Modular Fixturing for Assembly and Welding Applications

manufacturing
Modular Fixturing for Assembly and Welding Applications (MFS-TOPS-66)
Rigid, adjustable tooling that reduces configuration time and cost
Overview
Researchers at NASA's Marshall Space Flight Center have developed new, modular fixtures for holding metal in place during the assembly and welding of cylindrical and conical sections of rocket bodies. Previous methods required time-consuming design, fabrication, and assembly of expensive, project-specific fixtures, which often required up to 6 months of lead time and cost millions of dollars to complete. NASA's modular fixtures are designed to be adjustable and to easily form different fixture body configurations for rocket sections with various diameters and heights. This improved setup efficiency allows for a more rapid shift from one project to the next, reducing the time a newly designed fixture body is complete, allowing welding to begin in a matter of weeks rather than months. NASA is currently seeking licensees that may benefit from modular fixtures in large-scale manufacturing.

The Technology
NASA's researchers have designed modular fixtures to address inefficiencies in time, labor, and material costs due to the need to fabricate unique, monolithic fixture bodies for different segments of the Space Launch System (SLS). Before NASA staff can configure and weld rocket sections, they must assemble modular tooling atop a large turntable with radial grooves. Supporting braces (tombstones) that form the base of the modular structure slide into radial grooves. Other extending, clamping, and joining fixtures can be variously connected to the base structure to provide circumferential support for producing conical and cylindrical structures. NASA has used the tooling to produce structures with diameters of up to 27 feet. Depending on the desired application, the base can be scaled to produce larger or smaller diameters, and the grooves can be arranged with a longitudinal arrangement for production of parts with bilateral symmetry. The development of these modular fixtures required an initial investment similar to that of a single project's tool design and fabrication costs. Once produced, only a fraction of that time/cost is required to begin all subsequent projects. NASA has used this new, adaptable tooling in the construction of several different rocket stages, proving its cost-saving capabilities.
front image This graphic illustrates how NASA's development of modular fixtures significantly reduced its costs for designing, fabricating, and assembling welding tooling. *Project 1's cost of $1 million when using the modular fixture method includes the cost for the initial development of the modular fixture platform. Reuse of the modular fixtures results in future cost savings in subsequent projects.
Benefits
  • Modular fixtures can be reused and repurposed for multiple projects of various sizes.
  • Tooling design and configuration time is reduced by half.
  • Project costs are reduced by as much as an order of magnitude.
  • Modular fixtures can enable the economical adoption of friction stir welding.
  • Modular fixtures enable large-scale rapid prototype development in a wide range of industries.

Applications
  • Shipbuilding
  • Airframe assembly
  • Pressure vessel assembly
  • Commercial space launch vehicle assembly
Technology Details

manufacturing
MFS-TOPS-66
MFS-33208-1
9,662,751
Similar Results
Provided by Inventor
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.
front
A One-piece Liquid Rocket Thrust Chamber Assembly
The one-piece multi-metallic composite overwrap thrust chamber assembly is centrally composed of an additively manufactured integral-channeled copper combustion chamber. The central chamber is being manufactured using a GRCop42 or GRCop84 copper-alloy additive manufacturing technology previously developed by NASA. A bimetallic joint (interface) is then built onto the nozzle end of the chamber using bimetallic additive manufacturing techniques. The result is a strong bond between the chamber and the interface with proper diffusion at the nozzle end of the copper-alloy. The bimetallic interface serves as the foundation of a freeform regen nozzle. A blown powder-based directed energy deposition process (DED) is used to build the regen nozzle with integral channels for coolant flow. The coolant circuits are closed with an integral manifold added using a radial cladding operation. To complete the TCA, the entire assembly including the combustion chamber and regen nozzle is wrapped with a composite overwrap capable of sustaining the required pressure and temperature loads.
Square Structural Joint with Robotic Assembly Tool
The square form joint has several novel features to improve reliability, performance and robustness. Most simply, the square tubes are stronger than round for a specified maximum cross-section dimension. Structural benefits include nearly complete perimeter contact geometry for improved structural efficiency, improved cantilever beam response via linear bending response about y and z axis, and linear torsional response about x axis. Additionally, there is betterlinear axial response along x axis due to simple geometry and large contact surfaces, higher torsional/torque capability (about x axis), higher bending capability about all axes, higher axial capability, and is more cost effective to manufacture. It also offers a bonding strap and treated contact surfaces that provide electrical conductivity through the joint. Switching to square cross section joints provides packaging efficiency, along with numerous improvements for robotic assembly applications such as providing rotational registration, robotically compatible tool designs, both mechanical and visual indicators to verify locking operation, preload and capture spring forces with a unique stop plate in the drive train that can be designed to default to the assembled condition without a preload, yet spring back if forced toward unlocked. After assembly, preload can be adjusted for security. Designed for robust assembly, the robotic tools are built to actuate the joint.
TOP Front Image
Novel Overhang Support Designs for Powder-Based Electron Beam Additive Manufacturing (EBAM)
EBAM technology is capable of making full-density, functional metallic components for numerous engineering applications; the technology is particularly advantageous in the aerospace, automotive, and biomedical industries where high-value, low-volume, custom-design productions are required. A key challenge in EBAM is overcoming deformation of overhangs that are the result of severe thermal gradients generated by the poor thermal conductivity of metallic powders used in the fabrication process. Conventional support structures (Figure 1a) address the deformation challenge; however, they are bonded to the component and need to be removed in post- processing using a mechanical tool. This process is laborious, time consuming, and degrades the surface quality of the product. The invented support design (Figure 1b) fabricates a support underneath an overhang by building the support up from the build plate and placing a support surface underneath an overhang with a certain gap (no contact with overhang). The technology deposits one or more layers of un-melted metallic powder in an elongate gap between an upper horizontal surface of the support structure and a lower surface of the overhang geometry. The support structure acts as a heat sink to enhance heat transfer and reduce the temperature and thermal gradients. Because the support structure is not connected to the part, the support structure can be removed freely without any post-processing step. Future work will compare experimental data with simulation results in order to validate process models as well as to study process parameter effects on the thermal characteristics of the EBAM process.
Friction Stir Welding Apparatus
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.
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