Direct
Data Translators
New - Better
Direct data translators (Figure 2.2) provide a direct
solution which entails translating the modelling data stored in a product
database directly from one CAD system formal to another, usually in one step.
There usually exists a neutral database in a direct dala translalor The
structure of the neutral database must be general, governed by the minimum
required definitions of any of the modelling data types, and be independent of
any vendor format.
A good example for direct data translation is CADporter from !■ lysium™
(Dean. 2005). CADporter is not CAD software for making models, but rather a CAD
lile reader This product can read several different formats of CAD files from
various vendors Figure 2.3 shows an interaction between CAD vendors with
Elysium™ operated from within Solid-Works'Jt. As depicted, it is a two-way
transfer between the CAD systems. With this type of integration, a CAD system
can import a Pro/E® part and rewrite it to another vendor format such as Catia®
or AutoCAD*1 DWG format.
However, as the CAD model gets more complicated the chances that the
translation breaks down increase When this happens, the model needs to be
simplified or re-modelled. The remaining part of this section discusses some
of the above-listed product data exchange formats.
(Integrating advanced computer-aided design, manufacturing, and
numerical control: principles and implementations, Xun Xu, Pg:36)
There is no previous description.
Abrasive Machining
New-Better
Description
Abrasive machining is
;i material removal
process that involves the interaction of abrasive grits with the workpiece at
high cutting speeds and shallow penetration depths. The chips that are formed
resemble those formed by other machining processes. Unquestionably, abrasive
machining is the oldest of the basic machining processes. Museums abound with
examples of utensils, tools, and weapons that ancient peoples produced by
rubbing hard stones against softer materials to abrade away unwanted portions,
leaving desired shapes. For centuries, only natural abrasives were available
for grinding, while other more modern basic machining processes were developed
using superior cutting materials. However, the development of manufactured
abrasives and ■ better fundamental understanding of the abrasive machining
process have resulted in placing abrasive machining ami its variations among
the most important of all the basic machining processes.
The results that can
be obtained by abrasive machining range from the finest and smoothest surfaces
produced by any machining process, in which very little material is removed, to
rough, coarse surfaces that accompany high material removal rates, The abrasive
particles may be (I)
free: (2) mounted in resin on a belt (called coated
product): or. most commonly (3) close packed into wheels
or stones, with abrasive grits held together by bonding material (called bonded
product or a grinding wheel). Figure 26-1
shows a surface grinding process using a grinding wheel.
The depth of cut,/ is determined by the in feed and is usually very small.
0.002 to 0.005 in., so the arc of contact (and the chips) is small. The table
reciprocates back and forth beneath the rotating wheel. The work feeds into
the wheel in the cross-feed direction. Alter the work is clear of the wheel,
the wheel is lowered and another pass is made, again removing a
couple of thousandths of inches of mclal. The metal
removal process is basically the same in all abrasive machining processes but
with important differences due to spacing of active grains (grains in contact
with work) and the rigidity and degree of fixation of the grains. Table 26-1 summarizes
the primary abrasive processes. The term abrasive mat hitting applied
to one particular form of the grinding process is unfortunate, because all these
process are machining with abrasives.
(Degarmo's Materials and Processes in
Manufacturing, E. Paul DeGarmo,J. T. Black,Ronald A. Kohser, Pg:714)
Previous Description
Abrasive machining or
grinding is a chip-forming metal cutting operation. Most of us are familiar
with the grinding wheels, used to sharpen knives and other tools, and sand
paper which is used to smoothen surfaces and sharp corners. For grinding,
generally, a rotating grinding wheel is used as a tool. The grinding wheel and
sand paper consist of bonded abrasives. The abrasive grains have sharp edges
that project out and cut the chips. In grinding, the high circumferential speed
of the grinding wheel causes high friction and chips become red hot and fly as
sparks.
In
grinding and other abrasive machining processes, a very large number of tiny
cutting edges simultaneously cut the surface, each taking a very minute cut. (Elements of Manufacturing Processes,
Nagendra Parashar, p171)
Surface grinding
New – Better Description
Surface grinding is
an abrasive machining process in which abrasive particles, bonded into a
grinding wheel, remove small amounts of material from a workpiece. The grinding
wheel may be shaped to form a
variety of work-piece geometries.
Process
Characteristics
•
Produces very high
surface accuracy and smooth surfaces
•
Removes very small
chips from metallic or nonmetallic materials
•
Produces a flat or
formed surface
»
Uses abrasive grains in the form of a bonded wheel
• Is
primarily a finishing process Process Schematic
A bonded abrasive
wheel rotates at a high speed and is vertically fed into a reciprocating
work-piece. The abrasive grains cut very small chips from the workpiece
interface. Coolant is required to keep the workpiece cool and to wash the
chips away from the cutting area.
Workpiece
Geometry
Shown is a typical
example of a workpiece that can be smoother and flatter after surface grinding.
The surface roughness is usually between 8 and 32 microinches after grinding.
