A review of the machinability of copper-base alloys

Pergamon

A REVIEW

OF THE MACHINABILITY ALLOYS S. KUYUCAK

Department

of Natural Resources, Canada Metals Technology Laboratories, (Rwctred

OF COPPER-BASE

and M. SAHOO

Centre for Mineral and Energy Technology, CANMET 568 Booth Street. Ottawa, Canada, KlA OGI

3 1 Mu>, 1994: re~isrd

10 Nocemher

1994)

Abstract-Machinmg is widely used as the final shaping operation, and contributes significantly to the cost, of a manufactured product. As a result, it has been of paramount importance to develop easily “machinable“ alloys with minimal sacrifice of other properties. to reduce the associated fabrication costs. Until now. leaded brasses have been the industry standard for “free-machining” copper-base alloys. However, health concerns about the use of lead in alloys, especially in plumbing applications, will restrict their use. This has created a need for an alternative free-machining copper-based alloy, without lead. MTLCANMET has been involved in establishing such an alloy. The project was partially funded by the International Copper Association (ICA). and this review was undertaken to assist this effort to understand and summarize the data and concepts of the metal cutting process, assessment of machinability, and the metallurgical factors that contribute to an alloy’s machinability, from the standpoint of copper-base alloys. Resum&L’usmage constitue. dans la plupart des cas, l’etape finale de la mise en forme et contribue considerablement au cotit du produit manufacture. II s’ensuit que pour reduire les codts associes B la fabrication il est primordial de mettre au point des alliages faciles a usiner en sacrifiant le mains possible les autres proprietts qu’ils possedent. Jusqu’a mamtenant, dans l’industrie. les laitons au plomb ont constitue un etalon pour les alliages au cuivre facilement usinables. Toutefois, l’utilisation du plomb dans les alliages, en particuher dans les applications en plomberie, est source de preoccupations relatives g la same, ce qui en limitera I’utilisation. Ce fait a tree le besoin d’un alliage de rechange au cuivre. sans plomb et facilement usinable. Les LTM et CANMET ant participe a I’elaboration d’un tel alliage. Le projet a ete partiellement finance par TInternational Copper Association (ICA). L’etude a Bte entreprise dam Ie cadre de ces travaux en vue de comprendre et de resumer les donntes et concepts propres au prodde de coupe des metaux. d’evaluer I’usinabilitt de l’alliage et les facteurs mttallurgiques qui contribuent 5 I’usinabilite d’un alliage, du point de vue des alliages au cmvre.

NOMENCLATURE

M M,, M,

MC N R

T t

Area of primary shear plane Specific heat capacity Thickness of primary shear plane Cutting force (primary force in the direction of tool travel) Thrust force (secondary force m the direction of feed) Shear force acting along the shear plane Normal force acting perpendicular to shear plane Friction force acting along the tool face Thermal conductivity Length over which sticking occurs between tool and chip on the rake face Machinability index Machinability in terms of cuttmg temperature Machinability in terms of surface finish Machinability in terms of cutting force Normal force acting perpendicular to tool face Resultant force in a machining operation Cutting ratio or chip ratio Tool life Depth of cut

1, 1. Ir V\ M’ wt U\ II’ a ; ( 1’ P 0 7: 7> ; %

Chip thickness Cutting speed Chip velocity along the rake face Shear velocity along the shear plane Work done per unit volume during a machining operation Work done per unit volume due to friction at the tool face (secondary deformation) Work done per unit volume at the shear plane (primary deformation) Width of cut Rake angle Friction angle Shear strain Shear strain rate Coefficient of surface roughness Coefficient of friction Density Cutting temperature Friction stress Shear stress/strength Compressive stress/strength Shear angle Coefficient for chip sticking tendency

2

S. KUYUCAK

and M SAHOO.

A REVIEW

OF THE

MACHINABILITY

OF COPPER-BASE

ALLOYS

1. INTRODUCTION Machining covers a large collection of manufacturing processes designed to remove unwanted material, usually in the form of chips, from a workpiece. Most shaped products (castings, forgings, etc.) require machining as the final shaping operation. Machining is widely used, and contributes significantly to the cost of a manufactured product. The annual expenditure on machining in the United States, for instance, exceeds St00 biDion [I]. As a resuIt, much research and development has taken place to reduce these costs by developing more “machinable” alloys, with minimal sacrifice of other properties. Until now. leaded brasses have been the Industry standard for “free-machining” copper alloys. The annual North American consumption of these is approximately 500,000 tons. about half of which is for the potable-water (plumbing fixture) market. However, health concerns about the water quality and the lower acceptable lead contents will severely restrict the use of leaded brasses in the future. Already, current EPA/US regulations dictate that total lead discharge into potable waters from all sources should not exceed 15 ppb. This has created a need for an alternative free-machining copper-base alloy. without lead. Metals Technology Laboratories, Canada Centre for Mineml and Energy Technology (MTL, CANMET), has been involved in developing such an alloy. The prolect was partially funded by the International Copper Association (ICA). and this review was undertaken as part of this effort. A large volume of information on the machinability ol‘various alloy systems exists, but a comprehensive review interrelating the metallurgical factors with machinability has been found lacking for copper-base alloys. One such attempt was made in the form of a book published by the Copper Development Association [2]. Other reviewers covered the whole range of metals and alloys [i. 41. Therefore, an obvious need exists to assess the current state of the knowIedge accumulated exclusively for copper-base alloys over the past 40 years.

2. THE METAL CUTTING PROCESS: REFERENCES [Z--U] Machinability operations can comprise turning, facing. drilling, boring, reaming, tapping, threading, milling. sawing. broaching, and grinding. In spite of these varied operations. the metal cutting process can be described simply by considering the orthogonal cutting process, where only the forces in the direction of cutting F,, and the feed (or depth of cut) f-,. are considered, and the lateral forces can be neglected. Figure I illustrates this process. An important variable in a cutting process with a wedge shaped tool is the rake angle. 2: this is the angle that the rake face of the tool (over which the swarf slides) makes with the normal to the workpiece at the cutting edge. Mechanism of metal cutting essentially involves two localized shear deformations: one to deflect the newly formed swarf towards the rake face (primary deformation), and another to move it along the rake face (secondary deformation). In comparison, the energy required to create a new workpiece:chip surface is small, and can be neglected. The relative motion between the tool and the workpiece during cutting compresses the work material immediately ahead of the tool and induces

Work Piece

Fig.

