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Simulation technology proves to be path to real advantages.

Raw material costs continue to rise. Lead times keep getting shorter. Parts are getting more complex. Fortunately, technology is keeping pace with these increased demands--including the consolidation of previously separate machining operations on a single machine tool.

Formerly called mill-turn machines, the new breed of multitasking or multifunction machines is more complex to program, set up, and simulate. Additionally, multi-axes machining centers are being used on jobs previously done with simple three-axis milling machines. A significant decrease in the price of multi-axis machining centers has accelerated the acceptance of these machines, even among production floors that previously would not have considered buying a five-axis milling machine.

Now, operators have to learn how to set up and program these machines, thereby making accurate five-axis NC program simulation a mandatory tool. Without sophisticated simulation software, it's almost impossible to understand what's happening at the machine tool.

Machining a part in a virtual environment is like setting up and running the part on the machine tool. The minimum items needed to simulate a machining process are: the beginning stock, the NC program, and the tools used by the NC program. While running the simulation, the programmer can see exactly how each cut changes the shape of the part. This eliminates having to try to imagine how cuts from the current operation will affect subsequent operations.

During the cutting simulation, the software automatically detects problems such as cutting with improper feed rates, gouges, and collisions that could potentially scrap the part, break the cutter, or crash the machine. The programmer can easily identify the offending NC program block by mouse clicking on the error. The problem can then be fixed in the CAM software so that an error-free NC program is sent to the machine.

Further examination of the simulated cut part can reveal more problems. Is the resulting part dimensionally correct? Does it match the final desired shape? Was the correct material left for subsequent operations? Detailed measurement tools enable the user to verify dimensions such as wall and floor thickness, hole diameters, corner radii, scallop heights, depth, gaps, distances, angles, volumes, etc.

Additionally, simulation software typically provides the ability to automatically compare the simulated cut part with the original design. By embedding the design model inside the stock, the software compares the design to the in-process workpiece to reveal any differences such as gouges or excess material not removed by the machining processes.

After running the simulation and making sure that the NC program contains no errors and that the resulting part is dimensionally accurate and matches the design, the NC program can be run on the machine without wasting time on a "prove-out" or test part.

Total simulation

In an effort to avoid the expensive mistakes that inherently come with programming complex parts, processes, and machines, many manufacturers rely on machine simulation. Some CAD/CAM applications allow the programmer to visualize the machine during the programming stage. In most cases, however, it is not representing what happens after the CAM motion is post-processed. Often, differences are introduced during post-processing--some resulting in program errors that still require one or more manual prove-out/ repair cycles prior to going into production. Worse yet, an error introduced at this stage can result in a disastrous machine crash.

Only with software that simulates from post-processed code can the NC programmer hope to detect errors at this final stage. Most CAD/CAM systems store internal tool path motions, spindle speeds, and feed rates as machine tool-independent generic data. Data are output to a file in a neutral format, typically an APT variation. A post-processor receives this file and converts it into the specific machine tool instructions required to control the axis motion, tool changes, cutter compensation, coolant, and other auxiliary machine functions. Unless discovered by the independent simulation software, errors introduced at this stage will go undetected until there's a machine crash or during a manual prove-out run.

If a production floor hopes to eliminate the prove-out process without risking a crash, it is absolutely essential that the simulation software used have a comprehensive machine tool and controller definition. Any simulation should take into account tool length compensation, work offsets, local coordinate transformations, subroutines, cutter compensation, polar interpolation, virtual axes, etc. Additionally, devices such as sub-spindles and tailstocks must be easy to configure and simulate. Without these commonly used elements, it is impossible to detect many common causes of machine tool collisions.

No-fear machining

As more and more shops dive into the increased complexity of five-axis machining, the possibility for errors is much higher than with three-axis programming--especially when coupled with a programmer not experienced in five-axis machining. But with comprehensive machine simulation software, the user can see exactly what is happening on the machine, taking much of the fear and unknown out of the machining process. The NC programmer can test a variety of different machining strategies without tying up the actual machine.

New techniques for five-axis machining are continually being developed, and work is constantly being done to make software easier to use. No matter how good the software is though, it is important that all aspects of a company's machining operation be reviewed when making the transition to five-axis machining.

Another significant requirement in simulating five-axis cutting is the ability of the software to accurately model the material removal of each five-axis cut. As a result, virtually any milling profile can be used for material removal simulation, including complex five-axis milling cuts.

Multitasking machines increase the complexity even more. Because of the relatively small work envelope, densely packed tools, and multiple moving components, it is virtually impossible to visualize and predict interferences and tool collisions when programming a new job.

