4 Spindle Technology "TWIN˛"
The "2 Plus 4" principle has represented the most economical and efficient means of multi-spindle machining in manufacturing. This principle, centered around applications using 2 spindles and 4 clamped workpieces in hundreds of existing projects worldwide, has radically reduced cost per part scenarios for its users.
In today's highly competitive market, however, concerns for greater factory floor utilization and "non-productive" capacity lead to the question, "are more than 2 spindles - perhaps even 4 - for the simultaneous machining of workpieces, economically more reasonable?" This challenge has sparked an interesting development: The 4-spindle TWIN2 concept that's now being introduced to the world market for multi-spindle machining applications.
In answering this 2 vs. 4 question, a shop must first verify which productivity upsides will be realized by this concept. Figure 1 shows the productivity benefits with a 4-spindle solution on completely different manufacturing processes with different primary machining times. Contrary to the "logical" expectations, the 4-spindle solution with four clamped workpieces does not result in double the output, compared to a 2-spindle production with four clamped workpieces.
Figure 1. Comparison of productivity benefits with a 4-spindle solution on completely different manufacturing processes with different primary machining times. Contrary to the "logical" expectations, the 4-spindle solution with four clamped workpieces does not result in double the output, compared to a 2-spindle production with four clamped workpieces.
In the relationship between the primary machining time and the overall cycle time of the process, the actual output will usually increase by 60 percent to 70 percent by adding two more spindles. Research shows that individual exceptions with short time-consuming machining operations can reflect an increase of more than 80 percent. While twin spindle machining must double the capacity of the tool magazine, the four spindle solution requires a tool magazine to handle four times as many tools. The MC 531/TWIN˛ is equipped with 56 tool places in the standard version, for example, with options for magazines up to 120 tools.
One major factor in four spindle machining, with short tool-to-part contact times, is the load and unload sequences of the 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 result in less time when the operator is interacting with the machine, thereby allowing the operator to run multiple stations in a work cell set-up, while keeping a constant touch time protocol on each machine.
Under these conditions, for many workpieces studied by users, the "4 Plus 4" solution can result in major cost per part reduction. The simplicity of a common Z-headstock for twin spindles is well accepted and proven technology worldwide. The simplicity of this system is also used throughout this new TWIN˛ technology. Incorporating a state-of-the-art tool presetter, even single spindle manufacturing challenges with high accuracy demands can be realized with multi-spindle technology.
The outstanding productivity and high workpiece quality are the benchmarks by which multi-spindle centers are known. The expansion to this 4-spindle TWIN2 machining center technology is the logical consequence of the latest research and machine development strategies. For example, already in full production use at a STAMA customer in one of the BRIC markets is a new four-spindle TWIN2 machining center, currently doing ABS housing manufacturing and connecting rod machining. This is evidence of the simplicity and practical application of this new, highly productive manufacturing equipment.
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