INDEX THROWS AWAY THE RULE BOOK IN DESIGNING NEW LATHE

A world first is claimed by German turning machine manufacturer, Index, for its new C-Series of twin-turret, twin-opposed-spindle bar automatics, which sees the disappearance of the conventional compound slide for turret movement. In its place is a patented guideway system employing two plates sliding directly over the 75-degree slant bed. The turret is mounted on the front plate while the rear retaining plate is kinematically driven in X and Z.

The beauty of this system is that the distance between the turret centreline and the point at which it is driven is shorter than for a compound slide, making it several times stiffer. The result is greater rigidity and better damping, leading to higher accuracy machining, even for strenuous applications involving intermittent hard turning and reaming. Tool life is also extended.

The turret and drive plates are fitted with ceramic-coated, hardened tool steel strips at top and bottom which slide over a third plate of surface-hardened cast iron fitted into the bed, the latter plate being effectively sandwiched between the other two. The parallel kinematic drive to the rear plate is effected by three ballscrew-actuated rods at the back of the machine, two vertical and one horizontal. Glass linear scales provide positional feedback.

The system is faster than a compound slide, allowing rapid traverse rates of 25 m/min in X and 50 m/min in Z, and acceleration of 1g. As a result, the manufacturer says that the lathe reduces cycle times by between 10 and 30 per cent compared with other twin-turret, twin-spindle lathes on the market.

The compact turret design contributes to a small machine footprint, allowing four C-Series lathes to fit in the space occupied by three equivalent turning machines from other manufacturers. Additional space in the working area also makes for better access and chip evacuation. Both turrets are equipped with a 70 mm Y-axis for even greater versatility when mill-turning highly complex components.

Available in two sizes through sole UK agent, Geo Kingsbury Machine Tools, the Index lathes are called SpeedLine C42 and C65, the numbers representing the maximum bar capacity in millimetres. The 6.5 tonne machines are being built at the rate of one per day at the Index factory in Esslingen, where an 18-stage flow line and adjacent turret assembly line have been set up at a cost of EUR 1 million.

A full C-axis and 27 kW of spindle power are provided at both ends, delivering top speeds of 6,300 rpm and 5,000 rpm for the respective models. Clearance between the 140 / 160 mm diameter chucks for between-centres work is 615 mm. The patented, air-cooled spindles are manufactured in-house, allowing close quality control to be maintained.

The opposed spindle is not only powerful but also has the unusual option of 150 mm of X-axis movement in addition to 600 mm of longitudinal travel. By electronically coupling the movements with the X / Z motion of a lower, double-sided, 24-tool turret (optionally available in place of the single-sided version), Index provides the ability to have three tools in cut simultaneously.

This is achieved by deploying the upper 12-station turret and the left face of the lower turret to machine a component in the left hand spindle while the 'slave' right hand spindle follows the latter turret around, enabling a parted-off component to be machined using the right face of the lower turret. In other words, the X- and Z-axis movements of the lower turret resulting from the cutting cycle in the left hand spindle are continually allowed for in the programmed movements for back-working.

Driven tool capacity is 8 kW / 6,000 rpm, available at all 12 stations of each turret. Noteworthy also is polygon generation using a head mounted directly on the counter spindle rather than on a turret, ensuring vibration-free machining and hence greater accuracy and longer tool life, especially when cutting alloy steels. Control system is the Siemens 840D; and any bar magazine can be fitted to suit the customer.

Model of the Index C-Series lathe seen from the rear, showing the parallel kinematics employed to drive to the turret plate assembly.

The turret of the new Index C-Series lathe is mounted on a front plate linked to a rear plate driven by kinematic rods behind the bed. Fitted with ceramic-coated steel strips, the plates move over a hardened, cast iron insert in the bed structure.

The working area of the Index C42/65 showing three tools in cut simultaneously, made possible by endowing the right hand spindle with two linear axes so that it can shadow the lower turret as it assists the machining of a component in the left hand spindle.