Smith G.T. Cutting Tool Technology: Industrial Handbook

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Figure 204. Computer-Aided Design (CAD), utilised to select a corrosion inhibitor for an aqueous-based

cutting uid. [Courtesy of Cimcool]

Cutting Fluids 403

gies

. As an example of this phenomenon, anionic

emulsiers normally have corrosion inhibiting charac-

eristics, but these properties are usually so slight that

any side-eects are usually disregarded. However, by

using CAD, it is possible to nd emulsiers – normally

several are needed, whose side-eects add up syner

getically.

hen the correct emulsiers are selected and in the

right proportions, not only is the desired emulsifying

action obtained, but at least some of the required cor

osion protection also occurs. In Fig. 204, an example

of the ‘construction’ of a corrosion inhibitor system

using a variety of inhibitors – either singly, or in

ination – can be comprehended. Here, the ‘zero-line’

on the vertical axis of the graph represents: ‘no eect’ ,

while values greater, or less than zero represent a: posi

ive; or negative eects; respectively.

Such CAD for chemical compounds makes it pos-

ible to develop ‘atomised’ cutting uids far faster

than by previous techniques and oers the prospect of

discovering entirely new cutting uid combinations.

Computer analysis, oers a way to develop, analyse

and test new cutting uids, enabling very rapid modi



cations to be incorporated in order to meet new tech-

ical and commercial requirements. Further, these

CAD-based techniques guarantee a chemically-stable

product

ith the optimum properties, reducing the

risk of selecting the wrong type of cutting uid both

by the manufacturer and user. CAD product develop

ent still necessitates practical product testing, during

its development phase utilising standardised proce-

ures of: ‘calibration and laboratory test methods’ – to

model the computerised-uid data in a real-time cut-

ing environment.

8.6.1 Cutting Fluid – Quality Control

For practical reasons industrial cutting uid manufac-

turers have to use mass produced raw materials and

chemicals, which may be less pure than those used in

their formulations in the laboratory (Fig. 205). Not

only are there variations in quality, owing to variance

in the production process,

ut dierences can also oc

14 ‘Synergy’ , refers to the outcome when substances are com-

bined and produce ‘side-eects’ , which add to, or even amplify

each other, giving rise to a much stronger resultant eect.

cur depending on the raw material source and the sea-

sons of the year. In order to ensure constant quality

of the nished product despite these variations and

the factors which determine the quality of the raw

materials, they must be checked prior to entering the

cutting uid production processing stage. e labo

atory-based technique of computer-aided statistical

process control that ensures: ‘preventative quality con-

rol’ , will enable the researcher

o set the upper and

lower quality levels for a particular raw material – un-

er test. us, on the basis of these user-dened sta-

istically-acceptable levels, the correlation between the

analysis and the practical results can be determined.

Raw materials analysis using computer-aided design

in conjunction with sophisticated analysis equipment,

plays a vital role in any new cutting uid development

process.

An important criterion for the quality of the 

al cutting uid formulation is its stability. By com-

arison, synthetic cutting uids produce fewer prob-

ems than semi-synthetic and emulsion cutting uids,

in their development. In the case of the semi-syn-

hetic and emulsion

utting uids, not only must cool-

ng water and lubricating oil be brought together –

two naturally incompatible substances, they must also

‘persuaded’ to remain mixed together under widely

varying and extreme cutting and environmental con

itions. When dierent degrees of water hardness,

varying mix ratios and a diverse range of impurities

occur, they will strongly inuence the overall water-oil

system. e conventional way of stabilising such a sys

em is to add plenty of emulsiers. is action can lead

to excessive foaming, especially if the water is so,

which in itself necessitates adding anti-foam agents.

Anti–foam agents are an expensive alternative – par

icularly in a large central-based ‘Niagara’ reservoir-

type system feeding several machine tools in say, an

FMC/S (Fig. 203a), which here, by ‘anti-foaming dop

ng’ in any event, will only work for a limited period

of time.

