Reconditioned driller/borer has high precision

Edited by the Engineeringtalk editorial team Mar 18, 2009

Obled-Sacsum has reconditioned its Poreba boring and drilling machine using a Dualdrive rack-and-pinion-drive system from Redex Andantex.

This subcontractor of complex components now has a high capacity, precision machine capable of holding workpieces of up to 100 tonnes, with dimensions of 10m x 6m and a precision of +/-2/100mm on positioning.

High speed is a fundamental characteristic of this type of large capacity machine since it can work continuously on the same product for three weeks.

It contributes directly to the profitability of the production equipment.

The cost of the refurbished model is six or seven-times less than that of an equivalent new machine.

Obled-Sacsum, having first invested in the latest generation of numerical control, then dedicated its research efforts into precision and productivity benefits.

In this area, it is clearly mechanical drives that have largely contributed to the machine's improved performance.

The critical axis is the 10,000mm stroke X-axis, which is why the company decided to install a rack and pinion Dualdrive system from Redex Andantex.

The specifications were essential for circular profiles (circular interpolation on two synchronised axis).

'Before, this was impossible for us as the contours had to be carved,' said M Basile, head of maintenance.

'At present we are attaining tolerances of +/-2/100mm.' To guarantee this simultaneous rigidity, high level of precision and elevated dynamic capacity, Obled-Sacsum chose Dualdrive from Redex.

'We were satisfied with our first experience of Redex, which concerned the modification of the Z-axis on a large engine lathe with 8m stroke,' added Basile.

'On this machine we used a Dualdrive rack-and-pinion-drive system with mechanical preload.' Dualdrive has two fundamental characteristics: very high stiffness and rigidity, which allows assured, continuous servo control up to the load limit; and zero backlash, eliminated by using two pinions - one to drive the axis and one to preload.

In such a system, two parallel-mounted servo planetary reducers are electrically coupled.

The electrical preload uses a servomotor to drive each reducer, in order to simultaneously apply a frictional torque to the two pinions (to eliminate backlash) and a resulting torque for the overall drive of the system.

The high rigidity of the Dualdrive is derived from its design: the output bearings, which are reinforced by two tapered roller bearings, preloaded and generously oversized; and the output shaft pinion, which is machined directly on the output shaft.

The bearing itself is designed to support the pinion as close as possible to the applied force.

These features mean the Dualdrive offers exceptional rigidity for all axes, often allowing twice the loads and speeds of existing systems.

The Dualdrive design reduces radial deflection, which is the cause of 60 per cent of overall distortion.

In the case of Obled-Sacsum, the position is controlled in a closed loop by a linear encoder positioned on the X axis.