A very common failure in SLA, DLP and LCD resin printing occurs when the printed object does not remain attached to the build plate and instead cures on the release film at the bottom of the vat.
This failure is often described as:
- resin print stuck to FEP
- print stuck to vat film
- resin not sticking to build plate
- no part on build plate after printing
Although the visible result appears simple, the underlying cause is not always the same. In engineering terms, this failure usually reflects an adhesion imbalance during the first layers, often combined with insufficient bottom curing or excessive peel resistance.
What the failure looks like
Typical visible signs include:
- an empty build plate after printing
- a thin cured film remaining on the FEP or release layer
- a partially formed object attached to the vat instead of the build platform
- detachment after the first few layers
In most cases, the initial layers polymerize, but they do not achieve sufficient adhesion to the build plate relative to the adhesion and peeling forces acting at the vat interface.
Engineering interpretation
For the first layers to remain on the build plate, the following condition must be satisfied:
Build plate adhesion and cured-layer strength must exceed the adhesion and peel forces at the release film.
If this balance fails, the part remains stuck to the FEP instead of transferring to the plate.
This means that the problem is not always “insufficient exposure” alone. It may also involve:
- poor build plate preparation
- incorrect bottom exposure time
- too few bottom layers
- high peel resistance
- resin viscosity effects
- temperature-related curing instability
Main causes of prints sticking to the FEP
1. Insufficient bottom exposure
The most common cause is inadequate bottom curing. If the first layers do not receive enough energy, they may polymerize weakly and fail to anchor to the plate.
This is especially common when users apply standard exposure values from another printer or resin without considering irradiance differences.
2. Too few bottom layers
Even if the exposure time is high enough, too few bottom layers may provide insufficient anchoring thickness for the part to resist peel forces.
3. Build plate surface condition
If the build plate is contaminated, too smooth, improperly leveled or poorly prepared, adhesion may be lower than expected even when the resin is curing correctly.
4. Excessive adhesion to the FEP
A cured layer may adhere too strongly to the release film due to geometry, suction effects, viscosity or over-compression during the first layers.
5. Resin temperature and viscosity
Cold or highly viscous resins may show reduced flow, slower kinetics and less predictable first-layer behaviour, increasing the risk of adhesion imbalance.
6. Incorrect leveling or Z-zero setting
If the initial gap between the build plate and the vat is incorrect, the first layers may be over-compressed or insufficiently formed.
Failure mechanism in process terms
This failure is best understood as an imbalance between four factors:
- bottom-layer cure strength
- build plate adhesion
- FEP adhesion
- peel force during separation
If the cured layer is too weak, or the plate adhesion is too low, the first layers remain on the FEP. If the cured layer is strong but the adhesion balance is still unfavorable, the part may partially detach, tear or split during the first lifts.
How to diagnose the problem correctly
A structured diagnosis should begin with these questions:
- Did any cured material appear in the vat?
- Was there a thin film or a partial object stuck to the FEP?
- Did the part detach immediately or after several layers?
- Was the resin at a stable working temperature?
- Was the plate correctly leveled and clean?
- Was the bottom exposure selected using real printer conditions or only generic values?
If cured material appears in the vat but not on the build plate, the resin is receiving energy, but the adhesion balance is failing.
Corrective actions
Increase bottom exposure time
If bottom exposure is too low, increase it incrementally until the first layers consistently anchor to the build plate.
Increase the number of bottom layers
Adding bottom layers increases the anchoring thickness and helps transfer the part from the FEP to the plate.
Re-check leveling and Z-zero
Ensure that the build plate is correctly leveled and that the initial layer geometry is being formed under appropriate contact conditions.
Inspect and prepare the build plate
Clean the plate thoroughly and confirm that the surface condition is compatible with reliable first-layer adhesion.
Verify resin condition and working temperature
Ensure the resin is well mixed, free of debris and used within an appropriate temperature range.
Reduce excessive peel resistance where possible
If the geometry produces strong suction or difficult release, support strategy, orientation or process conditions may need adjustment.
Relationship with CRT
This failure frequently begins as an exposure selection problem. Bottom layers and first-layer anchoring should be interpreted in relation to the curing kinetics of the resin.
The 3Dresyns® Curing Rate Control System (CRT) helps users understand whether exposure conditions are aligned with the actual photopolymerization behaviour of the material.
Without this kinetic reference, users often increase or decrease settings blindly, which may temporarily solve one issue while creating others such as overcuring, excessive adhesion or dimensional loss.
Relationship with structured calibration
If the first layers can be made to adhere to the build plate, the next engineering step is to verify whether the chosen exposure conditions also produce correct dimensional behaviour.
This is why troubleshooting should not stop at “the part printed”. Exposure values that merely force plate adhesion may still produce dimensional drift, loss of detail or later-stage failures.
For this reason, build plate adhesion problems should be followed by verification using the 3Dresyns® structured calibration methodology.
Quick engineering summary
| Observed outcome | Most probable cause | First corrective action |
|---|---|---|
| No part on build plate, cured film on FEP | Insufficient bottom cure | Increase bottom exposure |
| Part detaches after first layers | Weak adhesion balance | Increase bottom layers and check plate preparation |
| Partial object on FEP | Build plate adhesion lower than vat adhesion | Review leveling, exposure and release conditions |
| Failure appears inconsistently | Temperature, viscosity or leveling variability | Stabilize resin and machine conditions |
When this problem is not really a bottom-exposure problem
Some users assume that every print stuck to the FEP must be solved by increasing bottom exposure. This is not always correct.
If the root cause is primarily mechanical or geometric, increasing exposure may only create stronger adhesion to the vat, more difficult release, brittle fracture or dimensional errors.
For this reason, the failure should be interpreted within the broader engineering workflow:
- check cure behaviour with CRT
- check dimensional consequences with structured calibration
- interpret morphology using the Failure Atlas