Driving Massive Composite Panels: REDEX Components in High-Speed Fiber-Laying Machines

While it’s no secret that carbon fiber materials are transforming the space industry thanks to their weight savings, they can be particularly challenging to apply to gigantic spacecraft structures such as those that make up reusable rockets. Not only do such large composite panels require hundreds of thousands of manufacturing hours, they often involve multiple machines that take up valuable space and add various inefficiencies to the process including increased tooling and maintenance.

Unfortunately, fabricating a large, automated fiber placement (AFP) machine with both the high laydown rates and surface coverage capability needed to produce giant panels and other large structures on schedule is beyond the means of many machine builders.

For example, a leading space company that designs and manufactures complete spacecraft and satellite components—including rockets greater than 100 ft in height—turned to a longtime REDEX partner to construct the large structures that will make up a massive carbon fiber composite reusable rocket. That meant the customer would have to create the largest AFP machine it has ever built in order to automate the construction.

An Enormous AFP Machine for Huge Rocket Panels Calls for Redex Precision

Upon deployment, the 100-ft.-tall rocket is expected to carry about 28,770 lb (13,050 kg) of payload. Building such an enormous carbon composite rocket requires a world-first carbon composite fiber placement machine. Given the magnitude of the project, Electroimpact custom-created an enormous AFP machine that measures 39 ft (~12 meters) tall, weighs 99 tons (90,000 kilograms) and will be able to lay 98-ft (~30 meters) carbon fiber composite lengths at a rate of 328 ft per minute (~100 meters per minute).

This towering AFP will produce, for example, the panels that make up the 91-ft. (28 meters) long interstage and payload fairing, the 22.9-ft. (~7 meters) diameter first stage and the 16.4-ft. diameter (5 meters) second-stage tank, as well as printing several smaller structures for the rocket. The custom AFP also includes an innovative variable spot size laser (VSSL) system, which significantly reduces error reduction time and dramatically increases layup speed, and a fully automated real-time inspection system. The system scans the laminated carbon composite for even the tiniest of defects, so they can be addressed before the machine applies the next layer of material.

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To help the machine lay down the large volume of carbon fiber quickly and accurately, Electroimpact uses REDEX machine drive components, precision gear rack and precision slew bearings to drive the X axis, rotator and C axis. The two companies have collaborated for more than 15 years on projects involving large aircraft structures.

The following outlines how REDEX components contribute to precise fiber composite placement and to reliable system performance during the rocket’s construction and operation.

Axis Requirements

The X axis, which moves the machine head horizontally to apply the carbon fiber, has a moving mass of ~198,400 lb (90,000 kg), top speed of 4.2 ft. per second (1.27 meters per second), 0.2g acceleration, a travel length of 65.6 ft. (20 meters) and a design life of 20 years. Four Fanuc Alpha 500/3000 HVIS servo motors accelerate the machine head.

To drive the axis, four REDEX SRP6 planetary servo reducers were chosen. Designed for the most demanding machines, these jumbo-size gearboxes are designed with large output bearings to provide the highest output stiffness on the gear rack of any high-precision servo reducer. They feature high torsional stiffness, low angular backlash, high tilting stiffness, heavy load capacity and high efficiency.

The Type M In-Line SRP6 gearbox they chose with a 21:1 ratio has a rated acceleration torque of 12,240 lb/ft. (16,585 Nm), a maximum input speed of 3,500 rpm and a maximum tilting moment of 35,400 lb/ft. (48,000 Nm). The X axis also incorporates 56 REDEX A11 Mod 10 gear racks. Each AGMA 12-quality rack has 30 case hardened and ground helical teeth. The racks measure nearly 3.3 ft. long (1 meter) and weigh approximately 152 lb (69 kilograms).

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REDEX modular racks can be mounted end-to-end to achieve any desired linear axis length. Thanks to REDEX SRP6 reducers including ultra-stiff output, precision pinions, and modular gear racks, the X axis boasts a design accuracy of ±0.0008 in. (±0.02 mm) with encoder position feedback.

Once four new and faster servo motors were installed, speed was increased by 50% with the same acceleration performance. The team chose SRP gearboxes and Mod 10 helical gear racks to ensure the setup provides long-lasting reliability. The rotator that holds and rotates the mold so that the fiber can be applied, is sized to accelerate a tooling inertia of ~3,678,200 lb/ft.2 (155,000 kg/m2) with angular acceleration of 75°/sec2 and is driven by two Fanuc Alpha 500/3000 HVIS servo motors along with two SRP5 right angle gear reducers.

Ratio 31.SRP5 gear reducers are capable of up to 10,050 NM maximum output torque, a maximum input speed of 4,000 rpm and maximum tilting moment of 22,140 lb/ft. (30,000 Nm). The rotator achieves accuracy to 6 arc seconds with an absolute encoder.

The C axis rotates the AFP head and uses an Andantex 3.88-ft. (1,184-mm) pitch diameter crossed roller slewing ring with external teeth providing high accuracy, stiffness and uniform rotational resistance.

Electroimpact described a smooth rack-and-pinion installation process. Their team began by adjusting the pitch line and pitch at each rack joint, starting from the center of each X bed, and the rack segments allowed for plenty of clearance along the run. They set the backlash according to REDEX specifications, resulting in ±0.1-mm pitch accuracy over 16 meters.

An Automatic Lubrication System with Distinctive Foam Pinion Simplifies Maintenance

Keeping large rack-and-pinion systems reliable over the demanding production operation using a conventional lubrication system is no easy task. Not only are these systems often cumbersome, but they can also be difficult to install.

Electroimpact employs the REDEX FlexxPump 411 (Gen 2) automatic lubrication system. It applies the correct amount of lubricant to the application point without the over- and under-lubrication—or messes—that can otherwise occur with conventional methods. In addition, the unit can allow onboard programming or control via the machine’s programmable logic controller.

Instead of using felt applicators, the unit comes with polyurethane foam pinions with an open-cell architecture. This allows the polyurethane foam to apply lubricants at their proper thickness while also absorbing excess lubricant. The open-cell structure also allows pinions to use higher viscosity lubricants. F01 grease is appropriate for open gears and rack-and-pinion drives. With FlexxPump, odometer-based lubrication metering from the CNC is handled automatically.

Top-Quality Components Launch Your Machines to Success

The AFP machine passed its final acceptance tests and is being installed at the space company’s facility. According to the rocket manufacturer, the autonomous machine is expected to save more than 150,000 manufacturing hours during the production process. This project exemplifies how rack-and-pinion or custom gears can support precise motion control requirements and stringent quality standards associated with the space industry.