It’s HIP to Be Additive: Advancing 3D Printed Metals with Hot Isostatic Pressing

Metal additive manufacturing (AM) is different from metalcutting and forming processes in beneficial ways. AM is different because it does not need tooling — a fact that brings new possibilities in terms of geometry as well as potential time savings. It is different because the process of building parts layer by layer generally means less waste is generated, arguably making the process more sustainable. And it is different for its workflow, one that can support on-demand production to reduce inventory and deliver parts as needed. A manufacturer embracing metal additive has more freedoms in terms of design, scale and lead time of production.

Despite these advantageous differences, however, AM also continues to be plagued by another difference: The material properties of a metal 3D printed part are simply not the same as a cast or forged part. One could argue that perhaps they don't need to be; perhaps qualifications and standards based on cast or wrought properties should be reevaluated for additive manufacturing. But another argument says that metal 3D printed parts don’t need to meet these standards as-printed. It may be enough that they meet them through subsequent processes. After all, even foundry parts require downstream steps — and answers for AM parts can be found in processes that already exist.

Aalberts Surface Technologies-Accurate Brazing sees this potential. The company, a global conglomerate of five divisions, specializes in heat and surface treatments, polymer coatings, brazing, and now postprocessing of metal 3D printed parts. That postprocessing capacity includes more than two dozen vacuum and air atmosphere furnaces spread across facilities in South Carolina, Connecticut and New Hampshire. But it is a different process, hot isostatic pressing (commonly known as HIP or HIPing), where the company sees the greatest potential for metal AM parts. While HIPing is already known to additive manufacturers (in particular, those using laser powder bed fusion), the company believes the process has not yet reached its full potential, and that it can be applied with greater effectiveness and economy as additive production scales.  

With this future in mind, Aalberts Surface Technology’s Greenville, South Carolina, location is equipped with two large HIPing furnaces from Quintus that command both attention and the bulk of this facility’s additive-focused services.

“Fifty percent of the HIPing work we do in Greenville is for additive parts,” says Craig Beaumier, director of business development. This is by design; while the facility also offers brazing services and vacuum furnace heat treat, it is intended to be the company’s Center of Excellence for postprocessing of AM parts.

Hot Isostatic Pressing and High-Pressure Heat Treat

The HIP process uses temperature, time and pressure to take material to its plastic state and essentially squeeze out any porosity, resulting in material densities up to 100%. The process can be applied to various types of materials, but in the 3D printing space has been used mostly on metal parts, and this is the area of opportunity that Aalberts is focused on.

While many additive manufacturers are already familiar with and even have integrated furnaces for heat treat in their production facilities, HIP capacity is much less common. The equipment is much larger and more expensive than a more conventional heat treating furnace, and requires up to a year of training to operate. Those hurdles, coupled with a scarcity in HIP services for additive, have resulted in underutilization of the process, Beaumier says. For metal 3D printed parts, HIPing offers an efficient avenue to both stress relieve these components and apply other process steps in the same cycle.

The exact service Aalberts offers with its HIP furnaces is high-pressure heat treat, or HPHT. Parts are loaded into cylindrical baskets and stacked in the furnace (“dim sum-style,” Beaumier says) to be pressurized, heated and cooled to achieve desired material properties. Each cycle is unique to the material and application, and can be modified to impart various characteristics to the parts inside. By manipulating the variables of time, temperature, and pressure, Aalberts can create HPHT cycles that combine stress relief, HIP, solution heat treatment and aging all in one, rather than performing these steps in separate processes.

“We’re taking traditional thermal processing and combining it all in one unit,” Beaumier says. Customers benefit from the chance to leverage one supplier for a range of postprocessing needs, plus reduced lead times compared to sending parts out for piecemeal services; Aalberts’ HIP services have an average turnaround time of about a week. The consolidated process also has potential benefits for the parts themselves; 3D printed components end up spending less time at elevated temperatures with this strategy, which improves process and quality control. 

Recipes for HIPing Additive Parts

Not to say that HIPing AM parts is without its challenges, because the properties of printed metals — that same difference that places hurdles before 3D printed parts entering industry — also pose a ramp-up challenge for HIP.

“Every printer’s a foundry, and they all behave differently,” Beaumier says. While HIPing processes are well-documented and understood for castings and forgings, the “recipes” for additive manufactured parts are still being established. Developing those recipes remains a key to Aalberts winning work for this process, and a problem that needs to be solved at large to bring the broad benefits of HIP to additive production.

“We will run dedicated cycles to show the customer proof-of-concept for this process,” Beaumier says. Right now, the focus is less on throughput and more on developing recipes and winning trust.

As these recipes become known, established and accepted, the use of HIP for production additive manufacturing will grow. At present, Aalberts is running its two Quintus furnaces regularly, and plans to add a third HIP furnace to support growing demand.

While additive manufacturing technologies will continue to improve at the same time, Beaumier doesn't see advances in 3D printing equipment as a potential replacement for downstream processing.

“Will we ever get away from HIPing? No, not for AM,” he says. “This is affordable insurance on the material,” and a policy that can be relied upon today, without waiting on advances in 3D printing.