Hot isostatic pressing. . . What is it? How is HIPing benefiting the medical industry? What is its place in additive manufacturing? In today's Technical Tuesday, Heat TreatToday is doing a deep dive into HIPing and its benefits. Check out these resources for some hot takes on HIPing.
What exactly is HIPing? It's taking over the additive manufacturing world. In this article, written in 2020 by Derek Denlinger, corporate lead metallurgist at Paulo, find out the answer and also discover the applications, materials, and advantages of HIPing.
"HIP was initially developed as a diffusion bonding technique. In diffusion bonding, high heat and pressure work together to weld similar or dissimilar metal surfaces without filler materials."
Product efficiency, reduced environmental impact, and improved process reliability are becoming more and more important everyday. HIPing's future has never been brighter. It's about to see a renaissance. To explore HIPing in depth, read this free ebook from Heat TreatToday and Quintus Technologies.
"Modern HIP machinery is an extremely good fit with the traditional heat treatment market, offering the opportunity to further adjust material properties through tailored HIP cycles."
Check out what Chad Beamer and Magnus Ahlfors at Quintus Technologies had to say about HIPing. Shrinkage, gas porosity, and lack of fusion between layers are all things that do not belong in medical implants. Implants manufactured with metal injection molding and casting often still contain defects, but HIPing eliminates those defects and produces a 100% dense material. HIPing is widely used across the medical industry to reduce the occurrence of these issues.
"The elimination of defects results in improved fatigue properties, ductility, and fracture toughness. For this reason, HIP is widely used for orthopaedic implants like hip, knee, spine, ankle, wrist as well as dental implants to ensure quality and performance and prevent early failure of the implant inside the patient."
High temperatures, high pressures. That's HIPing. Cliff Orcutt of American Isostatic Presses, Inc. describes HIPing as "pressurize sintering." Because of the high pressure, HIPing is faster and leads to less part deformation. In this episode of Heat Treat Radio, learn the many applications of HIPing (including ceramics) and learn if outsourcing is right for you.
"In HIP, since you’re starting with powders that are solid, you can blend things like graphite powder and steel. You couldn’t blend them very well in a molten state, but in here, you can. And, you can squeeze it to solid, you can get interlocking and bonding and diffusion bonding materials that you couldn’t otherwise. So, you can make things you couldn’t make any other way."
Canada’s Burloak Technologies will use hot isostatic press (HIP) technologies to push the limits of additive manufacturing (AM) to deliver new levels of mechanical performance and strength properties in parts for mission-critical applications. Providing rapid cooling under pressure will minimize thermal distortion and non-uniform grain growth in components, producing finished parts with optimal material properties and allowing Burloak to significantly increase production.
Peter Adams Founder and Chief Innovation Officer Burloak
As a full-service additive manufacturer, Burloak works with innovative companies in the space, aerospace, automotive, and industrial markets to rapidly transition their most challenging part designs to be additively manufactured at scale. The High Pressure Heat Treatment™ (HPHT™) capability of the new QIH 60 M URC™ HIP from Quintus Technologies facilitates this rapid transition. Combining high pressure, heat treatment, and cooling in a single process makes it possible to remove several operations from the AM production line, generating significant savings in both cost and time. Additionally, the press’s highly customizable cooling cycle can be programmed to stop at a specific temperature while maintaining the desired pressure set point.
The press's capability to rapidly cool under pressure, "is critical for Burloak as a full-service supplier for all customers, and, in particular, for the development of high-strength flight components," comments Peter Adams, founder and Chief Innovation Officer at Burloak. "Without this in-house capability, outsourcing this process would slow down our project timelines, add complexity to our processes, and risk damaging critical customer components as they would need to be shipped internationally."
The model QIH 60 press features a hot zone of 16.14 x 39.37 inches (410 x 1,000 mm), an area large enough to process any component printed on most powder bed machines, Mr. Adams notes. It operates at a maximum temperature of 2,552°F (1,400°C) and maximum pressure of 207 MPa (30,000 psi).
"We are very pleased to be chosen as their strategic partner in furthering the development of additive manufacturing," says Jan Söderström, CEO of Quintus Technologies, "and we look forward to sharing our applications expertise through our Quintus Care program."
