Automated Spot Welding

oregontrimmingAI and Robotics

Nov 2, 2013 (3 years and 7 months ago)

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Automated Spot Welding

Presentation Outline


History


Resistance Spot Welding


Robotics


Robot Spot Welding Systems


Automated Spot Welding in Industry


Possible Improvements



History


Before 1970


Simple, single
robot stand
-
alone cells


1970


General Motors
creates the first robot
integrated body assembly line.


24 robots


Indexing conveyor system


Now


In use by every major
auto manufacturer


Over 60 robots in one line


Cars receive thousands of spot
welds

Resistance Spot Welding


Heat for welding is generated by electrical
resistance (no consumable electrodes, shielding
gases, flux).


Total resistance is the sum of the following:


Resistance of the electrodes


Electrode
-
workpiece contact resistances



Resistances of the parts to be welded


Workpiece
-
workpiece contact resistances


Most common form of resistance welding

Resistance Spot Welding


Generated heat is
calculated using the
following equation:


H=I
2
Rt


H


heat generated, J


I


current, A


R


resistance,
W


t


time of current

flow, s

Resistance Spot Welding


Two cylindrical electrodes
contact an overlap of two sheet
metals.


Resistance heating combined
with applied pressure creates
the spot weld.


Weld nugget is typically 6
-
10
mm in diameter and 60

70% of
the joint thickness.


Currents range from 3000
-
40,000 A.


Weld time is typically between
0.6 and 0.8 seconds.



Spot Welding Guns


Welding tongs


Provides pressure


Electrode tip


Typically copper


Transformer


Provides the electrical
current.


Hard
-
mounted to the
end of the robot.


Spot Welding Guns

Important Factors


Surface must be clean
and smooth to
optimize bond strength


Shape and surface
condition of the
electrode tip.


Require access to both
sides of the joint.

Welding Controller


Microprocessor type welding
controls are most commonly
used.


Multiple welding sequences
can be programmed and
stored.


Any sequence can be called
up when properly interfaced
with the robot controller.

Robots


A robot is a re
-
programmable,
multi
-
functional manipulator
designed to move material,
parts, tools, or specialized
devices through variable
programmed motions for the

performance of a variety of
tasks.”



(Robotics Institute of
America)

Types of Robots

Revolute

Spherical


Cylindrical

Rectangular

Robot Manufacturers


ABB (US, Sweden)


Kuka (Germany)


Adept (US)


Seiko (Japan)


Kawasaki (Japan)



Typical Cost: 20
-
150 K


Welding Robots: 100 K+

Robots used in Spot Welding


Six
-
axis revolute
(most common)


Spherical


Rectangular

Robot Controller


Can control an entire cell
(multiple robots)


Robots typically
programmed offline.


Program downloaded to
robot controller.


XYZ world coordinate axes
referenced to electrodes at
the tips of the welding guns.


Programs allow for
mirroring.


Advantages Disadvantages


Possess a greater flexibility with
regards to re
-
programmability



Faster than human labor



Improved product quality


Expensive equipment can be
maximized in multiple work
shifts.


Reduction in the number of
accidents


Can be integrated in conditions
that are hazardous to humans



Automation makes work
stoppages less likely



Replacement of human labor,
resulting in higher unemployment


Unemployed and new users of
technology must be retrained
resulting in retraining costs.


Hidden disadvantages regarding
new technology not always
advertised


Hidden costs associated with added
technology needed for the robot to
function in the workcell. An entire
cell will normally cost 3 to 10 times
the price of the robot.


Robotic Spot Welding


Spot welding is the
most common
application for robots.


Robots wield a 200 lb
welding gun


Robot is programmed
to follow a specified
path placing spot
welds along the way.


30 welds per minute


Greater reliability and
productivity can be
achieved

Robotic Spot Welding Systems


Robots are equipped with
spot welding guns.


Safety walls surround the
robots to protect the
operator.


Two or more robots are
contained within a cell.


Assembly lines transport
work
-
pieces from one cell
to another.

A FlexiCell consists of: 1) The spot welding package
with robot and controller, 2) Interchange units, 3)
Operator protection devices, 4) Supporting frame
(including interconnections) which can be transported
without disassembly after commissioning

Source: ABB Robotics

Industry Applications


Largest application of
robotic spot welding


Operate 24 hour a day


Only 2% downtime


Effective utilization of
capital investment


Flexible


Can be
reprogrammed for a
new model


75 to 100% reduction in man
hours


Better control is maintained


Predictable output and
improved scheduling

Auto

Industry

Improvements


Robot Programming


More uniform language, easier interface


Servo motor to power weld gun


Better motion and force control


Lower noise, maintenance and life cycle cost


Bring smaller aiding robots into the workcell


12 robots per cell, for fixturing/part transfer


Faster cycle time


Floor space becomes more free


Sources


www.kuka.com


www.abb.com


www.kawasakirobot.com


www.adept.com


www.motoman.com


www.et.byu.edu/~ered/ME537/


Lane, J.D.,
Robotic Welding
, IFS, New York, 1987.



Designing Your Product for Robotics
, SAE Inc., Warrendale, PA, 1982.


Dorf, Richard C.,
Robotics and Automated Manufacturing
, Reston
Publishing Co. Inc., Virginia, 1983.


Kalpakjian, Serope,
Manufacturing Engineering and Technology
,
Addison
-
Wesley Publishing Co., Massachusetts, 1995.


Messler, Robert W.,
Principles of Welding
, John Wiley and Sons Inc.,
New York, 1999.