Next Generation NC Software Improves Productivity

With our recovering economy, mold and die makers are under in-creased pressure to improve their operations to obtain shorter leadtimes, improve quality of product and lower costs. The degree of manufacturing automation must be increased. In turn, the level of programming automation also must be improved to meet these requirements.

As manufacturers re-evaluate their operations, software vendors also must reconsider their priorities and place an even greater emphasis on new programming strategies that focus on improved productivity. Spurred by the mounting pressure to cut leadtimes and costs, the worldwide desire to reduce "total cycle time" is spawning some of the most unconventional thinking that the CAD/CAM industry has seen in years.

Today, the primary motivation in NC software development is to improve user productivity by making software that is easier to learn and use, production-reliable, highly automated and feature-rich, as well as supports techniques to collaborate and communicate information enterprise-wide. In a recent worldwide study of mold and die makers, the most important CAM software function was found to be strong three-axis milling. Within three-axis milling, some of the most highly desired features cited were effective gouge avoidance, user flexibility, automatic re-machining of uncut areas and machining over sculptured surfaces. Additionally, users are looking for more focused application solutions that specifically target certain industries such as moldmaking or diemaking. Users are searching for systems that can more easily and quickly generate toolpaths. Utilization of new cutting strategies, cutters, controllers and machine tools is a must for their survival. Users still need to apply their own unique expertise to the CNC machining strategy. They want better tools to analyze and optimize the machining process in order to best utilize the equipment they have. The next generation of three-axis NC milling is upon us. It combines the intelligence and speed of an interactive process-planning module with the efficiency and reliability of a new, state-of-the-art NC engine.

Process Planning

Next generation NC software invokes intelligent decision making based on graphical in-process feedback. An integrated knowledge engine intelligently establishes the minimum number of required parameters needed to define each milling strategy. To create the toolpaths to machine the mold core for a motorcycle faring, the user indicates the machining strategy, indicates a couple of parameters and an immediate preview of the result of the cutting strategy is shown. A different preview is displayed for each machining strategy according to the most pertinent information the user requires. Roughing operations are depicted with a 3-D model of the stock remaining. For re-roughing operations, the preview displays remaining material. Finishing and pencil trace strategies are portrayed with a toolpath. Clean up operations (machining only in the area that a previous tool has left material) are represented with a display of the area remaining to be machined.

In seconds, users can accurately examine the results of many different cutting strategies using a host of geometrical analysis tools such as cross-sectioning, measurement, etc. These special preview functions shorten process-planning time considerably. With full knowledge of the machining process known prior to committing to the number-crunching, the operator can execute and post process the toolpaths individually or together with the utmost confidence.

A process plan defines the machining operations required to transform the initial stock into the finished part. In a traditional machining process, the user would use his judgment and experience to select the necessary and required parameters. Even the most experienced programmers do not have the skills to select the required parameters correctly the first time. It is extremely difficult to predict the behavior of each toolpath when the combination of complex geometry and some 30 or 40 parameters dramatically affect the results. With each operation, the toolpath must be executed in order for the operator to review the result. Changes are then made to the parameters and the toolpath is calculated. This trial-and-error cycle continues for each toolpath in the process plan.

One example of the next-generation NC software system creates a unique preview model for each step of the process plan (see Figure 1). It displays the effect of the manufacturing step on the workpiece, and is updated instantly whenever any parameters of the operation are modified. Thus the entire process plan can be previewed and can provide an accurate prediction of the optimized toolpath. The process planning and toolpath programming timesavings exceed 75 percent, as compared to the present CAM software systems.

A unique set of algorithms and a data model that maintains the intermediate states of stock are used for toolpath calculations. Tool motions are created in relation to this model and provide gouge-free machining, minimum idle movements and adaptive feed control, which is based on actual tool load:

• Rough - Remove efficiently the bulk of the material.
• Re-rough - Machine the part to a specified material thickness.
• Finish - Create finish cuts with several strategies - parallel, spiral, WCUT.
• Clean up - Create paths to remove material left by previous tool.
• Pencil - Create paths at the intersection of surfaces.

Often machine tools do not physically achieve their programmed toolpath feed-rate due to the natural cutter direction changes inherent in the geometry being followed. In most shops, the CNC operator monitors the cutting process and manually adjusts the feedrate with the override dial. As the amount of material engaged increases, the operator reduces the feed and as the load decreases, the operator in-creases the feedrate. Substantial timesavings can be achieved by adapting the programmed feedrate to the volume of material engaged with the cutter during the toolpath creation process.

New NC software detects conditions where the chipload is too great (see Figure 2), and adjusts the feedrate to a more reasonable value. It then returns the machine to the higher feedrate when chipload allows. This results in the total machining time being dramatically shortened and machine tool operator interaction reduced. Users can achieve better cutting efficiency with optimized feedrates and protect the cutting tool, workpiece and machine spindle in those few places where the chipload momentarily increases. Ultimately, NC software will run completely automated and unattended, converting part models into machine G-Code. As more intelligence is put into CAM software, it will soon be possible to automatically select the machining processes, speeds, feeds and cutting tools, and automatically create the final G-Code program. The software will be able to learn from experts in each shop their preferred methods for machining different parts and then apply these techniques for the programming of subsequent parts. Mold and die makers should be encouraged that some of these new tools that are aggressively being developed for their industry are available today.