The Fraunhofer Institute for Manufacturing TechnologyandAdvanced Materials IFAM in Dresden has received a hot isostatic press. This HIP technology will permit researchers to deepen their expertise and refine processes for pressure-supported heat treatment, used to maximize theoretical density, ductility, and fatigue resistance in high-performance materials.
Applications for the new system from Quintus Technologies include the hot isostatic pressing and heat treatment of specialty materials such as nickel-based superalloys and intermetallic compounds like titanium aluminides, as well as densification of the unconventional microstructures associated with additive manufacturing (AM).
Dr. Thomas Weißgärber Director of the Branch Lab Fraunhofer IFAM Source: ifam.fraunhofer.de
The QIH 15L is equipped with Quintus’s Uniform Rapid Quenching® (URQ®) technology, which achieves a cooling rate of 103K/minute, while minimizing thermal distortion and non-uniform grain growth for finished 3D printed parts with optimal material properties. The press’s furnace chamber has a diameter of 6.69 inches (170 mm) and a height of 11.4 inches (290 mm) and operates at a maximum pressure of 200 [207] MPa (30,000 psi) and a maximum temperature of 2,552°F (1,400°C).
Acquiring the Quintus HIP allows Fraunhofer IFAM researchers to “strengthen their technological expertise in the field of pressure-supported heat treatment,” comments Dr. Thomas Weißgärber, director of the Branch Lab at Fraunhofer IFAM. “The new system is not only used for R&D projects but is also available as a service for carrying out predefined HIP cycles.”
The press model QIH 15L incorporates heat treatment and cooling in a single process known as High Pressure Heat Treatment™ (HPHT™). HPHT combines stress-relief annealing, HIP, high-temperature solution-annealing (SA), high pressure gas quenching (HPGQ), and subsequent ageing or precipitation hardening (PH) in one integrated furnace cycle.
Jan Söderström CEO Quintus Technologies Heat Treat Today
Consolidating these multiple steps in the HIP process brings several benefits for Fraunhofer IFAM. Several functions can be performed in a single location with fewer pieces of equipment on the production line. The Quintus press produces fast throughput and high work piece quality. It also enhances efficiency and reduces per-unit processing costs while generating savings in space, energy, and infrastructure.
“We have noted exceptional interest in new approaches that improve quality, lower cost, and reduce environmental impacts,” says Jan Söderström, CEO of Quintus Technologies. “HPHT is rapidly emerging as the go-to post-processing path to lean AM operations, and we are delighted to be working with Fraunhofer IFAM as its talented researchers expand the potential for high pressure heat treatment.”
The new system will be installed in the Innovation Center Additive Manufacturing ICAM® of Fraunhofer IFAM Dresden, where various technologies for additive manufacturing are a major focus.
(source: background image from ifam.fraunhofer.de and Quintus HIP image from Quintus Technologies)
Pulse plasma nitriding systems deliver uniform case-hardening and increased speed of processing when treating high wear parts.
Did you think purple was just a fashion statement? Explore the advantages, applications, and future of advanced pulse plasma nitriding in this Technical Tuesday.Heat TreatTodayhopes you enjoy this original content piece by technical writer Jeff Elliott in cooperation with PVA TePla.
Jeff Elliott Technical Writer Source: Jeff Elliott
When case-hardening the surface of steel, or steel alloy parts, commonly used in the transportation industry, such as gears, crank pins, dies, camshafts, the options have traditionally included one-of-three processes: carburizing, salt-bath nitrocarburizing and gas nitriding. Each process has advantages and disadvantages, but those seeking more precise control of the diffusion layer formation, depth of case hardening, and preservation of component dimensions are increasingly turning to plasma nitriding.
Although pulse plasma has been utilized for decades, advanced pulse plasma nitriding offers absolute control of the DC (direct current) pulsing signal. In addition, improved chamber design and construction allow for more precise temperature control and uniform distribution of the heat zone throughout the hot-wall chamber. The result is extremely consistent and uniform nitriding batch-to-batch and part-to-part, with less gas consumption.
“The benefits are more precise control of the diffusion layers, and its broader appeal to heat treat more diverse materials, beyond steel, that include titanium, stainless steel, and even aluminum,” says Thomas Palamides, senior product and sales manager at PVA TePla America.
