Introduction to Additive Manufacturing

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Introduction

What is Additive Manufacturing (AM)?

Additive manufacturing describes a process or general approach to build tri-dimensional objects from digital files. AM functions by “adding” material, layer by layer until the object is built. Additive manufacturing represents a “Technology Classification,” where different specific implementations of this approach can be developed. 3D printing is one of the technologies covered by this classification.  In 3D printing, a nozzle or a LASER “draws” layer after layer with special materials that are melted or bonded together until the final object is created. However, 3D printing is not the only additive manufacturing technology. Another example, one of the oldest available, is Laminated Object Manufacturing or "LOM", in which a laser or blade cuts out profiles from sheets (paper, ceramics, metals), which form the layers of the final part. Layers are bonded together using heat activated resin, ultrasonic bonding, or other techniques.

The definition given to it by the ASTM F42 Technical Committee, in charge of the standardization of many of the emerging AM technologies, is the following[10]:

"Additive Manufacturing (AM) is the process of creating a physical object through the selective fusion, sintering or polymerization of materials"
 

Figure 1: Slicing a Tri-dimensional object [20].
 

Figure 2: AM process by Stacking Layers - Conversion of a solid model of an object (a) into layers (b), only one layer is shown [16].
 

As mentioned, AM is a technology and process that manufactures 3D-solid objects from digital models. AM machines and 3D printers generate 3D solid objects for testing or assembling working mechanisms. AM is an alternative to machine tooling. Reducing hard tooling processes can provide opportunities for manufacturers to make customized products. AM technology has the potential to change the way we add value to various manufacturing settings. For low-volume production demand, AM generally provides shorter lead times than conventional manufacturing methods. Manufacturing systems that have low-volume production, prototyping (such as found in space payload development), and mold mastering are implemented in AM systems [15].

“Unlike most conventional manufacturing techniques, AM forms objects by building matter up, rather than removing it. Paired with computer-aided design (CAD) software, this technique affords the creation of new types of objects with unique material properties. But while AM is widely billed as ‘the next industrial revolution’, in reality, there are still significant hurdles for successful commercialization of the technologies” [37].

AM systems have been used by Fortune 500 companies for more than a decade and major progress has been achieved in AM over the last few decades. AM is proving to be an essential element for product designers and engineers. AM users anticipate that, in the future, AM will compete with mass production systems as it enables new alternatives in shape and function for production [15].

Traditional machine tooling or "Subtractive Technologies," such as CNC equipment, that remove unnecessary material from a solid volume layer by layer, have many differences and disadvantages over Additive Manufacturing, here a list of some of the most important ones:

Here is a short list of other advantages of Additive Manufacturing [11] that can be beneficial to the aerospace industry including payload and cubesat development:
 

Advantages

  • Complexity is free: The cost is less to print a complex part than a simple cube of the same size. The more complex (or, the less solid the object is), the faster and cheaper it can be made through additive manufacturing.
  • Variety is free: If a part needs to be changed, the change can simply be made on the original CAD file and the new product can be printed right away.
  • No assembly required: Moving parts such as hinges and bicycle chains can be printed in metal directly into the product, which can significantly reduce the part numbers.
  • Little lead time: Engineers can create a prototype with a 3-D printer immediately after finishing the part’s stereo lithography (STL) file. As soon as the part has printed, engineers may then begin testing its properties instead of waiting weeks or months for a prototype to be produced.
  • Little-skill manufacturing: While complicated parts with specific parameters and high-tech applications should be left to the professionals, even children in elementary school have created their own figures using 3-D printing processes.
  • Few constraints: Anything you can dream up and design in the CAD software, you can create with additive manufacturing.
  • Less waste: Because only the material that is needed is used, there is very little (if any) material wasted (depending on the AM technology in use, in some case waste can be recycled).
  • Infinite shades and materials: Engineers can program parts to have specific colors and also material properties in their CAD files, and printers can use a combination of materials and any color to print them (high-end multi-material color 3D printers).

Today, according to ASTM F2792 Standards, there are seven families of Additive Technologies (plus Hybrids), each one using different types of materials as it can be seen in Figure 3. Some of the most important characteristics of each family and also the types and properties of available materials are shown below.

Figure 3: Seven Families of AM Technologies plus hybrid according to ASTM F2792 Standards[3].
 

Independent of the type of AM machine, in general, there are always eight distinct steps in the process sequence:

  1. Conceptualization and CAD: Design the 3D part/model with Computer Aided Design (CAD) software.
  2. Conversion to STL: Transform the CAD file from the software format to a more open format as an STL file.
  3. Transfer and manipulation of the STL file on AM machine: Usually using a network, USB, or SD cards.
  4. Machine setup: Configuring the machine itself.
  5. Build sequence: Actual building of the 3D object.
  6. Part removal and cleanup: Remove from the machine, clean, and remove supports.
  7. Part post-processing: Surface finishing, hardening, etc.
  8. Application: Use of the part.

We will discuss these steps more in detail as this course progresses. The process steps can be summarized as shown in Figure 4:

Figure 4: AM Summarized Process Steps [36].
 

Let's watch a short introductory video about 3D Printing as one of the main Additive Manufacturing Technologies:


 

There are several names used for identifying AM, such as additive layered manufacturing (ALM), rapid manufacturing (RM), rapid prototyping (RP), layer manufacturing technique (LMT), and 3D printing. Stereo-lithography was a term used by 3D Systems Co., while 3D Printing was used by MIT researchers. The term additive manufacturing (AM) will be used throughout this course.