MJF elephant skin is a wrinkled, rough surface defect that MJF operators complain about on big parts and dense builds. In an r/AdditiveManufacturing thread about packing density, one operator said massive parts are “extremely prone to elephant skin or weird sunken surfaces,” and that high packing densities can bring poor accuracy and elephant skin too. So what drives it?
What is elephant skin?
It’s a surface quality problem that operators describe as wrinkled or textured skin, often alongside sinks. A technical disclosure on MJF ESD print modes published on Technical Disclosure Commons links elephant skin to “cold parts,” where the part doesn’t get enough fusing energy. It notes that fusing-lamp irradiance is the setting with the most influence on look and feel.
Is it a heat problem or a cold problem?
Sources point to two possible causes. The Technical Disclosure Commons paper ties elephant skin to too little fusing energy, or “cold parts.” The Reddit operator lists it among the problems that come with large parts and high packing densities, which they describe as heat-related. Either way, it’s a sign the part didn’t get the right, even amount of energy. Check both your print-mode energy settings and how heat builds up in the layout.
Does orientation matter?
Yes. A 2023 study in Materials (MDPI) on minimizing MJF deformation says printing flat parts horizontally is rarely done because it causes surface problems like sinks or elephant skin. The fusing and detailing agents can sit on the upper surface during printing.
What can the bureau control to prevent MJF elephant skin?
- Orientation: avoid large flat faces parallel to the build plane when cosmetics matter.
- Packing: don’t max out density on builds with large or heavy parts.
- Geometry: RapidMade and HP’s design guidance both push uniform wall thickness and hollowing thick sections to even out heat.
- Print mode: special print modes change energy settings, so check cosmetic results when switching.
What should you tell the customer?
If a part is large, thick or has big flat cosmetic faces, flag the risk at quote time. Offer a design change such as shelling, or a finish such as dyeing or vapor smoothing if appearance matters.
How do you learn from it?
Record defects by build with orientation, density and print mode. Over time, that shows which geometries and layouts actually produce elephant skin on your machines.
Related on the Solvi blog: MJF Warping: Why Large Flat Parts Warp; MJF Packing Density: How Full Should You Pack a Build?; MJF Cooling: Natural or Fast, How Should a Bureau Decide?.
Sources: r/AdditiveManufacturing packing density thread; Technical Disclosure Commons (MJF ESD print mode); MDPI Materials 16(23):7389; RapidMade MJF best practices; HP MJF design guidelines (Design for accuracy).