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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Optimization of a Welding Procedure for Making Critical Aluminum Welds on the LBNF Absorber Core Block

he LBNF Absorber consists of thirteen 6061-T6 aluminum core blocks. The core blocks are water cooled with de-ionized (DI) water which becomes radioactive during beam operations. The cooling water flows through gun-drilled channels in the core blocks. A weld quality optimization was performed to produce National Aeronautical Standard (NAS) 1514 Class I quality welds on the aluminum core blocks. This was not successful in all cases. An existing Gas Tungsten Arc Welding (GTAW) Welding Procedure Specification (WPS) was fine tuned to minimize, in most cases, and eliminate detectable tungsten inclusions in the welds. All the weld coupons however, passed welding inspection as per the piping code: ASME B31.3 Normal Fluid Service. Tungsten electrode diameter, type, and manufacturer were varied. Some of the samples were pre-heated and others were not. It was observed that larger diameter electrodes, 5/32 in., with pre-heated joints resulted in welds with the least number of tungsten inclusions. It is hypothesized that thinner electrodes breakdown easily and get lodged into the weld pool during the welding process. This breakdown is further enhanced by the large temperature differential between the un-preheated sample and the hot electrode.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Modular In-Chamber Electron Beam Welding – Process Planning: Welding, Cladding, Inspection, and Manufacturing

Electron beam welding (EBW) is commonly employed by industry today to join relatively thin section components. Industrial sectors which utilize the technology include; automotive, aircraft, aerospace, defense, medical, oil & gas, etc. The ability to produce single pass, thick section (up to 6 inches, 150mm) welds has also been available for more than 40 years; however, the technology has not been deployed for civil nuclear manufacturing and fabrication such as reactor pressure vessels, steam generators, or pressurizers. Instead, thick section joining is performed much in the same manner it has been for decades using submerged arc or gas tungsten arc welding processes. Recent research performed under U.S. Department of Energy (DOE) project DE-NE0008629 has demonstrated that the overall welding time to produce one major reactor pressure vessel (RPV) girth weld can be reduced from weeks to less than 90 minutes, while maintaining exceptional quality and inspection characteristics. The subject project (DE-NE0008846) investigates a modular in-chamber (MIC) EBW approach which allows various RPV sections to be joined within a “modular” chamber. The MIC-EBW approach utilizes individual modules that can be stacked and de-stacked to various heights to enable production girth welds to be performed at a given elevation. This report describes the various processing methodology necessary to complete major girth weldments for the NuScale Power small modular reactor including welding development, manufacturing, production sequence, inspection, and cladding.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2024

Optimization of a Welding Procedure for Making Critical Aluminum Welds on the LBNF Absorber Core Block

The LBNF Absorber consists of thirteen 6061-T6 aluminum core blocks. The core blocks are water cooled with de-ionized (DI) water which becomes radioactive during beam operations. The cooling water flows through gun-drilled channels in the core blocks. A weld quality optimization was performed to produce National Aeronautical Standard 1514 Class I quality welds on the aluminum core blocks. This was not successful in all cases. An existing Gas Tungsten Arc Welding Procedure Specification was fine tuned to minimize, in most cases, and eliminate detect-able tungsten inclusions in the welds. All the weld coupons, however passed welding inspection as per the piping code: ASME B31.3 Normal Fluid Service. Tungsten electrode diameter, type, and manufacturer were varied. Some of the samples were pre-heated and others were not. It was observed that larger diameter electrodes, 5/32 in., with pre-heated joints resulted in welds with the least number of tungsten inclusions. It is hypothesized that thinner electrodes breakdown easily and get lodged into the weld pool during the welding process. This breakdown is further enhanced by the large temperature differential between the un-preheated sample and the hot electrode.

