Jointed-arm robot handles insert loading and part removal. (Injection Molding: Close-Up).

It's not every day that you see a sophisticated, five-axis jointed-arm robot sitting on top of an injection molding machine. John Robinson has two of them. At up to $50,000 apiece, they are a major investment for his firm, Excel Injection Molding, a $3-million-a-year custom molding operation with 14 presses of 30 to 500 tons.

Robinson, president of Excel, started the firm in Hattiesburg, Miss., seven years ago. It molds parts mainly for local customers in medical, electrical, and appliance businesses. Being small doesn't stop Excel from taking a high-tech approach to its business. For example, Robinson notes that most of his projects utilize rapid prototyping to evaluate a part design before going to hard tooling. His firm can afford rapid prototyping by using the services of the state-funded Mississippi Polymer Institute (MPI) at the University of Southern Mississippi in Hattiesburg. MPI has a selective laser sintering (SLS) machine from DTM Corp. (now 3D Systems) to produce prototypes from polymer powder.

Robinson took a similarly high-tech approach to automating a four-cavity insert-molding job for an electrical part. Since the job uses DuPont's Zytel HTN high-temperature nylon, the molds are heated to 300 F. "I don't want someone reaching in there," Robinson says. Robotics were the obvious answer, but Robinson didn't go with a standard three-axis traversing-type parts remover. He chose a more expensive Motoman jointed-arm robot, even though it would be a bit slower. "I wanted more flexibility of robot movement," he says, "and I liked the high precision of the five-axis robot."

The Motoman robot is mounted over the stationary platen of the injection machine. It picks up four inserts from a station beside the press, and when the mold opens, the robot first picks out the sprue and then the four parts, and then it deposits inserts for the next cycle. One set of end-of-arm tooling (designed in-house with the help of some tooling experts at nearby Sunbeam Corp.) permits all these functions. Lastly, the robot deposits the parts at the operator station and picks up another load of inserts.

This job runs on a 270-ton press. A second, smaller Motoman robot is mounted on a 150-ton press. The robot not only keeps the operator safe, Robinson says, "It keeps us on cycle."

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Motoman Inc., West Carrollton, Ohio [phone], www.matoman.com