Patent Publication Number: US-2022212413-A1

Title: Method of creating a certified digital part file

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of creating a certified digital part file. 
     More particularly, the invention relates to a method of creating a certified digital part file capable of producing a certified part using a 3D printer. 
     BACKGROUND 
     The rise and proliferation of 3D printers has had a marked disruptive effect on the manufacturing industry globally and is progressively leading to the decentralisation of manufacturing. 
     3D printers enable businesses and consumers to fabricate a wide range of objects rapidly and cost effectively. 3D printers are now capable of producing increasingly complex objects, including in respect to geometrical complexity and materials used. It is expected that consumers will soon be able to create spare parts for complex machines, and even functional consumer products, in their own home. 
     A problem is evident where a product is designed for a particular requirement, and said product is replicated in shape alone, with material properties not being replicated. Where the product is required to be fit for purpose, a product replicated by 3D printing is difficult to certify as fit for purpose. 
     One example of such a problem is where a replacement component for a large scale industrial machine is required. The component to be replaced may be of a particular geometry and material, but a 3D printed component in a similar material does not necessarily have the required material properties to be fit for purpose. 
     Parts produced by conventional subtractive manufacturing means, for example machining a forged or casted part, are typically mass produced and certification of parts is carried out by ensuring the quality across a product batch. 
     For example samples of the materials used may be tested, possibly by destructive testing, to ensure the material properties are to a sufficient standard. 
     The parts may be produced using a repeatable process, so that testing of some samples of the parts may be sufficient to certify the quality of the batch as a whole. 
     The certified mass produced parts may then be stored and shipped upon demand. 
     Facilities in remote locations may therefore store components that are known to be prone to failure, or that are known to cause significant down time due to failure, in an effort to reduce the risks of costly down time due to such failures. 
     The storage and associated inventory of these components raises problems which could be avoided if such storage were not required. 
     This ability to ‘print’ spare parts for complex machinery enables a remote location to print a required replacement component without having to wait for an order from a supplier to be delivered, resulting in saved time and therefore reduced costs due to down time. 
     The problem introduced by such a system is with regards to certification of the parts produced, which may appear substantially identical to the part to be replaced, but have no means to determine whether the part is fit for purpose, or certified. 
     It is known that various factors can influence a 3D printing process, and variations in environmental conditions or machine parameters for example, can have a detrimental effect on the part produced, to the extent that it may be unfit for purpose. 
     Anomalies may be present during the production process, for example porosity, thermal or chemical imbalances. 
     Whilst it may be possible for a 3D printer to ascertain that an anomaly has occurred in some cases, many anomalies go undetected and imperfections resulting from anomalies are typically detected in post-production testing, such anomalies can adversely affect the properties of a part, making it unsuitable for use. 
     This ability to ‘print’ spare parts for complex machinery also poses a threat to original equipment manufacturers (so-called OEMs) and presents a corresponding risk to consumers. OEMs typically license only particular accredited persons and businesses the right to manufacturer and/or sell certified spare parts for equipment that they produce. By purchasing certified parts, consumers are guaranteed a certain level of quality and workmanship. 
     3D printing has made it much easier for unaccredited persons to create and sell spare parts without a licence from the relevant OEMs. Consumers can also attempt to print their own spare parts for machinery that they own. For industrial and mechanical equipment, such as automobiles, using uncertified spare parts of substandard quality can have catastrophic and, in some cases, fatal consequences. 
     A challenge faced by both OEM&#39;s and printer manufacturers is the capability of 3D printing a part which is certified for use, without the requirement for testing post production. That is therefore retaining the benefits of being able to produce locally and on-demand, as opposed to requesting a part delivered from a remote location. 
     Known digital files are unable to produce certified parts, and 3D printed parts produced using digital files presently require post production testing to be declared fit for use, which is not conducive to the aim of producing replacement parts at short notice. 
     Even where post production testing is used to verify part quality, the testing is obviously limited to non-destructive testing as the part is required for use, such limitations make it impossible to verify some aspects of a 3D printed part. 
