Cryogenic treatment of cutting tools

Stronger and more uniform microstructure. More dimensionally stable. Thoroughly Stress relieved. The benefits gained from cryogenically treating tool steels are similar to that of tungsten carbide, but the transformation of the material at DCT is slightly different. When cryogenically treating tool steels at F for an extended period of time it increases their strength and durability.

Converts retained Austenite to hard Martensite. Creates a more uniform molecular structure. Remedies surface and molecular imperfections prone to weakness. Increased hardness. Will fix a poor heat treatment. It has been said that machines do not die, people kill them. In many cases this is true, and many of the contributing factors to premature failure can be controlled by the end user.

However, if the equipment has been properly installed and maintained, exerting influence on the other factors may be difficult or impossible for the end user. Cryogenic treatment has been claimed to improve the wear resistance of steels and has been implemented in cutting tools since long.

Although it has been confirmed that cryogenic treatment improves the wear resistance and tool life, the process has not been standardized, with the results being inconsistent, varying from researcher to researcher [3].

The literature published in this regards reports that cryogenic treatment facilitates the formation of carbon clustering and increases the carbide density in the subsequent heat treatment, which further improves the surface quality and wear resistance of steels. Cryogenic treatment is a sub-zero thermal treatment generally given to ferrous tool materials. Studies on CT HSS tools show microstructural changes in the material that can influence tool lives and productivity significantly [4]. The life of cutting tool is affected by factors like cutting speed, feed and depth of cut, tool material, heat treatment of the tool, work material and nature of cutting.

The main characteristics of a good cutting tool material are its hot hardness, wear resistance, impact resistance, abrasion resistance, heat conductivity, strength, etc. Cutting speed has the maximum effect on tool life, followed by feed rate and depth of cut. All these factors contribute to the rise of temperature. That is why it is always said that an ideal tool material is the one which will remove the largest volume of work material at all speeds.

It is, however, not possible to get a truly ideal tool material. The tool material which can withstand maximum cutting temperature without losing its principal mechanical properties especially hot hardness and geometry will ensure maximum tool life, and hence will give the most efficient cutting of metal [5].

During the cutting operation, cutting tool is subjected to static and dynamic forces, high temperatures, wear and abrasion [6]. Singh [7] conducted experimentation on the effect of cryogenic treatment on machining characteristics of titanium alloy Ti—6A1—4V.

In his experimentation, he predicted the best rpm range for conventional milling of titanium alloy Ti—6A1—4V using HSS tool material. The specimen was a cryogenic treated cylindrical rod for which a cryogenic treated HSS end mill was used to generate a cavity. The mechanical properties, namely, surface roughness, surface hardness, metal removal rate, and tool wear rate of the machined surface, were observed to find out the best range of machining characteristics.

The results indicated that best machining range is between and rpm, surface roughness improves by Grewal [8] studied the effect of cryogenic treatment of the wire on machining performance of wire cut Electric Discharge Machine. He found in his study that metallic materials having high mechanical strength generally show a low electric conductivity, whereas those having a high electric conductivity generally show a low mechanical strength.

With the help of cryogenic treatment of wire, current carrying capacity of the wire can be increased. It is also expected that the cryogenic treated wire would have less chances of breakage during machining as compared to untreated wire because of increase in its toughness.

The word cryogenics has its origin in the Greek language where "cryos" means frost or cold and "gen" means generate.

Cryogenic processing has been around for many years but is truly in its infancy when compared to heat-treating. For centuries the Swiss would take advantage of the extremely low temperatures of the Alps Fridge Regions to improve the behavior of their steels. They would allow the steel to remain in the frigid regions of the Alps for long periods of time to improve its quality. Essentially, this was a crude aging process accelerated by the very low temperatures. What we now understand to have happened was the reduction of the retained austenite and the increase in martensite.

By performing this once secret process the Swiss obtained the reputation for producing a superior grade of steel [9]. For lights-out operation or lightly tended machining, longer, predictable tool life can make the transition to unmanned operation less stressful. However, to take full advantage of cryogenic treatment, a shop must include it in the planning process.

The turn around time must be calculated into the delivery schedule. Likewise, the cryogenic treatment process itself takes 2 days, so the time needed to send cutters to be treated needs to be calculated into the production schedule.

Of course, like many machine shops, Diversified Cryogenics included, one can bring the process in-house. Producing a keyway, spline or similar longitudinal feature on a turned part usually necessitates an additional, time-consuming, secondary operation on a broaching or slotting machine. That means moving the part to and from a secondary operation, an extra setup, additional labor and hourly machine costs and all of the other headaches that go with secondary operations.

Workholding for turning is usually fairly basic: The selection comes down to chucks or collets. This article looks at when to consider the collet chuck and what kind might be best for a given application. The rapidly increasing demand for high-value threaded parts with exceptionally high length-to-diameter ratios has created a lot of interest in thread whirling technology among American shops and manufacturers.

Cutting Tools. This chart shows service life of extrusion dies before and after cryogenic treatment. Thread Whirling Basics The rapidly increasing demand for high-value threaded parts with exceptionally high length-to-diameter ratios has created a lot of interest in thread whirling technology among American shops and manufacturers.

Subscribe to Production Machining Magazine. The Fundamentals of Chip Control. Here, the belief is that the carbide inserts shrink slightly during the cool-down phase of the treatment, creating some plastic flow within the micro-voids in between the carbide and the binder. When the carbide returns to ambient temperature, it leaves compressive stresses on the surface of the voids.

These compressive stresses, in turn, tend to counteract localized weakening caused by the voids, thereby resulting in an overall improvement in wear resistance. Taking advantage of cryogenics can result in significant cost savings from increased tool life.

Once a cutter is treated, it is treated for life. In addition to longer time in the cut, these tools wear less, so resharpening requires less material to be removed, so more regrinds can be done. For lights-out operation or lightly tended machining, longer, predictable tool life can make the transition to unmanned operation less stressful. However, to take full advantage of cryogenic treatment, a shop must include it in the planning process.

The turn around time must be calculated into the delivery schedule. Likewise, the cryogenic treatment process itself takes 2 days, so the time needed to send cutters to be treated needs to be calculated into the production schedule. Of course, like many machine shops, Diversified Cryogenics included, one can bring the process in-house. Producing a keyway, spline or similar longitudinal feature on a turned part usually necessitates an additional, time-consuming, secondary operation on a broaching or slotting machine.

That means moving the part to and from a secondary operation, an extra setup, additional labor and hourly machine costs and all of the other headaches that go with secondary operations.

Workholding for turning is usually fairly basic: The selection comes down to chucks or collets. This article looks at when to consider the collet chuck and what kind might be best for a given application.