LOFTY GOALS DEMAND PRECISE POSITIONING Verisurf metrology software helps Space Exploration Technologies maintain precision in the shop and on the launch pad for its vehicle development and launch services. With the retrieval of Dragon from the Pacific Ocean, Space Exploration Technologies (SpaceX, Hawthorne, CA) became the first commercial company to launch and recover a spacecraft from low-Earth orbit. Placed into space atop the company’s Falcon 9 launch vehicle, Dragon completed two orbits with speeds topping 17,000 miles per hour. After its three-hour, 50,000-mile flight, Dragon splashed down just one mile from the center of its targeted landing zone. This is the first of three test flights under NASA’s Commercial Orbital Transportation Services (COTS) program. Following two more test flights, Dragon will be delivering payload to the International Space Station, which the company plans to initiate by the end of 2011. For these future missions, SpaceX will again turn to its portable coordinate measuring machine (PCMM) systems to maintain the precision it achieved when first launching and returning Dragon from orbit. SpaceX is a different kind of company, in part due to its founder and CEO, Elon Musk, who was co-founder of PayPal and is the CEO of Tesla Motors. In a post-flight press conference, Musk says, “The reason I’m doing SpaceX is that I just happen to have a very strong passion for space, and I want us to become [a] true spacefaring civilization and even a multiplanetary civilization.” To make his goal a reality, SpaceX intends to change 40-year-old paradigms with a family of launch vehicles and spacecraft that increase reliability and performance while ultimately reducing costs by a factor of 10. The underlying philosophy is a focus on simplicity to both increase reliability and lower cost for vehicle development and launch services. According to Larry Mosse, SpaceX’s tooling operations manager, the company counts on its PCMMs to deliver this reliability and cost reduction. And it counts on Verisurf’s (Anaheim, CA) metrology software to drive all these devices in a powerful yet simple way. He says, “Verisurf metrology software is doing its part in maintaining precision in the shop and on the launch pad. We use it for everything from tooling fabrication to pre-launch preparation.” HITTING PRECISE MARKS Falcon 9 lifted off from Cape Canaveral AFS launch pad SLC-40 at 10:43 a.m. EST on December 8, 2010. At 10:52 a. m., Dragon entered low-Earth orbit. At 2 p.m., Dragon splashed down. At every point in this mission, the launch vehicle and spacecraft hit their marks precisely. According to the company, Falcon 9 delivered Dragon to orbit with “near bull’s-eye insertion,” and Dragon then splashed down in the center of its targeted landing zone. The accuracy of the flight path required careful alignment of Falcon 9’s sections and precise launch vector positioning. So, the SpaceX crew used its PCMM metrology systems, which included laser trackers and Verisurf software. Falcon 9 is 180 feet tall and has a 12-foot diameter. Nine of SpaceX’s Merlin engines power the first stage; the second stage uses one. Final assembly is completed at the launch site. To position and align Falcon 9’s components, SpaceX used laser trackers and Verisurf’s Build application, which is a virtual gage. The trackers fed measurement data directly to Verisurf, which reported, in real time, the accuracy of each section relative to the computer-aided design (CAD) model used in design and manufacturing. After assembly, the SpaceX crew raised Falcon 9 into its vertical launch position. To follow its intended flight path, launch specifications allowed the vector of the vehicle to deviate by only 0.02 degree over the 180-foot length. Mosse says that the crew again turned to the PCMMs and Verisurf Software to confirm a “ready-tolaunch” status. “The specs allowed the nose to be off of vertical by six inches,” he notes. “Verisurf reported that we had only a one-hundredths inch deviation east to west and threehundredths from north to south. And from the ground up, all sections were at their nominal positions.” UNDER CONTROL Mosse notes that this alignment accuracy was possible because of the controls used in manufacturing and assembly operations at the company’s Hawthorne, CA, facility. He cites one example: “We have a set of five fixtures that are used to position rocket components and drill a pattern of 144 holes. These holes dictate the alignment of Falcon 9’s sections.” As he did in preflight preparation, Mosse used Verisurf to place the fixtures before committing to the drilling operations. “With Verisurf, we are looking directly at the CAD model and the measurement results,” Mosse states. “We see the measurements reflected against the 3-D model. This makes the process faster and reduces mistakes.” He notes that before Verisurf his team had to interpret page-after-page of 2-D drawing dimensions. “We had to rely on people’s ability to visualize 3-D measurements from 2-D drawings, which results in interpretation problems,” he says. Before assembly, Mosse used his Verisurf solution to measure parts and tooling during fabrication and manufacturing. For example, SpaceX will drive both laser trackers and articulating arms with Verisurf when measuring composite tooling or weld fixtures. “We inspect these items to the CAD data. In many cases, we will inspect to profile tolerances only,” Mosse says. “We aren’t drawing-free, yet, but like the rest of the aerospace industry, we are striving to implement model based definition to achieve its many benefits.” For SpaceX the most important benefit is time. Model based definitions (MBD) with profile tolerances eliminate the time to document an engineering drawing; reduce the time to create inspection plans and reports, and accelerate identification and resolution of manufacturing issues. With an aggressive schedule and a 25-launch manifest over the next four years, including 12 space station deliveries, every moment counts. SpaceX’s philosophy for its launch into space