Additive manufacturing (also known as AM or industrial 3D printing) is becoming more widely adopted by manufacturers, especially in the aerospace and medical markets. Instead of stripping material away from a workpiece, in additive manufacturing, a CAD or 3D scanner directs the machine to add layers of metal material on top of each other, with each layer bonding to the preceding one. This bonding can be achieved using one of two methods: laser powder bed fusion (LPBF), which uses heat to fuse the layers; or binder jetting, which uses a binding agent (adhesive) between each layer of material that is subsequently burned off during secondary processing.
One of the main advantages of additive manufacturing is the ability to produce parts with complex geometries that can’t be achieved by traditional methods such as milling, turning, or casting. However, the nature of AM parts creates a few unique challenges that are important to consider for thermal processing.
Heat Treating for Additive Manufactured Parts
Some specifications for heat treating of AM parts exist, but since it is a relatively new method of manufacturing, standards are still being developed as AM becomes more widely adopted. The opportunities in the AM market have also attracted many entrepreneurs who are new to the manufacturing world. These factors often lead to manufacturers running into unexpected challenges when it comes to thermal processing for their AM components. Here are a few common challenges and how an experienced partner like Paulo can help you overcome them.
Distortion in AM Parts
We mentioned that AM can allow manufacturers to produce highly intricate, complex parts with tight tolerances that aren’t possible with traditional machining. While specialized processes can minimize the distortion that occurs during treatment (gas quenching, for example), a small amount of distortion will always result from thermal processing.
First, it’s important to select a heat treating partner that has precise process controls and can demonstrate the data that your parts run according to specifications. If you’re already confident in the accuracy of your parts’ heat treatment, then adjustments to the initial part design may be the next place to look.
The risks of distortion can be mitigated by precise adjustments to the part’s initial design to yield a geometry in the treated piece that will fit in the application. Paulo’s engineering and metallurgy team often advises our customers on these types of issues to ensure great results in each finished part.
Microstructure Challenges—Solidification and Resolidification of Each Layer
In laser powder bed fusion (LPBF), solidification and resolidification of each layer as the part is printed leads to a phenomenon called microsegregation. In this condition, the AM process itself creates a series of microscopic melt pools (essentially weld pools) throughout the part’s interior structure.
Although this can be advantageous by keeping the part’s microstructure very fine, those microscopic melt pools throughout can present segregation issues within the material, with particles separating into distinct zones and affecting the part’s overall structure.
This phenomenon can actually work in your favor, since homogenization of the microstructure can happen more rapidly in some AM parts, which reduces hold times during heat treatment. The key takeaway is that it’s important to select a heat treating partner who understands the nature of AM parts so that processes can be adjusted to yield optimal results.
Materials may or may not respond to heat treatment the same way when a part is produced through traditional processes versus when produced with AM.
For example, it’s difficult to 3D print pieces using materials containing high amounts of carbon, such as many steels. Carbon leads to issues in the microscopic resolidification that occurs in the AM process. It can affect expansion, contraction, shrinkage, and localized stresses, causing pieces 3D printed with high carbon material to have cracking issues once completed.
While carbon greatly complicates 3D printing, it is essential in many heat treatment processes. Still, many AM materials have been used in conventional manufacturing applications for years. To learn more about materials commonly used in additive manufacturing, visit our AM page.
Porosity Challenges and a HIP Solution
Yet another challenge that comes along with AM is porosity in the final part. Although welds and castings can develop porosity, in AM it’s a bit different, with elongated bubbles, for example, that conventional heat treatment doesn’t fully affect.
One proven method of eliminating porosity and voids in an AM-produced part is Hot Isostatic Pressing (HIP). HIP has become widely adopted and recognized as a best practice in secondary processing for additive manufacturing. Initially developed as a diffusion bonding technique where high heat and pressure work together to weld similar or dissimilar metal surfaces without filler materials, HIP eliminates porosity—the small bubbles of gas that can form during the solidification process of metals—and impart a homogenous grain structure throughout the whole part.
HIP is also ideal for the complex shapes many AM-produced parts feature. The pressurized gas used in HIP is driven into internal passages and blind features of complex parts, ensuring they achieve specified metallurgical characteristics while retaining their desired tolerance.
Questions About Heat Treating AM-Produced Parts?
Paulo has the metallurgical expertise and equipment capabilities to guide you regarding heat treating your AM-produced parts. Maintaining technology at the leading edge of heat treatment and modern materials, we can help you navigate and solve the new and complex areas of treating 3D printed parts.
To connect with a Paulo expert to discuss your heat treating needs for AM parts or request a quote, contact us.