12884654 robotic arc welding

7/29/2019 12884654 Robotic Arc Welding

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ROBOTICS ARCWELDING


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Introduction

Robotics Terminology

1. Robot:

An electromechanical device with multiple degrees-of

freedom (DOF) that is programmable to accomplish a variety

of tasks.

2. Industrial robot:The Robotics Industries Association (RIA)

defines robot in the following way:

An industrial robot is a programmable, multi-functional

manipulator designed to move materials, parts, tools, or

special devices through variable programmed motions for

the performance of a variety of tasks


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3. Robotics:

The science and technology of robots, and their design,

manufacture, and application.


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ASIMO, a humanoid robot manufactured by Honda


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Robotic Welding

The use of mechanized programmable tools

(robots), which completely automate awelding process by both performing the weld

and handling the part.


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ABB Robot Arc Welding


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Automation of Welding

Automation of welding became possible and

practical with the acceptance of continuous

electrode wire arc welding processes.

The advantage of automation welding is:

Consistency of quality welds

Repeatability

Reduction of production costs

Fewer scrapped parts

Increase your return on investment (ROI)

Faster cycle rates


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The robotic welding automation commonly have fivestations that is:

Arc Welding

GMAW (Gas Metal Arc Welding)

GTAW (Gas Tungsten Arc Welding)

Laser Welding

Spot Welding


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Automation of Welding

Automated welding system consists

of:

1. Welding arc

2. Master controller

3. Arc motion device

4. Work motion device

5. Work holding fixture

6. Welding program

7. Consumables


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Some of the equipment of the robotic


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Robotic Welding Concept

A special kind of electrical power is required to

make an arc weld.

The nozzle of the torch is close to the arc and will

gradually pick up spatter.

A torch cleaner (normally automatic) is often

used 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.


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Robotic Welding Concept

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


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Workcell


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Typical Arc Welding Robot


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The machine moves the arc, torch and welding headalong the joint.The person or operator performs a supervisory role andmay make adjustments to guide the arc, manipulate thetorch and change parameters to overcome deviations.Since the person is partially removed from the arc area,higher currents and higher travel speeds can be used.The fatigue factor is reduced and the operator factor isincreased. Productivity increases with a resultingreduction of welding costs. Arc motion devices fit into 5

categories: - Manipulator (boom and mast assembly) - Side beam carriages. - Gantry or straddle carriages. - Tractors for flat-position welding.

- Carriages for all-position welding.

ARC MOTION DEVICES


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The arc motion devices carry the welding headand torch and provide travel or motion relative tothe weld.

They are used for continuous wire processes, gasmetal arc, flux-cored arc and submerged arcwelding and also for gas tungsten and plasma arcwelding.

The motion device must be matched to the

welding process. Gas tungsten and plasma arc welding require

more accurate travel and speed regulation.

This must be specified because tighter tolerancesare used in manufacturing and the equipment will

be more expensive.


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MANIPULATOR consists vertical mast and a horizontal boom that carries the welding head. Theyare sometimes referred to as boom and mast or column and boom positioners.

Manipulators are specified by two dimensions:

The maximum height under the arc from the floor.

Maximum reach of the arc from the mast.

They are many variations of manipulators. The assembly may be mounted on acarriage that travels on rails secured to the shop floor. The welding power source

is usually mounted on the carriage. The length of travel can be unlimited thus the same welding manipulator can be

used for different weldment by moving from one workstation to another.

In selecting and specifying a welding manipulator, it is important to determine theweight to be carried on the end of the boom and how much deflection can beallowed.

The welding torch should move smoothly at travel speed rates compatible withthe welding process.

The manipulator carriage must also move smoothly at the same speed.Manipulators are one of the most versatile pieces of welding equipment available.

They can be used for straight-line, longitudinal and transverse welds and forcircular welds when a rotating device is used.


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SIDE BEAM CARRIAGE

Less expensive and less versatile than the boomand mast manipulator.

The side beam carriage performs straight-linewelds with longitudinal travel of the welding head.

Side beam carriages are available with high-precision motion depending on the accuracy usedin the manufacture of the beam and the speedregulation of the travel drive system.

The carriage will carry the welding head, wiresupply and so on and the controls for the operator.

The welding head on the carriage can be adjustedfor different heights and for in-and-out variations.

The welding arc is supervised by the weldingoperator who makes adjustments to follow jointsthat are not in perfect alignment.

