Ti-6Al-4V is a material extensively used within the aerospace and biomedical industry sectors due to its low weight, good mechanical properties and excellent bio-compatibility. Conventional manufacture of Ti-6Al-4V components traditionally involves the use of large amounts of raw materials and extensive machining operations, resulting in high energy consumption and significant material wastage. SLM produced parts offer significant benefits as they are manufactured to near-net shape, using less material and requiring less post-build machining.
There is interest in understanding and validating parts produced by SLM. A major barrier to the increased adoption of the SLM process within these industries is a concern over the existence of high residual stresses within components as they are built and the increased distortion and the reduced mechanical properties that result. It is acknowledged that process parameters, scanning strategies and bed pre-heat have a major influence on the development of internal residual stresses in the SLM-built part and a greater understanding of these interactions would help to remove this barrier. It is anticipated that the market within these and other industry sectors would significantly increase once design guide lines are established which can reduce the occurrence of residual stresses. An understanding of residual stresses in SLM will assist in the transfer of knowledge into other materials
The Selective Laser Melting (SLM) process is characterised by repeated heating and cooling of successive layers of powder during component manufacture, leading to rapid cooling effects and high temperature gradients within the build. As a result, the general microstructural features of titanium alloys produced by SLM are different to those obtained by conventional manufacture. These complex thermal effects promote the development of residual stresses within parts produced by the SLM process and hence affect material properties. In general, the residual stress profile consists of two zones of large tensile stresses at the top and bottom of the part, and a large zone of compressive stress in between. Consequently, merely removing the part from the baseplate on which it is built can cause significant undesirable distortion in the built component. The research within this CRP project seeks to understand and develop methods to reduce stress development within Ti-6Al-4V components manufactured using SLM. The effects of different laser processing systems, scanning strategies and novel pre-heat conditions within the build chamber will be investigated.
The objectives of this work are:
- To assess residual stress produced during SLM processing of Ti-6Al-4V, through measurement of dimensional change and distortion of test pieces.
- To identify relationships between scanning strategy and the level of distortion in SLM test pieces.
- The development of design guidelines for Ti-6Al-4V SLM test geometry to minimise the effects of residual stress.
- The validation of the design guidelines on an SLM component.
Relevant Industry Sectors