Hot drawing or cupping is a process for
making cup shapes of some depth (more than sev-
eral times stock thickness) and thick and seamless
tubes and cylinders from blooms, flat plate, or sheet.
The process is similar to cold deep drawing of sheet
metal (except that the material may be thinned
during the operation whereas in deep drawing the
material flows into the die and tends to thicken).
Tubular parts can be made when the cup formed in
one such operation is reheated and redrawn to a nar-
rower diameter; then reheated and pushed through a
series of draw bench dies that further reduce its
diameter and extend its length. Fig. 2A2 illustrates
both the cup-forming and redrawing operations. In
addition to the redrawing that produces cylinders
and seamless tubing, the process is used for forming
relatively simple shapes, usually cylindrical, in thick
material.
(Handbook of Manufacturing Processes, James G. Bralla, page: 34)
Hot Drawing(old)
Hot drawing is a process of making cup shaped or cylindrical components from a sheet metal blank,which is first heated to hot working temperature and later place on a die and a punch is hammered on it from the top,resulting into a cup shaped form.Hot drawing of the sheet metal blank into a cylindirical form is accomplished by repeating the operation of drawing at several stages,for example,the cup shaped product is heated again and drawn into a longer cylindirical pieced with reduced diameter.Further drawing is carried out on horizontal drawn-bench and the final finished cylinder with longer length and much reduced diameter.
This way,by drawing through a number of dies arranged in descending order of their diameter,reduction in wall thickness is gradual in various stages.The farther end of the drawn product being blind ,can be cut off the produce a long pipe with through the hole.Hot drawing is a useful process in the sense that the mechanical and chemical properties of the metal (under drawing )remain unimpaired.
The process is commonly used for the production of thick walled seamless tubes and cylinders.
(Manufacturing Processes,J.P.Kaushish, p.411)01.38 17/04/2011
2)Cylindrical Grinding(new)(machining)
Cylindrical grinding is used to produce external cylindrical
surfaces by removing material, creating
smoother surfaces, and providing more
precise dimensions. In all such operations, both the
grinding wheel and the work rotate. The grinding
wheel moves toward the workpiece to contact it and
away from the work after the grinding is completed.
However, in many cases, the wheel also traverses
the work or vice versa. There are two basic methods
for grinding the surfaces of components such as
shafts, axles, cylinders, and rolls: center-type grinding
and centerless grinding.
a. Center-Type Cylindrical Grinding
Center-Type Cylindrical Grinding is
performed on lathe-like machines. The workpiece
is usually held at each end on pointed centers and is
rotated about these centers. (It may also be held by a
chuck or other holding device.) The grinding wheel
normally rotates on an axis parallel to the axis of the
workpiece. The wheel and the workpiece contra-
rotate so that the contacting surfaces move in oppo-
site directions. After the wheel and the work have
made contact, there usually is axial motion between
the wheel and the work for the full length of the sur-
face to be ground, plus some overrun. The wheel
may also be fed only transversely into the work-
piece as it rotates. In this case, the wheel has either
a flat face or have a form dressed into it. The ground
surface of the workpiece, then, can have contours,
grooves, or whatever shape is dressed into the face
of the wheel. If tapered surfaces are desired, the
machine is set so that the axes of rotation of the work
and the wheel are not parallel. Long, slender parts,
and others subject to deflection or vibration during
grinding may be supported by a steady rest. Fig. 3C 1 a
illustrates the process.
b) Centerless Grinding
Centerless grinding is a process for
machining cylindrical surfaces wherein the work-
piece is not held between centers or in a chuck.
Instead, the work is supported by a work-rest blade
at the correct height and contained between two
wheels, as shown in Fig. 3Clb. One wheel is the
grinding wheel; the other is a regulating wheel.
The regulating wheel does not grind; it rotates the
workpiece at a constant rate of speed. The
process produces accurate diameters and round-
ness, with smooth surfaces in parts such as pins,
shafts, and rings. Both throughfeed and infeed
methods can be used, and production can be quite
rapid. The method is normally not applicable if
there are flats, keyways, or other interruptions in
the workpiece’s cylindrical surface. Conventional
centerless grinders can accommodate solid parts up
to about 7 in (18 cm) in diameter and rings and
tubing up to about .lo in (25 cm) in diameter.
(Handbook of Manufacturing Processes, James G. Bralla, page: 100)
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there is no old description
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3) Abrasive Belt Grinding(new)(machining)
Abrasive belt grinding uses an abrasive-
coated cloth belt to remove metal. The endless belt
runs between a drive wheel and a contact wheel,
and the workpiece bears against the belt at the con-
tact wheel. The abrasive grains on the belt are
arranged with orientation and spacing to optimize
metal removal rates. The process can provide faster
metal removal than grinding with a wheel and is
then often referred to as abrasive belt machining.
Metal-removal rates of 30 in3/min/in (193 cm3/
min/cm) of belt width are feasible with standard
belts.4 This rate is faster than those attainable with
milling machines, even under the fastest metal
removal conditions. Belts as wide as 10 ft (3 m)
allow the entire surface to be ground in one pass.
The process can provide lower heat levels than
grinding with an abrasive wheel because the belt
carries away heat effectively. Lubricants may be
used to facilitate the operation. The approach is
used for rough metal removal from castings, forg-
ings, and other shapes, especially when the work-
piece is large. Surface, cylindrical, and centerless
grinding can be performed with abrasive belts.
