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Overhangs Without Supports in Metal Additive Manufacturing: Benchmarking Capabilities of EBM and SLM

Explore the challenges of overhangs in metal additive manufacturing, compare EBM and SLM technologies, and discover methods to reduce stress and warpage in parts.

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Overhangs Without Supports in Metal Additive Manufacturing: Benchmarking Capabilities of EBM and SLM

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  1. Solid Freeform Fabrication Symposium 2012 Benchmarking capabilities of SLM and EBM to build overhangs without supports Pratik Vora Advanced Additive Manufacturing Group, The University of Sheffield

  2. Prof N. Hopkinson Prof I.Todd Dr K. Mumtaz Dr C. Majewski (Head of Group) AM at Sheffield Metal powder bed processes Polymer powder bed processes Dr P. Smith Dr F. Claeyssens Dr M. Gilbert Prof. R. Van Noort Design optimisation Dental applications Photo curing processes Other Activities Advanced Additive Manufacturing

  3. AM at Sheffield Mechanical Engineering Department 3D Systems SLS Formiga High Speed Sintering Object Eden 260V MicroFab Jetlab Materials Department Arcam EBM S12 Arcam EBM A2 Arcam EBM A2 Renishaw SLM 125 Optomec Aerosol Jet Dental School Object Printer V Flash

  4. 1) Requirement for supports in metal AM (powder Bed) - Powder Bed Metal Additive Manufacturing - Why Parts Warp, what size of overhang can be built? 2) EBM/SLM Overhang Experiments - EBM/SLM Technologies - Part Design/Warp Measurement 3) Reducing the Development of Stress within a Build - Heated Platforms - Novel methods (Anchorless Selective Laser Melting) Overview

  5. Most widely and extensively used AM process for the production of metal parts Metal AM (Powder Bed) • Uses thermal energy (laser or electron beam) to selectively fuse/melt regions of a powder bed • Produces high density fully functional parts in one step • Good material variety and part properties

  6. Requirement for supports Some geometries require support/anchors due to thermal warpage Rapid heating/melting and cooling/solidification Large thermal variations Stresses/warpage Limits geometric freedom, Incurs post processing and cost for anchor removal

  7. Requirement for supports Warpage 10mm 10mm Metal Anchors/Supports 7

  8. What size overhang? - Warping is a well known phenomenon in powder bed processes - What size unsupported overhang can be built using EBM and SLM processes? - Is one process better than the other at producing overhangs? - How can stresses be reduced?

  9. EBM S12 (Arcam) SLM 125 (Renishaw) EBM/SLM Overhang Expt. Laser Beam Inert atmosphere Powder bed pre-heating (<140◦C) Electron Beam Operates in vacuum Powder bed pre-heating (~750◦C)

  10. z x Test Part Design Thickness 0.5mm-3mm Overhang length 1mm-15mm

  11. Warp Measurement Data points • Warp Height • Warp Length L

  12. EBM Overhang Ti6Al4V 0.5mm thickness 1mm thickness Parameters • Beam Current: 10-15mA • Preheating Temp- 750ºC • Layer thickness: 70µm • Beam Speed: 500m/s 2mm thickness 3mm thickness

  13. EBM Effect of Thickness

  14. EBM Warp Height 15mm overhang 10mm overhang 5mm overhang

  15. z x SLM Overhang 3mm thickness 0.5mm thickness 1mm thickness 2mm thickness AlSi12 Parameters • Laser Power: 200W • Preheating Temp: 25/140ºC • Beam Speed: 300m/s • Layer Thickness: 50µm 140ºC Bed Temperature 0.5mm thickness 1mm thickness 2mm thickness 3mm thickness 25ºCBed Temperature

  16. EBM/SLM capabilities EBM and SLM were only capable of building 2mm overhangs unsupported without warpage. Thicker structures develop more stress leading to increased warpage/geometric distortion SLM: Preheating of 140ºC did not show improvement.

  17. Stress Reduction, how? • Warpage is clearly an issue for large overhanging geometries in both EBM and SLM processes. • How to reduce stress and remove requirement for supports • Reducing thermal gradient in powder bed. • Better understanding of processing parameters to reduce residual stress.

  18. Stress Reduction, how? Mechanical Testing Custom Designed Heated Platform, Developed with Renishaw Renishaw SLM 125 Heated Powder Bed Hot Bed Bench Testing

  19. Stress Reduction, how? Conventional SLM Novel Methods: Anchorless Selective Laser Melting (ASLM) +Heated powder bed ASLM (patented method) Eutectic Material Composition

  20. ASLM Atomic Percent Silicon 1414 ºC Al melts at 660°C Si melts at 1414°C Liquid Temperature, ºC Forms eutectic at Al 88%Wt. & Si 12%Wt. Eutectic solidification temperature 577°C 660.45ºC 577 ºC 12% Si Al Weight % Silicon Si Eutectic Hypo Hyper * Source: ASM Handbook

  21. Bed temp T ASLM Stage 1 Stage 2 Stage 3 Heated powder bed, mix of un-alloyed powders A & B Laser melts metal A & B forming a new eutectic (or hypo/hyper eutectic) alloy Bed temperature held at temperature T. Processed material cools uniformly Alloy of metal A & B formed Powder A & B remain solid Formed alloy held at elevated temperature in a stress reduced state Bed temp T Bed temp T Z (mix of metal A & metal B) (mix of metal A & metal B) (mix of metal A & metal B) X

  22. ASLM Low Melt Materials ASLM Component, BiZn Eutectic Alloy

  23. ASLM Mid Temp Materials Aluminium casting alloys Binary Phase Diagram Split alloy into 2 powders Thermodynamic Modelling Processing Window: = 600 – 500 = 100oC

  24. Summary • Already known that certain overhanging geometries require supports when built using EBM/SLM • Initial findings indicate overhangs greater than 2mm cannot be built (warp free) using EBM/SLM • Stress reduction can be achieved by a combination of powder bed pre-heating and eutectic material selection

  25. Thank you for listening Acknowledgments Renishaw PLC LPW Ltd

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