WELDING ROBOTS
SRI MITTAPALLI COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
BACHELOR OF TECHNOLOGY
IN
MECHANICAL ENGINEERING
DILEEP SAI KUMAR MURIKIPUDI
(18U91A0306)
2021-2022
[ii]
SRI MITTAPALLI COLLEGE OF ENGINEERING
(Approved by AICTE New Delhi, Affiliated to JNTUK, Kakinada)
(An ISO 9001: 2015 Certified Institution and accredited by NACC)
DEPARTMENT OF MECHANICAL ENGINEERING
CERTIFICATE
This is to certify that the thesis entitled, “WELDING ROBOTS” submitted by
Mr. M.DILEEP SAI KUMAR (18U91A0306), in partial fulfilment of the requirements
for the award of Bachelor of Technology for the academic year (2021-2022) .
SIGNATURE OF HOD
CONTENTS
CHAPTER 1
 INTRODUCTION
01
 INTRODUCTION TO AUTOMATION AND ROBOTICS
01
 INTRODUCTION TO WELDING
04
CHAPTER 2
 WHY CONTINUOUS ROBOTIC ARC WELDING?
06
 BENEFITS OF ROBOT ARC WELDING
06
 FEATURES OF ARC WELDING ROBOTS
07
 PROBLEMS FOR ROBOTS IN ARC WELDING
09
CHAPTER 3
 WHY ROBOT SPOT WELDING?
11
 BENEFITS OF ROBOT SPOT WELDING
11
 FEATURES OF SPOT-WELDING ROBOTS
12
CHAPTER 4
 ROBOTIC ARC WELDING SYSTEM
14
CHAPTER 5
 CONCLUSION
18
ABSTRACT
Welding being the major asset and salvation for mechanical engineering,
the seminar 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 seminar 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.
CHAPTER-1
INTRODUCTION
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 aerospace 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 configuration.
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.
SPOT WELDING
As he terms 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.
CHAPTER-2
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 breaks.
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 robot’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.
5. PROGRAMMING
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
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 irregularities.
Arc welding robots performing in a workshop
CHAPTER 3
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 difficulty.
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 robot’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-welding.
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 application.
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
CHAPTER-4
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.
RAWS
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.
MANIPULATOR
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.
SENSORS
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
CONTROL SYSTEM
Typical block diagram configuration of a control system for a robot joint.
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 manipulator’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.
WELDING POWER
SOURCE AND
Z
CONTROL
ROBOT
CONTROLLER OR
MASTER
CONTROL
ROBOT
MANIPULATOR
OR ARC MOTION
ELECTRODE
WIRE FEEDER
AND CONTROL
WELDING
CONTROL AND
INTERFACE
OPTIONAL
POSITIONER OR
WORK MOTION
AND CONTROL
BLOCK DIAGRAM OF RAWS
CHAPTER-5
CONCLUSION
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 recreational.
Not only will robotics improve our standard of living, it will also improve our
standard of life.
At the outset, I thank the one and only Supreme Omnipotent for
providing me with brimming vigor and spunk to exhibit my seminar, which
wouldn’t have been a successful one with out His grace.
I serve this opportunity to reveal my open