generated, for example, by means of a means 7 (not shown in FIG. 2) or an image recording device 7 for optical monitoring, such as a camera 7, for example.

The dimensions of the accumulation 5 such as a width 9 and/or a length 10 and/or a height 11 are determined from such an image of the accumulation 5 generated by the camera 7 . Furthermore, an angle 12 and a radius 13 can also be determined.

3 shows an arrangement 14 for discharging the particulate building material 3 and a means 2 for smoothing the particulate building material 3 over a building site 1 .

Such an arrangement 14 for discharging the particulate building material 3 can, for example, be what is known as a discharger, which is sometimes also referred to as an applicator, while the means 2 shown for smoothing the particulate building material 3 is, for example, a blade.

The discharger 14 has a storage container in which the particulate building material 3 to be discharged is stored. An outlet 15 for discharging the particulate building material 3 can be arranged at the lower end of the discharger 14 . In order to prevent particulate building material 3 from escaping from the discharger 14 in an uncontrolled manner, the discharger 14 has a corresponding closure means, which is not shown in FIG. 3 . This closure means is designed in such a way that it can open and close an opening in the lower area of the discharger 14 . In the event that particulate building material 3 is to be discharged from the discharger 14 and discharged onto the construction site 1, the closure means is opened. The particulate building material 3 is discharged and reaches the surface of the construction field 1 in the form of discharge 16. This priority of the discharge of particulate building material 3 is shown in FIG. The amount of particulate building material 3 to be discharged is influenced and controlled by changing an application parameter. In this case, an application parameter can change the amount of particulate building material 3 to be discharged per unit of time, while another application parameter changes the amount of particulate building material to be discharged per area.

If, for example, the quantity of particulate building material 3 to be discharged per unit of time and the speed of movement of the delivery device 14 in the direction of movement 4 over the construction area 1 are controlled accordingly, the particulate construction material 3 is discharged onto the surface of the construction area 1 very evenly and therefore with high quality .

As can be seen in FIG. 3, more particulate building material 3 is discharged than would be necessary to achieve layer thickness 6 . Since the means 2 for smoothing is also moved in the direction of movement 4 over the construction field 1, the accumulation 5 is caused by the excessive discharge of particulate construction material 3. As already described, an image recording device 7 such as a camera 7, which with its recording area 8 is aligned with the cluster 5, the cluster 5 is optically monitored and corresponding images of the cluster 5 are created by taking pictures or video recordings.

By means of these images or video recordings, for example, the dimensions of the height 11 and the dimensions of the width 9 are determined using suitable image processing software. Both of these determined dimensions are related to the amount of particulate building material 3 in cluster 5. It is generally accepted that an increase in the values for height 11 and width 9 corresponds to an increase in the amount of particulate building material 3 in cluster 5 point out If a comparison of the currently determined dimensions of the accumulation 5, ie the values for the height 11 and the width 9, determines that these deviate from the associated predetermined values or reference values, then the application parameters are changed. These application parameters are, for example, the amount of particulate building material 3 to be discharged per unit of time and the speed of the working means of the 3D printer in the direction of movement 4. The working means here are the discharger 14 and the means 2 for smoothing, i.e. a blade, for example.

In the event that one or more values for the height 11 or the width 9 or both are greater than the associated specified values, the speed in the direction of movement 4 can be increased, for example, until the dimensions again correspond to the specified values, with usually a tolerance range is defined.

Alternatively, in the event that one or more values for the height 11 or the width 9 or both become greater than the associated predetermined values, the size of the gap 18 can be reduced so that less particulate building material 3 is discharged.

The blade 2 is arranged in FIG. 3 at an angle or setting angle which corresponds to the angle 12 . Another application parameter that can be influenced according to the method is the angle or setting angle of the blade 2. In an alternative, the shape of the blade 2 can also be changed, which is not shown in FIG. In this case, the means 2 for smoothing would have several different blades 2, which can be moved automatically.

The process-related changes in the described application parameters for applying the particulate building material 3 can also take place differently in some areas. Of course, this presupposes that, for example, several arrangements 14 for discharging the particulate building material 3 are arranged in the 3D printer and/or that several means 2 for smoothing are arranged in the 3D printer. 4 shows an arrangement 14 for discharging the particulate building material 3 in a 3D printer, which can be moved horizontally over the building field 1 in the direction shown by the arrow 4 . The arrangement 14, which is also referred to as a so-called fluidizer, is shown in a snapshot, in which particulate building material 3 exits through the outlet 15 and reaches the surface of the building site 1 as discharge 16, in order to create a new layer of the particulate building material 3 there with a Form layer thickness 6. The means 2 required for this is not shown in FIG.

The arrangement 14, which is referred to below for short as the discharger 14, has a funnel-shaped storage container 17 for storing the particulate building material 3. This funnel-shaped reservoir 17 is designed to be longitudinal, with its length being a multiple of its width.

The reservoir 17 has an opening or an outlet 15 . In the lower area of the funnel-shaped reservoir 17, two blocking means 18 are arranged, through which the outlet 15 is formed. In the representation of FIG. 4, a ventilation gap 19 is formed by the left blocking means 18 on its upper side.

Such an arrangement of the blocking means 18 prevents particulate building material 3 from getting onto the building site 1 unintentionally, since a blocking cone from the particulate building material 3 closing the path is formed at the outlet 15 .

