SE1450569A1 - A method and apparatus for geometric verification in the additive manufacture of three-dimensional objects - Google Patents

Description

40 at least one image of the next molten layer (n + 1) and then compare these with a corresponding plane in the 3D design model.

OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is to provide a 3D geometric verification of three-dimensional objects during ongoing additive manufacturing of the object, which at least partially overcomes the above problems.

This object is achieved by the method defined in claim 1.

A method for geometric control of three-dimensional objects during the ongoing manufacture of the objects, wherein the manufacturing process comprises that layer by layer is added based on a digital CAD model of the object, and that each layer is fused after the layer has been applied. The method is characterized in that it repeats for each layer: - one or more pictures of the current layer are taken, - a digital 3D disc model of the current layer is created based on the taken one or more pictures, - a digital 3D copy of the object that manufactured is created based on the 3D disk model of the present layer and 3D disk models of previous layers, and - the geometry of the object being manufactured is verified based on the 3D copy of the object being manufactured and the 3D design model of the object.

The idea is to design a built-in system for real-time verification of dimensions / geometries in additive manufacturing processes. The verification process is iterative, takes place in parallel with the production and is suitable for powder bed technologies as well as for “Blown Powder Technology.” The invention makes it possible to detect any deviations from the 3D design model / CAD file in real time.

The basic idea is to, for each layer applied, take one or more pictures and create a 3D disc model of the current layer. The disc models are then compiled into a volume; a 3D copy of the physical object. The 3D copy is continuously compared with the original design model / CAD file. The system can then, based on the permissible tolerances of the original CAD file, be used to check and ensure the quality with respect to the geometry of the physical object. Since the comparison of the two models is iterative, the geometry verification takes place in real time during the ongoing construction process.

The system can verify complex internal surfaces / geometries even on objects of high density material that cannot be verified using other available techniques.

The system would eliminate the normally subsequent extra lead time for geometry verification - when the object is ready, the verification is also completed. Real-time verification is not limited by the complexity of the object or the number of objects in the building chamber, an entire batch or even different objects can be analyzed simultaneously. Production of faulty objects is at least greatly avoided or reduced. The powder material is, for example, metal or polymer.

The digital 3D disk model of the current layer is created based on knowledge of the layer thickness. The thickness of the layer is, for example, known in advance and is equal to the distance the base plate moves downwards after each applied layer, or is determined based on the images taken.

According to an embodiment of the invention, the method comprises detecting one or more edges of the layer based on the captured images, and creating said digital 3D model of the present layer based on the detected edges of the object.

According to an embodiment of the invention, the taken images show the temperature of the layer, and the edge of the present layer is determined based on the temperature gradient in the image.

According to an embodiment of the invention, said taken images show the temperature of the layer, and one or more edges of the layer are detected based on the inflection point of the temperature gradient in the image. An advantage of using the inflection point to detect the edge is that the inflection point will remain at the same position regardless of the cooling process for a period of time long enough to take pictures.

According to one embodiment of the invention, one or more images are taken after the present layer has melted and before the next layer is applied to enable detection of the temperature gradient.

According to an embodiment of the invention, said taken images show the temperature of the layer, and a plurality of images are taken at different times during a cooling process of the layer, and said digital 3D disk model of the present layer is created based on said plurality of images of the present layer. Consequently, the images are taken at different temperatures.

According to an embodiment of the invention, the one or more images are taken by means of an IR camera which measures infrared light. An IR camera makes it possible to detect temperatures and is less sensitive to smoke and aerosols.

According to an embodiment of the invention, said one or more images are taken by means of a stereo camera, and preferably an IR stereo camera. By using a stereo camera, it is possible to obtain a very accurate measurement of the object being built. The high-precision stereo camera is used to create images of each layer and then using advanced large-scale 3D model real-time comparison / geometry verification. image analysis and a number of discs, one can be created for 40 The check is also made based on specified tolerances for the CAD file / design model. The specified tolerances are determined based on the 3D design model.

