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welding robots full report
Post: #1

Welding being the major asset and salvation for mechanical
engineering, the seminars is all about the automation of major welding
processes used in industries using robots, which was hitherto done
manually under hazardous and perilous working environs. The seminars
dwells with two major industrial welding processes namely continuous
arc welding process and spot welding process. It also connects with
essential features of the robots used in these welding processes and
also the advantages and disadvantages of these industrial robotic
welding processes.

Welding technology has obtained access virtually to every
branch of manufacturing; to name a few bridges, ships, rail road
equipments, building constructions, boilers, pressure vessels, pipe
lines, automobiles, aircrafts, launch vehicles, and nuclear power
plants. Especially in India, welding technology needs constant
upgrading, particularly in field of industrial and power generation
boilers, high voltage generation equipment and transformers and in
nuclear aero-space industry.
Computers have already entered the field of welding and the
situation today is that the welding engineer who has little or no
computer skills will soon be hard-pressed to meet the welding
challenges of our technological times. In order for the computer
solution to be implemented, educational institutions cannot escape
their share of responsibilities.
Automation and robotics are two closely related technologies.
In an industrial context, we can define automation as a technology that
is concerned with the use of mechanical, electronics and computer-based
systems in the operation and control of production. Examples of this
technology include transfer lines, mechanized assembly machines, feed
back control systems, numerically controlled machine tools, and robots.
Accordingly, robotics is a form of industrial automation.
There are three broad classes of industrial automation: fixed
automaton, programmable automation, and flexible automation. Fixed
automation is used when the volume of production is very high and it is
therefore appropriate to design specialized equipment to process the
product very efficiently and at high production rates. A good example
of fixed automation can be found in the automobile industry, where
highly integrated transfer lines consisting of several dozen work
stations are used to perform machining operations on engine and
transmission components. The economics of fixed automation are such
that the cost of the special equipment can be divided over a large
number of units, and resulting unit cost are low relative to
alternative methods of production. The risk encountered with fixed
automation is this; since the initial investment cost is high, if the
volume of production turns out to be lower than anticipated, then the
unit costs become greater than anticipated. Another problem in fixed
automation is that the equipment is specially designed to produce the
one product, and after that products life cycle is finished, the
equipment is likely to become obsolete. For products with short life
cycle, the use of fixed automation represents a big gamble.
Programmable automation is used when the volume of production
is relatively low and there are a variety of products to be made. In
this case, the production equipment is designed to be adaptable to
variations in product configuration. This adaptability feature is
accomplished by operating the equipment under the control of program
of instructions which has been prepared especially for the given
product. The program is read into the production equipment, and the
equipment performs the particular sequence of processing operations to
make that product. In terms of economics, the cost of programmable
equipment can be spread over a large number of products even though the
products are different. Because of the programming feature, and the
resulting adaptability of the equipment, many different and unique
products can be made economically in small batches.
There is a third category between fixed automation and
programmable automation, which is called flexible automation. This is
more suitable for the mid volume production range. It must be
programmed for different product configurations, but the variety of
configurations is usually non-limited than for a programmable

Relationship of fixed automation programmable automation, and flexible
automation as a function of production volume and product variety.
Of the three types of automation, robotics coincides most
closely with programmable automation. An industrial robot is a general
-purpose, programmable machine which possesses certain human like
characteristics of present-day robots is their movable arms. The robots
can be programmed to move its arm through a sequence of in order to
perform some useful task. It will repeat that motion pattern over and
over until reprogrammed to perform some other task. Hence the
programming feature allows robots to be used for a variety of different
industrial operations. Like machine loading and unloading, spot
welding, continuous arc welding, spray painting etc.
The official definition of an industrial robot provided by the
Robotics Industrial Association (RIA) is as follows: An industrial
robot is a reprogrammable multifunctional manipulation designed to move
materials, parts, tools or special devices through programmed motions
for the performance of a variety of tasks.

