DESIGN OF CONTROL FOR THE DEVICE USING FOR THE DETERMINATION OF RESIDUAL STRESSES BY RING-CORE METHOD
Authors: Patrik Šarga , František Trebuňa , Branislav Grejták 
Published: July 2019

Urgency of the research. Residual stresses in machine parts and constructions greatly affect their service life and reliability. They are introduced into the manufactured object at each production process and their level can change significantly due to the operation of the product. Their main risk lies in the fact that they add up to the external load and can be the cause of the failure of the construction. Residual stresses can not be determined by simulation methods. They can only be determined using experimental methods. One of these method is the Ring-Core method, the principle of which is to form an annular groove around the strain gauge. Creating of annular groove releases the internal stresses, which can be recorded by a strain gauge. The quality of the formed groove has a significant impact on the overall results of residual stress determination, so it is important to make it as accurate as possible. For this reason, it is necessary to have the most reliable device to form an annular groove.
Target setting. Our goal was to design the drive and control for the measuring device for milling the annular groove.
This will make it possible to mill the annular groove more precisely, and the resulting residual stresses will be minimally affected by the inaccuracy of the groove.
Actual scientific researches and issues analysis. When designing the control of the device and preparing this paper, we took into account not only current sources – publications and papers dealing with the current state of existing measuring devices used for determining residual stresses by Ring-Core method, but – we also took into account our practical experience gained in numerous residual stress determinations by experimental methods.
Uninvestigated parts of general matters defining. A modified device requires thorough testing, which has not been implemented during the research for this paper.
The research objective. The goal of the research was to create a control for the existing mechanical measuring device used for creating annular groove for determining residual stresses by Ring-Core method.
The statement of basic materials. The original mechanical device was supplemented by actuators, which were designed to automate the movement in horizontal axes as well as in the vertical axis. Thanks to this, we have achieved greater precision when positioning the work tool above the center of the strain gauge. At the same time, the original equipment was completed with a servo motor that serves to drive the cutter. For all these elements, control by Programmable Logic Controller was proposed.
Conclusions. Our task was to design control for the original device used for residual stress measurement by the RingCore method. We needed to design drives to automate the device. For our needs, we decided to apply linear actuators selected according to the requested criteria. After designing of the electric drives and modifying of the original device, we proceeded to implement control by Programmable Logic Controller. After that, we created a control program in the Automation studio software. This modified measuring device is able to achieve a much higher precision of the annular groove milling, which makes it possible to deter-mine the residual stresses in the structures more precisely