The travel speed of the side beam carriage is

adjustable to accommodate different weldingprocedures and process.


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Precision side beam carriage Side beam carriage


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GANTRY OR STRADDLE CARRIAGES

Gantry arc welding machines are motion devices thatprovide one or two axes of motion.

It consist horizontal beam supported at each end by apowered carriage. The gantry structure straddles thework to be welded and the carriages run on twoparallel rails secured to the floor.

This provides the longitudinal motion and can be quitelong. The length of the gantry bridge determines thewidth of the parts that can be welded.

The torches are mounted on carriage that movesalong the gantry beam. This provides the transversemotion.

The travel speed of the carriages must be smooth andmatch the welding speed of the welding process. The one or more welding heads on the gantry bridge

will have power travel or will have adjusting devices tolocate the head over the weld seam.

Usually a maximum of two torches are provided for

transverse motion. And vertical motion should beavailable for adjustment.


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Gantry Welding Machine FSW gantry at EclipseAviation for welding stringers

and spars to aluminium cabin

panels


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TRACTORS FOR FLAT-POSITION

WELDING

A welding tractor is an inexpensive way ofproviding arc motion.

Tractors are commonly used for mechanized

flame cutting. Some tractors ride on the materialbeing welded while others ride on special tracks. The tractor should have sufficient stability to carry

the welding head, the electrode wire supply, fluxand the welding controls.

This method popular in shipyards and in platefabricating shops.

The travel speed of the tractor must be closelyregulated and smooth and related to the weldingprocess.

It must have sufficient power to drag cables. Amore specialized tractor carries two heads.


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Figure: Welding tractor for SAW Figure: Welding tractor, gun and track.


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CARRIAGES FOR ALL-POSITION WELDING

There are many requirements for mechanized verticalor horizontal position welding.

The gun is connected to the wire feeder by means ofthe standard cable assembly. In this case, an oscillatoris employed to provide lateral arc motion.

This type of welding carriage can be used in the flat,vertical, horizontal or overhead positions.

Adjustments can be made to align the torch to the jointand for maintaining this alignment. The track can beattached to the work with magnets or vacuum cups.

A special carriage known as a skate welder isdesigned to follow irregular joints contours inside

complex structures. Skate welder travel units are extremely compact and

carry a miniaturized wire feeder or only a torch. Skate welders are used for welding inside aircraft

assemblies.


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Figure: Overhead Figure: Horizontal

Figure: Vertical


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Arc Welding Robot

Arc welding robot is one of the most common

functions in industry today. During this process, electricity jumps from an

electrode guided through the seam, to the

metal product. This electric arc generates

intense heat, enough to melt the metal at thejoint.


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Other times the rod or wire is composed tobecome part of the weld. During the short timethat industrial welding robots have been in use,the jointed arm or revolute type has become by

far the most popular. The reason for the popularity of the jointed arm

type is that it allows the welding torch to bemanipulated in almost the same fashion as ahuman being would manipulate it. The torch

angle and travel angle can be changed to makegood quality welds in all positions. Jointed armrobots also allow the arc to weld in areas that aredifficult to reach.


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Robot Manipulator

The robot manipulator can be divided into twosections, each with a different function:

Arm and Body - The arm and body of a robotare used to move and position parts or tools

within a work envelope. Wrist - The wrist is used to orient the parts or

tools at the work location.

The robot manipulator is created from a

sequence of link and joint combinations. Thelinks are the rigid members connecting the

joints, or axes.


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Four Type of Industrial Robot

Gantry- These robots have linear joints and are

mounted overhead. They are also called Cartesian

and rectilinear robots.

Cylindrical-Named for the shape of its work

envelope, cylindrical anatomy robots are

fashioned from linear joints that connect to a

rotary base joint.


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Polar - The base joint of a polar robot allows for

twisting and the joints are a combination of rotary

and linear types.

Jointed-Arm-The arm connects with a twisting

joint, and the links within it are connected with

rotary joints. It is also called an articulated robot.


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Figure of Industrial Robot


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Control For Automatic Arc Welding

A control system is required to run thewelding program.

Mechanized and automatic welding have

more complicated programs and controladditional functions, including travel or

motion, torch position and fixture motion.

Adaptive welding, which varies weld

parameters in accordance with actual

conditions, has a complicated computer

control system that include sensing devices

and adaptive feedback.


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In semiautomatic, welding a control

mechanism in the wire feeder actuates

electrode wire feed and starts the welding

current and shielding gas flow when thewelder presses the gun trigger.


