Applied Welding Engineering:Robotic Arc Welding

Emi Rozaili B. Ramli 2005388606

Amir Hazwan B. Hamzah 2005389005

Mohd Taufik B. Asli 2005388302

Mohd Farziq B. Mohd Al’dilah 2006882607

Zairee Ezzam B. Zahuri 2005388439

Group Members:

Lecturer:Dr Ing Yupiter HP Manurung

Introduction Robotics Terminology1. 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”

3. Robotics:The science and technology of robots, and their design, manufacture, and application.

ASIMO, a humanoid robot manufactured by Honda

Robotic Welding

The use of mechanized programmable tools (robots), which completely automate a welding process by both performing the weld and handling the part.

ABB Robot Arc Welding

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

The robotic welding automation commonly have five stations that is: Arc Welding GMAW (Gas Metal Arc Welding) GTAW (Gas Tungsten Arc Welding) Laser Welding Spot Welding

Automation of Welding

Automated welding system consists of:1. Welding arc2. Master controller3. Arc motion device4. Work motion device5. Work holding fixture6. Welding program7. Consumables

Some of the equipment of the robotic

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.

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

Workcell

Typical Arc Welding Robot

The machine moves the arc, torch and welding head along the joint. The person or operator performs a supervisory role and may make adjustments to guide the arc, manipulate the torch 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 is increased. Productivity increases with a resulting reduction 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

The arc motion devices carry the welding head and torch and provide travel or motion relative to the weld.

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

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 tolerances are used in manufacturing and the equipment will be more expensive.

MANIPULATOR consists vertical mast and a horizontal boom that carries the welding head. They

are 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 a carriage 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 the weight to be carried on the end of the boom and how much deflection can be allowed.

The welding torch should move smoothly at travel speed rates compatible with the 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 for circular welds when a rotating device is used.

SIDE BEAM CARRIAGE Less expensive and less versatile than the boom

and mast manipulator. The side beam carriage performs straight-line

welds with longitudinal travel of the welding head. Side beam carriages are available with high-

precision motion depending on the accuracy used in the manufacture of the beam and the speed regulation of the travel drive system.

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

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

The welding arc is supervised by the welding operator who makes adjustments to follow joints that are not in perfect alignment.

The travel speed of the side beam carriage is adjustable to accommodate different welding procedures and process.

Precision side beam carriage Side beam carriage

GANTRY OR STRADDLE CARRIAGES Gantry arc welding machines are motion devices that

provide one or two axes of motion. It consist horizontal beam supported at each end by a

powered carriage. The gantry structure straddles the work to be welded and the carriages run on two parallel rails secured to the floor.

This provides the longitudinal motion and can be quite long. The length of the gantry bridge determines the width of the parts that can be welded.

The torches are mounted on carriage that moves along the gantry beam. This provides the transverse motion.

The travel speed of the carriages must be smooth and match 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 to locate the head over the weld seam.

Usually a maximum of two torches are provided for transverse motion. And vertical motion should be available for adjustment.

Gantry Welding Machine FSW gantry at Eclipse Aviation for welding stringers and spars to aluminium cabin panels

TRACTORS FOR FLAT-POSITION WELDING A welding tractor is an inexpensive way of

providing arc motion. Tractors are commonly used for mechanized

flame cutting. Some tractors ride on the material being welded while others ride on special tracks.

The tractor should have sufficient stability to carry the welding head, the electrode wire supply, flux and the welding controls.

This method popular in shipyards and in plate fabricating shops.

The travel speed of the tractor must be closely regulated and smooth and related to the welding process.

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

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

CARRIAGES FOR ALL-POSITION WELDING There are many requirements for mechanized vertical

or horizontal position welding. The gun is connected to the wire feeder by means of

the standard cable assembly. In this case, an oscillator is 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 joint and for maintaining this alignment. The track can be attached to the work with magnets or vacuum cups.

A special carriage known as a skate welder is designed 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.

Figure: Overhead Figure: Horizontal

Figure: Vertical

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 the joint.

Other times the rod or wire is composed to become part of the weld. 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.

