ROBOTIC WELDING A Seminar Report Submitted in Partial Fulfillment of te Re!uirement" for te De#ree of
BAC$ELOR OF TEC$NOLOG% In
&EC$ANICAL ENGINEERING b'
PRA(EEN SING$ BO)D$*+,-.,,-+-/0 )nder te Super1i"ion of
A""t2 Prof2 PRAS$ANT PRAS$AN T TRIPAT$I TRIPAT$I Department Department of &e3ani3al En#ineerin# Babu Banara"i Da" National In"titute of Te3nolo#' and &ana#ement Lu34no5 Affiliated to te
Dr2 A2P262 ABD)L 7ALA& TEC$NICAL )NI(ERSIT% *Formerl' )ttar Prade" Te3ni3al )ni1er"it'0
L)C7NOW
CERTIFICATE
This is to certify that Praveen Singh Boudh (1405440107), of Departent of !echanica" #ngineering, Ba$u Banarasi Das %ationa" &nstitute of Techno"ogy and !anageent, 'ucno have carried out the pro*ect or presented in this report entit"ed +Roboti3 Weldin# for the aard of Bache"or of Techno"ogy fro Dr- .-P-/- .$du" a"a Technica" niversity, 'ucno under our supervision is a record of or and sincere efforts carried out $y the-
Prof- S-P- .sthana
!r- Prashant Prashan t Tripathi
23D-
.sst- Professor
Dept- of !echanica" #ngineering
Dept- of !echanica" #ngineering
BBD%&T!, 'ucno
BBD%&T!, 'ucno
Date
AC7NOWLEDGE&ENT e deep"y ish to e6press our heartfe"t gratefu"ness and gratitude to the fo""oing peop"e ho guided and supported us in every step of y or&t is our p"easure to offer y sincerest gratitude to y guide &r2 Pra"ant Tripati , Professor, Dept- of !echanica" #ngineering, BBD%&T!, 'ucno, ho has guided and supported us throughout the pro*ect ith his patience and no"edge- 2is guidance, serenity, coitent, strictness and support he"ped us to cop"ete this ore ou"d "ie to e6press our heartiest gratitude to Prof2 S2P2 A"tana8 2ead of !echanica" #ngineering Departent, BBD%&T!, 'ucno, for his unconditiona" support and perission to use the departenta" "a$se are thanfu" to the facu"ty e$ers ho have $een the part of our seinar and presentations, for their va"ua$"e o$servations and guidance- e tae this opportunity to e6tend our regards to the "a$ instructors ho he"ped us ith their si""s and hard or during our pro*ecte are a"so gratefu" to respected Prof2 Dr2 Seetala4"mi 72 , Director, Ba$u Banarasi Das %ationa" &nstitute of Techno"ogy and !anageent, 'ucno, for providing us a great acadeic environent here e can transfor our se"f as asset of the nationina""y, e ou"d "ie to than y parents for their $"essing and care-
PRA(EEN SING$ BO)D$ *+,-.,,-+-/0
&%D#8 S9-%3-
T3P&:S
P.;# %31
1-
.BST9.:T
<-
93B3T #'D&%;
<
=-
#'D&%; P93:#SS
=
4-
93B3T SP3T #'D&%;
11
5-
'.S#9 93B3T #'D&%;
1>
>-
#'D&%; S.#T?
17
7-
.D@.%T.;#S
1A
A-
:3%:'S&3%
1
-
9##9#%:#S
<0
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 3 percent of installed robots. Welding robots typically use point!to!point programming to maneuver a welding gun. "obots weld more consistently faster and with higher #uality than humans
1. ROBOT WELDING When should robots be used for weldin!
A welding process that contains repetitive tas$s on similar pieces might be suitable for automation. %he number of items of any type to be welded determines whether automating a process or not. If parts normally need adjustment to &t together correctly, or if joints to be welded are too wide or in di'erent positions from piece to piece, automating the procedure will be di(cult or impossible. "obots wor$ well for repetitive tas$s or similar pieces that involve welds in more than one a)is or where access to the pieces is di(cult. Wh" robot weldin!
