1-Drill Jig (Group:Manufacturing)
There is no old explanation
New explanation
Drill jigs are used when it is necessary to move the workpiece, relative to the machine spindle, between machining operations. The workpiece is located and clamped to a movable member, which can be indexed to the required position, relative to the drill bush and then locked while each feature is machined.
There is no old explanation
New explanation
Drill jigs are used when it is necessary to move the workpiece, relative to the machine spindle, between machining operations. The workpiece is located and clamped to a movable member, which can be indexed to the required position, relative to the drill bush and then locked while each feature is machined.
Figure 19.15 shows a simple indexing drill jig
to produce four radial holes in the work-piece. The jig body 1 is equipped with
an indexing lever 3 for locking the job in the required position. The rotating
pin 5 and the indexing plate are located and clamped to the jig body, by means
of a locking screw 4. The jig body is also provided with bush plate 2, which
accommodates drill bush 7 for guiding the drill bit. For quick loading and
unloading the job in the jig, C-washer 8 and clamp 6 are used. Locating pin 9
and dowel pins 10 are used for proper location and fixing of bush plate in the
jig body.
After locking the rotating
pin by the indexing lever and the locking screw, a radial hole is drilled. The
job is indexed to the next position by loosening the locking screw and
disengaging the indexing lever. The rotating pin (with index plate and job) is
indexed to the next position and locked. The procedure is repeated till all the
four radial holes are drilled. The spring is held in position, by the spring
retainer 10.
(Narayana, K. L. (). Indexing Drill Jig. Machine Drawing (p.376) )
2- Austenitizing (Group: Material)
There is no old explanation
New explanation
Most steel heat treatments involve the formation of austenite, followed by cooling to 25oC at a rate which depends upon the quenchant used. This treatment usually requires an austenite that is homogeneous and single phase. It was found in the examination of the data on the formation of austenite that, in the range 800-950C, homogeneous austenite could be attained in about 1 h. This time was about the same no matter what the starting microstructure was.
(Narayana, K. L. (). Indexing Drill Jig. Machine Drawing (p.376) )
2- Austenitizing (Group: Material)
There is no old explanation
New explanation
Most steel heat treatments involve the formation of austenite, followed by cooling to 25oC at a rate which depends upon the quenchant used. This treatment usually requires an austenite that is homogeneous and single phase. It was found in the examination of the data on the formation of austenite that, in the range 800-950C, homogeneous austenite could be attained in about 1 h. This time was about the same no matter what the starting microstructure was.
It was also found that, in this
temperature range. the removal of dendritic segregation of the heavy elements.
e.g. manganese or chromium, is not feasible, and thus homogenization must be
carried out in a much higher temperature range prior to this type of
austenitizing. Another important aspect of austenitizing for final heat
treatment is that the austenite grain size is important, even though this phase
decomposes to other products upon cooling to 25oC. It is desirable
to keep this prior austenite grain size low. For deoxidized (killed) steels, it
was found that the nucleation and growth rate of austenite was such that the
austenite grain size, when complete austenite has just formed, remains
essentially constant for several hours in the temperature range normally
required for forming homogeneous austenite, i.e. in the range 850-950oC.
It is also important to note that this austenite grain size is in the range of
ASTM 6 to 8 no matter what the starting microstructure is.
Thus, upon austenitizing, the
austenite nucleates and grows in the starting microstructure, e.g. pearlite or
bainite, at rates such that within a few minutes in the range 850-950oC
no ferrite remains. However, the austenite contains undissolved carbides, but,
within a few minutes, these are dissolved and, within a few additional minutes,
the austenite is homogeneous. During this time, the austenite grain size
remains constant and, in this temperature range, will continue to be stable for
deoxidized steel for times long beyond that required to homogenize the austenite.
An important feature of the
formation of austenite in deoxidized steels is that, by the time the steel part
heats to the austenitizing temperature, the structure may be chemically
homogeneous and attain the stable grain size. Thus, for steel parts which are
not too small and which are austenitized in a gas atmosphere, the time to
attain a uniform temperature in the part is the main consideration. Additional
austenitizing beyond this time may not be necessary.
( Brooks, C. R. (1992). Austenitizing as the first step in heat
treatment. Principles of the
Austenitization of Steels (p. 143)
3-Counterblow Hammer (Group: Manufacturing)
New explanation
Counterblow hammers have two rams which strike one another. By
this means the forces in the frame are reduced as much as possible, so these
hammers need no bed or only a small one. The construction mass of a counterblow hammer is only one-third of that of a hammer with an anvil block which has the same work capacity. From the point of view of the drive, the counterblow hammer is a double-acting hammer with a powered upper ram.
