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1) Mig welding (Manufacturing)(better)

Mig welding is another arc welding technique. You may also hear mig welding
referred to as gas metal arc welding (GMAW) or wire welding. Mig welding is
becoming more and more popular, for several reasons. At the top of the list
is the fact that most people find mig welding to be easier to pick up than stick
and tig. Another big reason is the speed; done correctly, mig welding can
be quite a bit faster than stick or tig welding thanks to its continuously fed
wire electrode, which doesn’t require changing nearly as often as the stick
electrodes used in stick welding. You can just keep right on welding without
having to stop and change your electrode. Over the course of a welding proj-ect, that can definitely save you quite a lot of time.
Proponents of mig welding also cite the low amount of slag and spatter that
mig produces. That makes for a more pleasant welding experience, and
a much more pleasant cleanup experience. The low chance of distortion
(unwanted changes in a piece of metal’s shape) is also trumpeted by those
who love mig welding. Because the process is faster, you don’t need to apply
as much heat to the weld area for as long, so the metal is less likely to bend
and twist in nasty ways.
Of course, mig welding also has its downsides. For starters, mig welding
equipment is more complex than stick welding equipment, so it’s quite a bit
more expensive. The handheld part of the mig welding equipment (called
the mig gun) is often big and bulky, so it’s usually tough to mig weld in tight
spaces. Mig welding also relies on the use of a shielding gas to keep atmo-spheric contaminants away from the weld area, so the process doesn’t really
work very well outdoors (especially with any kind of breeze).
I save the details of the mig welding process for Chapters 9 and 10, but gener-ally speaking, here’s how it works: A wire feeder continuously feeds the wire

electrode to the weld area at a speed you control. That produces a steady
molten stream that you can easily direct however you want on the surface
of the metal you’re welding. The weld is completely covered with a shielding
gas (usually argon) to prevent impurities from fouling up the quality of the
weld; you control the flow of the shielding gas to suit your project’s needs.

Welding for Dummies, Steven Robert Farnsworth, p:16

Mig welding(GMAW)(old description)

Gas metal arc welding(GMAW) is an AW process in which the electrode is a consumable bare metal wire, and shielding is accomplished by flooding the arc wtih a gas.The bare wire is fed continuosuly and automatically from a spool through the welding gun.Wire diameters ranging from 0,8 to 6,5 mm are used in GMAW, the size depending on the thickness of the parts being joined and the desired deposition rate.Gases used for shieldind include inert gases such as argon and helium and active gases such as carbon dioxide.Selection of gases depends on the metal being welded, as well as other factors.Inert gases are used for welding aluminum alloys and stainless steels , while CO2 iscommonly used for welding low and medium carbon steels.the combination of bare electrode wire and shielding gases eliminates the slag covering on the weld bead and thus precludes the need for manual grinding and cleaning of the slag.The GMAW process is therefore ideal for makşng multible welding passes on the same joint

(M.Groover. Fundamental of Modern Manufacturing,third edition

page 711)

2) Tig welding(Manufacturing)(better)
The last type of arc welding is tig welding, which is sometimes called gas
tungsten arc welding or GTAW. One major advantage to tig welding is that it’s
extremely clean. If you’re tig welding correctly, you may very well go through
an entire project without having to spend any substantial amount of time
cleaning up. Tig is also extremely versatile. You can use tig welding to work
on a lot of exotic metals that just aren’t in play for, say, stick welding.
Tig welding has two big drawbacks. One is cost — you can definitely spend
a pretty penny on tig welding equipment and supplies, even for start-up. The
second drawback is lack of speed. You get a lot of precision out of tig weld-
ing, but you pay for it with time.
The tig welding process was originally developed in the 1940s to join alumi-
num and magnesium, but you can use tig welding to join all kinds of different
metals. The big difference in tig welding is that it uses a non-consumable
electrode that’s almost always made of tungsten. It also requires the use of
a water- or air-cooled torch, which holds the tungsten electrode and is con-
nected to the welding machine by a power cable. Like stick welding (see
the earlier section), tig uses an arc of electricity to heat metal to its melting
point, and you manipulate the puddle to join metals together. The major
difference is that tig welding uses a tungsten electrode. You can read more
about tig welding in Chapters 7 and 8.

Welding for Dummies, Steven Robert Farnsworth, p:17

Tig welding(GTAW)(old description)

Gas tungsten arc welding(GTAW) is an AW process that uses a nonconsumable tungsten electrode and an inert gas for arc shielding.The term tig welding(tungsten inert gas welding) is often applied to this process(in europe, wig welding is the term-the chemical symbol for tungsten is W, for wolfram).The GTAW process can be implemented with or without a filler metal.When a filler metal is used , it is added to the weld pool from a seperate rod or wire, being melted by the heat of the arc rather than transferred across the arc as in the consumable electrode AW process.Tungsten is agood electrode material due to its high melting point of 3410 C.Typical shielding gases include argon, helium, or a mixture of these gas elements.