Application of the particulate building material 3 to the building site 1 is achieved in that the particulate building material 3 is fluidized in the area of the outlet 15 . For this purpose, at least one porous gas outlet means 20 is provided in this area. Two porous gas outlet means 20 are arranged on the side walls of the storage container 17 in FIG. 4 . These two porous gas outlet means 20 each have a gas connection 21 which is connected to an external unit, not shown, which generates a gas whose gas pressure can be controlled. Each porous gas outlet means 20 has a gas-permeable porous material on its side facing the particulate building material 3 .

The gas whose gas pressure can be controlled by the external unit exits the porous gas outlet means 20 through the gas-permeable porous material in the direction of the particulate building material 3 in a uniformly distributed manner and flows through the particulate building material 3. This outflowing gas is shown in FIG. 4 by means of several small arrows shown at the porous gas exit means 20. The particulate building material 3 is fluidized by this escaping gas, as a result of which the particulate building material 2 is discharged via the outlet 15 , forming the discharge 16 , and reaches the construction site 1 .

Only one porous gas outlet means 20 is required to fluidize the particulate building material 3 . However, if the gas flows into the particulate building material 3 from two sides via two porous gas outlet means 20, the effect of fluidizing the particulate building material 3 is improved and a larger amount of the particulate building material 3 is discharged.

In order to control the amount of particulate building material 3 to be discharged, the pressure of the gas fed into the porous gas discharge means 20 is varied. For example, the fluidization of the particulate building material 3 can be increased or improved by means of a higher gas pressure, as a result of which more fluidized particulate building material 3 can exit through the outlet 15 and the size of the accumulation 5 (not shown) increases.

Alternatively, the fluidization of the particulate building material 3 can be reduced or worsened by means of a lower gas pressure, as a result of which less particulate building material 3 is discharged.

A dimension of the accumulation 5 can thus be controlled by controlling the gas pressure or the number of porous gas outlet means 20 used by the present method. Thus, the application parameter according to the method can be the amount of particulate building material 3 to be discharged per unit of time or the application parameter according to the method can be the amount of the particulate building material 3 to be discharged per area can be controlled or regulated by the number of porous gas outlet means 20 used. Another possibility for controlling or regulating these application parameters is the gas pressure used for the porous gas outlet means 20 . In a special variant, the gas pressure can for example be generated in a pulsating manner, as a result of which an improvement in the fluidization is possible and the quantity of the particulate building material 3 released can also be changed over time.

List of References

1 construction field

2 smoothing tools / blade

3 particulate building material

4 arrow / direction of movement

5 accumulation

6 layer thickness

7 Means of optical surveillance / image recording device / camera

8 recording area

9 width

10 length

11 height

12 angles / angle of attack

13 radius

14 arrangement for discharging the particulate building material / discharger / fluidizer

15 Particulate build material outlet

16 discharged particulate building material / discharge

17 reservoirs

18 blocking means

19 ventilation gap

20 porous gas vent means

21 gas connection

Claims

25 patent claims 1. A method for applying particulate building material (3) in a 3D printer, in which particulate building material (3) is discharged onto a construction area (1) and smoothed, characterized in that optical monitoring of the discharged particulate building material (3) is carried out by means an image recording device (7) in a work step of smoothing the particulate building material (3) in an area of an accumulation (5) of the particulate building material (3) that produces an image of the accumulation (5) and at least one dimension of the accumulation (5) it is determined from the image that the image of the cluster (5) and/or the at least one specific dimension is compared with an associated reference image and/or a predetermined reference value and that if the image of the cluster (5) deviates from the reference image and /or the specific dimension of the associated reference value for at least one order parameter the application of the particulate building material (3) is changed. 2. The method according to claim 1, characterized in that the accumulation (5) of the particulate building material (3) in front of a means (2) for smoothing the from a storage container (15) an arrangement (14) for discharging the particulate building material (3) particle-shaped building material (3) discharged onto the construction field (1), viewed in a direction of movement (4) of this means (2). 3. The method according to claim 1 or 2, characterized in that the optical monitoring of the accumulation (5) takes place from at least one direction onto the accumulation (5), with an image of the accumulation (5) or a partial area of the accumulation (5) in a side view and/or a front view and/or a perspective view is generated. 4. The method according to any one of claims 1 to 3, characterized in that dimensions of the cluster (5) are a width (9), a length (10), a height (11), an angle (12) or a radius (13). . Method according to one of Claims 1 to 4, characterized in that the application parameters for applying the particulate building material (3) are a quantity of the particulate building material (3) to be discharged per unit of time, a quantity of the particulate building material to be discharged per area, a movement speed of working means of the 3D - The printer over a surface of the construction field (1), an angle of attack of the means (2) for smoothing or a change in the quantity of the particulate construction material (3) to be discharged over a period of time. Method according to one of Claims 1 to 5, characterized in that the change in the quantity of particulate building material (3) to be discharged takes place over time at a fixed frequency. Method according to one of Claims 1 to 6, characterized in that the optical monitoring of the particulate building material (3) to be applied in the area of the accumulation (5) of the particulate building material (3) is divided into sub-areas, the sub-areas being in a longitudinal extent of the Collection (5) extend and cover the entire area of the collection (5) in their sum. Method according to Claim 7, characterized in that the application parameters for the application of the particulate building material (3) are changed differently in the partial areas. Method according to one of Claims 1 to 8, characterized in that the application parameters, quantity of the particulate building material (3) to be discharged per unit of time and quantity of the particulate building material to be discharged per area, are controlled by means of a fluidiser (14) in that a number of in the fluidiser ( 14) used porous gas outlet means (20) and / or that a pressure of the gas, with which the porous gas outlet means (20) are applied, are changed.