Porosity analysis
Low porosity is crucial for ensuring high material strength and a long product service life. Precise porosity analyses can identify such weak points at an early stage and ensure the quality and reliability of products.
Table of contents
- What is porosity analysis?
- Identifying pores, shrinkage cavities and inclusions
- Quality Analysis: your holistic porosity analysis from the experts
- Fast, reliable measurement results
- Measurement methods for porosity analysis
- Advantages of porosity analysis using industrial computed tomography
- What porosity parameters are there?
- How is porosity analysed?
- Reference sheets for porosity analysis
- Technical factors influencing porosity analysis
- Porosity and inclusion analysis for various applications
- In summary: porosity analysis
What is porosity analysis?
Porosity analysis is a method for analysing the material inside a component. It is designed to precisely identify and quantify volume deficiencies such as pores, shrinkage cavities and inclusions. This analysis plays a central role in the quality assurance and non-destructive inspection of components, especially in manufacturing industries.
Identifying pores, shrinkage cavities and inclusions
During component quality assurance, it is crucial defects such as pores, shrinkage cavities and inclusions are detected at an early stage. These flaws often occur during the manufacturing process and can have a negative impact on the stability, functionality and service life of a component.
Pore analysis
Pore analysis deals with the identification and evaluation of cavities within a material, which are referred to as pores. These cavities are usually caused by trapped air or gases during the manufacturing process, for example during casting or injection moulding.
Shrinkage cavity analysis
Shrinkage cavities are large cavities that often occur during the casting process and are due to the material shrinking during cooling. They can significantly impair the stability and strength of the component. Shrinkage cavity analysis is used to locate and evaluate these material deficiencies.
Inclusion analysis
Inclusions refer to foreign materials embedded in the component during the production process. These deficiencies can arise for various reasons, for example due to contamination of the source material or insufficiently clean production conditions. Inclusion analysis is crucial for determining the effects of these defects on the material and component quality.
Quality Analysis:
your holistic porosity analysis from the experts
We offer the complete spectrum for the detection and analysis of pores, shrinkage cavities and inclusions, including expanded porosity analysis as per the reference sheets P203, P202 and P201.
Fast, reliable
measurement results
- Non-destructive inspection and destructive inspection
- 3D computed tomography
- Evaluation of CT data using the software VGSTUDIOMAX from Volume Graphics and ZEISS Inspect, formerly GOM Inspect
- Elemental analysis of inclusions using EDX analysis
- Nominal-actual comparison
- Porosity analysis in metallic materials and coatings
Measurement methods for porosity analysis
Industrial computed tomography is the preferred method for highly precise, three-dimensional porosity analysis. However, there exist other methods that are also used to identify and analyse porosity. In the following, the focus is on a comparison of ICT and materialography as two central approaches.
Industrial computed tomography
Industrial computed tomography uses X-rays to create a series of cross-sectional images of the component, which are then combined to create a detailed, three-dimensional model. CT permits complete, non-destructive imaging of the internal structures.
Materialography
Materialography, on the other hand, is a destructive method in which a cross-section of the material is prepared and analysed microscopically. This technique permits a detailed analysis of pores and inclusions and is mainly used in metallic material inspection.
Advantages of porosity analysis using industrial computed tomography
During porosity analysis, industrial computed tomography (ICT) offers crucial advantages over other methods. Thanks to its non-destructive form of inspection, CT delivers particularly fast results and the component remains intact during the analysis. As such it is possible to analyse the same component several times or to monitor it at different stages of production. This aspect makes ICT the ideal choice for continuous process monitoring and optimisation.
3D computed tomography for precise pore detection
As part of CT, 3D computed tomography (3D CT) provides a comprehensive three-dimensional depiction of internal structures. In this way, defects, shrinkage cavities, inclusions and pores can not only be identified more easily, but also pinpointed extremely precisely.
In addition, 3D CT not only permits precise measurements on the object inspected itself, it is also possible to compare the results of the 3D measurement directly with the CAD data by means of a nominal-actual comparison.
What porosity parameters are there?
Numerous porosity parameters are used as crucial parameters for the evaluation of material quality. The most important parameters include the pore size, pore volume, pore density and distribution of the pores in the component. These parameters provide information about the extent to which the component is affected by porosity and the effect of this porosity on the structural integrity.
How is porosity analysed?
1
Data acquisition using CT
To begin with, the component is scanned using computed tomography. X-rays acquire the component in a series of 2D cross-sectional images, which are then combined to form a three-dimensional model. This process permits detailed acquisition of the entire internal structure of the component.
