A7.3 - Giant-Magnetic-Resistance - An Aplication in Nondestructive Testing
- Event
- SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg - Band
- Proceedings SENSOR 2009, Volume II
- Chapter
- A7 - Magnetic Sensors II
- Author(s)
- H. Pries - Volkswagen AG, Wolfsburg, Germany
- Pages
- 53 - 57
- DOI
- 10.5162/sensor09/v2/a7.3
- ISBN
- 978-3-9810993-5-5
- Price
- free
Abstract
Nondestructive testing (NDT) of steel parts is of great interest for industrial manufacturers to assure their quality. In some cases all parts have to be tested before or after being processed or sold. Only NDT methods can provide maximum quality at low cost.
One of the most serious defects that might occur in production is surface flaws. These flaws need to be detected as soon as possible to allow real-time improvement within the production process. Automated NDT systems are suitable for online process monitoring as well as identifying process deviations, especially with regard to the statistical reproducibility of results.
A well-known NDT method for surface flaws in ferritic steel parts is magnetic particle inspection (MPI). The presence of a flaw leads to a perturbation of the magnetic flux in the investigated area, which causes a leakage of the magnetic field. The most common method of detecting this leakage utilizes finely divided particles, which are held in suspension by a suitable liquid. The particles are often colored or coated with fluorescent dyes, which emit under ultraviolet light (UV). The inspection is usually carried out manually by an employee, often within the assembly line production. Although some automated systems based on computer-aided image analysis are in use, it has yet to become a commonly practiced method. Magnetoresistance (MR) sensors and scanning techniques are applicable in detecting small magnetic fields. In recent years some studies focused on first applying AMR sensors and later also GMR sensors in NDT techniques.
The paper will give a short review on magnetic particle inspection and will introduce a well suited GMRsensor made by SENSITEC that satisfies NDT requirements. An example is shown of how it may be used for constructing an automated in situ testing system for complex automotive parts, such as a steering rack. Results from laboratory evaluation on real part samples are given and discussed with regard to the sensor characteristics.