11th week Ebubekir Çantı 030070154

1) Precision Forging(new)(manufacturing)


Precision forging is a variation
of impression die forging with a closely-controlled,
more  extensive  forging  process,  accurately  con-
trolled blank  sizes, and carefully  designed  dies,  so
that the forgings produced are close to the net shape
required.  The  process  greatly  reduces  the  amount
of post-forging machining required. This is because
it  can  reduce  side-wall  draft  to  from  0  to  1"  and
permit  thinner  forging  walls,  smaller  radii,  and
smoother  surfaces.  Since  there  is  little  or  no
machining, the grain flow patterns are not disturbed,
extra  metal  does  not  have  to  be  added  to  compen-
sate,  and  strength-to-weight ratios  are  improved.
A key approach in the process is to provide forging
blanks of just the right size and shape with accurate
and consistent dimensions. A certain amount of trial
and error is usually required to develop a blank that
will  just  fill  the  die  completely  without  requiring
excess metal in any area. A preformed (preforged or
pre-machined)  blank  may  be  used.  One  method
sometimes  used  to  provide  accurate  blanks  is  the
use  of  powder  metal  preforms  since  the  powder
metal  process  can  provide  accurate and  consistent
forging  blanks.  Very  close  attention  to  all  process
details is required: workpiece temperature through-
out  the  billet,  descaling,  die  temperature  (dies  are
heated),  press pressure  and  stroke, and  lubrication,
are all of  vital importance.
The  precision  forging  process  is  often  used  to
produce  forged  gear blanks. Aluminum  is a  metal
commonly precision  forged. The metal  is heated to
about  800°F (425°C)  and  the  die  temperature  is
maintained  at  700  to  800°F  (370  to  425°C)  to
insure proper  metal  flow9. It  should  be  noted  that
precision  forging usually  requires higher  pressures
and stronger dies than  other forging methods, and,
because  the dies  are typically  run  hot, they  have  a
shorter die life.


Handbook of Manufacturing Processes, James  G.  Bralla, p:37

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2) Photochemical Blanking(new)(manufacturing)


Photochemical blanking is illustrated step-
by-step in Fig. 3S4. This process uses a photosensi-
tive resist, which is a light-sensitive material, as the
maskant. in chemical machining. The resist materi-
al is applied by  dipping, spraying, roller coating, or
flow-coating. The material  is hardened  in the areas
wanted  by  exposing  it  to  light  through  a  photo-
graphic  negative  whose  image  corresponds  to  the
shape of  the  part to  be produced.  This photo  nega-
tive is prepared in advance of the operation.
The usual procedure is to draw the blanked part,
greatly  enlarged, photograph  it, and create  a nega-
tive  the  same  size  as  the  part  to  be  produced.

The negative is attached  to the workpiece  after the
workpiece has been coated with the masking mate-
rial and it has dried. Normally, for blanking, a sim-
ilar  negative  is  attached  to  the  workpiece  on  the
opposite  side  but  in  precise  registration  with  the
first  one.  Blue  light  shone  through  the  negatives
hardens  (polymerizes)  the  resist  material  in  the
areas  exposed  to  the  light.  The  negatives  are
removed and the workpiece is processed  to remove
the unhardened portions of  the maskant. The work-
piece  is  then  immersed  in  the  chemical  reagent,
that  removes  the  workpiece  material  that  is  not
masked.  The  process  is  particularly  adapted  to
small, complex, and precise parts, made from very
thin  materials  that  are  not  suitable  or  feasible  for
conventional  blanking.  Photochemically  blanked

parts  are  burr  free.  The  electronics  industry  is  an
extensive  user  of  photochemical  blanking  and
machining in the production of  integrated  circuits,
circuit  boards,  and  other  components.  Shadow
masks  for  television  sets  and  screens  for  various
purposes  are made with the process.

Handbook of Manufacturing Processes, James  G.  Bralla, p:137



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3)Quenching(new)(manufacturing)

Carbonitrided steels may be
quenched in water, oil, or gas depending on the
allowable distortion, metallurgical requirements
(such as case and core hardness), and type of fur-
nace. For the alloy gear steels discussed earlier,
oil quenching is most commonly employed.
Quenching oil temperatures may vary from
approximately 40 to 105 °C (100 to 220 °F). Spe-
cial high-flash-point oils may be used at the
higher temperatures to minimize distortion;
sometimes, molten salt is used for the same rea-
son. In the normal range of oil temperature
(approximately 50 to 70 °C, or 120 to 160 °F), a
mineral oil with a minimum flash point of 170 °C
(335 °F) and a viscosity of 21 × 10–6 m2/s at 38 °C
(21 centistokes, or 100 Say-bolt universal sec-
onds, or SUS, at 100 °F) is commonly used. Spe-
cial oils containing additives for increasing the
quenching rate also may be used. To maintain
maximum quenching effectiveness, quenching
oils should have a low capacity for dissolving
water. Quenching oils that dissolve even small
amounts of water may lose effectiveness in 3 to 6
months; those that shed water completely may be
used significantly longer.


GEAR MATERIALS,
PROPERTIES, AND
MANUFACTURE, J.R. Davis Davis & Associates p:247


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