Robots Help Revive 40-Year-Old Tandem Press Lines

The Comau robot in each press cell is mounted on a cart that can be moved off-line automatically for die changes.

In the "thumb" of mitten-shaped Michigan, Active Tool and Manufacturing Co., Inc., has put the little town of Elkton on the manufacturing map in a big way. A first-tier supplier of automotive stampings, Active is applying state-of-the-art automation in its one-million sq. ft. Elkton plant--in particular, on two lines of 40-year-old tandem presses.

Eleven, seven-axis Comau robots (five on one line, six on the other) fully automate the handling of panels between presses. A large, robotically operated DEA coordinate measuring machine is doing some interesting things in the company's up-to-the-minute metrology lab.

Founded in 1928, Active Tool and Manufacturing Co. now has three stamping plants--one each in Elkton, MI, Sebewaing, MI, and Marion, IN. It also has an engineering and administration center located in Roseville, MI, and a tooling center in Detroit. Active is building a fourth stamping plant in Clinton Township, MI. This new facility will feature six 212-in. Schuler presses with the latest automation equipment. Active Tool and Manufacturing Co. has more than 2000 employees, including 750 at the Elkton plant.

The "U" and "T" Lines

Renovation of the first press line, designated the "U" line, was completed in 1992. All press mechanical units (clutches, brakes, gears) were rebuilt, and the old controls were replaced with Allen-Bradley programmable logic controllers. This 144-in. line was automated with the addition of five SMART-3 7.40 robots supplied by Comau Productivity Systems, Inc., Troy, MI. The line has six straight side tandem presses, including machines built by Clearing, Bliss, Toledo and Hamilton. Panels run on this line are for exposed parts, such as outer doors, hoods, deck lids and fenders.

A second line, the 135-in. "T" line, was renovated in 1994. It includes seven straight-side tandem presses by the same mix of manufacturers found on the "U" line. Panels run on the "T" line are for unexposed parts, such as inner doors, inner hoods and rails. The six Comau SMART-3 7.40 robots on this line were supplied and integrated by ISI Robotics, Inc., Fraser, MI. ISI now is the exclusive marketing source for Comau robots in the Western Hemisphere.

Prior to being updated, the presses in both lines were loaded manually and unloaded with press-mounted pneumatic extractors. The decision to use floor-mounted robots, rather than press-mounted load/unload devices (and inter-press transfer units), came after a detailed evaluation of the plant's needs.

General manager Paul Taylor elaborates: "We considered the size and shape of the parts we run and the fact that part changeovers are frequent and must be done quickly. We realized that we needed the flexibility offered by seven-axis, floor-mounted robots. They are very proficient at re-orienting parts between presses, so they don't require additional rotating and repositioning devices. The more we can simplify handling between presses, the fewer chances there are for marring or scratching the parts."

Interestingly, however, there's a time and place for both approaches to press automation. For example, in Active Tool's new plant being built in Clinton Township, MI, ISI Robotics will supply its Pathfinder press-mounted robots with ISI's Automation Products Group's Series IV tooling system. This equipment will be able to handle blanks as large as 78 in. x 200 in., weighing up to 150 lbs. These panels will be much larger and heavier than panels processed on lines served by articulated-arm robots.

Shaking Hands

For the most part, robot loading and unloading operations at the Elkton plant are pretty straight forward. Each robot extracts a panel from one press, indexes around and loads the panel into the next press. However, sometimes there's a different routine.

Active has developed a software program that can be used if one of the presses in a line isn't needed for a particular part run. In that case, a robot extracts a panel from a die and hands the panel through the empty press to the next robot. This "handshake" or handoff capability eliminates the need to setup conveyors, buckstands or other ancillary handling equipment. Also, it facilitates maintenance work on the empty press while the line is running. If necessary, the panel can be turned over as the second robot comes in for the handoff by receiving from the opposite side of the panel.

Another interesting operating feature is found at the head of the "U" line. In addition to a destacker and blank washer, there is an anvil-type pre-bender within the prestage table. It can pre-bend panels up or down, right or left, and is programmable. This provides the ability to run various parts requiring pre-bending without having to make hard tooling changes on the pre-bender itself.

15-Minute Changeover

Each Comau robot is mounted on its own transfer cart, which moves on rails set into the floor. Automatic shot pins ensure accurate cart location and rigid anchoring within the press cell. The carts, developed by ISI, facilitate moving the robots off-line automatically for die change.

Press line changeover time from one part to a different part is about 15 minutes. Four, fully automatic and programmable die carts supplied by Orchid International, Cambridge, Ontario, Canada, service the two lines. "New" dies are loaded onto the carts via an overhead crane.

Taylor says the use of four die carts instead of a full seven-cart "domino" system is a matter of economics. Seven carts would have meant a changeover time of only six minutes, compared to 15 minutes with the current system. "We really couldn't justify it," Taylor explains.

"Rather than apply all the bells and whistles that are available," Taylor continues, "we make decisions based on how automation affects our throughput. This means pieces per shift, per day or per month--not just pieces per hour. We try to keep things as simple as possible and mix in high tech to increase throughput. The ultimate goal is to offer the best value to our customers."

Robot tooling is another example of where some restraint in automating is evident. ISI Automation Products Group's Quad-Set end effectors--vacuum cups or grippers depending on the part being handled--are changed using a manual quick-change system. This is done within the die-change cycle. Automatic tool change can be added as Active Tool and Manufacturing Co.'s needs change.

A CMM First

One piece of equipment that has been more than justified at Active Tool and Manufacturing Co. is a large DEA coordinate measuring machine in its new metrology lab. According to Paul Taylor, it's the first machine of its kind to be integrated with stamping software. "It's designed for in-line checking of car bodies, but we integrated it into our operation to support our press lines, and also our tooling program. At one point, we took 11 sets of dies from one automobile manufacturer, finished secondary tryout and then ran samples without any hard-check fixtures."

Active Tool's reputation for turning out quality stampings took another big step forward with the addition of its metrology facility. As for the introduction of robots in the plant, Taylor offers these additional comments: "Robots have greatly reduced the number of repairs required on exposed panels while increasing our productivity significantly. And, as we automate, we gain more business and more work for our people. In fact, the workforce in this plant has grown from 500 to 750 people in the last year." MF