If the workpiece requires a finer surface finish, a lapping or honing
operation may follow grinding.
(Manufacturing
processes reference guide, Robert H. Todd,Dell K. Allen,Leo Alting, Pg:137
Previous Description
Surface grinding is
one of the most common operations, generally involving the grinding of flat
surfaces. Typically, the work-piece is secured on a magnetic chuck attached to
the work table of the grinder; nonmagnetic materials are held by vises, vacuum chucks,
or some other fixture. A straight wheel is mounted on the horizontal spindle of
the surface grinder. Traverse grinding occurs as the table reciprocates
longitudinally and is fed laterally (in the direction of the spindle axis)
after each stroke. In plunge grinding, the wheel is moved radially into the
workpiece, as it is when grinding a groove.
(Kalpakjian S.,
Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 809)
Plasma Arc Cutting
New – Better Definition
A
high-lcmperalure plasma stream strikes the workplace and I here is raptd
melting. It is used mainly for cutting thick sections of elcctricall)
conductive materials.
Any
gas is heated to very high temperature. The gas dissociates into free
electrons, ions and neutral atoms. This state of gas is called plasma and is
eleeiricall) conductive.
Plasma-Arc Torch
A plasma-are torch is
shown in the figure. An electric arc is maintained between the electrode (-vei
and workpiece (+vc). The primary plasma giw is heated to .li.OOOT and delivered
through a nozzle at a pressure of 1.4 MPa at a very high velocity. The
secondary gas or water is admitted to constrain the plasma jet and clean the
cut of molten material. When water is used il vaporises lo produce a thin layer
of steam to constrict the plasma jet. Water ensures high quality cuts, high
nozzle life and small heat-affected /one.
Plasma-Arc Cutting Speeds
The maximum
recommended cutting speed for plasma-arc machining depends upon the following
factors:
(10) Explain (he mechanics of material removal
in Electrochemical Machining (LC'M) process.
(11) What is Laser-beam Machining (LUMI
process? With the help of a suitable sketch, explain its working. Also give
scope of Laser-beam Machining application.
(12) How is the machining rate in liCM
affected hy the following?
(i)
Rate of Mow of electrolyte.
ii)
Temperature of electrolyte.
iii)
Applied voltage between tool and workpiece.
( 13) Explain the cutting action in electron-beam
machining. Describe al least
three
applications of the process.
( 14) Write a brief note on Plasma-Are Cutting
process.
(Fundamentals of Machining and Machine Tools, Singal R.K.
Et.Al,R. K. Singal,Mridual Singal, Pg:196-197)
Previous Definition
The plasma arc
cutting process severs metal bymeans highly concentrated arc jet that has
sufficient energy and force not only to melt the metal, but also to eject the
molten metal. Because melting rather than oxidation is the predominant cutting
mode plasma arc cutting can be used to cut any metal.
It is important to bear in mind
that plasma arc cutting is a fundamentally different process from oxyfuel
cutting, retying primarily on the heat generated by an electric arc to melt and
sever the parent material. Consequently, additional safety hazards exits from
operator should understand these hazards and take appropriate precautions.
Appropriate safety information is referenced in AWS C5.2-83 “Recommended
Practices For Plasma Arc Cutting.”
(Transportation
Research Board, National Research Council, NCHRP Report 384, Plasma Arc Cutting
of Bridge Steels, p.80)
Cold Welding (CW)
New
– Better Definition
Cold welding is a solid state process
of welding There is no heating or melting of the metal that forms the bond in
this process. The weld takes place at room temperature
The coalescence of
the metal surfaces occurs as a result of
the force applied It is possible to join most soft, ductile metals using this
method Also, dissimilar metals such as aluminum to lopper iron to topper, and
so on can he joined.
Early cold welding was
primarily done as soft welds, hut today it is possible to make lap, edge, and
butt joints. Spot welds can be nude
using portable, hand-operated tools. Figure 27-50.
Other types of joints require special machines
A
major factor in the success of the cold weld is that the Surface oxides and other contaminations be removed before welding. The best method
to clean the surface is with a power
wire brush. The surface must not be
touched after it is cleaned and the welding should be done as soon
as possible.
(Welding: principles and applications,
Larry F. Jeffus, 2002, Pg: 713-714)
Previous
Definition
According to American
Welding Society (AWS), “Cold welding(CW) is a solid-stade process in which
pressure is used at room temperature to produce coalescence of metals with
substantial plastic deformation at the weld.” Cold welding processes are
characterized by a notable absence of heat, whether appied from an external
source or generated internal to the process itself.
Cold welding is ideally suited
to the joining of dissimilar metals since no intermixing of base metals is
required or obtained. This allows inherent chemical incompatibilities that
would prevent or make fusion welding difficult to be overcome. The best example
is the cold welding of relatively pure aliminum to relatively pure copper to
produce electrical connections.
(Messler R. W., Principles of Welding,
2004, p.98)
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