Automation has expanded the average machine tool's functionality: Sensors, HMIs, and most importantly, coordinated axes and controls are making processes — particularly the cutting of curved paths — more exact. Where maneuvers are optimized to the limits of physics, automation can still make operations more efficient.

Nowhere is its integration more critical than in 2D shape cutting (in which plates or slabs are cut with noncontacting plasma, laser, water, and oxyfuel) or 3D part contouring — in which a traditional miller or router cuts material to make 2D or 3D parts.

These machines require more integration than most in other industries, because the motion isn't prescribed. Instead, paths continually change directions, and the cutting instructions for them (typically by CNC) must be meshed with the motion controls. Case in point: A fairly common contouring setup leveraging integration moves a workpiece-holding table as a separate spindle jogs over the part on its own trajectory.

Connecting the dots

AccuRing direct-drive rotary tables from IntelLiDrives have no brushmotors or gear trains to create hysteresis, windup, or backlash position errors. Accuracy to 5 arc-sec and bidirectional repeatability of 0.5 arc-sec make them suitable for contoured motion.

Directing a machine to cut shapes and contours requires interpolation — the mathematical filling in of points on a curved path between those known. Twenty years ago, interpolation for contours was executed through CNC by tiny successive moves in X and Y directions — a bit like drawing with an Etch A Sketch — to cut arcs by stepped approximation. This approach requires abundant computing power; it is slow where curves are tight or require particularly small “bites” to meet higher accuracy or surface-finish requirements; and the finished product is left with ridges.

Many newer contouring machines now leverage the power of CAD files and the curves that they mathematically define so economically. One such tool for cutting 3D parts is CAD/CAM software called Mastercam X5 from CNC Software Inc., Tolland, Conn. It executes dynamic milling that constantly adjusts the toolpath to make full use of flute length; a dynamic contour function uses an intelligent strategy to remove material along walls in multiple passes. Cutting motions are commanded in steady position-velocity-time sweeps for a smoother final product.

Another technique executed with the software, hybrid finishing, evaluates model shape and smoothly switches between constant Z cutting (in which material is roughed out in horizontal layers) and constant scallop machining — a kind of finishing that moves the cutting tool in regularly spaced passes, and lifts and plunges it vertically over raised and cutout features, to hold the small “ridges” of the final surface finish consistent.

MAG's HyperMach GTi series 5-axis profiler is stiff for aggressive cuts at any workzone position -- for parts from 2 x 4 to 2 x 8m. A CINCRON automation module adds flexible multi-machine and pallet arrangements; an open center allows chips to fall through to a conveyor, to prevent chip re-cutting and the need for a blow-off attendant.

Instead of defining arcs by successive X and Y moves, newer software drives along splines. These are curves mathematically defined with anchors and weighted handles that define how sharply the paths swerve to one direction or another. SigmaNEST (published by SigmaTEK Systems LLC, Cincinnati) is another CAD/CAM nesting software that defines moves in such a manner for sheet metal fabrication and profile cutting.

By default many of these software packages are written for PCs. It's characteristic of the industry: Many OEMs in shape cutting are smaller companies choosing to make their own controllers (usually PC-based) or buy controllers with an open network interface. It's no wonder then that there's a higher concentration of PC control than in other industries: PC-control specialist Beckhoff Automation LLC, Burnsville, Minn., for example, supplies a controller (and TwinCAT CNC automation software) to Messer Cutting Systems Inc., Menomonee Falls, Wis., for plasma cutting machines that execute Messer-written software called Global Control.

Advanced Kiffer Systems Inc., Cleveland, sells plasma beveling heads that can put angles on cuts at even the smallest of curves. Integrated controls coordinate axes; automatic homing quickens alignment.

Another setup is integrated CNCs that only work with servos from the same manufacturer. Elsewhere, many shape-cutting and contouring machines are still controlled with separate PLC, CNC, and robot programs. However, their isolated programming can't be fully synchronized or even summarized on one HMI, which makes it cumbersome to integrate multiple high-speed axes — and the sensors, actuators, and handling robotics that accompany them. Yet another “hybrid” setup (increasingly common) is open architectures that strike a balance between ease of use and flexibility — allowing OEMs to choose individual components from different vendors. Yaskawa America Inc., Waukegan, Ill., caters to these OEMs: The company sells no motion controllers or CNCs for shape-cutting applications, but offers servomotors and drives. Here, the OEM buys a CNC that works with multiple servos and chooses the best to meet a design's requirements.