Why is it called Additive Manufacturing?
Additive Manufacturing refers to the process, in which the workpiece is built up in successive layers or units. It's called additive manufacturing when an object is made by adding material rather than subtracting or reforming it.
How do Additive Manufacturing processes differ from conventional processes?
In Additive manufacturing, components are built up layer by layer and are not created by removing or reforming material as in conventional processes .
What are the application levels in Additive Manufacturing?
Rapid Prototyping and Rapid Manufacturing and repair
What are the advantages of Additive Manufacturing?
Customization, decreased costs, sustainability, efficient supply chains
What technologies make Additive Manufacturing possible?
Computer science, CAD technology, laser technology, material science
In what cases does Additive Manufacturing perform better than conventional processes?
In the production of complex, individualized and small components as well as in small series production
What are the important process branches of Additive Manufacturing?
Single-stage AM processes
Multi-stage AM processes
What factors can affect the end product?
Material type
Machine architecture
Energy input strategy
Material state
Why is Additive Manufacturing becoming more crucial in terms of current manufacturing trends?
Increasing product complexity and embedded functionality
Decreasing time to market
In which industrial areas does Additive Manufacturing play an important role?
Aerospace
Medical / Dental
Motor vehicles
Consumer goods
What is the difference between prototype and model? What are the 2 types of prototype/model?
A model is a representation of a product that is used to test and refine its design before the final product is produced. A prototype, on the other hand, is a working model of the final product that is used to test its functionality and performance.
Types: 1. visual model/ prototype, 2. functional model/ prototype
What is a Slicer? What is it used for?
Tool that decomposes the component into individual layers.
Why: cutting of 3D geometry by planes with constant distance (=layer height)
What is the stair stepping effect? How can it be reduced?
Layer-by-layer build process induces a geometrical error (steps in z-direction) -How: ➢Increased geometric accuracy ➢ Increased build time (= increased costs)
Which AM technologies need supports? What is the use of supports?
Material Extrusion (MEX) (Metal and plastic)
Powder Bed Fusion with Metals (PBF-LB/M)
Vat Photopolymerization (VPP)
Material Jetting
Why: increases statik strength
Engürel heat dissipation
Why is the orientation of the components important?
Necessity of support structure
Geometric accurancy
Surface quality
Mechanical properities
Why is it difficult to design AM components with conventional CAD programs?
Which 11 steps can be performed in a slicer to create a G-code for an AM system?
What geometrical dimension of a build job affects the build time most?
The number of layers and layers height
What physical event is the laser effect based on?
Active laser medya can emit radiation when their atoms drop from an excited energy state to a lower energy state. The energy between the two states corresponds to the energy of the emitted photon.
What are the categories of laser-matter interaction?
Reflection R
Refraction
Absorption A
Transmission T
Which parameters of a laser and the corresponding optics influence the spot size?
What is the Rayleigh length?
The Rayleigh length (zR) is a parameter that describes the divergence of a focused beam of light.
How are very high feed rates (up to 10 m/s) generated in additive and welding processes?
Which beam sources and wavelengths are established in which additive manufacturing processes?
What general characteristic structure do metals have?
There are 4 states of material (all metals) : plasma, gas, liquid and solid (crystallin or amorphous)
Why are metals thermally and electrically conductive?
Effect is explained by the Drude theory of metals, also known as the electron gas
+
• Electrons are delocalized which results in electrical and thermal conductivity
• Electrons are present in a gas like state and interact with the positively charged ions → characteristic for each type of metal
• As the kinetic energy is higher than the electrostatic force of attraction
→ Particles repel each other
What crystallite shapes can metals have?
Cubic
Hexagonal
Tetragonal
Which parameters determine the crystallite shape and size of metals?
Solidification
Thermal treatment
Cooling rate (size)
How is the crystallite shape of additively manufactured parts different from casting components?
Crystallite shape:
planar
cellular
columnar dendritic
Microstructure in Casting
1. Outer equiaxed dendritic
2. Columnar dendritic
3. Inner equiaxed dendritic
What is the requirement for the metal if it is to be used in single step metal Additive Manufacturing?
Should have a defined and consistent particle size distribution.
Metal alloy composition should be well-defined and consistent.
What metals are commonly used in metal Additive Manufacturing?
Steel And iron-based alloys
Titanium and titanium-based alloys
Nickel-based alloys
Aluminium
How is Inconel different from other metals?
Inconel is mainly used for high temperature applications. When heated, a thick stable oxid layer is formed, which protects the surface.Corrosion Resistance
How can powders for metal AM be manufactured?
Metal Powder Production
-Mechanical Crushing
-Atomization
-Electrolysis (rarely used)
-Chemical Reactions (rarely used)
How do powder and wire for AM differ?
What are the particular advantages of the DED process compared to other Additive Manufacturing Processes?
Directed Energy Deposition (DED)
1. **Rapid Build Rates:**
2. **Material Variety:**
3. **Repair and Cladding:**
What are the main categories of DED processes?
1 Laser-based Directed Energy Deposition
2 Directed Energy Deposition with an Arc
3 Cold Spray
What are the main differences between WAAM and wire DED-LB and the main differences in application?
