Post-processing in metal 3D printing

1. Introduction: The blind spot of additive manufacturing

When people talk about 3D printing, the focus is almost always on the printing process itself: the powder bed, the lasers and the build rate. But the reality of production is different: Post-processing often accounts for 40 to 60 percent of the total costs of an additively manufactured metal component.

If you want to economically transfer metal 3D printing to series production, you have to plan the process chain after printing just as meticulously as the component design.

2. Depowdering

After printing is complete, the component is completely buried in loose metal powder. This powder is expensive (often over 100 euros/kg) and almost 100% has to be recovered.

• Challenge: Especially with complex, internal cooling channels or bionic lattice structures, the powder often easily cakes ("sintering") or gets stuck mechanically.
• Solution: Modern depowder removal systems (e.g. Solukon) clamp the entire component including the construction platform. Through multi-axis rotation coupled with variable vibration frequencies (often supported by ultrasound or pneumatic knockers), the powder trickles out of even the finest capillaries.

3. Heat treatment (stress relieving)

The laser-based melting process creates enormous temperature gradients. The liquid melt pool solidifies in milliseconds on the colder layer below. This leads to extreme internal stresses in the component.

• Why before cutting it off? If you were to saw the component immediately from the solid construction platform, it would warp like a bimetal or, in the worst case, tear open.
• The process: The component is pushed (still on the platform) into a vacuum or inert gas furnace and, depending on the alloy, heated to 500 °C to 900 °C and slowly cooled. Only then is the structure relaxed.
• Special case of HIP: With Hot Isostatic Pressing (HIP), the component is compressed under extremely high pressure (argon gas, >1000 bar) and heat. This eliminates even microscopic pores 100% and is often mandatory in the aerospace industry.

4. Separating and removing the supporting structures

Support structures not only serve to support overhangs, but above all to weld the component to the ground and to dissipate the process heat into the construction platform.

• Cutting off: This is usually done using band saws or wire erosion (EDM). Eroding is more expensive, but leaves a perfect, flat surface.
• Support removal: This is often real manual work with pliers and cutters. The key here is DfAM (Design for Additive Manufacturing): design the component in such a way that it does not need any supports in the first place (e.g. teardrop shapes instead of flat overhangs). Alternatively, 5-axis CNC milling machines are used to automatically rough away the supports.

5. Surface finish and refinement

The surface of a powder-bed printed component is naturally rough (Ra 5 - 15 µm), as powder particles bake on the outer skin.

• Vibration grinding (trowalizing): The component is placed in a vibrating drum with grinding particles (chips). This smoothes the edges and surfaces very cost-effectively.
• Electropolishing / plasma polishing: Microscopic peaks of the rough surface are specifically removed in an electrolytic bath. Ideal for complex geometries and internal channels.
• CNC machining: Functional surfaces (bearing seats, threads, sealing surfaces) require a tolerance and smoothness that 3D printing cannot provide. These areas are always printed with an allowance (0.5 - 1 mm extra material) and then precisely CNC milled or turned at the end.

6. Conclusion: The integration of the process chain

Metal 3D printing is not a “plug and play” technology. The cost-effectiveness of a component is largely determined by the question: “How much manual work do I have to put into the component after printing?”. Automated post-processing cells and clever, support-minimizing design are the levers to massively reduce the costs per part.