%he most prominent advantages of automated welding are precision and productivity. "obot welding improves weld repeatability. *nce programmed correctly, robots will give precisely the same welds every time on wor$pieces of the same dimensions and speci&cations. Automating the torch motions decreases the error potential which means decreased scrap and rewor$. With robot welding you can also get an increased output. +ot only does a robot wor$ faster, the fact that a fully e#uipped and optimied robot cell can run for - hours a day, 3/ days a year without brea$s ma$es it more e(cient than a manual weld cell. Another bene&t of automated welding is the reduced labor costs. "obotic welding also reduces ris$ by moving the human welder0operator away from haardous fumes and molten metal close to the welding arc. Wh#t weldin $ro%esses #re suit#ble for robot weldin!
1ost production welding processes can be used in automated applications. %he most popular, used in perhaps 2 percent of applications, is the solid wire 41AW process. %his process is best for most high production situations because no postweld cleanup is re#uired.
&. WELDING 'ROCESSES Welding is the most economical and e(cient way to join metals permanently. Welding is used to join all of the commercial metals and to join metals of di'erent 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 &ller metal. %here are di'erent $inds of welding processes who all use di'erent sources of heat, for instance arc welding which uses an electric arc as a heat source. Another commonly used welding process is spot welding 5resistance welding6. Welding is considered to be the most comple) of all manufacturing technologies. In order to transform welding from a manual operation to an automated production process, it is necessary to understand the scienti&c principles involved.
&.1. ROBOT ARC WELDING "obot welding means welding that is performed and controlled by robotic e#uipment. In general e#uipment for automatic arc welding is designed di'erently from that used for manual arc welding. Automatic arc welding normally involves high duty cycles, and the welding e#uipment must be able to operate under those conditions. In addition, the e#uipment components must have the necessary features and controls to interface with the main control system. A special $ind of electrical power is re#uired to ma$e an arc weld. A welding machine, also $nown as a power source, provides the special power.
All arc!welding processes use an arc welding gun or torch to transmit welding current from a welding cable to the electrode. %hey also provide for shielding the weld area from the atmosphere. %he nole of the torch is close to the arc and will gradually pic$ up spatter. A torch cleaner 5normally automatic6 is often used in robot arc welding systems to remove the spatter. All of the continuous electrode wire arc processes re#uire an electrode feeder to feed the consumable electrode wire into the arc. Welding &)tures and wor$piece manipulators hold and position parts to ensure precise welding by the robot. %he productivity of the robot!welding cell is speeded up by having an automatically rotating or switching &)ture, so that the operator can be &)ing one set of parts while the robot is welding another. %o be able to guarantee that the electrode tip and the tool frame are accurately $nown with respect to each other, the calibration process of the %78 5%ool 7enter 8oint6 is important. An automatic %78 calibration device facilitates this time consuming tas$. T('ICAL CO)'ONENTS WELDING CELL,
O*
AN
INTEGRATED
ROBOTIC
ARC+
9. Arc welding robot -. 8ower source 3. Welding torch . Wire feeder . Welding &)tures and wor$ piece positioners /. %orch cleaner :. %78 calibration unit
&.1.1 ARC WELDING ROBOT
;uring the short time that industrial welding robots have been in use, the jointed arm or revolute type has become by far the most popular.
