June 4, 2010
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Cutting fluids are required to do many things simultaneously. These functions include:
- Cooling the work and cutting tool.
- Improving surface finish quality.
- Lubricating to reduce friction and cutting forces, thereby extending tool life.
- Minimizing material buildup on tool cutting edges.
- Protecting machined surface against corrosion.
- Flushing away chips.
In addition, cutting fluids must comply with all federal, state, and local regulations for human safety, air and water pollution, waste disposal, and shipping restrictions.
Types of Cutting Fluids
Cutting fluids fall into four basic types:
- Mineral oils.
- Emulsifiable oils.
- Chemical and semichemical fluids.
- Gaseous fluids.
Mineral Cutting Oils
Cutting oils made from mineral oil may be used straight or combined with additives. Straight mineral oils are best suited for light-duty (low speed, light feed) operations where high levels of cooling and lubrication are not required.
They are noncorrosive and are usually used with high machinability metals, such as aluminum, magnesium, brass, and free-cutting steel.
Mineral oils are often combined with animal and vegetable oils and contain sulfur, chlorine, and/or phosphorus. Their use is limited by high cost, operator health problems, and danger from smoke and fire. Mineral oils also stain some metals. They have a tendency to become rancid, so the tank containing them must be cleaned periodically and the fluid replaced.
When working in situations where cutting fluid mists or vapors are present, always wear an approved respirator. A simple dust mask is not sufficient protection.
Emulsifiable oils are also known as soluble oils.
They are composed of oil droplets that are suspended in water by blending the oil with emulsifying agents and other materials. Emulsifiable oils range in appearance from milky to translucent. They are available in many variations for metal removal applications that generate considerable heat.
Emulsifiable oils offer a number of advantages over straight cutting oils. They provide increased cooling capacity in some applications. They are cleaner to work with than other cutting fluids, and provide cooler and cleaner parts for the machinist to handle. These oils reduce the misting and fogging that are health hazards for machine operators. Because they are diluted with water, they offer increased economy and present no fire hazard.
Emulsifiable cutting oils can be used in most light- and moderate-duty machining operations. For economy and best machining results, these oils must be mixed according to the manufacturer’s recommendations. These take into account the material being machined and the machining operation performed. Fluid maintenance must be performed on a routine basis to control rancidity.
Water-based cutting fluids must never be used when machining magnesium.
Chemical and Semichemical Cutting Fluids
Chemical cutting fluids generally contain no oil. They have various rates of dilution depending upon use. A wetting agent is often added to provide moderate lubricating qualities.
Semichemical cutting fluids may have a small amount of mineral oil added to improve the fluid 51 lubricating qualities. Semichemical cutting fluid’s incorporate the best qualities of both chemical and emulsifiable cutting fluids.
Chemical and Semichemical cutting fluids offer the following advantages:
- Fluids dissipate heat rapidly.
- They are clean to use.
- After machining, residue is easy to remove.
- The fluids are easy to mix and do not become rancid.
Their disadvantages are:
- Some formulas have minimal lubricating qualities.
- Fluids may cause skin irritation in some workers.
- When they become contaminated with other oils, disposal can be a problem.
Compressed air is the most commonly used gaseous fluid coolant. It cools by forced convection
In addition to cooling the workpiece and tool, compressed air also blows chips away at high velocity. Workers in surrounding areas must be shielded from the flying chips.
Application of Cutting Fluids
Machining and grinding applications require continuous flooding of fluid around the cutting tool and work to provide efficient removal of the heat generated. Coolant nozzles must be positioned carefully so that, in addition to cooling the work area, the cutting fluid will also carry the chips away. In some machining operations, a conveyor system is used to remove chips and cutting fluid from the cutting area. The cutting fluid is filtered to remove contaminants and is returned to the machine’s coolant tank for reuse.
Evaluation of Cutting Fluids
It is not possible in this text’s limited space to -over all cutting fluids, nor does space permit recommending specific cutting fluids for every machining operation. This information can be obtained from data published by cutting fluid manufacturers. Recommendations for cutting fluid use are included in the chapters of this text dealing with each type of machine tool. In general, however, cutting fluids (gaseous fluids excepted) are compatible with HSS (high-speed steel) and carbide tooling. Since carbide tooling operates at higher cutting speeds and generates higher cutting temperatures, cutting fluids that have high cooling rates should be used in such applications.
Machining with ceramic tooling is usually accomplished without the use of cutting fluids.
April 1, 2010
The following information is directed toward indexable carbide tools but it can be applied to many other cutting tools, as well. It provides some basic guidelines designed to serve as a starting point for safe and reliable performance. Contact your Ingersoll Cutting Tools Company sales engineer or Cutting Tools Chicago aka General Cutting Tools for specific application assistance.
Use the most rigid cutter possible. This usually means the cutter with the largest diameter and shortest length. Use the best adaption possible. Integral tapers, such as a 50 V-flange, are better than straight shanks. When selecting straight shank tools, use a cutter with the largest diameter shank possible and a holder with the shortest length possible.
Effective cutting edges. When calculating feed rate, use the effective number of inserts. In extended flute cutters, the effective number of inserts is not the number of rows. Use the effective number listed with the specifications for each series of tools.
Carbide cutting tools have to take a “bite” to cut. Be sure to cut with an adequate chip load. Light chip loads can contribute to chatter, causing a cutter to “rub” instead of “bite.” This can also result in poor tool life. As a general rule, chip loads should not be less than .004″. Also, be sure to use Radial Chip Thinning Factors (RCTF) when calculating feed rates.
Chip recutting. Unlike HSS, carbide cutting tools cannot recut chips. Recutting chips will damage carbide. To evacuate chips, use air or coolant depending on the material being cut.
Generous amounts of coolant are required when low thermal conductivity, work hardening, and chip welding tendencies are evident. Use coolant only when necessary. Some materials cut better dry. In some applications, coolant causes thermal cracking of inserts and poor tool life.