Multi-Axis Robotic Positioning Machine

Manchester University's School of Materials, in conjunction with automation specialist Festo Ltd., has created an innovative robotic placement machine for carbon fiber ply. Intended to serve as a development platform, it looks set to establish new standards in carbon fiber manufacturing.

The machine, which is based entirely on Festo electrical drives and controls, has a 3D operating envelope and is capable of laying carbon fiber tow very flexibly, at up to 8mps.

Carbon fiber composites are traditionally constructed by laying a number of unidirectional or woven pre-impregnated "plies" over a tool mold, and then curing them with heat in an autoclave.

An alternative, less widely used method, involves the use of dry fabric plies and a resin infusion process. These traditional laying techniques are widely regarded as very inefficient and expensive – they can have material wastage levels as high as 40%.

Technology developments are constantly improving in this field and one major development is a process known as near-net shaping, an approach used with various industrial materials where the whole production process is geared to the final (net) shape of the product.

Near-net shaped carbon fiber processes involve laying down precise lengths of tow with the right orientation for the specific product. This orientation is the key: many components require higher strength in one direction, and by laying the fibers accurately and in defined patterns, component cross section is reduced and the strength-to-weight ratio is improved.

It is also a much more efficient process, with raw material wastage levels as low as 1% to 2%. But until now, it has been much slower than traditional techniques.

The Textile Composites Group at the University of Manchester is actively pursuing the near-net shaping approach, with particular reference to the specific needs of the aerospace industry.

According to Dr. Prasad Potluri, reader in textile composites, "We were looking for new ways of laying tow in predefined patterns. For the aerospace industry, we needed to develop lab-scale processes for products that can be 3m long and 2m wide, with a height of up to 500mm. So we required equipment capable of operating on a large scale and with great precision, which could also handle heavy spools of carbon fiber tow. We were also looking for fast operation, so the equipment had to be highly automated."

The carbon fiber industry already offers machinery that can utilize near-net shaped technology, but the costs run into the millions of dollars, and the systems do not provide the flexibility and development potential sought by Dr. Potluri. So the Group decided to develop its own solution. Funding for the new system came from Northwest Composite Centre, a center set up by the Northwest Regional Development Agency as part of its commitment to dynamic and sustainable economy for the northwest of England.

With funding in place, the next step was to find an automation specialist capable of designing and delivering the 3D spatial gantry system, which would form the heart of the Textile Composite Group's new machine.

As Dr. Potluri explains, "We are specialists in carbon fiber production, not robotics. We chose Festo because of the company's sheer range of motors and drives. We just specified our requirements, and Festo built a complete motion solution, right down to the control system and the software to operate it. Festo personnel also programmed and commissioned the system, and trained our post graduate PhD students on its use. As a result, we had a working solution up and running with minimum risk and hassle."

The new Robotic Tow Placement machine is capable of tow-laying speeds of up to 8m per second, and has a 3D operating envelope.

It incorporates two parallel 3m long belt actuators and a pair of 2m long belt actuators, with a vertical 600mm ballscrew drive for the Z-axis.

The actuators are driven by Festo synchronous AC servo motors and drives, and controlled from a central control cabinet. The control system incorporates a facility for DXF drawing import, to allow simple programming of complex 3D motion using the axes.

"We expect to be laying tow automatically on the machine and testing new processes and technologies within six months," says Dr. Potluri. "We will have up to three graduates developing on the machine, helping companies in the aerospace arena make high tech products for the future. And as well as developing new laying techniques on the machine, we'll be looking at new methods of consolidating carbon fibers instead of traditional autoclave. For example, we have a curing method using the Quickstep process from Australia, which uses a liquid heating system rather than air heating in an autoclave."