WO2022122745A1

WO2022122745A1 - Method for manufacturing a three-dimensional object, and apparatus for 3d printing

Info

Publication number: WO2022122745A1
Application number: PCT/EP2021/084623
Authority: WO
Inventors: Hendrik JAHNLE
Original assignee: Robert Bosch Gmbh
Priority date: 2020-12-10
Filing date: 2021-12-07
Publication date: 2022-06-16
Also published as: DE102020215655A1

Abstract

The invention relates to a method (100) for manufacturing a three-dimensional object (10), said method comprising the following steps: • a printing structure (11) which defines an interior (12) is produced (110) by means of 3D printing from a printing material (21); • the printing structure (11) is processed by means of an apparatus (50) for carrying out an abrasive process (115); • a filling material (22), which comprises at least one liquid or paste-like monomer, is introduced (120) into the interior (12); • the monomer is polymerised (130) to form a polymer (24). The invention also relates to an apparatus for 3D printing (30) and for carrying out a method (100) according to the invention, wherein a first print head (31) for the printing material (21), a second print head (32) for the filling material (22), and an apparatus (50) for carrying out the abrasive process (115) are provided.

Description

description

Title:

Method for producing a three-dimensional object and device for 3D printing

The present invention relates to a method, in particular a 3D printing method, for producing three-dimensional objects with a freely selectable shape and a device for 3D printing and for carrying out a method according to the invention.

State of the art

In conventional 3D printing (Fused Deposition Modeling, FDM), a thermoplastic printing material is melted and, in a liquid state, is selectively placed at the points that belong to the object to be manufactured. If the printing material then cools down, it solidifies again. In this way, objects with freely selectable shapes can be built up in layers.

When these layers are applied, for example, thermal distortion occurs on the component or threads form on the nozzle of the 3D printer. As a result, the dimensions of a component can change greatly, which disadvantageously results in an inaccuracy of the component. A reproducibility of the components is therefore difficult to achieve.

These and other factors influence the accuracy of the component in FDM 3D printing. The factors are very difficult to control and can often only be improved by constantly trying out and adjusting parameters. This process optimization is very time-consuming and it is difficult to achieve a result within the desired tolerance range.

The main problem with 3D printed plastic parts is their often low resilience in the direction of assembly. The layers built on top of each other can be separated from each other with little effort. In addition, depending on the build rate, the surface quality and tolerance accuracy is low. It is often possible to see the layers stacked on top of each other with the naked eye.

It is known from DE 10 2016 222 552 A1 to construct an external structure of a component using a first print head and then to fill this structure with a polymerizable filling material. This method makes it possible to produce components with increased strength, but the surface accuracy of the finished component is not optimal with this method either.

The object is to provide a method for producing an object and a device for 3D printing, with which a better surface quality of the object and thus improved reproducibility can be achieved.

Disclosure of Invention

The object is achieved by the method according to the invention, in particular a 3D printing method for producing three-dimensional objects with a freely selectable shape, and a device for 3D printing and for carrying out a method.

A method for producing a three-dimensional object was developed as part of the invention. In this process, a print structure is first produced from a print material using 3D printing. This print structure defines an interior space. The print structure is then processed using a device for carrying out an abrasive process. In a preferred development, a surface of the interior is processed by the device for carrying out the abrasive method. A filling material, which comprises at least one liquid or pasty monomer, is then introduced into the interior. Finally, the monomer is polymerized into a polymer.

The approach of processing the pressure structure by means of the device for carrying out the abrasive method, in particular by milling, counteracts the disadvantageous inaccuracy of the component in an advantageous manner. Furthermore, it is advantageously achieved that this process improvement improves the stability of the components, as well as their appearance and accuracy.

It is particularly advantageous to carry out the milling during the printing process, which increases the accuracy of the component. The use of a milling process therefore offers a time saving and also ensures a more precise reproducibility of e.g. components of a small series. Errors that could lead to uneven surfaces of the component can be avoided by the method according to the invention. These errors arise, for example, from thermal distortion due to immature thermal management or thread formation.

