Feature from the May/June 2022 issue of 3D ADEPT Mag, posted online in September 2022. Examples and product offerings reflect that period.
With a focus on additively manufactured medical devices.
Depowdering is an important post-processing step for powder-bed parts. Users need a controlled, repeatable process suited to their geometries. Automation can reduce some handling, but machine selection should start with part, material and final inspection requirements. Which functions should be assessed?
Before heat treatment, residual metal powder can bond to surfaces or inside channels and become difficult to remove. Depending on material, cycle and geometry, this can compromise a part. Depowdering should therefore be assessed at the appropriate process stage, particularly for medical parts and critical applications.
These difficulties concern access design, part motion, powder recovery and evidence of the result. Our analysis of metal powder removal discusses several constraints. Quality, occupational health and final-device compliance require complementary assessments.
Powder exposure can occur when depowdering laser powder bed fusion parts. NIOSH describes inhalation, skin-contact and fire or explosion risks. Controls depend on material and installation: containment, suitable extraction, procedures, training and risk assessment need consideration together. An automated machine alone does not demonstrate safety.
So, what are the technical features that will enable a powder removal machine to do the job well?
The first thing that one should understand here is that powder removal can be a very meticulous task, and when carried out manually, it can involve multiple steps to continuously check and inspect the part.
Automation can improve motion consistency and parameter traceability. It supports process control but does not, by itself, validate the process.
For medical devices, acceptance criteria and assessment methods need definition for intended use and relevant geometries. Operational repeatability is one part of that evidence.
A defined cycle requires verification, monitoring and maintenance. A change in material, geometry or settings may require reassessment; repeating the same program does not guarantee the same result indefinitely.
Equipment should allow suitable depowdering strategies, recording of relevant parameters and verification of results. Motion paths, vibration, duration and tools need to match the parts being processed.
An enclosed chamber and suitable powder handling can limit some exposure. An inert atmosphere may be required for a material and configuration; it does not remove every risk. Gas selection, atmosphere monitoring and personnel protection should follow installation risk assessment and manufacturer instructions.
Mass monitoring can support depowdering checks through successive measurements or comparison with expected mass. It does not alone prove that channels contain no residue: balance precision, supports, tolerances and part variability need consideration.
Motion and fixturing flexibility should match the intended geometries. Equipment may use multiple axes without a robotic arm. Additional tools or robotics are options to justify against the application, not universal requirements.
Channels and lattices need routes for powder to leave. A path calculated from CAD can help, but effectiveness needs checking on the actual part. Tools or jets must be compatible with delicate structures and containment; overly energetic treatment can damage fine features.
The table groups functions discussed in this 2022 feature. It helps compare application needs with equipment capability, without making every option mandatory.
| Function to assess | Scope and considerations |
|---|---|
| Table dimensions | Compatibility with part, supports, mass and fixturing. |
| Vibration | Suitable frequency and amplitude; check the result and part integrity. |
| Large-part access | Suitable loading and handling, using a crane or robot where needed. |
| Rotation | Orientations that allow powder to exit, validated for channels and supports. |
| Inert atmosphere | Where required: compatible gas, atmosphere control and risk assessment; no absolute guarantee against explosion. |
| Programming and traceability | Record cycles and verify repeatability; control changes. |
| Extraction and filtration | Distinct from air or gas jets, which can disperse powder. |
| Gloves and blow-off tools | Contained intervention compatible with powder, part and equipment. |
| Electrostatic control | Devices compatible with the installation; an ionisation unit is not suitable for every environment. |
| Cyclone | Particle separation from a flow; does not necessarily replace suitable filtration. |
| Enclosed collection | Controlled collection and removal of dust, suited to the material. |
Needless to say that each application is unique, and may therefore have its own requirements; which is why we recommend to look at the ins- and outs of your project: the environment, the appropriate equipment and even the final purpose after the removal of powders.
What about savings?
The question of savings increasingly becomes of paramount importance in a context of sustainability. This raises several other considerations regarding production, purchase, and the viability of the powder that we have addressed in a previous feature.
Savings depend on processing time, manual work avoided and rejects actually reduced. Scrap-part value varies widely and cannot be treated as a guaranteed saving. Investment, energy, gases, maintenance, inspection and waste management also belong in the calculation.
For a medical part, controlled depowdering can reduce residue and problems in later operations. Powder removal, cleanliness, biocompatibility and sterilisation must nevertheless be distinguished. The FDA’s 2017 technical guidance discusses cleaning challenges in complex geometries: no visible powder does not prove device sterility.
Concluding thoughts
The 2022 International Catalogue of AM Solutions provides a historical view of the offerings cited. It does not replace project assessment: a strategy effective for one part may not suit another.
The most important consideration has to be whether it makes sense or not to employ these solutions, since using automation for some parts may just be overkill, and may end up providing no real benefit to the business.
The ASTM F3335-20 guide cited here concerns residue assessment in powder-bed-fused medical devices. It does not provide universal acceptance limits or a complete occupational safety procedure. Biological evaluation should use the applicable parts of ISO 10993 and the device’s intended use.
This feature was first published in the May/June 2022 issue of 3D ADEPT Mag.
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