More important for cutting uid stability, is the

size and distribution of the oil droplets in the water

phase (i.e. see Fig 206-inset photomicrograph). It is

the even distribution of the many oil droplets which

ensures that the oil-water system is stable. e growth

of micro-organisms (Fig. 203b) aects the droplet size

and as a result, as these droplets spherically-increase in

size, the number and distribution of droplets decreases.

us, an oil-water system with many evenly-spaced

and small droplets, will be more stable than systems

404 Chapter 8

Figure 205. Laboratory-based testing procedures on cutting uid coolant products.

Cutting Fluids 405

where there are bigger, but fewer droplets present.

Both the size and distribution of these oil droplets has

an important inuence on the emulsion’s consequent

foaming behaviour, which in turn, is strongly aected

by the water hardness and any turbulence produced by

the machine tool, or from a centralised coolant supply

system (Fig. 203a).

Product Testing

ere are a number of possible tests for checking the

quality of a cutting uid and those most commonly

utilised are ‘stability tests’. S

uch tests measure not only

the physical stability, b

ut also tests for: bacteriologi-

cal stability – t

his latter term is sometimes known as

Figure 206. The method used to check a soluble cutting uid’s dilution, utilising a Refractometer. [Courtesy of Rocol Ltd.].

406 Chapter 8

a biostability test; biostatic properties; or resistance to

bacteria growth

. Foaming behaviour: a slight ten-

dency to foam is important for some types of machin-

ng operations, particularly when deep-hole drilling

operations are undertaken and more specically, in

grinding operations. ere are certain cleaning sys

ems available, such as ‘full-jacket cyclones’ a

nd ‘hydro-

cyclones’ , w

hich promote foam formation. However,

there are no s

tandard techniques for the measure-

ment of foam formation and collapse, although the

laboratory circulating pump method, i

s a reasonable

approximation of practical conditions. In this method,

the cutting uid is forced through a spray-head so that

the resultant spray falls onto the surface of the liquid

and the time taken for foam to form and then collapse,

is a measured – giving an indication of foaming be

aviour. Adhesion tests a

re oen undertaken, with low

adhesion representing a tendency f

or the cutting uid

product to build-up layers o

f deposit. is adhesion

test is usually used for synthetic products and again,

there is no r

ecognised standard test method; although

one technique used to soak a pile of washers in the

cutting uid for a certain time, then drying them out

and subsequently testing for adhesion, is sometimes

employed.

Compatibility tests f

or cutting uids,

with particular reference to paints a

nd elastomers by

visual inspection of painted sheet metal is oen

ar-

ied out

. Acid/alkaline tests are oen undertaken on

the cutting uid, as this aects both the machine tool

and health of the setter/operator

Once a cutting uid manufacturer has produced a

new formulated product, which has been subject to a

stringent laboratory testing programme, followed by

exhaustive practical trials and consequent analyses,

it is then made available, initially to their ‘prime cus

omers’ – for an ‘alpha-trial’ testing programme aer

which, the cutting uid is oered on the ‘open-market’

15 ‘Bacteriological test methods’ , typical of this type of testing

regime are the German Standards, denoted by DIN51367 and

DIN513368, but similar test Standards are listed in most of the

world’s technological countries.

16 ‘C

ompatibility tests’ , specially-prepared painted sheet metal

is fully- immersed in the cutting uid for a certain time, then

visually inspected for paint de-lamination, etc., according to

the German Standard: DIN53521.

17 ‘A

cid/alkaline tests’ , are important cutting uid tests and they

are normally measured under laboratory conditions with an

electrochemical pH meter, in accordance to say, the German

Standard DIN51369.

for customers world-wide. erefore, it is vital that the

correct c

utting uid is used in the machine tools, as it

will have serious consequences to the: machine tool’s

subsequent maintenance programme; likely produc-

ion output; machined workpiece quality and reliabil-

ty; together with the various health issues relating to

that of the setter/operator. e following section has

been included to help with the important decisions re

ating to the choice of cutting uid selection.

8.7 Selecting the Correct

Cutting Fluid

When choosing a cutting uid many factors have to be

considered, with the relative importance varying with

each individual circumstance. For the latter reason, it

not p

ossible to oer general rules for the selection

of a cutting uid. Inevitably, a compromise is neces-

ary, although a comprehension of the factors involved

makes it possible to achieve the best choice, under

given circumstances. So, when choosing a cutting uid

it should always be borne in mind that the machining

process plays an important role in: productivity and

eciency; operator health; safety; plus the quality of

work created.

