Your coolant has two primary jobs - lubrication and heat dissipation. The goal in coolant delivery is to inject the coolant as far as possible into the cut zone so that each wheel grit is lubricated throughout its entire contact run. This is not as easy as it looks though. You need to ensure your coolant system has sufficient pressure to obtain the required velocity needed for the particular operation at hand.
At the same time, having the proper flow rate and temperature control will help dissipate heat away from the cut zone. Laminar (also called coherent-jet) nozzles can improve the effectiveness of both the pressure and flow that the coolant pump is supplying.
Delivery of coolant into the cut zone as a laminar flow reduces the amount of turbulent air that is induced into the coolant stream. Air in the cut zone will decrease the cooling and lubricating efficiency of your coolant so it pays to get your flow as laminar as possible. Laminar nozzles are also more forgiving in terms of the distance your grind point can drift from the nozzle orifice allowing you more flexibility in your setup. If you also grind HSS, coolant delivery and flow to the cut zone are even more critical than for carbide grinding.
To keep sufficient coolant flowing into the cut zone, make sure your coolant nozzles are mounted relative to each wheel pack, ensuring your coolant nozzles are directed at the cut zone while remembering that the cut zone relative to the wheel can alter during the course of an operation and can differ for each operation you perform on the tool.
In some cases, you might find that directing one coolant jet tangential to the wheel, just in front of the cut zone “drags” coolant into the zone more effectively than directing the jet straight at the cut zone.
Keeping these factors in mind can benefit the grinding process by:
• Reducing dressing frequency
• Reducing wheel load
• Producing less thermal damage to the work piece
• Less coolant jet deflection caused by the vapor barrier surrounding the wheel
An often overlooked factor is the cleanliness of your coolant. If your coolant gets contaminated, it adds friction to your process and you’ll find you need to slow your feedrate down, the surface finish of your tools will degrade and your wheels will wear quicker. Dirty coolant cannot efficiently carry grinding swarf away from the cut zone therefore causing the grinding wheel to load up sooner than expected.
Micro sized tools are a good example where clean, temperature controlled coolant delivery are of the utmost importance. The high surface finish and tolerance requirements typically demanded in small tool manufacturing require the wheel to remain very free and sharp in its cutting action to avoid unwanted tool deflection. A good filtration system will help maintain your coolant in pristine condition.
In short, you want to keep your coolant injected deep into the cut zone and whether your grinding process requires heavy stock removal or the fussiest surface finish, good coolant filtration is a major contributor to efficient carbide tool production so keep your coolant clean and mean.