Ensuring Product Quality and Process Reliability of Laser-Based Additive Manufacturing By R.P. Martukanitz, University of Virginia and the Commonwealth Center for Advanced Manufacturing
L
aser-based additive manufacturing (AM) of metallic materials is receiving considerable attention for use in a wide range of industries based on its ability to dramatically increase design complexity with minimal increase in cost, capability to easily customize products, and capacity to act as a “point of manufacturing” for on-demand items. Because AM is currently considered a relatively low production-rate process that commands a premium, many of its potential applications are directed at high value components, and in most instances these components have high performance requirements. This requires that the process, which in the case of AM includes design, material, and processing conditions, are suitable for meeting the various performance requirements dictated by the application, as well as ensuring that the AM process is capable of repeatedly producing parts that meet these requirements.
T
he traditional method of maintaining a specified level of quality in a manufacturing process is to define and conduct the process based on a performance qualification protocol. This approach, which is used throughout many industries, relies on sufficiently defining and documenting the important parameters controlling the process that enables key performance requirements be met that are specific to the product and application. Test results are used to confirm that the process defined using these parameters are capable of meeting the requirements of the product. Once the process is established and provides the known outcome, these essential parameters are monitored and maintained. A concept for applying this approach to AM is shown in the below figure.
“
The concept shown above has been formulated to address several unique features regarding AM.
”
Concept for Utilizing a Performance Qualification Protocol for Additive Manufacturing CONCEPT FOR UTILIZING A PERFORMANCE QUALIFICATION PROTOCOL FOR ADDITIVE MANUFACTURING
T
he concept shown above has been formulated to address several unique features regarding AM. This includes the critical link between the design and manufacturing functions, important aspects of material feedstock quality and processing system stability, and potential use of process monitoring and/or sensing to ensure process reliability. The design and process definition or development stage is an iterative process. Once the design and process are defined, qualification of the material, AM system, and entire process is conducted by confirming that the resultant product will meet the intended performance requirements that had been established during the design and process definition stage. This is achieved by producing actual components or simulated components using the defined process and by testing the resultant product to confirm properties and/or characteristics that may define performance. The AM process is conducted while thoroughly documenting all material, systems, and processing conditions that may influence the process and resultant product. If the desired properties are attained from the
performance tests, the process is formally specified as being qualified to produce the design using these prescribed parameters and conditions.
E
ssential variables that define the process are monitored or verified to assure conformity. By continually tracking the variation of critical parameters and conditions, indications of trends may be used to intercede before exceeding established limits for controlling the process. Monitoring and controlling essential variables may also be augmented through real-time sensing of process characteristics. Various sensing methods have been developed that offer insight into the process, as well as improved resolution for assigning consistency to the AM process. These sensor techniques, as they relate to the laser-based powder bed fusion AM process, include high resolution imaging for identifying layer anomalies or defects, acoustic emission sensing for indication of crack generation, and diode sensors for measuring laser attenuation and process stability. Dr. Richard Martukanitz is a Professor of Materials Science and Engineering at the University of Virginia and a Fellow in Additive Manufacturing at the Commonwealth Center for Advanced Engineering. He has over 25 years of experience in the development and deployment of laserbased manufacturing technology and the DoD.
www.lia.org
1.800.34.LASER
17