Introduction
Sandra S. Poelsma , Wessel W. Wits , Marc B. Hoppenbrouwers , Henk A. Buining , Greg R. Hayes
University of Twente, Faculty of Engineering technology, Enschede, The Netherlands
TNO, Eindhoven, The Netherlands
Scan strategies
Selective Laser Melting uses a high power laser to selectively melt metal powder and thereby creating a 3D printed product layer by layer. Reduction of residual stress and deformations in SLM produced parts is essential, to increase the loading capabilities.
Inspiration for scan patterns out of the welding industry.
Scan strategy influences temperature gradient across the material.
Scanning parameters of interest for numerical model: Scan vector length, scan vector orientation, sequence of scanning the islands.
Residual stress
If the stress is too high, part delamination or breaking off the base plate can occur.
A high temperature gradient occurs due to fast movement of the laser and high solidification rate of the material.
The result of high temperature gradients accros the material is a high residual stress.
On-going work
Experimental validation of numerical model, by printing 3D metal parts with selective laser melting.
Numerical analysis
REDUCING RESIDUAL STRESS BY ADAPTIVE
SCANNING STRATEGIES IN SLM PRODUCED PARTS
Island scan strategy [3] Welding patterns [2] Contact information: Sandra S. Poelsma, BSc s.s.poelsma@student.utwente.nl Delamination of parts [1] 1 2 2 2 2 1 1
[1] - K. Kempen, L. Thijs, B. Vrancken, S. Buls, J. Van Humbeeck and J.P. Kruth, ’Lowering thermal gradients in selective laser melting by pre-heating the baseplate’, Department of Mechanical Engineering, University of Leuven, Belgium [2] - L. Jeffus, ‚’Welding principles and applications’, Delmar , 2012
[3] - L.N. Carter, C. Martin, P. J. Withers and M.M. Attallah, ’The influence of the laser scan strategy on grain structure and cracking behaviour in SLM powder-bed fabricated nickel super alloy’, Journal of Alloys and Compounds, volume 615, 338-347, 2014
[4] - J.P. Kruth, J. Deckers, E. Yasa and R. Wauthlé, ’Assesing and comparing influencing factors of residual stresses in selective laser melting using a novel analysis method’, Proceedings of the instituion of Mechanical Engineers, Part B: Journal of Engineering Manufactur, 226(6): 980-991, 2012
Assumptions:
o Absorption of laser power and melting of material are not
considered.
o Considering only macro residual stresses.
o Movement of laser is descritized.
A 3D coupled reduced transient Thermal Mechanical model of one layer. Total dimensions: 300 μm x 300 μm x 50 μm.
Boundary conditions:
T = 1600 C T = 200 C
Heat loss modelled as:
o Conduction to the base plate o Convection/radiation to
environment
Displacement on the underside of the powderbed is restricted in all directions.
Input
- Material properties (T).
- Scan vector length, 1 - 20 mm.
Case: scan vector length = 1 mm
0.75
Cooled down
Deformation Stress (Pa) Temperature (C)
Time(s)
initBlock o
o
preh
Deformation Stress (Pa) Temperature (C)
Time(s) 0.0115
After scanning
