Metal Additive Manufacturing: A Review
William E. Frazier
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William E. Frazier, Naval Air Systems Command, Patuxent River,
MD
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This paper reviews the state-of-the-art of an important, rapidly emerging, manufacturing technology that is alternatively called additive manufacturing (AM), direct digital manufacturing, free form fabrication, or 3D printing, etc. A broad contextual overview of metallic AM is provided. AM has the potential to revolutionize the global parts manufacturing and logistics landscape. It enables distributed manufacturing and the productions of parts-on-demand while offering the potential to reduce cost, energy consumption, and carbon footprint. This paper explores the material science, processes, and business consideration associated with achieving these performance gains. It is concluded that a paradigm shift is required in order to fully exploit AM potential.
1. Introduction
ASTM has defined additive manufacturing (AM) as a
process of joining materials to make objects from 3D model
data, usually layer upon layer, as opposed to subtractive
manufacturing methodologies. Synonyms: additive fabrication,
additive processes, additive techniques, additive layer
manufacturing, layer manufacturing, and freeform fabrication
(Ref 1). This definition is broadly applicable to all classes of
materials including metals, ceramics, polymers, composites,
and biological systems. While AM has been around as a means
of processing materials for, arguably, over two decades, it has
only recently begun to emerge as an important commercial
manufacturing technology.
In 2009, Bourell et al. (Ref 2) published a roadmap for AM
based on a workshop of 65 key people in AM. Their report
explored important facets of the AM including:
Design
Process modeling and control
Materials, processes, and machines
Biomedical applications
Energy and sustainability applications
In 2010, Frazier (Ref 3) published the results of a Navy
workshop entitled direct digital manufacturing (DDM) of
metallic components: affordable, durable, and structurally
efficient aircraft. A vision of parts on demand when and
where they are needed was articulated. Achieving the vision
state would enhance operational readiness, reduce energy
consumption, and reduce the total ownership cost of naval
aircraft through the use of AM. Specific technical challenges
were identified to address the quantitative objectives in the
areas of (i) innovative structural design, (ii) qualification and
certification, (iii) maintenance and repair, and (iv) DDM
science and technology. Top level findings include
High priority should be given to developing integrated
in-process, sensing, monitoring, and controls.
Machineto-machine variability must be understood and controlled.
Alternatives to conventional qualification methods must
be found; these are likely based upon validated models,
probabilistic methods, and part similarities. Part-by-part
certification is costly, time consuming, and antithetical to
achieving the Navy s vision of producing and using AM
parts on demand.
Priority should be given to the development of integrated
structural and materials design tools. This is needed to
accelerate the adoption of AM by the aircraft design
community and to promote new innovative structural designs
needed to save energy and weight.
Underline science of DDM needs to be developed.
Physics-based models are needed relating microstructure,
properties, and performance. New alloys must be developed to
optimize properties. An understanding of how to control
fatigue properties and reduce surface roughness, must be
developed.
Hederick (Ref 4) published a review of AM of metals in 2011.
Presented is a nice summary of the various AM technologies
and the dominate AM equipment manufacturers. AM
equipment was broadly divided into powder bed systems, laser
powder injection systems, and free form fabrication (FFF)
systems. Some of the major findings of the report include:
Materials processed using AM experience complex
thermal processing cycles. There is a need to better
understand the link between microstructure, processing, and
properties for AM fabricated parts, as well as developing
an AM materials database. He reports that there has been
a lot of work on Ti-6Al-4V, but not so much on other
alloys.
There is a need reduce the variance in properties and
quality from machine-to-machine across materials and machine
types. Therefore, closed-loop feedback control and sensing
systems with intelligent feed forward capability needs to
be developed. Further, the ruggedization of AM
equipment is needed.
AM can be applied to the manufacturing of parts that
cannot be made with standard machining practices. This
possibility enables novel design methodologies.
NIST held a workshop in December of 2012 and recently
published the results Measurement Science Roadmap for
Metal-Based Additive Manufacturing (Ref 5). Important
technology challenges were identified in the areas (i) AM
materials, (ii) AM process and equipment, (iii) (...truncated)