Multi Jet Fusion
MJFHP Multi Jet FusionHP Jet FusionPBF-LB/P (MJF variant)Tungsten-halogen infrared (IR) lamp spanning the full build platform width (up to 380 mm). HP thermal inkjet printheads deposit fusing agent (carbon-black absorber ink) at cross-section areas and detailing agent (non-fusing fluid) at part boundaries. The IR lamp passes over, absorbing energy preferentially where fusing agent was deposited. No laser required.
How it works
PA12 powder (or PA11, TPU) is spread in thin layers (~80 µm). An inkjet printhead array simultaneously deposits fusing agent (black ink, high IR absorptivity) at the desired cross-section and detailing agent (clear, low absorptivity) at boundaries and non-part areas. An IR lamp passes over the entire layer, fusing all agent-coated regions simultaneously. This parallel fusing mechanism is significantly faster than laser point-scanning and produces more uniform temperature distribution within each layer. At standard 30% virgin powder refresh rate, HP PA12 achieves near-full theoretical density (1.01 g/cm³) and slightly superior mechanical properties vs SLS PA12.
Parameter envelopes (1 material–machine combinations)
Layer thickness
80–80 µm
HP MJF operates at atmospheric conditions (no inert gas required). Build temperature is maintained by the IR lamp profile. Standard 30% virgin refresh rate for production. Layer thickness is fixed at 80 µm on all HP Jet Fusion 5xxx systems. Build rate up to 2500 cm³/h at standard quality mode.
Defect modes (3)
Agent Bleeding / Edge Roughness
Cause
Fusing agent wicking into adjacent unfused powder beyond the intended boundary. More pronounced at coarser powder PSD, higher fusing temperatures, or when detailing agent is insufficient at edges.
Indicator
Dimensional oversize at part boundaries (+0.1–0.3 mm). Rough, fuzzy surface at part edges. Colour bleed in full-colour MJF prints.
Prevention
Use HP-validated printing parameters. Check printhead nozzle condition regularly (missing nozzles reduce agent uniformity). For dimensional-critical features, add post-processing machining allowance of 0.3 mm.
Detection
- CMM or caliper dimensional measurement
- visual inspection
Aged Powder Degradation
Cause
Same mechanism as SLS PA12 — thermal degradation of recycled powder. MJF standard 30% refresh is more conservative than SLS 50:50, providing better aged-powder control.
Indicator
Reduced elongation at break. Property scatter increase across batch. Grey/dark colouration of parts (from accumulated fusing agent in aged powder).
Prevention
Maintain 30% refresh rate (HP recommended). Monitor elongation in production batch coupons. Dispose of powder exceeding thermal age threshold (HP defines build equivalent cycles).
Detection
- Tensile testing of coupons
- visual inspection
Grey Colour from Fusing Agent
Cause
The carbon-black fusing agent is absorbed into the part, making all standard MJF PA12 parts grey. Unlike SLS (white powder → light grey parts), MJF parts are inherently grey and cannot achieve white or light colours on standard Jet Fusion 5xxx systems.
Indicator
All parts are grey. Light colours (white, yellow, pink) are not achievable on standard MJF. Full-colour printing is only available on HP Jet Fusion 5600 series with CMYK detailing agents.
Prevention
Accept grey as the standard output colour. For white or light colours: use SLS PA12 (natural white) and dye/paint post-process. For full colour: HP 5600 system or post-painting.
Detection
- Visual inspection