The importance of sharp tooling is essential in order to meet the precision and process control that drives today's manufacturing. Such sharp tooling is expensive to maintain and replace. Heat treating the tooling and has proved to increase the useful life-time of a tool. Various types of materials have also proven to wear down tooling slower, but is restricted in use by the cost factor. Cryogenic tempering has proven to increase the tool life expectancy even more that just heat treatment, even as much as five times more.
Cryogenic tempering is the process in which a metal is cooled to extremely low temperatures so as to allow for restructuring the part. The cooling is done in stages so as not to produce micro-cracks in the surface. During the process the surface and internal stresses are relieved, the parts entire structure is changed, and most of the soft austenite is transformed into hard martensite. The process accomplishes these tasks by aligning the structures to create a more dense and homogenous material. In addition, little micro-fine carbide fills the gaps in the larger carbide structures. However, the parts dimension remain relatively unchanged.
Various types of low temperature tempering are available. Many places cool the parts to -120 F in their deep freezing methods. This process does not reach low enough temperatures to provide a significant level of stress relief and material restructuring. Others use liquid nitrogen to cool the surface or the entire part. This process introduces the part to thermal shock and micro-cracking. Deep cryogenic tempering has proven to increase tool life over any other method. Deep cryogenic tempering is a dry process that cools the part in stages to -300 F. This slow, dry process ensures that there will not be cracking of the surface.
Cryogenic tempering should not be a substitute for heat-treatment, but rather an addition. The material does not get harder, but rather is gets tougher. The toughness comes from the realignment of the parts structures, creating a more dense material. The material still needs to be heat-treated to establish the hardness.
The results of cryogenic tempering are significant for many metal type parts. In tooling the abrasive wear resistance is increased. This is due to the larger contact surface that reduces friction, heating, and wear. The enlarged contact surface is a result of the restructuring of the tool during the process. The chips that break off during work are fewer and smaller due to the more even surface finish. Since the restructuring is not confined to the surface, the tool may be re-sharpened and still hold the benefits of tempering. Since the tool did not increase in hardness, the tool is just as easy to re-sharpen as if it were not cold tempered. In fact, the tool may become easier to sharpen since the homogenous structure promotes a more uniform wear. The tool also becomes less brittle and the tensile strength increases.
The price of replacing tooling and the down time in retooling greatly overcome the price to freeze these parts. Industrial tools have a process price of $2.00 to $10.00 per pound based on the amount of weight to be treated. Other types of products or other companies have structure their price on the size of the parts. Comparing any of the freezing costs to the price of repairing or replacing tooling and downtime, the savings are tremendous.
Tools are not the only benefit to a manufacturing plant. Cryogenic processors have restructured larger units, such as engine assemblies, to improve their performance. They have found the machines to last longer, vibrate less, increase horsepower, provide better fuel economy, and many other part based positive effects. Other parts such as gun barrels and musical instruments have been tested and proved to provide better characteristics.