arc to weld in areas that are di(cult to reach. >ven so, a robot cannot provide the same manipulative motion as a human being, although it can come e)tremely close. In addition, jointed arm robots are the most compact and provide the largest wor$ envelope relative to their sie. Usually arc! welding robots have &ve or si) free programmable arms or a)es. *'!the!shelf programmable robot arms are today available from di'erent suppliers such as A??,
&.1.& ARC WELDING 'OWER SO-RCES
A welding power source must deliver controllable current at a voltage according to the re#uirements of the welding process. +ormally, the power re#uired is from 9 to 3 and from to A. %he various welding processes and procedures have speci&c arc characteristics that demand speci&c outputs of the welding machine. Automatic arc welding machines may re#uire power sources more comple) 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. %here are three types of arc welding power sources, distinguished according to their static characteristics output curve. %he constant!power 5786 is the conventional type of power source that has been used for many years for shielded metal arc welding using stic$ electrodes. It can be used for submerged arc welding and gas tungsten arc welding. %he constant!voltage 576 power source is the type normally used for gas metal arc and Bu) cored arc welding using small!diameter electrode wire. %he constant!current 5776 power source is normally used for gas tungsten arc and plasma arc welding. %he selection of a welding power source is based on 9. %he process or processes to be used -. %he amount of current re#uired 3. %he power available at the job site . >conomic factors and convenience
&.1. WELDING TORC/
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. %here are many types of welding torches, and the choice depends on the welding process, the welding process variation, welding current, electrode sie and shielding medium Welding torches can be categoried according to the way in which they are cooled. %hey 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 Bu) 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. %he major function of the torch is to deliver the welding current to the electrode.
92+2, WIRE FEEDER
Wire feeders are used to add &ller metal during robotic welding. %his allows Be)ibility in establishing various welding wire feed rates to suit speci&c re#uirements for an assembly. +ormally, the wire feeder for robotic welding is mounted on the robot arm, separate from the power supply.
%here are two basic types of wire feeders. %he &rst type is used for the consumable electrode wire process and is $nown as an electrode wire feeder. %he electrode is part of the welding circuit, and the melted metal from the electrode crosses the arc to become the weld deposit. %here are two di'erent types of electrode wire feeders. %he constant!power power source re#uires a voltage!sensing wire feed system in which the feed rate may be changing continously. %he constant!voltage system re#uires a constant feed rate during the welding operation. %he second type of wire feeder is $nown as a cold wire feeder and is especially used for gas tungsten arc welding. %he electrode is not part of the circuit, and the &ller wire fed into the arc area melts from the heat of the arc and becomes the weld metal.
&.1.0 WOR'IECE *I2ATION AND 'OSITIONING
In order to join parts successfully in a robotic welding application, individual parts must be aligned precisely and held securely in place while the welding is proceeding. An important consideration, then, is the design of a &)ture which holds the individual parts in the proper alignment. %he tool must allow for #uic$ 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. *ne starting point for positioning the wor$piece for robotic welding may be the &)ture already used for manual welding even though specialied
positioners are used to improve the versatility and to e)tend the range of robotic arc welding systems. %he usable portion of a robot wor$ 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 ma$ing the wor$piece more accessible to the robot welding torch. %he positioners used with robots also have to be more accurate than re#uired 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 a)es while welding. Cowever, loading and unloading stationary jigs of the robot cell can be time consuming and impractical. It is often more e(cient to have two or more &)tures on a revolving wor$piece positioner, despite a higher initial cost. With a revolving table for instance, the operator can load and unload while the robot is welding. *bviously, this speeds up the process and $eeps the robot welding as much of the time as possible. &.1.3 TORC/ CLEANER
8eriodic cleaning of arc welding guns is re#uired for proper and reliable operation of robotic arc welding e#uipment. %he high duty cycle of an automatic operation may re#uire automated gun cleaning. Systems are available that spray an antispatter agent into the nole of the gun. Additionally, tools that ream the nole to remove accumulated spatter and cut the wire are available. %he cleaning system is automatically activated at re#uired intervals by the welding control system.
&.1.4
TC'+
CALIBRATION -NIT
>nd!of!arm sensor and tool centre point calibration is a critical aspect of successful system implementation. >nd!of!arm sensing, in the conte)t of
robotic welding, is used to detect the actual position of the seam on the wor$piece with respect to the robot tool frame. Analysis of the pro&le data yields the relative position of the seam with respect to the sensor reference frame. If the sensor reference frame pose is $nown with respect to the end!frame of the robot, and the tool frame pose is $nown with respect to the end!frame, then the sensor data may be used to accurately position the tool centre point 5%786 with respect to the wor$piece. While end!of!arm sensor based control would appear to solve both robot accuracy and wor$piece position error problems, this is only so if the sensor frame, end frame, and tool frame are accurately $nown with respect to each other. Should the sensor be accidentally $noc$ed 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 bene&t from a sensor based correction system have been reluctant to implement such a system. What is re#uired is not only a techni#ue that enables the frames to be automatically calibrated, but that also enables the system to #uic$ly determine if recalibration is necessary. %his 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.