WAAM = source of fusion, electric current And build rate, resolution, layer height bigger than DED-LB
DED-LB = source of fusion, laser
What is the main feature of cold spray Additive Manufacturing?
Cold Spray Additive Manufacturing
Source of fusion = Speed of gas
Feedmaterial = powder
Transport of Feedmaterial = Gas jet
What are the main working principles of the PBF process?
Powder bed fusion processes are additive manufacturing processes in which thermal energy selectively and layerwise fuses regions of a powder bed.
As thermal energy, lasers or electron beams can be used.
What is powder coating? What coating method do you know?
Powder coating is a dry finishing process where pigment and resin powder, applied electrostatically, are cured on a surface at high heat for a durable and uniform finish, commonly used on metal.
Powder tank:
Powder is conveyed from above through a powder tank and then distributed by the coater, also tanks as part of the coater are established.
Dosing platform:
Powder is conveyed from the bottom to the top and distributed by the coater.
What scanning strategies do you know, and why are they used?
Scan strategies within one layer
Targeted influencing of the heat balance by adjusting the scan strategy
Scan strategies of different layers
• Compensation of anisotropic microstructure
• Symmetrical distribution of shrinkage and stress effects
• Control eigenstress and material density
How does the keyhole effect occur, and how is it characterized by the process defect and the depth-to-width ratio?
Keyhole formation:
High intensities and powers cause vapor capillaries.
The process drifts off to a deep penetration welding process
The consequences are overheating and development of gas pores.
(welding depth bigger than width of the weld pool) t/b > 1
What are the component defects in the PBF LB/M process window?
keyhole formation
gas pores
balling
lack of fusion
How does lack of fusion occur? And how does this phenomenon differ from the keyhole effect in terms of pores?
lack of fusion exposure speed + Beam power -
the keyhole effect exposure speed - Beam power +
What are the main characteristics of PBF-LB/M?
Layer by Layer build up
• Material used : Metal Powder
• high tempereture necessary for AM of metals
• laser is used at the main heat source
• Reduced Material waste: unmelted powder is removed
What are the main characteristics of PBF-EB/M?
Build process = layer-by-layer additive technique in vacuum
Source material = powder: metal alloys
PBF-EB/M process runs under high vacuum, since the electron beam can only be operated in this atmosphere
→ no protective gas flow but high vacuum
What are the build-up rates in the three main categories of metal AM?
• What are the chemical and physical differences between the three main polymeric classes?
Fusible: eriyebilir, soluble: çözünebilir
• What is the difference between an amorphous and semi-crystalline polymeric material?
Amorphous: low E-Modulus, transparent, no structure, soft
Semi-crystalline: high E-Modulus, partly structured, hard,
• What are influencing factors on the flow behavior of powders?
• Which materials are used in Material Extrusion and Powder Bed Fusion of Plastics respectively?
MEX: Thermoplastic polymers, Composite filament
PBF - LB/P: Plastic powder, filled Plastic Powder.
• What are the essential process steps and parameters of MEX and PBF-LB/P?
• Why is no support necessary for PBF-LB/P?
Plastic powders often exhibit (sergilemek) better flowability and self-supporting properties compared to metal powders.
Plastic Powders have besser stabiliy in powder bed.
• What is described by the „model of quasi-isothermal lasersintering“?
The isothermal laser sintering model processes semi-crystalline thermoplastics in a specific temperature range, allowing the material to be both molten and solid simultaneously in part building.
• What impacts and what is impacted by the energy density during PBF-LB/P?
Impacted by the energy density: Layer Connection
• What are common process errors in PBF-LB/P and how can they be reduced?
Energy density too low: Bad Surface finish
Energy density too High: Smoke and decolorization / yellow regious
• Which materials can be used in Vat Photopolymerization, Binder Jetting and Material Jetting?
Vat Photopolymerization = liquid resin
Binder Jetting = liquid powder, binder
Material Jetting = liquid resin
• Which process catogeries of Vat Photopolymerization are there?
Digital light processing VPP
Laser Vat Photopolymerization
• What is the difference between the free surface approach and the constrained surface
approach?
Direction of incident light:
Free surface approach: light from up
Constrained surface approach: light from down
• Why is CLIP so much faster than all other Vat Photopolymerization methods?
CLIP has less steps. It skips on steps like Separation, Re-Coating and Re-positioning.
advanced light and oxygen control
• What are influencing factors for Binder Jetting?
Machine
Process
Heating conditions
Powder
• What are the limitations of Material Jetting towards other AM processes?
Limitations
• Lower temperature resistance
• Materials slightly brittle (thermosets)
• Low UV-resistant (embrittlement and discoloration possible)
• Restrictions in the geometric freedom
• What are the typical process-related post-processing steps of PBF-LB/P? (MEX, BJT, VPP)
• Why is post-curing an essential post-processing step for VPP parts? Which material properties are affected?
• What is mass finishing? What is it used for? What are disadvantages and advantages of mass finishing?
(repeat for all other secondary post-processing methods, compare them)
• What are the essential post-processing steps in PBF/LB-M? Why is a suitable heat treatment important?
• Give 3 examples for required (process-related) post-processing and optional (secondary) postprocessing.
• What process requires machining as post-process?
DED
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