Internal Friction Reduction (IFR) Tool
manufacturing
Internal Friction Reduction (IFR) Tool (MFS-TOPS-102)
Cost-effective pin tool for self-reacting friction stir welding
Overview
NASA's Marshall Space Flight Center has developed a cost-effective pin tool for use in self-reacting friction stir welding (SR-FSW), making the SR-FSW process significantly more robust and cost-effective. The IFR Tool mitigates the internal friction that occurs between the weld pin and crown-shoulder during a SR-FSW weld. Testing with the IFR tool has shown a significant reduction in the number of defects found in SR-FSW welds, and the tool allows significantly longer SR-FSW welds to be performed. Utilizing the IFR Tool can reduce SR-FSW welding costs by reducing scrap/rework rates, reducing the number of pin tools required per unit weld length, and reducing the time spent changing out SR-FSW pin tools per unit weld length. Along with improving the cost-effectiveness of existing SR-FSW applications, the IFR Tool may also further expand the applications for which SR-FSW is a commercially viable solution.
The Technology
During SR-FSW, the wicking of substrate material into the gap between the crown shoulder and pin can lead to pinch load shifting–an increasing difference between the applied pin load and actual pinch load. NASA's IFR Tool mitigates pinch load shifting, enabling a more robust SR-FSW process due to better agreement between the applied pin load and the actual pinch load.
As pinch loads are not dynamically measured during welding, NASA has relied on defect rates and pin tool ejection loads to demonstrate the value of the IFR Tool. Large-scale welds were performed with both the IFR Tool and a standard pin tool. Weld inspections found a 90% reduction in defect generation rate for the IFR tool, and the first defect in the standard pin tool sample occurred at 300" compared to at 900" in the IFR Tool sample. There was also a drastic improvement in mechanical properties variations along the weld.
In another study, a series of 27.5' barrel welds were performed with both the IFR Tool and a standard pin tool. After welding, ejection forces required to remove the pin tools from their fixtures were measured. The standard pin tool ejection force was 9,400 lbs., nearly 5 times larger than that of the IFR Tool at 2,000 lbs . The large difference suggests that during welding, the standard pin tool would have been less responsive to substrate surface variations than the IFR Tool. Weld inspections supported this theory, as they found a significantly lower defect rate in the IFR Tool samples.
Benefits
- Reduces SR-FSW weld defect rates: in the same weld set-up, the IFR Tool achieved a 90% reduction in weld defects compared to a standard tool
- Enables longer SR-FSW weldments: the IFR Tool allowed for welds greater than twice as long as those with a standard tool
- Lowers SR-FSW welding costs: reductions in scrap/rework rates, number of pin tools used, and time spent changing out pin tools all contribute to lower welding costs
- Simple to produce and use: the IFR Tool is simple to produce and integrate into existing SR-FSW processes
Applications
- Aerospace
- Railway cars
- Construction
- Storage tank or cylinder manufacture
- Ship building
- Plastic welding
- Micro-scale electronics
Technology Details
manufacturing
MFS-TOPS-102
MFS-33686-1
Patent Pending
Similar Results
Conventional friction stir extrusion machine
Typical metal extrusion relies on heating large metal billets and then forcing the heated billet through a dye to extrude the geometry and length of interest. These processes require high energy inputs, expensive machinery to heat and manipulate the billets, and the length of the final part is limited by billet size. Thus, new ways to cost effectively and efficiently produce extruded parts are needed.
The C-FSE machine developed by NASA encompasses a non-rotating extrusion block and a rotating pin that extends through the chamber. The extrusion block has a close tolerance fit to the rotating pin to prevent material from escaping from the ends of the block. Raw metal feedstock is fed into one side of the chamber, the rotating pin interacts with the metal to generate plastic deformation and heat, and the metal is driven out the other side of the extrusion block through a customizable die. As the C-FSE machine does not require pre-heated billets, the extruded parts may be of any desired length. Further, the extrusion machine is modular in nature and may be retrofitted onto an existing FSW system, and the die may be easily replaced for varying extrusion geometries. The C-FSE machine has been prototyped and used to produce freestanding metal parts.
