The additive-manufacturing (AM) process as a whole involves turning 3-D CAD files on computers into finished products layer by layer –although AM specifically relates to the construction part of that process. What happens after the printing phase has concluded also matters, however, in order to ensure that products are ready for use. And the steps leading up to AM also need to be considered.

This article will look at the preparation, process and postscript to 3D-printing operations, with specific reference to how technicians can manipulate materials to minimize defects and maximize accuracy.

Recent testing has provided some essential information regarding post-printing treatments, specifically the role that vacuum heat treating plays in minimizing contamination and ensuring that components perform properly. But before we look at the research, it’s important to be clear about how the findings relate to broader 3D-printing techniques.

 

SLM Printing – Understanding Atmospheric Conditions

This article will generally discuss selective laser melting (SLM) technologies. SLM is a powder-bed-based manufacturing process that forms the basis for most 3D printing, so it’s likely to be relevant to many industrial operations.

When executing an SLM process, it is vital to tightly protect the materials being used. The atmosphere that surrounds powders used to create printing materials is all-important, determining whether defects and impurities develop. Done wrongly, SLM can lead to oxidization of the powder, which alters its melting point and warps the heat-treatment process during molding. So, before printing, attention must be paid to ensuring that atmospheric conditions are closely controlled.

 

Why Atmospheric Control is Essential in Printing Operations

Let’s assume that optimal conditions have been met, and printing powders have been created with the appropriate chemical makeup and minimal oxidization. Next comes the process of printing itself, and we again see the need for closely calibrated atmospheric conditions.

Atmospheric control is crucial when printing via SLM. When heat is applied to powders, the process is akin to continuous welding, where inert gases such as argon or helium are employed to ensure that oxygen does not contaminate the process. In SLM printing, the chamber interface should be inert and isolated from the molten pool. Even tiny amounts of oxygen can result in impurities, however, changing the colors and physical properties of finished products.

Both are situations that manufacturers need to avoid. But there are other considerations to factor in when guaranteeing the mechanical properties of components of other 3D-printed items, and these relate to the post-printing phase.

 

Post-printing: Using Heat Treatment to Ensure Mechanical Strength

When an item has been 3D printed via SLM-style processes, it is almost always advisable to apply a heat treatment to conclude the operation. There are a couple of good reasons for doing so.

  • First, heat treatment can have de-tensioning effects. During the printing phase, materials can accumulate internal stresses and tensions, which compromise mechanical properties – weaknesses that heat treatment can reverse.
  • Second, heat treatment can be used to optimize the properties of printed products, adding extra features such as heat resistance or tensile strength.

 

Vacuum Heat Treating Emerges as the Optimal Post-Printing Solution

But how is heat treatment carried out following AM procedures? Most commonly, heat is applied in the open air or controlled chambers. These may or may not involve vacuum containment. In experiments carried out by TAV VACUUM FURNACES on titanium superalloys, stainless steel, cobalt-chrome and nickel superalloys, however, it was found that vacuum conditions offer the best performance for post-printing heat treatment. 

Figures 1-8 show TAV’s vacuum furnaces and metal samples before and after heat treatment in vacuum furnaces. Derived from materials used by TAV’s clients, all of the results were verified by academic experts. The results should be illuminating for any manufacturer that relies on 3D-printed technologies.

 

Lessons for 3D-Printing Operations: Vacuum Conditions Matter

Several key takeaways emerged from TAV’s laboratory tests on SLM-printed materials, but the core lesson was that vacuum chambers tend to produce improved heat-treatment results no matter what materials are involved.

The use of vacuum minimizes the degree of surface contamination detected following 3D printing, improving the physical performance of components. It also enables technicians to carry out accurate, easily repeatable corrosion tests on printed components. And vacuum treatment can also have aesthetic benefits for printed components. Experiments found that surface flaws on components could be ameliorated via treatment, lending products a brighter appearance.

All of these benefits put together represent a significant set of advantages for vacuum-based heat treatment. And they should be of particular interest to manufacturers in demanding sectors such as aviation, automotive manufacturing or medical technology. Companies must adhere to very strict regulations and standards in these sectors, so it makes sense to use printing and post-printing methods that offer the highest level of accuracy. 

Overall, TAV’s testing suggests that any manufacturers using SLM-based techniques should investigate vacuum heat treatment, and it should become a mandatory part of the additive-manufacturing process in the future. 


For more information: Contact Alessandro Fiorese, chief engineer, TAV VACUUM FURNACES SPA, Via dell’industria 11- 24043 Caravaggio (BG) - ITALY; tel: +39 0363 355711; e-mail: info@tav-vacuumfurnaces.com; web: www.tav-vacuumfurnaces.com. In the U.S.: FURNACARE Inc., a TAV GROUP company, 100 Corporate Dr Ste A, Spartanburg, S.C. 29303; e-mail: info@furna.care; web: www.furna.care