NO MORE WASTE: ELIMINATE SCRAP AND REWORK ONCE AND FOR ALL

The Federal Reserve warns of deflation, yet raw material costs continue to rise while lead times keep getting shorter. At the same time, parts are not getting any simpler. Scrap and rework is simply not an option in today?s competitive marketplace. Fortunately, technology has been advancing to keep pace with these increased demands.

Developers of manufacturing software have been forced to quickly adapt to the latest machine tools and methods. Worldwide competitive pressures have been driving the trend towards more sophisticated methods, including combining previously separate machining operations on a single machine tool.

Additionally, multi-axis machining centers are being used on jobs previously done with simple 3-axis milling machines. This trend has been fueled by the availability of lower-cost multi-axis machining centers in the past few years.

?Over the past few years, even small and mid-size tooling shops have purchased 5-axis milling machines. They now have to learn how to setup and program these machines, making accurate 5-axis NC program simulation a mandatory tool,? says CGTech production marketing manager Bill Hasenjaeger. ?Without sophisticated simulation software, it?s almost impossible to understand what?s happening at the machine tool.?

SIMULATION BASICS
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.

?Simulation must accurately produce a feature-rich representation of the workpiece being machined. The simulated workpiece must be an accurate model that faithfully represents what the NC program is intended to produce. As design requirements demand more accurate component parts, the simulation software must improve accordingly,? notes Hasenjaeger.

Finally, 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 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.

SIMULATING THE ENTIRE MACHINE (FROM POST-PROCESSED CODE)
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 that sets the production schedule back weeks or more waiting for costly repairs.

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. That data is either output to a file in a neutral format, typically an APT variation, or held internally in a similar format.

A post-processor converts this neutral format into the specific machine tool instructions required to control axis motion, tool changes, cutter compensation, coolant, and other auxiliary machine functions. Unless discovered by the independent simulation software, any potential machine collisions introduced at this stage will go undetected until there?s an actual machine crash. Of course there?s always the option to do manual prove-out runs on each and every NC program, but who has the time?

If a shop hopes to eliminate the prove-out process without risking a crash, it is absolutely essential that the simulation software used has 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.

TAKING THE FEAR OUT OF MULTI-AXIS MACHINING
As more and more shops dive into the increased complexity of 5-axis machining, the possibility for errors is much higher than with 3-axis programming?especially when coupled with a programmer not experienced in 5-axis machining. It is not uncommon for a company to invest in a state-of-the-art 5-axis machine, only to end up using it as a 3-axis machine for fear of crashing it.

However, 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. In addition to avoiding any problem on the shop floor, the NC programmer can test a variety of different machining strategies without tying up the actual machine.

Owning the latest machine tool is only the start. Shops wishing to gain the maximum benefit from the investment of a new 5-axis machine must consider all the factors that contribute to efficient and safe operation. If a shop hopes to keep the machine from lying idle, it will want to make sure programmers are equipped with powerful computer hardware and the latest software. What good is a new machine if it?s sitting still waiting for the next NC program? Fortunately, an amazing amount of computing power can now be purchased at reasonable prices. This should be combined with a high-quality CAM system and accurate simulation software capable of simulating every feature of the new machine?using the same codes that will be sent to it.

?Accurate simulation software allows the manufacturing engineer to focus his creative energy on the production process,? states Hasenjaeger. ?Rather than spending time and energy worrying about ever-present problems in the complex NC machining process, a good NC program simulation software allows the engineer to utilize the best processes and practices, and invent new ones, while the software automatically takes care of detecting annoying (and potentially catastrophic) problems that naturally occur in any complex creative venture. Good NC program simulation software is a reliable tool that gives NC programmers the freedom to do the best possible job.?

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CGTech, 9000 Research Drive, Irvine, CA 92618, 949-753-1050, Fax: 949-753-1053, www.cgtech.com.