In Part I of this blog series, we discussed the importance of material testing and explored some of the types that exist. In this article, we will delve deeper into other aspects of material testing such as the process itself (how it is performed) or the quality standards that must be adhered to in order to ensure accurate and reliable results.
We hope that by the end of this article, you will have gained a better understanding of how material testing can be used to improve product design, performance, and safety, and why it is an essential part of many quality control and research processes.
Sample sacrifice in material testing
As we already mentioned in our previous post, one of the key aspects of material testing is that it often requires sacrificing a part of the material to be tested.
This means that the sample used for testing cannot be reused and must be disposed of after the testing is complete. However, the information gained from material testing can be invaluable in terms of improving the quality and reliability of the components produced in a foundry.
Inspection and testing of castings
Inspection and testing of castings encompasses five main categories: casting finishing, dimensional accuracy, mechanical properties, chemical composition and casting soundness.
1 – Casting finish
The surface finish of a metal casting can be impacted by various factors such as the type of mold or pattern used, the coating applied on the mold, and the process used for cleaning.
Currently, there are two main methods for measuring surface roughness, thus the evaluation of surface finish is mostly performed through visual comparison with a set of test panels of varying levels of roughness, or a roughness measuring gage.
2 – Mechanical testing
We already covered mechanical testing in Part I of this blog series. In brief, mechanical testing is an essential process in metal casting that evaluates the mechanical properties of the metal and the casting to ensure that they meet the required mechanical specifications.
These tests are crucial in ensuring the quality and reliability of the cast metal product, especially in applications where high mechanical strength is necessary.
3 – Chemical composition
An alloy’s performance capabilities are significantly influenced by its chemical makeup. Minor alloying elements that are introduced to the material have the potential to further alter its chemical composition.
Chemical analysis may be necessary to confirm the correct chemical composition is present to obtain a specific set of qualities, depending on how susceptible an alloy is to variations in its chemical composition.
4 – Casting soundness
Casting soundness refers to the absence of defects such as cracks, porosity, and inclusions within a casting. These defects can lead to the casting’s failure under stress, making soundness an essential aspect of inspection and testing.
Identifying and addressing any casting defects is critical to ensuring the final product’s quality and performance. Proper inspection and testing of castings can ultimately save time and money by preventing costly failures and reducing scrap rates.
5 – Dimensional accuracy
Dimensions of a casting may vary due to factors such as mold cavity expansion, the contraction of the metal as it cools, or heat treatment. We as patternmakers predict these material behaviors and compensate for the variations in the pattern’s design.
Castings are specified by setting a range of values that the dimensions can lie within because each casting’s dimensions will vary somewhat. The provider can choose the range between the lower and upper tolerance limits; the narrower the range, the harder it will be to make and test, and the more expensive the casting will be.
Quality standards in material testing
The chain of trust
Conformity assessment activities allow bodies to differentiate themselves by demonstrating that they have the necessary technical competence to carry out an activity. On the other hand, accreditation is a tool to build confidence in the proper execution of conformity assessment activities.
How does the chain of trust work in the market?
1 – Both the market and the public administration ask for guarantees of reliability.
2 – Companies have to demonstrate that the products, processes and services they offer are reliable and comply with (regulatory and market) requirements, and request an evaluator to carry out the relevant controls.
3 – Evaluators (laboratories, inspection, certification or verification bodies) must demonstrate their technical competence for the activity they perform.
4 – The accreditation body (an independent body that evaluates the evaluators and accredits their technical competence to issue reports and certificates) accredits this technical competence (and closes the chain of trust).
The Spanish system
Thus, there is one body and two fundamental standards in the material testing accreditation process in Spain:
Body
ENAC- Spain’s National Accreditation Body
ENAC is the entity designated by the government to operate in Spain as the National Accreditation Body in application of Regulation (EC) No 765/2008 of the European Parliament which regulates the operation of accreditation in Europe and requires each Member State to have a single accreditation body.
It ensures that the results of material testing are accurate, reliable, and in compliance with international quality standards. It also provides a solid basis for comparison and transfer of results between different laboratories. Accreditation by ENAC is a requirement for material testing results to be accepted and recognized globally.
Standards
ISO/IEC 17025
ISO/IEC 17025 enables laboratories to demonstrate that they operate competently and generate valid results, thus building confidence in their work both nationally and globally.
UNE-EN 10204
The UNE-EN 10204 is a standard that covers the quality requirements for steel products, including material testing. This standard sets the requirements and procedures for the inspection and verification of the quality of steel products before delivery. The UNE-EN 10204 is widely used in Europe and provides a common framework for evaluating the quality of steel products. This standard defines three levels of inspection documents:
- Level 2.2: Inspection certificate issued by the manufacturer, which confirms that the products have been manufactured in accordance with the agreed specifications and that the inspection has been performed on several occasions and in different productions at the manufacturer’s premises showing, in the certificate, an average of the test result obtained.
- Level 3.1: Test certificate issued by the manufacturer’s authorized inspection representative, which confirms that the products have been inspected and tested in accordance with the agreed specifications and that the results have been checked and approved by the inspection representative.
- Level 3.2: Test certificate issued by an independent third-party inspection and testing organization, which confirms that the products have been independently inspected and tested in accordance with the agreed specifications.
Each level provides a different level of assurance to the customer regarding the quality of the products they are receiving, and the appropriate level will depend on the customer’s requirements and the specifics of the transaction.
By providing clear and consistent inspection documents, UNE-EN 10204 helps to improve the transparency and reliability of the supply chain for metallic products.
Conclusion
Now we know that destructive testing of castings is an essential part of many quality control processes. Although it requires sacrificing a portion of the material, the information obtained from testing can be highly valuable in improving the quality and reliability of the components produced.
In addition, inspection and analysis of castings is crucial to ensure the performance of the final product, and quality standards in material testing are necessary to ensure the accuracy and reliability of the results.
In short, destructive testing of castings is an invaluable tool for the design, performance and safety of parts.