I. Schematic diagram for orthogonal cutting.

the primary deformation. This occurs over a very narrow region called the primary shear zone (or plane), and is shown by a broken line in Fig. 1. As the chip moves along the rake face of the toot, some sticking occurs between the tool and the chip, causing the secondary deformation in a narrow region along the rake face. The shear angle Q is the angle between the primary shear plane and the cutting direction, and is of fundamental importance. Together with M$ it determines the cutting (chip) ratio r = [: I,. and the resultant cutting force R. In general, high 4 results in low r and R, and is associated with good machinability, From the geometry of Fig. 1, the primary shear strain ;’ and the cutting ratio I can be shown to be: y= cot$+tan(4--cr)

t sin 4 r=;=cos(f$-z)

(1) rcoscx

Or tand = cos(+-g

(2)

Hence, by measuring the chip thickness t, and from a knowledge of the feed t and rake angle a, the primary shear angle 4 and the shear strain y can be calculated. Figure 1 shows a cube of workpiece in the feed zone going through the shear deformation under ideal, orthogonal cutting conditions. Primary shear strain in machining varies between 2 and 4, and the strain rate i;, from lo4 to 10’ SK’. (The primary shear plane, although thin, has a finite thickness d, and the strain rate can be shown to be $ = V,,/d, where V, is the shear velocity along the shear plane. as shown in the velocity diagram in Fig. 1. Shear plane thickness has a comparable magnitude to that of the feed, and the shear velocity to that of the cutting velocity; hence the shear strain rate can be expressed approximately by j= v/t t 101.1

S. KUYUCAK

and M. SAHOO:

A REVIEW

OF THE

In a machining process. the cutting and feed forces F, and & can be measured by dynamometers (resistance strain gauges). and the resultant force R calculated. R can then be resolved along the shear plane to give the shear force F, and the shear plane normal force F,,; and along the rake face. to give the rake face friction force F and the rake face normal force N. These forces are shown in the circular force diagram in Fig. 1. and bring about the two localized deformations in a metal cutting operation. The shear stress z,= F,/A,, where A,= tw,/sin+ (t is feed, w is width of cut), should be equal to the shear strength of the metal under compressive stress T,, at shear strain rate 7. and temperature T of the shear zone; and is considered to be a material constant independent of cutting parameters, tool material, or the cutting environment [5]. On the rake face. friction coefficient p = F,:N and the friction angle p = tan- ‘~1 depend on the degree of sticking/lubrication at the tool/chip interface. From the above, it can be inferred that the two shear deformations have a mutual dependence. The amount of friction on the rake face in secondary deformation affects the shear angle of the primary deformation, while the degree of temperature rise and plastic deformation following the primary shear direct]) influence the friction forces in the secondary deformation. An analytical description of a metal cutting process must therefore determine both primary and secondary processes simultaneously. This is a difficult task, but it has been tackled with some success using numerical analysis and slip line field (dislocation) theory. In an alternative approach, first used by Merchant, and later by Spick and Rowe [ 1I], it was shown that the system will be defined in such a way that the only the minimum work will have to be done in machining. This considerably simplifies the analytical treatment and yields valuable insight into the interrelated factors that play a role in machining. Using this premise in simple orthogonal cutting, for instance, the effect of rake face friction on shear angle, and, thus, machinability. can be established as follows: work required to produce a unit volume of chip is equal to the sum of primary deformation W, = t,y (assuming nonwork-hardening) and secondary deformation Wf=tf I wVJ~,WV, where 1 is the length over which sticking occurs on the rake face and M‘ is the width of cut. Making substitutions for I= xl/coscl (normally sticking is expected to occur within a projected length of feed over the rake surface (~/COW), x. is a multiple of this length. and may be considered as a fudge factor describing the degree of sticking tendency of the chip), and t,= t cos(4 -a):sim$. secondary deformation per unit volume may be written as W,=z, X/COW x sin&‘cos(#-a). Total work required per unit volume W= W, + W, is then a function of r, 4, x, and the shear strengths. A relationship between 4 and x. can be derived by solving d W/84=0 for a given LXand x. Assuming similar magnitudes for z, and TV, this yields: cos a cos(2~$

~ a) - x sin’4 = 0

0

OF COPPER-BASE

10

20

30 Shear

3

ALLOYS

Angle,

40

50

60

0

Fig.

1. Effect of rake face friction on shear angle, at different tool rake angles.

l

LOW ductility may cause the chips to break up during primary shear. This will limit the sticking length to the length of the fractured chips, and hence maintain a high shear angle. Ductile materials will give continuous chips, and are likely to stick longer on the rake face, resulting in a low shear angle. Increasing the rake angle increases the shear angle. However, this necessitates a smaller wedge angle, which increases the tool wear and also makes the tool weaker against breaks. High rake angle, therefore, is only used for difficult-to-machine, ductile materials. Lubrication, whether internal (caused by soft particles as in free-machining alloys) or external (caused by lubricants), will decrease the rake face friction, and therefore increase the shear angle.

l

l

In machining two-phase alloys at low speeds, sometimes a mass of metal adheres to the tool face, while the rest of the chip continuously flows over this stationary mass. This is called built-up-edge (b.u.e.), and indicates a high degree of bonding between chip and tool, such that the chip is constrained to flow over its own mass rather than slide over the tool surface. A b.u.e. increases the apparent rake angle, and hence the shear angle of the chip, and decreases the sticking length, and the cutting forces. but it causes poor surface finish, generally through the build-up and loss of the b.u.e.

3. ASSESSMENT OF MACHINABILITY: REFERENCES 112-141 The following factors machinability of an alloy:

are considered

in assessing the

(3)

can be solved for different rake angles, and Fig. 2 shows the effect of sticking tendency x of the chip on shear angle 4 for a given LX The graph highlights the following: l

MACHINABILITY

As sticking friction between chip/tool surface increases. shear angle decreases. Chips become thicker. and tool forces increase.

l Tool life 0 Surface quality l Chip form l Cutting force.

Although the above may be considered generally to be in decreasing order of importance, the order will depend on the type of operation. For instance, from a machinability stand

4

S. KUYUCAK

and

M. SAHOO:

A REVIEW

OF THE

point, in a finishing operation surface quality is of prime consideration, whereas in automated lathes, chip form has high priority to ensure its ease of disposal [ 151. Tools may fail for many reasons: flank wear occurs near the cutting edge, on the flank side; crater wear, on the rake face: the cutting edge may lose its sharpness; or may fail catastrophically by chipping/rupture of the tool point (as a result of excessive chatter) or thermal softening and plastic flow; concentrated wear in the form of a deep groove at the cutting edge, known as wear notch, may result [7, 161. Tool life may be measured as time for a given wear under set cutting conditions, or machinability in terms of tool life may be expressed as cutting speed that produces a predetermined tool life of, say, 60 min. The relationship between tool life Tand cutting speed Vis given by the Taylor equation VT” =constant. which, on a log-log scale produces a linear relationship. Since normal tools would take a long time to show measurable wear. it is common practice to use softened tools to determine the machinability indices related to tool life. In general, flank weal has been found to be the most dependable guide for measuring tool life; therefore. measures would be taken to minimize or eliminate other types of tool wear by the proper selection of cutting conditions. An example of this is given by Mills er al. [17] in determining the relative machinability of a;fi brasses: when softened tools failed catastrophically at the tool corner. cutting was carried out using a rear tool to undercut the workpiece, thereby preventing the test tool from cutting on the corner. Surface quality is defined in terms of surface finish and surface integrity. Surface finish includes surface roughness (tine irregularities, including feed marks), waviness (a more spaced surface texture caused by machine or work deflections or chatter), and flaws (such as cracks, nicks and scratches). and is closely tied to dimensional tolerances. Surface integrity. on the other hand, includes residual stresses and metallurgical effects such as burnishing. ANSI:ASME standards have been developed to measure and rate surface finish and surface integrity [13]. Ductile metals and metals prone to b.u.e. formation give low machinability ratings based on surface finish. Arzt [ 181, for instance, suggested that burr formation tendency of a metal can be measured by the ratio of its tensile elongation to yield strength. As well as the alloy/metal properties, machining conditions also play a role in the resulting surface quality: surface damage in machining red brass decreases with increasing cutting speed, rake angle. and lubrication [19]. In general. dull tools are the most common cause of poor finish. Flank wear increases the tool/workpiece contact, which, in turn, increases the size of the shear zone. Eliminating chatter through rigid tools. and by reducing feed. also improves surface finish [20. 211. Chip form may be classified as discontinuous, semi-continuous, and continuous chips. Examples of these are shown in Fig. 3. Discontinuous chips are a desired characteristic of ft-ecmachining alloys, and are preferred for their ease of automatic (continuous) disposal. Greater degree of automation over the years has made this aspect of machinability increasingly important. With the help of the chip curling tools (chip breakers), continuous chips can be made to curl. which help their breakage. Isler rt al. at Boillat S.A. in Switzerland classified curled chips as short (&3 spirals), medium (3-6 spirals), and long ( > 6

