HYBRID MANUFACTURING OF THREE-DIMENSIONAL COMPONENTS

Description

[0001] The present invention relates to the production of components as a composite of a three-dimensional shape and a filling material. State of the art

[0002] Three-dimensional objects of any shape can be created using 3D printing. Most 3D printers build the object layer by layer from the bottom up, adding material to the object at each position within the layer belonging to the object.

[0003] When building a new layer, molten material is often applied to already solidified material. Therefore, the strength with which two layers adhere to each other is often lower than the strength of a single layer against tensile stress or shear in the layer plane. Furthermore, 3D printing a solid form can take a very long time. Therefore, DE 10 2016 222 558 A1 discloses a 3D printing process in which a printed structure is filled with a monomer, which is then polymerized. Disclosure of the invention

[0004] Within the scope of the invention, a method for producing a three-dimensional object was developed.

[0005] The process begins with the provision of a three-dimensional form that defines an interior space. In particular, a structure manufactured using 3D printing, for example, can be provided as a three-dimensional form. This is particularly cost-effective for the production of small series with batch sizes in the single- or double-digit range, as high setup and tooling costs are eliminated.

[0006] A filler material comprising at least one liquid or pasty monomer is introduced into the interior space. The monomer is polymerized into a polymer, while the temperature of the filler material and / or the temperature of an outer surface of the three-dimensional mold is monitored. Based on the result of this monitoring, the quality of the object is assessed and / or at least one measure is taken to direct the temperature in a desired direction.

[0007] It was discovered that the polymerization of the monomer to the polymer only proceeds optimally within a comparatively narrow temperature window, while at the same time, especially in large-volume objects, the temperature of the filler material varies greatly during polymerization. For example, the polymerization of caprolactam to polyamide 6 proceeds optimally in the temperature window between 140 and 220 °C.

[0008] At the same time, the temperature of the filler material must not exceed the temperature at which the three-dimensional shape softens or even destroys. In this case, it would no longer be guaranteed that the ultimately produced object would have exactly the shape previously specified, for example, during 3D printing of the mold. For polyamide as a 3D-printable material for the mold, the limit is approximately 200 °C. Another important factor for the temperature dynamics is that polymerization is an exothermic reaction. Polymerization and crystallization heat are generated, with heat of output dependent on the reaction rate.

[0009] The spatial variation in temperature can be clearly understood using the example of a solid cup with a handle. Heat can build up inside the cup and potentially overheat the filling material. In the handle, however, the heat from the interior has a significantly shorter distance to travel to reach the outer surface.

[0010] Assessing the quality of the object can therefore include, for example, determining to what extent the temperature of the filling material was everywhere within the range intended for polymerization; to what extent the temperature of the three-dimensional shape locally exceeded a specified maximum value (or fell below a minimum value); with which temperature-time profile the object cooled; to what extent the temperature of the filling material and / or the three-dimensional shape deviates from a forecast determined on the basis of a model.

[0011] The temperature-time profile determines the crystallinity as well as possible mechanical stresses in the solidified filling material.

[0012] A temperature deviation from a predicted temperature may not have a direct physical impact on the quality of the object, but it can indicate that the manufacturing process did not proceed as planned in some respect. This then at least raises initial suspicion that the quality of the component may not match the original plan. For example, a leak may have occurred during the process, or the object may have become contaminated. Heating systems in the production facility may also have failed, for example.

[0013] Alternatively, or in combination with the quality assessment of the object, the temperature can be actively directed in a desired direction. Which measures are appropriate here can depend, for example, on whether the temperature needs to be adjusted locally in specific areas or globally.

[0014] For example, the temperature of a furnace in which the monomer is polymerized and / or the dwell time of the object in the furnace can be changed. In this way, the temperature can be adjusted globally. Furthermore, the change in the object acts from the outside inward, so that to a certain extent, the temperature can be adjusted preferentially in the outer area of ​​the object.

[0015] For example, the temperature at which the monomer is introduced into the interior of the three-dimensional mold can be changed. This also allows for global temperature correction. The temperature change propagates from the location where the monomer is introduced into the interior.

[0016] The object can also be locally heated or cooled, for example. For local heating, an infrared beam or a laser beam can be used. For local cooling, an air jet can be used.

[0017] In a particularly advantageous embodiment, temperature monitoring involves measuring the temperature at a number of locations and, using these temperatures, determining the temperature at at least one other location in the filler material and / or in the three-dimensional mold. The spatial distribution of the temperature can be used, for example, to determine the extent to which polymerization has been completed throughout the entire object. This, in turn, is crucial for the mechanical strength of the object, which must be verified, for example, as part of quality management.

[0018] For example, the locations where the temperature is to be measured can be scanned with an infrared thermometer. Alternatively, a thermal image of the object can be created, and the temperatures to be measured can be extracted from this thermal image.

[0019] The temperature at at least one additional location in the filling material can be determined, for example, using a parameterized model whose parameters are trained based on temperature measurements at locations within the filling material. The model then serves as a "digital twin" of the object, from which temperatures at any location within the object can be read.

