# Stereolithography

Resin stereolithography routes, orientation and support planning, washing and post-curing, and condition-specific finished-part acceptance.

Reviewed: 2026-11-01

Tags: processes, shaping, additive-manufacturing, polymers

Formlabs reports **46 MPa green**, **54 MPa after 5 minutes at ambient temperature**, and **62 MPa after 15 minutes at 60°C** for **Grey Resin V5**, ASTM D638-14. Post-cured specimens used **Form 4 at 100 µm**, **5 minutes in ≥99% IPA** and Form Cure. Match the printer, wash and cure when comparing results. [Formlabs Grey V5 data sheet, pp. 1–2](https://formlabs-media.formlabs.com/datasheets/2401898-TDS-ENUS-0.pdf)

Formlabs groups laser SLA, DLP and masked LCD exposure within stereolithography. Specify the exposure architecture and resin. Each cures a liquid photopolymer into a thermoset. [Formlabs: guide to stereolithography](https://formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing/)

## Define the process and delivered condition

In an inverted vat system, exposure occurs through the bottom of the tank and the platform moves to permit replenishment between layers. This differs mechanically from top-down arrangements. Exposure, resin flow and release behavior are part of the selected system; settings are not interchangeable simply because two printers use liquid resin. [Formlabs: stereolithography architectures](https://formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing/)

A useful process definition includes the printer model, resin name and version, material lot, layer setting, orientation/support plan, wash route, post-cure route and final finishing. The object removed from the printer is an intermediate state. A quote for an unwashed green print and a quote for a washed, post-cured, support-finished component describe different deliverables.

| Requirement | Information to agree |
| --- | --- |
| Fit and geometry | Controlled dimensions, datums, clearances, critical holes and interfaces |
| Surface | Cosmetic faces, support-contact exclusions, texture and permitted finishing |
| Material | Exact formulation, required properties, environment and conditioning |
| Internal features | Drainage, wash access, support removal and verification access |
| Delivery | Post-cure condition, finishing, inspection stage and documentation |

Choose a resin for the required function rather than a familiar marketing analogy. For example, 3D Systems describes Accura 25 as a polypropylene-like material for SLA; its own sheet identifies a specific liquid resin and post-cured properties. That description does not make it polypropylene or establish the behavior of an injection-molded PP grade. [3D Systems: Accura 25 data sheet, ©2018, printed 10-18](https://www.3dsystems.com/sites/default/files/2018-11/3d-systems-accura-25-datasheet-USEN-11-01-18-web.pdf)

## Orientation, supports and enclosed features

Orientation affects how features are supported and how successive layers load the developing part. Formlabs' orientation guidance discusses overhangs, islands, large cross-sections and deformation; it also warns that parts can sag or warp during post-curing. Its recommendations concern Formlabs SLA systems and do not supply a universal orientation angle for every geometry. [Formlabs: model orientation](https://formlabs.com/support/Model-Orientation/)

Place support contacts with the finished function in mind. A contact on a sealing face, snap feature or datum may require removal and inspection that a purely cosmetic surface does not. Define whether sanding, polishing, coating or machining is allowed and how much geometric change can be accepted. Successful slicing alone does not demonstrate that supports can be removed from every recess.

Hollowing creates additional process obligations. Formlabs' Form 4 design guidance recommends drainage openings to release trapped resin and avoid cupping-related failure. Those openings have to be planned around orientation and the actual resin/printer combination. Its numerical feature recommendations belong to the stated test configuration, not every stereolithography process. [Formlabs: Form 4 design specifications](https://formlabs.com/support/Design-specifications-for-3D-models-Form-4-generation/)

Ask how a closed or tortuous passage will be washed, drained and verified. A CAD cavity is not automatically a clean functional channel. Include any later plugging or sealing of process openings in the delivered-part definition.

## Washing and post-curing are material operations

Washing removes residual liquid resin. Formlabs explains that solvent contaminated with resin can leave residue as it evaporates, and that hollow parts and channels can retain resin, air or solvent. It recommends geometry-dependent washing and directs users to material-specific limits rather than unlimited soaking. Drain openings also allow cleaning fluid to reach internal surfaces. [Formlabs: washing prints](https://formlabs.com/support/Washing-Prints/)

Specify the appropriate solvent, wash equipment, bath condition, drying and post-cure procedure for the approved material route. Consult the actual resin and solvent safety data sheets when establishing handling and disposal. A resin's product name or a finished part's appearance is not a safety specification.

**Named material example.** Formlabs' Grey Resin V5 sheet, revision 01 of 20 March 2024, reports the following ASTM D638-14 tensile results:

| Reported state | Ultimate tensile strength | Elongation at break |
| --- | --- | --- |
| Green | 46 MPa | 22% |
| Post-cured 5 minutes at ambient temperature | 54 MPa | 15% |
| Post-cured 15 minutes at 60 °C | 62 MPa | 13% |

The post-cured data used Form 4, 100 µm Grey V5 settings, a five-minute Form Wash in ≥99% IPA, and Form Cure under the respective conditions. The sheet warns that geometry, orientation, settings and temperature can affect properties. These are reported material-test results, not minimum component allowables or a general cure recipe for other resins. [Formlabs: Grey Resin V5 technical data sheet, pp. 1–2](https://formlabs-media.formlabs.com/datasheets/2401898-TDS-ENUS-0.pdf)

For service qualification, establish required loads, duration, temperature, fluids, light exposure and any medical or contact requirements. Match evidence to that application and final process. A short tensile test, heat-deflection result or attractive surface does not establish long-term durability or regulatory suitability.

## Layer height is not a dimensional tolerance

Layer height describes the nominal build increment. Accuracy also depends on feature geometry, orientation, the material/process combination and finishing. Formlabs' Form 4 dimensional guidance explicitly ties its published results to Grey Resin V5, a specified layer setting, printers and post-cure condition. Use such results within their stated scope and agree acceptance for the actual part. [Formlabs: design specifications and test conditions](https://formlabs.com/support/Design-specifications-for-3D-models-Form-4-generation/)

**Original layer-count example.** Assume a part occupies exactly 30 mm in the build direction, excluding supports and raft, and every layer has identical thickness. At 0.100 mm, it occupies 300 layers; at 0.050 mm, 600 layers. Tilting that part so its build-direction extent becomes 45 mm gives 450 or 900 layers respectively. These are geometric counts only. They predict neither total print time nor dimensional error: exposure, replenishment, release motion, supports and machine scheduling are omitted. A 50 µm setting therefore cannot be presented as a ±50 µm finished-part guarantee.

## Qualification and handoff

Inspect in the agreed final state, after washing, post-curing, support removal and required finishing. Separate size/location, surface quality, residual material in passages and functional/material performance. Record any conditioning before measurement or testing. Establish whether inaccessible features need a different geometry, inspection method or representative qualification artifact before committing to production.

Provide the model/drawing revision, material/version, machine/process route, orientation and support constraints, post-processing condition, finishing permissions and acceptance plan. Require application-specific evidence for claims of strength, watertightness, temperature resistance or repeatability rather than transferring a printer specification to every part.

## Source versions

Reviewed 2026-11-01. The retrieved Grey V5 PDF explicitly states prepared/revision 01, 20 March 2024. The Accura 25 PDF carries ©2018 and printed code 10-18. Neither date is inferred from its hosting path. Formlabs' live support pages have no separately verified technical issue date here. The layer-count example and handoff recommendations are original.

## Related reference

[Manufacturing processes](../index.md)