Thermal Stir Welding Process

Jeff Ding
NASA Marshall Space Flight Center, Alabama

The patented thermal stir welding process is a new solid-state (meaning the weld metal does not melt during welding) welding process invented at NASA’s Marshall Space Flight Center. The unique welding process de-couples the heating, stirring, and forging elements of friction stir welding, and allows for the independent control of each element of the weld process. An induction coil first heats the weld joint material to a desired plasticized temperature, at which time the weld joint material moves into a through-thickness stir rod that stirs the already plastic material. The stir rod can be independently controlled to rotate at a desired rotational speed or RPM. Upper and lower non-rotating containment plates, also independently controlled, compress or squeeze the plastic weld zone to consolidate the plasticized material as it is being stirred. The stir rod protrudes through the center of the upper containment plate, through the weld material thickness, and is captured by the lower containment plate.

One of the more important aspects of the weld process is the capability to weld at a specific temperature using closed-loop temperature control (patent pending). There is no other weld process capable of doing this. The closedloop temperature control feature allows the operator to input a desired baseline temperature at which he wants to weld. An ultrasonic technology-based temperature sensor monitors the internal temperature of the plasticized weld nugget, in real time, during welding.

Another important aspect of the weld process is the capability to perform “angled” welds. Because the induction coil heats weld metal into a plastic condition, non-rotating containment plates can be shaped to accommodate weld joints of different geometries. For instance, the welding of flat plate material (as shown in the photo) obviously requires flat containment plates.

One of the most significant impacts on weld quality and strength is the temperature to which the weld nugget is subjected, especially in a solid-state weld process. The ability to control welding temperature through the weld metal’s plastic regime will have a significant impact on overall weld quality.

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Honorable Mentions

Self-Locking Actuator

Elias Taye, Chicago, IL

In most gear drives, due to inertial motion, the driven output shaft becomes the driving one and the driving input shaft becomes the driven one. This condition is known as back-driving. In order to prevent this condition, different types of brake or clutch devices are used, such as the self-locking worm gear with a low lead angle. However, worm gears have some limitations. These new selflocking gear actuators don’t have such application limitations. They can utilize any gear ratio from 1:1 and higher. They can be external, internal, or incorporated into a planetary gear stage or multistage gear systems. Their gear mesh efficiency is significantly higher than the worm gears, and closer to conventional gears. The self-locking gears may find many applications in many industries, where position stability is very important in control systems.

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Zebedee — Handheld Mobile Mapping Device

Elliot Duff, Pullenvale, Australia

Zebedee is a small, handheld device that consists of a lightweight LiDAR scanner with 30-m (100-ft.) maximum range and an industrialgrade MEMS inertial measurement unit (IMU) mounted on a simple spring mechanism. As an operator holding the device moves through the environment, the scanner loosely oscillates about the spring, thereby producing a rotation that converts the LiDAR’s inherent 2D scanning plane into a local 3D field of view. With the use of proprietary software, the range measurements can be projected into a common coordinate frame to generate an accurate 3D point cloud in real time. To achieve this result, the software must estimate the six-degree-of-freedom (6DoF) trajectory of the scanner on top of the spring solely from the available range and inertial data. Zebedee’s ability to selflocalize enables its use indoors, underground, and in covered environments such as dense forest. As a handheld sensor, Zebedee can go almost anywhere a human can go.

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