Unit 1 Comprehensive Quiz: FDM 3D Printing

Unit: 01 - FDM 3D Printing Duration: 30-45 minutes Passing Score: 70% Format: Multiple choice covering all modules Questions: 12

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Instructions

This comprehensive quiz covers all modules in the FDM 3D Printing unit. You should complete all module assessments before attempting this unit quiz. The quiz tests both factual recall and application of concepts across modules.

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What is the correct sequence of the FDM extrusion cycle from filament spool to deposited layer?

Heating → feeding → nozzle exit → cooling → pressure buildup

Filament feeding → heating past glass transition temperature → pressure buildup in hot end → nozzle extrusion → deposition and solidification

Pressure buildup → filament feeding → heating → nozzle extrusion → solidification

Nozzle extrusion → heating → pressure buildup → filament feeding → solidification

Submit

Explanation: The complete extrusion cycle begins with the drive mechanism feeding filament into the hot end, where it is heated past its glass transition temperature (Tg). As softened filament accumulates, back-pressure builds (100-500 bar typical). This pressure forces molten plastic through the nozzle orifice, where it is deposited onto the build surface and rapidly solidifies as it cools below Tg.

A student's PLA print shows strong first-layer adhesion but severe warping at the corners starting around layer 20. Which combination of settings would BEST address this?

Increase nozzle temperature by 20°C and reduce bed temperature to 0°C

Increase print speed to reduce time the plastic spends cooling

Add a brim for adhesion area, reduce cooling fan speed for the first 10 layers, and ensure bed temperature is 55-60°C

Switch to a 0.8mm nozzle to deposit more material per layer

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Explanation: Corner warping occurs when differential cooling creates internal stresses that overcome bed adhesion. A brim increases the adhesion footprint, reduced fan speed allows lower layers to cool gradually (reducing stress buildup), and proper bed temperature (55-60°C for PLA) keeps the base above its stress-relaxation point. Simply raising nozzle temperature would worsen stringing without addressing the root cause.

Why should layer height not exceed 75-80% of nozzle diameter?

Thicker layers use too much filament and increase material cost

The slicer software cannot calculate toolpaths for thick layers

The nozzle must be able to press each layer against the previous one for proper adhesion; exceeding ~80% prevents adequate compression

Thick layers cause the extruder motor to overheat

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Explanation: For proper layer adhesion, the nozzle must squish the extruded bead against the layer below, creating molecular diffusion at the interface. With a 0.4mm nozzle, maximum practical layer height is ~0.32mm. Beyond this, the nozzle cannot compress the bead sufficiently, resulting in weak inter-layer bonds and potential delamination under stress.

During a print, you hear a rhythmic clicking from the extruder and notice gaps in the deposited filament. What is the most likely cause?

The bed is not level

The filament spool is tangled

The extruder drive gear is skipping because the nozzle is partially clogged or the temperature is too low, creating excessive back-pressure

The print speed is set too slow

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Explanation: Clicking from the extruder indicates the stepper motor is losing steps — it cannot generate enough torque to push filament through the hot end. This is most commonly caused by a partial clog (carbonized filament in the nozzle) or insufficient nozzle temperature (plastic too viscous). The solution is to perform a cold pull to clear the clog or increase temperature by 5-10°C.

What is the primary purpose of support structures in FDM printing?

To make the print stronger by adding extra material

To help the print cool evenly on all sides

To provide a temporary scaffold for overhanging features that would otherwise collapse due to gravity during printing

To anchor the print to the bed so it does not move

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Explanation: FDM deposits material layer by layer. Any feature that extends beyond ~45° from vertical has no layer below to support it, so gravity would cause the molten plastic to sag or collapse. Support structures are generated by the slicer to bridge this gap, then removed after printing. Support removal can leave surface marks, so part orientation should minimize support needs.

You are calibrating a new FDM printer. The first layer shows parallel lines with visible gaps between them. What adjustment is needed?

Increase the nozzle temperature

Decrease the print speed

Decrease the Z-offset (move the nozzle closer to the bed) so the extruded lines are pressed together with no gaps

Increase the layer height setting in the slicer

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Explanation: Gaps between first-layer lines indicate the nozzle is too far from the bed. The Z-offset needs to be decreased (nozzle lowered) in small increments (0.02-0.05mm) until adjacent extrusion lines slightly overlap. A proper first layer shows lines that are pressed together with no gaps but are not so compressed that the surface appears translucent or the nozzle scrapes the bed.

