1-Press Brake (Old)
A press brake or brake press, is very efficient bending machine. Press
brakes are rated in two main categories: by tonnage and bed width. The tonnage
means the amount of force, in tons, the machine can exert in bending pressure.
This figure determines the thickness of metal it can bend. The bed width is the
width of the overall machine. Bed width determines how wide or how long a bend
the machine can perform.
(Sheet metal handbook, Ron Fournier,Sue Fournier, p. 37)
Press Brake(Old)
The press brake is a gap frame press with a very wide bed. A model has a
bed width of 9.15 m (30 ft) allows a number of separate dies (simple V-bending
dies are typical) to be set up in the bed, so that small quantities of
stampings can be made economically. These low quantities of part, sometimes
requiring multiple bends at different angles, necessitate a manual operation.
For a part requiring a series of bends, the operator moves the starting piece
of sheet metal through the desired sequence of bending dies, actuating the
press at each die, to complete the work needed.
(Groover M. P., Fundamentals of Modern Manufacturing: Materials, Processes
and Systems 3rd Edition, p. 465)
PRESS BRAKE (New) (Better) (Manufacturing Method)
Sheet metal or plate can be bent easily with simple fixtures, using a
press. Parts that are long, i.e., 7m(20ft) or more, and relatively narrow are
usually bent in a press brake. This machine uses long dies in a mechanical or
hydraulic press and is suitable for small production runs. The tooling is
simple and adaptable to a wide variety of shapes(Fig.7.23); furthermore, the process can
easily be automated. Die materials may range from hardwood (for low-strength
materials and small production runs) to carbides; for most applications,
carbon-steel or gray-iron dies are generally used.
(Kalpakjian, S., Schimd, S. R. , Manufacturing Processes for Engineering
Materials, Fourth Edition, p.356)
2-Parting Line (Previous) (Better)
Sand casting can be used to make virtually any size part, and it basically involves making a pattern out of a suitable material (e.g., foam, wood, or metal) and packing sand around it. Parting lines are used to allow the sand mold components to be disassembled from around the pattern and then reassembled after the part is removed. Sand cores are often inserted into the mold to form cavities inside the mold (e.g., the cylinders of an engine casting). Regardless of the design of the part, one must also consider that as the metal cools it shrinks (on the order of 5 to 10% for most metals), and that in order to remove the part from the mold without breaking the mold, a taper (draft) of about 1:10 is required. In addition, extra metal should be added to surfaces that will have to be machined (a machining allowance), and locating surfaces should be added so that the part can be fixtured to facilitate machining. Thus in order to specify a casting, there are a few basic guidelines one needs to know in order to minimize the work that a professional mold design engineer has to do to clean up your design. These guidelines are discussed below.
(Mechanical Engineering Handbook, Ed. Frank Kreith Boca Raton: CRC Press LLC, 1999,sec11, p68)
Sand casting can be used to make virtually any size part, and it basically involves making a pattern out of a suitable material (e.g., foam, wood, or metal) and packing sand around it. Parting lines are used to allow the sand mold components to be disassembled from around the pattern and then reassembled after the part is removed. Sand cores are often inserted into the mold to form cavities inside the mold (e.g., the cylinders of an engine casting). Regardless of the design of the part, one must also consider that as the metal cools it shrinks (on the order of 5 to 10% for most metals), and that in order to remove the part from the mold without breaking the mold, a taper (draft) of about 1:10 is required. In addition, extra metal should be added to surfaces that will have to be machined (a machining allowance), and locating surfaces should be added so that the part can be fixtured to facilitate machining. Thus in order to specify a casting, there are a few basic guidelines one needs to know in order to minimize the work that a professional mold design engineer has to do to clean up your design. These guidelines are discussed below.
