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 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.
INTRODUCTION TO AUTOMATION AND ROBOTICS
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.
INTRODUCTION TO WELDING
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.
CONTINUOUS ARC WELDING
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.
WHY CONTINUOUS ROBOTIC ARC 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.
BENEFITS OF ROBOT ARC WELDING
1. HIGHER PRODUCTIVITY
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
2. IMPROVED SAFTEY AND QUALITY-OF-WORK LIFE
Improved safety and quality-of-work environment result from
removing the human operator from an uncomfortable, fatiguing and
potentially dangerous work situation.
3. GREATER QUALITY OF PRODUCT
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.
FEATURES OF ARC WELDING ROBOTS
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.
1. WORK VOLUME AND DEGREES OF FREEDOM
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.
2. MOTION CONTROL SYSTEM
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.
3. PRECISION OF MOTION
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.
4. INTERFACE WITH OTHER SYSTEM
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
A typical arc welding robot
PROBLEMS FOR ROBOTS IN ARC WELDING
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
WHY ROBOT SPOT WELDING
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-
BENEFITS OF ROBOT SPOT WELDING
1. IMPROVED PRODUCT QUALITY
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.
2. OPERATOR SAFETY
Improved safety results simply because the human is removed
from the work environment where there are hazards from electrical
shocks and burns.
3. BETTER CONTROL OVER PRODUCTION OPERATION
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.
FEATURES OF SPOT-WELDING ROBOTS
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 SYSTEM
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
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
BLOCK DIAGRAM OF RAWS
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,
Â¢ INTRODUCTION TO AUTOMATION AND ROBOTICS 01
Â¢ INTRODUCTION TO WELDING 04
Â¢ WHY CONTINUOUS ROBOTIC ARC WELDING 06
Â¢ BENEFITS OF ROBOT ARC WELDING 06
Â¢ FEATURES OF ARC WELDING ROBOTS 07
Â¢ PROBLEMS FOR ROBOTS IN ARC WELDING 09
Â¢ WHY ROBOT SPOT WELDING 11
Â¢ BENEFITS OF ROBOT SPOT WELDING 11
Â¢ FEATURES OF SPOT-WELDING ROBOTS 12
Â¢ ROBOTIC ARC WELDING SYSTEM
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.