METHOD AND APPARATUS FOR MONITORING A QUALITY OF AN OBJECT OF A 3D-PRINT-JOB SERIES OF IDENTICAL OBJECTS

Abstract

An apparatus and method for monitoring a quality of an object of a 3D-print job series of identical objects, each object built from a multitude of stacked 2D-layers printed by a 3D-printer in an additive manufacturing process, including: determining a layer quality indicator of a currently printed layer of an object, comparing the determined layer quality indicator of the currently printed layer with a predetermined lower confidence limit of the layer, the predetermined lower confidence limit being calculated depending on layer quality indicators of previously completely manufactured objects complying with predefined quality requirements, and generating a warning signal, if the layer quality indicator of the currently printed layer has a value equal or lower than the lower quality limit is provided.

Claims

1. A method for monitoring a quality of an object of a 3D-print job series of identical objects, each object built from a multitude of stacked 2D-layers printed by a 3D-printer in an additive manufacturing process, the method comprising: determining a layer quality indicator of a currently printed layer of the object; comparing the layer quality indicator of the currently printed layer with a predetermined lower confidence limit of a corresponding layer, the predetermined lower confidence limit being calculated depending on layer quality indicators of previously completely manufactured objects complying with predefined quality requirements; and generating a warning signal, if the layer quality indicator of the currently printed layer has a value equal or lower than a lower quality limit; wherein the layer quality indicator is determined by machine learning means.

2. The method according to claim 1, wherein the lower confidence limit is determined by: for each object out of a subset of objects of the print job series, determining a layer quality indicator for each printed layer of an object; determining an object quality indicator for the completely manufactured object based on the layer quality indicators of all printed layers of the completely manufactured objects; and calculating a lower confidence limit for each layer depending on the layer quality indicators of those objects having an object quality indicator complying with predefined quality requirements.

3. The method according to claim 1, wherein at least one of the completely manufactured objects of the subset is inspected by material analytic means to confirm the calculated object quality indicator meeting the predefined quality requirements.

4. The method according to claim 1, wherein the lower confidence limit is re-calculated taking into account the layer quality indicators of each further completely manufactured object with an object quality indication complying with the pre-defined quality requirements.

5. The method according to claim 1, wherein an upper confidence limit and the lower confidence limit are provided by a standard deviation calculated depending on the layer quality indicator for each layer of completely manufactured objects complying with the predefined quality requirements of the object.

6. The method according to claim 1, wherein determining at least one fault detection and prediction value for each layer, each fault detection and prediction value depending on data of different data sources of the present additive manufacturing process, and determining the layer quality indicator depending on all fault detection and prediction results.

7. The method according to claim 6, wherein data sources are at least one of Computer Aided Design model of the object, images of the additive manufacturing process-, sensor data from the additive manufacturing process or settings of the additive manufacturing process.

8. The method according to claim 1, wherein a warning signal is generated, if layer quality indicators of subsequent layers show a common trend towards the lower confidence limit.

9. The method according to claim 1, wherein settings of the additive manufacturing process are automatically adjusted based on the generated warning signal.

10. An apparatus for monitoring a quality of an object of a 3D-print job series of same objects, each object built from a multitude of stacked 2D-layers printed by a 3D-printer in an additive manufacturing process, the apparatus comprising: at least one first processor configured to determine a layer quality indicator of a currently printed layer of an object, and comparing the determined layer quality indicator of the currently printed layer with a predetermined lower confidence limit of the corresponding layer, the predetermined lower confidence limit being calculated depending on layer quality indicators of previously completely manufactured objects complying with predefined quality requirements, and a signal generating unit configured to generate a warning signal, if the layer quality indicator of the currently printed layer has a value equal or lower than the lower quality limit, wherein the layer quality indicator determined by machine learning means.

11. The apparatus according to claim 10, comprising at least one second processor configured to determine the lower confidence limit by: for each object out of a subset of objects of the print job series, determining a layer quality indicator for each printed layer of an object; determining an object quality indicator for the completely manufactured object based on the layer quality indicators of all printed layers of the completely manufactured object; and calculating a lower confidence limit for each layer depending on the layer quality indicators of those objects having an object quality indicator complying with predefined quality requirements.

