MJF humidity is an easy variable to overlook until parts start changing with the seasons. In an r/AdditiveManufacturing thread comparing MJF and SLS, an operator who has run both said MJF is more sensitive to environmental humidity on the older machines, and that “too dry is especially bad for powder flow and density.” So what conditions should an MJF room hold?
What does HP specify?
HP’s guide “Process tuning your MJF to the design” says printer operating humidity should be 30–70% RH and operating temperature 20–30°C to avoid thermal fluctuations. It adds that some materials need a narrower range. HP 3D High Reusability PA 12 requires 50–70% RH, and HP’s PA 12 data sheet lists the same 50–70% recommendation.
Why does MJF humidity matter?
HP’s material safety data sheet for MJF PA 12 (as published by Shapeways) says to store powder away from moisture and heat, not above 60°C, and to avoid wet or humid environments. A technical disclosure on Technical Disclosure Commons describing an MJF chamber humidity tool says low or unstable humidity can cause inconsistent powder behavior, poor fusion, dimensional inaccuracy and more failed prints, especially in winter.
How does a real production floor handle it?
In an Additive Manufacturing Media video, Uptive Manufacturing showed how it controls conditions for its 13 MJF printers in Illinois. The room is held at 70–74°F year-round, with humidity between 30% and 70% using both humidifiers and dehumidifiers. Perforated ceiling air diverters spread incoming air gently to avoid hot or cold spots. Uptive’s goal is that parts printed in January match parts printed in July.
Does humidity affect calibration?
Yes. HP’s process tuning guide recommends doing fusing lamp calibration at 40–60% RH and checking the printer’s humidity reading against an external sensor.
What should a bureau do?
- Put independent temperature and humidity loggers in the print and powder areas.
- Check the data sheet range for each material you run, not just the printer’s range.
- Plan for seasonal swings with both humidification and dehumidification.
- Store powder sealed, away from heat and moisture, as the SDS directs.
- Record room conditions alongside each build so you can link quality issues to the environment.
Related on the Solvi blog: SLS Powder Cleanup: How to Keep Dust Under Control; MJF Elephant Skin: What Causes It and How to Avoid It; SLS Cooldown: How Hot Can You Unpack a Build?.
Sources: r/AdditiveManufacturing MJF vs SLS thread; HP “Process tuning your MJF to the design” (4AA7-4235ENW); HP PA 12 data sheet; HP PA 12 SDS (Shapeways copy); Technical Disclosure Commons humidity tool; Additive Manufacturing Media Uptive video.