Welding is a process of joining different materials. The large
bulk of materials that are welded are metals and their alloys although
welding is also applied to the joining of other materials such as
thermoplastics. Welding joins different metals or alloys with help of a
number of processes in which heat is supplied either electrically or by
means of a gas torch.
As he term suggests, spot welding is a process in which two
sheet metal parts are fused together at localized points by passing a
large electric current using two copper electrodes, hence producing the
weld. For relatively small parts a spot welding machine is used in
which the parts are inserted between the pair of electrodes that are
maintained in a fixed position. Where as for larger works such as in
automobile bodies a portable welding gun is used which consists of a
pair of electrodes and a frame to open and close the electrodes.
Arc welding is a continuous process as opposed to spot welding
which might be called a discontinuous process. Continuous arc welding
is used to make long welding joints in which an air tight seal is often
required between the two pieces of metals being joined. The process
uses an electrode in the form of a rod or a wire of metal to supply the
high electric current needed for establishing the arc. Currents are
typically 100 to 300A at voltages of 10 to 30GV. The arc between the
welding rod and the metal parts to be joined produces temperatures that
are sufficiently high to form a pool of molten metal to fuse the two
pieces together. The electrode can also be used to contribute to the
molten pool, depending on the type of welding process.
For robot applications two types of arc welding processes seems
to be most practical, namely: gas metal arc welding (GMAW) and gas
tungsten arc welding (GTAW). Gas tungsten arc welding is also called
MIG welding for metal inert gas welding.

Arc welding is performed by skilled workers who are assisted by
a person called fitter. The purpose of the fitter is to organize the
work and fixture the parts of the welder. The working condition of the
welder is typically unpleasant and hazardous. The arc from the welding
process emits ultra-violet radiations which is injurious to human
vision. As a result welders are required to wear eye protection in the
form of a welding helmet with a dark window. The dark window filters
out the dangerous, but it so dark that the welder is virtually blind
while wearing the helmet except when the arc is struck. Other aspects
of the process are also hazardous. The high temperature created in arc
welding and the resulting molten metals are inherently dangerous. The
high electric current used to create the arc is also unsafe. Sparks and
smoke are generated during the process are a potential threat to
operators. Because of the hazards for human workers in continuous arc
welding, it is logical to consider industrial robots for the purpose.

Factors that contribute to the increased rate when robots used
in batch production is the elimination of fatigue factor. Robots do not
experience fatigue in the sense that human workers do. A robot can
continue to operate in the entire shift with need of periodic rest
Improved safety and quality-of-work environment result from
removing the human operator from an uncomfortable, fatiguing and
potentially dangerous work situation.
Greater product quality in robot arc welding results from the
capability of the robot to perform the welding cycle with accuracy and
repeatability than its human counterpart. This translates into a more
consistent welding seam; one that is free of the start-and-stop builds
up of filler metal in the seam that is the characteristic of many welds
accomplished by human welders.
An industrial robot that performs welding must possess certain features
and capabilities. Some of the technical considerations in arc welding
applications are discussed in the following.
The robotâ„¢s work volume must be large enough for the size of
the parts to be welded. A sufficient allowance must be made for the
manipulation of the welding torch. Five or six degrees of freedom are
generally required for arc welding robots. The number is influenced by
the characteristics of the welding job and motion capabilities of the
parts manipulator. If the parts manipulator has two degrees of freedom,
this tends to reduce the requirement on the number of degrees of
freedom possessed by the robot.
Continuous path control is required for arc welding. The robot
must be capable of smooth continuous motion in order to maintain
uniformity of welding seam.
The accuracy and repeatability of the robot determines to a
large extend for the quality of welding job. The precision requirements
of welding job vary according to size and industry purpose, and these
requirements should be defined by each individual user before selecting
the most appropriate robot.
The robot must be provided with sufficient input/output and
control capabilities to work with other equipments in the cell. These
other pieces of equipments are automobile fixturing units, conveyors,
and parts of positioners. The cell controller unit must co-ordinate the
path and path of robot with operation of parts manipulator and the
welding parameters such as wire feed rate and power level.
Programming the robot for continuous arc welding must be
considered carefully. To facilitate the input of the program for
welding paths with irregular shapes; it is convenient to use the walk
through method in which the robot wrist is physically moved through its
motion path. For straight welding paths, the robot should possess the
capability for linear interpolation between two points in the space.
This permits the programmer to define the beginning and points of the
path the robot is capable of computing the straight trajectory between
the points.

A typical arc welding robot
1. A related problem is that arc welding is often performed in
confined areas that are difficult to access, such as insides of tanks,
pressure vessels, and ship hulls. Humans can position in to these areas
more readily than robots.
2. One of the most difficult technical problems is the variation
in the dimensions of the parts in a batch production job. This type of
dimensional variations means that the arc-welding path to be followed
will change slightly from part to part.
3. Another technical difficulty is the variations in the edges and
surfaces to be welded together. Instead of being straight and regular,
the edges are typically irregular. This causes variations in the gap
between the parts and other problems in the way the pieces mate
together prior to the welding process.

