Additive Manufacturing of Metals

Metal working has played a key role in the development of human civilization. Naturally occurring metals such as gold, began to take form in manmade metal objects as the Stone Age transitioned from gathered objects into the earliest forms of metal processing technology. Metal objects took the form of personal adornment, symbols of power, and tools of conquest. Thousands of years passed as metal extraction and forming technology slowly advanced to include alloys such as bronze and metals such as iron. The age of discovery led to the identification, extraction, refinement, and use of new metallic elements, alloys, and manufacturing processes. The dawn of the computer age enabled significant technical advances in decades rather than centuries. Information available to all leads to the convergence of technologies empowering individuals to design and manufacturing complex metal objects. That which was once the providence of Kings and Pharaohs, empires, armies, and captains of industry is now within our reach. This chapter provides a brief introduction to technical milestones leading to the development of additive metal process technology. Metal has empowered mankind with the ability to capture our visions, realize our dreams, and build objects that extend the power of our thoughts in time and space. Metal is often hidden in nature and requires time, labor, and energy to extract and form into useful objects. This elusive and mysterious nature of metal has been part of the allure in its ownership as the expense, capabilities, and skills needed to create complex metal objects has most often been out of reach to all but a few. Metal and energy, harnessed by man’s dreams, grant us the power to capture the present and create the future. Epics of human progress have been defined by metals such as bronze, iron, and steel; energized by the sun, fire, and electricity. Gold and silver have built world power and adorned our most prized possessions. Steel has built armies, skyscrapers, bridges, railways, and pipelines. Copper has joined together voices of people from across the world. But, the world is changing. In this new century, thoughts are created, captured, and shared as data across the planet at the speed of light. Information on any subject is at our fingertips, where and when it is needed. But words and images are not enough, we still need things to have, hold, and use. In a world where information is called the new power and bitcoins emerge as a new currency, it can all disappear in a flash. Metal endures. But first, where did it all start?

Novel applications and designs showcase the power and potential of 3D printing and additive manufacturing of metal. This chapter identifies the market segments where AM is making inroads and having the greatest impact. The momentum in advances of AM metal technology, historically driven by rapid prototyping for engineering applications, is rapidly changing and moving toward the production of high value components made of advanced materials. Application examples include critical products such as those certified for use in aerospace and for medical hardware. In addition, customized artistic designs and one of a kind personalized items are being created on demand. Unique designs and functions are being incorporated into parts unthought-of only yesterday. The potential to transform industry and realize significant cost and energy savings is demonstrated by the use complex cooling channels in hardware for the tool and die industry to high-performance heat exchangers and wear resistant coatings in the energy, oil and gas industries. Repair and remanufacturing of components with every increasing complexity using multiple and advanced materials is being demonstrated. This chapter provides examples of components and products within the hottest segments of AM metal technology, introducing the art of the possible.

The advantages offered by additive manufacturing intersect a wide range of industries, occupations, and potential users. This chapter provides various scenarios of the artist, student, inventor, business owner, engineer, or technology manager describing how additive manufacturing can combine with their skills, capabilities, and interests to assist the reader to place themselves within the context of this new technology. This chapter provides an introductory overview of the types and capabilities of current additive manufacturing systems that can best meet your application. A discussion of market and technology drivers asks key questions to assist the reader in clearly defining their needs and how the advantages or limitations of AM technology can drive the decision of whether or not to adopt AM technology. Questions are presented to address considerations such as material cost savings, energy and time efficiencies, and conversely what legacy drivers can impede the reader’s adoption of AM. Additive manufacturing of metal exists at the confluence of multiple diverse technologies with a language of terms borrowed from each. The reader is introduced to these terms and with the high level overview provided by this chapter, prepared to build an understanding of those technologies and materials fundamental to AM metal processing.

Additive manufacturing of metal exists at the convergence of a wide range of advanced technologies ranging from the design of computer solid models and computer-driven machines to high-energy beam processing of materials. Many technologists with diverse backgrounds are being drawn into additive manufacturing with little knowledge of or experience working with metals. This chapter provides a quick refresher of the building blocks of metal, its crystal or microstructure and the properties resulting from the chemistry of the specific metal alloy and the process used to form it into useful shapes. Simple examples are used to illustrate the wider range of forms and structures metal can take as a result of operations such as casting and rolling, then compared with metal processed by additive manufacturing methods. The non-metallurgist is introduced to less common forms of metal such as metal powders, wire, and electrodes as well as the microstructures formed by sintering and solidification. Less common materials such as composites, intermetallic, and metallic glasses are introduced as the potential use and application of these advanced materials is increasing as made possible by the adoption of additive manufacturing.

High energy heat sources used to melt and fuse metal are widely used in industry. While laser and electron beam processing have been in use for 50 years or more, and arc welding for more than a century, the fundamentals of these processes are often poorly understood. The increased automation of these metal processing systems further remove the operator or engineer from the basic function and control of these heat sources, the molten pool and ultimately the fused metal deposit. AM metal processing systems often operate within the confines of an enclosed chamber and at high speeds creating extremely small molten pools further obscuring the basic functioning of the process. This chapter describes the basic function of these heat sources, what happens when a high energy beam or arc heats a metal surface to melt and fuse powder or wire into shaped parts. The use of auxiliary and additional heat sources during AM processing and post-processing is introduced.