In addition, commercial heat treat shops and high-volume part producers can now select from multiple system configurations that offer flexibility, efficiency, repeatability, and throughput optimization. As a result, global manufacturers in machined parts, tool design, die forming, die cutting, medical device manufacturing, additive manufacturing, electric vehicles, trains, electric generators, and land-based power systems are now leveraging these systems to run a cleaner, more efficient operation.
Pulse Plasma Nitriding Advantages
For steel and steel alloys, case-hardening can be achieved by carburizing, nitriding, cyaniding, or carbonitriding. Although carburizing is a traditional approach, the part has to be raised above the A3 temperature (727°C or 1341°F) on the Iron-Carbon diagram, usually in the temperature range of 900-930°C (1652-1706°F) or higher. Since the solubility of carbon is higher in the austenitic state, than the ferritic state, a fully austenitic state is required for carburizing.
Along with the high temperatures and time-at-temperature associated with carburizing, parts can be distorted. Depending on the part, and its geometric tolerances, limited machining may also be required.
An alternative to carburizing is nitriding, a lower-temperature, time-dependent, thermo-chemical process used to diffuse nitrogen into the surface of metal.
Superior controls for the DC pulsing signal and improved chamber design allow for more precise temperature control. Source: Jeff Elliott
One method is salt bath nitriding. In this process, liquid immersion is required, and is typically conducted at 550 to 570°C (1022 to 1058°F). The source of nitrogen is a nitrogen-containing salt, such as sodium cyanide, often greater than 50% in concentration. However, with salt bath nitriding, post-bath cleaning is required to remove the residual cyanide-based treatment. In addition, there are disposal costs for salt and washing , also known as sodium hydroxide, environmental handling costs, as well as safety and operational liabilities.
Gas nitriding (500oC or 932°F) and gas nitrocarburizing (540-580oC or 1004-1076°F) are universally accepted procedures, and typically require a high concentration of ammonia (NH3), and a high amount of carrier gas flow (normal pressure process) compared with pulse plasma nitriding. The elemental nitrogen gas constituent diffuses into iron and forms hard nitrides. Because of the reduced temperature compared to carburizing, no quenching is necessary, and therefore the chance for distortion and cracking are lower.
Several disadvantages of gas nitriding are that it requires the use of flammable gases like ammonia, and high gas consumption compared to pulse plasma. Gas nitriding is also not able to treat rust- and acid-resistant steels (i.e. stainless steels with greater than 12% Cr content) due to the impenetrable layer of the protective surface oxide layer. Where as the energized pulsed plasma signal, during heat up, allows for the dissolution, or breakdown, of this thin protective layer, in effect cleaning the surface, allowing atomic nitrogen to penetrate.
With recent advancements in pulse plasma nitriding, however, a new level of precision and control is possible which results in uniform and consistent case hardening. Together with the advantages of using environmentally friendly gases only – in contrast to the use of ammonia in gas nitriding – plasma-based nitriding has become a focal point for additional innovations and a requirement for those that seek a more environmentally and safe solution.
In pulse plasma nitriding, parts are loaded into a heated vacuum chamber. After evacuating the chamber to a working pressure of 50 to 400 Pa, on a supporting fixture, to be covered by a bell chamber. The chamber is evacuated to below 10 Pa (7.5 x 10-2 Torr) prior to heating and a pulsating DC voltage of several hundred volts is applied between the charge (cathode) and the chamber wall (anode). The process gas in the chamber is then ionized and becomes electrically conducting. For this type of process, nitrogen and hydrogen gas mixtures and gases with carbon additions, like methane are often utilized.
Depending on treatment time and temperature, nitrogen atoms diffuse into the outer zone of components and form a diffusion zone. This can be is atomic nitrogen, dissolved in the iron lattice, as well as in the form of included nitrate deposition.
With recent advancements in pulse plasma nitriding, a new level of precision and control is possible. Source: Jeff Elliott
Adding further precision, innovators in advanced pulse plasma have discovered methods to optimize the process through better control of the pulses. In the PulsPlasma® process developed by PVA TePla AG Industrial Vacuum Systems, for example, a precision regulated gas mixture of nitrogen, hydrogen, and carbon-based methane is used. A pulsating DC voltage signal of several hundred volts is delivered in less than 10 microseconds per pulse to ionize the gas. This serves to maximize the time between pulses for superior temperature control throughout the chamber.
