The ABCs of X, Y, Z (and B & C)

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by Ed Robertson

Troubleshooting multi-axis CAM programming

No one ever approached CAM (Computer-Aided Manufacturing) thinking it was going to be easy to implement, but thinking about CAM can be reduced to three primary steps: the first may be called the “pre-processor”—importing digital data models, whether from inside design groups or outside customers and vendors.

Second is the toolpath planning and calculation process, the “processor.” Third is the communication from the CAM software to the machine tool language, the “post-processor.”   

Any process is likely to fail at its weakest point and the post-processor is often the weakest link. “Multi-axis post-processors often do not get high visibility during the selling process,” says Alan Levine, managing director, Open Mind Technologies, Needham, MA. “They should.”

Customers that overlook details about post-processors, such as sourcing, service, and testing,often question those same details after the purchase. It is reckless to make capital purchases of machine tools and software, without having defined a clear plan for post-processor implementation.

The APT (Automated Programming Tool) language was developed in the 1950s with US Air Force funding. APT includes the pre-processor or geometry commands, the processor for toolpath planning, and the post-processor defining machine tool commands and controls.

Some CAM software products still use APT language, but with a graphical user interface mask. Many existing post-processors use APT as a basis for post-processor translations between the CAM software and the machine tool, but it is too limiting today in many cases. 

Multi-axis and multi-task machines
The manufacturing world has progressed to more complex machine tools and applications. Multi-axis milling machines enable fewer setups, simplified fixturing, and shorter cutters in producing complex geometries. The intention is to perform multiple, even disparate process steps, such as milling and turning on the same machine tool. They also simplify handling and reduce floor space. Higher capital investment costs for these machine tools also provide clear return from improved results and shop productivity.

Such machine types also increase the burden on CAM software for programming tasks and post-processor capabilities. The mathematical foundation of multi-axis postprocessors
is more intensive. These solutions generally cannot be
prototyped by “hand programming” and reading output NC instruction files is not always good advice for reverse engineering postprocessor functions.

Editing options do exist. The TruePath Turn/Mill software package from CAMplete Solutions Inc., Kitchener, ON, is offered for Nakamura-Tome multi-tasking turning centres, and functions as an integrated suite of G-code editing, optimization, analysis and verification tools. CAMplete Turn/Mill was developed as a platform that combines G-code from CAM systems and hand-coded G-code into a set of programs that can be simulated, tuned, and optimized using detailed 3D Nakamura machine models. Among its functional modes are: Simulation. This includes full simulation of Nakamura turning centres and programs, and detailed tooling and workholding libraries. 

Jeff Fritsch, product manager at CAMplete Solutions, says the simulation “is extremely accurate, since the 3D machine models are provided directly by Nakamura-Tome Japan. For tooling and workholding, CAMplete has partnered with number of tooling and chuck manufacturers to have access to their 3D models, which further enhances the accuracy of the simulation.”

G-code Editing. It includes an edit capability that allows modification of posted or unposted data; and the ability to automatically update changes to both the toolpath and the G-code. CAMplete’s Fritsch says it also enables users to modify the code and verify the proper code syntax. 

“It enables the user to adapt code coming from another Fanuc based controller to make it run on the Nakamura-Tome machine.”

Optimization. It features wait-code editing, a function for reordering and moving operations, and one for fine-tuning, optimizing, and simplifying multi-tasking steps. 

Analysis. Includes monitoring capability for all aspects of machining motion, and indicators for true cutting speeds, axis velocity and acceleration, and motion deviations. “Since every aspect of the machine is taken into consideration (acceleration/deceleration, timing for particular functions of the machine) the cycle time presented by TurnMill is extremely close to the real machine cycle time,” says Fritsch.

Verification. G-code verification and verification of machine, tooling, and workholding using detailed Nakamura machine models.

Other options edit and reduce five axis movement automatically. 

Like many other CAM systems, FeatureCAM from Delcam, Windsor, ON, offers options for multi-axis machining. The key difference between FeatureCAM and other CAM systems is that it is featured-based, which means you can quickly and easily create reliable and consistent toolpaths even for the most advanced cutting edge multi-axis machines on the market today, says Mark Cadogan, vice president of sales for Delcam North America.

FeatureCAM 2013 offers a new series of options for three axis and five axis machining, plus turning and mill-turn. They include strategies for five axis, including flowline machining between two curves, pencil machining and corner re-machining. 

“These options are for simultaneous five axis machining and allow a better surface finish to be achieved as well as ensuring access to more areas within the part in a single set-up,” says Cadogan.

Another new capability in FeatureCAM removes sudden tool-axis changes during automatic collision avoidance and, instead, ensures a smooth transition takes place. In addition, the software offers the ability to smooth Azimuth and Elevation axes independently to remove excessive five axis movement. These options stabilize the rotary axis movement by maintaining a fixed-tool axis as far as possible, thus replacing constant five axis movement with a series of 3+2-axis segments having full five axis transitions between them.

Cadogan says Delcam has also improved the software for the turning and mill-turn modules. It has improved the definition of the initial stock and part alignmment, added support for semi-finish canned cycles “and curves of revolution can now be recognized from STL models.” Another new feature allows B axis rotary milling to be carried out on features that would otherwise require excessively long cutters. For multi-spindle, multi-turret machines, part transfers are now fully integrated into the FeatureCAM output.

Machine Tool Standards
In the future, custom post processors may be unnecessary. Earlier this year, Gibbs and Associates, developer of GibbsCAM software for programming CNC machine tools and a Cimatron company, announced it is supporting phase one of the DMG/Mori Seiki standardization initiative. It will ultimately provide DMG/Mori Seiki customers a smooth and reliable flow of programming data from any CAM system to DMG/Mori Seiki machine controls. This will enable the full use of the features of their machines and controls without the need for custom post-processors or machine simulation models. The technology is based upon DMG/Mori Seiki’s implementation of the standard APT language, with DMG/Mori Seiki extensions supported within GibbsCAM. 

This joint project is intended to address one of the main challenges that CAD/CAM and machine tool users often face: the need for a new post-processor and machine model for each of their machines. 

Currently, when a customer purchases a new CNC machine or a new CAM system for use with an existing CNC machine, he needs to work with both the machine tool vendor and the provider of the CAM system to implement a customized post-processor and machine simulation model to fully program and simulate the capabilities of the machine. This process can sometimes be much longer than expected, especially when the project requires the collaboration of two suppliers that do not always have the same level of detailed knowledge and understanding of each other’s products.  

In this new approach, the CAD/CAM vendor outputs DMG/Mori Seiki-specific APT data and DMG/Mori Seiki provides a postprocessor and simulation package for its CNC machine, eliminating the need for each CAM provider to develop a custom post-processor and machine model. With this approach, users will be able to start cutting parts immediately on their DMG/Mori Seiki machines. SMT

Ed Robertson is a contributing editor based in the Detroit, MI, area.
[email protected]


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