The method according to the invention makes it possible to produce components which have at least comparable properties to a plastic injection molded part. In this context, both the stability and the surface quality of the component are important.

In summary, compared to the prior art, the method according to the invention offers an improvement in the surface and an improvement in the tolerance range of the component, with the problem of thread formation and uneven contours caused by the pressure being able to be neglected.

As described, achieve objects, or components, produced with the method according to the invention, properties like those of a conventionally manufactured injection molded component, in particular what the surface quality, the Tolerance range and stability is concerned. This results in particular in the advantages that compared to an injection molded component, there is no need to produce an injection mold and this is therefore particularly attractive for small series. Furthermore, the complexity of the component is not limited, as is the case with conventional injection molding processes.

Furthermore, the function of the interior space in this context is to spatially limit the spread of the filling material when it is filled. For this it is not necessary that the interior is enclosed on all sides.

For example, a trough made of the printing material and open at the top also defines an interior space that can be filled with the filling material. The filling material is then trapped in this tub and cannot leak out. The interior can in particular define the negative form of an object structure to be produced from the polymer, or a part of such an object structure.

The term “3D printed” includes any manufacturing that uses 3D printing. The printed structure is therefore also produced using 3D printing within the meaning of the invention, if the printing material was cast, for example, in a mold which in turn was produced directly using 3D printing.

It was recognized that with the method according to the invention on the one hand significantly finer object structures can be manufactured from the polymer than according to the prior art and that a larger class of object structures can be manufactured at all. On the other hand, a smooth surface is produced by processing the surface of the interior space using the abrasive method, which advantageously results in a high surface quality of the interior space.

The high precision with which the printing structure can be manufactured through this process is carried over to the contours of the interior, which in turn determine the locations to which the filling material penetrates. There is no longer the boundary condition that the object structures have to remain independently stable until polymerization. However, it is still possible, the monomer s to polymerize bloc, so that there are no interfaces between sequentially polymerized areas within the object structures that consist of the polymer. The polymer is weakest at such interfaces and tends to break when the object is subjected to mechanical stress. The strength at these interfaces cannot be improved even by using reinforcing fibers, since the fibers do not span these interfaces.

When entering the interior, the filling material advantageously has a temperature that is lower than the melting temperature TM of the solidified printing material. Then the print structure is not attacked by the filling material. However, the filling material may also be warmer if and to the extent that sufficient heat can be dissipated through the pressure structure to keep the temperature of the pressure structure below its melting temperature TM.

In a particularly advantageous embodiment of the invention, a filling material is selected which contains at least one solid filler. This filler can perform any function. For example, the filler can be a recycled material, the use of which reduces the material cost of the manufactured object. The filler can also be, for example, a material that gives the object a required weight for its use.

In a particularly advantageous embodiment of the invention, a reinforcing material, in particular in the form of fibers, is chosen as the filler. Glass fibers, for example, are suitable. The use of such reinforcing materials in printing materials has hitherto led to a further conflict of objectives with regard to filigree structures, since a nozzle with a small orifice, which is required for filigree structures, tends to be clogged by the reinforcing materials. Functional reinforcement effects can be achieved by adding fibers, which bring about a significant increase in the mechanical properties. At the same time, the mechanical strength of the polymer is isotropic due to the polymerisation in one piece.

In a further particularly advantageous embodiment of the invention, the print material becomes the print structure with a first 3D print head assembled, and the filling material is introduced into the interior with a second 3D print head. In this way it can be ensured that the filling material only gets into the interior and other areas on the outside of the pressure structure are not contaminated.

In a further particularly advantageous embodiment of the invention, a water-soluble printing material is selected. This simplifies it in particular, in a further particularly advantageous embodiment of the invention, to remove the print structure from the object after the polymerization of the monomer. The printing material here can advantageously be PVA, for example.

PVA is a polyvinyl alcohol, a thermoplastic material, also water-soluble and is therefore well suited as a support material for 3D printing. Polyvinyl alcohol has excellent layer-forming, emulsifying and adhesive properties.

