Liquid nitrogen cooling turning new technology ICEFLY (Figure)

A new hard-car machining process is about to come out, and its developers say it can reduce the roughing time from the original 4 hours to 15 minutes. In addition, the process is also considered to reduce tool costs by 85% while improving workpiece tolerance and surface roughness.

The process was developed by Harding and Air Products and Chemicals Inc. on the principle of introducing liquid nitrogen into the slit during turning operations. In this process, liquid nitrogen cools the cutting tool to very low temperatures and prevents temperature rise in the workpiece, increasing the efficiency of the cutting operation and generating great benefits.

The process is called "IceFly", according to Ranajit Ghosh, technical director of air product company IceFly. The process can be used to replace the rough grinding operation, and the tolerance can be kept at 0.008 inches in roughing operations with a hardness of 78Rc. At the same time, the depth of cut and the spindle speed are increased.

ICEFLY(R) Machining Technology

Ghosh said in an interview that Air Products developed the process for applying liquid nitrogen in cutting operations about five years ago. The use of liquid nitrogen in the cutting process was originally developed for the production of flat steel heavy duty process rolls and support rolls. These rollers are made of hard-to-machine hardened steel. Ghosh said his company's cooling process is currently being used on five US machines that produce such rolls.

The cooperation between Air Products and Harding has enabled the process to be applied to a wider market and smaller parts.

Small parts, big challenges, low-temperature cooling of hard parts for a variety of parts is not a simple matter. When a cryogenic liquid is introduced during processing, the liquid easily reaches its boiling point (nitrogen has a boiling point of -320 degrees Fahrenheit or -196 degrees Celsius). A gas layer is formed between the liquid and the tool and the workpiece at a much higher temperature than the liquid, and the gas layer will become a thermal barrier.

For this problem, Air Products found a solution, Ghosh said: “The process is not as simple as pouring liquid nitrogen onto the workpiece. In doing so, a gas boundary layer is formed, which reduces heat transfer. Efficiency, almost eliminates the ability to transfer heat from the workpiece."

Air Products has developed a two-phase system in which special solid particles are suspended in liquid nitrogen. Combined with the velocity of the gas hitting the tool and the workpiece, these particles destroy the gas boundary layer. Liquid nitrogen is sprayed onto the tool and workpiece through a nozzle that can adjust its flow rate.

According to Ghosh, the nozzle is attached to the turret and the liquid nitrogen is supplied from the tank. The nozzle sprays liquid nitrogen directly onto the rake face of the tool.

The superior cold liquid removes heat generated during the cutting process and keeps the workpiece at a constant temperature. Harding's senior application engineer Tom Sheehy said that keeping the workpiece at a constant temperature guarantees constant cutting conditions and maintains precise tolerances, even if the depth of cut is deeper than usual.

In addition, liquid nitrogen keeps the tool in an extremely cold state. Ghosh says that cryogenic freezing changes the characteristics of ceramic knives, making them harder and tougher. Sheehy said. Such a ceramic cutter can cut a cemented carbide material having a hardness of more than 78 Rc at a depth of cut of 0.003 to 0.005 inches. Sheehy added that cryogenic refrigeration of ceramic tools can also be used for intermittent cutting of hardened materials. Sheehy said: "Cryogenic cooling makes ceramic tools stronger and more tough, so you can use a $15 ceramic tool instead of a $100 cubic boron nitride tool, and the performance is better."

The third processing benefit is that cold nitrogen can quench the workpiece and increase surface hardness.

Surface quality improvement Ghosh said: "In practice, we have found that the surface and subsurface hardness increases in the machined parts, the compressive residual stress increases, and the white layer decreases." He explained that the increase in compressive residual stress causes the part to increase. The fatigue strength. "White layer" refers to the unetched brittle layer found in the heat affected metal on the surface of the workpiece. It is believed that this layer is formed in certain steel compositions under certain processing conditions and with specific cutting tools. .

Ghosh said. Increasing the compressive residual stress and reducing the white layer can improve the wear and fatigue properties of the workpiece.

These benefits have changed the processing of rough-cut hard materials such as tool steels with high cobalt or chromium content and tool iron or tungsten carbide and tungsten steel. He said the process can also be used to process porous materials, such as powdered metal products, as well as other difficult-to-machine materials such as metal matrix composites. “No other process can be applied to all of these applications,” Ghosh said. In addition, he added that the process is environmentally friendly and easily retrofitted to existing machines.

Test Air Products and Harding tested the process on a pilot lathe at the former company in Allentown, Pa., and Thomas Thomas, a turnkey engineering manager at Harding, said they are testing the concept here. . He mentioned: "We see it as a process that can replace hard grinding."

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