12. The apparatus according to claim 11, comprising an input unit configured to receive a confirmed object quality indicator of at least one of the completely manufactured objects of the subset from a material analytic means and/or to receive data of at least one of Computer Aided Design model of the object, image data of the additive manufacturing process, sensor data and settings of the additive manufacturing process.

13. The apparatus according to claim 10 comprising a output unit configured to transmit warning signals to the 3D-printer.

14. A computer program product, comprising a computer readable hardware storage device having computer readable program code stored therein, said program code executable by a processor of a computer system to implement the method of claim 1.

Description

BRIEF DESCRIPTION

[0039] some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0040] FIG. 1 depicts a flow diagram of an embodiment of a method;

[0041] FIG. 2 depicts a schematic diagram of a hierarchy and systematic determination of the layer quality indictors;

[0042] FIG. 3 depicts a second embodiment of the method with a training phase;

[0043] FIG. 4 depicts an example of layer quality indicators for all layers of an object of the print-job series;

[0044] FIG. 5 depicts an upper and a lower confidence limit for all layers of an object of the print-job series;

[0045] FIG. 6 depicts an embodiment of a layer quality indicator determined for a currently printed object in relation to the upper and lower confidence limit previously determined;

[0046] FIG. 7 depicts an embodiment of all layer quality indicators of a completely manufactured object with a trend analysis evaluation; and

[0047] FIG. 8 depicts an embodiment of the inventive apparatus connected to a 3D-printer in schematic view.

DETAILED DESCRIPTION

[0048] Additive Manufacturing is a production process wherein 3-dimensional (3D) objects are produces by adding and fusing layers of material on top of each other, in contrast to common mechanical production like e.g. milling. The process is generally called additive manufacturing process or 3D-printing process. The production is based on digital 3D-models of the physical object and is therefore computer controlled. This so called computer-aided design, short CAD, is vector-based, since all 3D-objects can be characterized by using lines and points. A digital 3D-model, which is saved in a CAD-file, is converted into thin slices, the so called layers. The layer data are sent to the 3D-printer, which prints layer by layer on top of each other and that manufactures the 3D-object.

[0049] The general idea of the monitoring method, shown in FIG. 1, is to determine a layer quality indicator QI(Li), see step S1, which is calculated for each printed layer Li of a given CAD-model of an object automatically during the current printing print-job and compare it to a predefined lower confidence limit LCL(Li) of the corresponding layer Li, see step S2, to allow early measures in the printing process by generating a warning signal, if the current layer quality indicator is equal or below a lower confidence limit, see step S3. The layer quality indicator is determined by the same machine learning functions and is used during the training phase S0. The predetermined lower confidence limit LCL(Li) is calculated, see step S0, depending on layer quality indicators determined for all layers of previously completely manufactured objects complying with predefined quality requirements.

[0050] The training process step S0 is shown in detail in FIG. 3 and explained referring to a object 300 schematically depicted in FIG. 7. During the training step the lower confidence limit LCL is determined for each object out of a subset of more than one objects of the print-job series. For each printed layer L1, . . . , Ln of an object of this subset a layer quality indicator QI(L1), . . . QI(Ln) is determined, see step LS1. Subsequently an object quality indicator is determined for the completely manufactured object based on the layer quality indicators QI(L1), . . . QI(Ln) of all printed layers (L1, . . . , Ln) of the completely manufactured object, see step LS2. An upper confidence limit UCL(L1), . . . , UCL(Ln) and a lower confidence limit LCL(L1), . . . , LCL(Ln) is calculated for each layer L1, . . . , Ln depending on the layer quality indicators of those objects having an object quality indicator complying with predefined quality requirements, see step LS3.

[0051] The method ends in step S4, if all layers L1, . . . , Ln of the object 300 are printed and layer quality indicators QI(L1), . . . QI(Ln) are determined and evaluated. The method ends in step S5, if the print-job of the object is stopped before all layers L1, . . . , Ln are printed, e.g. as a consequence of a previous warning signal transmitted to the 3D-printer.

[0052] The printing process of each further object of a 3D-print-job series corresponding to the same CAD-model can now be evaluated in comparison to the previously determined sequences of layer quality indicators determined either in a dedicated training phase or determined continuously taking into account further sequence of layer quality indicators of a completely manufactured compliant object complying to predefined quality requirements of the object.

