Production Machining

NOV 2017

Production Machining - Your access to the precision machining industrial buyer.

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Getting Around According to Mr. Meo, around 90 percent of Koma's tilt/ rotary installations involve the use of what's called a "four- plus-one" approach to five-axis machining. "With this most common approach to five-axis machining, these shops are fundamentally trying to access five sides of the part, but don't necessarily require contouring capability for most of their applications. "Most shops are trying to get around the part with a single handling. e biggest killer in a machine shop is usually setup time, and using these accessories for positioning can reduce multiple setups. e idea is that with a tilt/rotary table, the shop can access five sides of a part without the need to stop the machine and re-fixture the part. Eliminating multiple handlings provides reduced runtime and better accuracy." In operating a four-plus-one system, one axis is always idle, but the axis selected to be idle can be changed at any point in the program. For example, the first machining operation may involve XYZ and A axes while the geometry of a second part may best be machined using XYZ and C axes. In effect, the four-plus-one system uses four programed axes at one time with the ability to actuate the selected fifth axis as needed. Simultaneous Five-Axis Machining Even though most of the work that moves across VMCs equipped with rotary/tilt tables requires positioning access for the cutter to machine the part, some applications do require simultaneous five-axis machining capability. For Koma, its line of rotary/tilt tables are capable of simulta- neous five-axis motion if an application needs it. One workpiece that is emblematic of the need for simultaneous five-axis machining is the turbine blade. Its geometry requires the cutter to be engaged with the work for the entire machining cycle in order to machine the blade satisfactorily. Because of its intricate geometry, full contouring is the only way to process the part. Making it Go e actuation mechanism for a rotary/tilt table generally uses a servo-drive worm screw and worm wheel setup to accurately move the rotary table and tilt components. According to Mr. Meo, Koma has recently introduced a new drive system for its rotary/tilt tables that company staff feels is an improvement over the traditional worm screw and worm gear mechanism. "We call it ball drive technology, and it has been success- fully integrated into our four- and five-axis tables," Mr. Meo says. "e new system is able to provide high-speed movement (100 ipm) with no mechanical backlash. e design of this new bi-directional actuation system elimi- nates wear compared with a conventional drive system, which maintains the accuracy of the unit over a significantly longer period." Movement is important, and these tables have software routines that control the acceleration and deceleration of the unit from one position to the next as part of the program. Also critical is the unit's braking capability. Cutting forces put a high demand on the static torque capability of a rotary/tilt unit. e Koma unit uses a dual tapered mechanical braking system that is pneumatically actuated. is mechanical system works in conjunction with the self-braking characters of the ball drive technology. In Control e machine tool's CNC is often the limiting factor for shop's planning on adding rotary/tilt table capability if the goal is simultaneous five-axis machining. While most controls can handle simultaneous four-axis machining, five-axis machining is generally not standard on a VMC's CNC. Mr. Meo recommends that if a shop anticipates moving from three-, four- or five-axis capability,it should check before making the original machine purchase. e difference between full five-axis simultaneous capability and the more common four-axis capability is a matter of cost, which becomes fairly insignificant when compared with added ability to machine complex workpieces later when a rotary/tilt table is added. :: Automation integration is among the capabilities Koma Precision can provide its customers to get the most productivity from a given installation. MILLING/MACHINING CENTERS 30 PRODUCTION MACHINING :: NOVEMBER 2017

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