The most common method is flooding, sometimes called flood - cooling because it is generally used with coolant-type cutting fluids. In flooding, a steady stream of fluid is directed at the tool–work or tool–chip interface of the machining operation.

A second method of delivery is mist application, primarily used for water based cutting fluids. In this method the fluid is directed at the operation in the form of a high-speed mist carried by a pressurized air stream. Mist application is generally not as effective as flooding in cooling the tool. However, because of the high-velocity air stream, mist application may be more effective in delivering the cutting fluid to areas that are difficult to access by conventional flooding.

Manual application by means of a squirt can or paint brush is sometimes used for applying lubricants in tapping and other operations in which cutting speeds are low and friction is a problem. It is generally not preferred by most production machine shops because of its variability in application.

CRYOGENIC COOLING

Metal cutting operations inherently generate large amounts of heat thus leading to numerous problems such as changes to the work-piece and tool material properties, thermal deformations,thermal damages, and many other problems associated with them. Different types of cooling methods are used to overcome temperature rise. Among them, the use of emulsion fluid is the most popular cooling methods, mainly because of economy and ease of use. However emulsion coolants have many drawbacks among some of the main concerns are pollution and harmfulness to humans. Above all emulsion coolant liquids have a major drawback in hard-to-cut metal cutting operations in that they cannot provide the required effective heat removal in machining such materials. As liquids possess viscosity they cannot penetrate into tight gaps and transfer heat efficiently. Hence emulsion coolants do not provide a good solution for cutting hard metals.

Cryogenic machining is a material removal process where the conventional cutting fluids are replaced with cryogenics such as liquid nitrogen, solid carbon dioxide, etc.

Cryogenic cooling is used for effective and fast removal of heat generated during cutting operations and is used for almost all types of materials with properties ranging from ductile to brittle, and metallic to organic etc. It has been shown that cryogenic cooling methods do provide better surface properties on the work-piece, extends tool life, reduces heat effects on work-piece, reduces dimensional deviations on work-piece, etc. Further it has been shown that cryogenic cooling would increase machinability of hard-to-cut material. Health, safety and environmental friendliness of using cryogenics have made it attractive for the machining industry. Unlike conventional emulsion cutting fluids which are widely used, cryogenics such as liquid-nitrogen, dry ice, etc. does not create health or environmental hazards. Unlike the conventional cutting fluids, liquid nitrogen is not re-circulated in the machine tool system. Liquid nitrogen absorbs heat generated during cutting operation and evaporates as a gas and is released to the atmosphere as it does not pollute the environment, or be harmful for people around.

There are three basic types of cryogenic cooling methods.

First is Cryogenic pre-cooling of the work-piece, also known as cryogenic cooling of work-piece and chip. In this method, the work-piece is cooled before machining. Most of the adaptations of this principle use a technique to cool the cutting area just before the cutting tool does the chip formation. A typical setup is flooding of the cryogenic using a nozzle over the cutting point just before the tool contacts with the cutting point.

The second method is indirect cryogenic cooling which is also known as cryogenic tool back cooling or conductive remote cooling, where the cooling takes place without any contact of cryogenic with the work-piece or the tool. Cooling is done by heat conduction from the work-piece and the tool to the cryogenic chamber placed at the tool face or the tool holder.

The third method is cryogenic spraying and jet cooling method. This is concerned with removing heat from the cutting point. Especially, it is focused on cooling the tool-chip interface with cryogens. Liquid nitrogen is injected in the form of a jet over the cutting area or sprayed into the cutting area using nozzles, and hence the consumption of liquid

DISPOSAL OF CUTTING FLUIDS

No matter how well you maintain the cutting fluid, eventually it will run out of steam and you have to dispose it. This, you have to do according to the law or face steep penalties.

Although the goal of waste disposal regulations is to completely eliminate pollution, this is rarely possible given the enormous costs and complexities of compliance. Practically, such legislation ensures a minimally polluted environment.

Now, the Resource Conservation and Recovery Act (RCRA) defines wastes in terms of their properties that can prove hazardous. It does not define them in terms of their state (solid, liquid, or gas) or composition.

Then, the Federal Environmental Protection Agency (EPA) identifies four hazardous characteristics for solid, liquid, or gaseous wastes. A waste is hazardous if it is any one of the following four:

• Toxic and leaches lethal doses into groundwater if managed improperly.
• Inflammable and can create fires during storage, transport, or disposal.
• Corrosive as identified by its pH value, for wastes with too low or too high pH values can affect human health and environment while reacting lethally with other wastes.
• Reactive or Unstable that can provoke explosions or emissions.

Depending on the composition and volume of wastes and the availability of treatment-disposal options, alternatives include:

• Ultra-Filtration: handles wastewater generated in metalworking by neutralizing the hazards of waste MWF, part-washer cleaners, detergents, and other oily waste water. Such systems with 100-300 gallons a day capacity cost about $5,000-$13,000 that is more economical than contract hauling. These are more effective than chemical treatment, are space-efficient, and easy-to-operate.

• Chemical Treatment alters the composition of wastes. This is not very viable for treating metalworking wastes and small machine shop owners can afford it only for pH control

• Contract Hauling is expensive. Employ it only if your shop generates less than 200 gallons of wastes or if these wastes are highly toxic or exceptionally complex

• Evaporators do not eliminate wastes, but only lower their volumes and, thereby, the associated disposal costs. They are easy-to-operate, space-efficient, and work well with all coolants. Plus, you do not need a great deal of chemical knowledge to operate them. You do need a lot of power to operate these and a lot of labor to clean them. Use them only when you run out of options

• Centrifuges separate only solids. Furthermore, they are expensive making them good only for pre-treatment

You can dispose waste MWFs directly in the municipal sewer (with the prior sanction of the appropriate authority) only if such fluid:

• Dissolves in water.

• Is non-toxic.

• Has pH between 6.0 and 9.0.

• Holds tramp oil below 100 mg/l concentration.

• Has non-toxic concentrations of heavy metal ions.

• Is regularly treated with biocides.

• Free of chips and fines.

  EFFECTS OF CUTTING FLUIDS