Original Date: 10/20/1997
Revision Date: 01/18/2007
Best Practice : Tow Placement of Advanced Composite Materials
The increased use of composite material in the F/A-18 E/F program created a challenging producibility problem for Northrop Grumman. The E/F version had almost twice the percentage of structural weight as the previous C/D version, requiring more composite structures and geometrically-demanding parts. In order to increase its manufacturing efficiency, the company set up an automated composite material ply lay-up in addition to its conventional manual ply lay-up method.
The automated part lay-up consists of a Cincinnati Milacron 15-axis, computer numerical control tow placement machine with an Acramatic 975 controller. Tow placement is a proven technology for situations where composite material is applied by an automated machine on complex tools. Northrop Grumman’s tow placement machine has two mandrel stations which enable an operator to set up one station while the other station is being used. The maximum mandrel length is 32 feet with a maximum diameter of 12.5 feet. The machine also has a 20-ton spindle weight capacity and a maximum machine speed of 1,800 inches per minute with a 2.87-inch compacting roller.
Major benefits of the tow placement machine include eliminating the ply cutting and material storage requirements. Material usage is now reduced to a minimum due to the near net shape lay-up. Processing costs for manual lay-up are typically measured in hours per pound. With the high material lay-up efficiency, processing costs for the automated lay-up can be measured in pounds per hour. For complex parts, Northrop Grumman has reported an 80% reduction in process time. In addition, part lay-up has become a much more repeatable process since installing the tow placement machine.
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