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Aluminum is the gold standard in lightweight construction. Whether in electric mobility, aerospace, or the electrical industry, this material is indispensable in modern manufacturing processes. However, traditional fusion welding quickly reaches its limits when it comes to joining. The friction stir welding – or FSW – fundamentally solves this problem. Combined with a CNC robot , it creates a flexible, cost-effective solution, even for components with complex geometries.
What is friction stir welding?
FSW is a solid-state joining process. This means the workpieces are not melted, but merely softened plastically through frictional heat and joined under high pressure. A rotating tool is guided along the joint line, generating the necessary process heat through friction.
The process was invented in 1991 at The Welding Institute (TWI) in the UK and has since established itself as the standard process for joining aluminum alloys, especially where conventional fusion welding is problematic.
Why traditional fusion welding reaches its limits with aluminum
Aluminum is sensitive to fusion welding. The most common practical problems are:
- Distortion: The high temperatures involved in fusion welding lead to thermal distortion, especially in thin-walled structures
- Porosity: Trapped gases form pores in the weld seam, reducing mechanical strength
- Hot cracking: Certain aluminum alloys are prone to cracking during solidification
- Complex seam preparation: Fusion welding requires precise gap dimensions and surface preparation
Friction stir welding structurally bypasses these problems: since no melting occurs, distortion, porosity, and hot cracking are largely eliminated. The result is weld seams with high mechanical quality and minimal need for post-processing.
The technical challenge: stiffness under load
During FSW, the robotic arm is subjected to axial forces typically ranging from 2 to 8 kN. In addition, transverse forces and torques cause the kinematics to deform under load. In a conventional industrial robot, this leads directly to path deviations—resulting in uneven weld seams or process failures.
Standard robots are simply not designed for this level of stress. Their measuring systems record the axis position at the motor, not on the output side. Consequently, gear compliance under load is not compensated for. The result: the path deviates from the programmed line under process force.
Secondary encoder technology as the key to process reliability
This is precisely where the MABI Robotic CNC precision robot comes in. The secondary encoders measure the actual axis position directly on the gear output side—under load, in real time. Gear compliance is thus continuously compensated. In combination with the Siemens SINUMERIK ONE controller, the system ensures constant feed rates and reliable path guidance, even under the high process forces of the FSW process.
Programming is carried out in G-code via Siemens NX CAM, identical to conventional CNC milling. For production planners and CNC specialists, this means: no teaching, no retraining, and familiar machine tool logic. The same robotic armused as a milling robot for subtractive machining can be retooled for FSW—without changing the basic setup of the cell.
Areas of application: where FSW with CNC robots shows its strengths
The combination of friction stir welding and CNC robots is useful wherever aluminum structures with high requirements for seam quality and geometric complexity are joined:
- Electromobility: Joining of battery trays, cooling plates, and structural housing components made of aluminum
- Aerospace: Welding of fuselage segments, structural components, and lightweight profiles
- Electrical industry: Joining aluminum housings and heat-conducting elements
- General lightweight construction: Wherever fusion welding is not an option due to distortion or alloy sensitivity
The flexibility of the CNC robot also allows for the processing of components with complex geometries that would be inaccessible on conventional FSW systems with rigid gantry designs. Linear axes expand the workspace for large-format structures as needed.
Conclusion: Solid-state joining with CNC precision
Friction stir welding is no longer a niche process. Wherever aluminum alloys need to be joined without compromising material properties through melting, FSW is the technically superior choice. The crucial question is not whether to use it, but which system to choose.
MABI Robotic AG relies on the MAX series CNC precision robot with secondary encoder technology and Siemens SINUMERIK ONE control, which reliably absorbs the high process forces of FSW and ensures precise paths even under load.