In a further particularly advantageous embodiment of the invention, after the filling material has been introduced, further printing material is applied by means of 3D printing. For example, if the printed structure includes a trough, this trough can be closed with a printed cover after the filling material has been introduced. It is then no longer necessary to subsequently open access to the interior.

In this case, the monomer in the filling material can optionally already be polymerized before the further printing material is applied. This additional printing material then fills up any shrinkage of the filling material. Furthermore, overhangs of the monomer can also be poured over the printing material and then printed over again with printing material.

Alternatively, the monomer can initially remain a monomer and only be polymerized at a later point in time. This is particularly advantageous if the additionally applied printing material defines a further interior space which, together with the first interior space, forms a coherent area filled with filling material. The monomer can then polymerize en bloc in this area, so that in the polymer ultimately obtained there is no interface formed by the boundary between the two interior spaces, and therefore no possible weak point either. If you want to switch between the application of print material and the introduction of filling material, in particular multiple times, the print head or print heads of the 3D printer used are advantageously designed in such a way that the discharge of print material or filling material by applying a negative pressure to the outlet opening, and / or by a valve closure of the outlet opening, can be prevented.

In a further particularly advantageous embodiment of the invention, the interior space is connected to a pressurized source for the filling material during the polymerization of the monomer. In this way, the shrinkage that occurs during the polymerization can be compensated for by further filling material being pushed in to the extent of the shrinkage. This shrinkage can be of the order of 10%. If, for example, the polymerization takes place at elevated temperature and the finished object is cooled to room temperature, there is only a further shrinkage of the order of 1%.

Access to the interior for feeding the filling material can be deliberately left open during 3D printing of the print structure. For example, the pressure structure can be set up on a base plate that has a passage for feeding in the filling material. The pressure structure can then be designed in such a way that a channel from this supply to the interior space remains open. However, access can also be established subsequently by means of a cut, a bore or a similar opening leading into the interior.

In a further particularly advantageous embodiment of the invention, the interior includes an insert to be embedded in the object. Such inserts can be conductor tracks, sockets and plugs, for example. In particular, electronic components or permanent magnets can also be inserts. Such inserts are heat-sensitive and therefore cannot be converted with many 3D printing processes that heat the printing material to temperatures of 200 °C and more. On the other hand, the filling of the interior space with the filling material does not necessarily depend on a specific minimum temperature. Not even the polymerisation of the monomer to form the polymer necessarily requires an elevated temperature, because the polymerisation can also be initiated and/or maintained by a catalyst, an activator and/or by UV light. It is also possible to activate the polymerization by briefly increasing the temperature so that it then continues automatically at a lower temperature. The insert is then only slightly thermally stressed.

In a particularly advantageous embodiment of the invention, caprolactam is chosen as the monomer and polymerized to form the polyamide PA6 as the polymer. In particular in connection with fibers as reinforcement materials, an object made of PA6 according to the invention can come very close to and even exceed the mechanical and technical properties of injection-moulded PA6. Thus, the creative freedom and function-oriented construction in the sense of additive manufacturing is combined with the process-specific advantages of injection molding, without accepting the specific disadvantages that these technologies bring with them.

Alternatively or in combination, propene can be selected as a monomer and polymerized to PBT as a polymer. Cyclic PBT or CBT can be chosen as the monomer and polymerized to PBT as the polymer. Finally, for example, laurolactam can also be selected as a monomer and polymerized to form the polyamide PA12 as a polymer.

In general, the method according to the invention can upgrade all 3D printing methods that work with thermoplastics. At the same time, injection molding can be substituted, especially in prototyping and in small series. In particular, the time and expense associated with each manufacture and modification of the injection mold can be avoided.

According to what has been said above, the invention also relates to a device for 3D printing and for carrying out the method according to the invention, wherein a first print head for the printing material, a second print head for the Filling material and a device for carrying out the abrasive process are provided.

In a preferred development, the device for carrying out the abrasive process is a milling machine.

The structure of the device or the printer can be referred to as a hybrid printer.

