DE102019200795A1 - Surface detection method for laser beam melting - Google Patents

Abstract

The invention relates to a method for surface detection for laser beam melting. The method comprises at least the steps of exposing a powder material (18) to a laser beam (14) so that a melt (30) is formed, detecting an optical signal (38) from at least one area of the melt (30), producing it of parameters describing the surface structure from the optical signal (38), and determining a roughness value (R) correlated to the parameters in a database (46) for the surface.

Description

The present invention relates to a method for surface detection for laser beam melting and an apparatus for performing such a method.

Laser beam melting is used particularly in the additive manufacturing of components. Generative manufacturing processes are used in particular to manufacture a component for rapid tooling, rapid pototyping or in the production of series products in the context of rapid manufacturing. In this method, the component to be produced is built up in layers from powder material, the powder material being applied in a powder layer on a substrate or an already produced part of a component in accordance with the layer to be applied, in order to then connect the powder material to one another and by melting or sintering the powder to create the component.

In order to produce a powder layer on the component, a powder bed can be used, in which the part of the component that has already been produced is arranged and is covered in the direction of the construction of the component by a powder layer that selectively corresponds to the contour in the cutting plane of the component to be produced to be deposited on the component. The surface of the powder bed is selected so that between the component already created and the surface of the powder bed there is the powder layer with the desired thickness, which is to be deposited as a solid layer on the component in the next step by melting or sintering and subsequent re-solidification. By selective melting or sintering according to the pattern of the component to be produced in the respective position and subsequent solidification, three-dimensional objects can be produced.

State of the art

From the DE 10 2016 121 594 A1 a method for improving the surface quality of additively manufactured components is known. After the deposition of a solid layer, at least the last deposited solid layer is cleaned of the powder material and the edge of the solid layer is reworked by softening the material before the next solid layer is deposited.

The background of the invention is that surface defects are a common problem in powder bed based additive manufacturing. These surface defects usually result from incorrectly delivered powder, poor process control, damage to the coater, dirt or process-related splashes in the powder bed. Such surface defects reduce the quality of the component produced in this way.

The object of the present invention is therefore to provide a method with which such surface defects can be detected economically.

Disclosure of the invention

The object is achieved by a method for surface detection for laser beam melting with the features according to claim 1 and a device for performing the method with the features according to claim 8. The dependent claims, which refer back in each case, represent advantageous developments of the invention.

The invention specifies a method for surface detection for laser beam melting. The method comprises at least the steps of exposing a powder material to a laser beam so that a melt is formed, detecting an optical signal from at least one area of the melt, generating characteristic parameters describing the surface structure from the optical signal, and determining one the parameters in a database correlated roughness value for the surface.

Exposure in the sense of the invention means that a certain area is melted with the laser beam, so that a melt is formed at least partially in this area. The parameters describing the surface structure are understood to be parameters on the basis of which direct conclusions can be drawn about the surface structure. The surface structure is formed, for example, by defects in the surface, the waviness and / or the roughness of the surface. Characteristics that allow conclusions to be drawn about the roughness of the surface are particularly preferred.

An estimate of the roughness of the current measurement can be made for the determined parameters on the basis of comparative measurements previously carried out and stored in the database, without having to carry out a corresponding measurement using the method. Rather, the roughness and thus also surface defects can thus be detected during the process. Appropriate countermeasures can be initiated based on these detected surface defects. This enables the components to be manufactured economically. This ensures high quality of the manufactured components.

In a preferred embodiment of the invention, if a limit value for the roughness value is exceeded, the corresponding section is exposed again for reworking. If the roughness is too large, the corresponding area can be melted again or polished with a laser. In this way, a minimum quality can be ensured for each layer, so that the component produced using the method is qualitatively improved.

In a further preferred embodiment of the invention, a new position is approached at a roughness value which is below the limit value. This means that production will continue. As a result, the component can be manufactured continuously with constant quality checks. The component can thus be manufactured quickly if a certain quality is maintained, so that checking the quality does not reduce the advantages of additive manufacturing.

The thermal radiation of the melt is preferably used as the optical signal. This means that the thermal radiation emitted by the melt is evaluated. This radiation is measured by a thermal radiation receiver. This means, for example, that no additional radiation source is necessary, so that a receiver for thermal radiation is sufficient. This makes the process economically feasible.

In an advantageous development, the parameters are generated on the basis of a brightness and / or darkness distribution of the optical signal. An image of the melt is generated by means of, for example, the thermal radiation received. On the basis of the radiation intensity, areas with high thermal radiation and areas with low thermal radiation are characterized by light or dark pixels. With a corresponding distribution of light or dark pixels, conclusions can be drawn about the resulting roughness. As a result, the resulting roughness can be estimated in a simple manner during the manufacturing process.

The parameters are advantageously generated on the basis of a texture of the optical signal. The texture is an essentially regular arrangement of the optical signal. On the basis of this essentially regular arrangement, the roughness specified for a corresponding texture stored in the database can be determined as roughness for the present texture.

In a further advantageous embodiment, a coaxial monitoring system is used to melt the powder material and to detect the optical signal. Such coaxial monitoring systems are already widely available on the market. It is therefore not necessary to develop an additional system in order to carry out the method according to the invention. As a result, the method according to the invention can be used economically.

The invention is additionally achieved by a device for performing the method according to the invention. The device comprises at least one laser device for melting a powder material, an optical device for detecting an optical signal, and an evaluation unit for generating parameters describing the surface structure from the optical signal, and for determining a roughness value for the surface correlated with the parameters in a database .

