Advanced Welding & CNC CAM
Friction Stir Welding (FSW) Pin Tool & Seam Vector Prepress Guide
Learn how to prepare CNC vector toolpaths, Archimedean shoulder scroll paths, triflute tapered pin profiles, and run-on/run-off tab trajectories for defect-free Friction Stir Welding.
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1. FSW Metallurgy, Shoulder Dynamics & Pin Geometry
Friction Stir Welding (FSW) is a solid-state joining technology widely used in aerospace, defense, EV battery trays, and high-speed rail extrusions. A non-consumable rotating tool consisting of a contoured shoulder and a profiled pin is plunged into the abutting seam of two clamped plates and traversed along the joint line.
Frictional heat generated between the tool shoulder and workpiece plastically softens the alloy without melting, while the rotating pin probe dynamically stirs and forges the plasticized metal from the advancing side (AS) to the retreating side (RS), producing a fine-grained, dynamically recrystallized equiaxed stir zone (nugget).
Key geometric parameters include:
- Shoulder Scroll Spiral (Archimedean): Inward-driving spiral channels engraved onto the flat or concave shoulder face force plasticized alloy back toward the pin root, eliminating surface flash and kissing-bond voids.
- Tapered Threaded / Fluted Pin: Triflute flats and counter-helical threads maximize volumetric swept action per revolution, delivering laminar flow without cavitation.
- Tool Tilt Angle (θ): A rearward tilt of 1.5° to 3.0° ensures the trailing edge of the shoulder exerts forging pressure on the consolidating weld pool.
2. Engineering Specifications & Tolerances
| Base Alloy | Thickness Range (t) | Optimal RPM (N) | Traverse Feed (v) | Recommended Tool Steel |
|---|---|---|---|---|
| Al 6061-T6 / 6082-T6 (EV Trays) | 3.0 – 12.0 mm | 1000 – 1500 RPM | 200 – 450 mm/min | H13 Tool Steel (52-54 HRC) |
| Al-Li 2195 / 2050 (Aerospace Tanks) | 2.5 – 8.0 mm | 800 – 1200 RPM | 150 – 300 mm/min | MP159 / MP35N Cobalt Superalloy |
| Al 5083-H116 (Marine Hulls) | 4.0 – 20.0 mm | 600 – 1000 RPM | 180 – 350 mm/min | SKD61 / H13 with Nitriding |
| Pure Copper C11000 (Busbars) | 2.0 – 6.0 mm | 600 – 900 RPM | 100 – 200 mm/min | Tungsten Carbide (WC-Co) / PCBN |
| Dissimilar Al-to-Cu Joints | 1.5 – 4.0 mm | 900 – 1400 RPM | 120 – 250 mm/min | Polycrystalline Cubic Boron Nitride (PCBN) |
3. CNC Vector Seam CAM & Toolpath Prepress Rules
- Run-On and Run-Off Entry Tabs: Always extend the DXF joint seam path by 25-40 mm beyond the part edges onto sacrificial run-on/run-off tabs to absorb plunge dwell instability and exit keyhole voids.
- Tangent Lead-In Plunge Vectors: Program a dynamic ramped helical plunge trajectory (0.5 to 1.5 mm pitch) rather than a static vertical plunge to prevent tool probe thermal shock and spindle overload.
- Anvil Clearance Offset: Set pin length in CAD to maintain exactly
0.20 - 0.40 mmclearance above the hardened backing anvil to prevent severe tool-anvil collision and carbide chipping. - Archimedean Scroll Vector Pathing: Generate 2D DXF scroll spirals with pitch equal to
1.2x to 1.8xpin thread pitch, oriented to pump plasticized metal inward relative to spindle rotation. - Offset Tool Centerline for Dissimilar Welds: In Al-Cu or Al-Steel welds, offset the FSW seam path vector 0.5 to 1.2 mm into the softer alloy (Al side) to control intermetallic compound (IMC) thickness below 2 µm.
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