In a first possible method, geometrically complex components can be produced in an advantageous manner, with a layer first being printed by the first print head. The resulting area is then covered with the milling head in such a way that a smooth and clean surface is created in the interior. This process is repeated layer by layer until the component is complete. Because of this process arrangement, it is also advantageously possible to process overhangs in a simple manner.

In another process, it is possible to first print the entire component and then refine it by milling. This process control is advantageous in the case of simple geometries of the component to be manufactured, whereby it must be ensured that the milling head can reach all relevant points on the surface of the interior space formed.

The accuracy of the component is advantageously improved by adding a milling operation during or after the printing process. The milling head follows the printed contours and can eliminate the inaccuracies caused by the pressure of the print structure.

Optimum adhesion of the component to the building board is essential during the process, especially the milling process, since the component would otherwise be detached from the building board by the forces that occur and the printing process would have to be stopped.

The method according to the invention, in which the print structure, which defines the interior space, is produced from a print material by means of 3D printing and the resulting print structure is produced by means of the device for carrying out the abrasive process is processed and a filling material, which comprises at least one liquid or pasty monomer, is introduced into the interior and the monomer is polymerized to a polymer, not only improves the surface quality of the printed component, but also its stability.

It is particularly advantageous to first print a layer of the support structure (shell) from PVA and then to process the inner walls of one layer with the milling process so that a smooth surface is created. These two processes are repeated alternately until the entire envelope is printed. After that, it is preferably filled with caprolactam. The subsequently hardened caprolactam is placed in a liquid container together with the printed shell, and the PVA shell dissolves in it. The resulting product advantageously has the same properties as a plastic injection molded part. However, since this process does not require the production of an injection molding die, this process is particularly attractive for small series.

Further measures improving the invention are presented in more detail below together with the description of the preferred exemplary embodiments of the invention with the aid of figures.

exemplary embodiments

Show it:

1 shows a flowchart of the method 100 according to the invention;

2 shows a device 30 for carrying out the method 100 according to the invention in one method step;

3 shows the device 30 for carrying out the method 100 in a further method step; 4 shows the device 30 for carrying out the method 100 in a further method step and

5 shows an object 10 in a further method step.

According to FIG. 1, in step 110 a print structure 11 is first produced. This print structure 11 includes an interior space 12. The print structure 11 is formed of water-soluble PVA.

The pressure structure 11 is then processed using a device 50 for carrying out an abrasive process 115, a surface of the interior 12 being processed abrasively by a milling machine 50 or a milling head 50 in order to improve the surface accuracy.

In this process step 110, 115, a layer is created which is printed by the first print head 31 and then the resulting area is traversed with the milling head 50 in such a way that a smooth or clean surface is created in the interior 12. This process is repeated layer by layer until the print structure 11 that forms the interior 12 is complete.

Alternatively, it is possible first to print the print structure 11 completely using the first print head 31 and then to refine it using the milling process 115 . This process management is advantageous in the case of simple geometries of the component 10 to be manufactured, it being necessary to ensure that the milling head 50 can reach all relevant points on the surface of the interior space 12 formed.

The interior 12 is then filled in step 120 with a filling material 22 containing reinforcing fibers 25 . In this case, the filling material 22 is brought into the pressure structure 11 . Optionally, further iterations can now take place, in which the pressure structure 11 is expanded 110, the newly created interior space 12 is abrasively processed 115 and corresponding interior spaces 12 are covered with filling material 22 120.

In step 130, the monomer contained in the filler material 22 is polymerized to form a polymer 24, with optional (step 135) further filler material 22 being supplied during the polymerization. Then, in step 140, the print structure 11 made of PVA can be removed by immersion in a water bath 55. The pressure structure 11 dissolves and the finished object 10 or component remains in the water bath 55 .

2 to 4 show a device 30 for carrying out the method 100 according to the invention in various method steps, the device for 3D printing and for carrying out the method 100 according to the invention, a first print head 31 for the printing material 21, a second print head 32 for having the filling material 22 and a device 50 for carrying out the abrasive process 115 .