&.& ROBOT S'OT WELDING
Automatic welding imposes speci&c demands on resistance welding e#uipment. *ften, e#uipment must be specially designed and welding procedures developed to meet robot welding re#uirements.
%he spot welding robot is the most important component of a robotied spot welding installation. Welding robots are available in various sies, rated by payload capacity and reach. %he number of a)es also classi&es robots. A spot welding gun applies appropriate pressure and current to the sheets to be welded. %here are di'erent types of welding guns, used for di'erent applications, available. An automatic weld!timer initiates and times the duration of current.
;uri ng the resistance welding process the welding electrodes are e)posed to severe heat and pressure. In time, these factors begin to deform 5mushroom6 the electrodes. %o restore the shape of the electrodes, an automatic tip!dresser is used. *ne 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. %he swivel unit also enables o'!line programming as all cables and hoses can be routed along de&ned paths of the robot arm.
T('ICAL CO)'ONENTS O* AN INTEGRATED ROBOTIC S'OT WELDING CELL,
96 Spot welding robot -6 Spot welding gun 36 Weld timer
6 >lectrode tip dresser 6 Spot welding swivel &.&.1 S'OT WELDING ROBOT
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 li$ely to perform as well because of the weight of the gun and monotony of the tas$.
Spot robots have more motion
welding should si) ore a)es of and be capable of
approaching points in the wor$ envelope from any angle. %his permits the robot to be Be)ible in positioning a welding gun to weld an assembly. Some movements that are aw$ward for an operator, such as positioning the welding gun upside down, are easily performed by a robot.
&.&.& S'OT WELDING G-NS
Spot welding guns are normally designed to &t the assembly. 1any basic types of guns are available, the two most commonly used being the direct acting type, generally $nown as a D7E!type gun, where the operating cylinder is connected directly to the moving electrode, and the DFE!type
5also $nown as GScissorsG or G8inchG6 where the operating cylinder is remote from the moving electrode, the force being applied to it by means of a lever arm. 7 guns are generally the cheapest and the most commonly used. %here 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. 8neumatic guns are usually preferred because they are faster, and they apply a uniform electrode force. Cydraulic spot welding guns are normally used where space is limited or where high electrode forces are re#uired
&.&. WELD TI)ER
An automated spot welding cell needs control e#uipment to initiate and time the duration of current. A spot weld timer 5weld control unit6 automatically controls welding time when spot!welding. It also may control the current magnitude as well as se#uence and time of other parts of the welding cycle. &.&.5 ELECTRODE TI' DRESSER
%he 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.
4ood weld #uality is essential and depends, to a considerable degree, upon uniformity of the electrode contact surface. %his surface tends to be deformed 5mushroomed6 with each weld. 8rimary causes for mushrooming are too soft electrode material, too high welding pressure, too small electrode contact surface, and most importantly, too high welding current. %hese conditions cause e)cessive heat build!up and softening of electrode tips. Welding of todayHs coated materials also tends to contaminate the face of the electrodes. As the electrode deforms, the weld control is called upon to GstepG up the welding current in order to compensate for GmushroomedG weld tips. >ventually, 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. %his process will improve the weld cycle but in either case, the line is stopped and time is lost.
