Advances in Friction Stir Welding Boost Building Speed and Versatility

The process of friction stir welding (FSW) continues to advance in terms of speed and applicability. The latest developments in FSW have significantly improved process feed rates, which in turn, allow manufacturers to adapt FSW’s underlying principles of force and friction to other production applications like additive manufacturing. 

FSW employs a cylindrical shoulder tool with a profiled pin that is rotated and plunged into the joint of two pieces of metal. The spinning tool friction and downforce then plasticize the metal before it reaches its melting point. No filler wire or shielding gas is needed as the plasticized material moves to the tool holder’s trailing edge where it is forged and cooled to a solid. Rotation, force and friction are the only components of FSW. 

Without voltage, current and heat input calculations, joints form at approximately 80%-to-90% of the base metal’s melting point, which almost invariably results in a bond superior to that of fusion welding. Standard steel-pin tool FSW creates several kilometers worth of full-penetration, defect-free welds with shorter setup time and consumables cost, improved safety and from any position or orientation. However, FSW is often slower than other welding methods in certain applications, but machine tool manufacturers have worked to rectify that issue for improved productivity.  

Mazak MegaStir, an innovator in the FSW space since 2002, has refined its patented polycrystalline diamond (PCD) tooling and paired its FSW technology with the robust and stable characteristics of Mazak’s machine tool technology. Doing so has improved FSW traverse speed by orders of magnitude over existing FSW capabilities. 

Currently, most manufacturers run FSW applications at an industry standard feed rate of between one meters and 1.5 meters per minute, with a maximum rate of approximately 3 meters per minute. However, Mazak has combined its MegaStir FSW technology with its HYBRID Multi-Tasking machines to give the process the stability, rigidity, precision and reliability that allows for FSW speeds up to 10 meters per minute. Plus, the company’s enhanced diamond tooling has shown only minimal wear after 1.6 kilometers of welding at the advanced commercialized traverse rate. 

In addition to gaining linear speed, the new FSW process takes full advantage of Mazak’s multi-tasking DONE IN ONEÒ part processing that completes virtually all a part’s machining in one cycle to significantly reduce setup times and helps shops meet the challenges of lean manufacturing in the face of workforce shortages. 

In a process similar to FSW, friction stir principles and technology are advancing the realm of additive manufacturing with the development of additive friction stir deposition (AFSD). Blending the elements of FSW and Hot Wire Deposition (HWD), AFSD deposits layers of metal using the friction from spinning and plastic deformation to join and build structures and components. The process produces a part or feature that is devoid of defects such as porosity, cracks and stresses normally associated with traditional melting and forging. AFSD also renders parts that have improved microstructures and fine grain patterns for increased strength and performance.

A material feed conduit passes through AFSD tooling that sits atop a base layer and deposits material onto the substrate. Like an extrusion process, squeezed material spreads onto the base, then agitators force it to blend with the layer below. The resulting part has properties equivalent to a forged structure without any loss of strength due to weak grain structure. 

As a manufacturing process, AFSD is set to have a significant impact on the current supply chain issues manufacturers face. As the numbers of global forging factories decrease, the wait for forged metal components is significantly increasing. Parts that previously took 36 weeks to produce now take 36 months, and AFSD is poised to fill that production gap as its technology improves. 

However, AFSD requires extremely high loads that generate a tremendous amount of thermal energy. This high heat poses a challenge for manufacturers when harnessing the process for the long runs necessary for commercial printing. 

Generally, AFSD tooling temperatures hover around 1,800 C (3,000+ F), with substrate temperatures running between 200–600 C (392–1,000 F). The challenge with AFSD to date has been producing tooling that allows shops to print at commercially feasible speeds and durations without it being destroyed by the thermal forces involved.

To that end, Mazak MegaStir has developed a liquid-cooled tool holder that addresses AFSD’s thermal challenges and lets manufacturers use the process at a commercially viable rate. Using glycol coolant, an integrated chiller and a proprietary design, MegaStir’s intelligent, liquid-cooled tool holder and the company’s ultrahard Polycrystalline Cubic Boron Nitride (PCBN) and carbide tooling withstand AFSD’s extremely high loads and forces. The combination provides eight times the heat removal rate of traditional systems.  

Mazak MegaStir is the exclusive tooling supplier for MELD Manufacturing, which is leading the charge in AFSD technology. The system is currently in operation with a major automobile manufacturer, running at a continuous rate of 10 meters per minute. Such continuous-feed operations typically require the use of an automatic loader. 

Breaking AFSD’s production speed barrier has drawn strong interest in further development of the technology, with military and defense interests at the front of the line. Any process that is effective in diminishing current supply chain bottlenecks is certain to become a powerful force in manufacturing. 

These latest advances in harnessing friction and force dynamics for welding and fabricating are major disruptors within the manufacturing sector and its output that feeds the supply chain of goods. As these technologies and techniques are more fully developed and refined, FSW and the related processes it prompts and inspires will play an increasing role in how products are manufactured.   

 Dale Fleck is the general manager at Mazak MegaStir. Email dfleck@mazakmegastir.com