Unit 2 Comprehensive Quiz: Resin / SLA 3D Printing

Unit: 02 - Resin / SLA 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 Resin / SLA 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 fundamental difference between FDM and SLA printing processes?

SLA uses heat to melt material; FDM uses light

SLA uses UV light to selectively cure liquid photopolymer resin layer by layer, while FDM extrudes melted thermoplastic filament

SLA is faster than FDM for all part sizes

There is no fundamental difference — both deposit material by extrusion

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Explanation: SLA (Stereolithography) is a photopolymerization process: a UV light source (laser or LED array) selectively cures liquid resin into solid polymer. FDM is a thermal extrusion process. SLA achieves much finer resolution (25-50 micron layers vs. 100-300 micron for FDM) but requires chemical post-processing and uses materials with different mechanical properties.

Why must nitrile gloves be worn when handling uncured resin, and why are latex gloves inadequate?

Latex gloves are too expensive for lab use

Nitrile gloves look more professional in a lab setting

Uncured photopolymer resin contains skin-sensitizing chemicals (photoinitiators and acrylate monomers) that penetrate latex gloves within minutes; nitrile provides a reliable chemical barrier

Latex gloves are slippery and you might drop the build plate

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Explanation: Uncured resin contains reactive acrylate monomers and photoinitiators that are classified as skin sensitizers. Repeated exposure can cause contact dermatitis and permanent sensitization (allergic reaction). Latex gloves are porous to these chemicals and degrade on contact. Nitrile gloves rated for chemical resistance (minimum 6 mil thickness) provide adequate protection. Gloves should be changed if contaminated or after 30 minutes of continuous resin contact.

What does the "exposure time" setting control on an MSLA (masked SLA) printer, and how does it affect print quality?

It controls how long the build plate stays submerged between layers

It controls how long the UV LED array illuminates each layer — too short causes incomplete curing (weak layers), too long causes light bleed (loss of fine detail)

It controls the temperature of the resin vat

It controls the speed of the Z-axis motor between layers

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Explanation: Exposure time determines the UV energy dose per layer (mJ/cm²). Insufficient exposure leaves partially cured, brittle layers that may delaminate. Excessive exposure allows UV light to scatter beyond the intended pixel boundaries ("light bleed"), causing features to be thicker than designed and filling in fine details like holes and channels. Optimal exposure varies by resin type and is typically 2-8 seconds per layer for standard resins.

After removing a completed print from the build plate, what is the correct post-processing sequence?

UV cure → wash → remove supports → sand

Remove supports → sand → UV cure → wash

Wash in IPA or cleaning solution (2 stages) → remove supports → final UV cure → optional sanding/finishing

UV cure → remove supports → wash → sand

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Explanation: The correct sequence is critical for part quality and safety. Washing first (in IPA or manufacturer-recommended solution) removes uncured resin from the surface. Two-stage washing prevents contamination: a dirty bath for initial rinse, then a clean bath for final wash. Supports are removed after washing (when they separate more cleanly). Final UV curing in a curing station (405nm, 5-15 minutes) completes polymerization for full mechanical properties. Curing before washing traps uncured resin under a hardened surface.

A student's resin print shows the first 5mm printed perfectly, but then layers begin shifting and distorting. What is the most likely cause?

The resin vat is running low on resin

The UV LED array is overheating

Suction forces between the cured layer and the FEP film are too high, causing the part to partially detach from the build plate during peel

The room temperature is too cold for the resin

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Explanation: In bottom-up MSLA printers, each cured layer must peel away from the FEP (fluorinated ethylene propylene) film at the vat bottom. As the cross-sectional area of the print increases, suction force increases proportionally. If this force exceeds the adhesion between the part and build plate, the part shifts or detaches. Solutions include: increasing bottom layer exposure (for stronger plate adhesion), adding a raft, orienting the part to reduce cross-sectional area, and slowing the lift speed.

Why is proper ventilation critical when operating an SLA printer, even when the printer lid is closed?

The UV light produces harmful radiation that must be vented

The printer motor generates fumes that need ventilation

Photopolymer resins emit volatile organic compounds (VOCs) including acrylate vapors that can cause respiratory irritation and sensitization with repeated exposure

Ventilation prevents the resin from overheating

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Explanation: Uncured resin continuously off-gasses VOCs at room temperature. While printer enclosures reduce airborne exposure, they do not eliminate it — resin handling, vat changes, and post-processing all create exposure. The workspace should have mechanical ventilation (minimum 6 air changes per hour) or a local exhaust system. A carbon-activated filter can supplement but should not replace room ventilation. Prolonged VOC exposure can cause headaches, nausea, and respiratory sensitization.

What is the purpose of "bottom exposure time" being significantly longer (30-60 seconds) than normal layer exposure (2-8 seconds)?