(Mechanical Engineering Handbook, Ed. Frank Kreith Boca Raton: CRC Press LLC, 1999,sec11, p68)
PARTING LINE (New) (Design Principle)
In general, the parting line should be along a flat plane, rather than a
contoured plane. Whenever possible, the parting line should be at the corners
or edges of castings, rather than on flat surfaces in the middle of the
casting. In this way, the flash at the parting line (i.e., the material running
out between the two halves of the mold; will not be visible. The location of
the parting line is important, because it influences mold design, ease of
molding, number and shape of cores, method of support, and the gating system.
Preparation of dry-sand cores requires additional time and cost, so these cores
should be avoided or minimized; this consideration can usually be made by reviewing
and simplifying the design of casting.
(Kalpakjian, S., Schimd, S. R. , Manufacturing Processes for Engineering
Materials, Fourth Edition, p.247)
3-Transfer molding(Previous)
in transfer molding, the thermosetting powder or
performs are placed into a separate well or pressure chamber above the mold
cavities. Here the material is plasticized by heat and pressure and injected
into the mold cavities as a hot liquid, where it is cured and becomes hard. The
curing time for transfer molding is generally less than required for
compression molding .The loading time is also shortened since larger performs are
used which can be heated more rapidly.
(manufacturing processes Myron L.Begeman 1969
p.672)
TRANSFER MOLDING(New)(Better) (Manufacturing Method)
Transfer molding represents a further
development of the compression-molding process. The uncured thermosetting
material is placed in a heated transfer pot or chamber(Fig.10.30). After the material is
heated, it is injected into heated, closed molds. Depending on the type of
machine used, a ram, plunger, or rotating screw feeder forces the material to
flow through the narrow channels into the mold cavity. This flow generates
considerable internal heat, which raises the temperature of the material and
homogenizes it. Curing takes place by cross-linking. Because the resin is
molten as it enters the molds, the complexity of the part and dimensional
control approach those for injection molding.
Typical parts made by transfer molding include
electrical and electronic components and rubber and silicone parts. The process
is particularly suitable for intricate shapes that have varying wall thickness.
The molds fort his process tend to be more expensive than those for compression
molding, and material is wasted in the channels of the mold during filling.
(Kalpakjian, S., Schmid, S. R., Manufacturing Processes for Engineering Materials,Fourth
Edition, p.602)
4-Tail Stock (Previous)
A tailstock is
provided at the right hand end of the bed. It can slide along the guide ways
provided on the bed and may be brought nearer to the headstock, if so desired.
It can then
be clamped or fixed on
the bed in that position. The tailstock has a spindle in the upper part of the
tailstock, the axis of which coincides with the axis of the headstock spindle,
both being at the same height above the bed. This spindle can be moved forwards
or backwards by rotating a hand wheel. The front portion of tailstock spindle
carries a ‘dead’ or ‘live’ centre. When a long work piece is held in the chuck
at the headstock end, it is supported at the tailstock end by moving forward
the tailstock spindle. Of course, there has to be a small conical hole in the
centre of the work piece, in which the tailstock centre may be inserted to
provide support. If the centre (being carried in its own bearings) rotates
along with the work piece, it is called a live centre. However, if the
tailstock centre remains stationary and work piece alone rotates, the centre is
called ‘dead centre’ and the conical tip of centre has to be lubricated with
grease to reduce the friction between the tailstock centre and the work piece.
(H.N.Gupta,
Manufacturing Processes 2nd Edition; Page:93)
TAIL STOCK(New)(Better) (Tool accessory)
Tailstock is a very
common accessory on a CNC lathe. Its main purpose is to support a part tat is
too long, too large, or needs to be pressed extra firmly against the jaws, for
example, in some rough turning operations. A tailstock may also be used to
support a finishing operation of a thin tubular stock, or to support a part has
a shallow grip in the jaws, to prevent it from flying out. On the negative
side, tailstock is usually in the way of tool motions, so make sure to avoid is
usually collision. A typical tailstock has three main parts:
- Tailstock body
- Quill
- Center
All parts are important in programming and setup.