Human welders are able to compensate for both these variations
by certain parameters in the welding process. Industrial robots
provided with sensors to monitor the variations in the welding process
and the control logic to compensate for part and weld gap

Arc welding robots performing in a workshop
For larger works on spot welding the welding guns with cables
attached is quite heavy and can easily exceed 100lb in weight. To
assist the operator in manipulating the gun, the apparatus is suspended
from an overhead hoist system. Even with this assistance, the spot-
welding gun represents a heavy mass and is difficult to manipulate by a
human worker at high rates of production desired on a car body assembly
line. There are often problems with the consistency of the welded
products made on such a manual line as a consequence of this
As a result of these difficulties robots have been employed
with great success on this type of production line to perform some or
all of the welding operations. A welding gun is attached as the end
effector to each robotâ„¢s wrist, and the robot is programmed to perform
a sequence of welds on the product as it arrives at the workstation.
Some robot spot-welding lines operate with several dozens of robots all
programmed to perform different welding cycles on the product. Today,
the automobile manufacturers make extensive use of robots for spot-

Improved quality is in the form of more consistent welds and
better repeatability in the location of welds. Even robots with
relatively unimpressive repeatability specifications are able to locate
the spot welds more accurately than human operators.
Improved safety results simply because the human is removed
from the work environment where there are hazards from electrical
shocks and burns.
The use of robots to automate the spot welding process should
also result in improvements in area such as production scheduling and
in process inventory control.
The maintenance of the robots and welding equipment becomes an
important factor in the successful operation of an automated spot
welding production line.
1. Robots must be relatively large. It must have sufficient
payload capacity to readily manipulate the welding gun for the
2. The work volume must be adequate for the size of the product.
3. The robot must be able to position and orient the welding gun
in places on the product that might be difficult to access. This might
result in need for an increased number of freedoms.
4. The controller memory must have enough capacity to accomplish
the many positioning steps required for the spot-welding cycle. In some
applications, the welding line is designed to produce several different
models of the product. Accordingly, the robot must be able to switch
from one programmed welding sequence to another as the models change.

A typical spot welding robot

Spot welding robot performing in a welding cell
Robotic arc welding (RAWS) is best suited for batch production
involving frequent design changes in a component and even where
different components are to be handled one after the other. This is
possible due to highly flexible system provided by RAWS. However the
justification for installation of such a system has to be looked
through return on investment by considering all the expenses (on
equipment, material handling devices, training, etc.) and the likely
savings on account of increased production, improved quality, savings
of energy, men-hours and materials due to the reduction in reworking of
components, lower turn over of employees in the shop and reduced burden
of strikes, etc.

The figure given above shows the various units involved in
robotic arc welding system (RAWS). The robotic arc welding system
consists of a manipulator, controller and power supply unit.
The robot consists of a manipulator which is a series of
mechanical linkages and joints capable of producing all sorts of
designed movements. The body, arm and wrist assembly of a robot is
sometimes called as a manipulator. Each link of a manipulator is driven
by activators which may be operated either hydraulic or pneumatic power
cylinder or electrical motors. The forearm of a robot can move in a
nearly spherical way, thus covering a large work volume and providing
greater application flexibility. It is easily possible to reach down
into or onto objects placed over the conveyor.
The robotic arc welding sensor system considered here are all
designed to track the welding seam and provide the information to the
robot controller to help guide the welding path. The approaches used
for this purposes divide into two basic categories:
1. Contact sensors.
2. Non-Contact sensors
Contact arc welding sensors make use of a mechanical tactile
probe to touch the sides of the groove ahead of the welding torch and
to feed back position data so that course corrections can be made by
the robot controller. Some systems use a separate control unit design
to interpret the probe sensor measurements and transmit the data to the
robot controller.
The second basic type of sensor system used to track the
welding seam uses no tactile measurements. A variety of sensors schemes
have been explored in this category.
Feedback devices or sensors are devices which are incorporated
to sense the positions of the various links and joints. The information
from these devices is fed to the controller. The sensors used in
robotics include the following general categories.
1. Tactile sensors
2. Proximity and range sensors
3. Miscellaneous types
4. Machine vision

Typical block diagram configuration of a control system for a robot
The information from the feedback devices is fed to the
controller. The controller initiates and terminates motion of the
manipulator in desired sequences and at desired points through
interfaces with and manipulatorâ„¢s and activators and feedback systems.
It also stores position and sequence data in memory and performs
complex arithmetic functions to control path, speed and position. The
controller is also lined with other auxiliary devices like power
source, wire feed unit, conveyor etc.
The control unit has a computer with lot of computational
capability. The movement of torch centre point installed at the end of
forearm of the robot can be controlled either by
1. Co-ordinate axis control motions
2. controlled path generation
Only the end points in case of linear path and three points in
case of circular path are specified and the computer automatically
generates the controlled path at the desired velocity including
acceleration and retardation.

