Automated Spot Welding

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Automated Spot Welding
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Presentation Outline

• History
• Resistance Spot Welding
• Robotics
• Robot Spot Welding Systems
• Automated Spot Welding in Industry
• Possible Improvements

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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

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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

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Resistance Spot Welding

• H heat generated, J
• I current, A
• R resistance, W
• t time of current flow, s

• Generated heat is calculated using the following
  equation
• HI2Rt

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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.

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Spot Welding Guns

• Welding tongs
• Provides pressure
• Electrode tip
• Typically copper
• Transformer
• Provides the electrical current.
• Hard-mounted to the end of the robot.

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Spot Welding Guns
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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.

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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.

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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)

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Types of Robots
Revolute
Cylindrical
Spherical
Rectangular
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Robot Manufacturers

• ABB (US, Sweden)
• Kuka (Germany)
• Adept (US)
• Seiko (Japan)
• Kawasaki (Japan)
• Typical Cost 20-150 K
• Welding Robots 100 K

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Robots used in Spot Welding

• Six-axis revolute (most common)
• Spherical
• Rectangular

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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.

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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.

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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

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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
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Industry Applications
Auto Industry

• 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

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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

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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.