8.7.1 Factors Affecting Choice

Probably the main factors that must be considered

when selecting a specic cutting uid are not always

apparently obvious, but some questions should be

raised, which might include:

•

Business philosophy – what are the relative con-

cerns and weightings given to goals such as: e-

iency; quality-conciousness; market and economic

position; of the company?

•

Production programme – what is the scale of pro-

duction, is it a: single item (i.e. one-o); a batch; or

mass production? Moreover, what machining pro-

esses are involved in the part’s production?

•

Hardware – what production plant and equipment

is there available for the machining of the compo-

ents? Are the machine tools supplied with cutting

uid individually, or delivered from a centralised

system? Are particular cutting uids recommended

by the manufacturer of these machine tools?

Cutting Fluids 407

•

Protection of people and the environment – to

what extent are the personnel exposed to cutting

uids: before; during; and aer use? Are there local

constraints on uid disposal?

e above criteria concerning cutting uid selection,

can be sub-divided into two distinct groupings – com

ercial and production, as follows.

Commercial Criteria

e commercial criteria determine the ‘weight’ to be

given to various production decisions. For instance, if

the time factor is more important than the cost factor,

then higher cutting speeds will be used and so the de

and placed on the cutting uid will be greater. If, dif-

erent materials and types of machining

rocesses are

involved in the production process, then a ‘universal’

cutting uid might be a better choice than a number of

dierent uid products, even if the latter uid compo

itions individually produced a better performance.

Production Criteria

In either one-o, or batch production, individual

machines tools are likely to have their own separate

cutting uid supply, however in a mass production

environment, uid centralised systems are the norm.

e production criteria for the choice of cutting uid

includes the: type of machining process; cutting con

itions – workpiece material, cutting data, tool mate-

ial, etc., together with the machine tool type and its

conguration

. us, on the basis of these produc-

tion-based decision criteria, an initial choice will nor-

18 ‘Machine tool conguration’ , take for example, the case of

an ‘orthogonal’ * machining centre, it relates to whether the

machine has a horizontal, or vertical spindle orientation, with

one, or multiple spindles present, having three, four, or mul-

tiple linear and rotary axis control and of the conventional,

or high-speed machining (HSM) variety. Most machine tools

today fall into the ‘orthogonal’ machining category, but some

‘non-orthogonal’ machining centres exists, which oer con-

tinuous kinematics that have multiple-axis control – for even

simple straight-line motion, oen available with omni-direc-

tional spindle orientations – for ease of cutter access to say, a

complex, or sculptured machine part geometry.

*Orthogonality of axes means that each axis is positioned at

90° with respect to each other, such as on a three-axis verti-

cal machining centre (i.e. X-, Y- and Z-axes, with the Z-axis

normally incorporating the machine’s spindle).

mally be made regarding the type of cutting uid to

be used – whether it is an aqueous-, or oil-based uid

type that is required.

8.7.2 Selection Procedure

When selecting a cutting uid, it is important to take

the uid manufacturer’s instructions into consider-

tion. If their recommendations are ignored, it may

render any previous guarantees invalid. Many of

these cutting uid manufacturers

pecify that certain

products be utilised, normally only applying them to

either special machining circumstances, or where dif



cult cutting conditions are likely to be encountered.

Equally, other cutting uid producers only specify the

general type of instructions, such as: what type of cut

ing uid to employ, for example, aqueous, or not, to

be used, on the contrary, some uid manufacturers do

not specify anything! Usually it is possible to rely on

the manufacturer’s specication tables which indicate

their most suitable product for a particular range of

machining operations. However,

before c

onsulting a

cutting uid manufacturer’s set of tables, the follow-

actors must be either known, o

r established. ese

crucial decisions include:

•

Type of machining operation – care must be taken

to ensure that correct and ecient planning of the

machining strategy for the successful completion

of the part is known and, the optimum machining

techniques to achieve this objective are conrmed,

•

Water characteristics – hard/so, chloride, sul-

phate, bicarbonate content has been both tested

and accurately established,

•

Type of workpiece material to be machined – with

due regard to machining of: work-hardening mater-

ials, or ‘sticky’ materials – aluminium and copper

alloys, etc.,

•

Type of machine tool ltration system – having ei-

ther: no ltration; sump

nly; paper lter; centri-

uge; etc.