43 PARTICLE ACCELERATORS↗
NASA NTRS2012

Effects of Fusion Tack Welds on Self-Reacting Friction Stir Welds

In order to know whether fusion tack welds would affect the strength of self-reacting friction stir seam welds in 2195-T87 aluminum alloy, the fracture stresses of 144 tensile test coupons cut from 24 welded panels containing segments of friction stir welds were measured. Each of the panels was welded under unique processing conditions. A measure of the effect of the tack welds for each panel was devised. An analysis of the measures of the tack weld effect supported the hypothesis that fusion tack welds do not affect the strength of self-reacting friction stir welds to a 5% level of confidence.

Nunes, A. C., Jr.↗
DOE OSTI2021

Evaluation of residual stresses in isothermal friction stir welded 304L stainless steel plates

Friction stir welding was performed on 304L SS plates in order to heal simulated cracks created by electrical discharge machining. Two different tool temperatures (825 and 725 °C) were chosen for this study. Both neutron diffraction and X-ray diffraction techniques were employed to evaluate the residual stresses along two orthogonal reference directions, longitudinal (syy) and transverse (sxx). The former technique was also used to measure residual stresses at various depths. It was found that, at 1 mm depth from the top surface inside the stir zone (SZ), the longitudinal component was tensile in nature while the transverse component was compressive. The nature and magnitude of the residual stress fields, and the position of the peak residual stresses were found to vary with the weld depth. The SZ of the 725 °C weld exhibited higher peak stress than 825 °C weld mainly due to a lack of stress relief at the lower temperature.

Friction stir welding, Steel↗
DOE OSTI2022

A New Perspective of Post-Weld Baking Effect on Al-Steel Resistance Spot Weld Properties through Machine Learning and Finite Element Modeling

The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistance spot welds (RSWs) has been determined by machine learning (ML) and finite element modeling (FEM) in this study. A deep neural network (DNN) model was constructed to associate the spot weld performance with the joint attributes, stacking materials, and other conditions, using a comprehensive experimental dataset. The DNN model positively identified that the post-weld baking reduces the joint performance, and the extent of degradation depends on the thickness of stacking materials. A three-dimensional finite element (FE) model was then used to investigate the root cause and the mechanism of the baking effect. It revealed that the formation of high thermal stresses during baking, from the mismatch of thermal expansion between steel and Al alloy, causes damage and cracking of the brittle intermetallic compound (IMC) formed at the interface of the weld nugget during welding. This in turn reduces the joint performance by promoting undesirable interfacial fracture when the welds were subjected to externally applied loads. The FEM model further revealed that increase in structural stiffness, because of increase in steel sheet thickness, reduces the thermal stresses at the interface caused by the thermal expansion mismatch and consequently lessens the detrimental effect of post-weld baking on the joint performance.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Computerized adaptive control weld skate with CCTV weld guidance project

This report summarizes progress of the automatic computerized weld skate development portion of the Computerized Weld Skate with Closed Circuit Television (CCTV) Arc Guidance Project. The main goal of the project is to develop an automatic welding skate demonstration model equipped with CCTV weld guidance. The three main goals of the overall project are to: (1) develop a demonstration model computerized weld skate system, (2) develop a demonstration model automatic CCTV guidance system, and (3) integrate the two systems into a demonstration model of computerized weld skate with CCTV weld guidance for welding contoured parts.

Wall, W. A.↗
NASA NTRS1979

Weld bead reinforcement removal: A method of improving the strength and ductility of peaked welds in 2219-T87 aluminum alloy plate

The results of a study to determine the degree to which the ductility and tensile properties of peaked welds could be enhanced by removing the reinforcing bead and fairing the weld nugget into the adjacent parent metal are presented. The study employed 2219-T87 aluminum alloy plate, tungsten inert gas (TIG) welding, and 2319 filler wire. The study concluded that significant improvements in peak weld, ultimate strength, and ductility can be obtained through removal and fairing of the weld reinforcing bead. The specimens so treated and tested in this program exhibited ultimate strength improvements of 2 to 3 percent for peak angles of 5.8 to 10 degrees and 10 to 22 percent for welds with peak angles of 11.7 to 16.9 degrees. It was also determined that removal of the weld bead enhanced the ability of peaked welds to straighten when exposed to cyclic loading at stress levels above the yield strength.

