Non-destructive evaluation of residual stress using the collaborative robot 

Brandon Mills

Research Problem

This research focuses on addressing the specific problem of residual stress detection, measurement, and monitoring. In many manufacturing processes, specifically welding and Wire and Arc Additive Manufacturing (WAAM), residual stress poses major problems. To give a welding example, the usage of a suboptimal clamping system during the welding process can greatly increase the residual stress and exacerbate any cracks or other defects​ [1]​. By addressing this problem, we aim to allow manufacturers to automatically monitor the residual stress during the manufacturing process and make changes to their setup in real time to relieve excessive residual stresses. This will lead to a reduction in the scrapping rate due to defects caused or worsened by residual stress and can increase a product’s overall lifespan. 

Aims and Objectives

The primary aim of this project is to explore the use of phased array probes for residual stress detection, measuring, and monitoring during and after the welding and additive manufacturing process, and additionally investigating the automation of these procedures. To achieve this, the following key objectives have been identified: 

a) Study of the advantages of using phased array probes for stress detection using the case study of wind turbine bolts 

b) Investigation into the use of Phased Array probes for a residual stress inspection of a welding sample through implementation of the Longitudinal Critically Refracted (LCR) wave technique  

c) Exploration of Phased Array probes for a residual stress inspection of a WAAM sample through implementation of the LCR wave technique 

d) Deployment of Phased Array probes and a collaborative robot for an automated residual stress inspection both WAAM and welding samples 

e) Implementation of an automated LCR, Phased Array system for high temperature and in-process residual stress monitoring applications 

Progress So Far

The following milestones have been accomplished during year 1: 

a) Demonstration of the advantages of the phased array probe for stress detection in bolts, which can be applied to residual stress measurements 

b) Created a program to specify required wedge angles and areas of interest on time of flight scan to aid in the acoustic wedge design process and increase ease of data acquisition 

c) Designed and tested a calibration block to investigate the penetration depth of an LCR wave, which will be a part of a calibration procedure whenever new acoustic wedges are designed 

d) Worked on manual LCR inspection as part of a WAAM round robin inspection with several universities and institutes, providing data and experimental experience 


[1] Y.Javadi, N.Sweeney, E.Mohseni, C.Macleod, D.Lines, M.Vasilev, Z.Qiu, C.Mineo, G.Pierce and A.Gachagan, “Investigating the effect of residual stress on hydrogen cracking in multi-pass robotic welding through process compatible non-destructive testing,” Journal of Manufacturing Processes, pp. 80-87, 2021.  

A close-up of a piece of metal

Description automatically generated with low confidence

Figure 1: Inspection of a welded steel plate using a wedge designed for the LCR method and using two 20-element phased  

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