An important feature of the RAWS is the searching and following
of the actual welding seam or groove or seam tracking in deviation of
pre-planned line. With out this facility, the programmed welding groove
would different because of errors due to imprecise component clamping
and assembly of improper fit up and inconsistent orientation of the
component etc. However seam tracking system takes care of these
problems and ensures the actual welding grooves to be as per programmed
welding grooves.


A substantial opportunity exists in the technology of robotics
to relieve people from boring, repetitive, hazardous and unpleasant
work in all forms of a human labour. There is a social value as well as
a commercial value in pursuing this opportunity. The commercial value
of robotics is obvious. Properly applied, robots can accomplish
routine, undesirable work better than humans at a lower cost. As the
technology advances, and more people learn how to use robots, the
robotics market will grow at a rate that will approach the growth of
the computer market over the past thirty years. One might even consider
robotics to be a mechanical extension of computer technology.
The social value of robotics is that these wonderfully
subservient machines will permit humans more time to do work that is
more challenging, creative, conceptual, constructive and co-operative
than at present. There is every reason to believe that the automation
of work through robotics will lead to substantial increases in
productivity, and that these productivity increases year by year will
permit humans to engage in activities that are cultural and
Not only will robotics improve our standard of living, it will also
improve our standard of life.

1. Robotics by FU, GONZALEZ, LEE
2. Robot Technology by JAMES G. KERAMAS
3. Industrial Robotics by MIKELL P. GROOVER, NICHOLAS G. ODREY,


At the outset, I thank the one and only Supreme Omnipotent for
providing me with brimming vigor and spunk to exhibit my seminars, which
wouldnâ„¢t have been a successful one with out His grace.
I serve this opportunity to reveal my open hearted gratitude
towards Dr. T.N Sathyaneshan, Head of the Department Mechanical
Engineering for permitting me to fulfill my obligation. My profound and
sincere thanks to
Mr. Alex Bernard Mechanical Department for his priceless guidance and
exuberant assistance throughout.
I am profusely indebted to my beloved parents and my only
sister, who have kept my spirits high and morale right.
In conclusion, I reiterate that my room mates and well wishers
have been head and shoulders above every one else in lending their
hands during this mighty climb.
Post: #2






Welding is manufacturing process in which to pieces of metal are joined by usually by heating them until molten and fused and by applying pressure. Welding operations performed by robot vastly. Welding of two types on e is arc welding and another spot welding.
In arc welding two metals are joined along its continuous path. An electric arc is generated there.
Spot welding is the largest application for industrial robots in US, accounting for about for 35 percent of installed robots. Welding robots typically use point-to-point programming to maneuver a welding gun. Robots weld more consistently faster and with higher quality than humans


When should robots be used for welding?
A welding process that contains repetitive tasks on similar pieces might be suitable for automation. The number of items of any type to be welded determines whether automating a process or not. If parts normally need adjustment to fit together correctly, or if joints to be welded are too wide or in different positions from piece to piece, automating the procedure will be difficult or impossible. Robots work well for repetitive tasks or similar pieces that involve welds in more than one axis or where access to the pieces is difficult.
Why robot welding?
The most prominent advantages of automated welding are precision and productivity. Robot welding improves weld repeatability. Once programmed correctly, robots will give precisely the same welds every time on workpieces of the same dimensions and specifications.
Automating the torch motions decreases the error potential which means decreased scrap and rework. With robot welding you can also get an increased output. Not only does a robot work faster, the fact that a fully equipped and optimized robot cell can run for 24 hours a day, 365 days a year without breaks makes it more efficient than a manual weld cell.
Another benefit of automated welding is the reduced labor costs. Robotic welding also reduces risk by moving the human welder/operator away from hazardous fumes and molten metal close to the welding arc.
What welding processes are suitable for robot welding?
Most production welding processes can be used in automated applications. The most popular, used in perhaps 80 percent of applications, is the solid wire GMAW process. This process is best for most high production situations because no postweld cleanup is required.