Tailstock Body:
Tailstock body is the
heaviest part of lathe tailstock. It is mounted to the lathe bed, either
manually during setup, or through a programmable option, hydraulically. Trully
programmable tailstock is normally available only as a factory installed option
and must be ordered at the time of machine purchase.
Quill:
Quill is the shiny
cylinder that moves in and out of the tailstock body. It has a fixed range of
travel, for example, a 75mm (3 inch) travel may be found on medium size lathes.
When tailstock body is mounted to the lathe bed in a fixed low a part change.
Part itself is supported by a center, mounted in the quill.
Center:
Center is a device
that is placed into the quill with a tapered end, held by a matching internal
taper and is physically in contact with part. Depending on design, if the tailstock
has an internal bearing, a dead center must be used instead. Machined part has
to be pre-centered (on the CNC lathe or before), using the same tool angle as
the tailstock center- normally 60 degree, A typical tailstock is illustrated in
Figure 44-4.
(Smid, P., CNC Programming Handbook, pp.426-427)
Diffusion Welding: (23:34 - 28.04.2011)
(Previous)
Diffusion
welding (DFW) is a solid-state welding process that results from the
application of heat and pressure, usually in a controlled atmosphere, with
sufficient time allowed for diffusion and coalescence to occur. Temperatures
are well below the melting points of the metals (about 0.5Tm is the maximum),
and plastic deformation at the surfaces is minimal. The primary mechanism of
coalescence is solid-state diffusion, which involves migration of atoms across
the interface between contacting surfaces. Applications of DFW include the
joining of high-strength and refractory metals in aerospace and nuclear
industries. The process is used to join both similar and dissimilar metals, and
in the latter case a filler layer of a different metal is often sandwiched between
the two base metals to promote diffusion. The time for diffusion to occur
between the faying surfaces can be significant, requiring more than an hour in
some applications.
(Fundamentals
of Modern Manufacturing: Materials, Processes, and Systems, Mikell P. Groover,
p. 731)
DIFFUSION WELDING (New) (Better)
(Manufacturing Method)
Diffusion
welding (DFW), or diffusion bonding, is a solid-state joining process in which
the strength of the joint results primarily from diffusion (movement of atoms
across the interface) and, to a lesser extent, some plastic deformation of the
faying surfaces. This process requires temperatures of about 0.5 Tm
(where Tm is the melting point of the metal on the absolute scale)
in order to have a sufficiently high diffusion rate between the parts to be
joined. The bonded interface in DFW has essentially the same physical and
mechanical properties as those of the base metal. Its strength depends on
pressure, temperature, time of contact, and the cleanliness of the faying
surfaces; these requirements can be lowered by using filler metal at the
interfaces. The principle of diffusion bonding actually dates back centuries,
when goldsmiths bonded gold over copper. To produce this material, called
filled gold, a thin layer of gold foil is first made by hammering; the foil is
placed over copper, and a weight is placed on top of it. The assembly is then
placed in a furnace and left until a good bond is obtained; this process is
also called hot pressure welding (HPW). The pressure required can also be
achieved by using mechanisms with different coefficients of thermal expansion.
In diffusion
bonding, the parts are usually heated in a furnace or a electrical resistance;
pressure may be applied by dead weights, by a press, by using differential gas
pressure, or from the relative thermal expansion of the parts to be joined.
High-pressure autoclaves are also used for bonding complex parts. The process
is generally most suitable for dissimilar metal pairs; however, it is also used
for reactive metals, such as titanium, beryllium, zirconium, and refractory
metal alloys. Diffusion bonding is also important in sintering in powder
metallurgy and for processing composite materials. Because diffusion involves
migration of the atoms across the joint, the process is slower than other
welding methods. Although DFW is used for fabricating complex parts in small
quantities for the aerospace, nuclear, and electronics industries, it has been
automated to make it suitable and economical for moderate-volume production.
(Kalpakjian, S., Schmid, S. R., Manufacturing Processes for Engineering
Materials,Fourth Edition, p.722)
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