Sub-article A/S - - - - 
Sustained Load 1 1 - - - 
Customized QMP A/S A/S A/S A/S - 
 Notes:         
 PCRD = Process Control Reference Distribution defined acceptance criteria     
 A/N = As needed        
 A/S = Acceptance as specified in the QMP/QPP      

Comp = Comparative assessment based on defined criteria in the QMP/QPP, 
or PPP in the case of Witness Articles or Witness Sub-articles    

>85% typical = Average to be within 15% of typical value 
See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications. 


 Witness Testing for Continuous Production Builds  

[AMR-24]  All AM parts manufactured by a continuous production build shall include witness 
specimens integral to the build of the types and quantities required in Table 7, Metals Witness 
Testing Quantities and Acceptance Results for Continuous Builds, and Table 8, Polymer Witness 
Testing Quantities and Acceptance Results for Continuous Builds, exposed to the same post-
processing as documented in the QMP and evaluated per the acceptance methodologies of Tables 7 
and 8. 

[Rationale:  Witness sampling is required to provide evidence of systemic process control 
throughout the build cycle.] 

See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications. 

The continuous production build process allows for a reduced quantity of witness specimens 
compared with independent builds. 

Witness specimen geometries may vary depending on the AM process being used. Witness 
specimens built alongside the part are capable of capturing a representative thermal history of the 
part. Some processes (e.g., DED) challenge this methodology. For these systems, material from tag 
ends, prolongations, or other features may be used as the material for witness specimens. 

For the purposes of this NASA Technical Standard, integral to the build means produced during a 
process development production run or during a part production run, and for the latter, 
simultaneously with the production part. 


Metals Witness Testing Quantities and Acceptance Results for Continuous Builds 
a. Minimum Quantities of Witness Specimen Types by Part Class 
 Class          
 A1 A2 A3 A4 B1 B2 B3 B4 C  
Tensile 4 4 4 4 4 4 4 4 2  
FH Contingency* 1 1 1 1 1 1 1 1 -  
Post-build Tensile** 4 4 4 4 4 4 4 4 2  
Microstructure 1 1 1 1 - - - - -  
Post-build Microstructure† 1 1 1 1 - - - - -  
Chemistry 1 1 - - - - - - -  
HCF - - - - - - - - -  
Low Margin Point A/R A/R - - - - - - -  
Witness Sub-article A/R - A/R - A/R - - - -  
Witness Article 1 for 6 - - - - - - - -  
Customized QMP A/R A/R A/R A/R A/R A/R - - -  
 Notes:          
 *FH contingency = Full-height contingency specimen for PBF only 
 **Post-build tensile = Post-build witness tensile specimens required for DED only 
 †Post-build microstructure = Post build microstructure specimens required for DED only 
 A/R = As required when specified in the PPP/QPP       

Sample direction should be chosen from the most process-sensitive orientation (typically the Z-direction)  
See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications 


b. Basis for Acceptance of Witness Specimen Results 
 Class          
 A1 A2 A3 A4 B1 B2 B3 B4 C  
Tensile CC CC CC CC CC CC CC CC >85% typical  
FH Contingency A/N A/N A/N A/N A/N A/N A/N A/N -  
Post-build Tensile* CC CC CC CC CC CC CC CC >85% typical  
Microstructure Comp Comp Comp Comp - - - - -  
Post-build Microstructure** Comp Comp Comp Comp - - - - -  
Chemistry A/S A/S - - - - - - -  
HCF - - - - - - - - -  
Low Margin Point DV Min DV Min - - - - - - -  
Witness Sub-article Comp - Comp - Comp - - - -  
Witness Article Comp - - - - - - - -  
Customized QMP A/S A/S A/S A/S A/S A/S - - -  
 Notes:          
 CC = Control chart statistical process control acceptance limits      
 A/N = As needed         
 A/S = Acceptance as-specified in the QMP/QPP       

Comp = Comparative assessment based on defined criteria in the QMP/QPP, or 
PPP in the case of Witness Articles or Witness Sub-articles     
 DV Min = Results exceed the design value in the MPS for that point condition  
 >85% typical = Average to be within 15% of typical value      
 *Post-build tensile = Post-build witness tensile specimens required for DED only 

**Post-build microstructure = Post-build microstructure specimens required for DED only 
See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications 


Polymer Witness Testing Quantities and Acceptance Results for Continuous Builds 
a. Minimum Quantities of Witness Specimen Types by Part Class 
 Class         
 A1 A2 A3 A4 B1 B2 B3 B4 C 
Tensile 
Not applicable per section 4.3.1.1.1 of this 
NASA Technical Standard 
4 4 4 4 2 
FH Contingency 1 1 1 1 - 
Microstructure - - - - - 
Flexural - - - - - 
Compression         
Density - - - - - 
Witness sub-article A/R - - - - 
Sustained Load - - - - - 
Customized QMP A/R A/R - - - 
 Notes:         
 FH Contingency = Full-height contingency specimen      
 A/R = As required when specified in the PPP/QPP      