Welding is the most economical and efficient way to join metals permanently. Welding is used to join all of the commercial metals and to join metals of different types and strengths.

A weld is produced either by heating the materials to the welding temperature with or without the application of pressure alone with or without the use of filler metal. There are different kinds of welding processes who all use different sources of heat, for instance arc welding which uses an electric arc as a heat source. Another commonly used welding process is spot welding (resistance welding).
Welding is considered to be the most complex of all manufacturing technologies. In order to transform welding from a manual operation to an automated production process, it is necessary to understand the scientific principles involved.

Robot welding means welding that is performed and controlled by robotic equipment. In general equipment for automatic arc welding is designed differently from that used for manual arc welding. Automatic arc welding normally involves high duty cycles, and the welding equipment must be able to operate under those conditions. In addition, the equipment components must
have the necessary features and controls to interface with the main control system.
A special kind of electrical power is required to make an arc weld. A welding machine, also known as a power source, provides the special power. All arc-welding processes use an arc welding gun or torch to transmit welding current from a welding cable to the electrode. They also provide for shielding the weld area from the atmosphere.
The nozzle of the torch is close to the arc and will gradually pick up spatter. A torch cleaner (normally automatic) is often used in robot arc welding systems to remove the spatter. All of the continuous electrode wire arc processes require an electrode feeder to feed the consumable electrode wire into the arc.
Welding fixtures and workpiece manipulators hold and position parts to ensure precise welding by the robot. The productivity of the robot-welding cell is speeded up by having an automatically rotating or switching fixture, so that the operator can be fixing one set of parts while the robot is welding another.
To be able to guarantee that the electrode tip and the tool frame are accurately known with respect to each other, the calibration process of the TCP (Tool Center Point) is important. An automatic TCP calibration device facilitates this time consuming task.
1. Arc welding robot
2. Power source
3. Welding torch
4. Wire feeder
5. Welding fixtures and work piece positioners
6. Torch cleaner
7. TCP calibration unit


During the short time that industrial welding robots have been in use, the jointed arm or revolute type has become by far the most popular. For welding it

has almost entirely replaced the other types except for the Cartesian, see (robot kinematics), which is used for very large and very small robots. The reason for the popularity of the jointed arm type is that it allows the welding torch to be manipulated in almost the same fashion as a human being would manipulate it. The torch angle and travel angle can be changed to make good quality welds in all positions. Jointed arm robots also allow the arc to weld in areas that are difficult to reach. Even so, a robot cannot provide the same manipulative motion as a human being, although it can come extremely close. In addition, jointed arm robots are the most compact and provide the largest work envelope relative to their size. Usually arc-welding robots have five or six free programmable arms or axes.
Off-the-shelf programmable robot arms are today available from different suppliers such as ABB, FANUC, PANASONIC, KUKA, MOTOMAN.


A welding power source must deliver controllable current at a voltage according to the requirements of the welding process. Normally, the power required is from 10 to 35 V and from 5 to 500 A. The various welding processes and procedures have specific arc characteristics that demand specific outputs of the welding machine.
Automatic arc welding machines may require power sources more complex than those used for semi-automated welding. An automatic welding machine

usually electronically communicates with the power source to control the welding power program for optimum performance. A power source for arc welding is designed to provide electric power of the proper values and characteristics to maintain a stable arc suitable for welding.
There are three types of arc welding power sources, distinguished according to their static characteristics output curve. The constant-power (CP) is the conventional type of power source that has been used for many years for shielded metal arc welding using stick electrodes. It can be used for submerged arc welding and gas tungsten arc welding. The constant-voltage (CV) power source is the type normally used for gas metal arc and flux cored arc welding using small-diameter electrode wire. The constant-current (CC) power source is normally used for gas tungsten arc and plasma arc welding.
The selection of a welding power source is based on
1. The process or processes to be used
2. The amount of current required
3. The power available at the job site
4. Economic factors and convenience


A welding torch is used in an automatic welding system to direct the welding electrode into the arc, to conduct welding power to the electrode, and to provide shielding of the arc area. There are many types of welding torches, and the choice depends on the welding process, the welding process variation, welding current, electrode size and shielding medium

Welding torches can be categorized according to the way in which they are cooled. They may be water-cooled with circulating cooling water or air-cooled with ambient air. A torch can be used for a consumable electrode welding process such as gas metal arc or flux cored arc welding, and shielding gas may or may not be employed.

