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When twins see double

Four spindles
Four spindles cutting four parts can reduce cost-per-part.

If a machine with 2 spindles simultaneously cutting 4 clamped parts radically reduces cost per part, does logic dictate that a machine with perhaps 4 spindles be even better?

To answer this 2 versus 4 question, shops must first verify which productivity upsides will be realized by the addition of spindles. The reason is that productivity benefits can vary between manufacturing processes with different primary machining times. And, contrary to logical expectations, a 4-spindle machine cutting 4 clamped parts doesn’t always double output as compared with a 2-spindle machine cutting 4 clamped parts.

According to Stama America, when considering the primary machining time and the overall cycle time of processes, actual output typically increases by 60 percent to 70 percent by adding two more spindles to the scenario. The company indicated that there are exceptions when it comes to short time-consuming machining operations, where output can increase over 80 percent in some instances.

Another point to consider is that twin-spindle machining requires double the tool magazine capacity, so a four-spindle machine would need to handle four times as many tools.

Stama added that one major key in four-spindle machining, with short tool-to-part contact times, is the load and unload sequences of workpieces. In such cases, as long as the machine isn’t equipped with a quick automatic loading/unloading system, pendulum machining is more advisable. This ensures parallel machining time while loading new workpieces.

Time for loading and unloading can then be as long as the actual cycle time of the machine. This will also reduce necessary operator intervention with the machine, freeing him or her up to run multiple stations in a work cell setup, while keeping a constant touch time protocol on each machine.

Stama and its customers studied many workpieces under such conditions and found that 4 spindles cutting 4 parts can deliver major cost-per-part reductions. Such was the case for one Stama customer who was machining ABS housings and connecting rods with Stama’s 4-spindle Twin2 machining center.

Stama’s twin-spindle technology has been well accepted and proven worldwide. The simplicity of the company’s common Z headstock for twin spindles is also incorporated in the new Twin2 4-spindle machine. The machine is a logical consequence of the company’s latest research and machine development strategies for providing productivity and high workpiece quality

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