“If you have a temperature variance of plus-minus 10 degrees within a batch, you will get completely different treatment results,” says Dietmar Voigtländer, sales manager at PlaTeG – Product Group with PVA Industry Vacuum Systems (IVS), Wettenberg, Germany, the manufacturer of PulsPlasma nitriding systems. “However, by controlling the pulse current by means of an exact pulse on and off time management, the overall temperature can be precisely managed with a uniform distribution, from top to bottom, throughout the hot wall chamber.”
A unique feature with this approach is that the system can be switched on to a stable glow discharge at room temperature. Most systems cannot do this because the generators do not supply stable plasma. To compensate, those systems must first be heated to 300-350°C (572-662°F) before plasma can be applied, adding time to the process.
[blocktext align="left"]“The benefits are more precise control of the diffusion layers, and its broader appeal to heat treat more diverse materials, beyond steel, that include titanium, stainless steel, and even aluminum." -Thomas Palamides, PVA TePla America.[/blocktext]Even the materials of construction used to manufacture the nitriding systems furnace itself have been optimized. In all systems, PlaTeG uses insulative materials developed in the aerospace industry to create a furnace wall as thin as 40 millimeters, compared to the industry standard of 150 millimeters. With less wall mass, the furnace requires less energy and time to heat, while still protecting workers that may accidentally touch the outside of the chamber.
With better overall control, advanced pulse nitriding furnaces offer multiple heating and cooling zones with each controlled by its own thermocouple. “This will create a very uniform temperature distribution within plus or minus 5 degrees Celsius (9 degrees Fahrenheit) from the bottom to the top of the furnace,” said Voigtländer.
Uniformity of temperature within a chamber pays a dividend beyond the consistency of nitriding results. With an even temperature throughout the chamber, the entire space is available for loading components which effectively increases the chamber’s capacity.
Stainless Steel – a Softer Steel
One of the key advantages of pulse plasma nitriding is that it is more suited to heat treating of high alloy materials such as stainless steel. When working with steels that have a higher chromium content, liquid nitriding can react with chromium and other elements, resulting in a loss of corrosion resistance.
Stainless steel has a natural passivation layer of chromium oxide, which inhibits corrosion. To bring nitrogen into the material, the chromium oxide layer must first be removed. With gas nitriding, removal of the passivation layer requires the application of a special gas chemistry, stainless steels can also be nitrided in salt baths, but only with a sacrifice of some level of corrosion resistance.
In the case of PulsPlasma nitriding, the treatment is applied directly through controlled ionic bombardment of the surface. By choosing a nitriding temperature below 450°C (or 842°F), and with exact control of the gas mixture, the material surface can be treated without reducing the corrosion resistance of the material.
Dies, Stamping & Injection Molds – a Harder Steel
Today, various molds and dies are used to shape everything from plastic bottles, to automobile quarter panels, to extruded wire, to metal injection molded (MIM) parts. Depending on the intricacy of the mold and die, it can cost a customer hundreds of thousands of dollars to fabricate. Customers require die longevity, while maintaining part tolerance, throughout the life of the die to ensure return-on-investment (ROI).
Despite being made of hardened steel, however, injecting melted resins at high temperatures and pressure into cavities over thousands of cycles begins to wear away and erode die edges, cavities, and moving components. Even the thermoplastic material can be abrasive, acting like sandpaper or leaving residue that wears down the surface. With the ever-increasing utilization of even more abrasive material, in the form of long glass and composite fibers, the amount of abrasion and friction within molds is increasing.
According to Voigtländer, pulse plasma nitriding is an ideal solution both to protect molds against damage and corrosion, but also because the diffusion of nitrogen increases the lubricity of the surface, facilitating quick removal of parts. “The diffusion of the nitrogen into the mold surface," he explains, "increases the fatigue strength of the material. In doing so, you can protect the surface against scratches… and increase the lifetime of the mold or die."
Sintered Parts
Pulse plasma nitriding also represents a strong option for sintered, or sinter hot isostatic pressing (HIP) components manufactured though additive manufacturing.
