1.Liquid Phase
Sintering (Manufacturing method)
Previous
Answer
Liquid phase sintering is a subclass of the sintering
process and can be defined as sintering involving a coexisting liquid and
particulate solid during some part of the thermal cycle. The most common way to
obtain the liquid phase is to use a system involving a mixture of two powder
metals in which there is difference in the melting temperatures between the
metals. The interaction of two powders leads to formation of a liquid during
sintering. The melted metal thoroughly wets the solid particles' leading to
rapid consolidation and giving rapid compact densification without the need for
an external force. It is' of course' essential to restrict the amount of liquid
phase in order to avoid impairing the shape of the part; Depending on the
metals prolonged heating may lead to diffusion of the liquid metal into the
solid or the dissolution of solid particles into the liquid melt. In either
case' the resulting part is fully dense (having no pores) and strong.
(Vukota Boljanovic, PH. D., Metal ShapingProcesses: Casting and Molding, Particulate
Processing, Deformation Processes, Metal Removal, p. 96)
New
Answer (better)
Conventional sintering (Section 16.3.3) is solid-state
sintering; the metal is sintered at a temperature below its melting point. In
systems involving a mixture of two powder metals, in which there is a
difference in melting temperature between the metals, an alternative type of
sintering is used, called liquid phase sintering. In this process, the two
powders are initially mixed, and then heated to a temperature that is high
enough to melt the lower-melting-point metal but not the other. The melted metal
thoroughly wets the solid particles, creating a dense structure with strong
bonding between the metals upon solidification. Depending on the metals
involved, prolonged heating may result in alloying of the metals by gradually
dissolving the solid particles into the liquid melt and/or diffusion of the
liquid metal into the solid. In either case, the resulting product is fully
densified (no pores) and strong. Examples of systems that involve liquid phase
sintering include Fe–Cu, W–Cu, and Cu–Co [6].
(Groover M.P., Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems 4th
Edition, pp. 361)
2.Chemical Machining (Manufacturing method)
Previous
Answer
Chemical machining or chemical milling is a process
used to dissolve the workpiece material in chemical solutions. Since the
chemical solutions used have the ability to dissolve all of the workpiece
material, the parts which are not to be dissolved would have to be applied with
a mask which resists the chemical action of the solution, so that only the
unmasked portion gets removed by the chemical solutions.
(Manufacturing Technology, Metal Cutting & Machine
Tools, McGraw-Hill, p. 293)
New
Answer (better)
Chemical machining (CHM) is a nontraditional process
in which material is removed by means of a strong chemical etchant.
Applications as an industrial process began shortly after World War II in the
aircraft industry. The use of chemicals to remove unwanted material from a
workpart can be accomplished in several ways, and different terms have been
developed to distinguish the applications. These terms include chemical
milling, chemical blanking, chemical engraving, and photochemical machining
(PCM). They all use the same mechanism of material removal, and it is
appropriate to discuss the general characteristics of chemical machining before
defining the individual processes.
The chemical machining process consists of several
steps. Differences in applications and the ways in which the steps are
implemented account for the different forms of CHM. The steps are:
1. Cleaning. The first step is a cleaning operation to
ensure that material will be removed uniformly from the surfaces to be etched.
2. Masking. A protective coating called a maskant is
applied to certain portions of the part surface. This maskant is made of a
material that is chemically resistant to the etchant (the term resist is used
for this masking material). It is therefore applied to those portions of the
work surface that are not to be etched.
3. Etching. This is the material removal step. The
part is immersed in an etchant that chemically attacks those portions of the
part surface that are not masked. The usual method of attack is to convert the
work material (e.g., ametal) into a salt that dissolves in the etchant and is
thereby removed from the surface. When the desired amount of material has been
removed, the part is withdrawn from the etchant and washed to stop the process.
4. Demasking. The maskant is removed from the part.
(Groover M.P., Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems 4th
Edition, pp. 644-645)
3. Electron beam machining (Manufacturing method)
There is no previous entry about Electron beam
machining.
New
answer
Electron beam machining (EBM) is one of several
industrial processes that use electron beams. Besides machining, other
applications of the technology include heat treating (Section 27.5.2) and
welding (Section 30.4). Electron beam machining uses a high velocity stream of
electrons focused on the workpiece surface to remove material by melting and
vaporization. A schematic of the EBM process is illustrated in Figure 26.12. An
electron beam gun generates a continuous stream of electrons that is
accelerated to approximately 75% of the speed of light and focused through an
electromagnetic lens on the work surface. The lens is capable of reducing the
area of the beam to a diameter as small as 0.025mm(0.001 in). On impinging the
surface, the kinetic energy of the electrons is converted into thermal energy
of extremely high density that melts or vaporizes the material in a very
localized area.