MACHlNABILlTY

OF COPPER-BASE

ALLOYS

spirals) [22]. They also showed that chip lengths will vary in a complex but well-defined manner with cutting speed and feed, creating regions of short, medium, and long chips, as shown in Fig. 4. They found that these regions can be displaced significantly to favour long, medium, or short chips for brasses with identical composition, but of different fabrication procedure. Changes in chip formation with cutting speed are shown for 60140 brass in Fig. 5 [23]. Henrikson in the United States and Murata in Japan gave a chip index by comparing the bulk density of chips to the density of the workpiece [24, 251. To find their bulk density, chips were packed by natural fall into a measuring cylinder and were weighed. Ratios varied from 0.02 for unbroken chips to 0.3 for well-broken chips. Tool forces and power consumption for a given feed and depth of cut are only important to ensure sufficient rigidity to prevent chatter. Otherwise, they are not a major concern in considering machinability per se, but are easy to measure and correlate well with other machinability parameters. Usually, a reduction in tool force indicates better machinability in terms of tool life, chip length, and surface quality. However, exceptions to the rule do exist, as in the b.u.e. formation. Machinability of copper alloys are commonly rated by comparing them to the free-machining brass (FMB, Alloy C36000), on a scale where FMB rates 100. These ratings were established when the high speed steel tools were dominant, and refer to relative tool life or relative cutting speed for a 60 min tool life, under standard cutting conditions. In terms of this machinability rating, copper alloys are classified in three broad categories (26, 271:

Free-machiningalloys have ratings between 70-100. They include the copper alloys with free-machining additives, such as the leaded brasses and copper, and copper containing sulfur, selenium, and tellurium. Readily machinablealloys have ratings between 30-70. They are the low leaded brass, and most two-phase alloys. Diicult-to-machine alloys have ratings less than 30. Pure copper and most single-phase alloys would be in this category. Tables l-3 gives the compositions, typical properties, and the machinability ratings of some copper-base cast and wrought alloys, grouped according to this classification. Although the three broad categories above give a general guideline, machinabilities can vary even for the same alloy, from one batch to another. In operating an automated lathe, it is important to know in advance the allowable number of machining operations between tool changes. Tool life tests. even with softened tools, take a long time to perform and are expensive. Therefore, attempts have been made to assign quick and accurate machinability indices. Good correlation. for instance, was found between tool temperature and flank wear. Accurate cutting temperatures have been measured for this purpose by employing a two-tool design in parallel or counter-balance turning, where each tool carries a thermocouple junction (Fig. 6) [25]. In Japan, Murata et (11. [28] suggested a composite machinability index that included tool life M,,= (0,/Q)’ 43, where 0” is the cutting temperature of the standard material (free-machining brass) and 0 is that of the test material; surface finish M,, = t,,:~, c is the surface roughness; and 1%4~-~ = F&IF,, Fc is the cutting force. Composite index is then the geometric mean of the three indices, M=(M,M,.~,L)“3. The effect of cutting

S. KUYUCAK

and M. SAHOO: A REVIEW OF THE MACHINABILITY

OF COPPER-BASE ALLOYS

5

Fig. 3. Examples of various chips produced by drilling m a machinability test. A press drill was set up to apply a constant load of 86 kg on a standard $’ drill bit turning at 141.5 rpm. Relative machinability rating was obtained by noting the chip forms and the time taken to drill a 12.7 mm (f”) deep hole. (a) Free-machining brass. Alloy C36000: type I chips, 8 s drilling time; (b) free-machining brass without lead: type 3 chips. 60 s drilling time; (c) sulfur copper: type 1 chips, 14 s drilling time; (d) de-oxidized copper: type 2 chips, 45 s drilling time; (e) Cu-Bt-In alloy: type 1 chips, 11 s drilling time; (f) silicon brass C87800: type 1 chips, 21 s drilling time. In comparison, low-leaded (0.12% Pb) silicon brass had similar sized chips, and 16 s drilling time. CuBi-In alloy and silicon brass are contenders for a lead-free, free-machining copper alloy [59].

temperature on tool life was recognized earlier by Ewe11 [2Y]. who tried to establish a correlation between heat dissipation rate from the tool tip kpc (product of thermal conductivity. density and heat capacity of the workpiece) with machinability. However, this ignores the heat generation term, which depends on the ductility and the strength of the metal. A more complete formulation for a machinability index based on cutting temperature would be [30]:

where u is the cutting energy per unit volume of metal removed, 1’ the cutting speed, and t the feed. However, temperaturedependent wear does not account for the effects of abrasion caused by hard particles, especially important in free-machining brasses. 4. EFFECT 4.1 Puw

!21,, = u

(41

copper

OF MICROSTRUCTURE MACHINABILITY

and predominantly

single-phase

ON alloys

Pure copper, because of its high ductility, is not easy to machine. Staley et al. studied the machinability of high con-

6

S. KUYUCAK

and M. SAHOO: A REVIEW OF THE MACHINABILITY

OF COPPER-BASE ALLOYS

Machinability of OF copper in terms of cutting force and chip thickness is not significantly affected whether it is in hard or annealed condition, but surprisingly, the ambient oxygen has a strong affect. Auger analysis reveals that when machining pure coppers, an oxygen-rich layer forms on the tool/chip interface (where the secondary deformation takes place) [32]. In rucuo. in the absence of oxygen, OF copper cuts with better surface finish at lower cutting force.