     The present invention attempts to overcome at least in part the aforementioned disadvantages of previous digital part files and methods of printing a certified part using a digital part file. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a method of creating a certified digital part file, the method comprising the following steps:
         a. using a 3D printing apparatus and a digital part file to print an initial test part in accordance with a print process, the digital part file comprising initial geometry and initial parameters, wherein an initial print data set is generated during the print process, and wherein the initial print data set comprises print conditions that correspond to locations on the initial test part during the print process,   b. testing the initial test part to detect one or more anomalies and type and locations of each anomaly on the initial test part,   c. referencing each of the anomalies to the print conditions in the initial print data set corresponding to the location of each anomaly, to generate an anomaly data set, wherein the anomaly data set comprises the type and location of each of the anomalies and the relevant print conditions corresponding to each of the anomalies,   d. referring to the anomaly dataset and generating modified parameters to prevent similar anomalies reoccurring in subsequent prints,   e. if necessary, generating modified geometry to prevent the anomalies reoccurring in subsequent prints,   f. generating a check data set derived from the anomaly dataset during preceding steps a. through to e. of the method, wherein the check data set comprises criteria defining acceptable and non-acceptable levels of anomalies for successful printing of the finished part,   g. generating a revised digital part file comprising the initial geometry or, if applicable, modified geometry, the modified parameters and the check data set,   h. using the 3D printing apparatus and the revised digital part file to print a further test part in accordance with a print process, wherein a further print data set is generated during the print process, wherein the further print data set comprises further print conditions that correspond to locations on the further test part during the print process, and wherein the print process is carried out in accordance with the check data set, to ensure that any anomalies detected in the initial test part are not present in the further test part, or are only present within acceptable levels,   i. repeating steps b. through to h. using the further test part, further print data set and further print conditions, and any subsequent iterations of each, until a successful test part is printed in which no anomalies beyond an acceptable level are detected during testing at step b, wherein the final digital part file, used to print the successful test part, comprises the initial geometry or final modified geometry if applicable, final modified parameters and the check data set, and whereby the final digital part file constitutes the certified digital part file.       

     Preferably, the method of creating a certified digital part file further comprises the following steps after the successful test part has been produced at step i.
         j. Printing multiple identical successful test parts, which are subsequently tested to confirm that no non-acceptable anomalies are present, and therefore verify the repeatability of the process, and where no non-acceptable anomalies are detected, the associated final digital part file constitutes the certified digital part file.   k. If anomalies at a level greater than acceptable are detected in one or more of the multiple identical parts, steps c. through to j. are repeated, until all multiple identical successful test parts are tested and no non-acceptable anomalies are detected, at which point the final digital part file, associated with the multiple identical successful test parts, constitutes the certified digital part file.       

     Preferably, the check data set comprises material and/or chemical properties of a finished part to be printed. 
     Preferably, the check data set further comprises go and no-go conditions, wherein the go and no-go conditions relate to, respectively, acceptable and non-acceptable criteria for successful printing of the finished part. 
     Preferably, the print conditions are measured by sensors of the 3D printing apparatus. 
     In accordance with another aspect of the present invention there is provided a certified digital part file for a 3D printing apparatus, the certified digital part file comprising geometry and certified parameters, wherein the certified parameters are derived from testing, wherein testing involves comparison of test parts printed using test parameters against corresponding test print data sets to determine a portion of the test parameters which has resulted in an anomaly detected in the test part, and modification of the test parameters to prevent similar anomalies being repeated. 
     Preferably certified parameters are derived from iterative testing of multiple test prints and corresponding test print data sets. 
     Preferably the print conditions are measured by sensors of the 3D printing apparatus. 
     Geometry may be modified in addition to parameters. 
     In accordance with another aspect of the present invention, there is provided a method of printing a certified part using a certified digital part file, the method comprising the following steps:
         a. Using a 3D printing apparatus and a certified digital part file to print a part in accordance with a print process, the certified digital part file comprising geometry, parameters and a check data set, the check data set comprising criteria defining acceptable and non-acceptable levels of anomalies for successful printing of the certified part,   b. During the print process, comparing print data generated by the apparatus with the check data set to indicate where a part of the printing process contains a non-acceptable anomaly.   c. Where a non-acceptable anomaly is detected, using the apparatus to recover the print process by taking corrective action if possible to remove the anomaly or reduce the anomaly to an acceptable level or, where the print process is not recoverable, abandoning the print process.       