Salt baths have historically been used to nitride sintered components. However, the process of immersing components in molten salt makes it very difficult to remove the salt from open surface porosity. When gas nitriding is used, the nitriding atmosphere permeates all open pores resulting in the entire component, the surface, and the core, being completely nitrided.
“With pulse plasma nitriding, the atmosphere goes through the pores and only the surface area is affected, leaving the core or base material soft,” said PVA’s Voigtländer. “Most designers prefer having a wear-resistant surface with a soft, elastic core.”
Increased Production Throughput
Nitriding is a batch process. Innovation in furnace design, through an optimized mechanical operation, can increase efficiency and increase production capacity. While the actual time for nitriding does not change, efficient loading and unloading scenarios plays an important part. The PlaTeG plant design can use any one of a Mono, Shuttle or Tandem footprint, to manage throughput, resources, and operations costs.
As a batch process, nitriding typically requires waiting for the prior batch to be treated, cooled, and unloaded before a new batch can be started. Shuttle and tandem extensions are now available to streamline the batch process.
Multiple system configurations can offer flexibility, efficiency, repeatability, and throughput optimization. Source: Jeff Elliott
With a shuttle extension, an additional vacuum chamber bottom may be added to a furnace. During a running nitriding process, the unloading of an earlier batch and the loading/preparing of a subsequent batch on the second vacuum chamber is possible. The cycle time therefore for two consecutive batches is reduced because of the overlapping of the time for unloading/loading of a vacuum chamber with the treatment time of the running process.
With a tandem extension there are two complete vacuum chambers which are operated alternately by the vacuum pumps, the process gas supply, the plasma generator and the control unit of the system. In situations such as unmanned weekend operations, an automatic process can be started and controlled for both batches in succession. With this type of operational structure, “it is possible to increase overall nitriding capacity by 30-60% annually,” according to Voigtländer.
Because plasma nitriding uses environmentally friendly nitrogen and hydrogen, the furnaces can be collocated with the machining of components without requiring a separate room. Moreover, the pulse plasma nitriding systems produce no polluting gases. This makes nitriding more efficient as part of an overall manufacturing process as an operator can locate the furnaces beside their drilling machines.
Pulse plasma offers significantly more precision in nitriding through the control of the mixture of gases, the controllability of glow discharge intervals, the design of the Pulsed signal, and the use of a highly insulated hot wall nitride furnace. Together with innovations in the design of the furnaces to streamline batch management in nitriding operations, manufacturers who depend on nitriding components can benefit from greater uniformity of results, better-protected materials, and increased throughput.
About the Author: Jeff Elliott is a Torrance, California-based technical writer. He has researched and written about industrial technologies and issues for the past 20 years. He wrote this article in cooperation with PVA TePla.
Heat Treat Todayis excited to bring you a NEW and FREE ebook this Technical Tuesday!
In an ever-changing world where production efficiency, reduced environmental impact, and improved process reliability are in focus, some well-known technologies are seeing a renaissance.
Hot isostatic pressing (HIP), is one such technology, which until now has been an essential process to densify porosity and improve the mechanical properties of materials for components. The outlook for HIP technology has never been brighter, helped by technology shifts that are accelerated by recent global events.
In this book written with the expert insights of Quintus Technologies, explore high pressure heat treating through the many facets of hot isostatic pressing.
Curious about proper gas atmospheres needed to meet high-tolerance standards for additive manufactured parts before, during, and after the heat treating process?
Learn about them in this detailed original content article from Heat TreatToday’sAerospace 2021 print magazine. The author, Lisa Mercando, Ph.D., is the marketing manager of strategic marketing & development at Air Products. You can access the other articles in our digital edition here. Enjoy the Technical Tuesday!
Lisa Mercando, Ph.D. Marketing Manager, Strategic Marketing & Development Air Products
In a world of rapid prototyping and production of metal components, it is imperative to have the proper gas atmosphere to produce quality parts. Argon, nitrogen, and helium are commonly used to create inert atmospheres in order to meet the high-tolerance standards required for additive manufactured (AM) aerospace parts. Industrial gases are used every step of the way from powder production to various additive manufacturing techniques to finishing processes that include heat treating and hot isostatic pressing (HIPing).
