Hardness & Residual Stress Depth Profiles NDE Scanner by 3MA Technology

Situation and Requirement on Residual Stress Measurement

In a car or truck valve springs are exposed to extreme conditions. Therefore, the requirements concerning the properties of the valve springs are challenging: both, the power tolerances as well as the relaxation tendency must be extremely low, and the fatigue strength should be sufficiently high.

In order to achieve and to ensure the best possible material properties and processing quality, in addition to modern manufacturing technologies the use of in-process quality assurance methods is crucial.

Spring Valves for example

To assess the production quality, the mechanical and technological characteristics of the components must be randomly tested. To do so, depth profiles of hardness and residual stresses of a spring are sampled in regular intervals on the inner surface of the spring. In case of destructive, viz. conventional metallographic and X-ray methods, this examination is highly time-consuming and expensive, thus impeding the increase of productivity and economic feasibility.

Non-destructive Solution for Hardness and Residual Stress synchronously

The aforementioned destructive testing methods can be superseded by a fast and cost-efficient nondestructive testing prodedure, the “3MA“ technique (3MA – “micromagnetic multiparameter analysis of microstructure and stress“). As a combination of hardware and mature process engineering 3MA testing technology comprises four micromagnetic testing methods: multi-frequency eddy current, analysis of upper harmonics, incremental permeability, Barkhausen noise.

The Hardness & Residual Stress Depth Profiles NDE Scanner allows the concurrent determination of various relevant quality characteristics of a material – e. g. hardness and residual stresses in different measuring depths – without destroying the specimen. The valve spring is inserted into the test system, then the test process is fully automatic.

Result of hardness test by Scanner in comparison to conventional inspection for measuring depths from 250 to 2000 μm

The valve spring is gradually rotated while its inner surface is scanned by sensors. At each test position seven nodes of the hardness profile and six nodes of the residual stress profile are determined locally resolved. The scanning of a spring coil takes less than a minute measuring time. A similar destructive test would take several hours.

If you want to know more details or you have further questions, please contact LAB Gages directly.

By using the Hardness & Residual Stress Depth Profiles NDE Scanner, valve spring is gradually rotated while its inner surface is scanned by sensors. At each test position seven nodes of the hardness profile and six nodes of the residual stress profile are determined locally resolved.

The scanning of a spring coil takes less than a minute measuring time.