How does infill percentage affect print strength and material usage?

Higher infill always produces stronger parts regardless of load direction

Infill has no effect on strength; only wall thickness matters

Higher infill increases compressive strength and material usage proportionally, but the relationship between infill and tensile strength plateaus around 40-60% for most geometries

Lower infill produces stronger parts because the hollow structure absorbs impact

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Explanation: Infill contributes primarily to compressive strength (resistance to crushing). For tensile and bending loads, wall/shell thickness matters more than infill. Most functional parts perform well at 20-40% infill; increasing beyond 60% adds material cost and print time with diminishing strength returns. The infill pattern also matters — gyroid and cubic provide more uniform strength than rectilinear.

What material property determines the minimum nozzle temperature required for successful FDM printing?

The material's tensile strength

The material's density

The material's glass transition temperature (Tg) — the nozzle must heat the filament well above Tg so it flows freely through the orifice

The material's UV resistance

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Explanation: Glass transition temperature (Tg) is the point where a thermoplastic transitions from rigid to pliable. For FDM, the nozzle must heat filament 30-40°C above Tg to achieve adequate flow. PLA (Tg ~60°C) prints at 190-220°C; ABS (Tg ~105°C) prints at 230-260°C. Printing below optimal temperature causes under-extrusion and poor layer adhesion.

A teacher asks you to print 30 identical keychains for a class. How should you optimize the slicer settings compared to a single prototype?

Use the same settings as a single print — quantity doesn't matter

Reduce infill to 15-20%, use a larger layer height (0.2-0.3mm), increase speed, and arrange multiple parts on the bed to batch-print — prioritizing throughput over surface finish

Increase infill to 100% for maximum durability

Print each one individually at maximum quality settings

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Explanation: Batch production requires balancing quality against throughput. For functional but non-critical items like keychains, reducing infill and increasing layer height dramatically cuts print time per unit. Arranging multiple parts on the bed means the printer runs fewer jobs total. A 0.3mm layer with 15% infill prints roughly 3x faster than a 0.1mm layer with 40% infill, with acceptable strength for a keychain.

Why is moisture in filament a problem for FDM printing, and which material is most susceptible?

Moisture makes filament too slippery for the drive gear; PLA is most susceptible

Moisture turns to steam during extrusion, creating bubbles, popping sounds, and rough surfaces; nylon is the most hygroscopic common FDM material

Moisture makes filament brittle; ABS is most susceptible

Moisture only affects print color; PETG is most susceptible

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Explanation: Water absorbed by hygroscopic filaments rapidly converts to steam at extrusion temperatures (190-260°C). Steam bubbles expand in the nozzle, causing audible popping, inconsistent extrusion, and a rough surface finish with visible pitting. Nylon absorbs up to 10% of its weight in moisture from ambient air and must be dried (60-70°C for 6-12 hours) before printing. PLA, PETG, and TPU are also affected but less severely.

What is the difference between a "brim" and a "raft" in slicer settings, and when would you choose each?

They are the same thing with different names

A raft goes around the part; a brim goes underneath

A brim adds flat rings around the first layer's perimeter to increase adhesion area; a raft prints a full sacrificial platform under the part — use brim for mild adhesion help, raft for small-footprint or warping-prone parts

A brim is for PLA only; a raft is for ABS only

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Explanation: A brim extends the first layer outward (typically 5-10mm) from the part perimeter, adding adhesion area with minimal material use. A raft is a complete multi-layer platform printed first, with the part built on top. Rafts are more effective for parts with small contact areas or materials prone to warping (ABS, nylon), but they consume more material, add print time, and can leave surface marks on the bottom of the part.

You are troubleshooting a print that shows strong walls but visible holes in the top surface. What is the most likely cause and fix?

The nozzle temperature is too high — reduce by 10°C

The bed is not level — recalibrate Z-offset

Insufficient top layers — increase the number of top solid layers in the slicer so the infill pattern below is fully covered

The filament is wet — dry it before reprinting

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Explanation: Holes or gaps in the top surface (called "pillowing") occur when there are not enough solid top layers to bridge over the infill pattern below. Most slicers default to 3-4 top layers, but at higher layer heights (0.3mm) or lower infill (10-15%), 5-6 top layers may be needed. Increasing top layers adds minimal print time but dramatically improves the surface appearance and structural integrity of the top face.

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Last Updated: 2026-03-19