Вторник, 26 февраля 2019 20:30

G-code simulation from CGTech makes the most of limited technical college resources

Anyone who’s attended technical college in pursuit of a machining certificate or associate’s degree in manufacturing knows it’s one of the more challenging trades to master—machinists are expected to understand cutting tools, feed and speed calculations, part measurement, properties of metals and plastics, trigonometry…the list goes on. One thing that’s especially important to know in today’s manufacturing world is G-code, the nearly universal language used to program computer numerical control (CNC) machine tools.

The ABCs of XYZ

G-code is an alphabet soup of letters and numbers, one designed to move the various machine tool axes through a complex metal cutting dance. With dozens of automated stock removal routines, cutter compensation codes, and machine control functions, even seasoned

machinists can be left scrambling for the programming manual. Making matters worse is that fact that modern machine tools are fast, offering spindle speeds upwards of 10,000 RPM and rapid traverse rates of 2,000 inches per minute or more.

At many colleges, this makes program prove-out a matter of one hand riding the feedrate override and the other hovering over the emergency stop button, a nail biting experience for instructors and student alike. After all, one bad line of code is all it takes to crash a piece of expensive equipment, thus delaying coursework and negatively impacting budgets.

With the right software tools and a little common sense, however, these problems can be prevented before the first chip is ever cut. That’s good news for anyone that operates a machine tool, but doubly so in a school environment, where fledging machinists pose a higher than average risk of questionable code. Better yet, that same software technology can be used to make tool paths more efficient, thus improving job profitability and tool life, important considerations in the post-graduation world of manufacturing.

Pioneering in Tacoma

Bob Storrar, machinist instructor at Bates Technical College, Tacoma, WA, has long been a champion of such technology. “We were the first ones in the state to use Vericut, and possibly the first in the entire US,” he says. “It’s been a big part of our program for nearly a decade.”

Vericut, an NC code simulation and optimization tool from Irvine, California-based software developer CGTech, is a graphical software package that works with all brands of machine tool controllers, detecting G-code errors and preventing collisions before they happen. Yet Storrar will tell you the biggest benefit of Vericut isn’t crash avoidance, but efficiency. “With 18 people in class, I don’t have time to go through three or four hundred lines of code for every student. It’s just not in the cards. Before implementing Vericut, a student would write up a program, load it in the machine, and I would stand there with my hand over the E-stop, sweating bullets through the entire dry run. It was always a guessing game what would happen.”

Now, each student checks his or her own work with Vericut, rather than relying on the instructor to help troubleshoot programs. There’s no more back and forth between the computer and the mill or lathe trying to figure things out. “I figure they are able to solve 75 to 80 percent of their problems on their own,” Storrar says. “They can see what’s happening right on the computer screen, so they don’t even come to me anymore except on difficult problems.”

When ready, students bring their completed project file to Storrar, who carries around a USB memory stick containing a perfect model of each assignment. Together they go through Vericut’s “Auto-Diff” function, which highlights discrepancies between the student’s part and how it actually should look. “Most of the time I don’t even have to tell them how to fix it,” he says. “They watch the simulation with me and say, ‘Oh, look. I made a mistake there in my trigonometry.’ It’s unbelievable how much time it’s saved me.”

No More Fire Drills

One hour north of Tacoma sits the city of Shoreline, WA, where manufacturing technologies instructor Keith Smith puts Vericut through its paces at Shoreline Community College. Smith agrees with Storrar’s assessment, and says offline simulation not only saves everyone a lot of grief, but is an effective learning tool as well. “In the old days, a student would have done his best on a program, then taken it out to the machine and quite possibly crashed and burned. Then it becomes a matter of getting the instructor’s attention long enough to help understand what went wrong. That’s not always easy to do, considering how many students we have in our programs. With Vericut, I can work with them in a no stress environment, going through their code one line at a time to find areas where they can improve. It’s a real teaching moment.”

Like Storrar, Smith has been using Vericut as part of the school’s curriculum for a number of years. Looking back, he says it would have been difficult to implement if it weren’t for the ready-made training material that comes with the system. With 22 online sessions, each containing several step by step tutorials, rollout was a matter of pointing students at the software and letting them work through the instruction materials at their own pace. Smith then reports completion of the course to CGTech, who issues a certificate to the student—a nice feather in the cap for future employment.

Says Smith: “There was one graduate who came for a visit recently. The shop he was working at had acquired Vericut before he started there, but nobody knew how to use it and they were dragging their feet on the rollout. So our former student piped up, ’Hey, I can help you with that,’ and got a chance to work in the programming office. It was a great experience for him.”

Another great experience is the virtual machine time that comes with Vericut use. Rather than arm-wrestle over limited CNC availability, students can run simulations until the cows come home, then plug their polished programs into the machine once all the kinks have been removed. This makes the most of equipment that may cost several hundred thousand dollars, and take weeks to repair in the event of a crash.

Smith gives students a different kind of crash course, turning 3rd quarter students loose as if they were working in an actual production shop. “I give them setup sheets, a program, and part drawings, then tell them to set up the machine and make some parts, just as in real life,” he says. “It’s kind of uncomfortable for them at first, because they don’t know what’s going to happen. What makes a big difference though is the Vericut video clip of the different machining operations, which I attach to each job. The student has the opportunity to review the videos and understand what’s going on. It makes life a lot easier for them.”

Smith is such a fan of Vericut that he recently volunteered his time to participate in a CGTech-sponsored workshop at the California Polytechnic State University in San Luis Obispo, to explain the benefits of machine tool simulation from an educational perspective. “Many of our students leave here and go to work in the surrounding aerospace industry. Everybody up here has very complex machines, and without some kind of sophisticated verification software, you just wouldn’t be able to machine parts. It’s very popular here.”

Not Your Father’s Pac-Man

A bit further north, Dave Lewis has used Vericut since the early nineties. The mechanical technology program head for the British Columbia Institute of Technology, Burnaby, BC, Lewis says Vericut is a perfect fit with today’s electronic-minded students. “Programming is a bit like a video game to them. A CAD/CAM system will basically do anything they ask of it, so you’ll find them burying a quarter-inch endmill a few inches deep in a block of steel. There’s no problem until you stick it on the machine.”

Vericut helps students avoid such machining faux pas. With many CAD/CAM systems, the workpiece is a block of material hanging in space—a programmer can see tool movement and material removal, but it’s a bit like watching a football game without the Astroturf, end zones, and field goals. Vericut, on the other hand, is able to model the entire machine tool, from the vise jaws and toolholders to the spindle nose and way covers. When a student makes a mistake with a tool length offset, or uses a rapid traverse movement rather than a controlled feedrate, the onscreen graphics make it abundantly clear there’s a problem.

“One of our parts is a gear block housing for a Baja car we designed and built as one of our capstone projects,” says Lewis. “There are a number of pockets in the body of the housing, some shallow, others quite deep. And what you often find is that students will just select the contour of the pocket for machining in the CAM system, and think everything is fine after that. But when you look at it closely, you’ll see they didn’t recognize that half the material is already gone. If they were to run that on the machine, it would be cutting air for a few hours.”

Vericut has functions that tell students the percentage of the time the cutter actually performed work, he points out. “Students can measure part features virtually—to check wall thickness, for example, or see that a drill cut through the back side of the workpiece because the offset was wrong.” Quite simply, adds Lewis, Vericut is a more reliable method of checking G-code than are CAM systems. “We find it very useful in finding errors and inefficient machining processes, without the need to tie up limited CNC machining resources. It also provides much better utilization of the instructor’s time. Overall, it’s a necessary tool for anyone teaching the machine trades.”





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