Robots take on composite layup

Aug. 21, 2003
Robots that can handle composite materials are finally a reality, offering the potential for faster production and lower costs.

David Groppe
   Composite Systems Inc.
   Arnold, Calif.

The PFE systems come fully integrated to the robot and system configuration selected by the customer. These systems are designed to be expanded as the need arises.

Composites are increasingly used in new applications as OEMs take advantage of excellent material characteristics, notably a high strength-to-weight ratio. Manufacturing advances are also aiding new developments.

For instance, improvements in plug and mold designs let engineers assemble complex parts. Lasers have assisted greatly in verifying material location and orientation for manual layup. Water-jet systems can generate holes and cutouts after layup is complete and the part is cured. And significant improvements in X-Y cutting systems and associated software have expedited material profiling.

Industry dilemma

However, a significant key to the continued use of composites is reducing, or at least limiting, the traditionally high manufacturing labor costs. Skilled personnel must perform the many and varied tasks associated with layup or placement of such materials, and this can limit which projects can be economically justified.

The number of “pounds-per-hour” that workers can produce is fundamental to the affordability of these advanced materials. Current manufacturing technology limits this number. Typical methods simply dictate more personnel to get more pounds-per-hour. At some point, however, labor costs escalate faster than production increases, making additional labor fruitless.

Systems that perform automatic layup are limited in the types and sizes of materials they can handle, as well as in the speed that material can be dispensed. For example, automated tape-laying (ATL) machines that place unidirectional tapes have been used in only a limited range of aerospace and marine applications. This is because they tend to be expensive, inflexible, and have material limitations.

Core placement is a factor, too. These materials vary in makeup and shape and must also be properly positioned during layup. Handling such material can be awkward at times due to size, shape, and the specific location where it must be placed. The issue of labor, again, plagues the process.

Enter robotics

Robots have long been used to perform a variety of manufacturing tasks, but their use in the field of composites has been limited. In some cases end-of-arm equipment has been used for water-jet cutting, drilling and tapping, material-handling, assembly, and fiber-placement applications.

But the nature of composite materials has limited more widespread use of robotics. The materials demand precise control and uniformity to produce a truly “engineered” product. Complicating matters, raw materials may vary widely in terms of the resin type and volume, and fiber characteristics. For example, commercially available material, whether dry or prepreg, comes in widths from 1 to over 60 in. Supply roll core diameters range from 3 to 12 in., with ODs to 26 in.

A robotic feed system has now been designed to accommodate these wide material variations, whether prepreg or semipreg, unidirectional or woven, with varying amounts of resin impregnated to one or both sides.

PFE technology

The Precision Feed Endeffector (PFE) has been developed to harness the flexibility and ease of programming associated with commercial robots and, at the same time, handle the wide range of commercial composite materials.

The PFE combines several processes associated with handling prepreg and semipreg composite materials. These include material feed, peeling off protective films prior to layup, profiling or cutting the material on one or both edges simultaneously, and discharging waste. It can also follow the mold surface during layup - whether concave or convex - without programming every point along a given path. Optional features include refrigeration of the material and reactivation of the resin to the required temperature prior to placement.

Based upon the specific process, an operator first loads a roll of material into the PFE feed station. This is usually done off-line at a tool crib located adjacent to the robot cell. The crib may house several PFE devices, set up and configured for specific materials and widths. The tool crib would also house end-of-arm devices for core placement and other functions required for a particular application.

The PFE opens in a clamshell fashion for easy access and service. When open, the operator pulls material through a series of drive rollers that both feed and provide tension in the cutting or profiling station. The drive system can be programmed to overcome variations in tackiness of different prepreg and semipreg materials, to ensure they easily pass through the system. Once material has been loaded, the operator peels a leader of the protective film and attaches it to an empty core for take up by the system.

The profiling station can accommodate different cutting methods, including drag knife, slitting, and ultrasonic devices. Waste material discharges just below this station. A series of pneumatic venturies linked to the profiling system apply bursts of air in two directions. One retains the layup material and forces it to continue through the tool. The second, simultaneous burst of air in the opposite direction directs waste material out of the device where it is captured for later removal.

A key element to the PFE is a suspension system that follows the part's surface contours as the robot moves. The suspension provides complete contact with the surface regardless of the supply roll width, and force can be programmed so as not to crush core material. Because the device provides controlled contact, debulking, to some extent, is a consequence of the layup itself.

A proprietary link between the robot and PFE coordinates material feed with robot travel. The robot, PFE, and roll of material share the same centerline, and a laser system monitors alignment to ensure material is placed properly. The cutting system receives pattern information in relation to the robot's programmed path. And the system does not need to perform complex calculations to perform the layup. Instead the suspension system verifies dimensional length just prior to material placement - significant where ply drop-offs or field build-ups are critical to a given layup.

Robot tracts or gantry systems enable layup over or within large mold tooling. The PFEs can be inverted, as well as connected together, end to end, for layup of large parts such as wings, boat or ship hulls, cylinders, and flat panels. Additional axes in the robot system can provide the ability to manipulate the mold.

In applications where two molds will provide mirror-image parts, gantry systems using at least two robots that share a common bridge can greatly reduce layup time. This will at least double the throughput rate, especially when a large portion of the programming is shared by both robots.

Feedrates in the 10-axis PFE may exceed 1,200 ipm, depending on the material. The device is manufactured in standard module widths, typically in 6-in. increments, assembled at the factory to a standard 60-in. width. However, special configurations are available. For example, combination PFE systems can provide angled layups. A 6-in. and a 24-in. PFE, for instance, could mount at 90° to each other and produce corners in a single pass. Cross configurations can also be used where unidirectional material must be placed at a right angle to a woven material, thus eliminating an additional pass by the system.

For wet layup applications, such as those associated with boat building, the PFE device works in a similar fashion with only a few additions. The dry fabric materials load and feed in the same manner as prepreg materials, except no protective films need be removed. The profiling and waste-removal stations are the same. However, additional attachments include resin supply and feed systems, which control the temperature and mix materials. The feed system applies resin to both sides of the material as it is being fed, just prior to placement, and monitors volume and viscosity on each side.

A flexible squeegee attachment added to the suspension system spreads and bleeds the resin through the material as it is placed. Excess resin is recycled.

Machine control

Control of the PFE system is PC/PLC based, incorporating both digital and analog inputs and outputs to monitor speeds and feeds in concert with robot movements. A proprietary chip negotiates with both devices in real time so they work together seamlessly. This hardware resides on the PFE so when tooling changes, the device carries the information needed to perform the assigned tasks.

Patterns that the profiling system must generate are simply fed to the system offline and verified through programming software supplied with the robot system. The operator has the option to program on the shop floor or call up predefined archived files.

These turnkey systems are typically equipped with an HMI (human-machine interface) that includes a customized touch screen. Icons let the operator test and cycle individual aspects of the system. The HMI also monitors layup, and the system may include cameras that watch specific aspects of the layup to ensure quality and provide documentation.

The PFE is meeting the demand for better composites and layup methods. It is suitable for aerospace and marine applications, blades for wind-energy systems, motor homes and semi-trucks and trailers, as well as furniture, residential homes, and other architectural applications.

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