MJF packing density is the number every bureau owner wants to push up, because a fuller build spreads the fixed cost of a print over more parts. Operators on r/AdditiveManufacturing recently argued over a vendor article claiming much higher packing figures than they see in daily production. So how full should an MJF build actually be?
Why does packing density matter so much?
Every build carries fixed costs: warm-up, powder layers, machine time and cooling. Australian reseller Motion X sums it up simply. The more parts you fit into one print, the lower the cost per part, and the fewer layers the printer lays down, the cheaper the job.
What range do operators actually run?
Motion X says 8 to 10% is the best range for part quality and strength, while 12 to 15% lowers cost per part considerably. In the Reddit thread, one operator said the most they could reach was 17%. Another said everyday production runs closer to 8 to 15%. A service-bureau commenter on a LinkedIn discussion said their SLS builds typically ran 6 to 8% and rarely went over 12% unless the parts were chunky. Treat these as field reports, not specs. Your number depends on your part mix.
What goes wrong when you pack too dense?
Heat. One operator in the thread said high packing densities oxidize powder at best, and at worst cause poor dimensional accuracy and elephant skin. Large or massive parts make it worse. HP’s tips guide also notes that lower packing density allows better temperature control and better mechanical properties.
Is MJF packing density the right goal?
Not by itself. The same LinkedIn commenter pointed out that what matters is real throughput per hour including yield. They also nested to an even Z distribution so thermals stayed consistent from layer to layer. A dense build that scraps three parts can lose to a lighter build that ships everything.
How do you make this repeatable?
- Set a target density range per material and part family, then log the actual density and yield for each build.
- Keep the stack short when speed matters, since print and cooling time scale with build height.
- Review scrap by build to find your real ceiling.
Solvi Auto-Nest packs MJF and SLS builds straight from the queue and gives the build tech a 3D review. It’s currently in pilot with founding partners, so ask about availability.
Related on the Solvi blog: MJF Elephant Skin: What Causes It and How to Avoid It; MJF Warping: Why Large Flat Parts Warp; MJF Cooling: Natural or Fast, How Should a Bureau Decide?.
Sources: r/AdditiveManufacturing packing density thread; Motion X MJF tips; HP MJF tips and tricks guide; LinkedIn discussion on packing density.