[0053] The layer quality indicator is determined in a two step approach, as shown in FIG. 2, by machine learning techniques, e.g. random forests, neural networks, Markov-Models or Gaussian classification. At least one, or several, detection and prediction values DP1, DP2, DP3 are calculated by a machine learning method based on different data sources. Data sources are e.g. the CAD-model of the object DS1, images from a power bed camera D2, time line data DS3 of sensors e.g. detecting a temperature and pressure of a melt pool or further process parameters D4 of the printing process. The data DS1, DS2, DS3 and DS4 of different data sources are also called multimodal data. Examples for multimodalities are powder-bed images, Meltpool images, time series sensor data and CAD data. The detection and prediction value is an indicator that a specific layer causes issues for the overall printed object. The usage of different multimodal data increases the reliability for detection of different type of issues or errors during the manufacturing process.

[0054] In a second step the detection and prediction results DP1, DP2, DP3 are aggregated into one value which is the layer quality indicator QI.

[0055] The layer quality indicator is a numerical value providing a probability for a layer contributing to a completely manufactured object complying with a predefined required quality. The numerical value can provide a percentage in the range between 0 and 100 or can be between the value 0 to 1 or normalized to any other interval. The layer quality indicator QI(Li) can be aggregated depending on the single detection and prediction values DP1(Li), DP2(Li), DP3(Li) of the layer Li, e.g. by taking a minimum value of all detection and prediction values DP1(Li), DP2(Li), DP3(Li) or by multiplying weighted detection prediction values or an addition of weighted detection and prediction results, e.g. providing an aggregated value of all detection and prediction values DP1(Li), DP2(Li), DP3(Li).

[0056] A detection and prediction value DP(Li) as well as the layer quality indicator QI(Li) shown in FIG. 2 as a graph are defined by the equation:

DP.sub.Li=(DS1.sub.L1,DS2.sub.Li, . . . ,DS4.sub.Ln)

[0057] The layer quality indicator of a layer Li is

QI(Li)=(DP1.sub.Li, . . . ,DP3.sub.Li).

[0058] The detection and prediction values DP1, . . . , DP3 and the layer quality indicator QI are calculated for each layer of an object of the print-job series.

[0059] FIG. 4 shows a sequence 10 of layer quality indicators for all layers L1, . . . , Ln one object 300 of the 3D-print-job series. For each of the layers L1, . . . , Ln one layer quality indicator QI(L1), . . . QI(Ln) is determined and shown as a function of the layers L of an object. As an example the layer quality indicator QI(Li) of a Layer Li is marked in FIG. 4.

[0060] A graph of layer quality indicator QI(L1), . . . QI(Ln) of all layers ordered by consecutive layers, also called a sequence of layer quality indicators and shown in FIG. 4, can be evaluated for the first printed object of a given CAD-model and every following object in new print-job of this print-job series. During the training phase a subset of objects of the print-job series these layer quality indicator is determined for each printed layer of an object. For the completely manufactured object an object quality indicator is determined based on the layer quality indicator of all printed layers after a print-job is finished. Additionally for the completely manufactured objects of the subset an evaluation of the quality of the object is performed by non-destructive inspection means to evaluate if the object needs the required features and therefore the required quality. If this is the case the sequence of layer quality indicator 10 as shown in FIG. 4 is used for calculating an upper and lower confidence limit.

[0061] For all these layer quality indicator sequences 10 of objects complying with the quality requirements a standard deviation of the quality indicator is calculated. E.g. the upper and lower quality limit is evaluated by adding or subtracting one or several times the standard deviation to the mean value of all considered layer quality indicator graphs for each individual layer. If a determined layer quality indicator QI(Li) for layer Li lies in a value range between the upper confidence layer UCL and the lower confidence limit LCL, the quality of the considered layer leads with a certain confidence to an completely manufactured object complying with the quality requirements.

[0062] The more objects of the 3D-print-job series are used for training the learning function to evaluate the detection and prediction results as higher is the probability that the detection and prediction value DP1, DP2, DP3 is correct.