is simplicity that yields reliability and savings. To achieve this, it counts on Verisurf. Mosse says, “With Verisurf, we have very quick assurance that we are in the proper 3-D space.” This, in turn, puts Falcon 9’s launch and Dragon’s orbit in their proper position in space. BENEFITS » Model based definitions (MBD) with profile tolerances eliminate the time to document an engineering drawing, reduce the time to create inspection plans and reports and accelerate identification and resolution of manufacturing issues. » The Verisurf solution measures parts and tooling during fabrication and manufacturing. » The Verisurf system shows the computer-aided design (CAD) model and the measurement results reflected against the 3-D model. SAVING MONEY WITH COMPARATIVE GAGES Aero-engine component maker Meyer Tool lowers hard gage costs with the software-driven Equator gage. Asoftware-driven comparative gage— Renishaw’s (Gloucestershire, UK) Equator system—is already starting to soften up the cost for numerous hard gages at aero-engine component maker Meyer Tool Inc. (Cincinnati). In its pre-launch application, one Renishaw Equator gage has eliminated at least four costly hard gages in a new work cell. The company’s custom hard gages can cost up to $20,000 each to design, build and maintain, according to Beau Easton, quality manager at the company. Meyer Tool designs, builds and maintains dozens of these costly gages every year for in-process measurement. Down the line, design changes on a part can add another $3,000 to $10,000 to reconfigure and qualify an existing gage. CUTTING THE COST OF HARD GAGES For in-process dimensional measurement, Meyer Tool principally relies on work-cell-based point-to-point contact gages, using pneumatic digital probes. Hard gages in the machining cell give fast feedback but are expensive. Design/ build of the part nest can cost $6,000, plus probes at more than $500 each, as well as verification studies and maintenance, Easton explains. “If we are producing a makecomplete nozzle, there could be six to 10 fixtures, each with six to 20 probes, and if a feature or tolerance on the part changes, it adds time for the gage to be altered and verified,” he says. When shown Renishaw’s Equator comparative gage and offered a pre-launch trial, Easton and SPC (statistical process control) Manager Bridget Nolan says they immediately recognized its potential. “We got involved with Renishaw’s introduction of the system and provided parts,” Nolan says. “Renishaw programmed them, and the results matched our coordinate measuring machine (CMM) results, whose group sets up, maintains and programs the company’s gages, fixtures and instruments.” COMPARATIVE GAGING, MASTERING AND REPEATABILITY The Equator system uses the comparison method of mastering and measuring familiar to anyone who uses dedicated gaging systems. A master component with features of known dimensions is used to “zero” the system, with all subsequent measurements compared to this part. The key to the Equator system is a highly repeatable and radically different metrology mechanism based on a parallel kinematic structure. This mechanism is lightweight, allowing rapid motion, yet very stiff and repeatable. The system uses Renishaw touch and scanning probes, styli and stylus change racks, and Modus Equator programming software. Cost-wise, three to five hard gages in a Meyer Tool work cell can all be replaced by one Equator—and the Equator can be used for multiple parts, switching between them in seconds, as well as reprogrammed for many other parts over its life. ASSIGNED TO A LEAN CELL The first Equator system is currently assigned to a lean machining cell in Meyer Tool’s shop. Demonstrating its adaptability, it integrates with Meyer’s Orion SPC system, maintaining a familiar look for machinists and shortening the learning curve. Orion communicates with the Equator’s Modus software, presenting the operator with results in the form of dimensional data and SPC charts that allow the operator to determine computer numerical control (CNC) offsets. “Keep in mind, the machinist sees variable data and can compare the current part with recent measurements, so it’s not just a pass/fail determination,” Nolan explains. “The parts must meet tolerances of ±0.001 to ±0.003 inch. Inspection time varies with the part but typically takes two to six minutes, well within the TAKT time of the cell, so the system easily keeps pace with machining operations.” MEASUREMENTS TRACEABLE TO ABSOLUTE CMM STANDARDS The Equator measurements at Meyer Tool are correlated with those from a CMM, using a CMM-calibrated master part. “The master part sets the values the Equator expects to find inside its measuring envelope while the software automatically applies the compensation values from nominal taken by the CMM,” Nolan explains. “It must check within 10% of allowable tolerance from nominal.” There is no need to remaster on every part change, though Meyer does remaster on a three-hour schedule to compensate for changes in the plant’s temperature. “The Equator system memorizes the master parts and validation scores, so we can switch parts as many times as needed during the three-hour window, and not have to remaster,” Nolan says. THE SOFT SOLUTION TO HARD GAGE COSTS With more than 100 hard gages costing $10,000 to $20,000 each throughout its facilities, Meyer Tool recognizes the potential cost advantages of a flexible, software-driven gaging system. “We are still expanding our knowledge and capabilities with the Equator system, but have high expectations it will ultimately alleviate a large part of our cost burden for hard gages,” Easton adds. BENEFITS » The Equator uses touch and scanning probes, styli and stylus change racks and programming software. » Cost-wise, three to five hard gages in a Meyer Tool work cell can all be replaced by one Equator. » The Equator can be used for multiple parts, switching between them in seconds, as well as reprogrammed for many other parts over its life.
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