The Metal 3D Printing Technology Report: Chapter 3: Post-processing for Metal AM

Understand the Future of Metal 3D Printing

The Metal 3D Printing Technology Report is your essential guide to the latest advances, applications, and real-world insights into additive manufacturing with metal. Packed with detailed case studies,  practical information, and interviews with industry leaders, this report reveals how metal 3D printing is transforming industries and pushing the boundaries of manufacturing.

Read the intro to the report here and an excerpt from chapter 3 below. 

Metal additive manufacturing generally requires extensive post-processing to achieve fully dense, usable parts. Processes that deposit metal mixed with a binder matrix (binder jetting, extrusion) are the most dependent on post-processing to achieve desired part characteristics, since the as-printed (green) parts are not fully metal. However, all processes, including powder bed fusion and DED, require some degree of post-processing.

In this chapter, we separate metal AM post-processing into four categories: debinding and sintering, CNC machining and milling, heat treatment, and quality assurance. (Another essential process, support removal, is not included due to its relative simplicity.) The first three of the three categories are concerned with the physical alteration of the printed parts to bring about the desired shape or material characteristics, while quality assurance is concerned with inspection. Metal 3D printing workflows may use any combination of the described post-processing techniques or other workflow-specific techniques not mentioned here.

Debinding and sintering

Printed metal parts made using binder jetting or material extrusion consist of both metal and a sacrificial binder material, so the binder must be removed to create a true metal part (as with metal injection molding (MIM)) before sintering to strengthen and densify the part. Exceptions include HP’s Metal Jet binder jetting technology, whose binder decomposes during sintering and which therefore does not require debinding. Sintering results in a degree of (anisotropic) part shrinkage, which must be factored into part design.

Binder is removed from metal parts using catalytic, solvent, thermal debinding, or a combination of the three. The appropriate method generally depends on the material and its binder.

A key advantage of thermal debinding is that the same furnace can be used for debinding and sintering. A lower temperature is used for debinding (usually under 500°C) before a higher temperature is introduced for sintering (usually above 1000°C). Several 3D printer manufacturers supply debinding and sintering furnaces that can be used for post-processing of metal parts. Another advantage of thermal debinding is that furnaces can be brought in-house with relative ease. By contrast, parts that require catalytic debinding (those produced using BASF Ultrafuse filament, for example) may need to be shipped to a third-party debinding specialist.

Debinding and sintering equipment producers include:

• Desktop Metal: Introduced its PureSinter high-purity vacuum in 2024, which is capable of sintering titanium to 98% density. Compatible with binder jetting, material extrusion, and traditional techniques like MIM.

• Markforged: Supplies the Wash 1 solvent debinding station (along with a separate sintering furnace) for use with its Metal X 3D printer. Uses Opteon SF-79 solvent.

• The Virtual Foundry: Wisconsin company supplying Filamet metal filament and sintering kilns (Virtual Foundry, FireX, FireX Max) with temperatures up to 1288°C.

Heat treatment

The rapid heating and cooling of metal additive manufacturing processes produce “heterogeneous microstructures and the accumulation of internal stresses,” the effect of which can be reduced via heat treatment. Heat treatment can remove internal stresses and improve hardness and fatigue strength. Without heat treatment, 3D printed metal parts are significantly outperformed by traditionally made (machined, cast, forged) equivalents. Heat treatment can be applied to parts made using a variety of technologies, including LPBF, DED, and binder jetting.

Different heat treatment processes may suit different metals. Some of the major heat treatment processes for 3D printed metal parts are outlined in the table below. Other processes like annealing, normalizing, and precipitating hardening may also be used on certain metals.

A handful of companies specialize in the heat treatment of metal 3D printed parts, providing services or manufacturing hardware such as furnaces and presses. Most companies in this field are established and previously provided heat treatment for conventionally manufactured metal parts.

Heat treatment companies include:

• Paulo: Missouri-based heat treatment expert founded in 1943. Provides HIP and other services. 

• Quintus Technologies: High-pressure machine manufacturer based in Sweden. Supplies HIP equipment to Paulo and others.

Surface finishing

Surface finishing technologies and techniques may be used for post-processing of metal parts produced using any metal additive manufacturing technology. Surface finishing techniques include but are not limited to sanding, abrasive blasting, vibratory finishing, dry electropolishing, and CNC machining.

• Sanding: Metal 3D printed parts may be subject to manual or automated sanding to remove surface imperfections. For parts produced using binder jetting or material extrusion, sanding the green part prior to debinding and sintering can increase surface quality.

• Blasting: Abrasive media blasting is another common post-processing technique for parts produced using LPBF and other technologies. Advantages of media blasting include speed and minimal impact on part dimensions. Media may include glass beads or alumina.

• Vibratory finishing: Tumbling is used to smooth the surface of metal parts and increase hardness. It requires less manual supervision than media blasting and can produce equivalent or better results. Chemically accelerated vibratory surface finishing or superfinishing is a related low-cost process in which a chemical solution is used to coat the metal, helping to remove peaks while maintaining valleys.

• Dry electropolishing: The patented DryLyte process from DLyte uses an electrical flow to create an ion exchange that removes material only from roughness peaks, keeping edges intact and accessing hard-to-reach corners.

• Machining: CNC machining can be used to turn near-net-shape parts into final parts, achieve tighter tolerances on critical features, improve dimensional accuracy, and produce the desired surface finish. Suitable machines include 3-axis, 4-axis, and 5-axis machining (milling) centers, as well as electrical discharge machining (EDM) centers.

Quality assurance

Quality assurance is an important area of post-processing for metal parts, particularly end-use or production parts in fields like aerospace, as parts must meet regulatory standards set by relevant industrial bodies. Traditional equipment like coordinate measurement machines (CMMs) may be used to assess dimensional accuracy, while internal inspection using CT scanners and other equipment is especially important as the microstructure and porosity of printed metal parts can vary. Automated quality assurance solutions are becoming more common as manufacturers look to make additive manufacturing as efficient as possible on the production line.

Key quality assurance processes for metal 3D printing include part measurement using CMMs and non-destructive testing methods like computed tomography (CT), ultrasonic testing, and conductivity testing, which are critical for analyzing the internal structure of printed parts. Other quality assurance processes that are not technically part of the post-processing stage include in-process monitoring, material selection and testing, and statistical process control.

“One of the big advantages of designing for metal AM is topology optimization, which allows you to take advantage of minimalist designs and minimal material usage to create the strongest and lightest parts. But you often run into these organic shapes and designs that are very difficult to inspect,” explains Matt Schmidt, Senior Solutions Engineer at Xometry. “How do we know that we have accomplished everything in that print to match the performance that we dictated during the optimization process? For that, 3D scanning becomes very critical, as does high-resolution CMM for evaluating the tolerances of 3D prints. CT and x-ray scans are also very important to study part microstructure and detect any porosity, voids or gaps in parts that could result in potential failures.”

Companies providing quality assurance solutions include:

• QC Labs: Non-destructive testing service provider to additive manufacturing and CNC machining users. Uses various technologies including CT scanning, ultrasonic testing, and digital radiography.

Theta Technologies: UK company specializing in non-destructive testing equipment. Its systems use nonlinear resonance technology to detect internal flaws in metal parts.

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