     Preferably, the criteria defining acceptable and non-acceptable levels of anomalies are derived from externals standards. 
     In accordance with another aspect of the present invention, there is provided a method of printing a certified part using a 3D printing apparatus and a knowledge base, wherein the knowledge base comprises anomaly patterns derived from a plurality of historical anomaly datasets, and a check data set comprising criteria defining acceptable limits for different types of anomalies, the method comprising the following steps:
         a. Using a 3D printing apparatus to print a certified part, wherein the 3D printing apparatus is configured to recognise an anomaly pattern, and to therefore detect when an anomaly is being printed,   b. Checking the anomaly against the check data set to determine whether the anomaly is within acceptable limits, and where a non-acceptable anomaly is detected, recovering the print process by taking corrective action if possible to remove the anomaly or reduce the anomaly to an acceptable level or, where the print process is not recoverable, abandoning the print process.       

     Preferably, anomaly datasets are added to a master anomaly dataset, wherein the master anomaly data set comprises aggregated anomaly data collected from all other 3D printing apparatuses that have used the method to create certified digital part files. 
     More preferably, the master anomaly dataset becomes a knowledge base, to provide a means to identify anomalies at any location during any printing process. 
     Throughout the description, the following numbering convention shall be adhered to:
           10 —initial digital part file     11 —further digital part file     15 —certified digital part file     20 —printing apparatus     30 —initial test part     31 —further test part     35 —successful test part     40 —initial geometry     41 —modified geometry     45 —final modified geometry     50 —initial parameters     51 —modified parameters     55 —final modified parameters     60 —initial print data set     61 —further print data set     65 —final print data     70 —print conditions     71 —further print conditions     80 —anomalies     85 —check data set     90 —anomaly dataset     91 —aggregated anomaly dataset     95 —anomaly patterns     100 —master data file     120 —knowledge base       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a flow diagram depicting the method of creating a certified digital part file  15  according to an embodiment of the present invention. 
         FIG. 2  is a flow diagram depicting the method of creating a certified digital part file  15  according to an embodiment of the present invention, comprising additional steps to verify repeatability. 
         FIG. 3  is a flow diagram depicting the method of creating a certified part  38  using a certified digital part file  15  according to an embodiment of the present invention, comprising enhanced steps to provide a means of certifying a printing process. 
         FIG. 4  is a flow diagram depicting the method of creating a certified part  39  according to an embodiment of the present invention, comprising additional and enhanced steps to assist with anomaly detection during a printing process. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , there is shown a method of creating a certified digital part file  15 , comprising the following steps;
         a. using a 3D printing apparatus  20  and a digital part file  10  to print an initial test part  30  in accordance with a print process, the digital part file  10  comprising initial geometry  40  and initial parameters  50 , wherein an initial print data set  60  is generated during the print process, and wherein the initial print data set  60  comprises print conditions  70  that correspond to locations on the initial test part  30  during the print process,   b. testing the initial test part  30  to detect one or more anomalies  80  and type and locations of each anomaly  80  on the initial test part  30 ,   c. referencing each of the anomalies  80  to the print conditions  70  in the initial print data set  60  corresponding to the location of each anomaly  80 , to generate an anomaly data set  90 , wherein the anomaly data set  90  comprises the type and location of each of the anomalies  80  and the relevant print conditions  70  corresponding to each of the anomalies  80 ,   d. referring to the anomaly dataset  90  and generating modified parameters  51  to prevent similar anomalies  80  reoccurring in subsequent prints,   e. if necessary, generating modified geometry  41  to prevent the anomalies  80  reoccurring in subsequent prints,   f. generating a check data set  85  derived from the anomaly dataset  90  during preceding steps a. through to e. of the method, wherein the check data set  85  comprises criteria defining acceptable and non-acceptable levels of anomalies  80  for successful printing of the finished part,   g. generating a revised digital part file  11  comprising the initial geometry  40  or, if applicable, modified geometry  41 , the modified parameters  51  and the check data set  85 ,   h. using the 3D printing apparatus  20  and the revised digital part file  11  to print a further test part  31  in accordance with a print process, wherein a further print data set  61  is generated during the print process, wherein the further print data set  61  comprises further print conditions  71  that correspond to locations on the further test part  31  during the print process, and wherein the print process is carried out in accordance with the check data set  85 , to ensure that any anomalies  80  detected in the initial test part  30  are not present in the further test part  31 , or are only present within acceptable levels,   i. repeating steps b. through to h. using the further test part  31 , further print data set  61  and further print conditions  71 , and subsequent iterations of each, until a successful test part  35  is printed in which no anomalies  80  beyond an acceptable level are detected during testing at step b, wherein the final digital part file  15 , used to print the successful test part  35 , comprises the initial geometry  40  or final modified geometry  45  if applicable, final modified parameters  55  and the check data set  85 , and whereby the final digital part file  15  constitutes the certified digital part file  15 .       

