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Development of Weldability Test Methods for the Powder-Feed Additive Manufacturing Process

 

Additive manufacturing (AM) is a materials joining process in which three-dimensional components are built directly from computer-generated design models. The designed components are digitally sliced into a series of layers and additively built, one layer at a time. In the powder-feed AM process, this is achieved by depositing metal powder particles into a laser-generated molten weld pool.

As the powder-feed process continues to become integrated into manufacturing, efforts are required to ensure build-to-build consistency. The multitude of variables associated with the process and their respective influence on final part characteristics need to be understood and controlled. It is essential to reduce the variance in part properties and quality across multiple materials and machine types. Therefore, in order address these issues, the development of standard “weldability” test methods for process assessment is essential.

In this project, a weldability test has been developed to evaluate the properties of parts built with powder-feed AM systems. The test was designed to assess porosity and lack of fusion defects, microstructure evolution, residual stress, surface quality and susceptibility to solidification cracking. With an initial focus on 304L stainless steel, the test consists of filling conical holes while varying process parameters such as travel speed, energy density, deposition rate and carrier gas. Additionally, the test has been utilized for comparison of powder performance between nominally identical input powders. Figure 1 provides images of sectioned samples built with 304L powders from different manufacturers (Powder A and Powder B). The builds were made with identical process parameters. In this case, Powder B exhibited excellent overall weldability compared to Powder A.

 

Figure 1: Comparison of 304L powder performance between different powder manufacturers.

 

The proposed weldability test provides an all-encompassing approach to evaluating the powder-feed AM process. Critical part characteristics can be analyzed as a function of multiple process variables. A fundamental grasp on these material and process variables will allow for the prediction and prevention of defects in future AM builds, thus saving the time and resources often required for process parameter redevelopments. Mitigating variance in part properties and ensuring build-to-build consistency will ultimately create a more efficient and productive manufacturing process.


Sponsor: Los Alamos National Laboratory (through NSF I/UCRC)

Graduate Student: Brandon Kemerling, The Ohio State University

Faculty Advisor: John Lippold, The Ohio State University

Industry Contacts: Matt Johnson, Dan Javernick