Cutting Tool Engineering
October 2012 / Volume 64 / Issue 10

Combining post-processors, verification

By Jeff Fritsch, CAMplete Solutions Inc.

More than ever, North American part manufacturers must constantly improve their processes and upgrade their technology to compete globally. As production runs continue to shorten and part geometries get more complex, 5-axis machine tools are starting to go mainstream. Many shop owners are taking advantage of the efficiency and return on investment possible with what once were considered specialty machines.

Even though the benefits of 5-axis machining are attractive, many potential users eye the technology with caution. Adding that 5th axis drastically increases the level of complexity, and programmers must consider new machining scenarios. New users can expect a learning curve, and it’s important to minimize errors during that time to get a timely ROI from such a significant capital investment.

The biggest benefit of 5-axis machining is its ability to produce complex shapes in a single setup. Having this flexibility and versatility increases machine throughput compared to performing the job in a series of setups and virtually eliminates the time and cost of preparing fixtures.

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All images courtesy of CAMplete Solutions

The blue path represents the CAM-programmed cutting tool trajectory, and the red path represents the actual physical tool motion when considering the machine kinematics. Having the proper verification software tools to analyze these differences is critical to overcoming 5-axis motion errors.

Another important advantage is the ability to apply significantly shorter cutting tools, because 5-axis machining enables the head to be lowered toward the workpiece and the cutter to be oriented toward the surface.

In addition, 5-axis technology eliminates the multiple setups required to reposition a workpiece at complex angles. Not only does this save time, it also reduces potential errors and the cost of tooling and fixturing to hold the workpiece.

With shorter tools, 5-axis machining can complete an entire part without refixturing it or applying the long tools required when producing a similar part with 3-axis machining. As a result, 5-axis machining delivers the final product in less time and with a finer surface finish.

Shorter tools automatically enable higher cutting speeds without putting excessive load on the cutter, increasing tool life and reducing breakages. This also reduces the tool vibration typically seen when machining deep cores or cavities with 3-axis machines.

When a company makes the plunge into 5-axis machining and programming, however, the possibility for errors becomes much higher than with 3-axis machining. Therefore, programming five axes makes some new users nervous.

Software packages are available to make this task less intimidating, such as the latest CAD/CAM software, but it’s important to make sure what is programmed is actually what will run on the machine.

The post-processor—the critical link between the programming software and the machine—is often the weakest link in 5-axis machining, but it doesn’t have to be. The post-processor is typically the weakest link because developers focus on creating toolpaths and tool motion in the CAM software instead of the post-processor. Also, given the large number of different machine styles, configurations and options to support, an application engineer must often modify a post-processor to the customer’s specifications, tying up personnel and the machine until the post-processor meets those requirements. And this modification would only be to support standard operations. As the customer gets more involved with the machine and explores its more advanced functions, the post-processor follows the same learning curve as the user did and evolves accordingly.

In the worst-case scenario, when implementing a new machine does not go as smoothly as planned, the software vendor can get stuck between a rock (the customer) and a hard place (the machine vendor) because the post-processor creates the particular commands required by the machine to follow the instructions programmed in the CAM system. Having an integrated and proven platform dedicated to a particular machine tool eliminates the need for lengthy post-processor prove-outs.

Considerations for 5-axis machining should not be restricted to a machine alone. It is important to recognize, understand and continuously view multiaxis decision making as a true optimization process. Also, users must be able to analyze exact machine behavior.

Verification software, such as CAMplete TruePath, is not only able to generate the proper code for a specific machine on the shop floor, it is also able to check programs for machine-specific errors. The software analyzes data on the design, tooling, fixturing and machine, and tells the user whether the program is viable or not.

CAMplete TruePath is unique by design. Each version of the software is dedicated to a particular machine tool model from one of our partners: GF AgieCharmilles, Hermle, Matsuura and Nakamura-Tome. As such, the machine tool builder provides CAMplete Solutions all the data relevant to proper machine operation. This includes the 3-D machine models (the same models used to build the machine), the exact options available on the machine and the G and M codes used by the controller. CAMplete then integrates this data into a unified platform, which includes the code generation (post-processing based on the exact machine kinematics and requirements) and accurate G-code simulation and verification. The simulation is directly controlled by the G code (NC program) that will run on the machine and all aspects of the machine, including tool changes, tool measurement and controller representation, are represented.

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CAMplete TruePath generates proven G code and verifies it using the machine builder’s 3-D models, such as the ones for the Matsuura MAM72-63V Mark II.

Verification software must accurately and exactly represent what will happen on the machine, which will take much of the anxiety out of programming. Various machining and fixturing strategies can be tested without having to physically prove them out on the machines and delay production.

Verification software should support all major CAM systems and not rely on their built-in post-processors. The native data is read directly, post-processed and the resulting G code is verified in the machine context.

By design, the CAM software only considers the tool motion relative to the part. As such, the CAM system’s post-processor will only create tool motion based on the part—not the machine. When “simulating” in the CAM system, the user is only verifying cutter-location data against the part. The simulation does not consider the particulars of the machine, such as axis ranges, pivot distances, center of rotations and acceleration/deceleration.

However, a simulation platform is only as effective as the level of detail it offers. It must support the specific G and M codes each machine requires. This includes advanced features, such as tool center point control for 5-axis machining, support for a tilted work plane and any other special functions of the controller, as well as the particular machine kinematics. This can only be achieved by directly importing controller parameters into the post-processor to produce code for the exact machine on the floor.

The core combination of post-processor and verification in CAMplete TruePath is based on the manufacturing CAD data used from the machine tool builder. This eliminates the approximations of using a model designed by a third party.

When purchasing a 5-axis machine, you should understand the impact of the post-processor and how to ensure its accurate output. Machine shops and their employees should be focused primarily on making parts—not software development. Today’s 5-axis machines have many options and complex logic. Having the peace of mind of knowing programs will run as intended allows the user to focus on programming, metalcutting and increasing productivity—not on debugging or troubleshooting the post-processor “black box.”

Unlike CAM software, which supports thousands of machine configurations to different levels of complexity, dedicated verification software is created to focus on a specific machine. In today’s market, making sure machines give you the capabilities your competitors don’t have is critical to success. CTE

About the Author: Jeff Fritsch is product manager for TruePath TurnMill for multitask machines at CAMplete Solutions Inc., Kitchener, Ontario. The company also distributes TruePath software for 5-axis milling machines. For more information, call (519) 725-2557 or visit www.camplete.com.
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