     To create a certified digital part file  10 , an initial test part  30  may be printed using the selected material (or materials) with the 3D printing apparatus  20 . 
     The initial test part  30  is printed using initial geometry  40  and initial parameters  50  determined as being appropriate for the desired part  30 . 
     The initial parameters  50  may include, but are not limited to, the travel speed of the energy beam, the power, intensity and focus of the energy beam, the rate of powder deposition and the preheating temperature of deposited powder, the powder bed and the baseplate of the 3D printing apparatus  20 . 
     The initial parameters  50  may also include material and/or desired chemical properties of the finished part. 
     Further examples of initial parameters  50  may include, but are not limited to, backing gas, oxygen level, vacuum or pressure level, lasing strategy, chemistry, layer height&#39;s, cooling profile after a print, atmosphere for cooling and post print treatments. 
     The initial test part  30  may be printed using initial geometry  40  and initial parameters  50 , but further in accordance with a check data set  85 . The check data set  85  in this case may be limited to criteria relevant to anomalies of a type which are measureable without testing of the initial test part  30 . 
     During the initial print process, the 3D printing apparatus  20  captures the initial print conditions  70 , to create an initial print data set  60 . 
     Print conditions  70  may be captured from the sensors or recording devices of the 3D printing apparatus  20 . 
     The initial print data set  60  may include the measurements of features of the initial test part produced  30 , and the conditions under which the initial test part  30  was printed. Measurements and conditions may include, for example, digital images of the initial test part  30  from multiple viewing positions, thermal, chemical and structural features of the initial test part  30 , and physical states, changes and conditions relating to the printing process and resultant initial test part  30 , such as oxygen levels, gas pressures and gas flows and dissipation of thermal energy. 
     The sensors and recording devices used to obtain the measurements and conditions may include high speed and resolution optical (and thermal) digital cameras and other sensors configured to obtain accurate readings during the printing process. 
     The initial print data set  60  may include data on every layer printed and the times at which the layers (and parts of the layers) were printed. Advantageously, this provides that a particular point in the print process can be identified, and data related to the initial print conditions  70  at the particular point in time and location can be retrieved. 
     The initial print data set  60  may include an image of each layer for example, which may assist with identifying voids or other imperfections on the initial test part  30  such as raised features or pockets. 
     The initial test part  30  produced as a result of the initial print process is then tested to ascertain whether it meets the requirements and is fit for purpose. 
     Tests which may be undertaken include destructive test and non-destructive tests, examples of tests may be x-ray, dye penetrant inspection and structural load testing, CT scanning, topological scanning, ultrasonic scanning and any other tests as required or deemed necessary 
     Tests may be performed by a third party and may be undertaken in compliance with appropriate standards. 
     The test results may identify any anomalies  80  within the initial test part  30 . These anomalies  80  may include any feature or aspect of the initial test part  30  that is present or missing that causes the initial test part  30  to fail the applicable tests. For example the initial test part  30  may not exhibit a particular characteristic, feature or property that it is required to have, as identified during the tests. 