Sample direction should be chosen from the most process-sensitive orientation (typically the Z-direction). 
See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications. 


b. Basis for Acceptance of Witness Specimen Results 
 Class         
 A1 A2 A3 A4 B1 B2 B3 B4 C 
Tensile 
Not applicable per section 4.3.1.1.1 of this 
NASA Technical Standard 
CC CC CC CC >85% typical 
FH Contingency A/N A/N A/N A/N - 
Microstructure - - - - - 
Flexural - - - - - 
Compression         
Density - - - - - 
Witness sub-article Comp - - - - 
Sustained Load - - - - - 
Customized QMP A/S A/S - - - 
 Notes:         
 CC = Control Chart Statistical Process Control Acceptance Limits     
 A/N = As needed        
 A/S = Acceptance as specified in the QMP/QPP      
 Comp = Comparative assessment based on defined criteria in the QMP/QPP    

>85% typical = Average to be within 15% of typical value 
See Tables 13 through 16 in section 5.5.3.5 for recommended test specifications. 


 Continuous Production Build SPC Requirements 

[AMR-25]  For Class A and B parts, to be eligible for continuous production build witness 
sampling, the AM machine shall be under SPC by meeting each of the following criteria: 

a. Machine maintains an active qualification status per NASA-STD-6033. 

b. Machine operates under the same or equivalent QMPs since the last successful SPC 
evaluation build or qualification build. 

c. Machine has produced an SPC evaluation build within 60 days, using the sample set 
given in Table 14 or Table 16 and meeting the requirements of section 5.5 of this NASA Technical 
Standard. 

d. A minimum of 30 data points are collected from at least 10 of the most recent builds to 
establish control charts for ultimate strength, yield strength, and elongation. 

 This will show a history of control. This requirement is for the formal establishment and 
reestablishment of control charts. Control charts are not to be updated on a continuing 
basis.  

e. Control charts for ultimate strength, yield strength, and elongation are established 
according to ASTM E2587 and controlled by the QMS, with control limits compatible with the 
applicable PCRD. 

 f. All witness specimens are exposed to the same post-processing as documented in the 
QMP. 

g. Builds with tensile results that violate control chart acceptance criteria are assigned a 
nonconformance in the QMS that initiates an evaluation of the part and the AM machine’s process 
history. 

h. Corrective actions are taken for any control chart nonconformance that cannot be 
specifically isolated to the nonconforming build. 

i. Any machine associated with an open SPC nonconformance is given inactive 
qualification status until the root cause evaluation concludes, the necessary corrective actions are 
complete, and the CEO concurs with the resolution. 

j. The root cause/corrective action record for a nonconformance contains the decision to 
either return the machine to active qualification or requalify the machine, and the bases for that 
decision. 


[Rationale:  The reduced witness sampling in continuous build operations depends on a rigorously 
defined, steady-state production environment that is monitored and controlled to provide rationale 
for part quality and reliability. These SPC requirements provide for that SPC environment.] 

Note that Class C parts should be treated as independent builds. Due to the reduced witness 
requirements for Class C parts, these SPC requirements are not warranted. 

Tailoring of the default 60-day SPC evaluation build interval may be proposed within the AMCP, 
with justification, if needed, to better suit the production environment. Alternative intervals may be 
set on the number of builds, machine hours, or other quantifiable metrics that provide monitoring at 
a comparable interval. 

All requirements of section 4.11.2 of this NASA Technical Standard have to be met prior to using the 
continuous production build SPC methodology. Builds used to develop the required history of 
control may be any that are conducted in full compliance with an approved QMP. Acceptance of 
builds prior to establishing the continuous production build SPC will need to be in compliance with 
witness testing for independent builds.  

4.12 Serialization 

[AMR-26]  For Class A and B parts, serialization (or equivalent) shall be used to provide part 
traceability to the AM build cycle, the location on the build area/platform within the build, all other 
production records, governing engineering documentation, and feedstock lots. 

[Rationale:  The AM process is sensitive to variation in process control, such that each instance of 
the process has the likelihood of uniqueness; traceability by part back to that process is essential to 
managing part and inventory risk.]  

4.13 Digital Thread 

The process of taking a design and creating a finished AM part requires the creation of multiple 
derivative files along the way. This can include, but is not limited to, computer-aided design (CAD) 
files, drawings, neutral geometry definition files, witness specimen geometry files, the part build file 
(i.e., parts, witness specimens, and support structures), Standard Tessellation Language (STL) files, 
tool path files, parameter files, log files, and execution scripts. Figure 5, Creating Electronic 
Records of Design/Creation of AM Parts, provides a graphical representation of the creation of 
these files, which should be considered only as an example as it contains only a fraction of the file 
types that can be derived during AM processing. These electronic records are considered in the 
same context of material traceability. It is required to know the source of each file and subsequent 
version control between files. In some cases, file operations are transient (e.g., the export of an STL 
or toolpath). In these cases, log files or other records are to document all parameters controlling 
the operation. The method for documenting and archiving these files will vary depending on the 
systems that are available at the CEO or qualified supplier. The requirements for configuration 


control will be satisfied as long as the files and associated records of parameters are kept under 
configuration control and are version controlled. 


