Using High-pressure Coolant

Internal machining capitalizes on the advantages of machining with high-pressure coolant

By Christer Richt

January 1, 2011

Proper application of high-pressure coolant has a positive effect on chip breaking and heat.

Applied at high pressure, coolant becomes much more effective in removing heat.

Machining with high-pressure coolant is not as intimidating as many often assume. 

As a rule, it can be achieved with standard tooling that is easily retrofitted to an existing machine. In some cases, it can even be used as part of the original equipment, providing an even greater advantage.

In fact, the majority of current CNC machines contain a coolant supply with sufficient flow and pressure, but it’s often an untapped asset that could provide substantial benefits, especially to shops working with challenging materials.

Chip formation and machining temperature are two of the main challenges when working with the exotic materials often encountered in the aerospace and energy industries. Even when performance and results already have been optimized with tooling and insert technology, adoption of high-pressure coolant machining can raise the ceiling for further improvements.

Titanium, superalloy, and some stainless steel machining often results in chip formation that proves troublesome. Long, unbroken chips can accumulate quickly into swarf that can damage parts and tools, as well as require frequent machine stoppages to clear the work area. This is especially true in medium- to finish-turning applications, in which chip thickness is more uncontrollable and chip breaking is typically more of a challenge.

These materials also possess relatively low thermal conductivity, making it difficult to transport heat away from the machining zone. The resulting high temperatures are hard on even the most modern inserts, increasing tool wear.

The Benefits of High Pressure

The proper application of a jet of high-pressure coolant has a positive effect on both chip breaking and heat. In fact, these benefits can be achieved even on a reduced scale through the use of a well-directed jet at lower pressures.

A high-pressure coolant system can break previously unbreakable chips. It also can enlarge the chip-breaking area for an insert geometry. This happens because the jet not only has a forming effect on the chip, but also cools it, making it more brittle and easy to break.

In terms of machining heat, the coolant forced into the cutting zone has a significant impact on transporting heat away from the part and tool. A coolant at flow can help stabilize component temperature, but it does not penetrate the barrier. Applied at high pressure, though, the coolant becomes much more effective in removing heat. This increases tool life and allows for the use of higher cutting data.

A fixed nozzle will help ensure optimal performance of a high-pressure coolant system and help eliminate inconsistency from the process. The design and quality of the nozzles and delivery through the cutting tools, toolholders, and spindle interface also play a crucial role in getting the most out of the system.

Internal Machining

Proper application of high-pressure coolant has a positive effect on chip breaking.

Internal machining is particularly well-suited to capitalize on the advantages of high-pressure-coolant machining. A number of unique tools on the market can be used in boring applications for all depths and sizes of holes.

Operations such as profiling; grooving; pocketing; and deep, straight boring typically are characterized as the most challenging for the use of coolant. A high-pressure system achieves suitable chip breaking in these applications and also provides efficient chip evacuation.

Modular boring bar systems offer a range of boring bars, adapters, and toolholders, giving shops the flexibility to build many different optimized tools from a limited inventory.

Geometric features common to many aerospace and energy components often provide challenges in terms of external and internal confined spaces. The use of high-pressure coolant with extended tools can achieve stability and accuracy, even with these long tool reaches. Some of these tools incorporate dampening characteristics, transforming traditionally problematic applications into secure and productive processes.

There are a few prerequisites to integrating high-pressure coolant into a machine.

For turning, the coolant system must provide a flow rate of at least 5.28 gallons per minute (GPM) and a basic pressure of 70 bar. In milling and drilling applications, the system must provide a flow rate of at least 13.21 GPM, to accommodate the extra nozzles on the milling cutter and large drill diameters.

Additionally, a few machine capabilities are necessary to integrate a high-pressure coolant system.

Throughout the machine’s coolant system, seals and valves should be confirmed to handle 70 bar and 5.28 GPM for turning or 10.56 to 21.13 GPM for multitasking. Use of the correct M-code is vital for operating the coolant pump, and when high volumes of coolant are required, it is useful to have a machine option allowing variable pressure.

Last, high-pressure coolant should be used to augment tooling optimization, not replace it.

Selection of the most suitable insert shape, geometry, grade, entering angle, and cutting data has a profound effect on performance and tool life.

A high-pressure coolant system can improve results even further, but it should never be used as a substitute for the right tools for an application. By approaching the application holistically, a shop can achieve and sustain a considerable competitive advantage.

For more information, visit www.sandvik.com.