     The initial test part  30 , and more particularly any anomalies  80  found, are then compared against the initial print data set  60 , and the corresponding portion of the initial print data set  60  is used to determine the initial print conditions  70  which resulted in the anomaly  80 . 
     For example, the anomaly  80  may be a void at a particular location on a particular layer. Review of the initial print data set  60  at the particular point on the particular layer provides the initial print conditions  70  which most likely resulted in the void being produced. 
     Each anomaly  80  that is identified and referenced to print conditions  70  at a particular portion of the initial print data set  60 , the cross referenced information forms an anomaly dataset  90 . 
     The anomaly data set  90 , therefore, identifies the type, nature, magnitude and possible location of each of the anomalies  80  identified, and the relevant print conditions  70  that are considered to lead to the anomalies  80  occurring. 
     The complete anomaly data set  90  that is formed may then be added to a knowledge database  120 . The knowledge database  120  comprises aggregated anomaly datasets  90  that may have been collected from any other 3D printing apparatuses that have also been used to create certified digital part files  15  using the method. 
     Using the anomaly dataset  90 , modified parameters  51  may be defined to prevent the anomalies  80  (or similar anomalies) occurring during a subsequent print process. 
     Additionally parameters  51  may be modified at a specific location during the print to eliminate anomalies  80  typically identified in these locations. 
     For example where a void was detected at a particular position on a particular layer, the modified parameters  51  may deposit additional powder at the location to prevent a void. 
     Further examples of parameter modifications may include, but are not limited to, increasing or decreasing heat input, increasing or decreasing beam speed and modifying powder deposition to overcome failures identified during the testing process. 
     Furthermore, modified geometry  41  may be generated to prevent the anomalies  80  reoccurring in subsequent prints. In some circumstances, the modified geometry  41  that is generated may provide that a part subsequently printed in accordance with the modified geometry  41  does not have exactly the same morphology as the initial test part  30  but nevertheless has the characteristics, properties and functionality required by the part, or has improved characteristics, properties and functionality. 
     For example, if an initial test part  30  fails a particular test, such as a structural load test, despite there being no anomalies  80  present in the failure region, the modified geometry  41  may increase the cross-section at the failure location, to prevent similar failures. 
     Similar anomalies  80  and corresponding modifications may be attributable to different parameters  50 , for example a thermal spike may cause one type of anomaly  80 , whereas a chemical imbalance may be created by a different type of parameter  50 . 
     Additional anomalies  80  may include positive or negative thermal spikes resulting in changed micro structure, porosity or chemical composition of the initial test part  30 . 
     As used herein an anomaly  80  includes any variation in a material that is not consistent with a uniform or desired set of chemical, material and physical characteristics. The nature of the anomalies  80  may vary in magnitude. 
     Further criteria may exist in the form of external standards, which define what may be an acceptable level of anomaly  80  for any given use. For example components with extreme structural requirements, such are aerospace components, may include a particularly narrow set of criteria when defining acceptable levels of porosity for example. 
     Alternatively, a replacement component for a tractor may have a much greater acceptable level of porosity. 
     The initial print data set  60  may be cleansed to remove unnecessary data so that only issues for the purpose of the comparison are shown. For example, this may be done by comparing the initial print data set  60  with another print data set generated when a perfectly printed object or material is created. This comparison allows non-anomaly based data to be removed from the initial print data set  60  so that only anomaly-related data (and corresponding location data) remains. Other methods may involve using machine learning or similar AI techniques to analyse the initial print data set  60  which may include, for example, comparing the initial print data set  60  with the knowledge base  120 . 
     It may be that an anomaly  80  is detected by one type of test which would not be detected by a different type of test. 
     It may therefore be required that multiple tests may be required to detect all anomalies  80 , and to therefore determine which initial print conditions  70  resulted in each anomaly  80 . 
     Anomalies  80  also vary in magnitude and frequency, and where anomalies  80  are sufficiently small or infrequent, the functionality of the part may be unaffected. 
     After the modified parameters  51  and (if any) modified geometry  41  have been created, a check data set  85  may then be generated which is derived from the anomaly dataset  90 . 
