Heat Treating for Additive Manufacturing
Quality Processing for Additive Manufacturing
Paulo provides heat treating and hot isostatic pressing for additive manufacturers in the aerospace, medical, tool & die, and automotive markets. Whether you’re an additive expert with parts in full production or just starting out, our engineering and metallurgy teams have the knowledge to make thermal processing for your programs run smoothly.
Microstructure Anomalies
Atmosphere control during the 3D printing process is critical to yielding quality parts. Absent proper atmosphere control, oxidation can occur in the powders, which can alter the melting point of the materials and lead to inconsistent or inaccurate heat treatment results. However, for parts that have undergone accurate printing, some porosity often remains. Heat treatment and hot isostatic pressing can reduce or eliminate these pores.
Microstructure Homogenization
In wrought parts and weldings, the melt pool undergoes solidification only once as the part cools. In additively manufactured parts, as layers of material are applied, the part is essentially being welded and re-welded on a microscopic scale. Once the AM part is finished, it contains a mural of weld pools, which can be advantageous for creating a fine microstructure that keeps the alloying elements spread out. AM parts are often faster to homogenize during heat treatment, which can reduce hold times.
Tight Tolerances for Complex Geometries
Complex geometries that cannot be achieved by conventional machining are often made possible by additive manufacturing, which is a distinct advantage for parts in the aerospace and medical markets. Precise, repeatable heat treatment and/or hot isostatic pressing ensures that the tight tolerances of these complex components are preserved during processing. Proper fixturing during heat treatment is also essential, and our engineering team can help you determine the best configuration for your parts.
Distortion and Part Design
In addition to optimized fixturing during heat treatment, part design also plays a key role in combating the effects of distortion. While accurate heat treatment and/or hot isostatic pressing minimizes distortion, some distortion is to be expected during processing. If you’ve been facing challenges with distortion in your AM parts, our team can work with you to ensure your initial part design is optimized to accommodate for distortion during heat treatment.
Additively Manufactured Components We Process
- Engine components
- Tensile bar specimens
- Hydraulic housings
- Flow straighteners
- Rolling cutter bits
- Fixed cutter bits
- Brackets
- Nozzles
- Heat exchangers
- Aluminum components
- Rocket booster engine cones
- Volutes
Additive Manufacturing Techniques
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Laser Powder Bed Fusion (LPBF)
Also known as selective laser melting (SLM) or direct metal laser melting, LPBF processes are replacing traditional casting methods for many applications. LPBF begins with a 3D CAD model of the part which is “sliced” into several layers. Powdered metal material is spread over each layer and bonded on top of the previous layer using a laser as a heat source.
Binder Jetting
The binder jetting method of additive manufacturing can be used with a variety of materials, including plastic and sand in addition to metals. Instead of using a laser as a heat source to adhere the powder metal layers to each other, a printhead precisely jets a binding agent on top of the powdered layer, and then the subsequent layer of powder is applied. Some metal components produced using binder jetting are placed in a sintering furnace after creation to burn off the binder. Hot isostatic pressing is then often applied to these components to reduce the porosity that the “burn-off” method creates, enhancing the overall density of the end part.
Heat Treatment and Thermal Processes for Additively Manufactured Components
Vacuum Heat Treating, Annealing, and Stress Relieving
Materials accumulate internal stresses during the 3D printing process which can compromise the mechanical properties of the parts. Vacuum annealing and stress relieving resolve these issues, eliminating the stress concentrations within parts so they are less prone to cracking during service or subsequent processing. Due to the controlled atmosphere, vacuum heat treating also minimizes surface contamination and lends a brighter appearance to parts.
Gas Quenching
The speed and method of quenching for additively manufactured parts are determined by the material and the desired hardness that results from the process. For example, nickel-based alloys generally require a harder quench to achieve the desired hardness. In addition, many specialty alloys specify controlled cooling rates which we achieve through furnace control and monitoring.
Hot Isostatic Pressing
Hot isostatic pressing enhances the density of additively manufactured parts and can assist in reducing part porosity. For AM parts, we can combine HIP with high-pressure heat treatment in a single cycle, a particularly advantageous process for cobalt chrome components specifically. HIP is ideal for components with critical dimensions (such as aerospace components or medical devices and implants) because pressure during treatment is applied uniformly to the entire surface of the part. An inert gas—most often, its argon—is preferred inside the HIP vessel because it assures that part surfaces won’t oxidize.
Vacuum Heat Treating, Annealing, and Stress Relieving
Materials accumulate internal stresses during the 3D printing process which can compromise the mechanical properties of the parts. Vacuum annealing and stress relieving resolve these issues, eliminating the stress concentrations within parts so they are less prone to cracking during service or subsequent processing. Due to the controlled atmosphere, vacuum heat treating also minimizes surface contamination and lends a brighter appearance to parts.
Gas Quenching
The speed and method of quenching for additively manufactured parts are determined by the material and the desired hardness that results from the process. For example, nickel-based alloys generally require a harder quench to achieve the desired hardness. In addition, many specialty alloys specify controlled cooling rates which we achieve through furnace control and monitoring.
Hot Isostatic Pressing
Hot isostatic pressing enhances the density of additively manufactured parts and can assist in reducing part porosity. For AM parts, we can combine HIP with high-pressure heat treatment in a single cycle, a particularly advantageous process for cobalt chrome components specifically. HIP is ideal for components with critical dimensions (such as aerospace components or medical devices and implants) because pressure during treatment is applied uniformly to the entire surface of the part. An inert gas—most often, its argon—is preferred inside the HIP vessel because it assures that part surfaces won’t oxidize.
Materials Used in Additive Manufacturing
Since many AM parts are produced at near net shape, machinability of the material is of less concern than for conventionally manufactured components. It is also difficult to print ferrous materials that contain a high carbon content because they are especially prone to cracking (this is because of the resolidification of material between layers occurring at the microscopic level). Most materials used in additive manufacturing have very low levels of carbon.
Titanium & Titanium Alloys
– Titanium 6-4 (Ti6Al4)
Inconel
– Inconel 718
Stainless Steel
– 316L Stainless Steel
– 17-4
Aluminum & Aluminum Alloys
– AlSi10Mg
Cobalt Chrome
– CoCr F75
Metallurgy Support for Additive Manufacturing
Whether you’re just getting your AM program off the ground or you already have production in full swing, our metallurgy team can help you solve problems and make decisions regarding your heat treatment and thermal processing. We help with the following situations:
- Whether to leave the parts on the build plate or cut them off prior to processing
- Testing to help with material selection and specification/recipe development
- Material selection advice
- Optimizing your part designs to account for and minimize the effects of distortion
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Let’s work together to enhance thermal processing results for your additively manufactured parts.
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