Background

• Isostatic pressing is a manufacturing process used to create powder metal or PM parts. The process allows for the manufacture of near-net parts, which means that the product is very close to finished after being made. This leads to a relatively low degree of waste in the process, with approximately 80-90 percent of base materials being part of the finished product when hot isostatic pressing is employed. The process creates parts with a uniform structure that is almost entirely without internal spaces or bubbles. This makes the process ideal for areas where parts are subjected to high degrees of stress and part failure could lead to catastrophic results, such as in the aerospace industry. However, hot isostatic pressing does have drawbacks. It is a slower and more expensive process than other powder metal production techniques. It is also limited to smaller production runs.
  
  

Pressing Process

• The process really begins with the metal powder. The powder must be produced using a gas atomization process. In essence, the metal is melted and then fed into an atomization mechanism. The molten metal is blasted with a pressurized gas (air or an inert gas) which breaks the metal into tiny droplets that then solidify. The metal powder that is used depends on the part to be made but could include steel, titanium or nickel alloys. Once the proper metal has been selected, a hermetic container (usually metal or glass) must be made in the appropriate shape for the part. In welded metal containers, it is essential that the weld allows for no leaks. The metal powder is then placed into the container. Once the powder is in place, the air must be removed from inside the container prior to any heating. The container is then sealed to maintain the integrity of the vacuum. The filled and sealed container must then be loaded into a hot isostatic pressing furnace.
  
  

• Once the container is in the furnace, it must be filled with an inert gas. Argon is the most commonly used inert gas for hot isostatic pressing, though other inert gases such as helium can also be used. The gas and container are then heated to a predetermined level. The inert gas becomes excited at higher temperatures and expands inside the furnace. This subjects the container to intense pressure and heat, which forces the container to apply pressure to the powered metal within. This causes the powdered metal to bond together into the shape of canister, producing the desired part.