Welding Digest

Additive manufacturing (AM) of metals is a growing field that builds on the knowledge of metal and alloy welding behaviors. AM creates new material by fusing metal feedstock layer by layer using a computer-controlled heating plan.

Both fusion welding and solid-state welding create joined structures larger than their inputs and, in that sense, are additive rather than subtractive like machining. AM brings in another level of planning to that metal-adding process and then focuses on the new material created at the completion of the process. Entire structural components can now be built from AM material and a single feedstock type that has been standardized.

Anyone involved with welding can see that making parts by AM is locally just another welding process. That is true both for powder bed fusion (PBF) processes, which use high energy density beams like lasers or electron beams, and directed energy deposition (DED) processes, which build using locally introduced feedstock. DED can use a variety of arc and beam processes. These same heat sources are used for welding.

Many industries are beginning to see how AM can fill certain niches for metal structures. These industries include aerospace and medical as well as areas of defense, energy, and pressure vessels, which have recently added documents providing for the use of AM. Because of increased interest in this process, AWS is working to develop improvements on the current AWS D20.1, Specification for Fabrication of Metal Components Using Additive Manufacturing, which covers a variety of AM processes. Your participation in the activities of code committees can make this and other AWS standards better.

The kind of niches that fit best for AM have production equipment pieces like molds and geometric, individually tuned parts, such as structural implants for medical, dental, and veterinary uses. AM has greater geometrical control than many shape-creation processes for metals, so that is one consideration that has been heavily discussed for PBF. Both DED and PBF demand less tooling than other processes to achieve final shapes, so the speed to final parts, particularly for small part runs, can be a big advantage. AM need not create all of a finished component since an original base is always needed. Rehabilitation and reshaping are other options for niches.

AM can push new developments that can be useful in other situations that fall more naturally in welding. For instance, arc DED builds new material using path planning and layered arrangements of arc weld beads, similar to multipass arc butt welds and fillet welds. The demands of AM for control in bead shape, position, and layer height are pushing the limits of arc DED processes for both tuning and closed-loop control. These improvements in control can then be available to robotic arc welding processes for butt and fillet welds.

New processes, procedures, machines, and feedstocks will be needed to achieve AM's potential for fast, reliable, and dependable fabrication of new components. That means there will be a lot of new building in this space.

This article was written by William Mohr (principal engineer, structural integrity, EWI, D20 chair) for the American Welding Society.