Reverse engineering and inspection software
In spaceflight, the first eight minutes are critical. This is when the greatest opposing forces of thrust and gravity are impacting the launch vehicle. The new NASA Space Launch System (SLS) will weigh 5.5 million pounds at liftoff, or roughly the weight of eight fully loaded 747 jets. Everything comes down to weight and the integrity of design and fabrication to insure success. Today, it costs $10,000 to send one pound of payload into orbit; since the entire launch vehicle makes the trip to low-Earth orbit, its net weight is a big consideration. The lighter the launch vehicle, the greater the payload can be.
AMRO Fabricating of El Monte, CA has been manufacturing precision machined and roll-formed Isogrid and Orthogrid rocket body panels since 1986. The company’s greatest challenge has always been weight. According to AMRO, if a single rib is out of tolerance by as little as .002, it will translate to hundreds of pounds of added weight across the launch vehicle. At the same time, being under size will compromise the integrity of the panel. To put this into perspective, if you were to scale down the SLS to the size of an aluminum soda can, the walls of the SLS would be ten times thinner than those of the soda can.
Every step in the manufacturing process of rocket body panels at AMRO is guided, inspected, and reported using metrology software, laser trackers, portable coordinate measuring machines (CMMs), ultrasonic gauges, and precision check fixtures. By the time a completed panel is crated for shipment, it has been probed, scanned, and inspected more than 20 times. Each panel is 12 feet × 24 feet × 4 inches thick; hogged out Isogrid and Orthogrid geometry provides lightweight structural integrity. Following completion of the manufacturing process, the finished formed panels are assembled into rings. Eight panels are used to create one ring measuring 27.5 feet in diameter and standing 24 feet tall. Five of these assemblies are stacked to create one SLS core stage. Once fully assembled, the height of the SLS will reach 371 feet in its crew configuration.
Aluminum plate material, milled to size, is hogged out to an Isogrid and Orthogrid structure using one of AMRO’s gantry CNC machining centers. Precision holes are drilled for fastening points and other features. While still on the machine bed, the part is deburred and spot-checked using ultrasonic thickness gauges. Design and machining considerations to take into account the final machined part will be formed into a curved structure.
The finished machined part is moved to a special vacuum table where it is subject to a defined inspection routine. Using Verisurf model-based definition inspection software, a laser tracker, and Leica T-Probe, all geometry, wall thicknesses, floor radius locations, hole positions, and diameters are confirmed within tolerances based the CAD model. The Leica T-Probe is an armless, wireless, “walk-around” device that allows the laser tracker to remain in one position while probing hidden, hard-to-reach surfaces such as behind grid walls. Verisurf software provides a 3D on-screen virtual view of the part and relative position of the probe during the inspection process. Real-time graphical inspection data is displayed showing the operator each inspection target as being in tolerance, out of tolerance low, or out of tolerance high. Following inspection, the software generates an AS9102 Inspection Report for the part.
Using one of five high-capacity break presses, finished machined parts are formed or rolled into specified curved profiles. The process relieves and distributes part stress inherent in the manufacturing of aluminum.
Precision check fixtures are used to insure the finished curved profile of the part is accurate, and overall dimensions are within tolerance. Measurement software is once again used to guide the assembly and inspection of these fixtures. Using Verisurf Reverse and model-based definition, AMRO is able to create precision build tools to match the surface profiles of the panels and support their manufacturing process. Parts are placed in check fixtures and adjusted until a perfect fit is accomplished.
Following forming, the part is placed in a trim fixture designed to precision-trim the outside dimensions to tolerance. In each case, metrology software and portable CMMs are used to create the fixture tools.
Finished parts undergo a final QC inspection using Verisurf software and a laser tracker. All dimensions, hole locations, diameters, radii, and surface profiles are inspected. A final AS9102 Inspection Report is generated.
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