An 8-station, 3-axis turret (including Y-axis movement) has a half-indexing mechanism that allows tools to be mounted in up to 16 positions, while multiple tool holders can further expand the number of cutters deployed. There is also Y-axis travel on a gang tool post, giving extra flexibility when machining at either spindle, especially as the counter spindle moves in the X axis as well as the Z axis.
In total, up to 45 tools can be resident in the working area. A superimposition function within the Mitsubishi M730VS control provides the potential for even shorter cycle times by enabling up to three tools to be in-cut simultaneously, at both spindles.
The 3.74-tonne BNA-42GTY enjoys the same build and thermo-symmetrical design as other lathes in the Miyano range. Slideways are hand scraped in all axes and have high damping characteristics, enabling heavy metal removal and helping to prolong tool life. Machine specifications include a 6000 rpm/11 kW main spindle with 0.001° C axis, a 5000 rpm/5.5 kW C-axis counter-spindle, and feed rates up to 30 m/min.
Numerous options are available, including high-pressure coolant, spindle air blow, chip conveyor, parts catcher, parts conveyor and drill-breakage detection. Likewise, the control can be augmented with the addition of helical interpolation, corner radiusing, synchronous tapping and multiple canned cycles.
The BNA-42GTY is the first Miyano machine to gain the benefit of Citizen's LFV chip-breaking software, until now exclusively provided on the manufacturer's Cincom Swiss-type lathes. The patented, two-axis chip-breaking functionality is part of the control's operating system and involves the axis servo drives and spindle drives.
Tool-tip position is oscillated by 20 micron, just sufficient to break the swarf, while the number of oscillations per revolution (mode 1) or the number of revolutions per oscillation (mode 2) determines the length of the swarf removed from any type of material. Users can define the exact chip length in the program, giving the ability to choose the optimum size for the swarf conveyor to handle efficiently.
The more exotic and difficult-to-chip the material, the more effective the LFV. As a result, high-pressure coolant is not needed to assist in breaking long stringy swarf, such as that generated when machining materials like stainless steel, copper and plastic. So, it is no longer necessary to stop the cycle to remove any accumulated swarf that is hampering the machining process. Shorter chips also take up less room in the swarf bin, so it needs emptying less frequently.
In some applications, particularly when processing exotic materials, productivity can be increased fivefold due to not having to stop the machine repeatedly to clear swarf that has entangled itself around the tool or workpiece, or both.
With LFV there is an element of air cutting, which allows more coolant to access the point of contact between the tool and the material. Enhanced coolant penetration lowers the operating temperature of the tip, so it can last five or even 10 times longer.
An LFV oscillation results in a turned face that is no longer flat by an amount measured in microns. The machine control knows where the oscillation took place and, on the second revolution, the high spot on the face is turned away. If required, on the third revolution the tool will finish the process to eliminate the waviness completely at that location.
As an element of air cutting - albeit miniscule - is introduced by LFV, productivity can be slightly reduced when the function is switched on. However, LFV can be turned off at the control, allowing the possibility of maximum output during attended day shifts when an operator is present to clear swarf. It may be, however, that these machine stoppages lower production output by more than LFV.
Switching the function on at night allows a ghost shift to be instigated without the fear of swarf build-up halting production during unattended running.