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- 11. a) Explain the difference between „subtractive manufacturing“ and „additive manufacturing. b) Give two example processes each. (5 points)Subtractive: removing material to get shape
Additive: attaching material through layer building to get shape
subtractive: drilling, milling, grinding
additive: Stereolithography STL, Solid Ground Curing SGC, Selective Laser Melting SLM - 22. Define the term “Additive Manufacturing” (1)Term for all processes which produce components by joining volume elements preferable in layers
- 33. Which two additive manufacturing processes use liquid starting material? (2)Stereo Lithography SLA
Material Jetting MJ - 44. Which two additive manufacturing processes use powder as starting material? (2)Selective Laser Sintering SLS
Multi Jet Fusion MJF - 55. Describe how the material extrusion (MEX)/fused deposition modelling (FDM) process works. Use a schematic diagram, if helpful (5) Materials like ABS, PLA… polymers are heated in a print head/ extruder
Material is extruded onto print bed with high accuracy
Print head and bed can be moved in various combinations (X, Y, Z-Axis)
After one layer, distance from the extrusion nozzle to the build level is increased by the thickness of one layer
Next layer
Individual layers are bonded together by conducting heat from the newly deposited layer
Support structures can be made from separate support materials (second print nozzle) - 66. Describe how the multi-jet fusion (MJF) process works. Use a schematic diagram, if helpful (5) Build chamber is heated just below fusion temp. of processed material
Coater spreads layer of polymer powder over moveable printer platform
Print head jets liquids (“agents”) at specific locations
Heat-conducting agent is jetted where the material shall fuse together
Heat-isolating agent is jetted where sharp edges are required
Transforming agent can be jetted to influence mechanical and physical properties
After jetting, layer is heated with infrared, melting and fusing the powder at the intended locations
Build platform moves in z-axis and process is repeated - 77. What is the difference in technology between multi-jet fusion (MJF) and material-jetting (MJ)? Which prototypes are suitable as functional prototypes? (6)MJ:
Polymers are jetted by drops onto the build platform through nozzles
Curing of liquid material through UV light
Various materials can be printed during process
Usage of photopolymers
Usage of huge number of nozzles
No usage of powder as support - 88. Describe how Laser-Powder Bed Fusion (L-PBF)/selective laser melting (SLM) works. Use a schematic diagram, if helpful (5)A layer of powder is rolled onto the building platform.
A Laser beam which is guided to the powder with the use of a mirror and a lense selectively melts some of the particles which thereby get fused together.
After this step the building platform is lowered, and the next powder layer is rolled over. Then the laser process starts again. - 99. Give two reasons, why it is difficult to get very fine surface structures with Laser-Powder Bed Fusion (L- PBF)/selective laser melting (SLM) (4)● powder size
● thermal conductivity - 1010. What are the challenges in the production of metal parts with Laser-Powder Bed Fusion (L- PBF)/selective laser melting (SLM)? (6)● surface quality (usually low because of powder size and thermal conductivity)
● difficulties in cleaning internal cavities
● process temperature near material melting point
● sometimes inert gas atmosphere necessary
● Powder appliance on a L-PBF part during the building process:
○ powder bed layer and part are not on identical height in z-Axis
○ this is because of the thermal shrinkage of the part
○ powder layer thickness on the part is larger than in the powder bed - 1111. Why is powder handling in Laser-Powder Bed Fusion (L-PBF)/selective laser melting (SLM) an issue? (4)For L-PBF or SLM the powder size distribution is between 15-45μm:
● The PSD has a large influence on both the minimum layer thickness and the resolution of the finest details in the component.
● Inappropriate combination of PSD and layer thickness can lead to in-situ separation as the mechanical blade pushes coarser particles out of the powder bed. This can lead to variations in construction quality in the vertical direction.
● The use of powders with a wide PSD and a high amount of fine particles results in components with a higher fracture density.
● However, the use of fine materials increases the risk of health and safety problems (inflammability, pulmonary mobility). - 1212. What are the functions of support structures in Laser-Powder Bed Fusion (L-PBF)/selective laser melting (SLM)? (5)● Support structures are needed in certain cases in order to construct overhanging structures so that printed layers do not fall down. Generally structures with an angle exceeding 45° need to be supported!
● to avoid thermal shrinkages that effect from the sintering process
● to avoid thermal stress - 1313. What are the functions of support structures in material extrusion (MEX)/fused deposition modelling (FDM) (2)Support surface is required for the printing Process and for sinter shrinkages
- 1414. What are the disadvantages of support structures in material extrusion (ME)/fused deposition modelling (FDM) (2)● There is rework necessary -> difficult to remove, marks or damage
● layers printed on support structures will be less perfect and less stationary than the solid layers
● additional materials means additional costs even thought support material is usually cheaper than building material - 1515. What are the disadvantages of support structures in Laser-Powder Bed Fusion (L-PBF)/ selective laser melting (SLM)? (4)● There is rework necessary -> difficult to remove, marks or damage
● layers printed on support structures will be less perfect and less stationary than the solid layers
● additional materials means additional costs even though support material is usually cheaper than building material - 1616. Describe the difference between direct and sinter-based (indirect) additive manufacturing processes for metals (2)Direct processes
The part is directly produced with the additive manufacturing machine.
Indirect processes
Additive manufacturing combined with traditional manufacturing. For instance, master patterns are made with 3D printing technologies which are then used for investment casting of final parts. - 1717. Give three examples of sinter-based (indirect) additive manufacturing processes (3)● metal extrusion/ fused filament fabrication
● binder jetting
● lithography based metal manufacturing - 1818. What are possible advantages of inter-based (indirect) additive manufacturing processes? (3)• non-weldable material possible
• sintered microstructure
• (surface finishing)
• (powder handling) - 1919. What are disadvantages of inter-based (indirect) additive manufacturing processes? (3)• sinter shrinkage
• support surface required for sintering
• three complex manufacturing processes
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- Karteikarten am Ohne Titel, erstellt von sandro sterrantino am 14/05/2020.
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- sandro sterrantino · Mai 2020
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