Card Set Information

2013-07-10 22:33:14
Andreas Gebhardt FH AACHEN

AFT exam
Show Answers:

  1. 1.1 Why there are no AM processes named and discussed in Chapter 1
    Chapter 1 discusses the application areas and provides a structure of AM process applications. This basic structure doesn't depend on certain processes.
  2. 1.2 What is the main characteristic of additive manufactured parts?
    • Almost any geometry can be made.
    • Due to the layer oriented process, all AM parts show stair stepping.
  3. 1.3 Why do technology level and application level have to be distinguished from each other?
    The technology level provides the theoretical and scientific background, while the application level defines the use and the benefit expected from AM.
  4. 1.4 What isthe difference between Generative Manufacturing and Additive Manufacturing
  5. 1.5 What is the relationship between Generative Manufacturing, Additive Manufacturing, and Layer-Based Manufacturing?
    Additive and Generative Manufacturing are generic terms that indicated that ther parts are buildt by adding the material or by generating it from volumes. Today, the technical realization of AM solely based on layers and therefore is called "Layer-Based Technology", "Layer-Oriented Technology", or even "Layered Technology". All three terms indicate identical processes.
  6. 1.6 What are the applications of Solid Images?
    Solid images are used to evaluated the general appearance, the shape, and the haptic properties of a part during product development. It is valuable  for product data control as well.
  7. 1.7 How do Solid Images and Functional Prototypes differ from each other?
    Solid images are just 3D pictures or statues, while functional prototypes show one or a limited number of the functionalities of the product.
  8. 1.8 Why do Follow-up or Secondary Rapid Prototyping processes not belong to the family of AM processes?
    Because the parts are not made layer-by-layer but using a casting tool (the mold).
  9. 1.9 Why are indirect processes often called Indirect Rapid Prototyping processes of simply Rapid Prototyping processes?
    Because the word "rapid" is fashionable and the users expects an improvement of the economic success.
  10. 1.10 Why does the term Rapid Tooling does not define its own application level?
    Making tools and tool components is technically identical with making final metal parts. The machines, the process, and the materials are identical. Therefore, both applications belong to the level Rapid Manufacturing. Only the CAD design differs depending whether the part (positive) or the mold for its production(negative) is made.
  11. 1.11 What is the difference between Functional Prototyping and Direct Manufacturing?
    Functional Prototyping leads to prototypes that show just a few selected functionalities of the final products, while Direct Manufacturing generates a part that is completely identical with the final product.
  12. 1.12 Why is Prototype Tooling an application, positioned between the application levels Manufacturing and Prototyping?
    Because the tool is made using prototype parts and methods, therefore it is considered a prototype, while resulting parts made from it show series quality , at least under special circumstances.
  13. 2.1 What is the principle of AM?
    The part to be produced has to be represented by a set of 3D CAD data. The data is virtually cut into layers thickness using a so called slice algorithm. This provides the contour data and the thickness of each layer.
  14. 2.2. Why do AM parts show stair - stepping effects?
    Because the layer thickness is constant, and there is only one contour per layer.
  15. 2.3. What are the two main steps of every AM process?
    • 1) Generating a single layer with a shape according to the contour and with a given layer thickness based on the slice data
    • 2) Joining the new layer on top of the preceding one
  16. 2.4 What is the typical layer thickness of AM parts made of plastics?
    Most of the machines process layers in the range of 0.1 mm but there are machines that deliver thickness of 0.016mm and the machines with approximately 0.2 mm thickness
  17. 2.5. Describe all AM processes
    give full description + key features
  18. 2.6 There are two AM processes that deliver multi-colored parts. Name both
    Extrusion, namely the Fused Deposition Modeling(FDM), and 3D printing, the powder-binder process.
  19. 2.7 There are two AM processes that deliver multi-colored parts. How do they differ from each other?
    FDM can process only one color at a time which is provided by the filament. 3D printing can process continuously colored part as it is known from 2D printers.
