Metal AM Without the Complexity
Metal FFF is the first technology that makes metal 3D printing accessible to any engineering team with a shop floor. No powder handling, no inert gas infrastructure, no $500K+ machine - just a printer, a wash station, and a furnace. This guide gives you the full picture: how the process works, what you can and can't make, real cost data, and when to reach for DMLS instead.
How Metal FFF Works
Metal FFF extrudes a bound metal filament or rod layer by layer - like FDM - then debinds and sinters the "green" part in a furnace to create a fully-metal component.
Metal FFF (also called Bound Metal Deposition / BMD) is the most accessible path to in-house metal 3D printing. The process has three stages: Stage 1 - Print: A filament or rod made of metal powder (~60% by volume) bound in a wax/polymer binder is extruded through a heated nozzle, building the part layer by layer - exactly like FDM. The result is a "green" part that is fragile and oversized (to compensate for sintering shrinkage). Stage 2 - Debind: The wax binder is removed via solvent wash (Desktop Metal) or catalytic debinding (Markforged). This takes 12–48 hours depending on part thickness and creates a "brown" part held together only by the remaining polymer backbone. Stage 3 - Sinter: The brown part is heated in a furnace to 1250–1400 °C (alloy-dependent) in an inert or reducing atmosphere (H₂/Ar). The polymer backbone burns off and metal particles diffuse together, shrinking the part 15–20% linearly and achieving 95–99% final density.
Print stage (2–24 hours)
Standard FDM mechanics: heated nozzle (120–220 °C for the binder), heated bed, layer-by-layer deposition. Layer heights: 0.1–0.2 mm. Print speed: 20–50 mm/s (slower than polymer FDM due to higher-density feedstock). Support structures use a ceramic-based release material that separates cleanly after sintering.
Debinding (12–48 hours)
Solvent debinding (Desktop Metal): parts immersed in a proprietary solvent that dissolves the wax binder, leaving the polymer backbone intact. Catalytic debinding (Markforged): nitric acid vapor breaks down the binder. Part thickness determines debind time - thicker walls take longer for solvent to penetrate.
Sintering (24–48 hours)
The furnace ramps to 1250–1400 °C over several hours, holds at peak temperature for 2–4 hours, then cools slowly. Total cycle: 24–48 hours including ramp-up, hold, and cooldown. Multiple parts can be sintered in a single batch - sintering cost per part drops with batch size.
Shrinkage: 15–20% linear
The most critical design consideration. The green part is printed ~18–20% oversized in all directions to compensate for sintering shrinkage. Shrinkage compensation is handled automatically by the printer software, but residual dimensional variation of ±0.5–2.0% is typical.
Ceramic release supports
Unlike DMLS metal supports (which must be ground/machined off), Metal FFF uses a ceramic interface layer between supports and the part. After sintering, the ceramic prevents the support from fusing to the part - supports snap off by hand. This dramatically reduces post-processing labor.
Final density: 95–99%
Standard sintering achieves 95–98% density. HIP (Hot Isostatic Pressing) can push this to >99%. Mechanical properties are typically 80–95% of wrought equivalents - sufficient for most non-flight-critical applications.
Pro Tip
Metal FFF's biggest advantage over DMLS is accessibility: a complete system (printer + wash + furnace) costs $100K–$200K vs. $500K–$2M+ for DMLS. This puts metal AM capability on the shop floor for the first time - no specialized facilities or powder safety infrastructure required.
Materials Guide
Metal FFF supports 5–6 alloys covering stainless steel, tool steel, titanium, and copper - fewer than DMLS but covering the most commercially important applications.
Metal FFF alloys are delivered as bound filaments or rods from the machine manufacturer. Material selection is more limited than DMLS, but covers the alloys most commonly needed for tooling, prototyping, and low-volume production.
