chap3

• Additive manufacturing (AM) is the formalized term for what used to be called rapid prototyping and what is popularly called 3D Printing
• Rapid prototyping (RP) is used in various industries to create system or part representations before final release or commercialization
• Improvements in the quality of output from RP machines have led to a closer link to the final product
• ASTM adopted the term additive manufacturing (AM) in 2009
• AM is defined as the process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing
• AM technology differs in the materials that can be used, how the layers are created, and how the layers are bonded to each other
• Common to AM technologies is the use of a computer, 3D modeling software, machine equipment, and layering material
• AM encompasses technologies like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), layered manufacturing, and additive fabrication
• AM parts are used for creating tooling or consumer products
• High-power energy source/laser technology enables parts to be directly made in a variety of metals
• AM technology has developed over time as materials, accuracy, and overall quality of the output improved
• AM, when used with other technologies, can significantly shorten product development times and costs
• Development in AM technology and materials has extended the output suitable for end use
• The key difference between 3D printing and CNC machining is that 3D printing is a form of additive manufacturing, while CNC machining is subtractive
• Advantages of CNC machining include great dimensional accuracy and compatibility with various materials like wood, metals, and plastic
• AM technology developed around polymeric materials, waxes, paper laminate, composites, metals, and ceramics
• AM technology produces a part in a single stage, while CNC machining may take weeks for the same process
• AM processes are not constrained in the same way as CNC, allowing for easier building of internal features and undercuts
• AM machines have variable resolution along different orthogonal axes, while CNC machines have accuracy mainly determined by positioning resolution along all three axes
• AM machines break up a complex 3D problem into a series of simple 2D cross-sections, while CNC machining of surfaces must normally be generated in 3D space
• In CNC machining, surfaces must normally be generated in 3D space
• Freeform surfaces can be extremely difficult to produce with CNC, even with 5-axis control or greater
• Undercuts, enclosures, sharp internal corners, and other features can fail if they are beyond a certain limit
• Many Additive Manufacturing (AM) machines have minimal options that must be selected
• The worst outcome in most AM machines is that the part will not be built well if the programming is not done properly
• Determining the program sequence for a CNC machine can be very involved, including tool selection, machine speed settings, approach position, angle, etc
• Incorrect programming of a CNC machine could result in severe damage to the machine and may even be a safety risk
• All AM parts must start from a software model that fully describes the external geometry
• Reverse engineering equipment, like laser scanning, can be used to create the required representation for AM parts
• Nearly every AM machine accepts the STL file format, which has become a de facto standard
• STL files describe the external closed surfaces of the original CAD model and form the basis for the calculation of the slices
• The shapes of the slices in AM represent cross-sections, with thick solid sections of material often removed and replaced with cross-hatching
• The direction of building in AM affects key aspects such as surface finish quality, build time, support structures needed, and trapped volume
• Trapped volume in AM refers to the amount of liquid resin that was entrapped by the processed or solidified region
• Part placement in AM is important for optimizing build time by closely packing multiple parts into feasible volumes
• Support structures in AM ensure the recoater blade will not strike the platform, improve layer thickness uniformity, and provide a means of removing the part upon completion
• Slicing the file in AM involves passing closely spaced horizontal planes through the STL file to generate a series of 2D cross-sections of the 3D object
• The final build file in AM includes the part and supports sliced, AM technology parameters set, and is sent to the AM machine for building
• The AM machine must be properly set up prior to the build process, including settings related to build parameters like material constraints, layer thickness, timings, etc
• Building the part in AM is mainly an automated process that requires superficial monitoring to ensure no errors have occurred