Feed

Fig. 4. Cutting speed vs feed diagram showing ditrerent zones of chip formation in free-machining brass: (A) short, (B) medium-long. and (C) long chips. from Isler.

ductivity copper without the free-machining additives [3 11. A high top rake angle is necessary when machining very ductile metals. Void formation on the chip underside occurs when rake angle is less than 45’ with oxygen-free (OF) copper, and 25 with electrolytic tough-pitch (ETP) copper, leading to poot surface finish. As the rake angle is increased, chips become continuous and acquire a side-curl in the shape of a flat sabrc. the degree of curl measured by an “exit angle”. ETP copper produces chips that break easily on contact with the workpiece or the tool flank. For OF copper. it is important to break these continuous chips with tools having a chip curler design. The design of the chip curlers depends on the chip exit angle. which in turn is affected by the cutting conditions. Both types of copper cause little tool wear, but the need for high rake angle necessitates a smaller wedge angle at the tool edge. making the tools fragile.

4.2 Fwe-machining additives to single phase alloys Copper can be made free-machining by the additions of sulfur, tellurium, and selenium [33-381. These additions form copper sulfides, tellurides, and selenides, respectively, and impart machinability at slight sacrifice of conductivity and ductility. Tellurium copper is used in electronic components, as sulfur is reputed to cause poisoning in these systems, especially under vacuum. Another restriction for sulfur copper is that it is not suitable for silver plating. A major drawback for tellurium copper is its lack of recyclability when the swarf is to be reclaimed, as tellurium cannot be removed by normal refining methods. The two commercial sulfur and tellurium coppers, Mueller Alloys 1470 and 1450, have 0.40.6% Te and 0.2-0.5% S, respectively [39, 401. Both alloys have 95% IACS electrical conductivity, and earlier it was suggested that tellurium copper had slightly better machinability than sulfur copper [38]. However. later research by BNF Metals Technology Centre in the LJnited Kingdom has shown that, when the chemical composition and structure are optimized, in many respects sulfur copper has better machining properties than tellurium copper [34].

Fig. 5. Different regimes ofchip formation wth cutting speed in 60 40 brass. (a) 7.5 m’min gives b.u.e.. causing a large increase in effective rake angle and small chip b.u.ejtool contact gives rise to a thm chtp: (b) 30 m/min, irregular shear and saw tooth chip; (c) 240 m nun. a comparatively umform and continuous chip [23]. (Tool moxes t’rom left to right.)

Leaded

C97600

tuckel bronre

bronze

bronrc iO.6

4

0.8

4

Sn

1

3

4

3 1.7 2 0.5

4

Ph

K

zn

4 40

propcrttcs


20

< 0.5

comnosttton ‘Ni

typtcal

35.5 37.5 3x 34.5

Nomtnal

I. C‘ompocttton~.

IO

I0

twt”/~,I ‘Al’

i 0.35 Fe 3 Fe 0.5 Te 0.3 s

CO.5 P

< 0.35 Fe ~0.1 Fe

c- I .5 Fe. c I Mn

I Fe

I St

Others

and machtnability

i Hard ! Hard Xs ext. Hard Hard f Hard As ext. CW Hard Hard Hard

A5 cast

alloys

310 360 I40 415 510 420 140 300 300 300 300

240 190 290 I80

200

Aa cast As cast As cast H-f

I IO I00

As cast As cast

0.5”,. YS MPa

of free cuttmg

C‘ondition

rattnpa

“Electrical conductivity is in % IACS. (Values for wrought products represent annealed condition.) ’ Relative machinability rating where C36000, free-machining brass rates 100. ’ These alloys have moderate machinability, but are machined wtth stmtlar feeds and speeds as the free-machining

Architectural br0nL.e Aluminum bronze Tellurium copper Sulfur copper Leaded copper

C38500 C62300 Cl4500 Cl4700 C18700

phosphor

Free-cutting

C-s4400

Wrought alloys c’36000 Fret-cutting brass C48500 Leaded naval brass c37700 Forging brass C33500 Low-leaded brass

Aluminum

Slitcon

brass

yellow

brass

Leaded

name

red brass semt-red brass

Alloy

Leaded Leaded

c95300

(‘asung alloys C83600 C84400 Cx5700 C85800 (‘87900

Alloy no.

Table

400 510 360 510 s50 370 410 600 330 330 330

480 520 590 320

380

240 230

25 IS 45 8 7 20 30 I5 20 20 20

25 25 I5 20

15

30 2x

% El

properttes

LJTS MPn

Typical

alloys 13. 37. 66 ~691

28 I2 95 95 96

20

90 50 80 80 80

90

I 00 80 80 60

70

42 26 27 26

55’ 5

80

X0

90 90

Machtnabtltty”

I.5

15

22

IS I5

Electrical conductivity

Hqh strength nxing;inc\c Mang;~nese bran/e Silicon bras Tin hronle Navy M brorxe

hronx

0.3

0 8

IO h

0 c

St1

” References as for Table I. “Electrical conductivity is in % IACS. (Values for wrought Relative machinability rating where C.36000. free-machining

Wrought alloys C22600 Jewelry bronze C26000 Cartridge . brass. 70”‘(0 C26800 Yellow brass ('27000 C46400 Naval brass c-46700 Nickel silver C77000 Alluminum hrotve C61300

C‘ustinp allo>\ C86200 CX6500 a7500 c905nn C92200

Alloy “0.

21
39

35

12.5 30

IX
products represenl brass rates 100.

CO.20

CO.05 <0.07
I.5

.-0.5

?Y I4 7 4.’

21

7

. 0 i

4 I

(wt”,“,) Al

annealed

Nommal composition Ln NI Ph

Fe Fe Fe Fe

condition.)

2.7 Fe

Fe

0.005 0.05 0.05 0.07


< < i <

4 St

3 Fe. 3 Mn I Fe. I Mn

Others

cast cast cabt cast cast

Hard Hard

: Hard

Hard

Hard Hard

Aa As A\ As 4s

Condition

600 400

360

410

3YO 430

330 I90 210 I50 120

M Pa

0.5”V YS”

3 35

20

510 700 580

x

5 8

20 40 20 IS 30

“4 El.

properties

510

460 520

660 490 470 310 280

UTS MPa

‘Typical

6 12

26

27

40 28

7 20 6 II I4

Electrical conductivity”

30 30

30

30

30 30

30 26 SO 30 42

Machlnahllity

S. KUYllCAK

and M. SAHOO:

A REVlEW

‘c 22 lr. -&2= ‘d’ v

XtG --

OF THE

MACHINABILITY

OF COPPER-BASE

c -

m

0

ALLOYS

9

IO

S. KUYUC‘AK

and M. SAHOO:

A REVIEW

OF THE

MACHINABILITY

OF COPPER-BASE

ALLOYS

insoluble in solid copper. hence the copper matrix is closest to pure copper in its physical properties, such as conductivity. Compared to S, Te, and Se additions. lead gives the best surface tinish after machining, but makes the copper hot short. 4.3 llupkr

or predominantly

multi-phase

alloys

These comprise brasses and bronzes with sufficient alloying elements such as zinc. tin, aluminum. or silicon, to introduce a significant quantity of second phase. The hard second phase imparts strength at some loss of ductility. As a result, swarf from these alloys is semi-continuous, it is made up of seemingly connected but structurally discontinuous chips, presenting a saw-toothed appearance on their rough surface [Z]. In the Fig. 6. Two-tool method ot’ cutting temperature measurement 111 extreme case. with alloys of low ductility such as phosphor counterbalance turning. according to Murata. bronze. turnings break up of their own accord into short chips. This discontinuity in chip formation is an essential feature in these alloys, and is caused by periodic slip. It also causes In a drilling operation. for mmimum drill penetration trme. vibration in machining these alloys. which leads to a greater optimum sulfur level has been found to be 0.40.5%. little tendency for chatter and tool breakages. improvement results at higher sulfur contents. For a similar Fine grain size and finely dispersed second phase within a performance. tellurium copper requires 0.5.5-0.65% tellurium copper phase matrix improves the machinability of duplex [33]. Sulfur copper also has the advantage of higher scmp value. alloys [41, 421. Low-temperature annealing of IX//~ brass, for where tellurium is an undesirable impurity in most grades of instance, produces a fine /&phase, which gives discontinuous copper-based alloys. Drill torque, the tendency for drills to chips and longer tool life. Even quenching from the annealing break, and the swarf thickness all decrease with increasing temperature rather than air cooling, can make a difference [43]. sulfur, although the surface finish remains unaffected. Usually, a refined structure is more effective in improving the In general, tool life increases with sulfur content. but the machinability of these alloys in terms of chip size, than is an results show a wide scatter [33]. A closer correlation is obtained increase in hardness. when the sulfide particle size distribution is considered. Fine In the absence of free-machining additives, and at low machparticles smaller than 1 pm and coarse particles larger than 6.h ining speeds. below 30 m min...‘, aifl brasses form b.u.e. on the pm have been found to be beneficial for tool life, whereas the rake face of the tools [20, 231. This increases the effective shear effect of intermediate-sized particles is not so significant. When angle. gives thin, discontinuous chips, and reduces tool forces the sulfur copper structure is characterized in terms of these and wear, but causes burnishing and poor surface finish. The two parameters, parallel iso-wear lines are obtained on a (no. b.u.e diminishes in size at higher speeds, chips become thicker of particles < 1 pm mm ‘) vs tno. of particles > 6.6 @cmmm ‘1 and their shape vary from a “saw-tooth” form to a more uniplot. Although this analysis stdl does not explain all the scatter form thickness. in tool life, a similar result with higher correlation coefficient was first observed for the distribution of lead particles in frermachining brasses (Section 5.3). Until now. lead has been the free-machining additive of choice At 0.8% S. a slower-cooled. static-cast sulfur copper has to brasses and bronzes. About 90% of machining is carried more of the coarser particles than a faster-cooled DC-cast out on leaded alloys [42], and a great deal of research has been metal, hence, has better machinability. Faster cooling only carried out to elucidate and optimize the effect of lead on increases the intermediate sized particles at the expense of the machinability. Auger electron spectroscopy (AES) shows that coarser ones, which do not help improve the machinability, .4s a monolayer of lead atoms forms on the machined surface of for impurities, Cu,O particles must be limited in sulfur copper. leaded brasses (Fig. 7) [44, 451. The monolayer forms at 0.9% oxygen greater than 0.03% causes crater wear. Pb, and at the same time the secondary shear zone disappears Structure-wise, sulfur copper does not have the tendency to from the swarf. Lead striations parallel to cutting direction, a form coarse agglomerates of stringers. as occur in tellurium few microns wide and approximately 0.5 pm deep, also form copper. Hence, tellurium copper requires lubrication for good and feed the monolayer. Machinability of brasses increases with surface finish, produces coarser swarf, and has greater tendency lead. up to 2.8% Pb. increasing the surface coverage and depth for the drill to wander (measured by the number of drill deflecof these striations. Zinc concentration also increases from 40 to tions greater than 1.25 ). which increases the likelihood of tool 80% on the swarf surface. External lubrication does not affect breakages. On the other hand, both tellurides (vs sulfides) and this surface enrichment of lead and zinc during machining. the copper matrix are softer m tellurium copper. resulting in Leaded free-machining brass effectively becomes self-lubricalessened tool wear. Cold working improves the machinability ot ting. Figure 8 compares the microstructures and the chip morsulfur copper but has no effect on the machinability of tellurium phologies of the unleaded brass and the leaded free-machining copper. brass. as well as those of the silicon brass, a lead-free alternative In addttion to sulfur, tellurium, and selenium. lead also is to Alloy C36000. used to make copper free-machining. At I% Pb. the machWolfenden [46] looked at the possibility of lead’s low melting inability rating of copper Increases from 20 to 80. Lead 1s pomt having any bearing on imparting free-machining proper-

S. KUYUCAK

and M. SAHOO:

bulk

Fig. 7. Lead depth

Pb

A REVIEW

OF THE

lava1

profile of a brass swarf by means of Auger Spectroscopy, from Stoddart.

Electron

ties.He found that melting only occursat the back of the rake face at higher speeds,and is not significant. The lubricating effect of lead is maintained at low speeds,when there is no melting, and is attributed to the high hydrostatic pressureand slip squeezingand spreadingthe leadparticleson the tool-chip interface.Leadis believedto act in three waysto promote freemachiningcharacteristics[47-49]: Lead reducesthe shear strain to fracture (ductility), as a result, discontinuouschips form in the primary shearzone by void-sheetmechanismof ductile fracture, initiated by lead particles,and runs from cutting edgeto free surface. Leadisdrawn out of the cupletsand isdepositedon the tool-chip interface,reducingthe friction coefficientandpreventing the formation of b.u.e. Lead also promotesa more pronouncedchip curl, which helpschip to fracture to give a fine swarf. The standardfree-machiningbrassesdiffer in North America andthe United Kingdomin the amountof p-phasethey contain. The American standardFMB (Cu, 36 Zn, l-3 Pb) is richer in copperand lower in /l-phasethan the British standard(Cu, 39 Zn, l-3 Pb). In many respects,the American standard has better machinability, especiallywith regardsto tool life, but the British standardproducessmallerchips [16, 501.This can be important whenmachiningvery smallparts(e.g. ball pointsfor pens)that needto be separatedfrom swarf by sieving. The BNF Metals ResearchCentre in the United Kingdom tried to optimize the FMB with regardsto lead content and distribution and the effect of impurities[3I, 5l-531. Drill penetration time and cutting force both decreasewith increasing lead content (Fig. 9). In singlepoint turning, however. machinability in terms of tool life increaseswith the concentration of smalland large lead particles(intermediate-sizedparticles not playing an important role). asfollows:

MACHINABILITY

OF COPPER-BASE

ALLOYS

11

increasingthe lead content from 3 to 4.5%. This processing route givesa favorable leadparticle sizedistribution, producing a great many smallparticles,yet retaining a sufficientnumber of the larger particles.Up to two-fold improvementin tool life hasbeenreportedby BNF with this newalloy. This wasrealized with the British standardFMB, the effect wassmallerwith the American standardFMB. The higherleadcontent reducedthe Izod impact strength by one third, but other propertieswere not affected. Another important considerationin highly machinablealloys is the presenceof hard particles[3, 17, 33, 54, 551.Although, mostsecondphaseparticlescausea reductionin shearstrain to fracture, and would be expected to aid machinability, hard particlescauseunduetool wear. In brasses,iron-rich particles containingsiliconup to 1pmdiameterareof particular concern, as both theseelementsare expectedimpuritiesin copper-base alloys. Silicon reducesthe solubility of iron in copper, hence, the conditionsunderwhich theseparticlescomeout of solution dependon the iron and siliconcontent, aswell asthe cooling rate of the castingprocess.In static-castmolds, iron particles occur at 0.15% Fe, 0.002% Si. In semi-continuous casting,the faster cooling rate preventstheseparticlesfrom coming out of solution up to 0.4% Fe. As long asiron is in solution, it does not have a detrimental effect on tool life. Eliminating ironrich particlesfrom the brassmatrix leadsto a further two-fold improvement in tool life over and above the gainsmade by increasingthe leadcontent. Tin is another impurity in brasses.Above about 0.5% it causesthe formation of hard y-phasearound /?-phase and grain boundaries.The presenceof tin-rich y-phaseshortenstool life, and, unlike iron-rich particles,also raisestool forces,drilling time under constant load, and impairsthe surfacefinish [54]. Other detrimentalparticles are oxides(silica) and zinc sulfide [55]. The latter can be prevented by treating the copper melt with magnesiumto scavengeany sulfur. Lead improves the machinability of brassesin all aspects except surfacefinish. Murata [28] found that, especiallyat low lead additions (0.5-1.5%), surfaceroughnessgoesthrough a maximum,then improves again at higher lead contents. The smoothestsurfacesare obtainedin lead-freebrasses,(Fig. 11). 3.5 Altematiues

to leaded,free-machining

alloys

Becauseof the health concernsabout lead, and its expected restrictionby legislation.alternativestrategieshavebeensought to reduceor eliminateleadin the FMBs, or prevent its discharge to potable water. A joint study, conducted by International Copper Association(ICA) and Copper DevelopmentInstitute (CDA), haveshownthat, amongthe known alloys,siliconbrass (C87600)would bea goodcompromiseasa lead-freealloy with adequatemachinability [56]. This alloy turned out to be more machinablethan a reducedlead alloy (C83450with 1.5% Pb), and wasjudgedto be 60% asmachinableasthe free-machining red brass(C83600).The authorspoint out that any replacement alloy would disrupt the leadbearingcopper scrapmarket, and M cc No. of Pb particles< 1pm) alsowould affect the pricesof the moreexpensiveraw materials. . (No. of Pbparticles> 8 pm)’ ’ The combinedeffect of the two would be a 2&35% increasein Hence, a plot of large vs smallparticlesin different FMBs raw material costs for a given part when leadedFMBs are produceshyperbola of iso-wear lines (Fig. 10). It has been completely replacedwith silicon brass.This increasein cost possibleto improve the FMB by implementinga fastercooling would be less(g-24%), if somelead can be tolerated in the rate process,such as semi-continuousvs static casting, and replacementalloy, allowingthe recyclingof leadedscrap.How-

Fig. 8. Microstructures and chip morphologies of the unleaded and leaded brasses, and silicon brass. From top to bottom on the right hand side: 65j35 brass. leaded brass C36000. and silicon brass C87800. On the left hand side are their respective chip morphologies showing the extent of cracks on a fine scale. The chip surfaces of leaded brass and silicon brass had high concentrations of lead and silicon-rich particles at the cracks.

respectively. Arrows show the direction of cutting [59].

ever. in a plumbing fitting, machining represents 20p60’:o of the manufacturing cost. Therefore. in a highly machined part. machinability has a greater effect on the final cost than the raw materials. Although silicon brass takes twice as long to machine compared to the leaded red brass. its cost of machining has been estimated to be only 4% higher [56]. The challenge is finding a replacement alloy for leaded FMBs that meets demands for adequate castability. solderability, plating characteristics. corrosion resistance. and pressure tightness, as well as adequate machinability and reasonable cost of raw mater&. Although in the past silicon brass has been reported to be difficult to solder and copperrnickel--chrome-plate. research at MTL has shown that good platability in this alloy can be achieved without difficulty [57]. For solderability. though. no

lead-free solder/flux combination has been found to wet the C87800 silicon brass adequately. One lead-free solder/flux combination has been reported to give good results on C87600, but has not been evaluated by the CDA Solder Flux Evaluation and Listing Program, for its effect on pitting corrosion of copper tube [56]. On new alloy development. attempts have been made to incorporate soft particles such as graphite or boron nitride into the brass matrix to render it free-machining without lead [58, 591. Because of the large difference in density between these particles and the copper matrix. and their nonwetting characteristics. achieving a homogeneous distribution is difficult. However, a claim has been made for achieving a good distribution of graphite particles in copper matrix using a simple

S. KUYUCAK

and M. SAHOO: A REVIEW OF THE MACHINABILITY

13

OF COPPER-BASE ALLOYS ._

I

1

som!continuousJy cast (127mm dia. billets) o static chill cast (127mm dia blllets)(pourQd In cast It-on moulds) 0 matorlals used In full-scale machining trials (219mm dia. semicontlnuously or statlc-chlll-

’

l

(al

l

o

ul

I I I I samicontinuously static chill cast iron mould)

I cast (poured

I

I

1

in a cast

z

-

Cast hQS

blllQtS) Of Qquai

225 coon nose wear lndlvldual

I

1101

2.6 2.8

I

3.0 3.2

speed. 1650

I

0

Depth of Cut = 1 mm Feed = 0.2 mm Rake Angle = 0’

i

for

avwagas

% 50 NUMBER

(b)

mm

4.2

load. 1 ij kg

rev/mm:

WQaC

I

3.4 3.6 3.6 4.0 LEAD,

spindle

I

tOOI

land wtdth, materials

cutting

min,

OF

II

100 150 200 260 PARTICLES LARGER THAN 8pm DIA /mm2

conditions : surface speed, feed rate. 0.076 mm/rev; depth

82

mlmin ; spindle of cut, 1.27 m m

speed.

300

1000

rev/

Fig. IO. Effect of number of small and large lead particles on tool wear during single-point turning of FMB having 57 I,?% Cu, from Davies.

? E ;

-1... ’ IO-‘.,

.-

Force - ---- . . Feed _--.

I OL-

L..

I-.

-

.~ . -~

. _.