Lovoy, C. V.↗
DOE OSTI2021

Weld Strength and Heat Affected Zone Size in Friction Welded NFA and CostE

Friction welding (FW) enables joining of dissimilar metals parts up to the limits of their strength. CostE and NFA are two high-temperature steel alloys used in land-based power generation. These alloys were joined with FW, and the effect of process parameters on post-welded structure and tensile strength was studied. Weld energy primarily determined the heat-affected zone (HAZ) thickness in both alloys. The highest joint efficiencies – up to 96% – resulted from contact strengthening of thin NFA HAZ regions, but too thin of a HAZ resulted in an unreliable joint. Conversely, thick HAZ regions consistently lowered the weld strength. Optimal welding conditions occur with sufficient energy to create a full bond but not so much to notably lower weld strength.

friction welding, rotary friction welding, nanostr↗
DOE OSTI2021

Solid-State Welding of the Nanostructured Ferritic Alloy 14YWT Using a Capacitive Discharge Resistance Welding Technique

Joining nanostructured ferritic alloys (NFAs) has proved challenging, as the nano-oxides that provide superior strength, creep resistance, and radiation tolerance at high temperatures tend to agglomerate, redistribute, and coarsen during conventional fusion welding. In this study, capacitive discharge resistance welding (CDRW)—a solid-state variant of resistance welding—was used to join end caps and thin-walled cladding tubes of the NFA 14YWT. The resulting solid-state joints were found to be hermetically sealed and were characterized across the weld region using electron microscopy (macroscopic, microscopic, and nanometer scales) and nanoindentation. Microstructural evolution near the weld line was limited to narrow (~50–200 μm) thermo-mechanically affected zones (TMAZs) and to a reduction in pre-existing component textures. Dispersoid populations (i.e., nano-oxides and larger oxide particles) appeared unchanged by all but the highest energy and power CDRW condition, with this extreme producing only minor nano-oxide coarsening (~2 nm → ~5 nm Ø). Despite a minimal microstructural change, the TMAZs were found to be ~10% softer than the surrounding base material. These findings are considered in terms of past solid-state welding (SSW) efforts—cladding applications and NFA-like materials in particular—and in terms of strengthening mechanisms in NFAs and the potential impacts of localized temperature–strain conditions during SSW.

36 MATERIALS SCIENCE↗
NASA NTRS1981

A summary of tests on Invar welded with 308L and 8N12 welding rods

The cost and difficulty in obtaining Invarod, the recommended welding rod to weld Invar, nessitated the investigation of substituting more readily available rods that would meet the cryogenic design criteria for the National Transonic Facility (NTF). Two weld rods, 308L and 8N12, were chosen as promising candidates. Four welded specimen plates were made; two plates for each type of weld rod. One plate from each of the 308L and 8N12 weldings was thermally cycled 50 times between 366 K and 89 K while the two remaining plates were not thermally cycled. Specimens were machined from all four plates for three types of tests: tensile, charpy impact, and guided-bend. The methods in making the specimen plates, conduction of the tests, test results, and conclusions leading to the selection of a weld rod are presented.

Cox, J. W.↗
NASA NTRS1986

Seam tracking performance of a Coaxial Weld Vision System and pulsed welding

This report describes a continuation of a series of tests on the Coaxial Weld Vision System at MSFC. The ability of the system to compensate for transients associated with pulsed current welding is analyzed. Using the standard image processing approach for root pass seam tracking, the system is also tested for the ability to track the toe of a previous weld bead, for tracking multiple pass weld joints. This Coaxial Weld Vision System was developed by the Ohio State University (OSU) Center for Welding Research and is a part of the Space Shuttle Main Engine Robotic Welding Development System at MSFC.

