If steels are hardened by heat treatment, then tempering or drawing is used in order to reduce brittleness, increase ductility and toughness, and reduce residual stresses. The term "tempering" is also used for glasses. In tempering, the steel is heated to a specific temperature, depending on its composition, and then cooled at a prescribed rate. Alloy steels may undergo teper enbirttlement, which is caused by the segregation of impurities along the grain boundries at temperatures between 480 C and 590 C.
(Kalpakjian S. Schmid S.R.,Manufacturing Engineering and Technology Sixth Edition in SI Units, p. 123)
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Objective:
To improve the toughness and dimensional stability of hardened workpieces.
Owing to the reciprocal relationship between the changes in duc-tility and
hardness caused by tempering, a compromise must be made for each application
case, e. g.: tools →low tempering temperature →hard; components →high tempering temperature →ductile.
Method:
The tempering temperature required for a certain hardness can be read off the
tempering curve. This does not take account of the influence of the melt and
the degree of hardening. More accurate data can be obtained by stepwise
tempering of a Jonthw test piece from a single melt. The degree of hardening in
the surface layer is obtained from the hardness measured on the hardened
component (Figure A.3.6a). This is used in Figure A.3.6b to find the suitable
tempering temperature.
(Berns, H., Theisen, W. (2008).
Tempering. Ferrous
Materials: Steels and Cast Iron (p.68). )
2-Hot pressing ( Group: Manufacturing)
Hot pressing is similar to dry pressing, except that the process is carried out at elevated temperatures, so that sintering of the product is accomplised simultaneously with pressing. This eliminates the need for seperate firing step in the sequence. Higher densities and finer grain size are obtained, but die life is reduced by the hot abrasive particles against the die surfaces.
(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems,4th Edition, pg. 377)
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Hot
Pressing. Hot pressing gives distinct advantages in comparison to pressureless
sintering in achieving full densities and minimal grain growth as shown, for
example, in nanograincd Fe-(Fe, Mo)6C,[188][189] TiN,[5]
ZrO2-A12O3,[164] or TiO2.[42]
Theoretical or near-theoretical densities and grain sizes less than 100 nm have
been achieved by hot pressing mechanically alloyed Fe-2% AI,[77]
Fe-10% A1,[78] Al-10% Ti,[190] Fe, Fe3A1 and
Ni3A1[191][192] and TiAI.[193] A grain size of only
16 nm has been retained in cryomilled Fe-10 wt% Al which was hot pressed at 823
K and heat treated for 1 hour at 1223 K.[78] This unusual stability
is attributed to nanometer dispersoids of y-A13 and AIN particles.[78]
Similar densification results with final nanosize structures have been reported
by hot pressing W-Ti and metal-nitrides composites.[194][195] Hot
pressing retained an amorphous structure in (Fe, Co, Ni)B alloys.[196]
Hot pressing of nanoceramics such as ZrO2,[64] TiO2,[197][198]
and CeO2[199]or nanoceramic composites such as ZrO2
– Al2O3,[200] Si3N4/SiC,
[201] and Al2O3/Ni[202] achieved
full densities and grain sizes below 100 nm, as well. Generally. the pressures
used in hot pressing span a large range from low (<100 MPa),[77][84][164]
to moderate (100-500 MPa),[64][78][198] and high pressure levels
(>0.5 GPa).[42][63][191][203] Increasing the pressure diminishes
the final grain size. Some meaningful examples are given by Hahn who sintered
nano-TiO2 to its theoretical density at 725-825 K ( ~0.35 Tm)
applying 1 GPa with no grain growth [63] and Araki, et al., who
densified mechanically alloyed Al-10.7 al% Ti powders to 98% under 2 GPa at 573
K with virtually no grain growth and retention of the initial Al
supersaturation.[203] A very high pressure application (>1 GPa)
retained grain sizes less than 75 nm in nearly fully dense ceramics such as TiO2
and Al2O3 sintered to 95% density[204][205] and aluminides (Fe2A1
and Ni3A1) sintered to 91-95% at 775 K.[191]
( Koch, C.C.(2002).
Pressure-Assisted Consolidation Methods. Nanostructured Materials: Processing,
Properties and Potential Applications (p.155). )
3-Forge Welding ( Group: Manufacturing)
According to American Welding
Society, “Forge Welding (FOW) is a solid-state welding process that produces a
weld by heating workpieces to welding [hot working] temperatures and applying
blows sufficient to cause deformation at the faying surfaces.” Without question,
forge welding was the earliest form of welding and is still used today by
blacksmiths among others.
4-Roll bonding ( Group: Manufacturing)
(Wessler R.W., Principles of welding:
processes, physics, chemistry, and metallurgy, 1999, p. 101)
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Forge
welding Forge welding is of historic
significance in the development of manufacturing technology. The process dates
from about 1000 BCE, when blacksmiths of the ancient world learned to join two
pieces of metal (Historical Note 30.1). Forge welding is a welding process
in which the components to be joined are heated to hot working temperatures and
then forged together by hammer or other means, Considerable skill was required
by the craftsmen who practiced it in order to achieve a good weld by present.day
standards. The process may be of historic interest: however. it is of minor
commercial importance today except for its variants that are discussed below.
