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Motoman Robot Spot Welding

ACS-084.jpgMedical Examination Tables

System meets all project goals and objectives, including making 58 spot welds and loading assembly onto outfeed conveyor within 330-second production cycle. System yields spot-weld nuggets 4.7 mm (0.19") to 6.34 mm (0.25") diameter. Welding electrode with flat face on the visible side of the cabinet and opposing electrode with 50.8 mm (2") radius help eliminate marking. Robot provides reliable, consistent production on two shifts, five days a week with 98 percent uptime.

Project Challenges

  • Provide compact, flexible robotic system to automate production of new design of medical examination tables with heavier weight capacity.
  • Spot welds must be mark-free due to aesthetic requirements.
  • System must allow time to fixture seven formed metal components, make 58 spot welds, remove welded assembly weighing approximately 25 kg (55 lbs), and load it onto a gravity-fed conveyor for delivery to a paint line – all in a 330-second production cycle.
  • Completed weldment is 1,185 mm x 521 mm W x 650 mm H (46.7" L x 20.5" x 25.6" H). Medical examination table components are primarily 18-gauge (1.2 mm/0.048") drawn-quality steel.
  • Provide reliable, consistent production on two shifts, five days per week, with an uptime of 98 percent.

Motoman Robotics Solution

Motoman Robotics provided a custom ES165 spot welding system, including:

  • Six-axis Motoman ES165 “Expert Spot” welding robot with XRC 2001 controller.
  • Robot mounting base – fabricated steel plate with 6" steel riser.
  • Integrated weld control system, with C-type servo transgun (water-cooled) and mid-frequency DC welding transformer.
  • Motoman MHT-450 headstock/tailstock positioner with 450-kg (992.25-lb) rated headstock load, 900-kg (1,984.5-lb) rated combined headstock/tailstock load; 9.8 rpm headstock speed; 4-second 180° rotation; and MotoMount™ compliant tool mounting system.
  • Operator station on stand-alone pedestal. Functions: Job Start, Emergency Stop, Hold, Alarm Reset, and Servo Power-up. Palm button for cycle start activation. Ready signal light and alarm indication light. Positioner auto/manual switch. Thumbwheel switch for program selection (up to 100 programmed jobs) and manual positioner jog joystick.
  • Common equipment base for robot controller and spot welding controller.
  • Cell guarding package, including 2.4-m (8') woven wire perimeter safety fence with two access gates and positive-break safety switches; arc flash protection curtains; and light curtain at positioner load/unload station.

Fixtures/Tooling Details

Customer supplied electro-magnetic tooling holds individual table assemblies in the headstock/tailstock fixture. This method enables panel and cross-member components on the inside of each assembly to be held securely by the magnetic force applied to the assembly’s outer side panels, while also allowing better access for the spot welding transgun. Fixtures include part-present sensor.

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