High powered computing hardware, software, and sophisticated computer-based sensing and control has migrated from the factory and entered the cloud and the home. We have become comfortable with computers, software applications, and computer-driven machines as they now exist in our homes in many forms ranging from smart phones to remote controlled toys. We now have access to low cost 3D printers in the studio, or down the street, and access to larger commercial machines over the Internet. It is useful to understand what the building blocks of these machines are and how they fit together to best choose AM metal printing capability. In this chapter, we discuss the range and capabilities of 3D solid model software, 3D scanners, and computer-aided design (CAD) that support AM. In addition, we introduce and discuss computer-aided engineering (CAE), computer-aided manufacturing (CAM), computer numerical control (CNC), and motion systems. Most importantly, we focus on the aspects of these technologies as applied to AM metals. You will be introduced to the STL or Stereolithography file format, originally developed for rapid prototyping of polymer materials and plastics, offering a simple solution to computer-defined surface geometry. The evolving need for interoperability and cross platform independence is discussed as well as the development of the 3MF file format.

3D printing and additive manufacturing brings together and continues to draw from advances within a wide range of technologies such as information, computing, robotics, and materials. Developments in all of these highly visible, high impact, and highly publicized sectors will undoubtedly be modified, adopted, and integrated into the evolution of advanced manufacturing. Advancements within technologies smaller in scope, such as 3D printing plastics, or less visible sectors such as powder metallurgy, laser and weld cladding will also continue to play an important role in the continued evolution of AM metal. It is useful to understand the origins of AM metal processing as derived from these technologies as they will continue to play an important role.

System configurations for additive manufacturing metal are most often described and differentiated by the heat source used, such as laser, arc or electron beam, how the feedstock is delivered, the type of feedstock used, such as wire or powder, or the size of the part produced ranging from in meters to millimeters. It is useful to understand the basic system configurations as they all feature different attributes and capabilities. There are advantages and limitations to each and it is important to the user to understand these variations to make an informed decision as per which is the best for their needs. This chapter provides a technical description of the basic functions and features of each type of system. In addition other hybrid process that begins with a 3D computer model and results in a metal part are also described as these can in some cases be a competitive option to those systems that go from model directly to metal. Processes that exist on the border of the more common definition of AM metal, such as those that produce parts at the micrometer and nanometer scale, are also introduced.

A strong attraction of solid freeform fabrication is the removal of design constraints imposed by commercial metal shapes and conventional processes; opening a whole new world of design possibilities. Commercial metal shapes associated with sheet metal, tubing, angle iron, pipes and plates will not be going away anytime soon, but add the possibility of forming flowing organic surface shapes, complex passageways, and unique internal or external structures, and we can begin to rethink what is possible when working with metal. The same thinking can release us from shape constraints imposed by creating features using drilling, shearing, bending, milling and casting or pressing into molds. This chapter will describe the AM design process and compare it side by side with the design process for conventional metal processing. We will include a few examples of how one method is better than the other and which is right for you. We will discuss the advantages and disadvantages of selecting one material over another. In addition, we will highlight a few examples of hybrid applications, combining the best of 3D printing, conventional and subtractive processing and how 3D metal printing can define a new design space for thinking outside the box. This chapter will build upon the existing body of metal working design knowledge, complement it, transform it and take it to levels not possible in years past.

The power of AM metal processing is realized from both the design freedom and the removal of many of the constraints imposed by commercial shapes (such as flat sheets, round pipes, etc.) and some of the constraints imposed by conventional processing (such as straight drilled passages, linear bends, etc.). This freedom comes at the cost of process complexity as the many process parameters available to the AM engineer are often poorly understood and hard to control. While AM machine vendors will offer parameter sets for a specific set of materials and often offer design and process consultation, AM users are often faced with designing and optimizing a prototype process along with designing and optimizing a prototype part. This chapter steps the reader through AM process development and the process of parameter selection to optimize part density, surface finish, accuracy, and repeatability while reducing build time, distortion, residual stress, other defects and conditions that may affect part quality or performance.

The build cycle of an AM part can be broken down into prebuild operations, the actual build, post-processing, and inspection. This chapter provides the reader with a typical scope and sequence of operations and considerations associated with these operations. This knowledge is useful for those users considering the purchase and establishment of an AM system capability as well as those utilizing service providers. Knowledge of post-processing and finishing operations is critical to the design process and plays a critical role in subsequent design or process improvements. Operations such as powder recycling, heat treatment, hot isostatic pressing, machining, and surface finishing are discussed as well as the application of nondestructive and destructive evaluation and defect detection as applied to AM metal parts. Ongoing efforts within industry to draft standards and certify AM produced part are described.

In this chapter, we identify current trends in government sponsored programs, universities, industry, and private enterprise, technology development, and adoption. Taking a higher level view we predict how the technology will connect these sectors and where we will see the greatest impact in the next 5 years. 3D printing and AM technology have been in development for at least the past two decades with the hard work of science and engineering being done at universities, national labs, and within corporate research labs. Advanced manufacturing has seen large investments on the order of billions of dollars driving a higher level of activity and high profile of media attention. The global impact of additive manufacturing is gaining momentum with high levels of funding seen at the government, university, and major corporation levels. Emerging economies are seeing the advantages of developing AM capabilities without the burden of historical infrastructures and as a potential means to leap frog the development of costly infrastructure or creating an advanced manufacturing infrastructure well suited to regional needs. Business, commerce, intellectual property, global, and social issues are discussed and reference leading national and global intelligence reports. The author concludes with a summary of the trends and destinations of highest impact for AM metal technology.