Case Studies / Arc Welding / Transportation Heavy Weldments

Rotary Welder Machine TendingA Pennsylvania manufacturer had a problem. Their production is dependent on welding and machining processes that historically generated a significant amount of scrap and rework. The original welding and machining process was responsible for the highest amount of defects in the plant, and it had done so for the past 30 years.

The process had been in place since the plant was built in 1970. When the robotic automation project was started, the customer soon realized that no one knew what the "true" process was. Every shift had a different equipment setup, so the part production and quality differed significantly shift to shift. According to the customer, "our first step was to understand the process, evaluate new ideas and refine as needed".

The critical welding process was completed by some rotary welders that were purchased when the plant was built. Not only did the welders have significant maintenance issues, but the welder torches had limited orientation options and generated a significant amount of rework due to pinholes in the weld.

After welding, the parts were loaded by the operator into a machine that removed the excess filler material. The material handling of a hot 75 lb. part was an ergonomic issue, and quality testing was not completed after the machining process. Any defects were detected late in the manufacturing cycle; consequently the value of the machining process was lost on any parts that were reworked.

When evaluating the process for automation, there were several sequential welding operations and final machining that required precise part alignment. It was evident that the initial part orientation could not be preserved with robot transfer. Significant process efficiencies could be gained by adding robotic handling and with a part weight exceeding 75 lbs., the ergonomic and cycle time benefits were clear.

The New Automated Process

  1. The part is made from two components that sit one inside the other. The parts are slid off a conveyor by the operator and into tooling on a rotary positioner. The operator verifies orientation of the parts one to another.
  2. After stepping clear of the light curtain, the cycle is initiated, and the turntable rotates to present the parts to an ES165D material handling robot.
  3. The handling robot picks the oriented assembly and transfers it to a Cognex based MotoSight™ 2D vision system to verify that the part is oriented correctly. After verification, the material handling robot loads the assembly into the part tacking fixture. If the alignment is incorrect, the part is placed on a reject conveyor to be adjusted by the operator.
  4. The tacking fixture clamps and centers the inner detail, allowing the first MA1400 welding robot to tack the components together. The fixture clamp retracts, allowing the robot to complete a large circular weld.
  5. The ES165D robot flips the part over and moves it to the "Side A" fixture. A spatter guard is loaded over the part, and the MA1400 welding robot makes four smaller circular welds.
  6. The ES165D robot removes the spatter guard, flips the part over and moves it to one of two "Side B" welding fixtures. It then picks and sets a spatter guard over the part. The second MA1400 welding robot makes a single smaller circular weld.
  7. The ES165D handling robot removes the spatter guard, picks the welded part and loads an open position on a cooling rack. The robot then moves to a machining center, picks a finished part and sets it on an outfeed conveyor. The robot then returns to the cooling rack, picks the coolest part, loads the machining center and starts the machining process.
  8. The process repeats.

The Solution

The custom engineered solution included the following items:

  • 2-MA1400 welding robots
  • 1-ES165D material handling robot
  • 1-Triple robot controller
  • 2-Miller Auto-Axcess® weld packages
  • 2-Binzel water-cooled torches
  • 1-ToolSight® torch alignment package
  • 1-Infeed conveyor
  • 1-Rotary indexing table
  • 1-Custom end-of-arm tool
  • 1-Fixture package
  • 1-MotoSight 2D vision package
  • 1-Controls package
  • 1-Cell guarding package

Lessons Learned

Once the customer understood their process, they began to test and try new ideas. Originally, they used a large counter bore which was expensive. Eventually, they began running carbide inserts, which lowered costs. Coolant was used with the counter bore, which caused chips to stick to the part and created a variety of process problems. After changing to inserts, parts could be run without coolant. This helped clean up and improve their process.

"Robotic machine tending has been really beneficial to us," said the customer. With 75 pound parts, it helps with safety and ergonomics. The robot is also able to load and unload spatter guards, which protects key areas of the part during welding. The consistency and improved part quality has provided significant benefits.

The Results

The old equipment produced a part every 11-12 minutes. With the new production cell, the part can produce a good part every five minutes, far outpacing other plant production. In the words of the customer, "the parts just pile up, till they shut the cell off".

Quality has improved significantly, and now the cell is delivering higher quality parts that don't require the same level of cleaning before the next step in the manufacturing process.

Previously we had two people dedicated to part rework. Those personnel are no longer necessary and have been reassigned. Post machining rework due to pin holes has virtually been eliminated.

Ref: ACS-machinetool

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