Robotic Assembly System Welds, Sizes and Leak Tests Two Models of Catalytic Converters Simultaneously

A flexible, automatic, robotic assembly system permits an automotive parts company to manufacture two models of catalytic converters with the same equipment and no changeover. The system is tooled to alternately manufacture two (2) different catalytic converters allowing the customer to minimize direct labor and reduce per piece capital equipment cost through an automated system concept. Operator activity is limited to loading of component parts  at the front of the machine.

The assembly system consists of the following equipment:

• Dial Welding Machine
  • Station 1: Manual load
  • Station 2: Idle
  • Station 3: Arc weld perimeter by robot
  • Station 4: Automatic unload by robot
• Two (2) Fixture Expander
• Two (2) Station Leak tester

DIAL WELDING MACHINE
The assembly system includes a four (4) station dial machine with an aluminum table, index unit and four (4) water cooled tooling fixtures (two (2) for each converter model). The two different types of fixtures are arranged alternately  around  the dial table.

The operator loads the lower stamping, the catalyst with protective wrapping, and the upper stamping in station #1.

The table fixture indexes through the idle station #2 and into the arc weld station #3. In the arc weld station the assembly is compressed together to assure proper alignment of the upper and lower stampings during welding. the catalytic converter is clamped to close the weld joint. To accomplish this pressing operation with alternate model fixtures being presented to the weld station by the dial, the machine includes a unique sliding bolster type upper press fixture at the arc weld station #3. During the index of the dial table, the upper fixture is indexed to match the lower fixture, with catalytic converter already loaded.

Because it is important to assure that the upper and lower stamping are properly aligned for welding and that the internal components are not crushed during the press operation, press force and ram position are monitored by a load cell and position encoder (LVDT). Additionally, this equipment can detect  if parts are missing or mis-loaded.

Once clamped, two (2) arc weld robots fusion weld the perimeter joint of the catalytic converter using the GMAW  process.  After welding, the part is indexed to the Station #4 where a material handling robot unloads the catalytic converter from the dial fixture and transports it through additional manufacturing operations before releasing it.

EXPANDER
The material handling robot  positions the converter  for sizing of  the inlet and outlet openings in the tooling of a free standing expander located adjacent to the dial machine. Without releasing the converter, the robot positions the converter for sizing of the first end, signals the expander to cycle, and then repeats the same operation for the second opening on a second set of expander tooling.

LEAK TESTER
The robot transfers the converter to one of two pressure decay leak test stations included in the work cell. The converter is positioned into an empty test station and the test station sequence is initiated. The robot advances to the second test station and unloads the tested catalytic converter placing  it in the accept unload chute or the reject unload chute.

Each leak test station includes a fixture for one model of the two catalytic converter assemblies. Fixtures include locators, clamps and sealing equipment for openings in the converter. The assembly is pressurized with approximately one atmosphere of air and a leak test panel monitors the assembly for a pressure loss. Sequencing of the pressure test equipment and evaluation of the test data is accomplished using standard available programmable controller equipment. Pressure loss in excess of  pre-established limits results in rejection of the assembly.

The machine includes a programmable controller housed in a NEMA 12 enclosure. A Man Machine Interface (MMI) panel with screen display and membrane touch buttons is provided for manual operation and set-up purposes. This system can produce 80 assemblies per hour based on a cycle time of 45 seconds at 100% efficiency. 

The machine was delivered as a completed project, fully tested at the WELDMATION facility in Madison Heights, Michigan.