Proving the old adage "Two heads are better than one," Makino's latest sinker EDM option, the high-speed rib head, brings maximum versatility to EDM machines. In the process it also brings up to 30 percent overall cycle time reduction and conducts highly accurate detail work.
The high-speed rib head is attached to an entirely new axis located within the Z-axis. Aptly named the W-axis, it retracts fully into the Z-axis and is powered by linear motors to achieve jump cycles up to 1,600 ipm. This high-speed motion, in turn, reduces out-of-cut time and flushes the workpiece more effectively. The end result is rough machining cycle times as much as 60 percent faster than conventional Z-axis rough machining.
PROVEN TECHNOLOGY
First introduced into the field in 1998, the high- speed rib head was developed to enhance roughing performance on larger sinker EDM machines while reducing rough machining cycle time on smaller mold details and rib cavities.
"Conventional sinker EDM machines rely solely on the Z-axis for carrying the electrode," says John Bradford, Makino's EDM applications specialist. "And while this results in very precise work, cycle times are longer. As cavity depth increases, burn efficiency decreases as chips are typically recut. We saw an opportunity to improve cycle times on applications with smaller details, thin ribs and deep cavities."
The high-speed rib head is currently available on five of Makino's larger sinker EDM machines, starting with the EDNC65 up through the EDNC207. The ability to handle small details on large molds brings added versatility to these machines.
"Apply this technology to a bumper mold application," says Bradford. "This large, complex mold can have detail work with a depth to diameter ratio of up to 100:1 (0.04" wide electrode up to 4.0" deep). A variety of large and small electrodes are required. With the high-speed rib head option, small detail work can be performed on the W-axis, and the balance of the work can be done on the Z-axis."
To handle the various electrodes, the rib head is designed to make tool changes simple. The rib head retracts fully into the Z-axis, providing a completely flat surface for tool changing. Interface tooling is used with a dovetail receiver system affixed to the mounting platen, so electrodes will fit either axis comfortably. The W-axis has plenty of clearance via a hole in the dovetail receiver.
MAKING WAVES
In addition to widespread use in the field, Makino has conducted test cuts and achieved a significant decrease in rough machining cycle times (see table below).
| HIGH-SPEED RIB HEAD CYCLE TIME IMPACT |
| Application |
Roughing Cycle Time Reduction |
| Blind Cavity Pocket |
41 percent |
| Through Rib Machining |
43 percent |
| Blind Rib Cavity |
51 percent |
At 1,600 ipm, the high-speed rib head provides jump motion eight times faster than the Z-axis. This high-speed motion also efficiently flushes the cavity without operator intervention.
According to Bradford, "the high-speed motion creates a hydraulic flushing, which clears chips and gas out of the burn, cleansing the cavity."
BLENDING BALLSCREWS AND LINEAR MOTORS
The ability of a large sinker EDM machine to provide fast and accurate detail work is due in large part to the use of ballscrews and linear motors.
"The rigidity and repeatability of the ballscrew and the linear motor's high speeds provide a perfect blend of each technology's strengths," says Bradford. "The compact, linear axis design enables high-speed movement without heat generation. The combination brings the mechanical advantages needed to perform rough and finish machining effectively."
For finishing, the ballscrew permits high accuracy, repeatability and the rigidity necessary to achieve a surface finish of 4uRmax or finer. This rigidity becomes even more critical to the application as electrode size increases.
Proving two heads are indeed better than one, Makino's high-speed rib head option is eliminating the age-old compromise of speed versus accuracy in sinker EDM machining.
Makino has created several demonstrations detailing the impact this option can have on a sinker EDM application. A streaming video demonstration of the rib head can be viewed by visiting www.makino.com/diemold.