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Welding in Space

The Missouri University of Science and Technology (Missouri S&T) Miners in Space weld group has been working to refine a welder that will provide a safe and effective way to weld in microgravity. One of the primary keys to achieving this is to understand how gravity affects the formation of a weld. Gravity appears to have an effect on the shape of a weld pool as well as its microstructure, thus altering the characteristics of the weld. The Miners in Space weld group has been studying and evaluating the strength of welds performed by conventional techniques in the presence of reduced gravity.

The experiment being used was designed to test the micro and lunar gravity effects on welds. The type of welder selected for the experiment is a Gas Metal Arc Welder (GMAW). Due to the wide use of aluminum in the aerospace industry and because of weight and cost, it has also been chosen for this experiment. The welder is attached to an automated arm that moves on a lead-screw system controlled by a computer. The welder's spool gun is attached to the automated arm to eliminate the risk of wire feed jams and enhance the quality of the collected data. The arc used to create the weld is formed with the help of argon gas. Once the arc is formed, the automated arm moves across the test plate containing the aluminum strips for welding. The arm travels down the strip, creating the weld. After the weld has formed, the arm returns to its initial starting point and proceeds to a fresh test strip and is ready to weld again. Because safety is of the highest importance, the entire welding process is contained inside a sealed metal box, which prevents the welding sparks from interacting with anything other than the aluminum. Once the welds are completed and the data are collected, the samples will undergo an array of tests to determine the characteristics of each weld, such as strength and the welds’ endurance to extreme temperature changes.

The purpose of this experiment is to make it possible to weld in space. To do this the results of the past experiments are used to gain further insight. By testing the effects of lunar gravity, microgravity, and increased gravity on welds and comparing that data to weld formations developed at normal-gravity conditions, it should be possible to find trends in the effects of gravity on the welds. These trends will help determine the necessary conditions for welding in space.

Analyzing the Results

Welds performed during the 2003 and 2007 reduced gravity flights had far greater porosity than normal-g welds and rather mediocre penetration. If the driving factor in reducing weld porosity is the buoyancy of the gas bubbles (they float out of the molten metal on Earth), these results would seem logical. Buoyancy forces do not exist in zero gravity; thus, the gas bubbles could not escape from the molten metal and left behind pores as the weld solidified. In general, the zero-g welds from 2003 had nearly half the strength of the control welds performed on the ground – an issue that could be addressed with a suitable design factor of safety.

However, the 2-g welds performed during the 2003 and 2007 Weightless Wonder flights raise interesting questions. While not as porous as the zero-gravity and lunar-gravity welds, they were still of lesser quality than control welds performed under normal gravitational conditions. Based on previous assumptions, if the lack of gravity increases weld porosity and decreases penetration and strength, then increased gravity should produce the opposite effect. Perhaps additional factors were at work; it was suggested that air pressure in the aircraft’s cabin, the aircraft’s somewhat variable electrical power supply, and even vibration occurring in flight may have affected results. To address this concern, control welds for the 2007 tests were performed aboard the aircraft during level flight; however, the team obtained similar results. The Miners in Space believe welding in space has many valuable applications, and are seeking to fly a modified version of the experiment for the 2007-2008 Reduced Gravity Student Flight campaign to better understand the characteristics of these welds.