Q NET Engineering GmbH
Case Depth Tester P3121
Ultrasonic testing instrument for testing the case depth of heat-treated parts
Content
- Situation
- Solution
- Method Description
- Advantages
- Applications
- Device Decription
- Semi-Automated Systems and Handling Equipment
Situation
Case hardening improves the wear resistance and the fatigue limit of dynamically stressed parts. These mechanical properties are primarily determined by the surface hardness, the hardening depth and the residual stress depth profile. The case hardness depth (chd) - or the thickness of the hardened layer - is essential for the quality of the case hardening process. Up to now, random samples using destructive methods were the only way to control the quality of hardening processes. Needless to say, the method was very costly and time-consuming.
Solution
Das The Fraunhofer Institute for Non-Destructive Testing (IZFP) has developed
an ultrasonic method for fast and non-destructive case depth testing. They reduce the effort and the costs of testing
and provide fast production control to ensure consistently high quality levels.
The testing device is used for optimizing production parameters, reducing downtime after inductor changes, for fast
production control and for quality management.
- Figure 1: Case Depth Tester P3121, notebook version
The Method
Ultrasonic waves are scattered where the density and/or the elastic material properties in a limited area of the part change within the sound beam. In general, the sound waves are scattered in all directions, some of them are also scattered back to the ultrasonic testing probe. On the one hand, the effect, meaning the magnitude of the scattered and backscattered sound energy, depends on the change of density and/or the elastic material properties within the volume range. On the other hand it depends on the relation of the geometric size of this volume range (scatterer) and the wave length of the ultrasonic waves.
The magnitude of the ultrasonic backscattering can be influenced by adjusting the wave length of the ultrasonic waves, e.g. by adjusting the ultrasonic frequency. Is the average grit size small in relation to the wave length of the ultrasonic waves, the scattering is low; in case of larger grits the effect is stronger. Eventually, grits that are much larger than the wave length reflect the sound.
The determination of the case hardness depth (Chd) is based on ultrasonic waves that are scattered back by the grits of the core material (see figure 2). The ultrasonic frequency and thus the wave length is adjusted in a way which makes the microstructure of the hardened near-surface zone cause only negligible scattering. When the acoustic pulse reaches the core material with a rougher grit structure (see figure 3), the ultrasonic waves are significantly scattered. The time needed by the acoustic pulse to travel from the surface of the material to the point where it is scattered indicates the thickness of the hardened zone.
- Figure 2: How ultrasonic backscattering works
Needless to say, the case depth determined by ultrasonic backscattering does not necessarily equal the case depth measured with metallographic-, micro-hardness- or any other established method. However, it is also evident that there is often a close correlation between the ultrasonic chd and the reference chd. The reason is that both depths, the depth of the core material and the case depth determined by established methods are influenced by the process parameters of hardening.
The following conditions will produce ideal results:
- The test parts are induction-hardened
- The test parts are forged, not cast
- The minimum case depth to be measured is 1.5mm, in some cases it is possible to measure smaller depths.
- There is no further microstructure between the martensitic and the core material
- The grit size of the core material is big enough to cause significant backscattering of shear waves with a frequency of 15 MHz.
- Figure 3: Transition between hardened area and basic microstructure
Advantages
- Testing device can be integrated into the production process
- High testing precision
- One testing process takes only seconds
- Fast testing of large quantities
- With adequate sensor adjustment also radiuses can be tested
- The device is portable (8kg) and suitable for mobile use
- The device is easy to adjust to the customer's needs
Applications
The following figure shows a typical application of the case depth tester:
- Figure 4: Applications
Device Description
- Notebook for industrial use
- 4 measuring channels / multiparameter sensor technology
- Test frequency: 5-30 MHz
- Battery- and mains-operated
- Software / operating system
- Windows NT TM, Windows XP, Windows 7
- Modular hardware build-up
- Modular software build-up:
Planning, testing and data export. The use of databases throughout the whole process enables your company to access and organise the planning and testing data via a connected company network. With the help of the report generator that is implemented in the software, the client is able to interactively generate master copies - Additional types of devices:
Stationary special testing machine; desktop version with scaleable hardware
Semi-Automated Devices and Handling Equipment
Depending on your needs, the case depth tester P3121 can be ordered as desktop version or as stationary device with handling equipment. In addition, semi-automated devices are available (see figure 5):
- Figure 5: Handling equipment and semi-automated devices (Source: IZFP)
Contact
Yvan LejeunePhone: +49 (0) 6 81/9 76 71 53
Fax: +49 (0) 6 81/9 76 71 58