Getting the Perfect Cure: Solving Resin Underexposure for Flawless Prints

by Christopher Lannon July 14, 2023

One of the trickiest aspects of resin 3D printing is dialing in the ideal exposure settings. Underexposure is a common issue that manifests as prints with soft spots, uncured tacky sections, or entire models failing to form properly. When resin lacks sufficient light exposure, full curing never occurs.

But with the right troubleshooting and calibration, you can master exposure and get perfectly cured prints every time. This guide covers:

Typical causes of underexposure
Fixes for different resin printer types
Methods for validating ideal exposure

What Causes Resin Underexposure?

Before adjusting any settings, it helps to understand what factors can lead to underexposure in the first place:

Incorrect exposure times - If resin's specified optimal settings are off, underexposure can happen. Each resin type has an ideal exposure window.
Weak UV intensity - Over time, UV LEDs and lasers lose power. Weak UV severely limits curing. Old resin can also block light.
Ambient temperature - Colder temperatures inhibit curing. Resin cures best around 25°C. Warmer is better for exposure.
Model orientation - Some orientations or hollow prints can limit light penetration into intricate areas. Rotating the model can help.
Resin viscosity - Thicker resins need more exposure time vs thinner formulations to fully cure.
Resin contamination - Partially cured resin remnants floating in the vat can block UV light and reduce curing.

Fixing Underexposure on LCD/MSLA Printers

LCD-based resin printers have the most leeway for adjusting exposure settings to fix underexposure:

Increase exposure time - Incrementally increase regular layer time by 1-2s until fully cured.
Increase bottom layers - More high-exposure bottom layers improve adhesion and strength.
Adjust bottom layer exposure - Higher times for initial layers compensate for model height and cure strength.
Increase lift speed - Slowing vertical lift allows more curing time and resin drainage between layers.
Add extra curing - Post-print UV curing in a separate chamber ensures full top surface curing.
Check UV power - Use a UV meter to validate LED grid power level and replace LEDs if degraded over time.

Correcting Underexposure on DLP Printers

DLP printers rely on a projected light source, limiting some exposure settings:

Lengthen normal exposure - If adjustable, incrementally add 1-2s to normal exposure until optimized.
Maximize UV lamp power - Increase projection lamp power for max curing intensity. But watch for overheating.
Use a lower layer height - Thinner layers get more cure-time and resin drainage relative to their height.
Angle model properly - Tilting models minimizes uncured hollows. Optimize angle for most surfaces getting direct exposure.
Add supports in hollows - Strategic supports in hollows/openings allow light to cure trapped resin.
Clean projector lens - Any resin or debris on the projection lens blocks UV light. Keep the lens pristine.

Confirming Optimal Exposure

Once you've tuned exposure, validate settings with test prints:

Exposure calibration tests - Dedicated calibration prints like cones check dimensional accuracy across different exposure levels.
Evaluate test models - Inspect test cubes for any uncured sticky sections indicating underexposure.
Test different resins - Optimal exposure can vary greatly between resin types. Dial in each resin independently.
Check internal curing - For opaque prints, inspect cut open samples internally for uncured sections.
Monitor ambient temperature - Record curing results relative to room temperature. Colder may require higher exposure times.

Careful calibration and validation testing of your resin lets you hone in on the perfect exposure settings to achieve flawless curing every time and avoid the headaches of underexposure. Follow the tips in this guide to efficiently troubleshoot and solve any curing issues.