Multis Get Back In Vogue

Remember the vast multi-spindle shops operated by the roller and ball bearing manufacturers? I know of many companies that ran rows of ACMEs and Conematics and then went almost completely over to CNC single-spindle automatics. Setups on the CNCs took hours—and less—instead of 1 to 2 days on a cam machine. However, these companies found they could not get the same production from a single-spindle CNC.

Also, the cost of replacing already depreciated multi-spindle machines with brand new CNC single-spindle automatics was not that attractive. In Europe, the likes of Tornos and Schutte began to attack the setup problem on multis with preset tooling, which sliced some hours from downtime. Installing CNC slides and replacing expensive form tools with single-point cutting also helped, provided that the single-point tool operation was not the longest operation out of six or eight cycles.

Some 15 years ago, Swiss Tornos, rather bravely, introduced an all-CNC multi-spindle automatic and sought brave customers. Tornos found some.

On high-value components, where the machining operation was only a small percentage of added value, a case for this multi-spindle could be made. It allowed the user to do things that could not be done on a cam-follower machine.

The development of digital servodrives, slicker preset tooling and fast-changeover collets, coupled with faster programming techniques, may be turning the tables again in favor of multi-spindle autos.

Tornos says it pioneered the ‘electronic cam’ control originally for its Deco 2000 CNC Swiss-type sliding head autos and has since applied it to its multi-spindle machines. A CNC program replicates the action of the cam.

Also, the development of high speed response servodrives allows the CNC, it is said, to faithfully reproduce the smooth actions of the cam. It is generally accepted that the sliding-head auto is the nearest a single-spindle auto can approach to the sheer output volume potential of a multi-spindle machine. Now the multi-spindle machine is stepping out in front again. Tornos introduced its MultiDECO 20/8, a 20-mm (3/4") eight-spindle automatic. Each machining setup is programmed individually, and in seconds one MultiDECO can swap from one job to a different job—assuming that the standard tool layout is suitable.

While Tornos has been developing the smaller capacity multis, Schutte concentrated on the larger machines. The German company has developed the Schutte Integrated Control System, which can manage up to 40 axes. The operator programs the CNC using either simulated cam templates or standard ISO commands. The software computes tool pre-setting values. It also coordinates the setting of toolholder assemblies and cutting tools.

The company has also produced Z-axis traverse units, which convert cross-feed and end-working slides into compound slides. These are found on the Schutte S51 PC six-spindle, a 51-mm (2") bar multi. All of the above developments bring tool setting time down to a few hours instead of 1 to 2 days.

Those keen on working at the right cutting speeds—cutting some ‘sticky’ austenitic stainless or problematic aircraft alloys—will always say that a single main drive to a multi-spindle layout means compromising on cutting speeds across spindles.

On Index Werke’s MS 36, six-spindle, 36-mm bar (1 3/8") multi, each spindle has its own AC drive motor. Also, there are ten cross-slides and six end-working slides that can have two-axis CNC.

Index will also sell the MS 32, a 32-mm (1 1/4") machine that comes with six counter-spindles, so if complex components machined in large batches at ‘one hit’ are wanted, this machine could be the one.

So, when you cruise around EMO in Hanover this month, on the lookout for faster ways of producing large batches, take a second look at the CNC multi-spindle machine and what it can do. Be prepared to be surprised.