The shiny future of metal additive manufacturing

Metal additive manufacturing (AM) is gaining popularity among fabricators for a wide variety of reasons, but the limits of what it can achieve have not nearly been achieved, making its future very promising.

AWS Publications | December 14, 2021 | Tech and Industries
Welding Digest ►  The shiny future of metal additive manufacturing

Metal additive manufacturing (AM) is gaining popularity among fabricators for a wide variety of reasons, but the limits of what it can achieve have not nearly been achieved, making its future very promising.

Over the past few years, AM processes have gained popularity among metal fabricators because they provide a way to make graded metal alloy structures, embed various sensors or particles into a product, or produce parts that are extremely difficult — if not impossible — to create using traditional manufacturing methods. Reduced time from design to finished product, reduced stock requirements, and significant reductions in fabrication equipment may be realized.

Early work in AM used processes heated by lasers or electron beams. These processes are still widely used today but have been supplanted based on tonnage by arc-based processes, which have high deposition rates. Among the laser-based processes, most applications still use metal feed-stock powders. Some are moving toward using wire-based or hybrid feedstocks, in which both powders and wires are used to increase deposition rates. These laser-based processes provide fabricated products with excellent dimensional tolerances but lack the widespread variety of materials found in arc-based processes.

Fig.1-Dec-14-2021-02-21-25-90-PMLaser-based AM of an as-fabricated component showing tight tolerances along with a good surface finish. (Photo courtesy of EWI.)

 

From the beginning, high-deposition electron-beam-based processes used feedstock wire. In contrast, processes developed to provide fine features and high tolerances used metal powders. Early deposition rates by wire-fed electron beam processing provided high deposition rates of clean, high-quality metals. This is still true for the processing of reactive metals, such as titanium, aluminum alloys, and refractory metals. However, arc-based processes provide much higher deposition rates for other alloys that can be processed in more typical fabrication shops.

Fig.2-1This titanium-alloy aerospace component, created with AM, replaced a forged component. (Photo courtesy of Sciaky Inc.)


AM Takes Center Stage

The reasons for AM’s use across many industrial sectors are varied and generally fall into four categories: development of well-documented material properties, flexibility, reduced supply chain, and speed from design to finished product.

Several years ago there was a dearth of materials properties and characteristics information for additively manufactured structures. Today, conferences are full of attendees providing results from mechanical and metallurgical testing of additively manufactured materials. These properties are vital to helping design engineers and fabricators understand the structural integrity of the products they fabricate. Over 50 technical papers were presented on AM properties and characteristics at the recent American Welding Society (AWS) FABTECH 2021 Professional Program as well as the International Institute of Welding 2021 Annual Assembly.


Flexibility

AM processes provide great flexibility in the types of structures that can be fabricated and the material systems that can be used. Few materials used in industry are not in the process of being included in an AM application. These range from several-hundred-pound steel or titanium forging replacements to extremely small pieces, many less than one pound for various consumer applications. Some require very high-quality considerations. Others are chosen for their ability to provide appealing cosmetic effects.

Fig.3-Dec-14-2021-02-21-25-92-PMBrackets showing the reduced material requirements of as-fabricated AM products compared to traditionally fabricated brackets. (Photo courtesy of EWI.)

 

Reduced Supply Chain

The development of additively manufactured products to replace other supply chain links was one of the original drivers in their use. The use of metal powders and metal wires as feedstock allowed fabricators to significantly reduce rough product lead times and, in many cases, reduce or eliminate several finishing steps. These advantages, however, must always be weighed against the difficulties of using additively manufactured products, such as high levels of residual stresses and distortion.

 

Speed from Design to Finished Product

Another feature of additively manufactured products is their streamlined design-to-finished-product flow. With appropriate computer-aided design files that feed directly into a computer numerical control AM system, the design can be directly printed. This removes the need for other types of fabrication processes that are typically used to create a rough or finished product. AM can also deliver a significant reduction of processing steps, including forging, forming, and casting on the front end of the manufacturing flow, followed by reduced or eliminated machining on the back end. Depending on the material and specification requirements, however, heat treating or hot isostatic pressing may be required.

 

Availability of Industrial Standards

The range of AM uses has made the development of AM standards difficult, but new standards are being promulgated new with great urgency. AWS led in the development of an AM general qualification standard (AWS D20.1, Specification for fabrication of metal components using additive manufacturing), and many have since followed.

 

Continued Growth into Niche Applications

Much polymer fabrication is being done using many types of AM processes, several of which don’t lend themselves to use with metals. However, the industry is always looking at some of the still-niche applications for AM of metal products. These niche markets have been enabled by the continuing development of AM processes and can be expected to grow. We have only just scratched the surface of what AM can achieve.

 

This article was written by Doug Kautz (strategic materials program analyst, Leidos Inc., Henderson, Nev.), William Mohr (principal engineer – structural integrity, EWI, Columbus, Ohio), and Ajay Krishnan (research leader – additive manufacturing, EWI, Columbus, Ohio) for the American Welding Society.