16735627 Cutting Fluids

8/6/2019 16735627 Cutting Fluids

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Cutting Fluids Used For Metal

Cutting

by Brian Boswell


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Infrared Picture Showing Tool Tip

Temperature


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Cutting FluidsThere are two main functions of cutting

fluid while machining, these are:

1. To remove heat generated in the

cutting and so limit the rise of

temperature at the tool cutting edge.

2. To lubricate the area of contactbetween the tool rake face and the

chip reducing friction.


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The Goal of Using Cutting Fluid:

is to improve surface finish and to

increase the tool life by minimising

abrasive wear and build-up edge on the

cutting tool.


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Additional important aspects of

cutting fluid are:

cuttings from the tool interface are

washed away.

the cutting fluid should not cause

corrosion to the workpiece or the

machine tool.


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Maximum and minimum tool

temperature generated during cutting

0

50

100

150

200

250

300

0 10 20 30 40 50 60

Time (s)

Tooltemperature(oC)

dry

wet


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Example of Heat Disposal From

Cutting Tool The power required to cut a material under

certain conditions is 1.97 W/mm3/s. A cut of

6.4 mm deep, with a feed rate of 0.25 mm/revat a cutting speed of 25 m/min. The work iscooled by a flow of 2.3 litres per min ofcoolant, specific heat capacity 3.56 kJ/kg0C,which conducts away approximately 90 ofthe heat produced. The mass of 1 litre ofcoolant is 0.92 kg.

Determine the rise in the temperature of thecoolant due to this cut.


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Volume of metal removed per second = 0.25 x 6.4 x25 x 1000 / 60

= 667 mm3

Power consumed in cutting = 667 x 1.97 = 1.3 kW

Heat produced per min = 1.3 x 60 = 78 kW

Weight of coolant supplied per min = 2.3 x 0.92

= 2.12 kg Temperature rise = 78 x 0.9 / 3.56 x 2.12 = 9.3 oC

Note: The temperature rise is dependent upon the

flow of the cutting fluid.


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Disadvantages of Wet Cutting Adds to the cost of machining of each

part.

Health issues.

Environmental costs.


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Air-cooling

Why use air??

Air-cooling has been tried before but

has never been considered as efficient

as traditional wet cooling.

Can it be improved?

Vortex tube air-cooling.


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Tool tip temperature before

machining has commenced

-4

-3

-2

-1

1

2

3

1 2 3 4

Time (s)

Tool

tiptemperature(oC

)

Ch13 Ch14 Ch15 Cold nozzle teemp.


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Tool tip temperature during

machining


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The Advantages OfAir

Cooling During Cutting

Reduced tool temperature during

machining below that achieved by liquidcoolant

Increase tool life

No environmental damage


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Top rake face after 7 minutes machining

at a cutting speed of 190 m/min

No cooling se Air-cooling being se


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Picture showing chips produced by a 2 mm depth of cut

at 0.23 feed rate, and cutting speed of 190 m/min.

The left hand chips produced during dry cutting

and the right hand produced during air-cooling


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Minimum quantity lubricant

(MQL) This method of cooling the tool tip uses a fine

mist of air-fluid mixture containing very small

amounts of cutting fluid delivered to thecutting zone through the spindle of the

machine tool. Typically this is sprayed

through a 1 mm diameter nozzle at a

pressure of 600 kPa and at a rate of 1 to 100cc/hr, which is approximately one ten-

thousandth of that used in using traditional

coolant.


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They considered three methods

to cool the cutting zone:

1. cryogenically freezing the workpiece;

2. heat conduction using a cold chamber

under the tool tip;

3. and spraying liquid nitrogen onto the

tool tip.


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Tool tip cooled by nitrogen

chamber positioned under thetool tip.


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Conclusion For The Use OfAir

Cooling During Metal Cutting


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The results obtained from using

compressed air combined with thevortex tube have shown that cooling thetool tip is effective.

The temperature recoded during air-cooling was found to be 60 rC which is40 rC cooler than that obtained duringtraditional wet machining.

There are no disposal problemsassociated with air-cooling unliketraditional liquid cooling.

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16735627 Cutting Fluids