SLA 3D Printing: How Post-Curing Changes Resin Strength

SLA 3D printing can produce detailed parts, but the finished part’s mechanical performance depends on more than the resin name. For engineers choosing material for a prototype or a medical application, a practical question is how post-curing changes strength—and whether curing alone makes a standard resin biocompatible.

Key findings

• Post-curing increased F-Grey tensile strength from 48.5 MPa to 54.1 MPa, an increase of 11.54%.
• A-Grey tensile strength rose from 28.1 MPa to 31.4 MPa after curing, an increase of 11.74%.
• F-BioMed had the highest measured tensile strength, 74.5 MPa; Ifun-BD had the lowest, 10.7 MPa.
• F-BioMed had the highest tensile modulus at 2.7 GPa, while Ifun-BD had the greatest elongation at break, 17.9%.
• Resin cost per specimen ranged from $0.25 to $3.62, calculated from material consumption only.

Why investigate post-curing?

Additive manufacturing builds an object layer by layer. In stereolithography (SLA), light cures liquid photopolymer resin to form each layer. Post-curing is an additional treatment after printing, intended to further cure the material. Because the final properties can depend on processing, knowing how this step affects a resin can help designers assess whether a printed part suits its intended purpose.

The paper also considers whether UV treatment might make standard resins an alternative to more expensive biocompatible materials. That is a motivation for the study, not a result it establishes: the experiments measured mechanical properties, not biological response. The tensile results cannot be used as proof that a standard resin becomes safe for contact with the body after curing.

The paper is by Adi Pandžić, PhD, a mechanical engineer. It appears in CNNTech 2022, in the Lecture Notes in Networks and Systems series, published in 2023.

Materials, printers and test method

The study compared four SLA resins: Formlabs Grey V4 (F-Grey), Anycubic Basic Grey (A-Grey), Formlabs BioMed Amber (F-BioMed) and iFun Denture Biocompatible Resin (Ifun-BD). Specimens were printed at a 0.05 mm layer height in a horizontal orientation. Layer height is the thickness of each printed layer.

F-Grey and F-BioMed specimens were produced on a Formlabs Form 3B printer. A-Grey and Ifun-BD were printed on an Anycubic Mono X 4K. All specimens were washed in 99% isopropyl alcohol. F-Grey and A-Grey were tested both with and without post-curing; F-BioMed and Ifun-BD specimens were tested after treatment. The study reports three specimens for each material group.

Specimen geometry followed ISO 527-2, and tensile testing was carried out according to ISO 527 using a Shimadzu AGS-X machine. The test speed, defined as the separation rate of the grips, was 5 mm/min. Tensile strength describes the stress a material withstands when pulled. Tensile modulus indicates stiffness in the elastic range, while elongation at break describes how far a specimen deforms before fracture.

What did the tensile tests show?

F-BioMed recorded the highest tensile strength, 74.5 MPa. Its tensile strength at break was 66.7 MPa, and its tensile modulus was 2.7 GPa. Ifun-BD had the lowest tensile strength, 10.7 MPa, the lowest tensile strength at break, 10.6 MPa, and the lowest modulus, 0.4 GPa. However, its elongation at break was the highest of the tested materials, at 17.9%.

Uncured F-Grey had a tensile strength of 48.5 MPa, compared with 54.1 MPa after curing. Its tensile modulus rose from 2.1 GPa to 2.3 GPa, while elongation at break fell from 7.3% to 6.4%. For A-Grey, tensile strength increased from 28.1 MPa to 31.4 MPa and modulus from 1.3 GPa to 1.5 GPa. Elongation at break decreased from 9.0% to 4.1%.

The comparison with manufacturers’ technical data sheets showed that measured tensile strength was 27.6% higher for F-Grey and 20% higher for A-Grey than the listed values. F-BioMed differed by about 2%. For Ifun-BD, the measured value was 10.7 MPa, compared with 55 MPa in the manufacturer’s data; the paper reports this as 80.5% lower.

Practical implications for engineers and designers

For product development, the results show that post-curing can increase the strength and stiffness of these grey resins while reducing elongation at break. Material selection is therefore a trade-off: high strength or stiffness does not automatically mean the part can deform more before breaking. These tests provide a comparison for the specific materials and settings used, not a universal property value for every SLA print.

The paper also reports resin use, print time and material price per specimen. F-Grey used 14.93 ml and took 135 minutes to print; A-Grey used 8.42 ml and took 21 minutes. F-BioMed used 14.54 ml and took 150 minutes, while Ifun-BD used 8.42 ml and took 21 minutes. Material-only costs per specimen were $2.22 for F-Grey, $0.25 for A-Grey, $3.62 for F-BioMed and $0.42 for Ifun-BD. These prices exclude the printer, labor and other costs. Since different resins were printed on different machines, the comparison does not isolate printer performance alone.

For students and researchers, the study is a useful example of why test conditions matter when comparing polymer properties. The paper reports that manufacturer data sheets should state printing parameters and the standards used for testing so users can interpret reported values in context.

Limitations and points to verify

The results come from three specimens per material group, one layer height, one print orientation and one tensile-test speed. The groups also differ in resin, printer and treatment. As a result, observed differences cannot be attributed to a single factor in every comparison. The results do not establish performance under other print settings, loading conditions or biological tests.

There is a discrepancy in the paper’s description of curing. The abstract says UV-cured specimens were treated for 10 minutes in a UV chamber, while the experimental-method table lists different material-specific times and, for some resins, temperatures. The table gives 60 °C for 30 minutes for F-Grey, 15 minutes for A-Grey, 70 °C for 30 minutes for F-BioMed, and 1 minute for Ifun-BD. This should be considered when interpreting or attempting to reproduce the experiment. The paper also cautions that manufacturers’ printing parameters can substantially affect the final properties.

Conclusion

In this comparison, F-BioMed had the highest tensile strength and modulus, while Ifun-BD had the lowest values for those properties and the greatest elongation at break. Post-curing raised tensile strength by 11.54% for F-Grey and 11.74% for A-Grey, while reducing elongation. These are mechanical-test findings, not evidence of biocompatibility. Any medical use requires separate evidence and appropriate verification of the material’s biological suitability.

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Author: Adi Pandžić, PhD in Mechanical Engineering

This article summarises a published research paper; please refer to and cite the original paper. About the author

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