Spatially resolved acoustic spectroscopy for selective laser melting

Richard J Smith,Matthias Hirsch,Rikesh Patel,Wenqi Li,Adam T Clare,Steve D Sharples

doi:10.1016/j.jmatprotec.2016.05.005

Richard J Smith, Matthias Hirsch + Show 4 more

Open Access

https://doi.org/10.1016/j.jmatprotec.2016.05.005

Copy DOI

Abstract

Additive manufacturing (AM) is a manufacturing technique that typically builds parts layer by layer, for example, in the case of selective laser melted (SLM) material by fusing layers of metal powder. This allows the construction of complex geometry parts, which, in some cases cannot be made by traditional manufacturing routes. Complex parts can be difficult to inspect for material conformity and defects which are limiting widespread adoption especially in high performance arenas. Spatially resolved acoustic spectroscopy (SRAS) is a technique for material characterisation based on robustly measuring the surface acoustic wave velocity. Here the SRAS technique is applied to prepare additively manufactured material to measure the material properties and identify defects. Results are presented tracking the increase in the measured velocity with the build power of the selective laser melting machine. Surface and subsurface defect measurements (to a depth of ∼24μm) are compared to electron microscopy and X-ray computed tomography. It has been found that pore size remains the same for 140W to 190W melting power (mean: 115–119μm optical and 134–137μm velocity) but the number of pores increase significantly (70–126 optical, 95–182 velocity) with lower melting power, reducing overall material density.

Highlights

Additive manufacturing is a rapidly growing area for complex part manufacture and encompasses a wide variety of different techniques, all of which have the property of additive accumulation of material to form the part
This paper introduces an inspection method, spatially resolved acoustic spectroscopy (SRAS), which can be used for material characterisation and defect detection for additive manufacturing (AM) parts (Clark et al, 2011)
This paper demonstrates offline inspection of polished Selective laser melting (SLM) material produced with different build parameters and shows how the changing parameters affect the measured acoustic velocity

Summary

Introduction

Additive manufacturing is a rapidly growing area for complex part manufacture and encompasses a wide variety of different techniques, all of which have the property of additive accumulation of material to form the part. The layer by layer SLM process uses a laser to melt a deposited loose powder layer into a fused object that is built up by adding more layers (Kruth et al, 2005). This manufacturing approach enables the construction of high complexity parts that, in many cases, cannot be made with traditional manufacturing routes. There are limitations to this technique; the relatively low build speed compared to traditional manufacturing processes means it is currently only economical for low volume, high value, high complexity parts. Identification of defects in complex geometry parts is difficult post build and the lack of in-situ NDE methods is preventing the proliferation of this technology (Tapia and Elwany, 2014)

Methods

Results

Conclusion