Learning Objectives
By the end of this section, students will be able to:
- Understand the importance of a fixed process.
- Understand the importance of having a disciplined change management process in AM.
- Understand how Certification and Qualification for AM will evolve as more experience and confidence is gained in the technology.
The design, manufacture, and use of AM parts should follow fixed design, fixed (also known as locked down) process and change management protocols used in modern industrial practice. This is in spite of the fact that by being a digital process that rarely requires tooling, it can be very easy from a practical standpoint to change either the design or the process. In essence, once a design or process is fixed (or locked down), any changes to the design or process need to be approved by the relevant engineering authority to ensure that the previously attained part qualification and system certifications are invalidated.
The approach for change management is much like that used for qualification of additional machines. Depending on the type of change, the amount of re-qualification can range from a minimal amount (first article testing without a destruct) to a full repeat of part qualification (design or process change) to repeat of machine and part qualification (process change). Standard practice in organizations using AM is to initially require that all changes be brought to a change control board (CCB) to decide what requalification is necessary. As the organization develops a history of change management, standard practices are then developed to more quickly determine and plan the re-qualification steps. A good indication of the need for some form of requalification can be gained from reviewing the key process variables. AMS 7003 (Laser Powder Bed Fusion Process) lists 34 key process variables. A change in any of these could potentially trigger a requalification.
Another type of change that can happen is maintenance or movement of the AM or post-processing machines. In the case of a minor maintenance action machine could be nearly identical to itself before the maintenance, which would often just require a simple IQ. In the case of a major maintenance action, the machine could be considered not similar, which would require IQ, OQ/PQ and part requalification. This would be similar if the machine is moved to a different location. In most cases, an IQ would be all that is required, unless the IQ fails, and a maintenance action is required. Like design or product change management, the initial requalification requirements for maintenance actions have a high level of oversight until history and standard practices are developed. In the case of intermittent production, or if a machine is idle for a period of time, some industries will require an IQ prior to resuming production, with a reduced OQ/PQ or part requalification potentially required as well.
Future Changes in Certification and Qualification
As a rapidly evolving technology, AM will continue to develop and mature. Along with the general maturation of the technology, certification and qualification will continue to mature to evolve as well. At this time, most organizations qualifying AM parts on systems that require certification are being very careful in their approaches. The primary changes in the future for certification and qualification will be to streamline those processes.
Because it is generally independent of the exact materials and processes used, certification will see fewer changes in the future. The primary change to certification will be a better understanding of material/process/property relationships that will enable a transition of design values from part-specific to part-family to feature-based. Advances in Integrated Computational Materials Engineering (ICME) combined with advancements in process simulation and part design/analysis codes will give designers and analysts the ability to predict properties based on the part design. While the design value tables may be multi-dimensional, versus the 2-dimensional format, it can be imagined that these could be simplified if the potential performance impact of lower design values is minimal.
Additional changes may include exploiting the same ICME advancements and developing the ability to more quickly generate design values as faster or more precise AM technologies are introduced. Also, we may transition NDT from post-build to in-situ, which may align with the future ability to undertake repairs during the build. This capability, along with the ability to predict maximum undetectable defect size will enable better analysis of critical components. Overall, we should we improved knowledge of the performance of AM-unique geometries to reduce the amount of full-scale component and system testing.
Changes in qualification will be based on obtaining a better understanding of the key process variables and the impact on part performance.
Qualifications changes may exhibit themselves in the following ways:
- A more extensive, but more automated IQ, that will be able to make a better determination of the status and health of a machine than is currently possible.
- A reduction in the number of builds and tests needed for OP or PQ, particularly due to improved IQ.
- Improved characterization and better definition of feedstock requirements to eliminate the need for any feedstock qualification save acceptance testing.
- Advances in process monitoring, process control, and in-situ NDT to eliminate the need for destructive testing for part qualification.
- Lot and part acceptance based on process monitoring and in-situ NDT of the build, along with process monitoring of key post-processes, such as thermal treatments.
- Integration of process monitoring with post-build evaluations as part of an integrated SPC program.