The device 50 for carrying out the abrasive process 115 is a milling machine 50. The structure of the device 30 or the printer can be referred to as a hybrid printer.

2 shows the device 30 during the method 110 for printing the print structure 11, with print material 21 being applied from the print head 31 to a build plate in the build chamber of the printer 30 and the print structure 11 thereby forming an interior space 12. The milling head 50 is ready, but not yet in use.

3 shows the device 30 during the method 115 for abrasive processing of the print structure 11 or the surface of the interior 12 by the milling head 50. The milling head 50 moves along the printed contours 55 of the print structure 11 and eliminates, for example, those that have occurred due to the pressure Inaccuracies and thereby produces a smooth surface at the milled points of the print structure 11. The print head 31 for dispensing the print material 21 is ready, but is not in use.

Fig. 4 shows the device 30 during the method 120 for introducing the filling material 22 into the interior 12 of the printing structure 11 by the second print head 32. Subsequently or during the filling process 120, the filling material 22, which comprises at least one liquid or pasty monomer, to a polymer 24 are polymerized 130. The filler material 22 is preferably caprolactam.

The hardened caprolactam together with the printed print structure 11 or shell is then placed in a liquid container or a water bath 55, the print structure 11 or shell made of PVA dissolving therein.

5 shows the finished object 11 or component in the water bath 55, with the surface 45 of the component 11 being exposed.

Claims

Expectations

1. A method (100) for producing a three-dimensional object (10), characterized by the following steps: a printed structure (11) which defines an interior space (12) is produced (110) from a printed material (21) by means of 3D printing; the pressure structure (11) is processed by means of a device (50) for carrying out an abrasive process (115); a filling material (22), which comprises at least one liquid or pasty monomer, is introduced (120) into the interior (12); the monomer is polymerized (130) to a polymer (24).

2. Method (100) according to claim 1, characterized in that the interior (12) defines the negative form of an object structure (28) to be produced from the polymer (24), or a part of such an object structure (28).

3. Method (100) according to one of claims 1 to 2, characterized in that a surface of the interior (12) is processed by the device (50) for carrying out the abrasive method (115).

4. The method (100) according to any one of the preceding claims, characterized in that a filling material (22) is selected which contains at least one solid filler (25).

5. The method (100) according to claim 4, characterized in that a reinforcing material, in particular in the form of fibers, is selected as the filler (25).

6. The method (100) according to any one of the preceding claims, characterized in that the printing material (21) with a first 3D print head (31) is assembled (110) to form the print structure (11) and that the filling material (22) is introduced (120) into the interior (12) with a second 3D print head (32).

7. The method (100) according to any one of the preceding claims, characterized in that a water-soluble printing material (21), in particular PVA, is selected.

8. The method (100) according to any one of claims 1 to 7, characterized in that the printing structure (11) is removed (140) from the object (10) after the polymerization (130) of the monomer.

9. The method (100) according to any one of claims 1 to 8, characterized in that after the introduction (120) of the filling material (22), further printing material (21) is applied by means of 3D printing (110).

A method (100) according to any one of claims 1 to 9, characterized in that the interior space (12) is connected (135) to a pressurized source of the filler material (22) during the polymerization (130) of the monomer.

11. The method (100) according to any one of claims 1 to 10, characterized in that

Caprolactam is chosen as the monomer and is polymerized (130) to form the polyamide PA6 as the polymer (24), and/or

Propene is chosen as monomer and polymerized to PBT as polymer (24), and/or cyclic PBT or CBT is chosen as monomer and polymerized to PBT as polymer (24), and/or

Laurolactam is chosen as the monomer and is polymerized to the polyamide PA12 as the polymer (24).

12. Device for 3D printing (30) and for carrying out a method (100) according to any one of claims 1 to 11, characterized in that - 16 - a first print head (31) for the print material (21), a second print head (32) for the filling material (22) and a device (50) for carrying out the abrasive process (115) are provided.

13. Device (30) according to claim 12, characterized in that the device (50) for carrying out the abrasive method (115) is a milling machine.