The first layers need more time because the resin is coldest near the vat bottom

The initial layers must bond strongly to the build plate to resist the peel forces encountered during all subsequent layers; longer exposure creates a stronger mechanical bond

The LCD screen needs time to warm up before reaching full brightness

Bottom layers are thicker and need more UV energy to fully cure

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Explanation: Bottom layers serve as the foundation — they must withstand cumulative peel forces from every subsequent layer. A typical bottom exposure of 30-60 seconds (vs. 2-8 seconds for normal layers) creates deep cross-linking between the cured resin and the textured/sandblasted build plate surface. Too little bottom exposure causes mid-print detachment; too much creates "elephant foot" (over-cured, flared base). Most slicers default to 5-8 bottom layers at extended exposure.

How should used IPA (isopropyl alcohol) contaminated with uncured resin be disposed of?

Pour it down the drain with running water

Let it evaporate in an open container outdoors

Expose it to direct sunlight or a UV source to cure the dissolved resin, then filter out the solid particles; the IPA can be reused and the cured solids disposed of as regular waste

Mix it with acetone to neutralize the resin, then dispose in regular trash

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Explanation: Uncured resin is hazardous waste and must not enter waterways. The most practical disposal method is UV exposure: setting the contaminated IPA in a clear container in sunlight (or under a UV lamp) causes the dissolved resin to polymerize into solid flakes. These can be filtered out, and the reclaimed IPA reused (though it degrades in effectiveness over multiple cycles). Cured resin solids are inert and can be disposed of as regular waste. Many labs maintain a "dirty IPA" sun-cure station specifically for this purpose.

Which resin property is measured by Shore hardness, and why does it matter for functional parts?

Shore hardness measures resin viscosity before curing

Shore hardness measures how fast the resin cures under UV light

Shore hardness measures the resistance of cured resin to surface indentation — it determines whether a printed part will be rigid (Shore D 70+), semi-flexible (Shore A 50-80), or flexible (Shore A below 50)

Shore hardness measures the resin's resistance to UV degradation over time

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Explanation: Shore hardness scales (A for softer materials, D for harder) indicate a cured part's flexibility. Standard resins cure to Shore D 75-85 (rigid, similar to hard plastic). Flexible resins (Shore A 40-80) produce rubber-like parts for gaskets, grips, or living hinges. Choosing the wrong hardness for an application leads to functional failure — e.g., a phone case in rigid resin will crack on impact, while a structural bracket in flexible resin will deform under load.

What causes "layer lines" to be visible on an SLA print, given that SLA resolution is much finer than FDM?

Layer lines on SLA prints are always a printer defect that indicates malfunction

SLA printers cannot print smooth surfaces due to the pixel grid of the LCD

Layer lines appear on surfaces that are angled or curved relative to the build direction — each discrete layer creates a stair-step pattern that is visible even at 50-micron resolution on shallow angles

Layer lines only appear when using low-quality resin

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Explanation: SLA prints are built in discrete horizontal slices. On vertical surfaces, layers are invisible. On angled or curved surfaces, the transition between layers creates a stair-step pattern. At 50-micron (0.05mm) layers, this is much finer than FDM but still visible on surfaces angled less than ~20° from horizontal. Orientation is key: rotate the part so critical surfaces are as vertical as possible. Post-processing with fine sanding (800+ grit) or a clear coat can further reduce visibility.

A student removes supports from a cured resin print and finds deep pitting and scarring where the supports attached. What should they do differently next time?

Use heavier supports with thicker contact points for a cleaner break

Remove supports before washing to take advantage of the softer surface

Use light or medium supports with smaller contact tips (0.3-0.5mm), orient the part so supports attach to non-cosmetic surfaces, and remove supports after the IPA wash when the surface is cleanest

Skip supports entirely and rely on the build plate for all adhesion

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Explanation: Support scarring is a common SLA quality issue. Minimizing it requires: (1) thin contact tips — 0.3-0.5mm is sufficient for most parts, (2) strategic orientation so supports touch hidden or non-functional surfaces, (3) removing supports after washing (uncured resin acts as a lubricant during support removal, and the wash reveals clean break points). Light touch-up with fine sandpaper (600-1000 grit) eliminates remaining marks.

Why must SLA-printed parts intended for outdoor use be coated with a UV-resistant clear coat?

The clear coat makes the part look shinier and more professional

Without a clear coat, rain will dissolve the cured resin

Cured photopolymer resin continues to absorb UV radiation from sunlight, causing progressive yellowing, embrittlement, and loss of mechanical properties over weeks to months

The clear coat is required for the resin to reach its full cured hardness

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Explanation: The same photosensitivity that allows UV curing during printing becomes a liability after the part is complete. Prolonged UV exposure from sunlight continues to cross-link the polymer, making it increasingly brittle while also degrading the chromophores (causing yellowing). A UV-resistant clear coat (containing UV absorbers and HALS stabilizers) blocks further photodegradation. Without protection, standard resin parts noticeably yellow within 2-4 weeks of sun exposure and become brittle enough to snap within months.

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Last Updated: 2026-03-19