SUNConferences, 17th Annual Conference of the Rapid Product Development Association of South Africa

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Micro-Scale Residual Stress Analysis of SLM Manufacture Ti-6Al-4V
Lucas Anderson, Thorsten Becker

Last modified: 2016-10-04

Abstract


A major problem in SLM manufacturing is the high residual stress that is present in the components in their as-built form. This high internal stress can cause parts to warp or crack when they are released from the build platform, which is far from ideal in terms of part wastage and manufacturing precision. Research has been conducted into the residual stress found in SLM manufactured Ti-6Al-4V at the component level, however no research exists on the residual stress present at the micro-scale level and how this stress affects the component as a whole. This project aims to fill that gap in literature by conducting an investigation into the residual stress profiles through the depth of individual build layers and how this affects the residual stress present in the part as a whole as well as how various build parameters affect the development of residual stress. This project also aims to identify how changes in build parameters affect the residual stress present in components at a small scale.

The methodology that will be used in order to measure the residual stress at the micro-scale will be adapted from techniques used to measure micro-scale residual stress in thin metallic films, whereby digital image correlation (DIC) is used in conjunction with focused ion beam (FIB) milling. The method works with the same principle as strain relaxation techniques used on the macro-scale, whereby material is removed and the strain relaxation in the area of the material removal is measured in order to calculate the stress present in that area. The three methods identified for testing are the micro-hole drilling method, micro-slot milling method and incremental micro-ring core milling method. Each of these methods has its benefits and its drawbacks and used in conjunction should provide a comprehensive image of the micro-scale residual stress present in the test samples. A major problem with using DIC in conjunction with FIB milling is the damage that occurs to the surface features during milling in terms of material re-deposition and ion implantation. This problem affects the results obtained through the micro-hole drilling method most significantly and has been observed in preliminary methodology tests that have been conducted.

Further testing will be conducted using the neutron diffraction method in order to corroborate the results obtained from the strain relaxation methods and add to the bigger picture of the residual stress.

Keywords


FIB; DIC; residual stress; neutron diffraction