Gangl, K. J.↗
NASA NTRS1993

Adaptive weld control for high-integrity welding applications

An advanced adaptive control weld system for high-integrity welding applications is presented. The system consists of a state-of-the-art weld control subsystem, motion control subsystem, and sensor subsystem which closes the loop on the process. The adaptive control subsystem (ACS), which is required to totally close the loop on weld process control, consists of a multiprocessor system, data acquisition hardware, and three welding sensors which provide measurements from all areas around the torch in real time. The ACS acquires all 'measurables' and feeds offset trims back into the weld control and motion control subsystems to modify the 'controllables' in order to maintain a previously defined weld quality.

Powell, Bradley W.↗
NASA NTRS2002

Thermal Stir Welding: A New Solid State Welding Process

Thermal stir welding is a new welding process developed at NASA's Marshall Space Flight Center in Huntsville, AL. Thermal stir welding is similar to friction stir welding in that it joins similar or dissimilar materials without melting the parent material. However, unlike friction stir welding, the heating, stirring and forging elements of the process are all independent of each other and are separately controlled. Furthermore, the heating element of the process can be either a solid-state process (such as a thermal blanket, induction type process, etc), or, a fusion process (YG laser, plasma torch, etc.) The separation of the heating, stirring, forging elements of the process allows more degrees of freedom for greater process control. This paper introduces the mechanics of the thermal stir welding process. In addition, weld mechanical property data is presented for selected alloys as well as metallurgical analysis.

Ding, R. Jeffrey↗
NASA NTRS2003

Thermal Stir Welding: A New Solid State Welding Process

Thermal stir welding is a new welding process developed at NASA's Marshall Space Flight Center in Huntsville, AL. Thermal stir welding is similar to friction stir welding in that it joins similar or dissimilar materials without melting the parent material. However, unlike friction stir welding, the heating, stirring and forging elements of the process are all independent of each other and are separately controlled. Furthermore, the heating element of the process can be either a solid-state process (such as a thermal blanket, induction type process, etc), or, a fusion process (YG laser, plasma torch, etc.) The separation of the heating, stirring, forging elements of the process allows more degrees of freedom for greater process control. This paper introduces the mechanics of the thermal stir welding process. In addition, weld mechanical property data is presented for selected alloys as well as metallurgical analysis.

Ding, R. Jeffrey↗
NASA NTRS2008

Effect of Weld Tool Geometry on Friction Stir Welded Ti-6Al-4V

In this study, flat 0.250" thick Ti-6Al-4V panels were friction stir welded (FSWed) using weld tools with tapered pins. The five different pin geometries of the weld tools included: 0 degree (straight cylinder), 15 degree, 30 degree, 45 degree, and 60 degree angles on the frustum. All weld tools had a smooth 7 degree concave shoulder and were made from microwave sintered tungsten carbide. For each weld tool geometry, the FSW process parameters were optimized to eliminate internal defects. All the welds were produced in position control with a 2.5 degree lead angle using a butt joint configuration for the panels. The process parameters of spindle rpm and travel speed were varied, altering the hot working conditions imparted to the workpiece. Load cells on the FSWing machine allowed for the torque, the plunge force, and the plow force to be recorded during welding. Resulting mechanical properties were evaluated from tensile tests results of the FSWjoints. Variations in the material flow were investigated by use of microstructural analysis including optical microscopy (OM), scanning electron microscopy (SEM), and orientation image mapping (aIM).

Querin, Joseph A.↗
NASA NTRS2014

Weld Nugget Temperature Control in Thermal Stir Welding

A control system for a thermal stir welding system is provided. The control system includes a sensor and a controller. The sensor is coupled to the welding system's containment plate assembly and generates signals indicative of temperature of a region adjacent and parallel to the welding system's stir rod. The controller is coupled to the sensor and generates at least one control signal using the sensor signals indicative of temperature. The controller is also coupled to the welding system such that at least one of rotational speed of the stir rod, heat supplied by the welding system's induction heater, and feed speed of the welding system's weld material feeder are controlled based on the control signal(s).

Ding, R. Jeffrey↗