     The check data set  85  may comprise a set of go and no-go conditions. The go and no-go conditions relate to, respectively, acceptable and non-acceptable criteria for successful printing of the finished part. The criteria comprise, respectively, acceptable and non-acceptable levels of anomalies  80  for successful printing of the finished part. 
     The check data set  85  may further be defined by external standards requirements. 
     Alternatively, an initial check data set  85  may be used when printing the initial test part  30 , where the criteria are derived from external standards. 
     In this case, the criteria of the check data set  85  may be limited to criteria relevant to anomalies of a type which are measureable without testing of the initial test part  30 . 
     The check data set  85  may then be aggregated with further anomaly  80  data contained in subsequent anomaly data sets  90 . 
     A revised digital part file  11  is then generated which comprises the initial geometry  40  or (if applicable) modified geometry  41 , the modified parameters  51  and the check data set  85 . The revised digital part file  11  may comprise other data, as necessary, relating to the anomalies  80  and that determine the subsequent operation of the 3D printing apparatus  20  to avoid reoccurrence (or acceptance of reoccurrence) of the anomalies  80 . 
     A second test part  31  is then printed using the revised digital part file  11 . When the second test part  31  is being printed, a further print data set  61  is generated using the sensors or recording devices of the apparatus  20 , the further print data set  61  comprising the further print conditions  71 . This further print data set  61  is compared with the check data set  85  during the print process. This comparison is carried out to ensure that the conditions that caused the anomalies  80  to previously occur are avoided, or the anomalies  80  are avoided within certain defined tolerances, error margins or acceptance limits. 
     The check data set  85  may be used to take corrective action when the second test part  31  is being printed, and to verify that the process has been undertaken within the acceptable limits, which can therefore be understood to not contain anomalies  80  of a magnitude and/or frequency which would cause the part to fail. 
     The steps described above are then repeated iteratively until a successful test part  35  is printed in which no anomalies above an acceptable level  80  are detected. 
     Where the second test part  31  is found to contain anomalies  80  during the testing process, the anomaly  80  data is referenced to further print conditions  71  at a particular portion of the further print data set  61 , the cross referenced information is added to the anomaly dataset  90 , thus forming an aggregated anomaly dataset  91 . 
     The revised digital part file  11  that exists on completion of the method, therefore, comprises the final revised versions of the initial geometry  40  and/or (as applicable) modified geometry  45 , the modified parameters  55 , print conditions  75  and the check data set  85 . The revised digital part file  11  may include further data, as necessary, relating to fabrication of the finished part. 
     It will be understood that the final revised digital part file  11  constitutes the certified digital part file  15 . The inclusion of the check data set  85  in the certified digital part file  15  further allows corrective and preventative action to be taken during the printing process, resulting in reduced scrap and increased conformance. 
     The check data set  85  may also allow a 3D printing apparatus  20  to determine whether, upon identifying an anomaly  80 , the printing process may be adjusted to rectify the anomaly  80 , or whether the part is not recoverable, at which point the process can be halted. Each layer may achieve a pass or fail result following comparison with the check data set  85 . Halting or recovering the printing process prevents wasted time and costs, by preventing an unrecoverable print from finishing its process. 
     Examples of anomalies  80  which may be recovered include a layer of insufficient thickness, where the parameters  51  of the subsequent layer may be modified to provide additional thickness over the desired area, or porosity within a layer, which may be filled or re-melted by redirecting the energy beam. 
     Referring to  FIG. 2 , there is shown a method of creating a certified digital part file  15 , comprising the steps described in  FIG. 1 , and further comprising the following steps after the successful test part  35  has been produced at step i.
         j. Printing multiple identical successful test parts  35 , which are subsequently tested to confirm that no non-acceptable anomalies are present, and therefore verify the repeatability of the process, and where no non-acceptable anomalies are detected, the associated final digital part file  15  constitutes the certified digital part file  15 .   k. If anomalies  80  at a level greater than acceptable are detected in one or more of the multiple identical parts  35 , steps c. through to j. are repeated, until all multiple identical successful test parts  35  are tested and no non-acceptable anomalies are detected, at which point the final digital part file  15 , associated with the multiple identical successful test parts  35 , constitutes the certified digital part file  15 .       

