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Milling With High Pressure Coolant (HPC)
There are no strict definitions of high and ultra high pressure coolant (HPC and UHPC
correspondingly). Traditionally, machine tools feature coolant supply at 10-15 bar
(145-217 psi) pressure. This level is now considered as low pressure. Some CNC machine tool MILLING TITANIUM
equipment producers manufacture what are known as “medium pressure” pumps; these have values
of up to 50 bar (725 psi). Various modern machining centers have the option to supply coolant at
rates of 70-80 bar (1000-1200 psi), which is considered as high pressure coolant. High pressure
coolant features coolant flow pinpointed to its target. Today the industry adopts machining with ultra
high pressure coolant that relates to pressure values of 100-200 bar (1450-2900 psi) and even higher.

There is growing interest in cutting with HPC due to the ultimate performance of this method,
especially when heat generation rate during machining is high. As milling titanium relates to processes
with intensive heat emission, it is no wonder that HPC has focused titanium manufacturers’ attention.

Heat generation is a permanent feature of machining. If heat generation is intensive,
the conventional low pressure coolant forms a vapor layer on the surfaces of a tool
and a workpiece. This layer acts as heat sealing, producing an insulating barrier
and making heat transfer harder, which significantly shortens tool life.

Pinpointed high pressure coolant penetrates the barrier and helps to overcome the problem.

• HPC improves tool life of a cutting edge due to reducing oxidation and adhesion wear
and increasing crack strength.
• HPC chills chips quickly, making them hard and brittle. The chips become thinner and smaller,
and they break away from the workpiece more easily. High-speed coolant flow removes
the chips. This significantly improves chip evacuation and prevents chip re-cutting.
• HPC improves chip evacuation because the chips diminish in size, and the high-velocity
coolant flow takes them away easily. It allows the design of cutters with smaller chip gullet,
leading to a higher number of cutter teeth. Effective cooling reduces the temperature in the
cutting zone, ensuring an increased angle of engagement AE (i.e. width of cut ae).

 Overall, HPC provides a good solution for increasing cutting speed
and feed rate for boosting productivity, which is based on:
- transforming improved tool life in higher cutting speed,
- increasing feed rate by using a tool with more teeth comparing with the
tool of same diameter that is intended for low pressure coolant,
- milling with greater width of cut.

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