&.&.0 S'OT WELDING SWI6EL
A major advancement in resistance spot welding is the swivel. %his unit permits passage of compressed air, cooling water, electric current and signals through di'erent channels within a single rotating unit. %his invention greatly improves total e(ciency of robotic spot!weld installations. >lectrical connection between swivel and transformer is minimal thus permitting ma)imum utiliation of access to spot!weld areas. ?asic advantages are
•
•
•
•
Jess wor$ space needed !+o mass of cables and hoses hanging from the robot arm, resulting in Boor space economy. Improved accessability ! Since no limitation on the robot wrist caused by any cables or hoses. Improved safety ! 4reatly improved safety factors through reduction of air, electric and water linesK now limited to #uic$!connect piping, and hoses within robot arm. Saving in capital e#uipment ! 7ompact weld!gun assembly accessable to areas formly bloc$ed by transformer, cables, and control bo)es. 1ore welds per station means big savings through fewer wor$ stations and less capital e#uipment. "educed try!out costs ! +o un! de&ned cables e)ist on the robot, which reduces programming time to minimum. %rue o'!line programming is now a real. %he swivel, which &ts directly onto the weld!gun &)ture plate without any hoses or cables, ensures the highest #uality condition of the spot weld. +o electrical degeneration on cables and no hoses that wear.
&. LASER ROBOT WELDING
%oday, there are more and more three!dimensional welding applications. %ypical of many is the welding of roofs in the automobile sector. Cere, the focusing unit of the laser is mounted on a /!a)is buc$ling arm robot, which e)ecutes the movements in space. 1ost fre#uently used are +d LA4 lasers, which allow Be)ible application of the laser light through optical &bers. ?ut 7*- lasers combined with Be)ible mirror movement can also be used.
%his is how bodies are created in car construction that are signi&cantly sti'er in case of a crash, for e)ample, and thus provide greater safety for passengers.
. WELDING SA*ET(
Welding is an established manufacturing process with $nown potential haards. 8otential safety haards associated with arc welding include arc radiation, air contamination, electrical shoc$, &re and e)plosion, compressed gases, and other haards. "obots were originally designed to perform the job functions of a human. %hey were designed to relieve humans of the drudgery of unpleasant, fatiguing, or repetitive tas$s and also to remove humans from a potentially haardous environment. In this regard, robots can replace humans in the performance of dangerous jobs and are considered bene&cial for preventing industrial accidents. *n the other hand, robots have caused fatal accidents.
%he introduction of robots re#uires appropriate safety features in order to protect both those wor$ing directly with the robot and others in the wor$shop who may not be aware of its potential dangers. %his can be provided in a number of ways. *ne of the best solutions for robot safety is to purchase a complete welding cell from a robotic integrator. A complete cell includes barriers, all necessary safety devices, and a method of loading and unloading the wor$station. >ach robot installation must be carefully planned from safety viewpoint to eliminate haards. When the robot is in operation it is necessary that people remain outside the wor$ envelope. ?arriers 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.. >mergency stop buttons should be placed on all operator panels, robot cabinets and robot programming panels. ?arriers 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.
5. AD6ANTAGES IN -SING WELDING ROBOT
At present relatively few &gures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are -. to 3. times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 9 parts0month which ta$es two or three shift per day there is an increase in number of parts output without di'erence in #uality, which is not necessarily so with manual shift wor$. Use of robot welding increases the Be)ibility. ?ecause it is easy to change the robot wor$ from to another just by changing the program. When the same time of wor$ is already done, the same programme can be fed and the time and cost of programming can be eliminated completely. ;ay 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 #uality 5decrease in grain sie, distortion6. In addition to increase the productivity it maintains the desired #uality throughout the reducing the rewor$ scrap.
It reduces welder fatigue and welder e)posure to the more haardous atmosphere.
CONCL-SION At present relatively few &gures are available on the economics of robot Welding machines, but it has been found that numbers of components produced by A robot are -. to 3. times greater than that produced manually over the same Span of the time. It can be said that for an output of more than 9 parts0month which ta$es two or three shift per day there is an increase in number of parts output without di'erence in #uality, which is not necessarily so with manual shift wor$.
RE*ERENCES
9. www.u$ros.com0robotMwelding -. www.weldingengineer.com 3. www.autotech!robotics.com . www.robot!automation.com . www.robot!welding.com
