wire technology process engineering and metallurgy pdf

PREFACE
Being in a family with several generations of professional practitioners in
metals processing and the teaching thereof, I suppose my writing of this
book was inevitable. Even so, I must clearly acknowledge two strong
influences outside of the family sphere. The first was the late Walter
A. (Al) Backofen, professor of metallurgy and materials science at MIT a
half-century or so ago.

 

 

While I received the benefit of some of his lectures,
his major impact was by way of his book Deformation Processing, AddisonWesley, 1972. This book was the first that I am aware of to teach deformation processing with major emphasis on D, the shape of the deformation
zone.

 

 

To be sure, D or its equivalent was utilized in some of the more
enlightened mid-twentieth century wire drawing research (most notably
that of J. G. Wistreich) and citations of the importance of deformation zone
geometry can be found in the literature of the 1920’s.

 

 

 

However, Backofen
powerfully employed it as a teaching tool, bringing together a considerable
array of mechanical analyses, process designs and mechanical metallurgical
phenomenology. As a young metallurgist, I assumed that just about everybody used D, only to find out that its work-a-day industrial applications had
been minimal.

 

 

 

In this context, I applied it (arguably even over applied it)
every chance that I had, and in the wire industry I believe it has been of
significant value. In any case, it is central to much of this book, and I have
Professor Backofen to thank.

 

 

 

The other influence that I would like to cite was Dr. Alan T. Male,
my manager during the years that I spent at Westinghouse Research
Laboratories. Alan was, of course, renown for his development of the
ring compression test that quantifies friction in forging (a brilliant application of deformation zone geometry, incidentally).

 

 

 

Moreover, he had
been a faculty member at The University of Birmingham and had an
instinctive and synergistic approach to applying rigorous research technique and perspective to industrial processing systems. He, early on,
directed my involvement in a wide variety of sophisticated wire processing studies, as well as in the supervision of industrial society seminars
and short courses.

 

 

When I left Westinghouse to join the faculty at
Rensselaer Polytechnic Institute in 1974, I had been given a thorough
education in wire processing, to go with my broader backgrounds in
metallurgy and metals processing.

The General Idea
1.1.1 Drawing
The concept of drawing addressed in this book involves pulling wire, rod,
or bar through a die, or converging channel to decrease cross-sectional area
and increase length.

 

 

 

 

In the majority of cases the cross section is circular,
although non-circular cross sections may be drawn and/or created by
drawing. In comparison to rolling, drawing offers much better dimensional
control, lower capital equipment cost, and extension to small cross sections.
In comparison to extrusion, drawing offers continuous processing, lower
capital equipment cost, and extension to small cross sections.
1.1.2 Wire, rod, and bar

 

In general, the analyses of wire, rod, and bar drawing are similar, and we
may use the term workpiece, or simply the term “wire,” when there is no
distinction to be drawn. However, there are major practical and commercial
issues to be addressed among these terms. Bar drawing usually involves
stock that is too large in cross section to be coiled, and hence must be drawn
straight. Round bar stock may be 1 to 10 cm in diameter or even larger.

 

 

 

 

 

Prior to drawing, bar stock may have been cast, rolled, extruded, or swaged

1.1.3 Materials
Essentially any reasonably deformable material can be drawn, and the general
analysis is the same regardless of the wire, rod, or bar material. The individual
technologies for the major commercial materials, however, involve many
nuances.

 

 

 

 

The drawing technologies are often divided into ferrous (steel) and
non-ferrous and electrical (usually copper and aluminum), although there
is specialty production and research and development interest in such highvalue-added products as thermocouple wire, precious metal wire, biomedical
wire, wire for high temperature service, superconducting wire, and so on.
Apart from the material drawn, drawing technology depends substantially on the materials used for dies (“carbide,” diamond, tool steel) and on
the materials or formulations used for lubricants and coatings.
1.2. HOW DOES DRAWING WORK?
1.2.1 Why not simply stretch the wire, rod, or bar?
It can be argued, at least in principle, that some of the objectives of drawing
could be achieved by simply stretching the wire with a pulling force. The
cross section could be reduced and elongation accomplished, but dies would
not be needed and the friction and metal flow issues presented by the die
could be avoided.

 

 

 

 

The principal problem with just stretching the wire with a pulling force
is the necking phenomenon. Basically, after a certain amount of uniform
stretching, all further elongation will be concentrated at a single location
(a neck), which will rapidly thin and break.

 

 

 

 

This occurs because the decrease

1.2.2 A simple explanation of the drawing process
In the drawing process, a pulling force and a pressure force, from the die,
combine to cause the wire to extend and reduce in cross-sectional area, while
passing through the die, as schematically illustrated in Figure 1.1. Because of
this combined effect, the pulling force or drawing force can be less than the
force that would cause the wire to stretch, neck, and break downstream from
the die. On the other hand, if a reduction too large in cross-sectional area is
attempted at the die, the drawing force may break the wire. In commercial
practice, engineered pulling loads are rarely above 60% of the as-drawn
strength, and the area reduction in a single drawing pass is rarely above 30
or 35%, and is often much lower.

 

 

 

 

A particularly common reduction in nonferrous drawing is the American Wire Gage (AWG) number, or about
20.7%. Many drawing passes are needed to achieve large overall reductions.
1.2.3 Comparison to other processes
The use of pulling or pushing forces, together with dies or rolls, is common
to many deformation processes1,2, as shown in Figure 1.2. Figure 1.2a illustrates