Inert gas atomization is the best method to obtain dense, spherical particles, which are best for AM applications where the desired particle size is usually less than 100 microns. Additionally, inert gas atomization greatly reduces risk for oxidation, providing a high level of powder purity and quality. Helium provides the best results when its superior heat transfer capabilities are needed. This process achieves the following properties: dense and spherical particles; high quality and purity metal powders; and narrow particle size distribution. We can provide high pressure gases for powder atomization and hydrogen-based atmospheres for powder reduction and annealing.
Image demonstrating metal additive manufacturing
To meet the high-tolerance standards required in additive manufacturing–particularly for aerospace–nitrogen and argon are commonly used to provide inert atmospheres. The use of helium, with its high thermal conductivity, offers an interesting option for minimizing the thermal distortion of elongated parts during printing. An inert atmosphere provides numerous benefits on a printed part by:
reducing oxidation of printed parts by lowering the oxygen concentration in the build chamber
improving safety through the inerting of combustible dust during powder handling and sieving
creating a stable printing environment by maintaining constant pressure in the print chamber
mitigating powder clumping in the feed tube
preventing part deformation by controlling thermal stress through effective cooling
Gas requirements differ based on the process being used and the material being printed.
Often, AM aerospace parts require additional processing to achieve the desired final properties. This is done mainly in the form of heat treating, sintering, or HIPing. All three processes have industrial gas requirements for preventing oxidation. Heat treating with argon, nitrogen, hydrogen, or a nitrogen/hydrogen blend can relieve internal stresses and enhance part properties such as strength, ductility, and hardness. In sintering applications, nitrogen/hydrogen blends or argon/hydrogen blends are important in producing near-net shape parts with increased strength and uniformity. High pressure argon is used in HIPing applications to provide fully dense parts with increased strength and reliability.
Image of a furnace heating metal parts
In addition to providing the bulk industrial gases required, the company has developed state-of-the-art process intelligence systems. These systems monitor atmosphere composition parameters to ensure the process is running with the desired gas atmospheres and provide alerts for any needed maintenance or adjustments. Decades of metals processing experience in gas supply, applications, process knowledge, and safety are applied to help improve heat treating efficiency and part quality.
Remote tank monitoring is one example of the company’s Process Intelligence™. Operators increasingly rely on data to closely track critical process parameters, such as the use and inventory of vital industrial gases. This tank monitoring system enables operators to remotely check their supply levels and monitor usage from a touch screen in the plant, on their laptop, or on their mobile device. Customized daily reports are a common way to stay current on their industrial gas supply.
For heat treatment operations using a furnace atmosphere that is flammable or potentially flammable, an inert purge gas – typically nitrogen – is utilized to help ensure safe operation. This system alerts operators to the condition of the liquid nitrogen supply and helps them remotely track their supply and usage of gases. Optional system alarms allow operators to safely initiate a controlled purge shutdown, enabling compliance with NFPA 86 by confirming they have adequate liquid storage levels, or ensuring their nitrogen piping temperature remains at a safe level. Typically installed near the furnace operation, the remote touch screen on the base station displays conditions of all bulk gas storage tanks and can use both audible and visual alarms to warn the operator of a potentially critical situation.
Tank Monitoring
In addition to using inert gases, such as nitrogen and argon for the 3D printing processes, GE Additive Manufacturing, located in Cincinnati, OH and a major manufacturing center for additive manufacturing, also performs post processing heat treatment/sintering on the metal parts to enhance part quality. Their capabilities allow for the production of quick, precise parts with high levels of accuracy, even on intricate shapes and geometries across multiple applications.
Conclusion
If you are prototyping and producing metal components, be sure to consider the importance of achieving the optimum gas atmosphere to efficiently make quality parts. The heat treat postprocessing of AM metal parts is often required to produce the high-quality parts specified for the aerospace industry.
About the Author: Dr. Lisa Mercando is the marketing manager, Strategic Marketing & Development, for Air Products’ metals processing industry. She has worked at Air Products for 28 years in a variety of roles and responsibilities and is the author of several patents and technical articles.
Hot isostatic pressing. . . What is it? How is HIPing benefiting the medical industry? What is its place in additive manufacturing? In today's Technical Tuesday, Heat Treat Today is doing a deep dive into HIPing and its benefits. Check out these resources for some hot takes on HIPing.
