Strategies for avoiding problems during drilling and especially deep-hole drilling operations include different types of coolant delivery. Three types of coolant systems are common: flood coolant, low-pressure through-spindle coolant and high-pressure through-spindle coolant.
With flood coolant, less and less coolant reaches the tool tip the deeper the drill penetrates the workpiece. Eventually, no coolant can get to the bottom, and machining occurs dry. As a result, chips become impacted in the flutes of the tool even though coolant is visibly flowing over the top of the hole. In fact, the hole ends up being dry cut, while the tool heats up and is subjected to premature wear or breakage.
The essence of successful deep-hole drilling requires a method of getting coolant down to the tip of the drill where it can remove heat and evacuate chips. Coolant-through-spindle systems provide the best solution.
Systems that deliver coolant at high pressure, such as the Cooljet coolant pressure systems, which boost coolant pressure to 70bar (1000psi), provide even better chip evacuation.
With high-pressure coolant-through-spindle systems, not only is pecking eliminated or reduced, but higher feed rates and spindle speeds also can be used. As a bonus, the system extends the life of the tool. High-pressure coolant-through-spindle systems provide the best scenario for decreasing cycle time and increasing tool life. The high pressure of the coolant breaks up chips and forces them up the flutes and out of the hole. Cycle times go down, because the pecking process is eliminated while spindle speeds and feed rates can be increased. With higher feed rates, chips tend to form better.
However, retrofitting a machine for high-pressure coolant supply can be a costly exercise and for many operations the extremely high-pressure of 70bar is not always necessary.
Medium-pressure coolant systems can be a good alternative, because they still have a positive effect on both chip breaking and heat. The coolant forced into the cutting zone at a medium pressure is more effective in removing heat than at low pressure and increases tool life and allows the use of higher cutting data.
The new Cooljet Medium-Pressure Unit features a fixed coolant flow of 30l/min (8gpm) at 20bar (300psi), a single high-capacity filter and a 150 litre (40 gallon) tank. The unit allows for a quick and affordable installation, without the need to modify the machine tool. A Plug&Pump interface developed by Cooljet allows rapid and intelligent connection.
According to Dimac Tooling, the medium-pressure system is an ideal alternative to high-pressure coolant, as it only requires around a third of the investment costs, at the same time delivering good chip evacuation, especially for bigger drills. Moreover, it can be applied to a wide range of machine operations and is not restricted to drilling. The high-capacity filter ensures the coolant drawn out of the machine is filtered and re-used, reducing operating costs.
- Fixed flow
- 30l/min (8gpm) at 20bar
- Single Filter
- 150 litre (40 gallon) tank
- On board
footprint (0.5m x 1m)
- Din connectors