Additive Manufacturing for the Aerospace Industry

Francis H. Froes,Rodney Boyer

• Publisher: Elsevier
• Year: 2019
• ISBN:
  9780128140635
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Additive Manufacturing for the Aerospace Industry explores the design, processing, metallurgy and applications of additive manufacturing (AM) within the aerospace industry. The book's editors have assembled an international team of experts who discuss recent developments and the future prospects of additive manufacturing. The work includes a review of the advantages of AM over conventionally subtractive fabrication, including cost considerations. Microstructures and mechanical properties are also presented, along with examples of components fabricated by AM. Readers will find information on a broad range of materials and processes used in additive manufacturing.

It is ideal reading for those in academia, government labs, component fabricators, and research institutes, but will also appeal to all sectors of the aerospace industry.

• Provides information on a broad range of materials and processes used in additive manufacturing
• Presents recent developments in the design and applications of additive manufacturing specific to the aerospace industry
• Covers a wide array of materials for use in the additive manufacturing of aerospace parts
• Discusses current standards in the area of aerospace AM parts

1

Introduction to aerospace materials requirements and the role of additive manufacturing

Francis Froes¹, Rodney Boyer^2,3 and B. Dutta⁴, ¹Advanced Materials Industries, Tacoma, WA, United States, ²School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai, P.R. China, ³RBTi Consulting, Bellevue, WA, United States, ⁴DM3D Technology, Auburn Hills, MI, United States

Abstract

The requirements for Aerospace Materials are presented including Specification details. The Additive Manufacturing (AM) techniques are described along with examples of parts fabricated by this method. Consideration is then given to different materials fabricated by AM including Metals, Ceramics and Polymers.

Keywords

Aerospace materials; additive manufacturing; metals; ceramics; polymers

1.1 Aerospace materials and their requirements

Aerospace materials are frequently metal alloys, although they also include polymeric based materials, that have either been developed for, or have come to prominence through, their use for aerospace purposes. Aerospace uses often require exceptional performance, strength or heat resistance, even at the cost of considerable expense in their fabrication or conventional machining. Others are chosen for their long-term reliability in this safety-conscious field, particularly for their resistance to fatigue loading. The field of materials engineering is an important one within aerospace engineering. Its practice is defined by the international standards bodies that maintain standards for the materials and processes involved, such as ASTM, AMS or company specifications (Table 1.1 shows specifications for additive manufacturing [AM]). Generally, not a lot of information is contained in company specs, but with the controls required, a company spec will be mandatory due to the complexity of the process, where the customer will want to know a lot more details than will ever get into a public spec due to protection of proprietary information. A further requirement is observer observation of fabrication of acceptable quality, including microstructures (Fig. 1.1).

Table 1.1

Specifications released and in-work for additive manufacturing (AM) components

Specification no.	Specification title	Status
AMS 4998	Titanium alloy powder, Ti–6Al–4V	Released—1977
AMS 4999	Titanium alloy laser deposited products, Ti–6Al–4V, annealed	Released—2002
AMS 7000	Additive manufacture of aerospace parts from Ni-base superalloy 625 via laser powder bed process	In work
AMS 7001	Ni base 625 superalloy powder for use in laser powder bed manufacturing of aerospace parts	In work
AMS 7002	Process requirements for production of powder feedstock for use in laser powder bed additive manufacturing of aerospace parts	In work
AMS 7003	Laser powder bed fusion process	In work
AMS 7004	Titanium alloy preforms from high deposition rate additive manufacturing on substrate Ti–6Al–4V stress relieved	In work
AS9100	Quality management systems—requirements for aviation, space, and defense organizations	Issued 1997, Current Rev. D, 2016

The AS (Aerospace Standards) are utilized for details with regard to quality management systems. They do not cover specific material requirements such as properties, inspection, etc.

Figure 1.1 Schematic showing powder bed fusion technology.

1.2 Additive manufacturing

In publications over the past few years [1–5], the cost of fabricating various titanium precursors and mill products has been discussed (very recently the price of TiO₂ has risen to $2.00 per pound and TiCl₄ to $0.55 per pound) and it has been pointed out that the cost of extraction is a small fraction of the total cost of a component fabricated by the cast and wrought (ingot metallurgy) approach. To reach a final component, the mill products must be machined, often with very high buy-to-fly ratios (which can reach as high as 40:1). The generally accepted cost of machining a component is that it doubles the cost of the component. The feedstock for AM can be a wire or a powder. Using powder, there are two basic approaches to AM: powder bed fusion (PBF) and direct energy deposition (DED), Figs. 1.1 and 1.2. The PBF technique allows the fabrication of complex features, hollow cooling passages, high precision parts, and single metal builds. The DED approach allows large build envelopes, high deposition rates, multiple materials, and addition of material to existing components. Mechanical properties are at least at ingot metallurgy levels (including fracture toughness). Examples of AM manufactured parts and parts which could be AM fabricated in an advanced engine are shown in Fig. 1.3.

Figure 1.2 Schematic showing DMD technology. DMD, Direct metal deposition.

Figure 1.3 (A) Examples of metallic parts fabricated by additive manufacturing. (B) The propulsion system for the F-35 lightening, which contains a substantial number of components that can be fabricated by additive manufacturing.

1.3 Additive manufacturing fabrication of various types of materials

The AM technique has been applied to metals, ceramics, and polymeric materials (Figs. 1.3–1.5)

Figure 1.4 Examples of ceramic parts fabricated by the additive manufacturing technique.

Figure 1.5 Examples of polymeric materials fabricated by additive manufacturing.

After the AM build, ceramic parts are porous and, if desired, can be infiltrated or fired in a postprocess step. This method is used for fine art ceramics. The primary advantages for 3-D printing, especially binder jetting (binder jetting is an AM process in which a liquid binding agent is selectively deposited to join powder particles. Layers of material are then bonded to form an object, for example by hot isostatic pressing) are low cost, high speed, scalability, ease of building parts in multiple materials, and versatility for use with ceramic materials. Originally evol...