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Automatic Welding Controllers

Programmers are designed to execute a welding program. As the

welding program becomes more complex, the controller must include

more electrical circuits.

To fully understand a welding program, it is necessary to understand the

terms used:

Preflow time: The time between start of shielding gas flow and arc

starting(prepurge).

Start time: The time interval prior to weld time during which arc voltage

and current reach a preset value greater or less than welding values.

Start current: The current value during the start time interval.

Start voltage: The arc voltage during the start time interval.

Hot start current: a brief current pulse at arc initiation to stabilize the arc

quickly.

Initial current: The current after starting buty prior to upslope.

Weld time: The time interval from the end of start time or endof upslope

to beginning of crater fill time or beginning of downslope.


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WELDING CONTROLLER


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Robot Controller

For robotic arc welding system, a much more

complex controller is required.

Controller include a high speed

microprocessor since coordinated,

simultaneous, continuos motion of up to eight

axis and all welding parameters may be

required.


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Robot Controller


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Robot Controller

The machine tool industry introduced numerical control(NC) years ago,these are known a Point To Point(PTP) control system.

Point are location in two dimension in one plane

For arc welding robot, the arc is moved from one point to the next in

space.

The location of the arc is known as the tool center point(TCP)

The path of the TCP is programmed and stored in memory.

For spot welding, pick and place and machine loading, point to point

playback is used.

For arc welding, playback of the arc motion is a continuos path in

space.

The robot controller must be cooerdinated so that each axis movement

begins and end at the same time.


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The method of teaching or programming the robot

controller:

Manual method: The manual method is not used for arc welding robot

but it is used mainly for pick and placed a robots.

Walk through: The walk through method requires the operator to move

the torch manually through the desired sequence of movement. . Each

move is recorded into memory for playback during welding. The welding

parameter are controlled at appropriate positions during the weld cycle.

Lead through: The lead through method is a popular way in

programming a robot. The robot welding operator accomplishes this

using the teach pendant. By means the keyboard on the teach pendant,

the torch is driven through the required sequence of motion. In addition,

operator inputs electrode wire speed, arc voltage, arc on, counters,output signals, job jump function and much more. All of this function are

related to a particular point along the taught path. In this way, if the

speed of robot is changed, it is not necessary to change the time for

certain actions to happen.


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Off-line programming:

Off-line programming involves the preparation of the program on a

computer. An appropriate languages must be used. The program is

entered into the robot memory very quickly. This increase the use of the

robot,since lead-through teaching ties up the robot during programming.

Off line programming is becoming more widely used, but requires

experienced personnel.


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Teach Pendant


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9) After this the robot will return to its home

position, ready for another cycle.10)At this points the weld should be checked for

quality.

11) The program should be checked and editedto improved the weld if necessary and tominimize the air cut path and increase air cutspeed.

12) When the weld quality is acceptable andcycle time is at a minimum, it is time to freezethe program and start production.


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Programming Robotic Welding

1. The PC or laptop mediates between the multi-modal input

devices (glove and speech) and the ABB robot.2. On the input side, it runs software that translates raw voice

and glove inputs into robot controller commands.

3. On the output side, it sends RAPID commands to the robotthat contain correct position and orientation informationbased on the appropriate coordinate transformations.


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Performing positioning tests


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Programming commands

Teach or Teach weld append current robot position to program

Teach or Teach weld with append pointed-to position toprogram

Run executes entire program

First or Last move to first or last program position

Forward or Backwardmove to next or previous program position

Modify modify the current program position

Delete or Delete all delete current program position or all positions Insert insert the current robot position before the current program position

Wet or Dry turning welding on or off

Current position get the current program position

Number of positions get the number of program positions

Learn program adds current program to LBO model/database

Move prediction moves to the next predicted program position


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Robotic sensor

Robotic sensor is a system that detects variations in parts andcompensates for the variation by shifting the robotic programs.

A sensor is effective when it is difficult to keep programmed points inconsistent locations and there are part accuracy problems requiring theoperator to frequently adjust taught robot points. When this occurs,sensors can be used to automatically shift the welding points.

Block Diagram of fuzzy controller


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TCP-Calibration Unit(Tool Center

point)

Tool Center point calibration unit

used to detect the actual position of the seam on the

workpiece with respect to the robot tool frame. 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 frameare accurately known with respect to each other.

12884654 robotic arc welding

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