Davim J.P. Tribology for Engineers: A Practical Guide

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229

Tribology in manufacturing

Commonly used lubricants and typical

(friction coefﬁ cient) values in wire and tube

drawing

Table 5.25

Material Wire drawing –

lubricant

Wire

drawing

–

Tube

drawing

– lubricant

Tube

drawing

–

Steel Mineral oil + fat

+ EP additive

Phosphate +

emulsion

0.07

0.1

Phosphate

+ soap

0.05

Al and Mg

alloys

Mineral oil +

fatty derivatives

0.03 – 0.15

(mixed ﬁ lm)

Soap 0.07

Cu and Cu

alloys

Mineral oil +

fatty derivatives

0.03 – 0.15

(mixed ﬁ lm)

Soap ﬁ lm 0.05

Ti alloys Fluoride

phosphate +

soap

0.1 Metal +

soap

0.07

Refractory

metals

Copper +

mineral oil

0.1 Copper +

mineral oil

0.1

5.5 Tribology of drawing

Drawing is a process where the size of a work piece is reduced

by pulling through a constriction. No friction is required

between work piece and die in wire drawing and tube drawing

on a ﬁ xed plug. Moderate friction is needed on the plug for

drawing tubes and frictional of a bar is beneﬁ cial when drawing

a bar. Lubricants are applied in drawing to reduce friction,

wear, and temperature and the method of application is critical

in drawing. Drawing without a lubricant results in material

pick-up. Dry drawing is conducted with soap, whereas wet

drawing is conducted with viscous oils or aqueous emulsions.

Most practical drawing is conducted under mixed ﬁ lm regimes

where lubricants, soaps and extreme pressure additives can

yield the best results at various stages of drawing. The most

commonly used lubricants in drawing are shown in Table 5.25.

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5.6 Tribology of extrusion

Extrusion refers to the metalworking process that pushes

metal through a constriction of known geometry and friction

is generally unnecessary and undesirable. Friction on the die

increases extrusion pressure and impairs the homogeneity of

deformation. Friction also contributes to heat generation

and limits attainable reductions and speeds in hot

extrusion. Extrusion can be fully lubricated or unlubricated.

Unlubricated extrusion is essential for extruding tubes, hot

extrusion of aluminium alloys with ﬂ at dies, and non-

isothermal extrusion of copper alloys. The most commonly

used lubricants in extrusion are shown in Table 5.26.

5.7 Tribology of forging

In simple open die forging operations, friction induces in -

homogeneity of deformation and increases forging pressures.

Commonly used lubricants and typical

(friction coefﬁ cient) values used in extrusion

of metals

Table 5.26

Material Hot extrusion –

lubricant

Hot

extrusion

–

Cold

extrusion

– lubricant

Cold

extrusion

–

Steel Graphite 0.2 NA NA

Al and Mg

alloys

None Sticking

friction

Lanolin 0.07

Cu and Cu

alloys

Graphite 0.2 Castor oil 0.03

Ti alloys Graphite 0.2 NA NA

Refractory

metals

Glass coating

plus graphite on

die

0.05 NA NA

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Tribology in manufacturing

Lubrication is beneﬁ cial in reducing die wear and other duties

such as reducing local forging pressure. Lubrication in cold

forging relies on compounded oils and semi-solids such as

fats, soaps, and waxes. For severe working, MoS

may be

used. In hot forging applications, lubricants are based on oil

based graphitic solutions, or graphite free solutions. The most

commonly used lubricants in forging are shown in Table 5.27.

5.8 Tribology of sheet metalworking

Friction does not affect the processes of shearing, blanking,

and punching itself, but lubrication is used to reduce die

Commonly used lubricants and typical

(friction coefﬁ cient) values used in forging

operations

Table 5.27

Material Hot forging –

lubricant

Hot forging

–

Cold forging

– lubricant

Cold forging

–

Steel Soap

Graphite in

water

Salt solution

0.3

0.2

Lime + oil

Copper + oil

Phosphate +

soap

0.1

0.05

Al and Mg

alloys

Graphite in

water

0.3 Lanolin

Phosphate +

soap

0.07

0.05

Cu and

Cu alloys

Graphite in

water

0.15 Fat: wax

(lanolin)

Zinc stearate

(soap)

Graphite or

MoS

grease

0.07

0.05

0.07

Ti alloys MoS

0.2 Zinc

Fluoride-

phosphate +

soap

0.1

0.05

Refractory

metals

Glass +

graphite

0.05 NA NA

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Tribology for Engineers

Commonly used lubricants and typical

(friction coefﬁ cient) values used in sheet

metalworking operations

Table 5.28

Material Shearing

– lubricant

Bending

– lubricant

Press working

– Lubricant

Press

working –

Steel Pickle oil,

emulsion of

mineral oil

and EP

additives

Pickle oil,

emulsion

of mineral

oil and EP

additives

Phosphate +

soap, wax,

graphite in

grease, metal

+ emulsion

0.05

Al and Mg

alloys

Emulsion of

mineral oil

and EP

additives

Emulsion

of mineral

oil and EP

additives

Soap or

lanolin,

polymer,

graphite

coating

0.05

Cu and Cu

alloys

Soap

solution,

mineral oil +

fat, emulsion

of mineral oil

and fat

Soap

solution,

mineral oil

+ fat,

emulsion

of mineral

oil and fat

Tallow,

pigmented

tallow, soap

0.05–0.1

Ti alloys Mineral oil +

EP additives

Mineral oil

+ EP

additives

Wax, polymer,

ﬂ uoride

phosphate +

soap

0.05–0.07

Refractory

metals

Mineral oil +

EP additives

Mineral oil

+ EP

additives

MoS

graphite,

Al-Fe-Bronze

dies with wax

0.2

0.07

wear. Sheet metalworking dies tend to wear by adhesive,

abrasive, fatigue and chemical wear mechanisms. Bending

places minor demands on lubricants, whereas in spinning

and ﬂ ow turning, high pressures require good lubrication.

Stretching processes require good lubrication as friction

governs the shape of the component to be produced. In deep

drawing, lubricants dominate the level of LDR values

requiring high viscosity lubricants. The most commonly used

lubricants in sheet metalworking are shown in Table 5.28.

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Tribology in manufacturing

5.9 Conclusions

This chapter has focused on tribology in manufacturing

processes from the viewpoint of understanding the

fundamentals of sliding friction in those processes and the

use of lubricants to control friction in manufacturing

processes such as machining, drawing, rolling, extrusion,

abrasive processes and processing at the micro and

nanoscales. The chapter also provides data on the type of

lubricants used in manufacturing practice and how the

lubricant controls friction to achieve a variety of different

effects at various length scales. It should be noted that there

is a lack of genuine data of how lubricants affect the tribology

of manufacturing at the micro and nanoscales and this must

surely be the challenge for future engineers working in this

exciting ﬁ eld.

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234

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