CT in Plastics Development and Modern Production Techniques

February 22, 2021 | Gina Naujokat

The Institute for Plastics Technology in Stuttgart (IKT) shows several examples to demonstrate how computed tomography supports the development of new materials and additive manufacturing processes.

The development of new materials in the plastics sector and new production technologies such as Additive Manufacturing has picked up speed over the last ten years. This technological evolution is accompanied by non-destructive testing with X-rays not only providing important services in quality assurance but moreover, supporting research and development particularly using high-resolution computed tomography. With the data set of a CT scan and the three-dimensional visualization of the test object, material samples can be examined in detail. In addition to detecting defects, porosities, or material inclusions, deviations in wall thicknesses, alignments of fibers, or the homogeneity of foams can be precisely analyzed. This allows conclusions to be drawn about the respective manufacturing method, which can be corrected and optimized accordingly.

Modern, fiber-reinforced plastics have the advantage of greatly reducing the weight of components and are used in the aerospace and automotive sectors. The aim is to save fuel or to switch from conventional to new forms of propulsion in the course of electromobility. In addition to the common injection molding process, additive manufacturing is frequently used when it comes to very complex geometries and for the more efficient production of small series and prototypes.

To ensure the stability and functionality of the components, computer tomography is used during development and production. It provides reliable information about the internal structures and, additionally, the data sets can be used for corresponding functional simulations.

The Institute of Plastics Technology (Institut für Kunststofftechnik - IKT) at the University of Stuttgart has been using a Comet Yxlon FF20 CT inspection system with a 190kV nano-focus transmission tube. They research numerous application areas in plastics technology, including materials and processing techniques as well as the development of new products. Manufacturing processes and various materials are closely examined for their specific applications.

[Visualizations and analyses: Amira-Avizo Software]

Fused Deposition Modeling (FDM): The FDM technology is an additive manufacturing process used for complex component geometries and in prototyping. Since these components are still inferior to injection molded parts in terms of their mechanical properties, the deposition of the individual filaments is checked using computer tomography to obtain information for optimizing the manufacturing process.

Layered Composite: This detail of a layered composite shows the structure of continuous glass fibers deposited layer by layer in 0°/90°/0° orientation. This manufacturing method finds its application for components in aircraft, boat, and automotive construction, as they have strength like metal alloys, but are much lighter. In the CT volume, one can clearly see the fiber orientation and reliably analyze the material for delaminations, voids, or deformations due to external influences (e.g. impacts).

Short-Fiber-Reinforced Polyamide: This specimen is made of short-fiber-reinforced polyamide welded by ultrasound. The orientation of the fibers is an important criterion for the strength of a component. With computed tomography, the fiber orientation can be completely determined in a three-dimensional volume. Previously, this was only possible using very complex micrographs, which do not allow a full three-dimensional view. The method is also suitable for the optimization of injection molded components (determination of fiber orientation and -length) and the validation of process simulations.

Foams: Foams are mainly used for thermal insulation, but also in lightweight construction. They can be optimized for their respective purpose by influencing the size and distribution of the pores in the manufacturing process. This is a foam sample in the size of a corn kernel. Figure 1 shows the complete CT volume, which is digitally cropped in Figure 2, revealing the pores. In image 3, the negative view is used. The material is masked out and the air regions are visualized in color to examine the pore structure. It can be clearly seen that the pores decrease in size from the inside to the outside. The CT software can be used (among others) to calculate the volume and shape of each individual pore in relation to its position. With this data, it is possible to optimize the manufacturing processes according to the requirements and to influence the mechanical or thermal insulation properties.

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