Module 1: Assessment Quiz

Module: U1M1 - FDM Technology Fundamentals Duration: 20-30 minutes Passing Score: 70% (10 of 14 questions) Format: Multiple choice, matching, and scenario-based

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Questions 1-3: Extrusion Process Fundamentals

During the FDM extrusion process, which of the following is the correct sequence?

Filament melts → pressure builds → nozzle extrudes → plastic solidifies

Pressure builds → filament melts → nozzle extrudes → plastic solidifies

Filament melts → plastic solidifies → nozzle extrudes → pressure builds

Nozzle extrudes → filament melts → pressure builds → plastic solidifies

Submit

Explanation: The filament must first reach the glass transition temperature (Tg) to soften. As the drive mechanism pushes the softened filament, back-pressure builds up in the hot end. Once sufficient pressure is achieved, plastic is forced through the nozzle and immediately begins cooling upon contact with the build platform.

What is the role of back-pressure in the FDM extrusion system?

Back-pressure cools the nozzle to prevent drooling

Back-pressure keeps the nozzle full and prevents material leakage during travel moves

Back-pressure reduces the melting point of the plastic to enable faster printing

Back-pressure compresses the plastic to increase its tensile strength

Submit

Explanation: Back-pressure (100-500 bar typical) is generated as the drive mechanism compresses the softened filament. This pressure keeps molten plastic in the nozzle chamber between extrusion events. Without adequate back-pressure, the nozzle would leak or "drool" during non-extrusion moves, creating stringing and unwanted material on the print surface.

A student notices their PLA prints have weak adhesion to the build platform. They increase the nozzle temperature from 200°C to 220°C. Why would this likely make the problem worse?

Higher temperature increases plastic viscosity, making it harder to extrude

Higher temperature causes the plastic to cool faster on the platform

Higher temperature causes the plastic to flow too much, creating a flat blob instead of a proper layer

Higher temperature reduces the glass transition temperature (Tg), making it harder for layers to bond

Submit

Explanation: Adhesion problems are usually caused by bed temperature or nozzle distance, not nozzle temperature. Increasing nozzle temperature makes the plastic more fluid, causing it to spread excessively and lose layer definition. The correct approach is to check bed temperature (PLA typically 20-60°C) and ensure proper bed leveling.

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Questions 4-7: Printer Architecture

Which component is responsible for measuring nozzle temperature and feeding the measurement back to the printer's control firmware?

Thermistor

Heating cartridge

Stepper motor

Proximity sensor

Submit

Explanation: A thermistor is a resistor that changes resistance with temperature. The printer measures this resistance and converts it to a temperature reading. This feedback allows the firmware to maintain a stable nozzle temperature by turning the heating cartridge on and off via PID control.

In a standard Cartesian FDM printer (e.g., Prusa i3), which axis is typically controlled by moving the build bed?

X-axis

Y-axis

Z-axis

All three axes

Submit

Explanation: In standard Cartesian printers, the X-axis is controlled by moving the nozzle carriage left/right, the Y-axis is controlled by moving the build bed forward/backward, and the Z-axis is controlled by raising/lowering the bed height. However, some Cartesian printers move the carriage in the Y direction instead of the bed.

What is the purpose of the heat sink and cooling fan below the nozzle?

To heat the filament before it enters the nozzle

To prevent unwanted heat transfer up the hot end and into the mechanical components

To cool the plastic immediately after extrusion for faster layer bonding

To regulate the bed temperature during printing

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Explanation: The heat sink dissipates unwanted heat away from the heating block down toward the filament guide. The cooling fan blows air across the heat sink to prevent heat from traveling upward, which would cause the filament to soften prematurely and jam.

A printer with a flexible/wobbly frame is more likely to produce parts with which of the following defects?

Layer shifts and misalignment, dimensional inconsistency

Over-extrusion and blob-like features

Under-extrusion and layer gaps

Warping and curl-up at corners

Submit

Explanation: Frame rigidity is essential for XY accuracy. A flexible frame allows the nozzle to shift slightly during rapid movements, causing layers to misalign vertically (layer shifts). This also introduces dimensional creep where repeated movements compound the error.

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Questions 8-11: Material Properties

Which of the following materials has the LOWEST glass transition temperature (Tg) and is therefore the easiest to print?

