Qualification for AM Feedstocks, Machines and Processes

Summary

Machines and processes used to produce critical components for defense, aerospace, and medical applications must first be formally qualified. While qualification procedures vary between applications or industries, the goal of qualification can be summarized as the collection of sufficient data to demonstrate that a machine or process will function as expected.  The variety of AM processes available to users and the variety of process variables used to produce an individual part make statistical-based qualification through empirical testing particularly burdensome.  Currently no AM machines or processes are qualified for critical defense or aerospace applications. Non-critical AM processes have been qualified using empirical testing with fewer tests, but the cost and time remain high, encouraging companies to keep the resulting data proprietary.  There are generally three different paths to qualification: 1) statistical-based qualification rooted in extensive empirical testing, 2) equivalence-based qualification achieved through moderate testing to demonstrate a new material or process is equivalent to a previously qualified material or process, and 3) model-based qualification where a material’s or process’ performance is demonstrated in a computer model and verified with minimal testing.  Developing the measurement science to support equivalence-based qualification and model-based qualification will enable AM users to qualify materials and processes without the high cost and time required by statistical-based qualification and without the high level of uncertainty associated with model-based qualification.  NIST’s excellence in measurement science and its standing as a neutral third party with a broad public forum make it the ideal place to develop test methods and protocols, provide reference data, and establish minimum requirements needed to achieve more rapid qualification.  This measurement science will ease the qualification process in aerospace and defense applications, and lead to a better understanding of AM and more confidence in AM products used in all industries.

Description

Objective - To develop, utilize, and analyze test methods and protocols for characterizing the feedstocks, machines, and processes in metal-based additive manufacturing to enable optimum usage and to reduce the cost and time needed for qualification.

What is the Technical Idea?

Qualification of AM machines and processes is critical to enabling the AM industry to crack into the defense, aerospace, and medical industries. There are generally three different paths to qualification: 1) statistical-based qualification rooted in extensive (and costly) empirical testing, 2) equivalence-based qualification achieved through moderate testing to demonstrate a new material or process is equivalent to a previously qualified material or process, and 3) model-based qualification where a material’s or process’ performance is demonstrated in a computer model and verified with minimal testing.  Currently no AM machines or processes are qualified for critical defense or aerospace applications. Non-critical AM parts have been qualified using statistical approaches, but the high cost in time and money encourage companies to keep the resulting data proprietary.  NIST will focus on developing the measurement science to reduce the time and cost related to qualification of machines and processes used in the AM part production.  This will entail test methods and protocols to distribute the cost of statistical approaches, and reference data to support equivalence-based qualification and model-based qualification.  These will enable AM users to qualify machines and processes without the high cost required by building and empirically testing hundreds or thousands of AM parts.  

NIST is a non-regulatory body, therefore actual qualifications and their specific protocols will be left to regulatory bodies (e.g., the Federal Aviation Administration).  However, NIST will deliver measurement science that will establish the foundation for qualification of machines, processes, and parts used in AM at reduced cost.  This will be accomplished by developing novel test methods and protocols, leveraging work in other EL AM projects, and collaborating with key industrial and academic researchers.  

The high cost of statistical-based qualification is mainly the result of the time and money required to complete the extremely large number of tests.  It is likely impossible to achieve qualification without some amount of testing, especially in the case of getting the first AM material or process qualified.  However, it is possible to distribute the burden of testing by improving the AM industrial commons.  This project will define protocols for round robin testing and produce a publically available materials database to allow multiple contributors (both large and small) to add trusted data to the existing knowledge base.

What is the Research Plan?

The project addresses and contributes towards the following high-priority gaps identified in the 2018 ANSI AMSC Standardization Roadmap:

• Machine calibration and preventive maintenance
• Machine qualification
• Harmonization of AM qualification and certification terminology
• Qualification standards by part categories
• Harmonizing qualification and certification terminology for process parameters

In order to help AM community to qualify machines, this project will focus on the functional characteristics of the machines used for metal AM processes.  Machines used for metal AM processes combine several critical functions for successful fabrication of complex products.  These functions include generation of uniform thin layers of metal powder (PBF processes) or delivery of metal powders with adequate flow rate to deposition location (DED processes); energy delivery (including laser beam characteristics and quasi-static and dynamic positioning); and providing proper process environment (chemical composition and gas flow characteristics).  Performance metrics of these functions and the methods to assess and communicate them among the stakeholders must be developed.

This project will also focus on developing the measurement science to support equivalence-based qualification methods and will leverage the outputs of other AM projects (particularly Metrology for Multi-physics Model Validation and AM Part Qualification projects) in the MSAM program to develop use cases/guidelines for model-based qualification.

Furthermore, ongoing round robin studies will be extended to include more types of materials (e.g., IN718, SS17-4, and possibly Ti64), additional performance testing (e.g., fatigue performance, micro hardness), and multiple build orientations.