(
Groover, M.P. (2010). SOLID
STATE-WELDING PROCESSES. Fundamentals of Modern Manufacturing: Materials,
Processes, and Systems (p.733). )
4-Roll bonding ( Group: Manufacturing)
A brief discussion of the processes that apply severe plastic deformation to a work piece in order to create small grains and thereby increase the strenght is followed by a detailed description of one of these methods: that of accumulative roll bonding. The process is presented first, followed by a detailed discussion of a set of experiments. In that process ultra low carbon steel strips containing 0,002% C were rolled at 5000C. Strips of 32 layers were created. The mechanical attributes after Rolling and cooling were examined and the development of edge cracking was monitored. The metal’s yield and tensile strenghts increased by 200-300% while the ductile dropped from pre-rolled value of 75 to 4%. The Rolling process was stopped when cracking of the edges became pronounced. The shear strength of the bond was about 60% of the yield strength in shear. The accumulation of the retained strain after dynamic recovery caused cracking at the edges. A potential industrial application of the accumulative roll bonding process, that of the creation of tailor rolled blanks, is discussed.
(John G. Lenard,Primer of flat rolling, First Edition, Abstract Section)
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5-Laser cutting machine ( Group: Manufacturing Technology)
Laser cutting machine controls the path of the laser that can cut through sheet metal, thus increasing the capability for producing a wide variety of shapes accurately, repeatedly, and economically, as well as eliminating the need for punches and dies. However, as expected, the surface produced by punching has different characteristics than that produced by laser cutting.
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In
the roll-welding (ROW) or roll-bonding process, shown schematically in Figure
32-12, two to more sheets or plates of metal are joined by passing them simultaneously
through a rolling mill. As the materials are reduced in thickness, the length
and/or width must increase to compensate. The newly created uncontaminated
interfaces are pressed together by the rolls. and coalescence is produced. Roll
bonding can be performed either hot or cold and can be used to join either
similar or dissimilar metals (such as the Alelad aluminums— a skin of
high-corrosion-resistance aluminum over a core of high-strength aluminum —or
conventional steel with a stainless steel cladding). The resulting bond can be
quite strong, as evidenced by the roll-bonded "sandwich" material
used in the production of various U.S.coins.
By
precoating select portions of one interface surface with a surface with a
material that prevents bonding, the roll-bonding process can be used to produce
sheets that have both bonded and nonbonded areas. Subsequent heating in an oven
or furnace can cause the no-bond coating to volatilize. The resulting pressure
expands the no-bond regions, producing flow paths for gases or liquids. A
common example of this technique is in the manufacture of refrigerator freezer
panels, where inexpensive sheet metal is used to produce structutal panels that
also serve to conduct the coolant.
( Black, J.T. Kohser, R.
(2012). Roll Welding or Roll Bonding. Degarmo's Materials and Processes in
Manufacturing (p.900). )
5-Laser cutting machine ( Group: Manufacturing Technology)
Laser cutting machine controls the path of the laser that can cut through sheet metal, thus increasing the capability for producing a wide variety of shapes accurately, repeatedly, and economically, as well as eliminating the need for punches and dies. However, as expected, the surface produced by punching has different characteristics than that produced by laser cutting.
(Kalpakjian S. & Schmid S., Manufacturing Engineering and Technology, p.23)
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Laser
cutting found its first applications in the sheet-metal industry. Prior to
this, simple pattern cutting had been done using a stamping machine, while
complicated contour cutting had been done by laser. A hybrid machine comprising
of the stamping part and laser pan was used, which allowed a single machine to
perform both kinds of cutting. Although the number of flat-metal laser-cutting
machines surpasses that of three-dimensional machines, the latter is the better
application of a laser. In the automotive industry, laser robots are being used
increasingly, because they are ideal for the three-dimensional cutting of
hydro-formed components.
Laser
processing is a non-contact and inertia-free type of processing. The movement
of the beam is free compared to a machine that is a large "lump of
metal." In contrast to ordinary machines, which have only a limited amount
of movement, a laser machine can be thought of as being "flexible."
Any kind of processing can be performed by writing the appropriate software.
Take a press machine as an example. A die needs to be prepared and the
processing will be done using this die. In the case of laser processing, on the
other hand, different kinds of products can be manufactured simply by switching
the programming. Custom products can thus be manufactured at lower cost. When
such products begin to hit the market, it is likely to have a huge impact on
people's thinking and society as a whole.
( Dashchenko, A. (2003). Evolution
from Flat Machine to Laser Robot? Manufacturing Technologies for Machines of the Future:
21st Century Technologies (pp.762-763). )
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