307 Exam 1 Review Flashcards
Describe the Vat Photopolymerization process.
process in which liquid photopolymers in a vat are selectively cured by light activated polymerization
What is the powder bed fusion (PBF) additive manufacturing process?
thin layers of powder are spread over a build plate and selected areas of the powder bed belonging to the part model are fused with an energy source
What was the first commercially implemented PBF process?
Selective Laser Sintering
What materials can be used in the PBF process?
Thermoplastics, metals, ceramics
Among the four primary binding mechanisms in the PBF process, which has the slowest fusion speed?
1. Solid State Sintering
2. Chemically Induced Binding
3. Liquid Phase Sintering (Partial Melting)
4. Full Melting
Solid State Sintering
Among the four primary binding mechanisms in the PBF process, which mechanism primarily works with ceramics, and which one works with metals?
1. Solid State Sintering
2. Chemically Induced Binding
3. Liquid Phase Sintering (Partial Melting)
4. Full Melting
Chemically Induced Binding for ceramics, Full Melting for metals
Among the four primary binding mechanisms in the PBF process, which mechanism raises concerns about part porosity, and how can it be addressed?
1. Solid State Sintering
2. Chemically Induced Binding
3. Liquid Phase Sintering (Partial Melting)
4. Full melting
Chemically induced binding, can be addressed with post processing techniques
What is the difference between sintering and melting?
Temperature, sintering involves no or partial melting
Are all metal additive manufacturing systems using a point-wise method and metal powder?
No, sheet lamination process uses an entire metal sheet
How can we categorize additive manufacturing techniques?
Type of material (metals, ceramics, plastics–thermoset & thermoplastic)
Form of Raw Material (Powder, droplet, liquid, etc.)
Binding Mechanism (melting, sintering, etc)
Energy Source (Thermal, laser, electron beam, etc.)
What was the first commercialized additive manufacturing process?
Stereolithography (SLA), Vat Photopolymerization
Why do the color of Vat Photopolymerization-fabricated parts change over time?
The photopolymers are sensitive to light (UV in particular) and ambient temperature, causing it to degrade over time.
In the stereolithography process, where does the maximum irradiance occur as the laser hits on the resin surface?
in the center
What parameters affect the penetration depth and the cure depth?
Material characteristics for penetration depth.
Cure depth is affected by the penetration depth, max irradiance, and critical exposure.
What is the primary material type used in the Selective Laser Sintering Process?
polymers, metals, ceramics, composites and sand
What is the primary material type used in the Electron Beam Melting process?
Metal
Why do we need to add support structures for the metal powder bed fusion processes?
To prevent excessive warping of the part
Is it true that finer particle sizes are better for the Powder Bed Fusion Process?
Finer particles lead to smoother surface finish and better accuracy, but they are more difficult to spread and handle.
Why does the Powder Bed Fusion Process require relatively longer printing time than other AM processes?
The need for pre heat and cool-down cycles
What is the purpose of the environmental control unit used for in the SLS process?
Temperature control and providing low pressure or inert atmosphere
Why are thermoplastic materials well suited for the PBF process?
relatively low melting temperatures, low thermal conductivities, and low tendency for balling
What are the key differences between Stereolithography and Selective Laser Sintering systems?
Selective Laser Sintering requires heat control but does not need support generation
Why aren’t thermosets used in powder bed fusion processes?
They can’t be melted and re-solidified
What is the purpose of the molten constituents in the Liquid Phase Sintering (Partial Melting) binding mechanism? (Powder Bed Fusion Process)
They have a lower melting temperature which allow it to melt and bind the solid particles together
Sintering becomes increasingly rapid as the temperatures approach the _________ temperature.
Melting
Which PBF binding mechanism is the slowest for selectively fusing regions out of all PBF processes?
Solid State Sintering
The time it takes for fusion by ______ is much longer than fusion by ________.
sintering; melting
What binding mechanism is described as the use of thermally activated chemical reactions between two types of powders, or between powders and atmospheric gasses to form a by-product which binds the powders together?
Chemically-Induced Sintering
Which PBF binding mechanism is primarily used for ceramic materials?
Chemically-Induced Sintering
What is the biggest disadvantage of the chemically-induced sintering binding mechanism?
The need for post processing due to part porosity concerns
What happens when there is too much residual heat energy for bonding in extrusion based processes?
Too much energy causes previously deposited material to flow, which may result in a poorly defined part
What happens when there is insufficient residual heat energy for bonding in the extrusion based processes?
Insufficient energy results in a distinct boundary between new and previously deposited material
For extrusion based systems, what type of energy causes the bonding?
Residual Heat Energy
What is the key challenge of extrusion based systems that use heat?
Achieving sufficient residual heat energy, which can be affected by printing speed and temperature
Which parts of the FDM system control movement of the vertical and horizontal axis?