Electron beam machining is used for a variety of
high-precision cutting applications on any known material. Applications include
drilling of extremely small diameter holes—down to 0.05 mm (0.002 in) diameter,
drilling of holes with very high depthto- diameter ratios—more than 100:1, and
cutting of slots that are only about 0.001 in (0.025 mm) wide. These cuts can
be made to very close tolerances with no cutting forces or tool wear. The
process is ideal for micromachining and is generally limited to cutting operations
in thin parts—in the range 0.25 to 6.3 mm (0.010 to 0.250 in) thick. EBM must be
carried out in a vacuum chamber to eliminate collision of the electrons with
gas molecules. Other limitations include the high energy required and expensive
equipment.
(Groover M.P., Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems 4th
Edition, pp. 641)
4.The Grinding Wheel (Equipment and tooling)
Previous
Answer
The grinding wheel is a cutting tool which utilizes a
multitude of abrasive particles as cutting edges. the abrasive particles are
held together in the general shape of a disc by a bonding material to form the
grinding wheel. on the surface of the grinding wheel abrasive particles form
many very small chips which in their sum total can represent a significant rate
of metal removal
(Moltrecht, K.H.
Machine shop practice 2. Edition. page 318)
New
Answer (better)
The grinding wheel is usually disk-shaped, and is
precisely balanced for high rotational speeds. The reader can see grinding in
action in our video clip titled Basics of Grinding.
Agrinding wheel consists of abrasive particles and
bonding material. The bonding material holds the particles in place and
establishes the shape and structure of the wheel. These two ingredients and the
way they are fabricated determine the five basic parameters of a grinding
wheel: (1) abrasive material, (2) grain size, (3) bonding material, (4) wheel
grade, and (5) wheel structure. To achieve the desired performance in a given
application, each of the parameters must be carefully selected.
*Abrasive Material: Different abrasive materials are
appropriate for grinding different work materials. General properties of an
abrasive material used in grinding wheels include high hardness, wear
resistance, toughness, and friability.
*Grain Size: The grain size of the abrasive particle
is important in determining surface finish and material removal rate. Small
grit sizes produce better finishes, whereas larger grain sizes permit larger material
removal rates.
*Bonding Materials: The bonding material holds the
abrasive grains and establishes the shape and structural integrity of the
grinding wheel. Desirable properties of the bond material include strength,
toughness, hardness, and temperature resistance.
*Wheel Structure and Wheel Grade: Wheel structure
refers to the relative spacing of the abrasive grains in the wheel. In addition
to the abrasive grains and bond material, grinding wheels contain air gaps or
pores, as illustrated in Figure 25.1. The volumetric proportions of grains,
bond material, and pores can be expressed as
where
Pg
= proportion of abrasive grains in the total wheel volume,
Pb = proportion of bond material, and
Pp = proportion of pores (air gaps).
Wheel grade indicates the grinding wheel’s bond
strength in retaining the abrasive grits during cutting. This is largely
dependent on the amount of bonding material present in the wheel structure—Pb in Eq. (25.1).
*Grinding Wheel Specification: The preceding
parameters can be concisely designated in a standard grinding wheel marking
system defined by the American National Standards Institute (ANSI) [3]. This
marking system uses numbers and letters to specify abrasive type, grit size,
grade, structure, and bond material.
(Groover M.P., Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems 4th
Edition, pp. 604-608)
5. Work
hardening (Manufacturing method)
Previous Answer
There is no
previous entry about Work hardening.
New Answer
In Figure
3.4, note that stress increases continuously in the plastic region until
necking begins. When this happened in the engineering stress–strain curve, its
significance was lost because an admittedly erroneous area value was used to
calculate stress. Now when the true stress also increases, it cannot be
dismissed so lightly. What it means is that the metal is becoming stronger as
strain increases. This is the property called strain hardening that was mentioned
in the previous chapter in the discussion of metallic crystal structures, and
it is a property that most metals exhibit to a greater or lesser degree.
Strain
hardening, or work hardening as it is often called, is an important factor in
certain manufacturing processes, particularly metal forming. Consider the
behavior of a metal as it is affected by this property. If the portion of the
true stress–strain curve representing the plastic region were plotted on a
log–log scale, the result would be a linear relationship, as shown in Figure
3.5. Because it is a straight line in this transformation of the data, the
relationship between true stress and true strain in the plastic region can be
expressed as
(Groover M.P., Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems 4th
Edition, pp. 45-46)
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