2
Segmentation of volume deficiencies
Specialised software is used to segment the volume deficiencies, separating them from the rest of the material structure and marking them as independent areas. This segmentation makes it possible to precisely determine the size, shape and position of the affected areas. In this way, critical points can be precisely pinpointed and their potential influence on component strength evaluated.
3
Analysis, measurement and evaluation
The software now measures the size, volume and position of the segmented pores. Parameters such as the pore volume ratio are calculated to assess the material integrity. The component is then evaluated in accordance with standards or reference sheets (e.g. BDG reference sheet P 203), which specify the acceptable pore sizes and distributions as well as when a component is considered defective.
4
Porosity key
A permissible porosity is specified in the form of a key. This so-called porosity key serves as a reference for evaluating porosity parameters such as pore size, pore volume or pore density in the component based on specified criteria. It specifies which pores are considered critical and which are still within the tolerances.
Reference sheets for porosity analysis
BDG reference sheets (BDG – Federal Association of the German Foundry Industry) are important standards and documents for porosity analysis and are often used in industry to evaluate the quality of cast components. The reference sheets P 201, P 202 and P 203 are particularly relevant; these documents focus on the detection, analysis and evaluation of pores and other volume defects in castings.
VDG P 201 and BDG 202
VDG specification P 201 and BDG reference sheet P 202 together provide a comprehensive basis for non-destructive porosity analysis. P 201 makes it possible to classify basic pore parameters such as maximum surface porosity and pore diameter in two-dimensional sectional images. P 202 extends this analysis with additional parameters, including the number of pores and the smallest distance between them.
BDG reference sheet P203
BDG reference sheet P 203 extends porosity analysis to the third dimension and makes it possible to analyse entire volume deficiencies in 3D models. It includes the three-dimensional characterisation of pores in terms of their size, shape and position, as well as the targeted evaluation of functionally relevant areas in the component. This reference sheet is crucial for the precise evaluation of defects in more complex components and in critical areas.
Technical factors influencing porosity analysis
The accuracy of a porosity analysis depends on several crucial variables. Careful calibration and adjustment of these parameters is therefore essential for ensuring precise, informative results.
Voxel size
The voxel size, i.e. the resolution of the CT images in three dimensions, plays a key role in the precision of the porosity analysis. Smaller voxel sizes permit more detailed depiction of internal structures and defects, as they offer a higher spatial resolution. An excessively large voxel size can result in the failure to detect smaller pores or fine details, which would impair the accuracy of the analysis.
Grey value contrast
Grey value contrast is crucial for distinguishing between different areas of the material and the pores they contain. A high grey value contrast improves the software's ability to distinguish pores from the rest of the material structure. Insufficient contrast can lead to the failure to detect pores or the inaccurate detection of pores, which can falsify the analysis results.
Threshold specification
Threshold specification is the process of specifying a limit above which an image area is identified as a pore. Choosing the right threshold is critical as it influences which areas of the image are considered pores and which are interpreted as material. Too low a threshold may result in the detection of smaller or less significant pores, while too high a threshold may miss larger or significant defects.
Porosity and inclusion analysis for various applications
Automotive
In the automotive industry, porosity analysis is used to analyse safety-critical components such as cylinder heads, gearbox housings or other functional components for defects such as pores, shrinkage cavities and inclusions. Thanks to industrial computed tomography, such defects can be acquired and analysed non-destructively, ensuring the quality and reliability of the components.
Additive manufacturing
Porosity poses a significant risk in additive manufacturing, because porous components are susceptible to cracks and structural weaknesses. Industrial computed tomography is used to determine precisely the proportion of pores and permits the acquisition of the exact position and size of the pores, shrinkage cavities and the shrinkage cavity-to-volume ratio. This information makes it possible to assess precisely and optimise the quality of the parts manufactured.
Plastics industry
With the increasing requirements on tolerances in plastic injection moulding, precise porosity analysis is becoming more and more important. It enables air inclusions and porosity to be detected at an early stage and the precise checking of the quality of injection moulding. Detailed porosity and inclusion analyses contribute to the optimisation of the manufacturing process and ensure component quality, especially during initial sample testing.
In summary: porosity analysis
Porosity analysis makes it possible to identify precisely any faults or defects such as pores, shrinkage cavities and inclusions in components. Industrial computed tomography in particular has proven to be an effective method for completely acquiring the internal structure of components and depicting them in three dimensions. Compliance with standards such as the BDG reference sheets and the use of modern software solutions ensure the reliable and precise evaluation of porosity and other defects.