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.

Robot Manipulator The robot manipulator can be divided into two

sections, each with a different function: Arm and Body - The arm and body of a robot

are 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. The links are the rigid members connecting the joints, or axes.

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.

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.

Figure of Industrial Robot

Robot Safety Depending on the size of the robot’s work

envelop, speed, and proximity to humans. safety considerations in a robot environment

are important and particularly for programmers and maintenance personal who are in direct physical interaction with robots.

Control For Automatic Arc Welding

• A control system is required to run the welding program.

• Mechanized and automatic welding have more complicated programs and control additional 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.

• In semiautomatic, welding a control mechanism in the wire feeder actuates electrode wire feed and starts the welding current and shielding gas flow when the welder presses the gun trigger.

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.

Travel start delay time: The time interval from arc initiation to the start of work or torch travel.

Crater fill time: The time interval following weld time but prior to burnback time, during which arc voltage or current reach a preset value greater or less than a welding values. Weld travel may or may not stop at this point.

Crater fill current: The arc current value during crater fill time. Burnback time: The time interval at the end of crater fill time to arc

outage, during which electrode feed is stopped. Arc voltage and arc length increase and current decreases to zero to prevent the electrode from freezing in the weld deposit.

Downslope time: The time during which the current is changed continuosly from final taper current or welding current to final current.

Upslope time: The time during which the current change continuosly from initial current value to the welding value.

Postflow time : Time interval from current shutoff to shielding gas. Weld cycle time: The total time required to complete the series of

events involved in making a weld from beginning of preflow to end of postflow.

WELDING CONTROLLER

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.

Robot Controller

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.

Programmer Function

accept the input of many point locations. relate welding parameter to the path tought. store this information in memory. play it back to execute a welding program. The major points of interest are the teach

mode, memory and playback or execution.

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.

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.

Teach Pendant

Weld Execution

1) Weld can be made only when the power is on all components, electrode wire is installed, and the controller is in playback or operate mode

2) The material must be in the fixture and ready3) Pushing the start button will initiate the operation4) The robot will move the torch to the start point.5) The welding equipment will begin its cycle of operation (gas preflow,

start the arc).6) The robot controller will determine that the arc has started and then

start motion.7) Points along the taught path will initiate other activities programmed8) At the end of the taught path, the welding equipment will terminate the

weld program and the robot controller will determine that the electrode wire has separated from has separated from the work

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 edited to improved the weld if necessary and to minimize the air cut path and increase air cut speed.

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

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 robot that contain correct position and orientation information based on the appropriate coordinate transformations.

Performing positioning tests

Motion and control commands “Stop” or “Halt” – emergency stop “Disable” or “Enable” – disable or enable multimodal control

Position slaving Orientation slaving “Jog” with – move the robot along one of the world frame xyz axes

“Joint [1-6]” – select a joint “Joint plus” and “Joint minus” - move the selected joint “Scale Bigger”, “Scale Biggest”, “Scale Smaller”, “Scale Smallest”, or “Scale Normal” – change scaling “Move” – move to the most recently taught point “Home” – move to home position “Safe” – move to safe position “Unwrap” – unwrap from extreme joint position

Programming commands “Teach” or “Teach weld” – append current robot position to program “Teach” or “Teach weld” with – append pointed-to position to

program

“Run” – executes entire program “First” or “Last” – move to first or last program position “Forward” or “Backward”– move 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

Robotic sensor Robotic sensor is a system that detects variations in parts and

compensates for the variation by shifting the robotic programs. A sensor is effective when it is difficult to keep programmed points in

consistent locations and there are part accuracy problems requiring the operator to frequently adjust taught robot points. When this occurs, sensors can be used to automatically shift the welding points.

Block Diagram of fuzzy controller

End-of-arm sensor and tool centre point calibration is a critical aspect of successful system implementation. End-of-arm sensing, in the context of robotic welding, is used to detect the actual position of the seam on the workpiece with respect to the robot tool frame.

Result of welding pool control. (a) with control ; (b) with control

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 frame are accurately known with respect to each other.