| Alloy | UTS (MPa) | Density (%) | Key Properties | Best For | Available On |
|---|---|---|---|---|---|
| 17-4 PH Stainless | 800–1000 | 96–99 | High strength, age hardenable, corrosion resistant | Tooling, fixtures, structural prototypes | Desktop Metal, Markforged |
| 316L Stainless | 480–550 | 96–98 | Excellent corrosion resistance, weldable | Medical, fluid handling, chemical environments | Desktop Metal, Markforged |
| H13 Tool Steel | 1200–1500 | 96–98 | Excellent hot hardness, wear resistant | Injection mold inserts, die casting tooling | Desktop Metal, Markforged |
| Ti-6Al-4V | 850–950 | 96–98 | High strength-to-weight, biocompatible | Aerospace prototypes, medical devices | Markforged |
| Copper (C10200) | 200–250 | 95–97 | Highest thermal & electrical conductivity | Heat sinks, EDM electrodes, bus bars | Desktop Metal, Markforged |
| A2 Tool Steel | 1400–1600 | 96–98 | Air-hardening, very high wear resistance | Cutting tools, gauges, wear components | Desktop Metal |
Pro Tip
For most applications, start with 17-4 PH - it's the most forgiving Metal FFF alloy with the widest process window and best dimensional consistency after sintering. Switch to specialty alloys (H13, Ti-6Al-4V, copper) only when a specific property demands it.
Design Guidelines (DFM)
Metal FFF design rules combine FDM constraints (nozzle access, overhangs) with sintering constraints (shrinkage, sag, wall thickness).
Metal FFF design is a hybrid of FDM design rules (extrusion-based constraints) and powder metallurgy rules (sintering-based constraints). The green part must survive handling; the brown part must survive the furnace. These guidelines assume Desktop Metal / Markforged standard parameters.
| Feature | Recommended | Minimum | Notes |
|---|---|---|---|
| Wall thickness | 2.0 mm | 1.0 mm | Thin walls may sag during sintering; support from below |
| Overhang angle | <40° from vertical | <45° | Same as polymer FDM; ceramic release supports used |
| Unsupported span | <15 mm | <25 mm | Gravity causes sag during sintering; add supports for spans >15 mm |
| Hole diameter | ≥2.0 mm | ≥1.0 mm | Small holes may close during sintering - drill/ream to final size |
| Max part size | 150 × 200 × 150 mm | - | Desktop Metal Studio; Markforged similar range |
| Aspect ratio | <8:1 (height:width) | - | Tall thin parts may lean during sintering |
| Internal channels | ≥3 mm diameter | ≥2 mm | Debinding solvent must reach all internal surfaces |
| Flat areas | Add support ribs or setters | - | Large flat surfaces sag under gravity at sintering temperature |
| Text / engraving | ≥1.0 mm wide, ≥0.8 mm deep | - | Coarser than DMLS due to larger layer heights and shrinkage |
| Shrinkage compensation | Automatic (18–20% scaling) | - | Software handles it, but expect ±0.5–2.0% residual variation |
Pro Tip
Design for the sintering furnace, not just the printer. The green part may print perfectly but sag, warp, or crack in the furnace if not properly supported. Add ceramic setter tiles under large flat surfaces and support tall features with sintering-compatible structures.
Debind + Sinter Workflow
The debind+sinter workflow is what makes Metal FFF fundamentally different from DMLS - it's a batch process that takes 2–4 days but requires minimal operator skill.
Unlike DMLS (where the part comes off the machine as solid metal), Metal FFF produces a green body that must go through two additional processing stages. The total turnaround from print to finished metal part is 3–5 days.
Print → Green part (2–24 hours)
The printer builds the part from bound metal filament/rod. The green part has the consistency of soft chalk - handle with care. Complex internal geometries print well because the process follows FDM mechanics.
Debind → Brown part (12–48 hours)
Solvent or catalytic debinding removes the primary wax binder. The remaining polymer skeleton holds the part together with just enough strength to transfer to the furnace. Part thickness drives debind time: a 5 mm wall may need 24 hours; a 15 mm wall may need 48 hours.
Sinter → Metal part (24–48 hours)
The furnace ramp profile: (1) slow ramp to 400–600 °C to burn off polymer backbone, (2) ramp to peak sintering temperature (1250–1400 °C), (3) hold at peak for 2–4 hours, (4) slow cooldown. The part shrinks ~18% linearly and densifies to 95–99%.
Batch processing economics
The furnace can sinter many parts simultaneously - marginal cost per additional part is near zero (just electricity and gas). This makes Metal FFF extremely cost-effective for batches: sintering 1 part costs the same as sintering 30. Always batch your sintering runs.