A torch can be described according to whether it is a straight torch or has a bend in its barrel. A torch with a bend is often used for robotic arc welding applications to provide access for the weld.

The major function of the torch is to deliver the welding current to the electrode. For consumable electrode process this means transferring the current to the electrode as the electrode moves through the torch.
A second major task of the torch is to deliver the shielding gas, if one is used, to the arc area. Gas metal arc welding uses a shielding gas that may be an active gas usually carbon dioxide or a mixture of an inert gas, normally argon, with CO2 or oxygen.
The welding torch is mounted to the robot flange with a matching mounting arm. Preferably an anti collision clutch is used to prevent damages on expensive weld equipment in case of sticking electrode and crashes during installation and start-up.


Wire feeders are used to add filler metal during robotic welding. This allows flexibility in establishing various welding wire feed rates to suit specific requirements for an assembly. Normally, the wire feeder for robotic welding is mounted on the robot arm, separate from the power supply. For robotic welding, a control interfaces between the robot controllers, the power supply and wire

feeder is needed. The wire feeding system must be matched to the welding process and the type of power source being used.

There are two basic types of wire feeders. The first type is used for the consumable electrode wire process and is known as an electrode wire feeder. The electrode is part of the welding circuit, and the melted metal from the electrode crosses the arc to become the weld deposit. There are two different types of electrode wire feeders. The constant-power power source requires a voltage-sensing wire feed system in which the feed rate may be changing continously. The constant-voltage system requires a constant feed rate during the welding operation.

The second type of wire feeder is known as a cold wire feeder and is especially used for gas tungsten arc welding. The electrode is not part of the circuit, and the filler wire fed into the arc area melts from the heat of the arc and becomes the weld metal.


In order to join parts successfully in a robotic welding application, individual parts must be aligned precisely and held securely in place while the welding is proceeding. An important consideration, then, is the design of a fixture which holds the individual parts in the proper alignment. The tool must allow for quick and easy loading, it must hold the parts in place securely until they are welded together and must allow the welding gun unrestricted access to each weld point.

One starting point for positioning the workpiece for robotic welding may be the fixture already used for manual welding even though specialized positioners are used to improve the versatility and to extend the range of robotic arc welding systems. The usable portion of a robot work envelope can be limited becuse the
welding torch mounting method does not allow the torch to reach the joint properly. Special positioners eliminate some of these limitations by making the workpiece more accessible to the robot welding torch.
The positioners used with robots also have to be more accurate than required for manual or semiautomatic welding. In addition the robot positioner controls must be compatible and controllable by the robot controller in order to have simultaneous coordinated motion of several axes while welding.
However, loading and unloading stationary jigs of the robot cell can be time consuming and impractical. It is often more efficient to have two or more fixtures on a revolving workpiece positioner, despite a higher initial cost. With a revolving table for instance, the operator can load and unload while the robot is welding. Obviously, this speeds up the process and keeps the robot welding as much of the time as possible.


Periodic cleaning of arc welding guns is required for proper and reliable operation of robotic arc welding equipment. The high duty cycle of an automatic operation may require automated gun cleaning. Systems are available that spray an antispatter agent into the nozzle of the gun. Additionally, tools that ream the nozzle to remove accumulated spatter and cut the wire are available. The cleaning system is automatically activated at required intervals by the welding control system.


End-of-arm sensor and tool centre point calibration is a critical aspect of successful system implementation. End-of-arm sensing, in the context of robotic welding, is used to detect the actual position of the seam on the workpiece with respect to the robot tool frame.
Analysis of the profile data yields the relative position of the seam with respect to the sensor reference frame. If the sensor reference frame pose is known with respect to the end-frame of the robot, and the tool frame pose is known with respect to the end-frame, then the sensor data may be used to accurately position the tool centre point (TCP) with respect to the workpiece.
While end-of-arm sensor based control would appear to solve both robot accuracy and workpiece position error problems, this is only so if the sensor frame, end frame, and tool frame are accurately known with respect to each other.
Should the sensor be accidentally knocked out of position, the robot system becomes a highly consistent scrap production facility. Indeed, this very concern has been one of the reasons why some companies that would benefit from a sensor based correction system have been reluctant to implement such a system. What is required is not only a technique that enables the frames to be automatically calibrated, but that also enables the system to quickly determine if recalibration is necessary. This second capability is perhaps the more important in practice, since it can be reasonably assumed that any calibration error will be caused by an unanticipated event that could occur during any welding cycle.