Vertical axis movement is controlled by the linear stage/build platform
The horizontal axis movement is controlled by the extrusion head and plotting system
What general factors affect the extrusion process in FDM systems?
- Input pressure
- Temperature
- Material characteristics
- Gravity
- Etc..
What can be done to address the challenges of FDM systems when it comes to changing direction while printing?
Use lower speed plotting for the part outline and faster speed plotting for part interior.
What types of materials are commonly used in Extrusion Based AM?
Thermoplastic polymers
True/False: Liquification of material is always necessary in Extrusion Based processes?
False, raw liquid material can be used
What is the type of manufacturing process that produces a product completely with zero or minimal post processing?
Net Shape Process
Name at least three different types of net shape manufacturing processes
Forging, drawing, extrusion, rolling
Sheet metal forming, bending
Die casting, investment casting
Injection Molding
Name three different types of subtractive manufacturing processes.
Lathing, milling, grinding, drilling
Water jetting, laser cutting, etc
What is the purpose of the scanning galvanometers in Vector/Laser Scan Stereolithography?
They direct the path of the laser beam
When is subtractive manufacturing a preferred process?
- Large scale production of large and low complexity parts
- Fabricating finished metal parts
- Parts require high mechanical strength and durability
- Better surface finish
True/False
For the photopolymerization process, you cannot change the penetration depth once the material is chosen.
True, the penetration depth is dependent on the material characteristics
What is the cause for the accuracy challenge in Vector Scan and Mask Projection Stereolithography, and how can it be addressed?
Non-uniform light intensity which can be addressed by calibrating and adjusting the intensity of light pixels using gray scale
Which PBF process uses a moving laser beam that sinters heat fusible powders in areas corresponding to the CAD geometry model one layer at a time to build the solid part?
Selective Laser Sintering
Fused Deposition Modeling is an example of an extrusion based approach that uses _____ to control the material state.
Temperature/heat
What are the two main factors that affect the accuracy and surface finish of powder bed fusion processes?
Operating conditions and particle sizes
True/False:
Accuracy and surface finish of liquid-based processes are typically inferior to that of powder based processes.
False; accuracy and surface finish of liquid-based processes are typically better than powder based.
What causes the warping of parts during powder bed fusion processes?
High residual stresses
True/False:
Supports are required for most metal powder bed fusion processes.
True; to prevent the part from excessive warping due to high residual stresses.
True/Fasle:
Materials with high thermal conductivity result in better accuracy in PBF processes.
False; low thermal conductivities result in better accuracy.
Loose powder is a sufficient support material for _____ powder bed fusion. (Polymer or metal?)
Polymer
What fusion mechanisms does the EBM process use?
Melting and solidification
Which PBF process typically has a better surface finish, Electron Beam Melting or Selective Laser Sintering?
Electron Beam Melting; SLS can require more post processing for smoothness
Fill in the missing characteristics of the powder delivery system of PBF processes:
1. Reservoir of sufficient volume
2. Correct volume for powder to be transported
3.
4.
- Smooth, thin, repeatable layer.
- Do not create excessive shear forces.
Fill in the missing characteristics of the powder delivery system of PBF processes:
1.
2.
3. Smooth, thin, repeatable layer.
4. Do not create excessive shear forces
- Reservoir of sufficient volume
- Correct volume for powder to be transported
What are the three universal characteristics of the powder feeding in PBF processes?
- Deal with friction and electrostatic forces
- Prevent explosion
- Protect other instruments from powder interference
Which materials are generally described as compounds that consist of metal oxides, carbides, and their combinations?
Ceramics
What is the definition of critical exposure in the photopolymerization process?
The exposure at which resin solidification begins to occur
Fused deposition modeling and thermojet technology fall under which category?
- liquid polymer
- discrete particle
- molten material
- solid state
- metal
- hybrid
Molten Materials
Most direct metal systems work using a ____ ______ method, and nearly all of them use ____ _____ as inputs.
point-wise; metal powders
What is the benefit of hybrid manufacturing systems?
provides greater flexibility, precision, and efficiency in producing complex parts
Which Stereolithography process uses a digitial micromirror device for precise control of curing an entire cross-section of the part at once?
Mask-Projection Stereolithography
Which stereolithography process uses an infrared laser to trigger the chemical reaction?
Two-Photon Stereolithography
What does the nozzle diameter determine in FDM processes?
The minimum feature size that can be created
Describe the fused deposition modeling process.
uses a heating chamber to liquefy polymer that is fed into the system as a filament. Filament is then pushed into the chamber by a tractor wheel arrangement, which generates the extrusion pressure.
What are the three general characteristics of an extrusion based system?
- material must bond \to material that has already been extruded, so that a solid structure can result
- must be able to start and stop the flow of material
- It must move the extruder upwards, or move the part downwards.