-~

_

0

3 4 Content, wi% Fig. 9. Effect of lead content on drill penetration time (a). and cutting force (h) 1 Lead

2

casting technique and wetting agents. Graphite powders coated with copper and nickel have also become available, which should help their wetting characteristics [60]. Both graphite and boron nitride have hexagonal-layered structures and lubricating properties. They would help machinability by towering the shear ductility of the alloy, hence helpmg to break up the swari into small-sized chips at the primary shear plane- and reducing the power requirement for machining. However, unlike lead. they are not ductile and would not be expected to spread out and cover the tool-chip surface ar the secondary shear zone. Hence, their lubricating property would be more limited. Another idea was to introduce MnS inclusions into the brasses (manganese sulfide has been used in free machining steels [61]). However, in brasses. a complex zinc- manganese sulfide forms. which actually reduces the machinability. One must also bear in mind that the machinability of steels and brasses have different scales of magnitude: the free-machining steels rate only 20 against the standard free-machining brass C36000. A significant development in this regard has been the intro-

duction of a bismuth alloy developed by AT&T Bell Laboratories [62]. Bismuth, by itself, severely embrittles the copper, even at quantities as small as 0.001%. This is caused by the high wettability of liquid bismuth, which forms a continuous network around the solidifying copper grains. Bismuth, having a rhombohedral structure, is intrinsically brittle, and its presence at the grain boundaries leads to intergranular failure. To prevent the formation of intergranular films, the dihedral angle between the liquid inclusion and the copper must be increased to a value greater than 60’. This has been achieved by reducing the surface tension of copper through addition of a third element. such as P. In, or Sn. that is soluble in copper but not in bismuth. When the diff‘erence in surface tension between copper (1.3 N m-‘) and bismuth (0.35 N mm’) is reduced, the net effect would be an increase in the dihedral angle. Once the embrittting effect of bismuth is circumvented, the

7

Surface Roughness,Fm “$83

/

0

Oepth of Cut = 1 mm Feed=D.l2mm

OF

“rJ-

i

21.

B ! 2 1t i_0

i I 25

50 Cutting

75 Speed,

100

m/mln

Fig. I I. Effect of lead on surface roughness. from Murata.

14

S. KUYUCAK

and M. SAHOO:

A REVIEW

OF THE

copper and brass alloys prepared with I o/o Bi, 0.5% In additions are highly machinable and comparable to the leaded FMB. based on the power-consumption-in-drilling test ratings [62]. Full scale machinability tests have not yet been reported for the bismuth alloys. Bismuth, unlike lead. is not toxic. Indeed, its compounds have various therapeutic uses in the pharmaceutical industry [63]. Although its availability has been a greater concern, a case has been made for an adequate supply of bismuth once its price rises to about $1. I kg ’ ($5 lb-‘) [63]. The American Foundrymen’s Society has recently formed a consortium to study the viability of bismuth and bismuth-selenium additions to Cu-Zn-Sn red brass for free-machining applications. To this end, CANMET carried out a literature review and analysis in bismuth and selenium supply. demand, and toxicity. and made recommendations to further develop these alloys [64]. Another approach to reducing the lead discharge from leaded FMB parts has been to treat these parts in a suitable solvent to remove the surface layer of lead [65]. Research at the University of Florida indicates that lead can be removed with a 0. I N sodium acetate/acetic acid solution at 45 C and pH 4 in less than 1 h. A 10 ppm benzotriazole. corrosion inhibitor, is added to prevent dezincification and concurrent dissolution of copper. The solution can be stripped from lead and recycled. Surfaces treated in this way did not show any lead discharge (< 1 ppb. detection limit of ICP analytical technique) in a lead teachate test.

5. SUMMARY

AND CONCLUSIONS

In highly machined parts. the cost of machining represents a large portion of the total cost of a manufactured part. Therefore, the use of machinable alloys is essential in realizing significant economies in manufacturing. Most metals are made machinable by incorporating soft, second-phase particles into their structure. These act in two ways to impart machinability: l

l

They reduce shear ductility, causing swarf to break up into small chips at the primary shear plane. This action reduces the power required for machining and also the temperature rise at the cutting edge, extending the toot life. They reduce shear strength at the secondary shear zone (sliding friction between the toot’chip interface) by way of internal lubrication. This action improves surface finish. and further reduces the toot forces, increasing the shear angle. thus reducing the chip thickness and making it possible to use low or negative rake angles. Low rake angles enable machinists to design more robust toots with high wedge angles.

Until now, lead has been the addition ofchoice for copper-base alloys, as it supremely fulfils both these functions. However. health concerns about the use of leaded alloys, especially in potable water systems, may preclude their use in plumbing alloys. Among the existing alloys, silicon brass has been evatuated to be the best lead-free alloy with adequate machinability. Engineering new free-machining alloys to replace the leaded brasses has been very challenging, nevertheless. sigmficant progress has been made with copper-bismuth alloys. Another cre-

MACHINABILITY

OF COPPER-BASE

ative approach components in a Lead discharge reported to have test [66-693 A~,knorr/~,~f~emrn~s~ Copper Association Canadian Copper ance in searching MTL personnel providing quality

ALLOYS

taken has been to treat the machined solvent to dissolve the surface layers of lead. from such treated components has been been reduced to less than I ppb in a teachate

-The authors would like to thank the International for their financial support in preparing this review, and Brass Development Association for their assisttheir data base and providing timely abstracts, and P. Newcombe. C. Bibby, D. Ashe for their help in material for figures and tables.

REFERENCES 1. ASM. Met& Handbook, 16, Machining, 9th edn. ASM Int., Metals Park. OH, 1989, p. v. 2. Anon., in The Machining ofCopper and its Alloys, CDA Publ. No. 34. Copper Development Association. UK, 1939 (revised 1952). 3. G. J. Hill, Metullurgiu 80, 3-l I, 59-63 (1969). 4. J. E. Williams, E. F. Smart and D. R. Milner, Metallurgiu 81, 310. 51 60 (1970). 5. J. T. Black, in Metals Hundbook. 16, Machining, 9th edn. ASM Int.. Metals Park. OH, 1989, pp. 7--l 1. 6. P. H. Cohen, in Metals Handbook, 16, Machining, 9th edn. ASM Int.. Metals Park, OH, 1989, pp. 13-18. 7. S. Kalpakjian, in Marks ‘Standard Hundbook,for Mechanical Engineers. McGraw-Hill, 1987, Ch. 13.4. 8. E. M. Trent, in Metal Curt&g. Butterworths, 1977. 9. E. J A. Armarego and R. H. Brown. in The Machining of Metals. Prentice-Hall, Englewood Cliffs, NJ. 1969. 10. B. F von Turkovich, in Handbook ofHigh Speed Machining Technolog), (edited by R. I. King). Chapman and Hall, NY, 1986, p. 38. 1 1. G. W. Rowe and P. T. Spick, Truns. ASME (I), J. of Engngfor Ind. 89. 530-538 (1967). 12. C. S. Zimmerman, S. P. Boppana and K. Katbi. in Metals HundhooX. 16. Muchinimg. 9th edn. ASM Int.. Metals Park, OH, 1989, pp. 63947. I?. M. Field. J. F. Kahles and W. P. Koster. in Metals Handbook, 16. ,Mrrchlniny. 9th edn. ASM Int.. Metals Park, OH. 1989. pp. 19-36. 14. L. Alden. in Metals Handbook, 16. Machining. 9th edn. ASM Int., Metals Park. OH. 1989 pp. 37-48. 15. K. Okushima, J. Japan Copper Brass Res. Assn 4,4-8 (1965). 16. B. Hodges. .Ausrrulusiun Eng. 56, 50-51 (1963). 17. B. Mills. A. H. Redford and A. W. J. Chisholm. Annals CZRP 27, 45-8 ( 1978). 18. P. Arzst, Metalworking 23. 44 5 (1967). 19. S. Jeelani, and K. Ramakrishnan, J. Mater. Sci. 20,301 I-17 (1985). 20. Anon., Machining rod handbook -sopper, brass, bronze, CDA Rep. No. 702:9. 1979, 31 pp. 21. J. E. Williams, The effects of internal inclusions on the machining performance of copper and iron alloys, Final Rep., Army Res. Office. N. Carolina, Aug. 1977. 22. P. Isler. G. Barbezat and W. Form, Metals Mater. Met. Reo. 5, 265 6 11971). 23. J. E. Williams, E. F. Smart and D. R. Milner. Metallurgia 81. 56 (1970). 24. E. K. Henrikson, ASME Paper No. 53-5-9. 25. R. Murara, Machinability testing of copper alloys, JCDA Rep. No. 78, Dec. 1972. 14 pp. 26. Anon., Practical suggestions for machining copper, brass, bronze, and nickel-silver, (Trade Lit.). Publ. B-3. Anaconda, Brass Div., Waterbury, CT. 1969, 36 pages. 27. T. F. G. Fitzmaurice, American Machinist 113. 103-14 (1969). 2X. R. Murata and H. Takeyama, J. Japan Copper Brass Res. Assn 11, 70 77, 78-87 (1971). 29. J. R. Ewell, American Machinist 109. 72-74 (1965). 30. M. (’ Shaw. Metal Curting Principles. Oxford University Press, 19x4.

