Smooth 5-axis machining

Fanuc has introduced a "Smooth TCP" function for its 30i and 31i-A5 Series CNC control systems.

The function is a selectable mode in Tool Centre Point Control, and improves the actual motion path of the axes in a 5-axis machine program and so contributes to a uniform tool traversing movement. The benefits gained are smoother surfaces and shorter cycle times. Tool compensation features addressing compensation of tool length, direction and radius are standard options, "Smooth TCP” compensates deviations in the tool orientation. In addition Smooth TCP also ignores redundant commands related to tool centre-point position. The cause of, and starting point for, Smooth TCP are 5-axis machine programs generated by CADCAM systems in which the respective milling paths and direction vectors are established for a tool. Even with 100 per cent reliable correspondence, part programs will contain discontinuities concerning the alignment of the tools. Even when these deviations only amount to a few tenths of a degree, they give rise to compensating movements in the rotatary axes, which in the end will result in slowed movement or even in path movement being stopped. The result is visible traces on the workpiece surface and loss of time, which was approximately 10 per cent on average in different tests. In extreme cases, time savings of up to 44 per cent could be achieved with Smooth TCP. Furthermore, another positive side effect is the minimisation of machine or tool wear due to avoidance of jerk in the motion profile. With an activated Smooth TCP function, the CNC control system detects all the discontinuities in the tool position in advance. The user employs parameters to define a tolerance band within which the control system makes appropriate corrections in the execution of the machine program and provides for a more uniform tool movement. Tolerances of around ±0.5° are generally selected for finish machining. It also pays to use Smooth TC for roughing, since considerably shorter machining times can be achieved. In this case the tolerance band can be set a little larger.