Motion System Design

Putting a spring in their step

Increasing productivity and economy is easily done with CNC-multi spindle automatic lathes because they can process several components at the same time. These machines from Index, Esslingen, Germany, combine these advantages with the precision and short set-up times of single spindle CNC machine tools. The company's CNC-multi spindle automatic lathes can be used for series production of parts as well as for low volumes.

Another design advantage is that the lathe's workspace is easily accessible for retooling. When fully equipped with tooling there is still enough space to allow free swarf flow. Numeric control of all functions means a reduction in changeover times, allowing the Index lathe to change to a new component in less than an hour, rather than the typical changeover time of up to 10 hours for a conventional multi spindle lathe. The result is that machining small batch sizes becomes a viable option.

At the heart of the new lathe is the spindle drum with six individual spindle motors. Its working precision is made possible by a 3-part tooth design (which is typically only used with single spindle machines), support from an arrangement of tool carriers, and compensation adjustments made by the control system. Each of the six spindle motors can be independently controlled, allowing the optimum cutting speed for each process step and/or each particular tool and maintaining a constant cutting speed when facing.

These CNC-multi spindle automatic lathes are often used for series production. If an over-run crash occurs, damage to the feed axis would decommission the entire machine, not only causing costly repairs, but also costs from loss of production. Index machine tools eliminate machine downtime from over-run crashes by protecting the feed axles of their new lathes with Ringfeder friction springs (Ring-springs). In the event of an over-run crash, this load limiting safety device needs to absorb a force of 28,000 N. Ringfeder Ring-springs were chosen as the most appropriate solution, because of their efficiency as a mechanical spring system. A Ring-spring not only absorbs energy by the elastic modulus of the material, but also by the friction on its tapered contact surfaces. This friction spring offers precise energy absorption within a minimal space, is more efficient than either coil or disc springs, and is independent of the load speed or ambient temperature.

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