Employing robots to automate repetitive machine-tending tasks is nothing new to manufacturing, nor is the notion that the main reason for doing it is to reduce labor costs. But for contract manufacturer and molder Nyloncraft Inc. (Mishawaka, IN), automating enabled the company to add labor in key areas where it was needed to support growth, without having to hire new employees. This strategy was part of the companys recent push to reduce labor costs, says Nyloncraft automation engineer Carl Smith.
When Smith joined the company in 2004, he had spent the previous four years helping another molder apply automation to its shop. Since then, Nyloncraft has integrated several material handling, machine-tending robots onto its shop floor. The automation investment was part of a $10 million expansion of the companys thermoplastic molding operations.
Smith’s first automation try involved three injection molding workcells, placing robots in the center of each cell to remove parts from the machines, facilitate value-added operations such as drilling and component insertion, and then palletize the parts.
Now, each of the three cells, which measure 10 by 12 ft, features a six-axis Motoman UP50 robot with 50-kg payload, and an Applied Robotics CXC30 tool changer that enables quick and automatic switching of end-of-arm tooling (EOAT). Through the use of tool stands and programming, the three cells combined can produce eight different piston models with minimal changeover time.
The robots are high-speed models designed by Motoman with a streamlined body that helped Smith optimize cell layout. They move molded parts from the presses through a series of tasks within the cell. Robot speed peaks at 250°/sec in some axes and 170°/sec in other axes. Maximum payload is 50 kg; reach is 3.6m vertically and 2m horizontally, with repeatability of ±0.07 mm.
The pistons made are 8-10 inches in diameter and 6-10 inches tall, and weigh 3-4 lb. They replace aluminum air-rise suspension components, providing a 33cost reduction and 25weight reduction, according to Nyloncraft.
Some of the molded pistons require a mechanical sprue-cutoff operation, some require a drilling operation, and some have inserts added. Every part moves to a visual inspection station, where a Keyence CV700 system checks for holes, inserts, and proper part identification. Average cycle time: 70 seconds.
Parts that pass inspection move via robot to a two-tiered conveyor system for palletizing; parts that fail inspection move to an outgoing parts chute. The robot also places a prefolded cardboard separator at the start of each pallet and between each layer of parts; the cardboard pieces have a 3-inch folded edge to contain the pistons. Pallets hold as many as 250 parts and eight layers.
An aluminum custom-designed storage rack in each cell solved the cardboard-staging challenge. Each rack holds four pieces of folded cardboard, which have to be placed in a specific orientation to allow the robot to pick them up using a suction-cup EOAT and place them on the pallet, says Smith. Since each layer fills up in about 30 minutes, the four cardboard separators allow the cell to run untended for a 2-hour cycle.
After automating the three palletizing cells, in mid-2006 Smith turned his sights toward automating a pair of new injection molding cells that produce large end-gate covers and spoilers for full-size pickup trucks. One cell features a 1500-ton Cincinnati Milacron press, the second a 1750-ton Engel press; both include Motoman HP165-100 robots with NX100 controls, and an Applied Robotics MXC160 tool changer that enables the cells to adapt quickly to manufacturing either the spoilers or the covers. Parts are 3.5-4 ft long and weigh 2-3 lb; EOAT with vacuum cups and grippers stabilizes the parts during transfer.
Nyloncraft chose the high-speed HP165-100 robot for its extended work envelope, 100-kg payload, 4.1m vertical reach, 3.0m horizontal reach, repeatability of ±0.2 mm, and NX100 control that features a Windows CE programming pendant, fast processing, and a robust PC-based architecture.
Now, after the robot carries the parts from the mold to a fixture, the new gate-cutoff process uses a set of rollers mounted to a trolley that rides over the fixtured parts. As the trolley moves, the rollers apply pressure to the top and sides of each part and a knife cuts the gates from the part. The Nyloncraft toolroom developed the cutter.
We had to do a lot of development work to guarantee that the parts locate precisely in the fixture during each cycle, stresses Smith, and that the mold and ejectors are in the same position for each cycle. This ensures that the robot accurately locates the parts in the cutoff fixture and also accurately controls the amount of pressure applied to grab the parts. Too much pressure and we would mar the part. Average cycle time has been refined to just 50 seconds, nicely surpassing the 1-minute goal.
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