How is metal filament made?

Metal filament is primarily made by blending fine metal powder with a polymer base material, which is then extruded into a usable filament strand for 3D printing. This process creates a material suitable for additive manufacturing, often resulting in parts with a unique metallic finish and added weight.

The Fundamental Process: From Powder to Filament

The creation of metal filament involves a sophisticated process that combines metallurgical and polymer processing techniques. The core idea is to homogeneously distribute fine metal particles within a polymer matrix, which then allows the material to be extruded into a consistent filament diameter.

1. Compounding and Mixing: The first critical step involves mixing a fine metal powder into a base material. This base material is typically a thermoplastic polymer, which acts as a binder. The metal powder (e.g., stainless steel, copper, bronze, titanium) is carefully selected for its properties and particle size, ensuring it can be uniformly dispersed. This mixture is often processed in a specialized compounding extruder, where heat and shear forces ensure a thorough and homogeneous blend, preventing agglomeration of the metal particles.
2. Pelletization: After compounding, the molten mixture is cooled and then cut into uniform pellets. These pellets serve as the raw material for the final filament extrusion stage.
3. Extrusion: The pellets are fed into a filament extruder. Here, they are melted again and pushed through a precisely sized die under controlled temperature and pressure. This forms a continuous strand of filament. The extrusion parameters are crucial for maintaining consistent diameter and preventing voids within the filament.
4. Cooling and Spooling: As the filament exits the die, it is rapidly cooled, often in a water bath or with air jets, to solidify its shape. Tension is applied to maintain the correct diameter as it is then wound onto spools, ready for use in 3D printers.

Key Components

The quality and properties of metal filament are heavily dependent on its constituent materials:

• Metal Powder: The choice of metal powder dictates the final properties of the printed part. Common choices include:
  • Stainless Steel (e.g., 316L, 17-4 PH): Known for strength and corrosion resistance.
  • Copper: Excellent thermal and electrical conductivity.
  • Bronze: Aesthetic appeal, often used for decorative purposes.
  • Titanium: High strength-to-weight ratio, biocompatibility.
    The particle size and shape of the powder are critical for proper flow and binding.
• Base Material (Polymer Binder): The polymer binder holds the metal particles together during printing. Its properties influence printability, flow characteristics, and, for some filaments, how easily it can be removed during post-processing. Common binders include:
  • PLA (Polylactic Acid): Easy to print, biodegradable.
  • PVA (Polyvinyl Alcohol): Water-soluble, often used as a temporary support material.
  • Specialized Polymers: Such as polyolefins, waxes, or EVA (Ethylene-vinyl acetate), especially for filaments designed for debinding and sintering.

Beyond Production: Two Main Types of Metal Filaments

It's important to distinguish between the two primary types of "metal filaments" available, as their intended use and properties differ significantly after printing:

Metal-Filled Polymer Filaments (Composites)

These are the most common type of metal filament for desktop FDM 3D printers. They contain a significant percentage of metal powder (often 50-85% by weight) mixed into a polymer base.

• Characteristics: The polymer remains the primary matrix even after printing. While they provide a unique metallic finish and added weight, the printed objects are still largely plastic. They can often be polished, aged, or patinated to enhance their metallic appearance.
• Applications: Ideal for creating visually appealing models, artistic sculptures, prototypes, props, and decorative items where the aesthetics of metal are desired without the need for full metallic strength or conductivity. They are processed like standard polymer filaments.

Bound Metal Filaments (for True Metal Parts)

These filaments are specifically engineered to enable the production of solid, functional metal parts through a multi-stage process. They contain a very high percentage of metal powder and a small amount of polymer binder that is designed to be removed.

• Characteristics: After printing, the "green part" is not fully metal. It requires subsequent post-processing steps to become a dense, pure metal object.
• Post-Processing Steps for True Metal Parts:
  1. Debinding: This process removes the polymer binder from the printed "green part." It can be done chemically (e.g., solvent bath) or thermally (e.g., heat treatment in a furnace). The removal of the binder creates a porous "brown part."
  2. Sintering: The debound "brown part" is then heated in a high-temperature furnace, typically just below the metal's melting point. During sintering, the metal particles fuse together, densifying the part and shrinking it to its final solid metal form. This results in a fully metallic, strong, and often functional component.
• Applications: Used for creating functional prototypes, low-volume manufacturing of complex metal parts, and specialized tooling where the mechanical properties of true metal are required.

Comparative Overview

Ensuring Quality

The production of high-quality metal filament relies on stringent quality control at every stage. This includes precise measurement of powder-to-binder ratios, consistent temperature control during extrusion, and accurate monitoring of filament diameter. These measures ensure reliable print performance and the desired properties in the final printed object.