[0020] To train the model, for example, test objects can be produced into which temperature sensors are embedded at specific positions within the interior of the three-dimensional mold. These temperature sensors are cast in when the filler material is added and cannot be removed once the filler material has solidified. Therefore, this type of temperature monitoring cannot usually be carried out on objects intended for their intended use or sale. However, once the model has learned the relationship between the temperatures measured in accessible locations, on the one hand, and the temperatures prevailing in inaccessible locations inside the filler material, on the other hand, measuring the temperatures in the accessible locations is sufficient to at least approximately determine the temperature profile inside the object.The model can, for example, include a machine learning model, such as a neural network. When setting up the model, existing know-how from classic filling simulation from injection molding can be used, for example.

[0021] For the insertion of temperature sensors into locations inside the three-dimensional shape for training the model, access points can be kept clear, especially during preparation of the three-dimensional shape. The three-dimensional shape then no longer needs to be modified manually.

[0022] In a particularly advantageous embodiment, locations where temperature measurement is intended are marked and / or prepared when the three-dimensional mold is prepared. For example, a hole or a depression can be made in the three-dimensional mold at these locations to locally reduce the wall thickness of the three-dimensional mold. The temperature measured at these locations then closely follows the temperature of the filler material.

[0023] In a further advantageous embodiment, at least one location on the outer surface of the three-dimensional mold is selected as the location for the temperature measurement, where a local maximum or minimum temperature is expected due to the geometry of the mold. These temperatures are already meaningful in themselves, since in the context of polymerization, the main concern is to keep the reaction temperature within a predetermined range. Prominent locations with regard to a local minimum or maximum temperature include, for example, inner edges, holes, or areas with the greatest wall thickness of the three-dimensional mold.

[0024] The invention can be fully or partially computer-implemented and thus embodied in software. Thus, the invention also relates to a computer program with machine-readable instructions that, when executed on one or more computers, cause the computer(s) and a manufacturing plant controlled by the computer(s) to carry out the method. In this context, embedded systems and process controllers capable of executing machine-readable instructions are also considered computers.

[0025] The invention also relates to a machine-readable data carrier and / or a downloadable product containing the computer program. A downloadable product is a digital product that can be transmitted over a data network, i.e., downloaded by a user of the data network, and which can be offered for immediate download, for example, in an online shop.

[0026] Furthermore, a computer can be equipped with the computer program, the machine-readable data carrier or the download product.

[0027] Further measures improving the invention are presented in more detail below together with the description of the preferred embodiments of the invention with reference to figures. Examples of implementation

[0028] It shows: Figure 1 an embodiment of the method 100 and Figure 2 a cross-sectional drawing of a three-dimensional object 1.

[0029] Figure 1 is a schematic flow diagram of an embodiment of the method 100 for producing a three-dimensional object 1.

[0030] In step 110, a three-dimensional mold 2 defining an interior space 21 is provided. According to block 111, a 3D-printed structure can be provided as a three-dimensional mold 2.

[0031] In step 120, a filling material 3, which comprises at least one liquid or pasty monomer, is introduced into the interior space 21

[0032] In step 130, the monomer is polymerized into a polymer. Meanwhile, in step 140, the temperature 3a of the filling material 3 and / or the temperature 2a of an outer surface of the three-dimensional mold 2 is monitored.

[0033] Based on the results 2a, 3a of this monitoring, the quality 1a of the object 1 is evaluated in step 150. Alternatively, or in combination with this, at least one measure 4 can be taken in step 160 to direct the temperature 2a, 3a in a desired direction.

[0034] According to block 141, monitoring the temperature may involve measuring the temperature 2a, 3a at a plurality of locations. Then, according to block 142, using these temperatures 2a, 3a, the temperature 2a#, 3a# can be determined at at least one further location in the filling material 3 and / or in the three-dimensional mold 2. For this purpose, locations where a temperature measurement is intended can be marked and / or prepared, for example, according to block 112, when the three-dimensional mold 2 is provided.

[0035] According to block 141a, in particular, for example, at least one location on the outer surface of the three-dimensional shape 2, at which a local maximum or minimum of the temperature is to be expected due to the geometry of the shape, can be selected as location 2a for the temperature measurement.

[0036] According to block 142a, in particular, for example, the temperature (2a#, 3a#) at the at least one further location in the filling material 3 can be determined using a parameterized model whose parameters are trained based on temperature measurements at locations within the filling material 3. To facilitate these measurements for training the model, access points for inserting temperature sensors at predetermined locations in the interior 21 of the mold 2 can be kept free, in particular, for example, according to block 113, when providing the three-dimensional mold 2.

[0037] The evaluation of the quality 1a of the object 1 may in particular comprise, for example, determining to what extent the temperature 3a of the filling material 3 was everywhere within the range intended for polymerization (block 151); to what extent the temperature 2a of the three-dimensional shape 2 locally exceeded a predetermined maximum value (or fell below a predetermined minimum value) (block 152); with which temperature-time profile the object 1 cooled (block 153); to what extent the temperature of the filling material 3 and / or the three-dimensional shape 2 deviates from a forecast determined on the basis of a model (block 154).