According to an embodiment of the invention, the method comprises: - a first 3D tolerance model with minimum dimensions is defined based on the 3D design model of the object and permissible minimum tolerances for the object, - a second 3D tolerance model with maximum dimensions is defined based on the 3D design model of the object and permissible maximum tolerances for the object, and - verifying that the dimensions of the 3D copy of the object being made are within the first and second tolerance models are performed. The geometry of the object being manufactured is verified on the basis of a 3D tolerance model with minimum dimensions and a 3D tolerance model with maximum dimensions. It is verified that the surfaces of the 3D copy lie between the surfaces of the two tolerance models.

According to one embodiment of the invention, the manufacturing process of the object is allowed to continue as long as the dimensions of the object being manufactured are within specified tolerances, and the manufacturing process is stopped automatically, if the specified tolerances cannot be maintained.

It is easy to see that the method according to the invention, which is defined in the appended set of method claims, is suitable for executing a computer program with instructions corresponding to the steps of the method according to the invention when running on a processor unit. Although not expressly stated in the claims, the invention comprises a computer program product in combination with the method according to the appended method claims.

This object is also achieved by the apparatus defined in claim 9.

The apparatus comprises: - one or more cameras arranged to take one or more pictures of each of the layers of the object during the manufacture of the object, - an image processing module configured to, during the manufacture of the object, create digital 3D disk models of the layers in the object based on the images taken, and to create a digital 3D copy of the object made from the 3D disk models created so far by the object, and - a verification model to check the geometry of the object made during the production of the object based on comparisons of 3D the copy of the object being manufactured and the 3D design model.

According to an embodiment of the invention, said one or more images are taken by means of an IR camera which measures infrared light. According to an embodiment of the invention, said one or more images are taken by means of a stereo camera, and preferably an IR stereo camera.

Brief Description of the Drawings The invention will now be explained in more detail by describing various embodiments of the invention and with reference to the accompanying figures.

Fig. 1 shows an example of a temperature gradient and inflection point in a layer after fusion of the layer.

Fig. 2 shows a flow chart of an example of a process flow comprising a method according to the invention.

Fig. 3 shows a block diagram of an example of an apparatus according to the invention.

Detailed Description of Preferred Embodiments of the Invention Creating Layer Images For each powder bed layer, an analysis cycle is performed. A thin layer of metal (or polymer) powder is applied on top of the previous layer. Heating with laser or electron beam starts and depending on the complexity of the current layer, one or more layer image analysis sequences are performed. The analysis sequences will be synchronized with the heating sequence. The edge of the current layer is characterized by a distinct temperature gradient and can thus be detected, ie the position of the edge is equal to the inflection point of the temperature gradient. See Figure 1. The inflection point is defined as the point where the second derivative of the temperature gradient changes sign.

The camera (s) must be placed inside together with the cabinet laser / electron beam equipment to obtain a high image quality on each layer after the fusion process. Therefore, the lenses will be exposed to metal vapor from the fusion process. IR light has the ability to penetrate a smoke-filled environment and thus IR stereo cameras are a suitable choice for this type of manufacturing process.

To avoid sublimation on the camera lens, flush it with an inert gas. To protect the camera's electronics from intense heat radiation during the same melting process, it is equipped with a mechanical shutter.

Depending on the complexity of the object, the choice of production method, powder material and other limitations that may arise during the development of the idea, a number of options in (s), IR stereo camera (s), conventional (visible light) stereo camera (s) and laser scanner (s) would ). high-speed image-based methods may be relevant including IR camera 40 To obtain a high quality image using IR cameras, the temperature gradient must be distinct and the heat loss to the surrounding powder bed must not be too great. Nevertheless, it is preferable that the entire layer is completely fused (ie the production cycle for the specific layer is completed). Multiple image processing may be necessary and must shorten the fusion process during the production of a layer (ie the fusion is synchronized to add pauses in laser or electron beam- must stop while the image is being created) To achieve process optimization, control over the melt pool is important. Often, lack of control over the melting pool is the cause of poor quality. During the image processing where the edge of the bearing is detected, information is also obtained about defects in the surface and melt pool quality. By quality in real time, the fusion sequence and can avoid too hot or cold areas in the next layer. verify surface adjustments are made to correct Create Disk Models There are different methods for determining the thickness of the layer image. An accurate 3D layer model, a disc model, can be created with stereo cameras to gain knowledge of the upper surface and edge of the previous layer and the surface and edge of the new top layer, and combine this with knowledge of the distance between two layers (the production table moves downwards with fixed step length, for example 20 μm).

