Automated NC Programming Moves To New Dimension

The CAD/CAM industry has been talking about automatic tool path generation for a long time, and individual vendors have achieved varying degrees of success. Most of the discussion has centered on "feature-based" NC where the CAM system stores generic machining processes for common part features—such as holes, pockets, chamfers, and so on—and then automatically triggers those routines based on the specific geometry of the workpiece. As such, automatic NC has mainly applied to 2.5-axis production machining where standard features are common.

But truly automated tool path generation has been slow going for those seeking optimized programs in the 3D world of molds and dies because so much of a well-tuned machining strategy depends, not on predictably symmetrical forms, but on the more randomly flowing topology of cores and cavities. That is changing quickly, however, as CAM developers are now building much more intelligence into their systems to analyze 3D geometry and then generate appropriate machining routines for the work at hand.

An excellent example of such technology is the Cimatronit Version 9.0 system from Cimatron Technologies, Inc. (Burlington, Ontario). As the company describes it, "Intelligent NC" is a combination of automatic NC tool path generation, knowledge-based machining and constant knowledge of stock remaining. Moreover, it includes hybrid wireframe, surface and solid modeling as well as advanced mold making tools.

If that just sounds like a lot of software buzzwords, perhaps we should speak more plainly about what this technology can do. First of all, it allows users to use a variety of tools to import and/or construct geometry in the first place. Simple forms are most easily handled with wireframes; complex shapes demand surfaces. But merging these elements into a solid model can pay big dividends when you need to add or subtract volumes from one another, or to split volumes as must be done when establishing parting lines in a mold. The Cimatron system allows all these construction techniques to be used in a single model, and stored in a unified database.

The ability to automatically analyze geometry becomes critical when it comes time to generate machining routines. As tool shop machinists know, different types of surface topography demand different machining strategies. For example, you don't machine a wall with a five-degree draft angle the same way you machine a 45-degree slope. But you do probably want to machine most 45-degree slopes in the same way. Through the ability to analyze surface vectors, the Cimatron software has the capability to recognize and classify these respective surface areas, and to associate them with standardized machining processes, much like feature-based machining. Referred to in Cimatron parlance as "equi-technological regions," this ability to tie process to topology is the lynchpin to truly automated and optimized 3D machining.

Processes are stored in the form of "templates" that specify the logic by which a machining routine is to be generated, which is then applied to the specific geometry of an individual region. Templates can be built by going into tool path mode to directly create a machining process, or into procedure mode to establish a general machining strategy. Once a procedure is established, the user can pick a region, apply the procedure and then post the output in order to get a realistic estimate of cycle time.

The software also has other features that help streamline the total tool design-through-manufacturing process. As for the modeling capabilities, an expanded toolkit includes an advanced parametric surface modeler and a dimension-driven, feature-based solid modeler with the flexibility to incorporate fully associative surface data into the solid model. The system can automatically or semi-automatically detect and create the parting line and runoff surfaces to separate the core and cavity of a mold. Mold assembly is fully associative to the design model, allowing changes in the design model to be automatically reflected in the mold assembly. Moreover, the Moldbase application incorporates slides, inserts and user-defined catalogs or components that allow users to modify their mold catalog of choice.

An electrode function automatically extracts all relevant geometry with the area identified for burning for the core and cavity, and places it within a predefined block on a predefined base. It then sets all extracted electrodes in the correct orientation for machining and creates a detailed list of all electrodes with burn locations and depths.

Knowledge of stock remaining allows all of these machining routines to be constructed more efficiently, and more safely. Most obviously, it allows tool paths to be applied only where there is material to be cut, eliminating unnecessary air cutting. But it also facilitates other process checks such as gouge checking rapid traverse moves or checking for real interference with toolholders and extensions.