Additive Manufacturing

1	Basics, Definitions, and Application Levels

To understand the characteristics and the capabilities of additive manufacturing (AM), it is very helpful to take a look at the systematics of manufacturing technologies in general first.

1.1	Systematics of Manufacturing Technologies

Orientated on the geometry only, manufacturing technology in general is divided into three fundamental clusters [Burns, 93, AMT, 14]:1

1. subtractive manufacturing technology,

2. formative manufacturing technology, and

3. additive manufacturing technology.

With subtractive manufacturing technology, the desired geometry is obtained by the defined removal of material, for example, by milling or turning.

Formative manufacturing means to alter the geometry in a defined way by applying external forces or heat, for example, by bending, forging, or casting. Formative manufacturing does not change the volume of the part.

Additive manufacturing creates the desired shape by adding material, preferably by staggering contoured layers on top of each other. Therefore it is also called layer (or layered) technology.

The principle of layer technology is based on the fact that any object, at least theoretically, can be sliced into layers and rebuilt using these layers, regardless of the complexity of its geometry.

Figure 1.1 underlines this principle. It shows the so-called sculpture puzzle, in which a three-dimensional (3D) object has to be assembled from more than 100 slices. Therefore the layers have to be arranged vertically in the right sequence using a supporting stick.

Additive manufacturing (AM) is an automated fabrication process based on layer technology. AM integrates two main subprocesses: the physical making of each single layer and the joining of subsequent layers in sequence to form the part. Both processes are done simultaneously. The AM build process just requires the 3D data of the part, commonly called the virtual product model.

It is a characteristic of AM that not only the geometry but the material properties of the part as well are generated during the build process.

1.2	Systematics of Layer Technology

In this section the commonly used terms in AM are addressed. The related characteristics as well as their interdependency and the hierarchical structure are discussed.

In this book the generally accepted so-called generic terms are used, and alternatively used names are mentioned.

Generic terms and brand names have to be distinguished from each other. If they are mixed, which happens quite often, this frequently leads to confusion. As brand names are important in practice, they are addressed, explained, and linked to the generic terms in Chapter 3, where the AM machines are presented.

1.2.1

Application of Layer Technology: Additive Manufacturing and 3D Printing

Additive manufacturing is the generic term for all manufacturing technologies that automatically produce parts by physically making and joining volume elements, commonly called voxels. The volume elements are generally layers of even thickness.

Additive manufacturing is standardized in the US (ASTM F2792) and in Germany (VDI 3405), and is commonly used worldwide.

As alternative terms, additive manufacturing (technology) and additive layer manufacturing (ALM) have minor acceptance.

3D printing is about to replace all other names, including additive manufacturing, and to become the generally accepted generic term for layer technology in the near future. This is mainly because it is very easy to understand. Everyone who can operate a text editor (a word processor) and a 2D office printer easily understands that he or she will be able to print a 3D object using a 3D design program (a part processor) and a 3D printing machine, regardless of how it works.

NOTE: Additive manufacturing and 3D printing are used as equal generic terms in this book. While in Chapter 1 this is expressed by always writing additive manufacturing /3D printing (or AM/3DP). In the following chapters only additive manufacturing or AM is used in order to shorten the text volume.

Beginners should realize that 3D Printing is also the brand name of a family of powder binder processes (see Section 3.6), originally developed by MIT and licensed to Z-Corporation (now 3D Systems), Voxeljet, and others.

1.2.2

Characteristics of Additive Manufacturing

Layer technologies in general and additive manufacturing in particular show special characteristics:

• The geometry of each layer is obtained solely and directly from the 3D computer-aided design (CAD) data of the part (commonly called a virtual product model).

• There are no product-related tools necessary and consequently no tool change.

• The material properties of the part are generated during the build process.

• The parts can be built in any imaginable orientation. There is no need for clamping, thus eliminating the clamping problem of subtractive manufacturing technologies. Nevertheless, some processes need support structures, and the orientation of the part influences the parts’ properties.

• Today, all AM processes can be run using the same so-called STL (or AMF) data structure, thus eliminating data exchange problems with preprocessors as used in subtractive manufacturing.

Additive manufacturing/3D printing therefore ensures the direct conversion of the 3D CAD data (the virtual product model) into a physical or real part.

As scaling can be done simply in the CAD file, parts of different sizes and made from different materials can be obtained from the same data set. As an example, the towers of a chess set shown in Fig. 1.2 are based on the same data set but made with different AM machines and from different materials. The range of materials includes foundry sand, acrylic resin, starch powder, metals, and epoxy resin.

One of the biggest AM parts of all is the tower shown in Fig. 1.3 with a height of approximately 2.5 m, which is higher than the general manager of the Voxeljet Company, Mr. I. Ederer.

By contrast, Fig. 1.4 shows a tower made by micro laser sintering. It is approximately 5 mm high.

AM/3DP allows manufacturing of geometric details that cannot be made using subtractive or formative technologies. As an example, the towers on Fig. 1.2 contain spiral staircases and centered double-helix hand rails. The details can be seen on a cutaway model displayed in Fig. 1.5.

Another example of geometries that cannot be manufactured using subtractive or formative technologies is shown in Fig. 2.5.

All AM/3DP processes mentioned here will be explained in detail in Chapter 3.

1.3	Hierarchical Structure of Additive Manufacturing Processes

For a proper definition of the terms used, it is very helpful to distinguish the technology and its application from each other. Subtractive manufacturing, for example, marks the technology level, and drilling, grinding, milling, and so on are the names for its application (or the application level).

The technology of additive manufacturing/3D printing is divided in two main application levels: rapid prototyping and rapid manufacturing. Rapid prototyping is the application of AM/3DP to make prototypes and models or mock-ups, and rapid manufacturing is the application to make final parts and products.

The manufacturing of tools, tool inserts, gauges, and so on usually is called rapid tooling. The term often is regarded as an independent hierarchical...