[0063] Also after the training phase the upper and lower confidence limit, UCL and LCL, can be refined by evaluating a mean layer quality on all layer quality indicator sequences so far determined complying with the predefined quality requirements. This means that each layer quality indicator sequence of a completely manufactured object within determined object quality indicator complying to the quality requirements is included into the sample of considered layer quality indicator sequences. Accordingly the upper confidence limit UCL and the lower confidence limit LCL can be recalculated depending on the new number of layer quality indicator sequences complying to the predefined quality requirements.

[0064] During a current printing process of a layer Li the layer quality indicator QI(Li) is determined according to step S1 as shown in FIG. 1 and FIG. 3. In a further step S2 the determined layer quality indicator QI(Li) of the currently printed layer is compared with a predetermined lower confidence layer LCL(Li) of the corresponding layer Li. If the layer quality indicator QI(Li) is above the lower confidence limit LCL the value is stored and the same process is performed for the next layer. If the layer quality indicator is equal or below the lower confidence limit a warning signal is generated, see step S3, and transmitted to the additive manufacturing process. Such a sequence of quality indicators 11 is shown in FIG. 6. Here the layer quality indicator QI(L1, . . . , Li1) of the layers L1, . . . , Li1, marked with reference sign 11, show the value between the upper and the lower confidence layer UCL, LCL. At layer Li the layer quality indicator QI(li) is lower than the lower confidence layer LCL(Li) and accordingly a warning signal is generated.

[0065] In case the determined layer quality indicator Li shows a value above the upper confidence layer a warning signal can also be generated. In this case the warning signal can be used to adapt the settings of the manufacturing process e.g. by lowering the amount of material powder for this layer as this high confident layer indicates that the present settings for the layer can be optimized e.g. to save material.

[0066] Further a trend analysis can be performed taking into account not only the layer quality indicator QI(Li) of the currently printed layer Li, but also a subset of preceding layer quality indicators 12 of preceding layers, see FIG. 7. If the layer quality indicators of the subset of layers already show a gradient value below a certain value a warning signal will also be generated.

[0067] The warning value can trigger different actions. E.g. parameter settings of the additive manufacturing process can be adjusted. Especially early warnings from a trend analysis may lead to an adaption of the setting of the 3D-printer. This can lead to a healing of an issue occurred in layer Li by subsequent layers printed with adapted settings. Therefore a self-healing process without any interaction of an operator can be achieved. The layer quality is continuously monitored in this way until the last layer of the object is printed and a completely manufactured object is created. For each of these completely manufactured objects the sequence of layer quality indicator values is determined and stored.

[0068] Besides an automatic adaption of settings, the warning signal can be sent to a supervision monitor to inform an operator, that the print process for each a boundary conditions if no interaction will be started.

[0069] A monitoring apparatus performing the described method is shown in FIG. 8. The monitoring apparatus 100 comprises a first processor 110 configured to determine a layer quality indicator QI of a currently printed layer. The first processor 110 is also configured to compare the determined layer quality indicator QI(Li) of the currently printed layer Li with a predetermined lower confidence limit LCL of the corresponding layer evaluated during the training phase S0.

[0070] The monitoring apparatus comprises further at least a second processor 130 configured to perform the training phase, which is to perform the steps LS1, LS2 and LS3 of the training phase as serial as shown in FIG. 3.

[0071] Further on a signal generating unit 120 is included and configured to generate the warning signal. Further on an input unit 140 is configured to receive data from the different data sources, e.g. a camera 310 or a sensor 320 of a 3D-printer 200. The input unit 140 is also configured to receive data from a material analytic means 400 which provide measured information on the object quality indicator based on a non-destructive material analytic method. The material inspection means 400 may provide information to the monitoring apparatus 100 via the 3D-printer 200 or it might be connected directly to monitoring apparatus 100. The 3D-printer 200 shows schematically printed layer L1, . . . , Ln, which form a completely manufactured object 300.

[0072] All methods and method steps can be implemented by corresponding means which are adapted for performing the respective method steps. All functions provided by particular means can be a method step of the method.

[0073] The scope of protection is given by the claims and not restricted by features discussed and the description as shown in the figures.

[0074] The present invention is not limited to the described example. The present invention also comprises all combinations of any of the described or depicted features.

[0075] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0076] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.