Abrasive belts can also be used for hand grinding
and polishing.
(Handbook of Manufacturing Processes, James G. Bralla, page: 104)
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there is no old description
-----------------------
4)Ferrimagnetism
Ferrites exhibit a kind of magnetism known as ferrimagnetism (Fig. 1.2d) that is in
some ways similar to both ferromagnetism and antiferromagnetism. In ferrimagnetic
materials, since ions are placed on two different types of lattice sites, such that
spins on one site type are oppositely oriented to spins on the other lattice site
type, they tend to be compared to antiferromagnetic materials. However, one of the
resultant magnetizations on the two lattice sites is stronger than the other, so that the
result is a total non zero, spontaneous magnetization. Since antiferromagnets are not
strongly magnetic, and ferrimagnets have a spontaneous and non-negligible magne-
tization, ferrimagnetic materials are often compared to ferromagnets. And similar
to ferromagnetic materials, an increase in temperature brings about a disturbance
in the spin arrangement that culminates in completely random orientation of spins
at the Curie temperature. At this temperature, the ferrimagnet loses its spontaneous
magnetization and becomes paramagnetic (Fig. 1.2d). Ferromagnetic materials also
have a Curie point above which they exhibit paramagnetic behavior [3].
Example 1.1. Comment on the consequences of adding different concentrations of
Ge to Fe3O4 thin films
Answer: Magnetite, a ferrimagnetic material with extensive history and diverse
technical applications, finds use today in advanced areas such as spintronics or spin
valves due to its half–metallic character. Nevertheless, the tunnel magnetoresistance
behavior on which these modern applications are based (discussed in later chapters)
encounters some problems when Fe3O4 is used as an electrode grown epitaxially
on a MgO single crystal. In this case, the interface between the magnetite electrode
and tunnel barrier is complicated and difficult to control. To solve some of these
problems, researchers have prepared the magnetite film by sputtering of a composite
target with added Ge, in order to suppress the iron deficit which occurs during the
sputtering process [4]. Ge is thermodynamically stable in a magnetite matrix, and
it was confirmed that by adding 5 at% Ge, a thin magnetite film is still obtained.
Furthermore, these magnetite thin films are ferrimagnetic, even though Ge has been
added. Nevertheless, higher concentrations ( 14%) of Ge result in the magnetite
films becoming paramagnetic. The advantage of adding Ge seems to be that it
ensures formation of only the magnetite phase, whereas sputtering the magnetite
target without Ge results in two phases, magnetite and hematite. The latter fact is
detrimental to the electrode/tunnel barrier interface characteristics of spintronics
applications.
Magnetism Basics and Applications, Carmen-Gabriela Stefanita, page: 8
5) Ferromagnetism
We should finally mention ferromagnetism; however, given that so many concepts
in this book apply directly to ferromagnetic materials, they will be frequently
discussed, and, therefore, no section alone can be dedicated to them. In essence,
ferromagnetic materials have a permeability that depends on the field strength
and on the previous magnetic history (see Hysteresis Loop mentioned above).
They approach magnetic saturation as the field strength continues to increase,
meaning that the material can only be magnetized to a finite limit. Ferromagnets
contain spontaneously magnetized magnetic domains, where a magnetic domain is
an entity with a total domain magnetization. This is a small, magnetized region
containing many atoms with individual magnetic moments that align parallel to
each other, against the forces of thermal agitation. The domain magnetization of one
domain is usually oriented differently with respect to the total domain magnetization
of neighboring domains. A historically early and rather crude representation of
magnetic domains is shown in Fig. 1.3.
We could ask – why would magnetic domains be spontaneously magnetized?
The formation of magnetic domains is due to minimization of the total energy, as
will be discussed in the next chapter. This implies that, under every condition of the
ferromagnet, the domain structure will strive to remain stable, and will, therefore,
change until it finds this stability point if onditions change. We know from quantum
mechanics [5, 6] that the spontaneous domain magnetization is a result of unpaired
electron spins from partially filled electronic shells. These spins align parallel to
each other as a result of a strong exchange interaction. Since the arrangement
of spins depends on temperature, so does the spontaneous domain magnetization.
When the total resultant magnetization for all magnetic domains is zero, the
ferromagnetic material is said to be demagnetized. However, an applied magnetic
field changes the total resultant magnetization from zero to a saturation value.
When the magnetic field is decreased and thus, reversed in sign, the magnetization
of a ferromagnetic material does not retrace its original path of values, with the
material exhibiting so called hysteresis. A strong ferromagnet exhibits a relative
susceptibility of the order of 106, which is a large value as compared to other
types of materials. It explains why ferromagnets can be easily magnetized, while
other kinds of magnetic materials fall short on their ability to respond to a
magnetic field. The spontaneous magnetization of ferromagnets disappears above a
certain temperature called Curie temperature Tc, when they become paramagnetic.
Technically, ferromagnets are considered a subclass of paramagnetic materials;
nevertheless, in time they have been placed in a class of their own. Historically,
ferromagnetic materials were the only ones considered “magnetic”; however, this
interpretation has changed recently, given that so many other types of materials
respond to a certain extent to a magnetic field.
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