Figure 5—Creating Electronic Records of Design/Creation of AM Parts 

 Maintaining File Identity and Integrity in the Digital Thread 

[AMR-27]  All electronic files relevant to the digital thread for an AM part shall be controlled by 
the QMS within a file management system with full version control and appropriate security, with 
an allowance for files to be removed from the file management system only if they are fingerprinted 
with a cryptographic hash to ensure unambiguous identity and integrity of the file. 

[Rationale:  Maintaining unambiguous identity and integrity of all files in the digital thread is 
essential to controlled production of AM parts. A version-tracking file management system is 
considered adequate for these purposes as long as the files remain within the file management 
system. Files, or copies thereof, that have to be removed from the file management system for 
transfer to a remote server-based system or by any portable storage device are at risk for 
corruption or tampering. Fingerprinting of every file removed from the file management system 
provides the means to control identity, version, and integrity of the file.] 

Files in scope of this requirement (those relevant to the digital thread) are all files necessary to 
reproduce fully all aspects of the part design, preparation for the build, and the build and post-build 
processes. Note that to maintain the validity of the files in the digital thread, software used to 
process the files also have to be controlled for compatibility in version and configuration.  

The 128-bit MD5, SHA-2, and SHA-3 cryptographic hash are examples of industry standard 
algorithms that may be used to fingerprint digital files and ensure sustainable configuration 
management. 

In accordance with NRRS 1441.1, NASA Records Retention Schedules, and contract and QMS 
requirements, all part records are archived for the prescribed period and remain fully traceable, 
including those provided by external suppliers for operations such as heat treating, machining, or 
inspection. All witness specimen test results and records, as well as nonconformance 
Process
Example Files 
Generated
Design
• Parametric 
(Solid Model 
CAD, NURBS)
• Point Cloud 
(Scanned)
• Etc. 
Build Operation
• Executable 
Toolpaths
• Companion 
Files
Build File Set Up
• Additive pre-
processing 
(Remeshing, 
etc.)
• Toolpathing
(Mesh  CNC)
Design Analysis
• FEA 
(Structural, 
Topologic Opt.)
• CFD (Thermal, 
Aerodynamic)
• Etc.
Digital Thread / Digital Product Definition


documentation, are included in the certification of compliance records for the part. When complete, 
it is recommended that a final, summarized certification-of-conformance record be generated to 
demonstrate that all requirements have been met, all nonconformances have been resolved, and the 
part is fit for service. 

 Part Model Integrity 

[AMR-28]  For Class A and B parts, a methodology for verifying the integrity of part model(s) 
throughout all stages of the digital part definition associated with the AM process shall be 
documented and implemented via the AMCP. 

[Rationale:  Verification of the digital part definition ensures that subsequent and derivative digital 
products are produced to the correct and uncorrupted files. Model validation’s role in digitally 
identifying discrepancies can be crucial for ensuring the integrity of downstream AM products.] 

Conformance to this requirement can be demonstrated by using a methodology that includes 
considerations for digitally sensitive processes (e.g., meshing process and subsequent analysis for 
the quality of meshed models). Software characterizing and controlling embedded information 
within the digital part definition can be crucial to supporting an assessment regarding digital 
quality. Common practices to maintain part model integrity ensure that data formats, coordinate 
systems, and digital tolerances are identified and conserved through the digital thread. Although 
software validating portions of the digital thread exist (e.g., those providing CAD validation), 
demonstrating part model integrity requires the combination of numerous digital considerations 
identifying and controlling the AM process. These practices are supported through standards (e.g., 
ASME Y14.41, Digital Product Definition Data Practices: Engineering Product Definition and 
Related Documentation Practices, and ASME V&V 40, Assessing Credibility of Computational 
Modeling through Verification and Validation: Application to Medical Devices). It should be noted 
that standards for quality assurance of digital aspects of the AM process are still being actively 
developed; consequently, the number of relevant standards demonstrating digital product control 
will increase with the maturity and adoption of AM.  

 On-Machine Execution 

[AMR-29]  Any unplanned modifications to the build file on the machine during AM process setup 
and/or execution shall be assigned a nonconformance and traceable via a records management 
system controlled by the QMS. 

[Rationale:  Modifications to the build file during process execution is a deviation from the QPP.]  

Some AM software requires the location of the digital model to be placed or located in the build 
volume on the machine. Location in the build volume is considered part of the QPP; therefore, a 
placement in the build volume that differs from this location is considered a nonconformance. At the 
point of build file execution, digital alterations to the build file are treated as a nonconformance. 


4.14 Production Engineering Record 

[AMR-30]  For Class A and B parts, the AM part production process