Dynamic CNC developments give control to Heidenhain TNC users

According to Heidenhain, Dynamic Efficiency combines effective control routines with intelligent machining strategies, while also exploiting the machine's full potential and simultaneously limiting mechanical loads/process-induced vibrations. Dynamic Precision is said to combat machining errors caused by dynamic machine movement and improve machining accuracy by combining 'crosstalk' compensation, active vibration damping and load motion, as well as position adaptive control. Part of the Dynamic Efficiency library, Heidenhain says that active chatter control (ACC) reduces the occurrence of chatter to permit improved in-feed rates by applying 'damping' to increase the cutting rate at which chatter will arise. ACC detects chatter through the measuring signals of the feed drives, then uses the drives – up to a frequency range of 100 Hz – to withdraw energy from the vibration. Because ACC operates in a frequency range below the tool's engagement frequency, TNC users can define when ACC will be used. Separate parameters can be selected for each tool. According to Heidenhain, experiments involving the milling of a range of metals and cutters saw ACC boost metal removal rates by up to 25% in cases where chatter was a process-limiting factor. ACC also improved tool life as well as having a positive effect on the machine main spindle, guideways, ballscrews and bearings, says the company. Dynamic Efficiency is also said to embrace functionality for adaptive feed control – to optimise feed rates depending on machining conditions – and trochoidal milling, which accelerates the roughing of slots and pockets. Dynamic Precision's compensation of acceleration-dependent positioning errors (CTC) is part of Heidenhain's software solution that measures any errors at the tool centre point and provides simultaneous compensation. The value of these errors and the parameters involved are either known in the control (acceleration) or can be determined by measurement (machine stiffness). Dynamic acceleration – in the direction of the axes (and in axes that are perpendicular to the direction of acceleration) – causes forces that can briefly deform parts of the machine. The mass and inertia that is generated can therefore create pitching movements during braking and acceleration. The resulting positioning errors are proportional to the acceleration of the moving feed axes. The values of these errors also depend on the stiffness of the guideways, the distance between the feed force application point and the centre of mass, as well as the distance between the centre of mass and the tool centre point. Such errors are not recognised by the machine's position encoders, so the feed axis servo-control cannot react to them. Use of CTC, however, has proved that up to 80% of mean error can be reduced, thereby reducing jerk (changing acceleration) significantly and machining time, says Heidenhain. It is claimed that this decrease in jerk has seen contouring times reduced by up to 15% and mean error half that attained without CTC . Dynamic Precision includes functionality for active vibration compensation, position-dependent adaptation of control parameters, and load- and motion-dependent adaptive capabilities. Heidenhain TNC 640, 620 and 320 control systems will be shown on the company's stand.