The traditional role of metalworking fluids is two-fold: lubrication and chip flushing. Whether the application calls for oil or water-based coolant, its function in the operation is to form a hydraulic bushing between the cutting edge and the workpiece that helps the transfer of heat from the tool tip to the chip and then expedites the heated chip’s removal from the cutting zone.
Application of coolant is generally done using indirect flooding of the cutting zone by means of externally mounted tubing. In today’s manufacturing environment, many shops are re-evaluating the way coolant is used in metalworking—especially in turning.
Because it is a continuous cutting process, turning—and drilling—demand the cutting edge be in contact with the workpiece throughout the operation. Back in the day when cutting data were calculated around HSS, flood coolant was sufficient to keep temperatures low enough so the tool kept its edge because feeds and speeds were relatively low.
At today’s machining rates, made possible by advances in machine tools and the use of cemented carbide cutting tools, if coolant is applied conventionally into the machining zone at temperatures as high as 1,832°F (1,000°C), instant evaporation takes place. This leads to formation of a pressurized vapor zone that effectively prevents the flow of low-pressure coolant to reach the cutter edge, hence the development of high-pressure coolant systems on modern machine tools.
However, high-pressure coolant alone is only one part of the equation. To get the benefits of high-pressure coolant systems the flow must be properly aimed on the spot where it is needed. Sandvik Coromant has recently introduced a line of cutting toolholders that harnesses the machining possibilities of high-pressure coolant, which can lead to increased productivity or an increase of as much as 50 percent in tool life.
Called CoroTurn HP (high pressure), these new holders work with the Capto system of modular quick-change tooling. The new system can be applied to any machine equipped with high-pressure coolant supply and Capto couplings including multitasking machines, VTLs and turning centers.
The toolholder is equipped with two to three nozzles positioned and directed depending on the type of tool and application it is intended for. The nozzles are positioned close to the cutter/workpiece interface and, using coolant supplies of 1,000 psi, actually perform an additional function of chip control.
In operation, the HP toolholder penetrates the heat-affected zone created by the cutting action using small nozzles to cool the insert faster and more effectively and allow optimal chip control. The nozzles create a hydraulic wedge between the top surface of the insert and underside of the chip being cut from the workpiece, helping reduce insert wear and breaking the chips into smaller pieces for quicker evacuation from the cutting zone.
Although chip control in roughing operations is less critical, applying coolant precisely using the HP holder reduces cutting temperature and allows for higher cut speeds or longer tool life. Finishing operations, on the other hand, always present chip control problems because of their reduced depth of cut and feed rate. Moreover, as more shops look to perform automated production in either untended or lightly tended machining, eliminating the accumulation of “bird’s nests” is an important benefit.
Thus, applying high-pressure coolant correctly will affect productivity because of the potential for higher cutting speeds and longer tool life with fewer machine stoppages along with better predictability and security for automatic production.