MJF 3D printing

MJF 3D printing (Multi Jet Fusion) is a powder bed fusion process developed by HP, in the same family as SLS 3D printing. Instead of a laser tracing each layer point by point, it processes the whole layer at once with inkjet printheads and an infrared heat source.

A recoater first spreads a thin layer of powder, typically about 0.08 mm. Printheads then jet a fusing agent onto the cross-section of the part and a detailing agent along its edges, which keeps the surrounding powder from fusing and sharpens the edges. As the infrared lamp passes over, only the printed areas melt, because the agent absorbs the energy far better than bare powder. The unfused powder supports the parts, so no support structures are needed and parts can be nested side by side and stacked in the build volume.

The most common material is PA12 polyamide (nylon 12), followed by PA11, glass bead filled PA12, polypropylene and flexible TPU. The agent makes parts dark gray, so they are usually dyed black. PA12 strength is similar in all directions (tensile strength typically around 45 to 50 MPa), although elongation at break along the Z axis tends to be lower. Dimensional accuracy is usually ±0.2 to 0.3 mm for parts up to about 100 mm; for larger parts it is given as a percentage of the dimension (around 0.3%). The most common machines have a build volume of roughly 380 × 284 × 380 mm.

Compared with SLS, MJF tends to be faster when the build is fully packed and gives slightly finer detail and a smoother surface. SLS offers a wider choice of materials and white parts that can be dyed in many colors. After printing, the powder cake must cool under controlled conditions before the parts are unpacked and bead blasted in post-processing. Most of the unfused powder can be reused after mixing it with fresh powder.

Choose MJF 3D printing for functional prototypes and end-use polyamide parts that carry real loads: housings, enclosures, brackets, snap fits, air ducts, cable grommets and assembly fixtures. Since it needs no supports, it handles complex shapes with internal channels, lattice structures and moving assemblies printed in one piece.

Its real strength is low-volume production of tens to thousands of parts. The build volume holds many parts at once, and quality stays consistent between parts and between jobs. MJF therefore serves as bridge production until the injection mold is ready, or permanently for products where a mold would never pay for itself.

Bulky solid sections make a part needlessly expensive, lengthen cooling and raise the risk of sink marks and warping. Design walls of uniform thickness, usually at least about 1 mm, hollow out thick volumes and give enclosed cavities escape holes for the powder. Large flat parts can warp, so stiffen them with ribs.

Expect a dark gray color and a slightly porous surface that absorbs liquids and dirt. If you need a color other than gray or black, watertightness or an easy-to-clean surface, agree on painting, sealing (impregnation) or chemical smoothing. Leave a clearance of a few tenths of a millimeter at joints and between moving parts printed as one piece. In your request for quote, state the material, surface finish, critical dimensions with tolerances and quantity, because the price depends on part volume and on how many parts fit into the build.