NB I

n the case of the centrifuge, semi-synthetic

products are not r

ecommended, while washable l-

ters should only be utilised with synthetic, or semi-

synthetic products.

As a general ‘rule of thumb’ , emulsions with EP addi

ives should be employed for heavy cutting work, whilst

synthetic products are normally best when cutting at

high speeds. By way of an illustration, if one consid

408 Chapter 8

ers multiple machining operations undertaken on

machining centres, the cutting uid should be chosen

for the range between the highest and lowest cutting

speeds. Once a particular uid product has been se

ected, it is still necessary to carry out a practical test

as only aer such testing, will it conrm if the correct

choice was made. At this stage in the selection proce

ure and even at some point later, support from the

cutting tool manufacturer in the form of: systematic

sampling procedures; laboratory testing and technical

advice could prove very informative – particularly for

applications where heavy cutting uid consumption

anticipated.

8.8 Care, Handling,

Control and Usage –

of Cutting Fluids

So that the properties of a cutting uid can be main-

tained giving it a long and reliable service life, correct:

storage and handling; usage and mixing with labelling

– having instructions for use; and care; are essential

requirements.

An indispensable part of any overall cutting uid

control, is suitable handling and storage at the user’s

premises, as it provides a continuous replenishment

and service facility for the monitoring of uids at, or

near to the machine shop.

All c

ontainers of cutting oil

should always b

e clearly marked with their end usage

for

se within the factory. When storing these cutting

oils, the grade most frequently utilised are best kept

on simple robust stillages, or for larger quantities, in

covered tanks, with an adequate supply of: taps; hand-

pumps; funnels; measures; and drip-trays; to ensure

proper handling and to avoid intermixing of grades.

is potential uid contamination is one of the most

important aspects when dealing with soluble oils, in

order to obviate any emulsication troubles and pos

ible coolant separation issues.

In large manufacturing companies, where bulk

delivery of cutting uids are being made-up prior

to delivery, it is important that all storage tanks for

the reception are properly identied, with appropri

te markings immediately changed once a new grade

is adopted. Unfortunately, one oil looks much the

same as any other and if not properly identied (i.e.

marked-up), as to the grade identication and its end

usage, this could lead to some costly machining mis

akes (e.g. part-scrappage problems) within the pro-

uction machining facility. e reception of drums of

cutting uid and oils, requires certain safeguards, to

protect the mutual interests of both the supplier and

user alike. For instance, the supplier should be noti



ed at once if there is obvious drum damage, or the

odd drum is leaking. Full drums of uid should never

be just dropped-o the delivery vehicle from its plat

orm, as a rim, or seam may be damaged and leakage

of the contents could potentially be a problem, apart

from the real risk of personal injury of a heavy drum’s

unchecked motion! For example, a typical full drum

weighs about 200 kg and if dropped from the vehicle’s

loading platform – normally a height of just over a

metre, the impact force will be considerably greater

than its ‘dead weight’ – due to gravitational inuence,

thus the uncontrolled careering drum is a

ajor ac

ident waiting to happen! So, when unloading full

drums from a road vehicle, always use: a drum skid

;

hoist, or fork-li truck.

When the handling of cutting and lubricating oils

has developed into a lthy job, this is reected in the

storage facility, which in some companies is the most

neglected part of the factory. Under such conditions, it

is oen dicult, if not impossible to avoid both wast

ge and contamination of lubricants, thereby leading

to issuing the wrong oil for the present machine tool’s

cutting requirements. Equally, a clean well-organised

oil storage facility is an invaluable asset to any engi

eering plant and no eort should be spared to create

and maintain these optimum conditions, this being es-

ential to a trouble-free operation.

