The Advantages of Hot Isostatic Pressing
There is an array of methods used to shape form ceramic powders including injection molding, extrusion, hot isostatic pressing, slip casting, gel casting and tape casting. Injection molding is known to form many plastic parts found in the average household and extrusion can be used to make a ceramic rod used for building facade. Hot isostatic pressing (HIP) is a forming method that can be used to form both metallic and non-metallic materials into a variety of different products. HIP increases the density of ceramic materials and can reduce the porosity of metals.
Hot isostatic pressing can create high quality casts at lower prices compared to traditional machining methods. To improve overall quality HIP chambers heat, then gradually cool products. Quality jeopardizing gas bubbles are removed during this this stage of the process, ensuring a higher quality part. Ceramic knives with black colored blades are produced with an additional hot isostatic pressing step to improve toughness.
The HIP process involves sintering a compact in a pressure vessel at high temperatures. The pressurized gas used to create the pressurized atmosphere in the chamber is usually either Argon or Nitrogen. Common pressures can go from 15,000 psi to 44,000 psi. To put that into perspective, the U.S. Navy’s best submarines can withstand about 1,500 psi while submerged. Although to be fair, submarines are much larger, making it more difficult to hold back greater pressures.
To cause a consolidation of powder particles, healing voids and pores, hot isostatic pressing combines pressing and sintering. Resulting from the part shrinking and densifying, a high strength structure is formed. This process can be performed without a mold but cold isostatic pressing must be used first to compact the product and then sintered to close the interconnecting porosity. The part can then be processed through hot isostatic pressing.