thermo-mechanical model development and experimental validation for metallic parts in additive manufacturing
Open Access
- Author:
- Denlinger, Erik Robert
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 05, 2015
- Committee Members:
- Panagiotis Michaleris, Dissertation Advisor/Co-Advisor
Reuben H Kraft, Committee Member
Eric Russell Marsh, Committee Member
Allison Michelle Beese, Committee Member
Edward William Reutzel, Committee Member - Keywords:
- Additive Manufacturing
Distortion
Residual stress
Ti-6Al-4V
Inconel
FEM
Powder-bed - Abstract:
- The objective of this work is to experimentally validate thermal and mechanical finite element models of metallic parts produced using additive manufacturing (AM) processes. AM offers advantages over other manufacturing processes due the fact that it can produce net and near-net shapes directly from a digital drawing file. Parts can be produced on a layer by layer basis by melting wire or powder metal using a laser or an electron beam. The material then cools and solidifies to form a fully dense geometry. Unfortunately the large thermal gradients cause a buildup of residual stress often taking parts out of tolerance or causing failure by cracking or delamination. To successfully reduce distortion and residual stress in metallic AM parts without expensive and time consuming trial and error iterations, an experimentally validated physics based model is needed. In this work finite element (FE) models for the laser directed energy deposition (LDED), the Electron Beam Directed Manufacture (EBDM) process, and the Laser Powder-Bed Fusion (LPBF) process are developed and validated. In situ distortion and temperature measurements are taken during the LDED processing of both Ti-6Al-4V and Inconel 625. The in situ experimental results are used in addition to post-process residual stress measurements to validate a thermo-mechanical model for each alloy. The results show that each material builds distortion differently during AM processing, a previously unknown effect that must be accounted for in the model. The thermal boundary conditions in the model are then modified to allow for the modeling of the EBDM process. The EBDM model is validated against in situ temperature and distortion measurements as well as post-process residual stress measurements taken on a single bead wide Ti-6Al-4V wall build. Further model validation is provided by comparing the predicted mechanical response of a large EBDM aerospace component consisting of several thousand deposition tracks to post-process distortion measurements taken on the actual part. Several distortion mitigation techniques are also investigated using an FE model. The findings are used to reduce the maximum distortion present on the large industrial aerospace component by 91~\%. Finally, the modeling work for the LDED and the EBDM processes is extended to Laser Powder-Bed Fusion (LPBF) processing of Inconel 718. The necessary boundary conditions and material properties to include in the models are identified by comparing the model with in situ experimental results.