A SEMINAR REPORT ON
‘ ROBOT WELDING TECHNOLOGY ’
BY
GARAD HARIPRASAD DNYANOBA
[ B2210823 ]
DEPARTMENT OF MECHANICAL ENGINEERING
A.I.S.S.M.S’S.
COLLEGE OF ENGINEERING, PUNE
[ 2003-2004 ]
A SEMINAR REPORT ON
‘ ROBOT WELDING TECHNOLOGY ’
BY
GARAD HARIPRASAD DNYANOBA
EXAM NO. [ B2210823 ] ROLL NO. 4123
UNDER THE GUIDENCE OF
Mr. S.V. CHAITANYA
A.I.S.S.M.S. COLLEGE OF ENGINEERING
PUNE – 1
DEPARTMENT OF MECHANICAL ENGINEERING
2003-2004
CERTIFICATE
THIS IS TO CERTIFY THAT THE SEMINAR REPORT ENTITLED
‘ ROBOT WELDING TECHNOLOGY ’
SUBMITTED BY
GARAD HARIPRASAD DNYANOBA
EXAM NO. B2210823
FOR PARTIAL FULFILMENT FOR THE AWARD OF DEGREE OF B.E.
IN MECHANICAL BRANCH OF THE
UNIVERSITY OF PUNE, IS APPROVED.
GUIDE H.O.D.
PROF. Mr. S.V. CHAITANYA PROF. V.N.PHADKULE
EXAMINER
INDEX
SR.NO. /TOPICS
/ PAGE NO.1. / ABSTRACT / 1
2. / ROBOT WELDING / 2
3. / WELDING PROCESS / 3
4. / ROBOT SPOT WELDING / 11
5. / LASER ROBOT WELDING / 16
6. / WELDING SAFETY / 17
7. / ADVANTAGES / 18
8. / CONCLUSION / 19
9. / REFERENCES / 20
ACKNOWLEDGEMENT
It give me a grate pleasure to present this seminar report on “ ROBOT WELD TECHNOLOGY ” FINAL YEAR degree course in MECHANICAL ENGINEERING.
With great pleasure, I wish to express my deep sense of gratitude towards seminar guide Prof. S.V CHAITANYA and other staff members for the valuable guidance in preparation of this seminar report.
Finally I would like to thank my all friends for their cooperation for completing this seminar report.
GARAD HARIPRASAD D.
EXAM NO. B2210823
B.E. MECHANICAL.
ABSTRACT
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
1. Robot welding
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.
2. WELDING PROCESSES
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.
2.1. ROBOT ARC WELDING
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.
TYPICAL COMPONENTS OF AN INTEGRATED ROBOTIC ARC-WELDING CELL:
1. Arcweldingrobot
2. Powersource
3. Weldingtorch
4. Wirefeeder
5. Welding fixtures and work piece positioners
6. Torch cleaner
7. TCPcalibrationunit
2.1.1 ARC WELDING ROBOT
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.
2.1.2 ARC WELDING POWER SOURCES
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
2.1.3 WELDING TORCH
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.
2.1.4 WIRE FEEDER
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 feederis 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.
2.1.5 WORKPIECE FIXATION AND POSITIONING
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.
2.1.6 TORCH CLEANER
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.