ABS (Tg ≈ 105°C)

Nylon (Tg ≈ 47-90°C)

PLA (Tg ≈ 60-65°C)

PETG (Tg ≈ 75-85°C)

Submit

Explanation: PLA has a low Tg (~60-65°C), which means it softens at relatively low temperatures. This allows lower nozzle temperatures (200-210°C) and minimal bed heating (20-60°C), making PLA the easiest material for beginners.

A student is designing a part that must flex without breaking. They're considering PLA, PETG, Nylon, and TPU. Which material should they choose?

PLA - it's the cheapest

PETG - it has balanced properties

Nylon - it's strong and ductile

TPU - it's specifically designed for flexibility and stretching

Submit

Explanation: TPU (Thermoplastic Polyurethane) is a flexible material designed to stretch and bend without breaking. Nylon is also flexible, but TPU is more easily printable. PLA is brittle and would crack under bending; PETG has moderate flexibility but not as much as TPU.

Why does damp filament (moisture-absorbed) produce poor-quality prints?

Moisture increases the Tg, requiring higher nozzle temperatures

Moisture acts as a plasticizer, reducing the Tg and causing inconsistent extrusion

Moisture evaporates in the nozzle, creating gas bubbles that weaken the plastic

Moisture freezes at room temperature, causing filament jamming

Submit

Explanation: Water molecules inserted into the polymer chain act as a plasticizer, lowering the Tg and making the plastic more fluid at normal print temperatures. This causes inconsistent extrusion (wet/dry cycles creating stringing and under-extrusion). Damp filament should be dried in an oven or filament dryer before printing.

A printed ABS part is oriented with its layers parallel to the XY build platform (flat orientation). Compared to the same part oriented vertically (layers perpendicular to the platform), how would its strength differ?

No difference - material strength is isotropic

The flat part is stronger in the Z-direction (perpendicular to layers)

The flat part is weaker in the Z-direction (perpendicular to layers) - it will delaminate more easily

The strength is identical, but the part will warp differently

Submit

Explanation: FDM parts are anisotropic - they're stronger along the extrusion direction (layers bonded together) than perpendicular to it (between layers). The flat-oriented part has weak inter-layer bonding in the Z-direction and will delaminate easily if flexed perpendicular to the layers.

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Questions 12-14: Scenario-Based Application

You're troubleshooting a new ABS print. The print starts beautifully, but after 5 minutes, the edges begin to curl upward and lift off the platform. What is the PRIMARY cause?

The nozzle temperature is too high

The bed temperature is too low, causing rapid cooling and differential shrinkage

The filament is damp

The print speed is too slow

Submit

Explanation: Curling edges (bed corners lifting first) is the classic sign of warping due to insufficient bed temperature. ABS shrinks significantly as it cools; a low bed temperature (below 80°C for ABS) causes the first layer to cool too fast, creating unequal shrinkage. The warm upper layers contract more than the cooler bottom, causing curl-up.

A student has a failed print in their hand. The print has visible layer lines, and you can easily separate layers by hand. The nozzle used was 0.4mm. What is the most likely problem?

The layer height was set too high (>0.2mm)

The nozzle temperature was too low, causing poor layer fusion

The print speed was too fast

The bed temperature was too high

Submit

Explanation: If you can manually separate the layers, it indicates weak inter-layer bonding. This occurs when: 1. Nozzle temperature is too low - plastic doesn't melt the previous layer sufficiently. 2. Print speed is too fast - insufficient dwell time on the previous layer for fusion. 3. Layer height is set too high - nozzle pushes new material too far above the previous layer. Most commonly, low nozzle temperature is the culprit.

You're designing a part that must withstand bending and occasional impacts. You have a choice: print it in PLA with layers parallel to the XY platform, or print it in PETG with the same orientation. Which is better and why?

PLA is better - it's cheaper and easier to print

PETG is better - it has higher impact resistance and ductility than PLA

They're equally suitable - material choice doesn't matter for impact resistance

PLA is better because it has a lower Tg and won't fail from thermal stress

Submit

Explanation: PETG is superior for impact applications. PLA is brittle and shatters suddenly under impact; PETG absorbs impact energy by flexing and dissipating it. PETG's higher tensile strength (50-60 MPa vs. 50-70 MPa for PLA) and ductility make it more suitable for mechanical parts. Both materials are anisotropic, but PETG's superior impact resistance matters more than the orientation in this case.