Automatic welding imposes specific demands on resistance welding equipment. Often, equipment must be specially designed and welding procedures developed to meet robot welding requirements.
The spot welding robot is the most important component of a robotized spot welding installation. Welding robots are available in various sizes, rated by payload capacity and reach. The number of axes also classifies robots. A spot welding gun applies appropriate pressure and current to the sheets to be welded. There are different types of welding guns, used for different applications, available. An automatic weld-timer initiates and times the duration of current.

During the resistance welding process the welding electrodes are exposed to severe heat and pressure. In time, these factors begin to deform (mushroom) the electrodes. To restore the shape of the electrodes, an automatic tip-dresser is used.
One problem when welding with robots is that the cables and hoses used for current and air etc. tend to limit the capacity of movement of the robot wrist. A solution to this problem is the swivel, which permits passage of compressed air, cooling water, electric current and signals within a single rotating unit. The swivel unit also enables off-line programming as all cables and hoses can be routed along defined paths of the robot arm.

1) Spot welding robot
2) Spot welding gun
3) Weld timer
4) Electrode tip dresser
5) Spot welding swivel


A robot can repeatedly move the welding gun to each weld location and position it perpendicular to the weld seam. It can also replay programmed welding schedules. A manual welding operator is less likely to perform as well because of the weight of the gun and monotony of the task.

Spot welding robots should have six ore more axes of motion and be capable of approaching points in the work envelope from any angle. This permits the robot to be flexible in positioning a welding gun to weld an assembly. Some movements that are awkward for an operator, such as positioning the welding gun upside down, are easily performed by a robot.


Spot welding guns are normally designed to fit the assembly. Many basic types of guns are available, the two most commonly used being the direct acting type, generally known as a C-type gun, where the operating cylinder is connected directly to the moving electrode, and the X-type (also known as "Scissors" or "Pinch") where the operating cylinder is remote from the moving electrode, the force being applied to it by means of a lever arm. C guns are generally the cheapest and the most commonly used. There are many variations available in each basic type with regard to the shape and style of the frame and arms, and also the duty for which the gun is designed with reference to welding pressure and current.
Pneumatic guns are usually preferred because they are faster, and they apply a uniform electrode force. Hydraulic spot welding guns are normally used where space is limited or where high electrode forces are required


An automated spot welding cell needs control equipment to initiate and time the duration of current. A spot weld timer (weld control unit) automatically controls welding time when spot-welding. It also may control the current magnitude as well as sequence and time of other parts of the welding cycle.


The function of the electrodes is to conduct the current and to withstand the high pressures in order to maintain a uniform contact area and to ensure the continued proper relationship between selected current and pressure. Uniform contacting areas should therefore be maintained.
Good weld quality is essential and depends, to a considerable degree, upon uniformity of the electrode contact surface. This surface tends to be deformed (mushroomed) with each weld. Primary causes for mushrooming are too soft electrode material, too high welding pressure, too small electrode contact surface, and most importantly, too high welding current. These conditions cause excessive heat build-up and softening of electrode tips. Welding of todayâ„¢s coated materials also tends to contaminate the face of the electrodes.
As the electrode deforms, the weld control is called upon to "step" up the welding current in order to compensate for "mushroomed" weld tips. Eventually, the production line will have to be shut down in order to replace the electrodes or to manually go in and hand dress the electrodes. This process will improve the weld cycle but in either case, the line is stopped and time is lost. Furthermore the deformed electrodes have caused unnecessary high consumption of energy and electrodes.
In automatic tip dressing, a tip dresser is mounted on the line where it can be accessed by the welding robot. The robot is programmed to dress the electrodes at regular time intervals. The dressing can be done after each working cycle, after every second cycle, and so on. It depends upon how many spot-welds are done in each cycle. For welding in galvanized sheet, dressing after about 25 spot-welds is recommended. The dressing takes approximately 1 to 2 seconds, and is performed when the work pieces are loaded, unloaded and transported. Maintaining proper electrode geometry minimizes production downtime and utility costs and increases weld efficiency.