  20. 2.8 Why should a 3D printed parts (powder binding process) not be used in structural tests?
    Because the properties of the part are defined by the quality of infiltration rather than by the build process and the powder - binder material system used.
  21. 2.9 How do the master models have to be prepared for RTV?
    They have to be polished. Ducts and vents need to be added. The part lining has to be defined.
  22. 2.10 What processes can be used to join metal sheets when using LLM for metal parts?
    Diffusion welding, soldering, powder welding, mechanical bolts.
  23. 3.1 Why can AM prototypes be made on the same machine, using the same process, and the same material that are used to make AM products?
    • Whether a part is a prototype or a product does not depend on the machine or the material used, but on the part design. The part will be a product if it meets the AM design criteria and the AM material data.
    • If it is designed to meet the series manufacturing requirements, but made by AM and from AM materials, it will be a prototype  independently from the AM Machine and material.
  24. 3.2 What kind of AM process is preferably used to make cores for sand casting and why?
    Laser Sintering and 3D printing of foundry sands and polymer based binder. It is very much the same material used in conventional sand casting.
  25. 3.3 What industry branch uses stereolithography preferably?
    The application of an AM process, for instance stereolithography, is not a question of the industry branch, but of the part characteristics. If fine details have to be processed, good surface quality is demanded, and only low temperatures are applied, stereolithography is the preferred AM process. This is valid for any industry branch.
  26. 3.4 What materials can be processed with metal laser sintering or laser melting processes?
    Laser melting delivers dense metal parts. The processes are developed to process commercially available metal powders. A wide variety of blends that lead to alloys can be used if the powder has been validated. The powders offered by the manufacturers of AM machines can be regarded as validated. Materials are mild steel, tool steel, stainless steel, Co-Cr alloy, titanium, aluminum, and others. Copper is supposed to enter the market.
  27. 3.5 Where do the 3D data needed for processing come from
    In Engineering data mostly come from 3D CAD design and can be directly derived from the CAD data by a STL post processor. In the medical field most of data come from CT scans of patients. In industry, there is a growing tendency to used specialized CT scanners as well, because this allows for non destructive overall data verification.
  28. 3.6 What AM processes can be used to make colored parts?
    • If just one color is needed, then most of the AM processes can do it. It is easier in Fused Deposition Modeling, because the colored material is available and can be changed quickly. If stereolithography or sintering is used, the whole build chamber has to be filled with the desired colored material.
    • Two colors, due to two materials, can be processed Object Connex Machine. Multi colored parts can be made by the Z Corp 3D printing process. It even allows to process bitmap based textures. On the downside the color is placed just on the surface.
  29. 3.7 Architects have been using scaled models for many years and developed high non-AM modeling skills. How can AM improve architectural modeling?
    All part of the architecture models that can be processed by non-AM technologies, such as milling and cutting, should be made by those methods. AM is useful when freeform surfaces or very detailed parts are requested. in practice, models will be composed from Am and non-AM parts. if color is needed and manual painting should be be avoided, 3D printing is very helpful.
  30. 3.8 Am processes often are not very suitable for making a small series of parts or parts with defined properties such as transparency or elasticity. How can AM be used in those cases?
    AM delivers a very good geometrical model in a short time. If it is not directly applicable, it could be used as a master part for secondary rapid prototyping.
  31. 3.9 How do toys for children and adults differ and how is AM affected by this?
    Toys for adults are mainly for display, and require very good surface details and filigree structures even in the prototype phase.  That is why polymerization is often used for these applications. Toys for children need to be robust, which often has to be proved even in the prototype phase. In such cases, sintering or extrusion of plastics are typically used. 
  32. 3.10 What are the two AM based approaches for making medical implants for head surgery?
    • Based on the data of the defect, either a wax type master for precision casting can be made by polymerization or sintering of plastics or waxes, and then turned into titanium parts by casting.
