The powder chain goes hand-in-hand with the AM processing chain. It is a reciprocal and interdependent relationship whereby powder properties impact on the processing characteristics (spreading, melting…) and where, in return, the processing steps and efficiency affect the powder characteristics.
This close intertwined relationship complicate the control of the AM process and can dramatically influence the final components properties or the recyclability efficiency of the powder.
So how do you prevent powder contamination or properties variations?
Where in the manufacturing chain can powder contamination occur? Can you prevent it?
1. Procure the right powder
2. Receive (and test) it, store it, handle it, load it in the machine
3. Process it properly/efficiently
Efficient processing means that you endeavour to produce components with suitable properties AND calibrate the processing parameters for maximum powder longevity/reusability.
I know! I know! As if finding suitable parameters to meet the host of requirements wasn’t enough, you’ll say! Manufacturing speed for commercial viability, mechanical properties, surface roughness, production yield, density... the list goes on!
Processing is tricky enough without adding any more stringent requirements, right?
Think again. This one could actually make your life easier in the long run!
But first, how do you maximise powder longevity , or minimise feedstock contamination, during processing?
Key contaminants generated during machining results from spatter formation. Spatter, fumes/condensate will deposit over the un-melted particles and contribute to change its properties. Elimination spatter formation and you’ll get rid of the by-products of inefficient processing.
This actually compounds to make your life easier: working in pure melting mode - although it may be slower - provides you with more control over the process. Without spatter, you could arguably get rid of the laminar gas flow in your machine (its sole purpose is to 'brush' away the spatter and fumes out of the beam path) and you won’t unnecessarily contaminate the remaining un-melted powder with spatter and condensate (the black soot that coats the walls of the build chamber and ends up everywhere). Hence in a perfect world, you could actually get rid of the recycling step altogether, avoid powder waste and increase powder recyclability.
4. Unload and recycle [sieve] it properly
- monitoring the variation in powder and particles properties (PSD, particles morphology, chemical pick up,…) and ensuring this can be rectified to match the properties of the original powder;
- using metrology techniques that are quick and efficient.
 W.J. Sames, F. Medina, W.H. Peter S.S. Babu and R.R. Dehoff, EFFECT OF PROCESS CONTROL AND POWDER QUALITY ON INCONEL 718 PRODUCED USING ELECTRON BEAM MELTING, 8th International Symposium on Superalloy 718 and Derivatives,TMS (The Minerals, Metals & Materials Society), 2014