WAAM: Metal 3D Printing

TL;DR

  • Technology: Wire Arc Additive Manufacturing (wire deposition by arc)
  • Material: Wire 1.6-2.0 mm diameter (Al, Fe from rolling mill)
  • Productivity: ~60-180 kg/day (3 cells) for complex parts
  • Application: Robot bodies, brackets, frames, tooling

Overview

WAAM is a metal 3D printing technology where a robotic arm melts wire with an electric arc and deposits material layer by layer. It is an industrial alternative to powder-based 3D printing, faster and more economical.

Operating Principle

flowchart TD
    subgraph INPUT["INPUT"]
        WIRE["Wire 1.6 mm diameter<br/>from drawing line"]
    end

    subgraph WAAM_CELL["WAAM CELL"]
        ROBOT["6-axis robot"]
        TORCH["Welding torch"]
        ARC["Electric arc<br/>~5000C"]
        FLUX["Flux shielding<br/>FCAW-S"]
        TABLE["Rotary table"]
    end

    subgraph POST["POST-PROCESSING"]
        GRIND["Abrasive<br/>grinding"]
        FINISH["Finishing"]
    end

    subgraph OUTPUT["OUTPUT"]
        PARTS["Finished parts<br/>bodies, frames, brackets"]
    end

    WIRE --> ROBOT
    ROBOT --> TORCH
    TORCH --> ARC
    FLUX --> ARC
    ARC --> TABLE
    TABLE --> GRIND
    GRIND --> FINISH
    FINISH --> PARTS

    style INPUT fill:#f0e68c
    style WAAM_CELL fill:#fff3cd
    style POST fill:#d4edda
    style OUTPUT fill:#cce5ff

Process: 1. Robot feeds wire to the torch 2. Electric arc melts the wire (and workpiece surface) 3. Molten droplet solidifies, forming deposited layer 4. Robot moves 1-2 mm, deposits next layer 5. Layer by layer the part grows

WAAM Cell

Robotic Arm

Parameter Value
Type 6-axis industrial robot
Payload 10-20 kg (torch + wire)
Positioning accuracy +/-0.1 mm
Travel speed 0.5-2 m/s
Material Steel Fe + Al (local production)

Difference from Earth robots: Lightweight Al construction (low gravity 0.38g), no lubrication (operates in 0.1 atm O₂).

Welding Torch

Parameter Value
Type FCAW-S (Flux-Cored Arc Welding — Self-shielded)
Current 150-300 A
Voltage 20-30 V
Power 3-9 kW
Wire feed 3-8 m/min
Wire Flux-cored with flux core (TiO₂+CaO+MgO+Fe)

Why FCAW-S? - Flux creates shielding gas and slag cover when heated - No external gas required — argon is not imported - Flux components are 100% local: TiO₂ (titanium line), CaO (MRE slag), MgO (magnesite), Fe - Earth analogs: Lincoln Electric Innershield, ESAB Coreshield

Flux-cored wire production: steel strip → forming into tube → flux filling → drawing to Ø1.6-2.0 mm

Rotary Table

Parameter Value
Diameter 1-2 m
Load capacity 500-1000 kg
Rotation speed 0.1-10 rpm
Tilt +/-45 degrees

Purpose: Allows robot to deposit complex parts by rotating them to optimal angles.

Materials for WAAM

Material Application Productivity
Aluminum (Al) Robot bodies, brackets ~3 t/day
Iron (Fe) Frames, structural elements ~1 t/day

Wire source: Rolling mill (drawing line)

Productivity

Parameter Value
Deposition rate 1-3 kg/hour per cell
Number of WAAM cells 3 (per factory)
Operation 20 hours/day
TOTAL ~20-60 kg/day per cell
For 3 cells ~60-180 kg/day

Why not more? - WAAM is slower than casting but allows complex shapes without tooling - Used for parts that cannot be cast (hollow bodies, complex geometries)

Post-Processing: Abrasive Grinding

After WAAM, the part has a rough surface. Finish machining is done by grinding (not milling).

Grinding Cell

Parameter Value
Type Centaur-M robot with abrasive head
Number of axes 6 (manipulator) + rotary table
Drive power 3-5 kW
Spindle speed 3000-6000 rpm
Tool Al₂O₃ abrasive wheels (corundum, local)

Advantages over CNC: - No imported high-speed spindle (20,000 rpm) - Al₂O₃ abrasive produced from regolith (unlimited) - Same Centaur-M robot, just different tool - Dry machining in vacuum (no coolant)

Machining accuracy: +/-0.05 mm (sufficient for bodies and frames)

Typical Parts Produced by WAAM

Part Material Mass Print time Application
Crab-M body Al 50 kg 20 hours Crab-M robot
Centaur-M frame Al 30 kg 12 hours Centaur-M robot
Caster brackets Fe 20 kg 8 hours Continuous casting
Assembly tooling Fe 10 kg 5 hours Jigs, fixtures

Advantages of WAAM

Advantage Description
No tooling No molds, dies, casting patterns needed
Rapid prototyping New part in 1 day (casting takes weeks)
Material savings Only required metal used (casting has 30-50% waste)
Complex geometry Cavities, internal channels, organic shapes

WAAM Limitations

Limitation Solution
Low speed Use for complex parts, simple ones by casting
Surface roughness Abrasive grinding (Al₂O₃)
Abrasive wear Al₂O₃ corundum — local production, replacement every 1-2 days

Energy Consumption

Component Power Quantity TOTAL
WAAM cell (robot + torch) 10 kW 3 30 kW
Grinding cell (robot + head) 5 kW 2 10 kW
Exhaust ventilation 5 kW 1 5 kW
Automation 5 kW - 5 kW
TOTAL ~50 kW

Maintenance

Operation Frequency Performed by
Torch replacement 1 month Centaur-M
Abrasive wheel replacement 1-2 days Centaur-M
Rotary table cleaning Daily Crab-M
Robot calibration Weekly Automation

Quality Control

Parameter Control method Standard Action on deviation
Porosity In-process monitoring (arc current, WAAM cameras) <2% Parameter correction
Dimensions Touch probe +/-0.1 mm Rework by grinding
Cracks Visual (Centaur-M cameras) No visible defects Reject
Hardness Mechanical hardness tester Per specification Heat treatment

See Also