Programming machine tools: It's all about the software

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NUM: Simplified use of five-axis machine tools

The latest version of NUM's Flexium software includes an enhanced Rotation Tool Centre Point (RTCP) function with tool vector programming, which is designed to greatly simplify the use of 5-axis machine tools.

As one of the first developers of the Rotation Tool Centre Point (RTCP) function, NUM continues to develop this feature to meet the changing needs of machine builders and end users. The company's RTCP implementation includes twenty-four predefined kinematic configurations. The Flexium+ CNC systems are able to accommodate different kinematics on the same machine - for example, when different milling heads are required.

NUM's basic RTCP function, which is called via ISO code G151, offers a number of user-specific variants. The function can be activated with an inclined coordinate system or after a positioning movement. In both cases, the CNC system automatically calculates the mechanical offset to ensure that the tool centre is always in contact with the defined workpiece surface as the rotary axes move. The RTCP function can also be activated via the actual positions of the rotary axes.

Part programme is made independent of the machine kinematics

The programming of 5-axis machines has often been perceived as tedious. The rotary axes are usually programmed directly with their angular position. This has the advantage that one can imagine the position of the machining head when looking at the part programme. The disadvantage, however, is that the part programme depends on the kinematics of the machine and cannot be transferred to another 5-axis machine without modification.

With the tool vector programming option of NUM's RTCP function, the direction of the tool can be determined by the components of the vectors along the X, Y and Z axes, making the part programme independent of the machine kinematics.

In certain circumstances, physically aligning the workpiece to be machined on the machine is a complex procedure. To increase productivity, the NUM Flexium+ CNC system can compensate for positioning deviations (including angles) in these cases by applying appropriate correction values. The workpiece remains misaligned, but the CNC system is aware of the deviations and automatically compensates for them.

Roughing and finishing with adjustable smoothing levels

NUM's Flexium software, version 4.1.00.00 or higher, now has a special HMI (Human-Machine Interface) through which the corresponding correction values can be entered. The coordinate system resulting from the offsets and rotations is called the Balanced Coordinate System (or BCS) and the compensation function is called 3DWPC (3D Workpiece Compensation).

In addition, the software now includes a function that helps machine users speed up roughing operations and achieve optimum surfaces during finishing. The new function, which is accessed via ISO code G732, simplifies parameter optimisation and automatically calculates presets for roughing and finishing with adjustable smoothing levels. The machine operator can select a range of properties and call up an optional smoothing algorithm to reduce mechanical vibrations and smooth the workpiece surface.

To further assist machine operators, NUM has also introduced an algorithm that keeps the speed constant at the pivot point. Part programmes generated by CAD/CAM systems often consist of a large number of small G01 segments, resulting in speed fluctuations that affect surface quality. The new algorithms maintain a constant speed at the pivot points during the movement of the rotary axes, so that the discontinuities can be smoothed out.

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