environmentally conscious design & manufacturing

Environmentally Conscious Design & Manufacturing (ME592)

Date: March 20, 2000 Slide:1

Environmentally Conscious Design & Manufacturing

Class 7: Cutting Fluids

Prof. S. M. Pandit



• 100 million gallons of cutting fluid is consumed annually in the United States

• Environmental degradation, Health Hazard

• Need to reduce cutting fluid use

Background and Motivation



C u ttin g F lu id s

+ A d d it ives

S tra ig h t O ils

+ A d d it ives

E m u ls ion s

O il B ased

+ A d d it ives

S yn th e tics

+ A d d it ives

S em i-syn th e tic

C h em ica l

Additives: Organic (Aromatic hydrocarbons)Inorganic (Chlorine, Sulphur, Phosphorus)Biocides, Odorants

Background and Motivation



Introduction

Functions of Cutting Fluids

• Heat transfer- Tool wear & life- Dimensional accuracy

• Lubrication

• Chip flushing, corrosion prevention, cleaning



Introduction

Questions addressed

Why use fluid?Dimensional errordue to heat transfer

How (health hazard)? Exposure to mist



Dimension Error - 1

Surface error

• How we define surface error in the boring experiments:-

Angular position

Out of roundness



Dimension Error - 2

• Single tool boring of aluminum cylinders

• Radial, tangential and axial forces cause deformation



Boring experiments:

Sources of dimensional error:• Thrust force• Heating effects

Role of Fluids on Heat Transfer



Heat Transfer Model

w d2dz2 - 2 H + g(z,t)/k = wq/t

g(z,t): heat source strength, k: Thermal conductivity, H: Ratio of convection coefficient and thermal conductivity.



Temperature History



Surface Error



Cutting Fluid Mist

Mist: formed by condensation or

atomization -- size range from submicron to

20 microns.

Such aerosols are generated during

machining operations such as drilling,

milling, boring, drilling and turning.



Health & Env. Effects - 1

• NIOSH:-1.2 million are exposed to cutting fluids [Hands et al., 1996]

• Bacteria / fungi in cutting fluid produce toxins [Thorne et al., 1996]

• Mist collectors are sometimes ineffective [Leith, 1996]



• Airborne particulate from 5 mg/cu. m to

0.5 and 0.1 mg/cu. m (UAW and OSHA)

• Aerosols from PM10 to PM2.5 and

PM1.0 (EPA)

Health & Env. Effects - 2



Mist in Machining

Modes of mist formation

(1) Liquid film disintegration- Low velocity- High velocityof fluid impact on workpiece

(2) Evaporation / Condensation



Mist in Machining

• Experiments

with mist

formation

during turning



Liquid Film Disintegration

Boundary Layer Theory

Flowing Fluid Film Thickness

Mean droplet diameter of the same order of magnitude as film thickness

Thickness varies inversely with distance and Reynold’s number



Turbulent Splatter

Empirical correlations

• Splatter occurs when the dimensionless group proportional to the Weber number and inversely proportional to the nozzle diameter exceeds 2120

• The fraction splattered can also be predicted (2.5% for high values of the dimensionless parameter)



Drop Mode

Drop diameter (maximum) can be predicted with good experimental correlation by considering equilibrium of surface tension and centrifugal forces.



Ligament Mode

At high flow rates, empirical relations predict ligamentdiameter, which is related to the drop diameter

Ligament diameter

Drop diameter



Evaporation / Condensation

• Supersaturated vapor (P0/Ps>1) will

recondense

• The rate of droplet growth is proportional

to supersaturation and drop size and

inversely proportional to temperature



Mist Droplet Motion

• For very low flow rates (Re < .001), small

particles (diameter < 0.1 micron) experience

Brownian motion

• At higher flow rates and larger particle sizes,

the spatial and temporal aerosol distribution

is a function of gravity and drag



Summary

What have we discussed?

• Effect of using Cutting Fluid on surface

error in boring operations

• Understanding the mechanism of mist

formation

environmentally conscious design & manufacturing

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