Shining through: insights with computed tomography

Article of 18 December 2013 

Computed tomography being developed at Festo in action

Gingerbread biscuits on a plate, lights blazing in all the gardens and a smell of cookies and fir trees: in six days it is Christmas. Who wouldn't like to take a sneak preview of the wrapped up Christmas presents when curiosity gets too much? Computed tomography would be ideal for this – it shines through objects in a non-destructive manner with the aid of X-rays and also shows their innermost secrets.

“We have never used it to x-ray Christmas, but it is certainly feasible,” smiles Katharina Steinlein, head of analysis diagnostics at Festo. She is responsible among other things for computed tomography, which is used in the development department of the manufacturer of automation technology for quality testing, defect analysis and the optimisation of injection moulding tools.

Secrets revealed – here the X-ray image of a chocolate egg with toy
Secrets revealed – here the X-ray image of a chocolate egg with toy

Non-destructive x-ray

For this purpose, the seven tonne appliance uses x-rays, which shine through the component. Whilst the x-ray image is being taken, the workpiece rotates slowly in front of the x-ray source, resulting in many individual images from different perspectives. A piece of software uses this to work out a 3-D volume.

In order for a usable image to be developed, depending on the material, the accumulated wall thickness of the parts may be 10 (steel) to 400 mm (plastics). “When the material is thicker, it can no longer be adequately x-rayed and the reconstruction process becomes too inaccurate,” explains Katharina Steinlein.

Another factor that needs to be taken into account is the size of the parts: with the computed tomography system at Festo, objects with dimensions up to a height of 300 mm and a diameter of 300 mm can be x-rayed. “So the Christmas presents may not be bigger than this either,” says Katharina Steinlein.

Support for development and production

Computed tomography is used at Festo to support product development, but also production. The images taken are helpful for the quality control of die cast parts, for example – defects such as pores or cavities inside them can thereby be easily detected. When it comes to plastic injection moulding, computed tomography helps to optimise the tools. With new components, for instance, a faster and uncomplicated target-performance comparison of the injection moulded parts can be carried out with the CAD model to tell whether the tool needs to be reworked. Later in the production process, a comparison of parts produced at the start and later in the series can be used to tell whether the injection mould has worn away in places.

The creation of a full 3-D model, including calibrating the appliance and processing the image data, takes around two hours. So anybody who secretly wants to take a look behind the packaging on their Christmas presents has to display a little patience.