S. KUYUCAK

and M. SAHOO:

A REVIEW

OF THE

31. M. A. Staley. E. F. Smart and M. L. H. Wise. in C‘opper ‘X3. The Metals Society, London, 1983. pp. 30. I-30.12. 32. J. A. Williams and W. M. Stobbs, Mera1.c Tech. 6. 424-32 (19791. 33. D. W. Davies, Metals Tech. 3, 272 -84 (1976). 34. D. W. Davies, &ctrical Rw. I%, I85 -6 (1975). 35. Anon.. The machinability of Amsulfalloy (Trade Lit.). Amco Sales. Div. of American Metal Climax. 1975. 17 pp. 36. Anon.. CDA No. 147-Sulfur copper, Mueller alloy No. 1470 (Trade Lit.). Data Sheet No. 31. Mueller Brass Co., Port Huron. MI, 1971. 4 pp. 37. E. Bresciani, Tech. Bull. 38. 6 ( 1965). 38. C. S. Smith, AIME Trans. 128, 325-34 (1938). 39. Anon., CDA No. 145 -Tellurium copper. Mueller alloy No. 1450 (Trade Lit.), Data Sheet No. 31. Mueller Brass Co., Port Huron. MI, 1971. 4 pp. 40. Canadian Copper and Brass Development Association. CIDEC Technical Report No. 22. Aug. 1966. 8 pp. 41. S. Tada and S. Ikeno, J. Japan Copper Brm Res. Am 22. 44-51 (1983). 42. L. G. Martm, Canadian Copper 56. 8 IO (1974). 43. S. Muromachi and S. Tada. J. Japan Copper Bras.\ Res. AS.VI 10. 146-9 (1971). 44. C. T. H. Stoddart and C. Lea. Mrr. Marer.. Nov.. 27-28 (1979). 45. C. T. H. Stoddart, C. Lea. W. A. Dench. P. Green. and H. R. Pettit, Metals Tech. 6, 176-84 (1979). 46. A. Wolfenden and P. K. Wright. Metals Tech. X. 297.-302 (1979) 47. N. Gane. Philos. Maq. .4 43. 545-66 (1981). 48. N. Gane; in Fracture-at Work. the 4th Tewksbury Symp. on Fracture, Univ. of Melbourne, Australia. Feb. 12--14, 1979, pp. 13. I 13.22. 49. S. Zaiman. J. Japan Copper Brass Res. 4s.w 9. h&70 (1979). 50. J. Seidel, IL Rame 4, 15-38 (1966). 51. D. W. Davies. J. Insfitute o/Metal.\ 101. 125-37 (1973). 52. J. E. Bowers, Metallurgia 49. 55-61 (1982). 53. E. C. Mantle, Copper 3. 11~ 13 (1972). 54. S. Muromachi and S. Tada. Bull. Japan fmt. Mrrtrls 9, IO&l3 (1970).

MACHINABILITY

OF COPPER-BASE

ALLOYS

I5

55. R. M. Winter and H. Burghoff, Engng Conf Tech. Paper EM66 169. ASTME, 1966. 14 pp. 56. W. H. Dresher and D. T. Peters, ICA and CDA Internal Report, 1991. 57. M. Sahoo, J. L. Dion, M. Elboujdani. and V. S. Sastri, Permanent mold casting of copper-base alloys, MTL 93-8 (TR-R). Metals Technoloev Laboratories. CANMET. Ottawa, Canada, Contract Report fo;ICA Project No. 452A, 1993. 58. P. K. Rohatgi, S. Ray, D. Nath and N. Church, Cast lead-free copper graphite composite alloys with improved machinability, 92159. 96th AFS Casting Congress, Milwaukee, WI, 3-7 May 1992. 59. M. Sahoo. J. L. Dion, S. Kuyucak, and M. Shehata, A feasibility study of the production of free-machining brass without lead, MTL 93-6 (TR-R). Metals Technology Laboratories, CANMET, Ottawa, Canada, Contract Report for ICA Project No. 471, 1993. 60. M. Castro, Superior Graphite Co., Chicago, IL, Private Communication, 1993. 61. R. Milovic and J. Wallbank, in The Machinability of Engineering Maferials. ASM Int., Materials Park. OH, 1983, pp. 2341. 62. J. T. Plewes and D. N. Loiacono, Adu. Mater. Proc., Oct., 23-27 (1991). 63. J. T. Plewes and T. D. Schalbach, Mod. Cast., Feb., 32-33 (1993). 64. L. V. Whiting and M. Sahoo, Modified red brass with bismuth, MTL 93-43 [CF). Metals Technology Laboratories, CANMET, Ottawa, Canada, Contract Report for AFS Project BI-I, 1993. 65. D. T. Peters et al., Removal of lead from leaded brass surfaces, 92170. 96th AFS Casting Congress, Milwaukee, WI, 3-7 May 1992. 66 Anon., in Metals Handbook, 16, Machining, 9th edn. ASM Int., Metals Park, OH. 1989, pp. 805-l 3. 67. CDA. Standards Handbook-Copper, Brass, Bronze; Cast Products, ,411op D&a/7. Copper Development Association, New York, 1973. 68. CDA. Standards Handbook-Copper, Brass, Bronze; Wrought Mill Products, Alloy Data/2. Copper Development Association, New York, 1978. 69. ASM, Met& Handbook, 2, Properties and Selection: Non-ferrous .411o.vs and Special Purpose Materials. 10th edn. ASM Int., Metals Park. OH, 1990, pp. 265,356.