Support removal (5–15 min/part)
Ceramic release material prevents supports from bonding to the metal part during sintering. After sintering, supports snap off by hand or with light tapping. This is dramatically easier than DMLS support removal (which requires grinding or machining).
Optional: HIP for full density
Hot Isostatic Pressing (HIP) at 1000–1200 °C and 100–200 MPa of argon gas closes residual porosity, pushing density from 95–98% to >99%. Required for fatigue-critical or safety-critical applications. Adds $50–200/part.
Pro Tip
The debind+sinter cycle is the bottleneck - not the print. Plan your workflow around furnace batch scheduling: print multiple parts during the day, start debinding overnight, load the furnace on the next day. A single furnace cycle can process 10–30+ parts.
Cost Analysis
Metal FFF costs 30–60% less than DMLS per part for simple geometries - and the capital investment is 3–5× lower.
Metal FFF economics are fundamentally different from DMLS: lower machine cost, lower material cost (bound filament vs. atomized powder), and batch sintering that amortizes furnace time across many parts. The trade-off is looser tolerances and lower density.
| Cost Component | Metal FFF (in-house) | DMLS (service bureau) | Notes |
|---|---|---|---|
| System cost | $100K–$200K (printer + wash + furnace) | $500K–$2M+ | Metal FFF: 3–5× lower capital investment |
| Material (17-4 PH) | $100–200/kg (bound filament) | $60–100/kg (powder) | Metal FFF feedstock costs more per kg but less per part |
| Machine rate (print) | $5–15/hr | $80–200/hr | Metal FFF printers are far simpler machines |
| Debind + sinter | $10–30/batch (gas + electricity) | - | Amortized across batch; near-zero marginal cost per part |
| Post-processing | $5–20/part (support snap-off) | $50–300/part (grind + machine) | Ceramic release supports vs. metal supports |
| Est. cost (bracket, 1 pc) | $50–150 | $150–400 | Metal FFF 30–60% cheaper for simple shapes |
| Est. cost (bracket, 20 pc) | $25–60/ea | $100–250/ea | Batch sintering drives Metal FFF advantage at volume |
Payback calculation
If you're sending 5+ metal parts/month to a DMLS service bureau, a Metal FFF system ($150K) pays for itself in 12–18 months. At 20+ parts/month, payback drops to 6–9 months. Factor in eliminated shipping time and IP protection.
Batch sintering is the cost lever
A sintering run costs ~$50–100 in gas and electricity regardless of part count. Sintering 1 part: $50–100 furnace cost. Sintering 20 parts: $2.50–5.00/part furnace cost. Always batch your sintering runs for maximum efficiency.
When Metal FFF is NOT cheaper
Complex geometries requiring tight tolerances (±0.004″) or full density (>99.5%) still favor DMLS. Metal FFF post-machining costs can erode the savings if many features need tight tolerances. Evaluate total cost including secondary operations.
Pro Tip
The real ROI of in-house Metal FFF isn't just cost - it's speed and iteration. Print a metal prototype in 1 day, sinter in 2 days, test on day 4. Via DMLS service bureau, the same cycle takes 2–3 weeks. That 10× faster iteration loop is the strategic advantage.
Metal FFF vs DMLS
The decision framework for choosing between accessible, in-house Metal FFF and high-performance DMLS.
Metal FFF and DMLS serve different needs. Metal FFF is "metal printing for the shop floor" - accessible, affordable, good-enough for most applications. DMLS is "metal printing for mission-critical parts" - expensive, complex, but unmatched in density and geometric capability.
| Factor | Choose Metal FFF When… | Choose DMLS When… |
|---|---|---|
| Budget | Capital budget <$200K or per-part budget is constrained | Capital budget >$500K or service bureau cost is acceptable |
| Density requirement | 95–99% density is acceptable for your application | >99.5% density is required (fatigue-critical, pressure vessels) |
| Tolerances | ±0.020″ (post-sinter) or ±0.005″ (post-machined) is adequate | ±0.004″ as-printed is needed, or complex features must be tight |
| Geometry | FDM-compatible shapes (no extreme overhangs or internal lattices) | Conformal cooling, topology optimization, internal lattice structures |
| Part size | Parts fit within 150 × 200 × 150 mm | Parts up to 400 × 400 × 400 mm or larger |
| In-house vs. outsource | You want metal AM in-house (no powder safety infrastructure) | Service bureau or dedicated AM facility with powder handling |
| Iteration speed | You need metal prototypes in 3–5 days, iterating frequently | You're building production parts with 2–3 week lead times acceptable |
| Alloy range | 17-4 PH, 316L, H13, Cu, or Ti-6Al-4V meets your needs | You need AlSi10Mg, Inconel, CoCr, or maraging steel |
Pro Tip
Think of Metal FFF as the "CNC mill" of metal AM - accessible, versatile, good-enough for 80% of applications. DMLS is the "5-axis EDM" - expensive and specialized, but essential for the remaining 20% where geometric complexity and material properties are non-negotiable.
