Indirect cooling of a cutting tool
A cutting tool having a cutting element such as an insert is cooled indirectly by a micro-channel heat exchanger that is mounted against the rear face of the insert. The heat exchanger is formed with an internal cavity that receives a coolant such as a cryogen. The cavity may include fins to enhance the removal of heat by the cryogen from the insert. Coolant inlet and outlet tubes are coupled to the interior of the heat exchanger to supply cryogen to the cavity. The flow rate of cryogen required to cool the insert during a given machining operation is less than one percent of the amount of standard coolant required to cool the same insert during the same machining operation.
1. A device for indirectly cooling a cutting tool element that is mounted on a cutting tool holder, the cutting tool element having at least one cutting tool edge, the device comprising:
a heat exchanger mounted in the end of the cutting tool holder between the cutting tool element and the cutting tool holder, the heat exchanger having an external surface and an internal surface; and,
a source of coolant for supplying coolant at less than ambient temperature to the internal surface of the heat exchanger; whereby the external surface of the heat exchanger is in heat exchanging relationship with the cutting tool element and coolant that is supplied to the internal surface of the heat exchanger removes heat from the heat exchanger to cool the element.
2. The device of claim 1 further comprising:
a heat exchanger manifold and a cover plate comprising the heat exchanger, whereby when the cover plate is mounted on the heat exchanger manifold, a cavity is formed in the interior of the heat exchanger.
3. The device of claim 2 further comprising:
a coolant inlet tube coupled to a first aperture in the heat exchanger and a coolant outlet tube coupled to a second aperture in the heat exchanger, the coolant inlet tube coupling a source of coolant to the cavity of the heat exchanger.
4. The device of claim 3 further comprising:
a plurality of heat transfer fins positioned in the cavity of the heat exchanger, whereby the heat transfer fins enhance the ability of the heat exchanger to remove heat from the insert.
5. The device of claim 4 wherein the cutting tool element is a cutting tool insert.
6. The device of claim 4 wherein the cutting tool element is brazed or otherwise permanently affixed to the cutting tool holder.
7. The device of claim 4 wherein the cutting tool element is integral with the cutting tool holder.
8. The device of claim 4 further comprising:
a coolant inlet zone in the cavity, the coolant inlet zone including the aperture for the coolant inlet tube and being adjacent to the at least one cutting edge of the element, whereby the coolant entering the cavity first enters the coolant inlet zone to provide maximum cooling to the at least one cutting tool edge of the element.
9. The device of claim 8 further comprising:
a plurality of channels formed between the parallel heat transfer fins, whereby coolant in the cavity flows from the first aperture to the coolant inlet zone and through the channels between the heat transfer fins to provide cooling for the element.
10. The device of claim 9 further comprising:
a coolant outlet zone formed in the cavity on the opposite side of the cavity from the coolant inlet zone, whereby the coolant enters the cavity on one side of the heat exchanger, and is conducted through channels formed between the parallel heat transfer fins to the coolant outlet zone on the opposite side of the cavity.
11. The device of claim 10 whereby the sides of the heat transfer fins are perpendicular to the at least one cutting tool edge and the ends of the heat transfer fins are at an angle to the at least one cutting tool edge so that the coolant inlet zone has the shape of a triangle with the inlet from the coolant inlet tube being located in the triangle.
12. The device of claim 1 further comprising:
a thermal insulator positioned on the end of the cutting tool between the cutting tool body and the heat exchanger, whereby the exchange of heat between the cutting tool body and the heat exchanger is reduced.
13. The device of claim 1 further comprising:
a thermal conductor positioned between the heat exchanger and the element, whereby the exchange of heat between the element and the heat exchanger is increased.
14. The device of claim 10 further comprising:
liquid nitrogen comprising the coolant, whereby liquid nitrogen enters the coolant inlet zone from the coolant inlet tube, passes through the channels between the heat transfer fins, and enters the coolant outlet zone before exiting the cavity of the heat exchanger by means of the coolant outlet tube.
15. The device of claim 14 whereby the liquid nitrogen is able to reduce the temperature of the insert during machining a workpiece by more than 200 Kelvin compared to machining the workpiece using dry machining techniques.
16. The device of claim 14 whereby the liquid nitrogen is able to reduce the temperature of the insert when machining a workpiece using a flow rate that is less than one percent of the flow rate required for synthetic coolants when machining the same workpiece.
17. The device of claim 14 wherein the liquid nitrogen in the heat exchanger uses the latent heat of vaporization of the liquid nitrogen to remove heat from the element.
18. The device of claim 1 further comprising:
liquid nitrogen comprising the coolant that is supplied to the internal surface of the heat exchanger, whereby the liquid nitrogen in the heat exchanger uses the latent heat of vaporization of the liquid nitrogen to remove heat from the cutting tool element.