ADDITIVE MANUFACTURING ACTUAL LATEST
ANSWERS AND QUESTIONS SET A+
✔✔Temperature in Liquification (Extrusion based Systems) - ✔✔materials in the
chamber should be kept molten at the lowest possible temperature; high temp requires
additional cooling; some polymers degrade with high temps and some could burn and
contaminate the chamber with residue or there could be clogging issues
✔✔Extrusion Based Systems -Material Categories - ✔✔high temp materials are divided
into 2 main categories- semi-crystalline and amorphous (difference in molecular
structure) ; Amorphous is better bc it can be extruded in viscous paste
✔✔Amorphous Materials - ✔✔randomly ordered molecular structure with no sharp
melting point; soften gradually and viscosity lowers as temperature rises; these
materials change viscosity when heated but are seldom easy flowing as semi-crystalline
materials
✔✔Extrusion-Based Systems: Materials - ✔✔isotropic in flow, shrinking uniformly in the
direction of the flow and transverse to flow; amorphous exhibit lower mold shrinkage
and less tendency to warp; viscosity is high so that they will maintain shape after
extrusion and will enable quick solidification
✔✔Extrusion-based Systems: Most popular material - ✔✔ABSplus; lower strength
(interfacial regions in layers, voids)
✔✔Extrusion - ✔✔size and shpae determined by nozzle; larger nozzles have higher
flow but less precision; diameter of the nozzle determines the smallest feature that can
be built
✔✔Flow (through nozzle) relation - ✔✔material flowing through the nozzle is controlled
by the pressure drop between the chamber and the atmosphere (mass flow = f(pressure
drop, nozzle geometry, viscosity)
, ✔✔Solidification in Extrusion-based Systems - ✔✔extruded material should remain in
same shape and size; forces against gravity and surface tension; cooling and drying
effects are non-linear; minimize shrinkage and distortions while cooling
✔✔how can distortion and shrinkage mitigation can be achieved? - ✔✔ensuring the
temperature differential between the chamber and the surrounding atmosphere is
minimized; ensuring cooling precess is gradual and slow
✔✔Positional Control - ✔✔a typical system has the deposition head move in XY
horizontal plane; platform indexes separately in the Z direction for layer control
✔✔Positional Control: Linear Drivers must be - ✔✔(1) able to accelerate/ decelerate to
accomodate speed and build times (2) responsive to changes in speed and direction (3)
perform the above with little "backlash"
✔✔positional control: Issues with change of directions and part accuracy - ✔✔any time
there is a change in direction, the plotting head must decelerate and also accelerate; at
some point the instantaneous velocity of the head will be zero; if the extrusion does not
slow down or completely stop with these turns and changes, excess material will be
deposited
✔✔Do FDM machines deposit the outer contour patterns at a different speed than the
infill material? - ✔✔yes the outer contour patters are deposited more slowly because
more precision is needed than the infill areas
✔✔Extrusion Based Systems: Bonding - ✔✔heat based systems rely on residual energy
to activate the surface on the adjacent regions, thus bonding; gel based systems must
contain residual solvent or wetting agent in the extruded material to bond the adjacent
regions
✔✔Too much energy when bonding (extrusion based systems) - ✔✔will cause
previously solidified material to flow, which will affect part quality and precision
✔✔insufficient energy when bonding (extrusion based systems) - ✔✔might cause
adhesion with a distinct boundary between the old and newly deposited material
✔✔"Rafts" - ✔✔special case of support material; they constitute a sacrificial layer to
ease separation from build platform and help with the integrity of various built
components
✔✔Support generation - visually - ✔✔separation might be easier if we can tell the two
products apart
ANSWERS AND QUESTIONS SET A+
✔✔Temperature in Liquification (Extrusion based Systems) - ✔✔materials in the
chamber should be kept molten at the lowest possible temperature; high temp requires
additional cooling; some polymers degrade with high temps and some could burn and
contaminate the chamber with residue or there could be clogging issues
✔✔Extrusion Based Systems -Material Categories - ✔✔high temp materials are divided
into 2 main categories- semi-crystalline and amorphous (difference in molecular
structure) ; Amorphous is better bc it can be extruded in viscous paste
✔✔Amorphous Materials - ✔✔randomly ordered molecular structure with no sharp
melting point; soften gradually and viscosity lowers as temperature rises; these
materials change viscosity when heated but are seldom easy flowing as semi-crystalline
materials
✔✔Extrusion-Based Systems: Materials - ✔✔isotropic in flow, shrinking uniformly in the
direction of the flow and transverse to flow; amorphous exhibit lower mold shrinkage
and less tendency to warp; viscosity is high so that they will maintain shape after
extrusion and will enable quick solidification
✔✔Extrusion-based Systems: Most popular material - ✔✔ABSplus; lower strength
(interfacial regions in layers, voids)
✔✔Extrusion - ✔✔size and shpae determined by nozzle; larger nozzles have higher
flow but less precision; diameter of the nozzle determines the smallest feature that can
be built
✔✔Flow (through nozzle) relation - ✔✔material flowing through the nozzle is controlled
by the pressure drop between the chamber and the atmosphere (mass flow = f(pressure
drop, nozzle geometry, viscosity)
, ✔✔Solidification in Extrusion-based Systems - ✔✔extruded material should remain in
same shape and size; forces against gravity and surface tension; cooling and drying
effects are non-linear; minimize shrinkage and distortions while cooling
✔✔how can distortion and shrinkage mitigation can be achieved? - ✔✔ensuring the
temperature differential between the chamber and the surrounding atmosphere is
minimized; ensuring cooling precess is gradual and slow
✔✔Positional Control - ✔✔a typical system has the deposition head move in XY
horizontal plane; platform indexes separately in the Z direction for layer control
✔✔Positional Control: Linear Drivers must be - ✔✔(1) able to accelerate/ decelerate to
accomodate speed and build times (2) responsive to changes in speed and direction (3)
perform the above with little "backlash"
✔✔positional control: Issues with change of directions and part accuracy - ✔✔any time
there is a change in direction, the plotting head must decelerate and also accelerate; at
some point the instantaneous velocity of the head will be zero; if the extrusion does not
slow down or completely stop with these turns and changes, excess material will be
deposited
✔✔Do FDM machines deposit the outer contour patterns at a different speed than the
infill material? - ✔✔yes the outer contour patters are deposited more slowly because
more precision is needed than the infill areas
✔✔Extrusion Based Systems: Bonding - ✔✔heat based systems rely on residual energy
to activate the surface on the adjacent regions, thus bonding; gel based systems must
contain residual solvent or wetting agent in the extruded material to bond the adjacent
regions
✔✔Too much energy when bonding (extrusion based systems) - ✔✔will cause
previously solidified material to flow, which will affect part quality and precision
✔✔insufficient energy when bonding (extrusion based systems) - ✔✔might cause
adhesion with a distinct boundary between the old and newly deposited material
✔✔"Rafts" - ✔✔special case of support material; they constitute a sacrificial layer to
ease separation from build platform and help with the integrity of various built
components
✔✔Support generation - visually - ✔✔separation might be easier if we can tell the two
products apart