(M.Groover. Fundamental of Modern Manufacturing,third edition page 714)

3) THERMIT WELDING (TW)(Manufacturing)(better)

Thermit material is a mechanical mixture of metallic aluminum and processed iron oxide. Molten steel is produced by the thermit reaction in a magnesite-lined crucible. At the bottom of the crucible, a magnesite stone is burned, into which a magnesite stone thimble is fitted. This thimble provides a passage through which the molten steel is discharged into the mold. The hole through the thimble is plugged with a tapping pin, which is covered with a fireresistant washer and refractory sand. The crucible is charged by placing the correct quantity of thoroughly mixed thermit material in it.

In preparing the joint for thermit welding, the parts to be welded must be cleaned, alined, and held firmly in place. If necessary, metal is removed from the joint to permit a free flow of the thermit metal into the joint. A wax pattern is then made around the joint in the size and shape of the intended weld. A mold made of refractory sand is built around the wax pattern and joint to hold the molten metal after it is poured. The sand mold is then heated to melt out the wax and dry the mold. The mold should be properly vented to permit the escape of gases and to allow the proper distribution of the thermit metal at the joint. A thermit welding crucible and mold is shown in figure 5-41.

Headquarters Department of Army, Operator’s Circular Welding Theory and Application, p: 151

Thermit Welding (TW)(old description)
It may be of forge or fusion kind of welding. Fusion welding requires no pressure. Thermit welding process is depicted in Fig. 17.29. It is a process which uses a mixture of iron oxide and granular aluminium. This mixture in superheat liquid state is poured around the parts to be joined. The joint is equipped with the refractory mold structure all around. In case of thermit pressure welding, only the heat of thermit reaction is utilized to bring the surface of metal to be welded in plastic state and pressure is the applied to complete the weld. The temperature produced in the thermit reaction is of the order of 3000°C. Thermit welding is used for welding pipes, cables, conductors, shafts, and broken machinery frames, rails and repair of large gear tooth.
(Introduction to Basic Manufacturing Processes and Workshop Technology,Rajender Singh,p335)

4) ITERATIVE LEARNING CONTROL (ILC)(control)(better)

In 1978, Uchiyama presented the initial explicit formulation of ILC in Japanese. In 1984, Arimoto et al. first introduced this method in English. These contributions are widely considered to be the origins of ILC. One motivation for the development of ILC is the industrial robot, which repeats the same task from trial to trial. Humans can learn from repeat training, and scholars have tried to find a scheme to implement such a learning ability in the automatic operation of dynamic systems. This scheme is known as iterative learning control, and has mainly focused on batch processes.

Y. Wang et al. / Journal of Process Control 19 (2009) 1589–1600, p:1590

Iterative learning control (ILC), a relatively a new technique within the arsenal of the control engineer, is a technique for improving the transient response and tracking performance of any physical system that is required to execute a particular operation repeatedly (such as a manipulator that might be programmed to do spot welding in an automobile manufacturing assembly line). By observing the error in the output response after each operation and using the error to modify the input signal to the system, ILC attempts to improve the system performance. In other words, ILC is a technique for systems with repetitive or iterative operations, which are modified based on the observed error (or are programmed to learn) to control the input signal at each repetitive operation

(Modeling, Sensing and Control of Gas Metal Arc Welding,Desineni Subbaram Naidu, S. Ozcelik, K. Moore D. S. Naidu-1st edition, (2003),P.179)

5) Feedback Linearization Technique(control)(better)

Most feedback linearization approaches are based on input-output linearization or state-space linearization.

In the input-output linearization approach, the objective is to linearize the map between the transformed

inputs (v) and the actual outputs (y). A linear controller is then designed for the linearized input-output

model, which can be represented by (4.4) with r ≤ n and w = y. However, there is an (n–r)-dimensional

subsystem that typically is not linearized,

η˙ = q(η, ξ) (4.5)

where η is an (n–r)-dimensional vector of transformed state variables and q is a (n–r)-dimensional vector

of nonlinear functions. Input-output linearization techniques are restricted to processes in which these

so-called zero dynamics are stable.

In the state-space linearization approach, the goal is to linearize the map between the transformed

inputs and the entire vector of transformed state variables. This objective is achieved by deriving artificial

outputs (w) that yield a feedback linearized model with state dimension r = n. A linear controller is then

synthesized for the linear input-state model. However, this approach may fail to simplify the controller

design task because the map between the transformed inputs and the original outputs (y) generally is

nonlinear. As a result, input-output linearization is preferable to state-space linearization for most process

control applications. For some processes, it is possible to simultaneously linearize the input-state and

input-output maps because the original outputs yield a linear model with dimension r = n.

Feedback Linearizing Control, Michael A. Henson, p:3

Feedback Linearization Technique(old description)

Most physical systems operations are nonlinear in nature and hence they should be described by means of nonlinear mathematical models. Since nonlinear models are not convenient for control purposes, due to both theoretical and computational reasons, they are often linearized by using appropriate exact or approximate linearization techniques. Among them, feedback linearization control law and a state variable transformation (diffeomorphism) such that the closed loop system model becomes linear, in the new coordinate variables. However, feedback linearization requires some strong constraints to be satisfied by the original nonlinear system, and thus its applicability is quite restricted. If, in addition, the original system is characterized by uncertain parameters, external disturbances and unmeasured state variables, as is the case of bioprocess control systems, the linearization problem becomes particularşy complex and almost inextricable.

(Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2003 (ICCMSE 2003),Yazar:T.E. Simos, Page 90)