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Machining That’s Out of this World

The whole world watched as the Jet Propulsion Laboratory (JPL) in Southern California, successfully completed the high-profile Pathfinder mission to Mars. But before “Pathfinder” became a household name, it took teams of JPL engineers, programmers, and machinists thousands of hours of work to build the now famous craft. It was a challenging task. The department responsible for programming and machining the most of the parts to assemble Pathfinder consists of two full-time programmers and 18 machinists who relied on the latest software technology to assist them.

To meet the challenge, employees in JPL’s Mechanical and Hardware Fabrication department use VERICUT, a NC simulation and verification software program from CGTech in Irvine, California. VERICUT is an advanced solids-based package that interactively simulates the material removal process of an NC tool path. The program depicts three to five-axis milling/ drilling and wire EDM operations as well as 2-axis turning and combination mill/turn machining. VERICUT enables an NC programmer to verify the accuracy and quality of the tool path using a computer. Inefficient motion or programming errors that could potentially ruin the part, damage the fixture, or break the cutter can be corrected before the program is run on an NC machine tool.

JPL has used VERICUT for three years now. Scott Vanderzyl is an NC Programmer on JPL’s technical staff for manufacturing. His responsibilities at the laboratory include NC programming, training, procurement, and software implementation. JPL uses VERICUT for part verification by running their Computervision tool paths over the raw stock. This enables the programmers to visualize the machining process and the changes to the in-process material. They are also able to check cutter load conditions, rapid feed moves, and most importantly, avoid potential machine crashes, or “issues.” Once the simulated machining process is complete, they use an ‘automatic-differencing’ feature in the program to compare the complete machined model to the original STL design model to check for any gouges or excess material left on the part.

“VERICUT enables us to see what will happen on the machine,” says Vanderzyl. “It is a big help in off-line programming because it enables the machinist to view a ‘playback’ simulation so they will be more comfortable with the part program when they machine. Consequently, we’re more productive which is important because this is an extremely dynamic environment – design changes happen rapidly as we’re building parts.”

Taking advantage of the latest software technology reduces the department’s prove-out time. One of the more challenging parts to create was the Pathfinder’s back shell interface plate (BIP; the part on the craft that interfaces between the lander assembly and the launch vehicle assembly and acts as a protective heat shield). This was the first time the group had used Computervision on a major project, and only the third part programmed with the new CAM system. Additionally, because of the dynamic nature of the project, it required 30 separate design changes during the course of manufacturing process. It was also the first time the team used entirely metric measurements in the programming and machining. At the same time, the made the move to an almost paperless manufacturing environment. And they just completed a switch from a micro VAX system to a UNIX system.

In a project of this importance, quality is a paramount concern. And the BIP required some difficult machining. Once the 30″ diameter part was programmed, it needed to be machined on a 20″ x 40″ machine. Because the part was too big for the machine, it required a lot of flipping and rotating to complete, further complicating the process. All of the walls on the part were undercut, making it more complex and making entry/exit moves more difficult. It also had thin walls (.050 thick in many places).

These kinds of manufacturing challenges would be daunting under any circumstance, let alone a high-profile project with millions of dollars riding on its success or failure. Without a software package like VERICUT, the project would have been more difficult, and would have taken more time. According to Vanderzyl, “We would’ve had to have been much more careful during machining, and would have had to keep extra parts around as a security measure in case we crashed or gouged the part.”

Because VERICUT does not distinguish between metric vs. inch and only thinks in terms of number of units, the team was able to make the conversion smoothly, confident that the computer simulation would catch any mistakes. As any NC programmer can testify, using a new CAM system can take some getting used to. VERICUT gave the programmers added confidence in their new CAM software. Also, the move to a paperless environment did not prove to be a problem. In fact, the team discovered that even during the first project, it was much more efficient and the information easier to understand. VERICUT enabled the designers and programmers see exactly what they were building as and in-process model in different stages of the machining cycle. They were able to cross-section the model and check all it’s dimensional characteristics which helped in the design process. Machinists were also able to see exactly what would take place on the machine once they were ready to go forward with the final program. “VERICUT was a primary means of communication of what we were building and how we were doing it,” said Vanderzyl. “During the course of the project, the part went through around six or eight major design changes, and in each of those there were several modifications. VERICUT enabled our programmers and machinists visualize the changes, and keep the whole part and process manageable.”

Time was a critical factor in the Pathfinder project. Delays could end up costing big money. VERICUT enabled the team to meet the deadlines on their part of the project by avoid long, costly manual prove-outs. VERICUT was also a necessary tool because of the size of the part Vanderzyl said. Without it, the team would have had to verify the part in sections by doing a number of different prove-outs on smaller chunks of wax or foam. Instead, all verification was done on the computer screen. In the end, the NC department was able to shave approximately 25% off the time it took to complete the entire project.

And what’s it like to see a craft that you helped build roaming around on another planet? “Well, at first there is the anticipation and hoping everything goes right,” said Vanderzyl. Afterwards, it’s relief when it lands and we get the data it was sent to get – NASA invested a lot money, and we (JPL) did our job. Then there is the excitement and pride in the accomplishment on a professional level, something no one has ever done before. There is a lot of emotion to be part of a project that is unlike any other ever undertaken. It’s a sense of pride you can’t get anywhere else.”