One area of interest would be to test whether stereo cameras for IR images can not only detect the upper surface, but also the vertical surface of the current layer below the powder bed top and thus create an even more accurate copy. In any case, advanced image processing is necessary to achieve a high-quality digital copy for accurate and fast geometry verification. based on shall / should horizontal To determine the extent of the last applied layer put this in known. known. the temperature gradient be known. relation to the design model, should / should should / should the point of inflection, and that the temperature gradients be At least that temperature gradient be Preferably also the vertical Create 3D copy By using high-precision IR stereo camera to create copies of each layer in the powder bed after laser or electron beam fusion (depending on the choice of AM technology), a large number of disc models can be created and compiled into one volume, a 3D digital model (a 3D copy of the physical object). The method can also be called reverse engineering, but the advantage of using a 3D image of each layer is to get an electronic model that 40 reflects not only external but also internal geometries / surfaces as well as built-in defects, pores etc.

In parallel with the physical object being built, a 3D digital copy is created in real time.

Verify geometry To some extent, of course, the physical object will always deviate from the theoretical one. relation to the CAD file limitations / tolerances with regard to thermal expansion. With regard to the permissible What is interesting is how large the deviation is in given limitations / tolerances. Therefore, the design model / original must contain the tolerances, a 3D tolerance model with minimum dimensions must be created, as well as a 3D tolerance model with maximum dimensions. The geometry of the real-time 3D copy of the object must then fit between these two surfaces. By continuously comparing the real-time 3D copy with the maximum and minimum tolerance models, a continuous quality assurance of the construction process can be ensured.

Process control The quality assurance software can control the construction process and allow production to continue as long as the dimensions are within specified tolerances, and conversely automatically stop the production process if the specified tolerances cannot be maintained. Thus, the production of incorrect objects can be avoided and the cash action greatly reduced.

Further development could be to add intelligence to the system, an adaptive behavior based on knowledge of the results of previous production cycles, and thereby in time correct a construction process that is about to exceed given tolerances and thereby avoid production stoppages.

Process flow Figure 2 shows a flow chart of an example of a process flow including the method according to the invention. The process flow comprises the following steps: First filling of a box Powder preparation. Powder is added.

Preparation of stock. Powder leveling.

The camera shutters close.

Gas flushing of camera lenses starts.

Fusion of layers starts.

Fusion of layers stops.

The camera shutters open.

IR image (s) are created.

. Image analysis is performed: The edge of the layer is detected by tracing the inflection point of the gs? W? Ø? Wewwv temperature gradient. Any cavities are located. 11. A disc model is created based on layer image (s). 40 12. Disc models of each layer are compiled into a 3D copy of the physical object. 13. The 3D copy is compared with the original design file with regard to given tolerances. 14. Corrective feedback from the image analysis.

. The base plate in the building chamber is lowered a distance equal to the thickness of a layer. 16. Process steps 2-15 are repeated until the object is completed. 17. Camera shutter closes. 18. Ventilation of the building chamber starts. 19. Gas purge of lenses stops.

. The finished item is removed. 21. The process is repeated from step 1.

It is preferred that the execution of steps 10-14 be performed by a computational unit consisting of software code components, such as a computer program, consisting of instructions for performing the steps in the method, and hardware, such as a processor, memory and input / output devices, for to execute the instructions of the computer program.

Figure 3 shows an example of an apparatus for geometric control of three-dimensional objects.

