Thesis-2013-Bochuan Liu.pdf (8.7 MB)
Further process understanding and prediction on selective laser melting of stainless steel 316L
thesis
posted on 2013-11-13, 11:23 authored by Bochuan LiuAdditive Manufacturing (AM) is a group of manufacturing technologies which
are capable to produce 3D solid parts by adding successive layers of
material. Parts are fabricated in an additive manner, layer by layer; and the
geometric data can be taken from a CAD model directly. The main
revolutionary aspect of AM is the ability of quickly producing complex
geometries without the need of tooling, allowing for greater design freedom.
As one of AM methods, Selective Laser Melting (SLM) is a process for
producing metal parts with minimal subtractive post-processing required. It
relies on the generation and distribution of laser generated heat to raise the
temperature of a region of a powder bed to above the melting point. Due to
high energy input to enable full melting of the powder bed materials, SLM is
able to build fully dense metal parts without post heat treatment and other
processing.
Successful fabrications of parts by SLM require a comprehensive
understanding of the main process controlling parameters such as energy
input, powder bed properties and build conditions, as well as the
microstructure formation procedure as it can strongly affect the final
mechanical properties. It is valuable to control the parts’ microstructure
through controlling the process parameters to obtain acceptable mechanical
properties for end-users. In the SLM process, microstructure characterisation
strongly depends on the thermal history of the process. The temperature
distribution in the building area can significantly influence the melting pool
behaviour, solidification process and thermal mechanical properties of the
parts. Therefore, it is important to have an accurate prediction of the
temperature distribution history during the process.
The aim of this research is to gain a better understanding of process control
parameters in SLM process, and to develop a modelling methodology for the
prediction of microstructure forming procedure. The research is comprised of
an experiment and a finite element modelling part.
Experimentation was carried out to understand the effect of each processing
control parameters on the final part quality, and characterise the model
inputs. Laser energy input, build conditions and powder bed properties were
investigated. Samples were built and tested to gain the knowledge of the
relationship between samples’ density and mechanical properties and each
process control factor. Heat transfer model inputs characterisation, such as
defining and measuring the material properties, input loads and boundary
conditions were also carried out via experiment.
For the predictive modelling of microstructure, a methodology for predicting
the temperature distribution history and temperature gradient history during
the SLM process has been developed. Moving heat source and states
variable material properties were studied and applied to the heat transfer
model for reliable prediction. Multi-layers model were established to simulate
the layer by layer process principles. Microstructure was predicted by
simulated melting pool behaviour and the history of three dimensional
temperature distribution and temperature gradient distribution. They were
validated by relevant experiment examination and measurement.
Funding
Loughborough University
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© Bochuan LiuPublication date
2013Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en