    • Alternatively, the implant can be made directly by laser melting. The direct AM production is faster, the lost wax casting is cheaper. If major changes are needed, the part made by casting can be modified and and redone very quickly at low cost.
  33. 3.11 How are AM and conformal cooling linked?
    Conformal cooling requires 3 D channels following the surface of the mold as closely as possible. Shaped channels like this cannot be drilled or cast, although there are exceptions. Layer oriented AM is the only way to manufacture such channels, by means of metal laser melting.
  34. 4.1 Why can AM deliver parts with almost unlimited complexity of geometry?
    Since any part can be sliced virtually, any part can be composed of its slices, regardless of complexity.
  35. 4.2 What kind of AM processes are capable of processing materials that have variable properties within a part?
    AM processes creating parts voxel-by-voxel can basically change the properties of each voxel.
  36. 4.3 Give at least three examples for material properties that can be varied within a part?
    Flexibility, color, or the composition of different materials.
  37. 4.4 Why can AM processes deliver arbitrary number of parts?
    AM works layer by layer, independently if layers are identical or not.
  38. 4.5. What hinders traditional (non AM) process from making individual parts?
    Non AM processes need tools, and tools require a comparably large quantity of identical parts in order to realize a return on investment for the tools
  39. 4.6 Why does individualization NOT depend on selected AM process?
    Individualization is a strategy to meet the customer's requirement. It basically is a design method that first of all defines the product. This product can be manufactured  by several AM processes that might fit. Whether the process is right or not is not a question of the strategy, but of its application.
  40. 4.7 Why is AM-based worldwide networked local production more likely to be realized than a technology based on other digitally controlled manufacturing techniques (such as CNC milling)?
    Because all AM machines can be run with the same type of STL data files, while most CNC programs need machine dependent pre-processors
  41. 4.8 What the characteristics of self- customization ?
    Self customization  is defined by the design and manufacturing of a personalized object by the customer's own AM device, preferably by a fabber.
  42. 4.9 By which criteria can individualized and personalized products be distinguished?
    • Individualized products are focused on the target customer group. They are produced in small series, but still in series. Depending on the break even point, both non-AM and AM processes can be used.
    • Personalized products are designed only for one person. This definitely requires an AM process.
  43. 4.10 How can hinges be made in one piece using AM?
    The space needed for the hinges to rotate is occupied by the unsintered powder. After the build it is removed, and the hinges can rotate.
  44. 5.1  Why is anisotropy an important problem for AM
    Building a part layer-by-layer causes bonding problems between the layers that depend on the material and the way bonding is done.
  45. 5.2 Which plastic AM processes show anisotropic effect and to what extend?
    From quasi-isotropic to anisotropic: polymerization, laser sintering, FDM, 3D printing and layer laminate manufacturing.
  46. 5.3 Why does metal laser sintering is more isotropic than plastic laser sintering ?
    Because the material is molten completely, thus creating  the name selective laser melting.
  47. 5.4 What the pros and cons of qualifying materials in-house vs getting them from a supplier?
    • Pros: well known material, proprietary composition and build files, lower price
    • Cons: Higher price, dependent on supplier, lack of knowhow.
  48. 5.5 How do the powders and processes for plastic laser sintering differ from sinter coating?
    Additives and process details, such as shielding gas and preheating, suppress local evaporation, oxidation, and other inter-process effects and interaction with the environment
  49. 5.6 What are typical grain sizes for polyamide sintering?
    20 to 50 micros
  50. 5.7 What kinds of plastics can be processed by AM? Plot the in plastic triangle
  51. 5.8 How can hinges be made in one build? what geometrical parameters(clearance) have to taken into account?
    As film hinges or by leaving some unsintered layers for clearing; 0.3 to 0.8 microns
  52. 5.9 Why does AM not have clamping problems? How are parts fixed?
    Because they have supports or are held by the powder
  53. 5.10 What does "relative fit" mean? Why is it only relevant for AM?
    Part fit although they are not geometrical correct, because they are put face to face and close together in one build.