The apparatus comprises a camera 30 arranged to take one or more pictures of the respective layers of the object during manufacture of the object. The camera 30 is, for example, a stereo IR camera. A stereo camera is a type of camera with two or more lenses with a separate image sensor or frame for each lens. This allows the camera to simulate human binocular vision and therefore provides an opportunity to capture three-dimensional images, a process called stereo photography. An IR camera, also called an infrared camera or thermal camera or a thermographic camera, is a device that creates an image based on infrared radiation, similar to an ordinary camera that creates an image with visible light. Instead of 450 to 750 nanometers for a visible-light camera, IR cameras operate with wavelengths as long as 14000 nm (14 μm) - The device further includes an image processing module 32 configured to, during the manufacture of the object, create digital 3D disk models of the object's layer based on the images taken, and to create a digital 3D copy of the object made based on the hitherto created 3D disk models of the object, and a verification module 34 configured to check the geometry of the object during the production of the object. objects made based on comparisons of the 3D copy of the object being made and the 3D design model of the object. The image processing module 32 and the verification module 34 are, for example, software modules running on a computer 36. However, the image processing module 32 and the verification module 34 can also be implemented by other processors such as programming logic, such as FPGA, an ASIC or a simple microprocessor. The output of the verification module 34 may be a control signal or a command to the manufacturing process to allow the manufacturing process to continue as long as the dimensions of the object being manufactured are within specified tolerances, and to automatically stop the manufacturing process if the specified tolerances cannot be maintained.

The present invention is not limited to the embodiments shown, but may be varied and modified within the scope of the following claims. For example, one or more visible light cameras can be used to obtain images on the surface of the fused layer structure as well as the surrounding powder structure, and then the image processing detects the difference in surface structure and thus the edge.

Claims (10)

10 15 20 25 30 35 40 10 Patent claims A method for geometric verification of three-dimensional objects during the manufacture of the objects, the manufacturing process comprising adding successive layers based on a digital 3D design model of the object, and melting each layer after the layer has been applied, characterized in that the method comprises repeated times for each layer: - one or more images of the current layer are taken, - a digital 3D disk model of the current layer is created based on the taken one or more images, - a digital 3D copy of the object being created is created based on 3D the disk model of the present layer and 3D disk models of previous layers, and - the geometry of the object being manufactured is verified based on the 3D copy of the object being manufactured and the 3D design model of the object. The method of claim 1, wherein the method comprises detecting one or more edges of the layer based on the captured images, and said digital šD disk model of the layer being created based on the detected edges of the object. The method of claim 2, wherein said images taken show the temperature of the layer, and the edge (s) of the layer are detected based on the inflection point of the temperature gradient in the image. A method according to any one of the preceding claims, wherein said taken images show the temperature of the layer, and a plurality of images are taken at different times during a cooling process of the layer, and said digital 3D disk model of the present layer is created based on said plurality of images of the layer. present stock. A method according to any one of the preceding claims, wherein said one or more images are taken by means of an IR camera arranged to measure infrared light. A method according to any one of the preceding claims, wherein said images are taken by means of a stereo camera, and preferably by using an IR stereo camera. A method according to any one of the preceding claims, wherein the method comprises: - a first 3D tolerance model with minimum dimensions defined based on the 3D design model of the object and object, - a second 3D tolerance model with maximum dimensions defined based on the 3D object and allowable minimum tolerances for the design model of maximum allowable tolerances for the object, and 10 15 20 25 11 - verification that the dimensions of the 3D copy of the object being manufactured are within the first and second tolerance model is performed. A method according to any one of the preceding claims, wherein the manufacturing process of the object is allowed to continue as long as the dimensions of the object being manufactured are within specified tolerances, and the manufacturing process is stopped automatically, if the specified tolerances cannot be contained. An apparatus for geometric verification of three-dimensional objects during the manufacture of the objects, the manufacturing process comprising successively adding powder layers based on a digital 3D design model of the object, and melting each of the layers after it has been added, characterized in that the apparatus comprises: - one or more cameras (30) arranged to take one or more pictures of each of the object's layers during the manufacture of the object, - an image processing module (32) configured to create digital 3D disk models of the layers during the manufacture of the object of the object based on the images taken, and to create a digital 3D copy of the object made from hitherto created 3D disk models of the object, and - a verification module (34) configured to verify the geometry of the object being made during the manufacture of the object. based on the 3D copy of the object being manufactured and the šD design model of the object. The apparatus of claim 9, wherein said camera is an IR camera adapted to measure infrared light, and preferably an IR stereo camera.