If soluble cutting uid – ‘coolant’ , is mixed in bulk,

the storage tank should be clearly marked with the:

product’s name; reference code; and concentration.

is simple but vital tank identication avoids mis

akes in issuing the wrong coolant, or dilution concen-

ration to a prescribed machine tool, while providing a

reminder of the required contents when mixing a fresh

uid batch.

Soluble oil concentrate must not be exposed to

cold climatic conditions and allowed to freeze, since

this ‘cryogenic eect’ might adversely aect the

19 ‘Oil-drum skids’ , when robustly designed/produced, allow the

controlled sliding to ground-level of full drums o a vehicle’s

loading platform, without potential health risks to the compa-

ny’s work-force.

Cutting Fluids 409

concentrate’s stability – when subsequently used.

Further, bulk drum storage outside should if possible,

be under protective cover, but if this is not the case,

then drums should be placed onto their sides and

not stored upright (i.e. ‘bung-side up!’). If they were

to be stored upright, then any standing rain water

can collect on the drum’s top and owing to daily tem

erature uctuations, any water can be sucked into the

barrel – even through the unopened top. ese small

amounts of water may destabilise the concentrate,

leading in the worst scenario to complete separation

of the concentrate into distinct

ayers. In this state,

the concentrate becomes completely unusable, as uid

in such a condition, will be unlikely to adequately

remix. Consequently, it is advisable that some form

of space heating for undercover uid storage is desir

ble, to minimise wide temperature uctuations, this

being particularly relevant during winter months, as

the oil viscosity appreciably changes (i.e. thickens),

with more sluggish ow-rates causing delays in both

its delivery and usage. When not in use, all lubricant

containers should be kept closed, thus avoiding entry

of abrasive foreign matter. So, whenever possible,

indoor storage of cutting uids and lubricants is to be

ecommended.

all o

il storage facilities have a real potential for

a catastrophic and explosive re hazard. S

ucient re

extinguishers – of the correct type and size, should be

strategically placed at easily-accessible points around

the oil storage facility and positioned at ground level

with unobstructed access to them. Any oily paper

waste and sawdust

present, requires prompt disposal

to minimise re risk. Any o

il storage facility is strictly a

non-smoking zone, f

or obvious reasons.

8.8.1 Product Mixing – Preparation of

a Aqueous-Based Cutting Fluids

As mentioned, cutting uids are usually supplied to

the customer in the form of concentrates and the ease

20 ‘Sawdust’ soaked in oil is a likely re source, so rather than

use this to soak up oil-spillages, use specially-produced gran-

ules that are non-ammable and oil absorbent.

NB ese oil absorbent granules are usually readily available

and can be purchased from most leading-lubricant supply

companies.

with which they can be mixed together with water var-

ies, depending upon the amount of oil they contain.

Concentrates with high oil concentration may require

vigorous stirring in order to form an emulsion. While

other products containing little oil are oen supplied

‘preformed emulsions’ , i

n which the concentrate has

previously been mixed by the

utting uid manufac-

rer with water to form a stable emulsion. ese lat-

er ‘preformed concentrates’ , only require them to be

stirred into water at the correct dilution ratio, in order

to prepare them for use.

Correct preparation of the emulsion is essential

if the cutting uid is to provide its optimum perfor

ance. By preference, the water supply should not be

excessively hard (i.e. <300 ppm – total hardness) and,

it should be of ‘drinking quality’ – thereby not infected

with any bacteria.

Hand Mixing

With the production need for relatively small volumes

of aqueous-based coolants, the emulsion can be pre-

ared as follows:

1. Choose a suitable-sized volume mixing vessel – not

the machine sump, nor a galvanised container,

2. Carefully ll with the measured amount of water,

3. Slowly add a measured amount of concentrate while

continuously stirring – with a top-to-bottom stir

ing action – this being the most ecient action,

until the emulsion is fully-formed,

4. Steadily add the newly-mixed emulsion to the ma

hine tool’s sump.

