Safe application of compressive residual stresses - ECOsense technology enables reliable deep rolling
The service life of components exposed to dynamic stress is improved by mechanical surface treatment. The method of choice here is often deep rolling. This process not only leads to a hardening of the material, but also introduces compressive residual stresses into the component. Residual stresses are present even when no external loads are applied. They counteract the propagation of cracks so that, for example, microcracks in a component propagate less quickly or only occur at a later stage.
These positive effects for the performance of a component are, however, a challenge for production and especially for quality assurance (QA), as residual stress depth curves can only be measured destructively. This is usually done by removing material (e.g. using the drill hole method) or directly by measuring the crystal lattice spacing using X-ray diffraction and step-by-step material removal.
This poses major challenges for QA in particular, as an essential property of the component cannot be measured. Fortunately, the deep rolling process is a very reproducible process that is influenced in particular by rolling contact geometry and applied rolling force. So, if you roll with the correct rolling body, the rolling force can be used as a control variable.
Factors influencing the rolling force during deep rolling
With hydrostatic rolling tools, hydraulics are used to press the rolling ball onto the surface. This is a force-controlled process and is therefore ideal for deep rolling. With mechanical tools, on the other hand, there are several other influencing variables that can lead to deviations in the rolling force.
With this type of tool, a roller is pressed onto the surface via a spring. The deflection of the spring and therefore the rolling force is adjusted by the tool infeed through the machine tool. This means that errors in the tool setting parameters, tool wear or even deviations in the shape of the component can have a direct effect on the rolling force. If, for example, the cutting tool is incorrectly calibrated, the machining diameter is no longer correct and too much or too little rolling force is generated simply because the spring deflection in the tool changes. Wear on the turning tool can have a similar effect. Indeed, rolling produces a clean, smooth surface, even though the diameter deviates and the rolling force is no longer correct.
Every process is documented thanks to the digitalization of deep rolling tools
As described, the rolling force is the most important variable for setting compressive residual stresses. With ECOsense technology, the rolling force can now also be measured for every mechanical deep rolling tool. ECOsense consists of a small measuring box that is capable of converting the spring deflection directly into a rolling force, documenting and transmitting it to a downstream unit via Bluetooth.
ECOsense therefore basically offers process monitoring specifically for the requirements of deep rolling. In the past, systems from the machining industry were usually used for this purpose. These are usually completely oversized and therefore unattractive in terms of price for this application.
ECOsense data can be transferred to an external device for further processing. This is done via a Bluetooth connection, which enables secure 1-to-1 communication. This means that no additional devices can access the encrypted data in parallel.
Two options are available for data processing. Firstly, a simple Android app can be used to display the rolling force live. PDF logs can be created for each process and the rolling forces can be monitored within limits using various methods.
There is also the option of connecting ECOsense directly to the machine via a gateway. In this case, the data can be processed by the machine or shared within the company via network. This means that all relevant stakeholders have access to the information and log files can be created automatically.
