Surface Integrity in Additive- Subtractive Manufacturing Processes
Abstract
The surface integrity of components is an important topic in any manufacturing
process. Surface integrity is defined as the surface capability of a workpiece after
being modified by a manufacturing process. Attributes of the surface integrity include,
roughness, residual stresses, and mechanical properties. These have a direct
influence on the product functionalities in terms of fatigue, fracture, corrosion resistance,
and wear. Additive Manufacturing (AM), and specifically Selective Laser
Melting (SLM) are modern manufacturing processes, capable of building 3D component
layer by layer. Although AM has the potential to revolutionize manufacturing,
little is known about the resulting structural integrity and surface condition
of AM parts. Further, future production systems will consist of hybrid-process
chain, where as an example, the capabilities of AM and subtractive processes are
combined to produce high-added value components. This thesis investigates the
resulting surface integrity of AM component from a process mechanics and microstructure
point of view, aiming to make a contribution to the understanding
of the fundamental mechanisms leading to the surface integrity of SLM of 316L
Stainless Steel and subsequently after a magnetic-abrasive polishing and burnishing
(MAP/B). Experimental investigations using advanced microstructure characterization
and physics-based modeling of residual stresses serve as the basis for
the research made herein. The thesis consists of an introductory overview detailing
the context and approach employed. Five appended papers represent the
main contribution of this thesis. Along with a literature review, the main method
of study employs advanced microstructure investigation associated with simulations,
based on analytical modeling of the residual stresses resulting from SLM.
The main contribution of this work is identifying and addressing a number of core
challenges related to the surface integrity in SLM. The reuse of recycled powder
and its influence on the component quality is investigated in the first paper. Then,
the second and third papers are addressing the analytical modeling of temperature,
thermal stresses representing a comprehensive model to predict residual stress in
SLM. The fourth paper, investigate the resulting surface integrity and specifically
the residual stresses after (MAP/B) of an AM part. Finally, the process planning
of an abrasive process to achieve desired surface behavior is investigated using a
physics-based model in the fifth paper.