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The pressure is definitely on at Jet Propulsion Laboratory (JPL, Pasadena, CA), where scientists, engineers and technicians are working evenings and holidays to design, manufacture and test the cruise stage and descent stage instruments and rover for the Mars Science Laboratory (MSL) project.
Gerald Clark, a senior quality engineer and leader of quality assurance inspection services for JPL, says that the MSL project is a galactic-scale prototyping operation with tens of thousands of parts in various stages of product development. In most cases, the assigned team will only make three or less of any single component for the project.
The first group of components and assemblies will be used for a variety of destructive and nondestructive testing. The second will be sent on the Mars mission. An identical rover will stay behind in a simulated Mars environment lab, where it will be used to run through anticipated maneuvers before they are attempted millions of miles away on Mars.
In addition to managing a team of 10 people and personally doing a good deal of the inspection work, Clark’s job also includes the assessment and acquisition of personnel, equipment and measurement services needed to validate more than 10,000 parts, components and assemblies.
While the methodology for fabrication of hardware for the MSL project is called “concurrent engineering,” for Clark and his team it means “everything happening at once.”
Clark used to work in a conventional military/aerospace manufacturing environment, in which design, planning and manufacturing were tightly regimented. “At first I thought our engineers and manufacturing people were a bunch of cowboys,” says Clark. “It seemed like they didn’t have rigid controls in place. But when I stepped back and looked at this short-run, one fabrication lot manufacturing environment and saw how successful the lab has been over many previous missions, I decided that I was the one who needed to adapt.”
Integration is KeyClark concluded that if his lean team was going to keep up with the frenetic workflow and get the massive concurrent part validation job done, it was essential for quality team members to be specialists-not in measurement equipment and software, but in helping design and manufacturing engineers develop and meet acceptance criteria for specialized parts that have absolutely no tolerance for failure. In fact, a number of coordinate measuring machines (CMMs) and other equipment that did not have an easily understood common interface were, at Clark’s recommendation, shipped out the door.
Today JPL has CMMs of various sizes as well as an articulating arm with tactile probes and laser trackers, all equipped with interoperable PC-DMIS Enterprise Metrology Solutions (EMS) software from Wilcox Associates Inc. (North Kingstown, RI). In addition, many of the more than 200 contract part manufacturers and all of the independent measurement labs that JPL uses can measure parts and generate standardized reports using the same measurement software in conjunction with many different types of measurement system hardware. As a result, the lean inspection team has many different options for keeping up with the lab’s unpredictable workflow.
Regardless of the measurement device they will be used with, common measurement programs are typically generated at JPL during early design and manufacturing stages at an off-line programming station. Ultimately, these programs are used throughout the widely dispersed concurrent engineering and manufacturing enterprise to generate standardized outputs: PDFs, RTF files or PC-DMIS program data files.
The first programming step at JPL involves importing Rev A of the computer-aided design (CAD) model into PC-DMIS as a step file from Unigraphics. At this point an engineer will work with a quality staffer to specify the most important design intent criteria and appropriate datums. A member of the lean inspection team will then create the program using point-and-click programming techniques.
Because the entire spacecraft is essentially a prototype, design criteria may not be nailed down until after manufacturing has already begun. “We have one pass to make something that has never been made before and achieve something that has never been done before,” says Clark. “Design refinements continue throughout the fabrication and assembly process.”
For example, it was determined that some important components had to be trimmed down to reduce their weight. This made it necessary to add stabilizing structures to the parts for improving the strength-to-weight ratio. In turn, the altered design and manufacturing processes made it necessary to change the key characteristics and measurement strategies when it came time to measure the part-something that happens quite frequently.
When the time comes to validate a completed part, the design has typically progressed from Rev A to Rev E, F or G. Revising the program may require further consultation with an engineer, after which changes to the metrology programs can be made very quickly. The open architecture of PC-DMIS allows changes to be made to the program at any location in the program and in any sequence.
Never a Typical DayWith so many parts in various stages of design and manufacturing, it is hard for Clark and his co-workers to predict what will be on the agenda for any given day. “Sometimes you don’t know from hour to hour what job is going to be coming up,” says Clark. “As much as 80% of our hardware is manufactured off lab by various suppliers. We can see when they are due, and we will program the most complex parts in advance so that they are not bottlenecks in the inspection area.”
However, JPL’s schedule is not weekly -it is daily to hourly. “We are constantly in contact with each other,” says Clark. “If you get this one, I’ll pick up that one and that sort of thing. Having common software on different measuring systems gives us the freedom to adapt to this very fluid environment. We often make last minute changes on who inspects what, where and with which equipment.”
A good example of this is the ability to do source inspections remotely via e-mail. Clark recently did three in one day, and two a day is not unusual. Instead of traveling to the manufacturing location for the part runoff, Clark has his manufacturing partner e-mail him the measurement program and all of the point data that has been collected, minus the CAD model to reduce the size of the file.
“We just can’t afford to have a person out on the road doing single source inspections,” says Clark. “As long as we can get the data, PC-DMIS allows us to analyze anything about the alignment used or relative location of features. Having data you can analyze is at least as good as having a person go to the plant and witness the inspection. We can even manipulate that data later to answer ‘what if’ questions.”
For example, Clark explains that if all holes on one side of a part are found to be skewed, an operator can ask, “What if I shifted this side of the part over? Would it bring the entire hole patterning in? Is the patterning good unto itself but just off in respect to another side of the part?”
“You can play all these games in the software to analyze the discrepancies you find and work with the engineer to determine the acceptability of the part,” says Clark. “So we can remotely give source inspection approval or recommend changes that will bring the part into conformity with our needs while the part is still at the supplier, and we continue to accomplish other inspection work back in our own lab.”
JPL acquired an arm-type measurement system with PC-DMIS Portable interoperable software and then integrated it into the lean team’s inspection processes. Now it is being used for on-machine inspection of components. With very little modification, programs written originally for use on a CMM can be used with the arm. This came in handy recently when JPL decided to measure some parts on machine at a supplier so that if modifications were needed, they could be accomplished while the part was still in its original setup in the machining fixture.
JPL also has extended the measurement range of its CMMs by using the measurement arm to pick up features that fall outside the CMM’s measuring envelope. This can be done either by incorporating the arm and the CMM into the same program or importing the data captured by the arm into the master program. In either case, JPL avoids the time and expense of sending parts to an independent lab for measurement.
When parts are far too big to be measured at the lab, JPL has access to a gantry style measurement system, which it rents during the graveyard shift of one of the JPL’s machining suppliers. JPL also uses the services of independent inspection labs to handle workflow volume spikes. No matter where the parts are measured, the inspection equipment all uses the same measurement software so that programs and reporting are consistent throughout JPL’s inspection supplier base.
Clark says the greatest contribution of interoperable software is the flexibility it gives the lab to control when, where and how a part will be measured and by whom on a daily and hourly basis. “PC-DMIS EMS enables the transfer of the inspection plan through a single part program, executable on various inspection equipment at various facilities,” says Clark. “When conditions change, it gives us options-and having options is very good. Our interoperable software takes the focus away from the measurement contraptions themselves and allows the lean inspection team to focus on the big picture goal of qualifying all the parts that are going to take the spacecraft, rover robot and instrumentation on another successful Mars mission.”
Wilcox Associates Inc., a Hexagon Metrology company