Understanding the Metal FFF 3D Printing Process: From Printing to Sintering

Metal fused filament fabrication (FFF) is the most accessible, easy‑to‑use, and affordable metal 3D printing technology. Industries such as aerospace and automotive already rely on Metal FFF to produce functional parts with speed and precision.

Metal FFF follows a three‑step workflow—print, debind, and sinter—mirroring the principles of metal injection molding (MIM). The following guide breaks down each phase so you can understand how raw metal is transformed into finished components.

Metal FFF’s 3‑Step Workflow

These printers are specialized FFF machines that use MIM feedstock. They produce “green” parts that must be debound and sintered before they become usable.

Because sintering causes a predictable 15‑20 % shrinkage, green parts are deliberately scaled up by this margin during printing.

• Printing: Metal powder bound in a thermoplastic is extruded layer‑by‑layer onto a vacuum‑sealed sheet, creating a green part.
• Debinding: The green part is washed in a solvent bath that removes most of the plastic binder, yielding a brown part.
• Sintering: The brown part is heated in a controlled atmosphere furnace to burn out remaining binder and fuse the metal powder into a finished component.

Step 1: Printing

Metal FFF machines operate like conventional FFF printers but use a vacuum‑sealed sheet instead of a standard bed. The process steps are:

• Slice the model in software.
• Place a vacuum‑sealed sheet on the build plate.
• Start the print and allow the metal filament to extrude.
• Release the vacuum once the part is complete.
• Peel the green part from the sheet.

Dual‑extrusion printers combine MIM feedstock with a ceramic release filament. The MIM nozzle prints the part and supports, while the ceramic nozzle ensures easy separation after sintering. Markforged offers six industrial‑grade filaments—A2 tool steel, D2 tool steel, Inconel 625, Copper, H13 tool steel, and 17‑4 PH stainless steel.

Step 2: Debinding

Debinding removes the bulk of the binder, converting the green part into a brown part ready for sintering.

In the wash station, the part is submerged in a solvent bath—typically Opteon SF‑79—designed to dissolve the primary binder efficiently while being environmentally responsible.

Key steps:

• Place green parts into the wash basket.
• Lower the basket into the solvent and seal the lid.
• Open the lid after the wash cycle and remove the parts.
• Transfer the parts to an air‑dry chamber.
• Remove the dried parts once they are dry.

The solvent creates micro‑pathways, allowing it to penetrate deeply and remove binder uniformly.

Step 3: Sintering

Sintering is the decisive final stage, where the brown part is heated in a precise, controlled atmosphere furnace. The process removes residual binder and fuses the metal powder into a near‑solid part.

Key stages:

• Intermediate heating burns out remaining binder via micro‑pathways created during debinding.
• High‑temperature sintering causes the part to shrink 15‑20 % to its final dimensions, achieving >95 % density while maintaining a closed‑cell infill.
• The ceramic interface material turns to fine dust, allowing easy separation from supports and raft.

Typical furnace operations include:

• Load the parts onto a setter plate.
• Insert the plate into the furnace.
• Seal the door.
• Initiate the sintering cycle.
• Allow the process to run to completion.

Free Metal 3D Printing Resources

• Metal 3D Printing Fundamentals
• E‑Book: Metal FFF Applications and Case Examples
• Comprehensive Guide to Metal FFF