A NEW THRESHOLD IN SURFACE FINISHING

In most mold & die shop operations, the manufacture of these components has always been the most challenging aspect of production, owing to the form and fit of contours, pockets and runners, to cite a few examples. The surface finish issues have always created problems, especially when hardening and remachining were involved. It was a given that the better you wanted the finish, the longer the machining time would be.

As with most assumptions from bygone days, modern technology simply flies in the face of this old maxim. In this case, the latest CNC technology is providing an advanced surface capability that requires high cost neither on the machine nor machinist. Innovative mathematical algorithms in the CNC can literally look-ahead to calculate the forward and backward path motions identically. As a result, smoother workpiece surfaces can be achieved by carrying out the line-by-line milling operations for mold and diework.

When coupled with the proper drives, today?s CNC can utilize its highly sophisticated floating point accuracy to produce tolerances in the nanometer range on a consistent basis. This precision is not simply available for closed loop position control, but also for closed loop current regulation and even closed loop speed control, as well as drive sensor and encoder feedback evaluation. Coupled with the smooth jerk limitation of the look-ahead features in the acc and dec, such technology yields further benefit in time savings.

As the horse head thermograph shown here displays, the superior accuracy can be accomplished in less machining time than traditionally possible. An additional collateral benefit is less wear on the mechanical components of your machine tool, since the smoother acc and dec possibilities significantly improve the service life, reducing downtime and improving overall productivity in the shop.

Using a far more dynamic feedforward control feature than CNC technology had available just a few years ago, today?s advanced CNC can calculate and practically anticipate errors as early as the set point output and compensate for them in advance. In this way, maximum contour integrity can be maintained. Likewise, contour deviation can be completely eliminated during axis reversal, due to an integrated quadrant error compensation feature. Basically, this means the surface of the workpiece remains consistent, even at those junctions involving circular and trochoidal path movements.

Combined with compensation for the inaccuracies of ballscrews and other mechanical components on the machine, as well as the rapidly emerging temperature compensation integration technology, the CNC you can now buy on your machine tools can literally think its way to a better finish.

When the block sequences don?t provide the necessary data to achieve the desired finish, furthermore, the surface finish technology embedded in a high-end CNC likewise utilizes the latest spline mathematics to produce the optimum finish in the least amount of machining time, as also shown in the graphic provided here.

For the busy job shop that utilizes even the compact class of machine tools, the new CNC technologies now offered by many machine builders can also substantially improve the workpiece surface quality while actually reducing time to first part, as well, owing to the simulation strategies onboard.

While it is never advisable to use the machine CNC for programming, the simulation software embedded in many advanced CNC platforms will now provide real time calculations of the run time for a proposed cycle, while also offering the chance to spot possible problems in tool path and workpiece collisions.

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Randy Pearson is the sales support manager for U.S. dealers and OEMs of Siemens Energy & Automation, Motion Control Business, 390 Kent Avenue, Elk Grove Village, IL 60007, www.siemenscnc.com. As a longtime veteran of the machine tool industry, his special interest is the training aspect on CNC machine tools, through various seminars and classes the company conducts at votech schools and on-site at shops, as well as at Siemens training facilities around the country. If you have questions or comments on this or other CNC topics, call Randy at 847-640-1595 or email him at randy.pearson@siemens.com.