In hot isostatic pressing (HIP), parts are heated to very high temperatures in a sealed chamber capable of generating very high pressures in the presence of an inert gas. The goal of the process is to improve the mechanical properties of cast or additive manufactured parts.
The combined influences of heat and pressure close pores or voids that form when parts are cast or additive manufactured. A side benefit of the process is that it’s carried out at similar temperatures as homogenization treatments. For this reason, HIP can eliminate the need to execute separate homogenization treatments in some cases.
How HIP works: An evolution
HIP vessels are much like vacuum furnaces in that they’re both precision-controlled batch-type equipment. But HIP vessels cram atmosphere into the chamber to dramatically increase pressure; vacuum furnaces suck it out. HIP was invented in the mid-1950s as a dissimilar metal diffusion bonding technique. In diffusion bonding, high heat and pressure inside a vessel cause the surfaces of distinct parts to slowly meld into one another.
Metallurgists understood that HIP could also overcome the problem of casting porosity. Casting porosity refers to small gas pores that form during metal solidification in the casting process. The pores remain after the metal solidifies, making parts weaker. Hot isostatic pressing eliminates the pores, greatly enhancing mechanical performance.
Today, hot isostatic pressing is recognized as a supplement to additive manufacturing. Just as pores often form during casting, the additive manufacturing process can lead to voids in parts. Because additive manufacturing has been recognized as a viable and cost effective way to make complex aerospace components and medical implants, hot isostatic pressing is in-demand.
HIP is ideal for components with critical dimensions because pressure during treatment is applied uniformly to the entire surface of the part. An inert gas—most often, it’s argon—is preferred inside the HIP vessel because it assures that part surfaces won’t oxidize.
Common examples of parts that undergo HIP include:
- Turbine blades found in jet engines or power generation facilities.
- Medical implants like artificial hips, knees or vertebrae.
- Metal injection-molded firearm components.
Parts treated with HIP display:
- Better fatigue resistance and improved performance at extreme temperatures.
- Improved resistance to impact, wear and abrasion.
- Improved ductility.
These mechanical properties are ideal for parts in high-temperature, high-stress service such as jet engine or gas turbine blades.
HIP vessel capabilities
The HIP vessel in use in Paulo’s Cleveland Division is a Quintus model QIH 122. With a 26-inch diameter and a 68.9-inch height, the vessel can reach over temperatures of over 2,550 degrees Fahrenheit and pressures up to 30,000psi. That’s almost twice the pressure recorded at the bottom of the Mariana Trench in the Pacific Ocean, 36,000 feet below the sea surface.
We chose our HIP model for its additional thermal processing capabilities. It comes with highly controllable rapid-cool features and can HIP and solution treat parts at the same time.
Committed to performance
In 75 years in business, our goal hasn’t changed: We’re here to help our customers be more successful. As manufacturing techniques advance, we’re committed to investing in new equipment and developing new thermal processes to ensure maximum performance of critical parts.