Automatic Mixing

When larger volumes of emulsion cutting uid are

required, then it is advisable to use a purpose-built

and designed uid mixer (Fig. 208). ese proprietary

mixing devices incorporate the following features:

•

ey can directly-connect to a standard water tap,

•

ey can be screwed directly into a large uid con-

centrate drum,

•

ere is adjustment for the automatic dispensing

of the correct emulsion dilution ratio of: ‘oil-to-wa-

er’ ,

•

e uid mixer incorporates a non-return valve, to

ensure that the emulsion cannot leak-back into the

drum’s contents.

410 Chapter 8

Most uid mixers operate based upon the ‘venturi

principle’

and because of this, there will usually be a

degree of uctuation of the dilution, if the water pres-

ure should change during its operation – particularly

if other equipment within the factory draws water

when required. In view of any potential water pressure

variation, it is normal practice to use a water supply

that is not subject to such uctuations. Many local

water authorities may well require that a header tank

with an air gap is used, to prevent any possibility of

contamination of the water mains. When mains water

is used,

any local authorities will provide the nec

ssary water quality information, but if another water

source is used, it will need to be analysed by the user.

In Fig. 207, the graph illustrates the results of concen

ration measurements, taken from zero → 6%, obtained

by dierent techniques, such as:

•

Refractometer assessment – more on this apparatus

shortly,

•

Measurement of the total alkalinity of a product

containing nitrate,

•

Boron determination by Atomic Absorption (AA)

method,

•

Measurement of the total alkalinity of a product

not containing nitrate,

•

Hypothetical ‘real’ concentration ‘R’ , set arbitrarily

at 3%,

•

Determination of anionic emulsier content (b) @

water hardness of 10° GH,

•

Determination of anionic emulsier content (a) @

water hardness of 10° GH,

•

Determination of nitride content,

•

Determination of anionic emulsier content (a) @

water hardness of 30° GH.

NB W

ater hardness can be easily determined with suf-

cient accuracy using indicators in tablet form, while

the pH value and bacteria count can be estimated as

21 ‘Venturi principle’ , is: ‘A convergent-divergent duct in which

pressure energy is converted to kinetic energy at the throat.’

When utilised with its associated ‘Venturi meter’ , this being

a ow meter in which the pressure drop in a Venturi is used

to give an indication of ow. [Source: Carvill, 1997]Where in

the case of emulsion dilution ratios, this uid mixer arrange-

ment – with the apparatus situated in the top of the drum and

connected to the water supply – can be employed and then

subsequently adjusted in-situ, to give the desired coolant mix-

ture.

described in the following section. For more detailed

analysis, then laboratory facilities are necessary, this

assistance is oen provided by the cutting uid manu-

acturer’s laboratory service department.

8.8.2 Monitoring, Maintenance

and Testing of Cutting Fluid –

in Use

While in use the cutting uid is subject to various in-

uences that may aect its properties. Such inuen-

ial factors include: leakages from the machine tool’s

lubrication and hydraulic systems (i.e. ‘tramp-oil’);

surface contamination on the work piece: prior to ma

hining; or by people: spilled drinks; food particles;

environmental inuences. It is paramount that the

health monitoring of a cutting uid is on-going and

undertaken at periodic intervals, whilst spot-checks

may also be necessary in order to detect undesirable

changes in the uid’s properties, enabling corrective

action to be taken, as appropriate. Hence, the

oni

oring of the cutting uids are fundamental to their

life, but a relevant question could be raised: ‘What

characteristics do we have to monitor?’ Probably the

most common cutting uid tests, include the following

measurements:

•

Concentration,

•

pH (Alkalinity),

•

Corrosion protection,

•

Fluid stability,

•

Bacteria count.

e above tests will shortly be considered in more de-

ail, in the appropriate section. Prior to this, it is im-

ortant to ensure that the machine tool is thoroughly

cleaned, before a new ‘charge’ of cutting uid is poured

into either the machine’s reservoir, or to a central cool

nt distribution tank – supplying the needs of several

machine tools.

Machine Cleaning

It is important to any cutting uid system that it is cor-

rectly cleaned before fresh uid is introduced, if the

optimum performance from it is to be obtained. Such

machine tool cleaning procedures, should include the

following stages:

Cutting Fluids 411

Figure 207. The graph illustrates the results of the concentration measurements using dier-

ent methods. [Courtesy of Cimcool]

412 Chapter 8