The advantages mentioned for the method can be achieved with such a device.

In an advantageous embodiment of the invention, the laser device and the optical device are formed by a coaxial monitoring system. As a result, the optical device and the laser device do not have to be developed separately. Rather, a system that is already available on the market can be used. Such a device can be provided economically.

• 1 Ausführungsbeispiel einer Vorrichtung zum Durchführen des erfindungsgemäßen Verfahrens,
• 2 Ausführungsbeispiel des erfindungsgemäßen Verfahrens zur Oberflächendetektion für Laserstrahlschmelzen, und
• 3 Beispielgraph für die mit dem Verfahren ermittelten Rauigkeitswerte im Vergleich zu den realen Rauigkeitswerten.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. It shows:

• 1 Embodiment of a device for performing the method according to the invention,
• 2nd Embodiment of the inventive method for surface detection for laser beam melting, and
• 3rd Example graph for the roughness values determined with the method in comparison to the real roughness values.

In 1 is an embodiment of an apparatus for performing the method according to the invention (see 2nd ) shown. The device comprises a laser device 14 with which a powder material 18th that in the form of a layer on an already solidified material 22 rests via one of the laser device 14 emitted laser beam 26 , is melted. In a small area around the powder material 18th incident laser beam 26 becomes a melt 30th generated. After cooling, this melted area is solidified.

The device additionally comprises an optical device 34 with an optical signal 38 which is caused by the thermal radiation of the melt 30th is delivered, is detectable. That from the optics 34 detected optical signal 38 is sent to an evaluation unit 42 forwarded with which the optics device 34 connected is. The evaluation unit 42 analyzes the optical signal 38 and generates the parameters describing the surface structure using a distribution of brightness and darkness. These parameters can be without units.

From a database 46 , which in this embodiment in the evaluation unit 42 a roughness value for the surface is determined for these parameters. The in the database 46 The roughness values stored for the parameters were determined using real samples. This becomes the during the melt 30th the actual roughness value determined by a subsequent measurement using, for example, a microscope.

The real roughness value measured for the determined parameters is stored in the database 46 filed together. A roughness value can be determined for the corresponding parameters using a large number of such value pairs. The resulting accuracy is sufficient to decide whether an area needs to be reworked.

2nd shows an embodiment of the method according to the invention for surface detection for laser beam melting. In a first step 50 becomes the powder material 18th with the laser beam 26 exposed. In this area the powder material 18th melted so that a melt 30th arises. After the first step 50 in a second step 54 the optical signal 38 from the melt 30th detected. From this optical signal 38 be in a third step 58 generates the parameters describing the surface structure.

In a fourth step 62 is based on these parameters in the database 46 correlated roughness value R is determined for the surface. It is then checked whether the roughness value R exceeds a limit value R _G. If the roughness value R is greater than the limit value R _G , the first step is made again 50 started, so that the corresponding section is reworked.

If the roughness value R should be below the limit value R _G , then in a fifth step 66 be moved to a new position. As a result, a component produced in this way can be manufactured quickly and a limit value R _G for the roughness value R can be ensured in each layer.

In 3rd is an example graph for the roughness values R determined by the method in comparison to the real roughness values R _{R is} shown. In this example graph, six test specimens are sorted on the X axis with increasing real roughness value R _R. The roughness values R of these test specimens were measured during the process using the method according to the invention. The roughness values R determined are in a first curve 70 shown. In addition, a second curve shows 74 the real roughness values R _{R of} this test specimen, which was measured after the process.

The data show that the measured during the process roughness values R tends to allow an estimation of the real roughness values R _R from a size of the real roughness R _R, so that this can be determined during the process.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 102016121594 A1 [0004]

Claims (10)

Method for surface detection for laser beam melting, the method comprising at least the steps: - Exposing a powder material (18) with a laser beam (14) so that a melt (30) is formed, - detecting an optical signal (38) from at least one area of the melt (30), - Generating parameters describing the surface structure from the optical signal (38), and - Determining a roughness value (R) correlated to the parameters in a database (46) for the surface. Procedure according to Claim 1 , characterized in that if a limit value (R _G ) for the roughness value (R) is exceeded, the corresponding section is exposed again for reworking. Procedure according to Claim 1 or 2nd , characterized in that at a roughness value (R) which is below the limit value (R _G ) a new position is approached. Method according to one of the preceding claims, characterized in that the thermal radiation from the melt (30) is used as the optical signal (38). Method according to one of the preceding claims, characterized in that the parameters are generated on the basis of a brightness and / or darkness distribution of the optical signal (38). Method according to one of the preceding claims, characterized in that the parameters are generated on the basis of a texture of the optical signal (38). Method according to one of the preceding claims, characterized in that a coaxial monitoring system is used for melting the powder material (18) and for detecting the optical signal (38). Device for performing a method according to one of the preceding claims, wherein the device comprises at least: - Laser device (14) for melting a powder material (18), - Optical device (34) for detecting an optical signal (38), and - Evaluation unit (42) for generating parameters describing the surface structure from the optical signal (38), and for determining a roughness value (R) correlated with the parameters in a database (46) for the surface. Device after Claim 8 , characterized in that the laser device (14) and the optical device (34) are formed by a coaxial monitoring system. Computer program product with program code means for performing the method according to one of the Claims 1 to 7 , if the computer program product on an evaluation unit (42) of a device according to one of the Claims 8 to 9 expires or is stored on a computer-readable data carrier.

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