The “2 Plus 4” principle has represented the most economical and efficient means of multispindle machining in manufacturing, according to Stama. The company has implemented this principle, with two spindles and four clamped workpieces, in hundreds of existing projects worldwide, resulting in radically reduced cost-per-part scenarios for its customers.
In today’s highly competitive market, however, Stama has recently conducted discussions with its customers concerning greater factory floor utilization and “nonproductive” capacity, leading to the question: Are more than two spindles—perhaps even four—for the simultaneous machining of workpieces economically more reasonable? This challenge has sparked an interesting development at the company: the four-spindle TWIN2 concept that’s now being introduced to the world market for multispindle machining applications.
In answering this two vs. four question, a shop must first verify which productivity upsides will be realized by this concept. Contrary to logical expectations, the four-spindle solution with four clamped workpieces does not result in double the output compared to a two-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 to 70% by adding two more spindles. Individual exceptions with short time-consuming machining operations can reflect an increase of more than 80%, according to Stama research.
While twin-spindle machining needs to double the capacity of the tool magazine, the four-spindle solution requires a tool magazine to handle four times as many tools. The Stama MC 531/TWIN2 is equipped with 56 tool places in the standard version, for example, with options for magazines up to 120 tools.
One major key 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 is not 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 setup while keeping a constant touch time protocol on each machine.
Under these conditions, for many workpieces studied by Stama and its customers, the “4 Plus 4” solution can result in major cost-per-part reduction. With over 25 years’ experience in TWIN spindle technology, the simplicity of a common Z-headstock for twin spindles from Stama is a well accepted and proven technology worldwide.
The simplicity of this system is also used throughout this new TWIN2 technology. Incorporating a state-of-the-art tool presetter, even single-spindle manufacturing challenges with high accuracy demands can be realized with multispindle technology. The outstanding productivity and high workpiece quality achievable are the benchmarks by which Stama TWIN spindle centers are known. The expansion to this four-spindle TWIN2 machining center technology is the logical consequence of the company’s latest research and machine development strategies.
Already in full production use at a Stama customer in one of the BRIC (Brazil, Russia, India, China) markets is a new four-spindle TWIN2 machining center doing ABS housing manufacturing and connecting-rod machining.