     Parts with more stringent certification needs may require that a number of identical tests are undertaken to ensure repeatability of the process. In such cases the geometry  45  and parameters  55  associated with the successful test part  35  may be used to print a number of identical successful test parts  35 . 
     The number of successful test parts  35  required may be determined by the requirements of the part or operator, for example critical parts may require a high number of successful test parts  35  to be tested to certify, whereas less critical parts may not require additional parts to be printed at all. 
     The identical successful test parts  35  may then undergo testing to ascertain whether all the successful test parts  35  are fit for purpose. 
     Where one or more successful test parts  35  fail the testing, investigation may be required to check for anomalies  80  which may have caused the failure. 
     Further parameter  55  modifications may be made, and subsequent additional test parts  35  printed. 
     A digital part file  15  is considered to have been certified once a required number of identical successful test parts  35  have been printed using particular parameters  55  and geometry  45 , and all the identical successful test parts  35  have completed the testing process without non-acceptable anomalies  80  being detected. 
     The particular parameters  55  and geometry  45  used to create the successful test part  35  are used to create the certified digital part file  15 . 
     Once a certified digital part file  15  has been created, a master data file  100  is stored, which may include the history of all previous prints and associated parameters  50 , print data sets  60  and test results, so that the entire verification process is available. 
     The comparison of test results against the print data set  60 , and the use of this information to identify parameters  51  which lead to anomalies  80 , allows anomalies  80  to be consistently kept within acceptable limits, thus enables a part which has been printed using a certified digital part file  15  to be considered certified, potentially without the need for further testing. 
     It is recognised that some requirements for post-production processing or testing may remain, depending on the requirements. Therefore the method described does not entirely remove the need to any post production processing in all cases. 
     Examples of post-production testing which may still be required include heat treatment, stress relief, surface treatments and third party testing. 
     A part produced using a certified digital part file  15  may therefore be understood to be a certified part  35 . 
     In use, OEMs or part owners may store certified digital part files  15  of critical components, for example those which lead to substantial costs due to failure. 
     The availability of certified digital part files  15  overcomes the problem of 3D printed parts not being fit for purpose without post-productions testing, and therefore allows rapid replacement of a failed part. 
     The availability of certified digital part files  15  also overcomes the problem of storing parts for replacement in the event of a failure, and the associated inventory issues with such storage. 
     Where a certified part  38  is required, for example following the failure of a component, the certified digital part file  15  is requested by an end user, using a 3D printing machine. 
     The end user will typically have a requirement for a certified part  35  capable of performing under certain conditions. 
     If the end user were to download an object file from an uncertified source, or to scan an existing part in an effort to reproduce the part, the end user would have no way of knowing whether the part would perform under the required conditions. The end user would be required to undertake post-production testing, or may have no option other than the order the certified replacement part from the OEM. 
     Where the end user requests the certified digital part file  15 , the aforementioned process ensures that the geometry  45  and parameters  55  used to print the part, will result in a certified part  35  capable of performing under the required conditions. The process has been proven by the multiple tests from which the parameters  55 , and possibly geometry  45  have been derived. 
     As the process may have been used to create and verify a number of parts, the certified digital part file  15  has been proven to be able to produce certified parts  35 , which may be sufficient in some cases. However, if the certified digital part file  15  is supplied to the 3D printing apparatus  20 , and the printing process is carried out without further monitoring, external factors may result in further anomalies  80 . 
     Known 3D printing apparatus do not have a means of recognising some anomalies  80 , and therefore do not have a means of certifying the production process without a degree of post-production testing, even when supplied with a certified digital part file  15 . 
     Furthermore, adequate post-production testing may not be available, or even possible without destruction of the part. 
     For example, a 3D printing apparatus  20  may be knocked during the printing process, or the different geographical location, relative to the 3D printing apparatus  20  on which the certification process was undertaken, may be subject to different environmental conditions, which may in turn result in new anomalies  80  occurring. 
     Where the prevalence and magnitude of these new anomalies  80  are considered to be significant, the certification of the part may be at risk, even though the certified digital part file  15  was used. 