The lower ram is moved by a coupling with the upper ram; this coupling is mechanical (steel bands, Figure 22.6) or hydraulic (Figure 22.7)
Today, hammers with mechanical couplings (Figure 22.6) are no
longer built.
( Tschätsch, H. (2006). Counterblow hammers. Metal Forming Practise: Processes - Machines -
Tools (p.271) )
4-Redrawing
and Reverse Drawing (Group:Manufacturing)
Reverse Redrawing
When high drawing ratios are required, the process is decomposed into two or several steps, in order to increase the formability by preventing localisation of the deformation in the cup wall. Re-drawing processes are usually sorted out in two categories: direct and reverse re-drawing.The first one corresponds to a process in which the different punches are always in contact with the same blank side whereas during reverse re-drawing, the punch travel occurs in two opposite directions and the outside of the part during the first stage becomes the inside of the part in the second stage. The advantages of the reverse process are a more compact tooling, without new positioning of the part in-between the two stages, a better surface aspect than in the case of a direct process because the outside is in contact only once with the die radius and finally a smaller number of bending–unbending operations. (Experimental and numerical study of reverse re-drawing of anisotropic sheet metals S. Thuilliera,*, P.Y. Manacha, L.F. Menezesb, M.C. Oliveira)
When high drawing ratios are required, the process is decomposed into two or several steps, in order to increase the formability by preventing localisation of the deformation in the cup wall. Re-drawing processes are usually sorted out in two categories: direct and reverse re-drawing.The first one corresponds to a process in which the different punches are always in contact with the same blank side whereas during reverse re-drawing, the punch travel occurs in two opposite directions and the outside of the part during the first stage becomes the inside of the part in the second stage. The advantages of the reverse process are a more compact tooling, without new positioning of the part in-between the two stages, a better surface aspect than in the case of a direct process because the outside is in contact only once with the die radius and finally a smaller number of bending–unbending operations. (Experimental and numerical study of reverse re-drawing of anisotropic sheet metals S. Thuilliera,*, P.Y. Manacha, L.F. Menezesb, M.C. Oliveira)
There is no old explanation for
Redrawing .
New and better explanation
Direct Redrawing
Reducing the cup to a smaller diameter with greater height is called
redrawing (Fig. 9.39). During redrawing, the cup first sits on top of the
drawing die ring. The punch and blankholder must fit inside of the cup.
In contrast to the first draw, the conical shape of the drawing
ring exerts a normal force to the sheet, pressing and further deforming it
against the drawing ring.
Reverse Redrawing
Reverse redrawing of a cup is shown in Fig. 9.40. In reverse
drawing a sheet is initially formed into a shape, such as a cup. This is
followed by a punch traveling in the opposite direction, which reverses the
direction of the material, hence turning the cup inside out.
Reverse drawing can accumulate material in certain locations in order to aid the subsequent drawing of noncylimIrical and other shapes, such as cups with large flanges.
The first and reverse draws are generally
executed in one operation, using a hollow punch.
( Boljanovic, V. (2010). Deep drawing practise. Metal Shaping Processes: Casting and Molding, Particulate Processing, Deformation Processes, Metal Removal (pp.239,240) )
5-Satellite terminals (Group: Communication)
New explanation
Satellite systems differ substantially from terrestrial ones in
terms of number and diffusion of adopted standards, type of offered services,
and latency of technology innovations. An accurate analysis must be carried out
to evaluate the effective impact of software radio technology on space
segments.
Satellite terminals may
be roughly classified depending on a set of common char-acteristics:
Adopted satellite access standard: receiving only DVB-S/S2, interactive DVB-RCS,
S-UMTS or proprietary
access;
Power and size availability: battery powered hand-held, battery powered portable,
AC powered fixed terminal;
Access modes: single
standard access, multi-standard access with user selection,
multi-standard access
with automatic selection;
User mobility:
stationary, slow intra-spot motion, fast inter-spot motion.
Under this incomplete classification, we can assert that
software signal processing can be succchsfully applied to stationary AC powered
receiving only fixed terminals. This is a feasible application of software
radio, but it is not convenient, since the benefits from reconfiguration in
this case are marginal. A portable or hand-held terminal will get a significant
benefit in terms of usage and offered services from the ability to switch
between different access modes. In this case the technological effort is consistent
for the limitations on power and terminal size, but the convenience is high.
The main issues
affecting the design of new generation satellite terminals can be simplified in
three key points: the terminal size and portability, the accessed bandwith and
the integration with other communication systems.
( Enrico Del
Re,Marina Ruggieri (2008). Reconfigurability for Satellite Terminals:
Feasibility and Convenience. Satellite Communications and Navigation Systems
(p.554) )
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