Automated Spot Welding

1. Automated Spot Welding

2. Presentation Outline • History • Resistance Spot Welding • Robotics • Robot Spot Welding Systems • Automated Spot Welding in Industry • Possible Improvements

3. 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

4. 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

5. Generated heat is calculated using the following equation: H=I2Rt H – heat generated, J I – current, A R – resistance, W t – time of current flow, s Resistance Spot Welding

6. 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.

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

8. Spot Welding Guns

9. 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.

10. 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.

11. 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)

12. Types of Robots Revolute Cylindrical Spherical Rectangular

13. Robot Manufacturers • ABB (US, Sweden) • Kuka (Germany) • Adept (US) • Seiko (Japan) • Kawasaki (Japan) • Typical Cost: 20-150 K • Welding Robots: 100 K+

14. Robots used in Spot Welding • Six-axis revolute (most common) • Spherical • Rectangular

15. 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.

16. 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. Advantages Disadvantages

17. 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

18. 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

19. 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 Industry Applications AutoIndustry

20. 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

21. 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.