Considering resonant frequency, Index-Werke has redesigned of CNC turning centres to reduce vibration and double the machine structure stiffness to maximise metal removal rates.

Index-Werke noted that the higher the resonant frequency (RF) of a machine tool’s structure, the greater is its inherent stiffness Consequently it becomes more difficult for machining forces to induce vibration

This article was originally published on Manufacturingtalk on 26 Aug 2003 at 8.00am (UK)
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So Index has redesigned its patented SpeedLine C-type CNC mill-turning centres to increase their RF above that of all other lathes on the market.

Geo Kingsbury Machine Tools, launched the machines in the UK at the recent MACH 2008 machine tool exhibition.

Using the RF measure, the Index C-type lathes are over twice as stiff, or rigid, than the existing Index G-series models of equivalent capacity.
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The company said that there is more scope for finding the ’sweet spot’ for any combination of toolholder, cutter and workpiece material.

The design allows depth of cut to be increased for maximum metal removal rate.

* Improved surface finish - as well as increasing productivity, the increased rigidity and lower machine tool vibration also ensure good surface finish of the machined part, said Index, as well as prolonging tool life and reducing noise.

Index said that better damping leads to higher accuracy machining, even for strenuous applications involving intermittent hard turning and reaming.

The SpeedLine C-type 42mm and 65mm bar automatics, when launched in 2005, were the first in the world to replace conventional compound turret slides with two interconnected steel plates sliding directly over the machine bed.

The recent redesign of the range has seen these machines improved and two new models introduced with 30mm and 90mm bar capacities.

The defining characteristic of the lathes that provides such high RF and stiffness hinges on the actuation of the turrets.

Each is mounted on a front plate while an interconnected rear retaining plate is driven kinematically from behind the machine bed.

The critical advantage is that the distance between the turret centreline and the point at which it is driven is much shorter than for a compound slide.

Up to 14 tools can be used in each of the three turrets in the following manner.

* Turret 1 moves in X-,Y- and Z-axis above the spindle centreline and works at the main spindle.

* Turret 2 mounted below the spindles operates in X-, Y- and Z-axis at either end.

* The motion of upper turret 3 is restricted to the X-axis and works only with the counter spindle, which moves in the Z-axis.

Three tools can be in cut simultaneously for high productivity.

There are two sizes of machine frame, designated C100 and C200.

The former is the ‘host’ for the 30mm and 42mm bar capacity spindles and the latter (shown at MACH 2008) is for the 65mm and 90mm spindles.

Distance between the main and counter spindles is 510mm and 710mm respectively.

All models are fast, with 1G acceleration in X- and Z-axis up to 60m/min for the smaller machines and 50m/min for the larger models.

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