     To ensure that the part produced by a printer using the certified digital part file  15  is itself a certified part  38 , the printing process used to print the part may also need be certified. 
     Referring now to  FIG. 3 , there is provided a method of printing a certified part  38  using a certified digital part file  15 , the method comprising the following steps:
         a. Using a 3D printing apparatus  20  and a certified digital part file  15  to print a part  38  in accordance with a print process, the certified digital part file  15  comprising geometry  45 , parameters  55  and a check data set  85 , the check data set  85  comprising criteria defining acceptable and non-acceptable levels of anomalies  80  for successful printing of the certified part  38 ,   b. During the print process, comparing print data  65  generated by the apparatus  20  with the check data set  85  to indicate where a part of the printing process contains a non-acceptable anomaly  80 .   c. Where a non-acceptable anomaly  80  is detected, using the apparatus  20  to recover the print process by taking corrective action if possible to remove the anomaly  80  or reduce the anomaly  80  to an acceptable level or, where the print process is not recoverable, abandoning the print process.       

     Where the method of  FIG. 3  allows a print process to be certified, and therefore produce a certified part  38  using a certified digital part file  15  and a certified printing process, this is done in part using the check data set  85 , which comprises the test results of the iterative testing used to derive the certified digital part file  15 . 
     Whilst this check data set  85  is able to be used to provide a means to recognise anomalies  80  in a particular location of a particular part, as the information is based on the iterative testing of a number of similar parts, the information may be, to some extent at least, limited to such parts. 
     Referring now to  FIG. 4 , there is shown a method of printing a certified part  39  using a 3D printing apparatus and a knowledge base  120 , wherein the knowledge base  120  comprises anomaly patterns  95  derived from a plurality of historical anomaly datasets  90 , and a check data  85  set comprising criteria defining acceptable limits for different types of anomalies  80 , the method comprising the following steps:
         d. Using a 3D printing apparatus  20  to print a certified part  39 , wherein the 3D printing apparatus is configured to recognise an anomaly pattern  95 , and to therefore detect when an anomaly  80  is being printed,   e. Checking the anomaly  80  against the check data set  85  to determine whether the anomaly is within acceptable limits, and where a non-acceptable anomaly  80  is detected, recovering the print process by taking corrective action if possible to remove the anomaly  80  or reduce the anomaly  80  to an acceptable level or, where the print process is not recoverable, abandoning the print process.       

     The anomaly patterns  95  stored in a knowledge base  120  are able to provide a means to identify anomalies  80  at any location during any printing process. 
     Whilst the comparison of the test results against the print data set  60  at a particular location of the test part  30  may be used to determine the parameters  50  used at said location, and therefore to assist with creation of modified parameters  51 , this is specific to the particular location of the particular part, and is recorded against the part file associated with the particular part. 
     As more tests are undertaken, and results comparing more anomalies  80  with more corresponding print data sets  60 , a knowledge base  120  may be created, and anomaly patterns  95  can be identified and stored in the knowledge base  120 . 
     As more anomaly patterns  95  are identified, the size of the knowledge base  120  increases. 
     The analysis of the patterns can be used to identify the parameters  50  which may result in an anomaly  80 , regardless of the location within the part. For example it may be discovered that a particular rate of powder deposition may result in more voids than previously anticipated. 
     It may further be recognised that a combination of particular parameters  50  may result in an anomaly  80 , but not when only one of the parameters  50  is used. For example a particular beam intensity may cause excessive melting at a particular speed of traverse. 
     Where anomalies  80  are identified that are produced repeatedly, regardless of the location within the part, their respective anomaly datasets  90  can be used to define anomaly patterns  95 . 
     The anomaly patterns  95  can be used to identify when a 3D printing apparatus  20  is producing an anomaly  80 , which can therefore be used to carry out corrective or preventative actions during a print process, thereby increasing the efficiency of the 3D printing apparatus  20 . 
     The check data set  85  may be altered for different parts and part requirements, what constitutes an acceptable level of anomaly  80  may vary depending on the requirements of the part, and as such, a check data set  85  may be selected which is appropriate for the part to be printed. 
     Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.