QMT Features: October 2011
Robotic simulation
New, powerful methods of non-destructive inspection (NDI) and non-destructive testing (NDT) will make composites for aerospace safer

The use of carbon fibre composite materials is spreading wider than its traditional motor manufacturing base into aerospace and beyond. As a result, new, powerful methods of non-destructive inspection (NDI) or non-destructive testing (NDT) are required to ensure that materials have the necessary strength to perform effectively in their expanding roles. Applied Computing & Engineering Ltd (AC&E), based in Daresbury, is at the forefront of new developments in robot simulation software that ensure composite materials are safe.

Carbon fibre composite is an effective high strength, low weight material. It has been used in smaller aircraft for years. The drive to reduce the cost of air travel, meet environmental responsibilities and cope with the rising cost of fuel has led the aircraft industry to demand lighter passenger aircraft with improved performance.
Carbon fibre composite is the obvious material of choice, but ensuring the production process eliminates manufacturing defects in the material is a challenge – and not one that can be overcome by conventional techniques.

The porosity problem
The process of manufacturing carbon fibre composite (baking many layers of carbon fibre coated tape in an autoclave) hardens the material, but can lead to gaps or bubbles opening up between the tape layers leaving the structure vulnerable. Such imperfections determine the porosity of the material and can affect mechanical performance, which is why porosity values must typically be lower than 2.5%. Spotting bubbles and cracks in a black, opaque material, however, isn’t easy.

Scanning at the limits
Ultrasound scanning, of the sort used in pre-natal care, is traditionally used to determine porosity in carbon fibre materials. Yet the size and shape of, for example, an aircraft panel demands new capabilities of the scanning software.
Additionally, ultrasound scanning requires the use of water as a sound conducting medium meaning inspection of the part has to be fast, but at a suitably high resolution to pick up any flaws or anomalies.

Manually operated devices can’t deliver the required speed and accuracy, and the traditional choice of a Cartesian axes machine no longer offers the accuracy required for scanning more complex shapes like engine nacelles and structural stiffeners.

Computer simulation based off-line programming (OLP) methods for robots have been available for some time but early OLP techniques were developed predominantly for the automotive industry and are not suitable for programming NDI robots.

New software, new standards
To create simulation software suitable for passenger aircraft AC&E knew the resolution of the scan would need to increase dramatically. At the same time the speed of the scan would need to increase to meet throughput requirements.
And since the scanned components are irregular shapes, AC&E knew that advanced collision anticipation and avoidance also had to be a key part of the software. The solution was to avoid contact with the subject of the scan.

AC&E technical director, Yash Khandhia explains: “Typically, in robot programming, you ‘teach’ the robot to operate in simple plains. Where there is an obstacle there can be a collision causing costly damage to both robot and component. In contrast, AC&E’s software automatically programmes the robot to scan the structure without making contact with it. This allows complex structures, as well as flat panels, to be scanned without risk.”

This new generation of automated scanning software does more than avoid collisions. It achieves the faster scan times at greater resolutions that the new carbon fibre composite applications require.

Yash Khandhia: “AC&E encounters different NDI requirements and procedures depending on who we are working with.  Currently the basic minimum sizes of scanning for defects in composites are equivalent to 6mm x 6mm or a flat bottom hole with a 6mm diameter. However we are beginning to see projects where a 3mm diameter test is required. When this happens the number of points to be checked in areas such as aircraft wings will number in the hundreds of thousands. Our customized software automatically programmes a robot for this level of inspection in a way that is unique in the industry.”

AC&E expects its new software system to find applications far beyond its current uses in automotive and aerospace manufacturing. “We expect this form of NDI software will appeal to the shipbuilding industry, particularly pleasure boats,” says Yash Khandhia. “We also expect it to play a pioneering role in defence related manufacturing, for example in the construction of unmanned drones, which are extensively carbon fibre composite.”l
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