The C-FSE machine is at technology readiness level (TRL) 4 (component and/or breadboard validation in laboratory environment) and is available for patent licensing.
Stronger Plug for Friction Pull Plug Welding of Thick Plates
Friction Pull Plug Welding (FPPW) is the process necessary to plug the hole that is left behind as a friction stir weld (FSW) joint is completed and the pin tool of the welder retracts from the joint. FPPW involves a small, rotating part (plug) being spun and simultaneously pulled (forged) into a hole in a larger part. Much work has been done to fully understand and characterize the process and its limitations. FPPW worked very well for building large rocket sections such as the circumferential welds of the upper stages of NASA's Ares rocket, and to repair the external tank. Engineers were challenged to adapt FPPW to accommodate the thicker plates new alloy combinations of the SLS. The new hybrid plug solves the issue of the plugs snapping due to the increase torsion and moment stresses when joining thicker plates. The new hybrid plug, with a steel shank, makes FPPW more practical and robust. The new plug has been used to make space-qualified parts at NASA, and the plug welds are as strong as initial welds.
Ultrasonic Stir Welding
Ultrasonic Stir Welding is a solid state stir welding process, meaning that the weld work piece does not melt during the welding process. The process uses a stir rod to stir the plasticized abutting surfaces of two pieces of metallic alloy that forms the weld joint. Heating is done using a specially designed induction coil. The control system has the capability to pulse the high-power ultrasonic (HPU) energy of the stir rod on and off at different rates from 1-second pulses to 60-millisecond pulses. This pulsing capability allows the stir rod to act as a mechanical device (moving and stirring plasticized nugget material) when the HPU energy is off, and allowing the energized stir rod to transfer HPU energy into the weld nugget (to reduce forces, increase stir rod life, etc.) when the HPU energy is on. The process can be used to join high-melting-temperature alloys such as titanium, Inconel, and steel.
New motors for next-generation in-space servicing
Satellites and other spacecraft require maintenance and service after being deployed in orbit, requiring a wide variety of tools that perform multiple maintenance tasks (grip, cut, refuel, etc.). Current drive systems for the tool interfaces on the robotic arms that perform these service tasks are not as robust nor packaged properly for use in the ATDS. The ATDS is one part of a larger in-space servicing system (example shown in the figure below) that must be versatile and perform multiple jobs.
Here, innovators at the NASA Goddard Space Flight Center have developed new BLDC motors to provide the torque necessary to drive the wide variety of tools needed for in-space servicing. The four motors provide torque to the coupler drive, linear drive, inner rotary drive, and outer rotary drive of the ATDS. The new BLDC motors will enable the tools attached to the ATDS to be operated in multiple modes of operation.
Each of the four motors have been customized with different speed and torque capabilities to meet the different performance requirements of the various actuator drive trains while maintaining a common gearhead across all the motors. Further, the packaging surrounding the motors has been tailored to reduce the overall weight of the motors and reduce the motor footprint to meet the needs of the ATDS. The BLDC motors for the ATDS are available for patent licensing.
Abnormal Grain Growth Suppression in Aluminum Alloys
Heat treatment of the deformed welds is desirable in order to restore the properties of the alloy negatively affected in the weld region. In these alloys, abnormal grain growth frequently occurs in friction stir welds during solution heat treatment, and is known to degrade key materials properties, such as strength, ductility and toughness. The innovation of inserting an intermediate annealing step covered here reduces abnormal grain growth during post-welding heat treatment, thereby allowing optimum mechanical properties. This is important where Al-Li alloys (and other heat treatable alloys) are friction stir welded followed by deformation processing and high performance, high reliability structural components are required for aerospace vehicles.