A major advancement in resistance spot welding is the swivel. This unit permits passage of compressed air, cooling water, electric current and signals through different channels within a single rotating unit.
This invention greatly improves total efficiency of robotic spot-weld installations. Electrical connection between swivel and transformer is minimal thus permitting maximum utilization of access to spot-weld areas.
Basic advantages are:
¢ Less work space needed -No mass of cables and hoses hanging from the robot arm, resulting in floor space economy.
¢ Improved accessability - Since no limitation on the robot wrist caused by any cables or hoses.
¢ Improved safety - Greatly improved safety factors through reduction of air, electric and water lines; now limited to quick-connect piping, and hoses within robot arm.
¢ Saving in capital equipment - Compact weld-gun assembly accessable to areas formly blocked by transformer, cables, and control boxes. More welds per station means big savings through fewer work stations and less capital equipment.
Reduced try-out costs - No un-defined cables exist on the robot, which reduces programming time to minimum. True off-line programming is now a real. The swivel, which fits directly onto the weld-gun fixture plate without any hoses or cables, ensures the highest quality condition of the spot weld. No electrical degeneration on cables and no hoses that wear.


Today, there are more and more three-dimensional welding applications. Typical of many is the welding of roofs in the automobile sector. Here, the focusing unit of the laser is mounted on a 6-axis buckling arm robot, which executes the movements in space. Most frequently used are Nd: YAG lasers, which allow flexible application of the laser light through optical fibers. But CO2 lasers combined with flexible mirror movement can also be used.

This is how bodies are created in car construction that are significantly stiffer in case of a crash, for example, and thus provide greater safety for passengers.
Furthermore, laser welding always requires access from one side only, so newdesigns are now possible that could not nave been implemented by means of traditional resistance spot welding.


Welding is an established manufacturing process with known potential hazards. Potential safety hazards associated with arc welding include arc radiation, air contamination, electrical shock, fire and explosion, compressed gases, and other hazards. Robots were originally designed to perform the job functions of a human. They were designed to relieve humans of the drudgery of unpleasant, fatiguing, or repetitive tasks and also to remove humans from a potentially hazardous environment. In this regard, robots can replace humans in the performance of dangerous jobs and are considered beneficial for preventing industrial accidents. On the other hand, robots have caused fatal accidents.
The introduction of robots requires appropriate safety features in order to protect both those working directly with the robot and others in the workshop who may not be aware of its potential dangers. This can be provided in a number of ways.
One of the best solutions for robot safety is to purchase a complete welding cell from a robotic integrator. A complete cell includes barriers, all necessary safety devices, and a method of loading and unloading the workstation.
Each robot installation must be carefully planned from safety viewpoint to eliminate hazards. When the robot is in operation it is necessary that people remain outside the work envelope. Barriers or fences should be in place around the robot. All doors and maintenance openings must be protected by safety switches, and the weld areas must be safe guarded so that the power is immediately removed from the robot when a door is opened.. Emergency stop buttons should be placed on all operator panels, robot cabinets and robot programming panels. Barriers must be designed to completely surround the robot and eliminate the possibility of people climbing over or under to get inside the barrier. Signal lights must be arranged on the robot or in the robot area to indicate that the robot is powered.


At present relatively few figures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are 2.5 to 3.5 times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 100 parts/month which takes two or three shift per day there is an increase in number of parts output without difference in quality, which is not necessarily so with manual shift work.
Use of robot welding increases the flexibility. Because it is easy to change the robot work from to another just by changing the program. When the same time of work is already done, the same programme can be fed and the time and cost of programming can be eliminated completely.
Day by day the cost of welding consumable are increasing. Using robots by Slightly changing the edge preparations from normal gap to narrow gap welding lot of consumable can be served with improved weld quality (decrease in grain size, distortion). In addition to increase the productivity it maintains the desired quality throughout the reducing the rework scrap.
It reduces welder fatigue and welder exposure to the more hazardous atmosphere.


At present relatively few figures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are 2.5 to 3.5 times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 100 parts/month which takes two or three shift per day there is an increase in number of parts output without difference in quality, which is not necessarily so with manual shift work.


















EXAM NO. B2210823
Post: #3
robots full report

Post: #4
Welding Processes

A Brief History of Welding

Late 19th Century
Scientists/engineers apply advances in electricity to heat and/or join metals (Le Chatelier, Joule, etc.)
Early 20th Century
Prior to WWI welding was not trusted as a method to join two metals due to crack issues
1930’s and 40’s
Industrial welding gains acceptance and is used extensively in the war effort to build tanks, aircraft, ships, etc.
Modern Welding
the nuclear/space age helps bring welding from an art to a science
Post: #5
plss addddd the ppt on robotic welding and report in this site is totallly equipped and is the best
Post: #6
to get information about the topic "welding robots full ppt" refer the link bellow

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