Overcoming Common Resin 3D Printing Curing Issues
One of the most crucial yet tricky steps in resin-based 3D printing is dialing in the perfect cure time and exposure settings. Photopolymer resins solidify from a liquid to solid state through exposure to UV light. But achieving an even and thorough cure without defects requires balancing many factors.
Issues during the curing process can lead to prints with poor detail, cracks and fractures, low strength, sticky surfaces, and more. This guide examines the most prevalent resin 3D printing curing problems hobbyists encounter and methods to optimize exposure for successful prints every time.
Overexposing resin to too much UV light is one of the most common causes of curing problems. The extra exposure time causes excess solidification and chemical reactions that damage the print quality in several ways:
- Loss of finer details - Longer curing dissolves small features and can exaggerate layer lines as resin overflows beyond its boundaries.
- Discoloration - Chemical inhibitors in resin that prevent overcuring can leave residue or react with oxygen, causing yellowing.
- Lower strength - Excessive cross-linking in the cured resin makes it brittle and more prone to cracking.
- Resin overflow - Overflow resin sticking to surfaces creates rough patches or layers covering details.
Signs of overexposure like rounded edges or surfaces covered in tacky overflow resin are a clue to reduce exposure times. Each resin has an optimal exposure window that fully cures the print without going overboard.
Dialing in Exposure
The ideal exposure settings depend on factors like the resin type, layer height, temperature, printer model, and orientation. Finding the “sweet spot” requires testing:
- Start with manufacturer recommended settings, then reduce times in 1-2 second increments.
- For each exposure test, check for loss of detail or weak points.
- The best exposure shows clean details without uncured areas.
- Keep ambient temperatures consistent to limit other variables.
Many resins also cure in two steps – an initial exposure to adhere the layer, followed by a secondary exposure to finish curing. Play with adjusting both settings separately to prevent under and overexposing.
If exposure tests don’t improve print quality, the issue may be inadequate UV output. Check the following:
- LED/laser array intensity, pattern, and uniformity
- Lens and vat cleanliness or damage
- Vat FEP film tension
- Ambient temperature not exceeding resin limits
Having consistently functioning UV curing hardware makes dialing in exposure easier and more reliable over time.
The counterpart to overexposing is underexposure – not providing enough UV light and time for the resin to fully harden. This results in prints with:
- Weak, rubbery surfaces and supports
- Deformed shapes as uncured resin continues spreading
- Cracking or fractures as resin remains partially uncured
- Tacky surfaces that attract dirt and other uncured resin
Though less damaging than overexposing, inadequate curing prevents prints from developing full strength or accuracy. Slowly incrementing exposure times and testing curing improves this.
If upping exposure time doesn’t cure resin, look for these potential causes:
- Expired resin with reduced reactivity
- Resin contaminated with inhibiting substances
- Ambient temperatures being too cold, slowing cure rate
- Insufficient UV lighting power due to age or defects
- Vat film needing replacement due to reduced light transmission
- Resin viscosity too high relative to exposure times
Checking resin quality, printer hardware condition, and environmental factors helps troubleshoot underexposure issues.
Dense shapes and overhanging sections especially prone to underexposure benefit from tweaking support settings:
- Increase contact area and thickness of supports on tricky surfaces.
- Minimize distance supports must span between model and build plate.
- Use heavier supports to reduce flexing and leaking during curing.
Optimized orientation and supports ensure adequate curing throughout the print.
Achieving Even Curing
The perfect exposure settings won’t help if the UV light can’t penetrate and cure resin evenly throughout the vat. Spots that cure faster or slower than surrounding resin will warp or weaken the final print.
Try these tips for consistent curing:
- Regularly calibrate resin printer build platforms to keep vat gap even.
- Gently stir resin between prints to prevent settling and inconsistencies.
- Use a turntable for rotating intricate or tall prints to expose all sides.
- Minimize temperature fluctuations that may alter curing speeds.
Dialing in the right bottom exposure and heavy supports for overhangs also contributes to uniform curing. Be patient and methodical when tuning both printer settings and environment to see the best curing consistency.
Preventing Oxygen Inhibition
Oxygen in the air can partially inhibit photopolymerization, leaving tacky uncured resin on print surfaces. Known as oxygen inhibition, this effect is commonly seen as a sticky residue on surfaces and brittle edges.
Limit oxygen’s impact on curing with these strategies:
- Use resin specially formulated to reduce oxygen inhibition
- Cure prints in an inert gas atmosphere like nitrogen or argon
- Ensure sufficient bottom exposure time for initial layers
- Let prints fully post-cure under UV light after printing
Giving prints a quick post-curing blast eliminates the tacky outer layer. Clean off any residues under UV light instead of with tools to avoid damaging the print.
Fine-tuning Exposure FAQs
How do you know if a print is underexposed or overexposed?
Overexposed prints tend to have rounded corners, overflow resin covering details, brittleness and cracks. Underexposed prints feel tacky, rubbery, and deform easily with low strength.
Can temperature affect resin curing?
Yes, resin cures optimally around 20-25°C. Warmer temperatures cure resin faster, while colder temperatures slow the reaction. Maintain steady workshop temperatures.
Should you shake resin before printing?
Gently swirling or stirring resin before a print ensures uniformity. But avoid vigorous shaking which introduces bubbles into the resin.
How long should bottom exposure layers be?
Bottom layers typically need 8-10x longer exposure than normal layers. 30-60s exposures help the print strongly adhere to the build plate.
Can UV resin be cured in sunlight?
Yes, but sunlight is not recommended as it is extremely difficult to control exposure levels. Fully cured resin requires very prolonged solar exposure.
Perfecting resin curing takes patience and attention to many variables. But carefully dialing in and testing exposure settings, checking printer hardware, and controlling environmental factors will help you achieve flawless curing to produce the best quality prints.