Application of Hot Isostatic Pressing
Since its invention in the early 1950s, the technology of hot isostatic pressing has been favored in a wide variety of applications. The technology of hot isostatic pressing is a production method known as densified casting. Its applications range from the consolidation of metal powder to the compaction of ceramics, and it has found use in a variety of other fields as well, including additive manufacturing (3D printing technology).
Currently, casting consolidation and heat treatment take up about 50% of HIP units. Hot isostatic pressing will probably spread quickly to more applications in the future due to the rising interest in ceramic additive manufacturing in the aerospace and automotive industries in recent years.
Introduction to Hot Isostatic Pressing
For hot isostatic pressing, components must be heated in either a high pressure or vacuum environment. To effectively expand and create a pressure atmosphere in the hot isostatic pressing furnace, the gas must be introduced in advance. The hot isostatic pressure cycle and the material composition both affect this startup process.
With hot isostatic pressing, an inert gas (such as argon or nitrogen) is used to apply intense pressure (50-200MPa) and heat (400-2000°C) to the surface of the processed part; these conditions cause the material to flow plastically and diffusively, filling any voids beneath the surface. How to maintain productivity while achieving the highest theoretical density of processed parts is the current hot isostatic pressing technical challenge.
In hot isostatic pressing with pure argon, pressure is typically applied at 100–200 MPa. Gases like hydrogen and carbon dioxide are infrequently used, whereas other gases like nitrogen and helium are occasionally used as well as combinations of different gases. In some specialized fields, both lower and higher pressures may be employed, and which gases are used ultimately depends on the application field. Special precautions must be taken when using helium, argon, and nitrogen due to their relatively high cost and the fact that hydrogen can explode at the wrong concentration.
In order to efficiently remove the heat produced in the furnace and quicken cooling, the HIP pressure vessel is crucial. In order for the density to increase in close proximity to the theoretical density during hot isostatic pressing, enough time must be needed for the formation of necking and pore closure.
Through the thin-walled prestressed winding unit, the hot isostatic pressing process can achieve a uniform and quick cooling process. The wire wound technology uses a thin-walled prestressed wound cylinder, wire wrapping, and internal water cooling ducts to create an effective heat exchanger between gas-gas and gas-water. The cooling rate would be significantly lower and it would be impossible to achieve truly rapid cooling in the absence of such a thin-walled solution. The wear on the furnace is decreased by uniform cooling, which also significantly lowers maintenance expenses and the cost of purchasing replacement worn parts. The production efficiency is increased by 70% when compared to the natural cooling process, and the density is increased to almost 100% of the theoretical density. The additional cost to achieve this density varies depending on the material for large HIP production systems.
Through uniform and quick cooling, the hot isostatic pressing process can achieve relatively quick cycle times, which can reduce cycle times by nearly 70% by cutting processing costs and lengthening investment depreciation times. For small and medium-sized HIP units, for instance, it can save twice as much time and still allow for the realization of heat treatment in HIP. Additionally, by combining hot isostatic pressing and heat treatment in the same piece of machinery, it is possible to produce high-performance products in a short amount of time at a reduced cost.
Advantages of Hot Isostatic Pressing
(1) Increase product density;
(2) Improve the mechanical properties of products;
(3) Boost productivity;
(4) Less waste and scrap.
Conclusion
Hot isostatic pressing can form metallurgical bonding (diffusion bonding) between materials, can repair internal pore defects, make designs lighter, improve ductility and toughness, reduce performance fluctuation, and lengthen service life(depending on the alloy system, the fatigue life of the part is increased by nearly 10 times).