Following OptiPath

Ingersoll Cutting Tools Co., Rockford, IL, implemented NC program optimization software into its operation about three years ago. Now, no job is sent to the production floor without first being optimized using CG-Tech's VERICUT software optimization module--OptiPath. "When we first implemented OptiPath the operators were skeptical. However, it wasn't too long before the operators were calling the NC programmers and telling them when they forgot to optimize the tape," says systems engineer Paul Gerardy. "Often times, even though the optimization process seems like an extra step for the NC programmers, it actually makes the programming easier. When we first implemented OptiPath, we had the NC programmers record time savings for every job that they processed for about a period of a year. From that it was shown that we easily save $250,000 to $500,000 year after year after year in cycle/machine time."

Optimization software works by analyzing either the post-processed NC program (G-codes) or the direct CAM system output. It then divides the tool motion into a number of smaller segments determined by user-defined settings in the software. Based on the amount of material removed in each segment, the software assigns the best feedrate for the cutting conditions. The software then outputs a new NC program, identical to the original one but with improved feed rate settings. It does not alter the tool path trajectory.

In addition to more efficient feed rates, optimized NC programs usually result in parts with better surface finishes. Thanks to the constant chip load of an optimized program, tools last longer and machines run smoother. Some operations looking to increase capacity have even found implementing optimization software to be an alternative to buying additional machines.

Many NC programmers may or may not be aware of the machine operator who adjusts speeds and feed rates at the machine, the experienced pro who can tell, just by the sound of the machine, when speeds and feed rates should be reduced or when they can be increased. It's not until the machinist retires, when jobs start taking longer and tools are breaking, that the operation realizes how much knowledge left with the machinist. Optimization software offers a way to capture this valuable information before it leaves the company for good.

To configure optimization software, the NC programmer and machinist can allow the software to configure itself, or they can rely on their own expertise. Often, a combination of the two techniques works best. Modern optimization software includes a "learn mode" feature where settings are captured from an NC program that is known to run well. The captured settings are saved to a library and can be applied to other NC programs that use the same or similar tools. Users have found this method to be an excellent way to get a good starting point for key optimization settings such as volume removal rate, chip thickness, and surface speed. Of course, when the shop has a NC programmer or machinist who already knows good cutting techniques, he can apply his expertise and enter the settings manually. Once successfully implemented, there is no reason for a machinist to adjust feed rates "on the fly" at the machine. And, this information will still be around long after the machinist has left the company.

Advanced features

The current version of VERICUT ties all the complex processes together with the ability to create inspection instructions, CNC inspection programs, and automated process documentation. With accurate feature-rich in-process model of the simulated work piece, the inspection and process documents utilize and accurately reflect the state of the work piece at any stage of the process. These automatically generated documents can be used for on the floor or in-process documentation, NC programming documentation, or capturing valuable process information generated during the session.

Going a step further, many companies are finding that they don't want to wait for a CMM machine to tell them they made a mistake a few hours/days ago. They want to cut, measure and continue cutting without any unnecessary delay. An in-process model is also what makes it an ideal place to create CNC probing sequences. This in-process feature geometry is not available anywhere else in the CNC manufacturing process and makes on machine probing a practical reality.

Help wanted

Many larger companies are focusing more narrowly on their internal engineering expertise. The large internal engineering systems' support organizations of the 1980s and 1990s are either much smaller or gone altogether. However, the need for engineering system support did not disappear; instead it is being transferred to outside vendors. This can take the form of outsourcing all system support to a third-party hardware and software support vendor, or the original software provider could be required to perform on-site training and integration services and provide on-going custom support.

"Our customers are so busy they want their new software to 'just work,'" says CGTech's product marketing manager Bill Hasenjaeger. "They expect a fast start-up and short learning curve, and only want to know enough details to do their job. We are now typically asked to do on-site training, integration services, and provide ongoing standard and custom software support. CGTech has had to add staff worldwide to meet these increasing demands."

As worldwide competition increases and customers demand more from manufacturers, it is critical that shops have a full arsenal of tools to ensure that the parts they produce are right the first time. Simulating CAM output to view basic work piece material removal is no longer enough. If they hope to survive, shops must operate as efficiently as possible; modern simulation and optimization software has become a valuable tool to minimize the cost and time of production while increasing product quality. It has evolved into an important process that protects and frees up CNC machines, eliminates the prove-out step, and even creates in-process reports that can be utilized throughout the company. CGTech,
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Title Annotation:software solutions
Publication:Tooling & Production
Date:Jul 1, 2006
Previous Article:Tooling life improvement wins over a challenging customer.
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