Technological advances in machining are a tug of war between machine, tools and software. These advances include machines with additional axes for both milling and turning adding increased functionality and reducing the number of process planning operations. Machines are becoming more versatile and automated while CAM software for programming maximizes their capabilities, and tooling has become more multifunctional with broad acceptance of modular tools.
The question of highpressure coolant usually arises when investment in the latest machine technology is being considered. Now that 1,000-psi coolant delivery is a standard option on most hightech machines, the question is: What are the considerations and benefits of using highpressure coolant?
With high-pressure cooling, the coolant effectively removes heat generated by the cutting process before it can accumulate and increase temperatures to the point at which tooling and workpiece surfaces are damaged.
With traditional flood cooling — which delivers coolant at low pressures — , the high performance levels of modern machine tools generate so much heat that the coolant is heated beyond its boiling point and creates a blanket of vapor that insulates the cutting zone from the coolant. That reduces the coolant’s ability to remove heat.
High-pressure, highvelocity coolant eliminates the vapor barrier so the heat that is generated is removed effectively at a high rate.
Another advantage of highpressure coolant is that it can penetrate to the tool’s cutting edge to provide a short shear zone that leads to the creation of thin chips that readily break into small pieces over the base material. On the other hand, low-pressure or flood coolant results in a long shear zone that produces a thick chip in many materials that does not readily break. The result is long, stringy chips that are hard to control and can wreck havoc on machine equipment and require manual removal. Broken chips that fall away from the tool and workpiece, or are blown away by the force of the coolant, prevent these chip-related problems. For secure lights off production, chip control is critical to productivity.
Harnessing the coolant pressure, producing a highpowered controlled jet and delivering the coolant to the correct position on the cutting tool to ensure a consistent performance is a challenge.
The days of an external coolant pipe have gone. Through-spindle and throughtool coolant delivery eliminates previous plumbing difficulties, and now are the norm for the rotating spindles that are on machining centers and multitasking machines.
One example of an effective high-pressure coolant delivery system for turning centers, vertical turning lathes and multi-task machines is the CoroTurn HP system from Sandvik Coromant (www.coromant.sandvik.com/us).
This system automatically plumbs coolant through a standard, Coromant Capto, machine-adapted clamping unit. Through either the turret or spindle, the Coromant Capto coupling directs a high pressure coolant jet through small nozzles that are mounted close to the insert cutting edge. The resulting increase in velocity of the coolant jet produces a hydraulic wedge that lifts the chip from the material, while reducing the temperature quickly and effectively and improving chip control.
Tool change is fast, and the nozzle position is fixed to the correct point on the insert for consistent performance. The nozzle position does not require adjustment for each tool change.
Sandvik Coromant says there are several benefits over traditional methods in the application of 1,000-psi coolant when turning with this system, including:
Improved chip control for finishing all materials.
Increased tool life when machining difficult materials, such as stainless steels, titanium and Inconels.
As much as a 50 percent increase in cut capability at the same cutting parameters.
And, the ability to increase cutting speed by 20 percent in aerospace materials, such as titanium and nickel alloys, while maintaining the same cutting distance.
Although coolant normally is detrimental to tool life with ironbased materials, coolant always is recommended for milling aerospace materials, such as titanium and nickel alloys.
The predominant aerospace milling operation is 2D profiling and pocketing with long edge or porcupine cutters. Supplying high-pressure coolant, to every insert to evacuate the chips provides process security and longer tool life.
The challenge with long edge cutters is the high number of inserts/ coolant holes; the larger the coolant hole diameter and number of holes the greater the pump volume that is required to deliver the required pressure.
The new Sandvik Coromant CoroMill 690 long edge cutter was developed for 2D profile milling of titanium components. The cutter is highly resistant to axial forces and its four cutting edges provide productive and economical machining.
CoroMill 690 has threaded holes for installing nozzles and holes can be blocked off when not required. The nozzle with 0.04-in. hole size reduces the pump volume requirement while maintaining the high-pressure flow. For example, the reduction from 0.1-in. coolant hole to 0.04-in. nozzle reduces the flow requirement from 125 gallons per min. to 14 gallons per min. for ten holes at 1,000 psi coolant pressure.