Applications & Use Cases
Metal FFF dominates where accessibility, cost, and iteration speed matter more than absolute density or geometric complexity.
In-house metal prototyping
The flagship use case: print, debind, and sinter metal prototypes in 3–5 days without leaving the building. Eliminates 2–3 week service bureau lead times and shipping costs. IP stays in-house. Iterate designs 2–3× faster.
Custom tooling & mold inserts
H13 tool steel inserts for injection molds, die casting tools, and forming dies. Conformal cooling isn't as sophisticated as DMLS (limited by FDM geometry constraints), but straight-line channels still improve cycle time by 10–20%.
Jigs, fixtures & assembly aids
17-4 PH stainless fixtures replace machined steel at 30–50% of the cost. Print custom go/no-go gauges, welding fixtures, and CMM holding tools. Metal FFF parts are strong enough for production floor use.
End-use parts (low volume)
When annual volume is <500 units and full-density DMLS isn't required. Brackets, connectors, housings, and structural components in 17-4 PH or 316L. Cost: $25–100/part vs. $150–400/part for DMLS.
EDM electrodes
Copper EDM electrodes with complex profiles that would require 5-axis CNC. Metal FFF prints copper with sufficient conductivity for EDM applications. Turnaround: 3–4 days vs. 2 weeks for CNC copper.
Replacement & legacy parts
Reverse-engineer and print replacement metal parts for legacy equipment. Particularly valuable in defense, oil & gas, and industrial maintenance where OEM parts are unavailable and CNC programming + setup doesn't justify a one-off run.
Pro Tip
Metal FFF's strategic value is iteration speed, not per-part cost. The ability to print a metal prototype, test it, modify the CAD, and reprint - all within one week - fundamentally changes how hardware teams design metal components.
Common Mistakes
Metal FFF mistakes are usually discovered after 48 hours of sintering - making each failure expensive in time, not just material.
Handling green parts roughly
Green parts have the strength of soft chalk. Dropping, flexing, or gripping a green part too hard will crack it - and the crack will propagate during sintering into a full fracture. Use gloves, support the part from below, and store on flat surfaces.
Designing unsupported spans that sag in the furnace
At sintering temperature (1300+ °C), the part is soft and yields under gravity. Unsupported spans >15 mm will sag visibly. Design ceramic setter tiles or sacrificial support columns under long spans and overhangs.
Expecting DMLS-level tolerances without post-machining
Metal FFF post-sinter tolerance is ±0.020″ (±0.50 mm) - 5× looser than DMLS. For mating surfaces, always plan for CNC post-machining. Design features to be oversized with machining stock (0.5–1.0 mm per side).
Incomplete debinding
If debinding is cut short, residual binder trapped in thick walls creates gas during sintering - causing blisters, voids, and cracks. Follow manufacturer debind times exactly, and add 20% extra time for parts with wall thickness >10 mm.
Not batch-loading the furnace
Sintering 1 part costs the same furnace time as sintering 30. Running single-part sinter cycles wastes 90% of furnace capacity. Queue up parts and batch-sinter for maximum cost efficiency.
Assuming Metal FFF replaces DMLS
Metal FFF is a complement to DMLS, not a replacement. It can't match DMLS on density (>99.5%), tolerances (±0.004″), surface finish (150–400 Ra µin), or geometric complexity (lattices, conformal cooling). Use each where it excels.
Pro Tip
Create a sintering log: record part ID, alloy, green weight, brown weight, sintered weight, and dimensions before/after sintering. This data builds your understanding of actual shrinkage rates for your specific machine and helps you hit tolerances consistently over time.
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