[0038] The measure 4 for controlling the temperature 2a, 3a may in particular comprise, for example, to change the temperature of an oven in which the monomer is polymerized and / or a residence time of the object 1 in the oven (block 161); and / or to change the temperature at which the monomer is introduced into the interior 21 of the three-dimensional mold (block 162); and / or to locally heat or cool the object 1 (block 163).

[0039] Figure 2shows, by way of example, a snapshot of the implementation of method 100 during the filling of filler material 3 into a three-dimensional mold 2. The three-dimensional mold 2 is shown in a sectional view and has an inlet 22 for the filler material 3 as well as three risers 23a-23c through which air can escape from the mold 2 so that it does not offer any resistance to the filling of the filler material 3. Twelve measuring points aI are marked on the outside of the three-dimensional mold 2. At these measuring points aI, the temperature 2a of the outer surface of the mold 2 is measured according to block 142 of the method 100. Using a previously trained model, the temperature 3a# at any location within the filler material 3 in the mold 2, here at points m and n, can be calculated from the temperatures measured at locations aI according to block 142 of the method 100.The directly measured temperatures 2a at the outer surface of the mold 2 as well as the calculated temperatures 3a# at other locations within the filling material 3 can then be . be used in step 150 of the method 100 to evaluate the quality 1 a of the object 1 composed of mold 2 and filling material 3, and / or be used in step 160 of the method 100 to determine a measure 4 with which the temperature 2a on the outer surface of the mold 2, and / or the temperature 3a in the filling material 3, can be directed in a desired direction.

Claims

1. Process (100) for producing a three-dimensional object (1) comprising the following steps: • a three-dimensional mould (2) which defines an interior (21) is provided (110); • a filling material (3) which comprises at least one liquid or pasty monomer is introduced (120) into the interior (21); • the monomer is polymerized (130) to afford a polymer, characterized in that the temperature (3a) of the filling material (3) and / or the temperature (2a) of an external surface of the three-dimensional mould (2) is monitored (140); and • on the basis of the results (2a, 3a) of this monitoring the quality (1a) of the object (1) is evaluated (150) and / or at least one measure (4) is taken (160) to direct the temperature (2a, 3a) in a desired direction.

2. Process (100) according to Claim 1, wherein a structure produced by 3D printing is provided (111) as the three-dimensional mould (2).

3. Process (100) according to either of Claims 1 to 2, wherein the monitoring of the temperature comprises measuring (141) the temperature (2a, 3a) at a plurality of sites and using these temperatures (2a, 3a) to determine (142) the temperature (2a#, 3a#) at at least one further site in the filling material (3) and / or in the three-dimensional mould (2).

4. Process (100) according to Claim 3, wherein at least one site on the external surface of the three-dimensional mould (2), at which a local maximum or minimum of temperature is to be expected due to the geometry of the mould, is selected as a site (2a) for temperature measurement (141a).

5. Process (100) according to any of Claims 3 to 4, wherein the temperature (2a#, 3a#) at the at least one further site in the filling material (3) is determined (142a) with a parameterized model whose parameters are trained using measurement of temperature at sites within the filling material (3).

6. Process (100) according to any of Claims 3 to 5, wherein sites at which measurement of temperature is intended are marked and / or prepared (112) during provision of the three-dimensional mould (2).

7. Process (100) according to any of Claims 3 to 6, wherein access paths for introduction of temperature sensors to predetermined sites in the interior (21) of the mould (2) are kept clear (113) during provision of the three-dimensional mould (2).

8. Process (100) according to any of Claims 1 to 7, wherein evaluation of the quality (1a) of the object (1) comprises determining • to what extent the temperature (3a) of the filling material (3) has in all regions been in the range intended for polymerization (151); • to what extent the temperature (2a) of the three-dimensional mould (2) has locally exceeded a predetermined maximum value or fallen below a predetermined minimum value (152); • the temperature-time profile with which the object (1) underwent cooling (153); • to what extent the temperature of the filling material (3) and / or of the three-dimensional mould (2) diverges (154) from a forecast calculated on the basis of a model.

9. Process (100) according to any of Claims 1 to 8, wherein the measure (4) for directing the temperature (2a, 3a) comprises • altering (161) the temperature of an oven in which the monomer is polymerized and / or a residence time of the object (1) in the oven; and / or • altering (162) the temperature at which the monomer is introduced into the interior (21) of the three-dimensional mould; and / or • locally heating or cooling (163) the object (1).

10. Computer program containing machine-readable instructions which, when executed on one or more computers, prompt the computer(s) and a production plant controlled by the computer(s) to perform the process (100) according to any of Claims 1 to 9.

11. Machine-readable data carrier and / or download product comprising the computer program according to Claim 10.