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One part of the metal-cutting equation that is sometimes overlooked, however, is the choice of an appropriate cutting fluid. With today’s system approach to metal-cutting, use of the right metalworking fluid has become just as much a part of the solution as the other elements. In fact, at least one company is now integrating cutting fluids and cutting tools into effective metal-cutting systems. Following are some things to consider when choosing your next cutting fluid. The Four Key Questions There are four vital pieces of information that are necessary when choosing a cutting fluid. They are:
What Are You Cutting? The first question – “What are you cutting?” – is often the most difficult to answer, because most shops handle a variety of workpiece materials on a regular basis. If the answer is an unequivocal “aluminum,” or “stainless steel,” or “cast iron,” the selection of a cutting fluid can be quite simple and straightforward. Unfortunately, that is seldom the case in anything but a high-volume plant. Where aluminum or other non-ferrous metals are a significant part of the mix, a non-staining cutting fluid is a must. Generally speaking, this will be a semi-synthetic with special ingredients to prevent bi-metallic corrosion and staining of non-ferrous workpieces. Where the ferrous metals predominate, however, a more general purpose semi-synthetic or hybrid fluid might be a more economical choice. What Is the Chemistry of Your Water? The second question – “What is the chemistry of your water?” – is probably the single most common reason for the success or failure of a cutting fluid. Very few plants invest the money necessary to install effective water purification systems using deionization or reverse osmosis technology. Unfortunately, the chemicals present, or not present, in the water used to reconstitute a cutting fluid make a tremendous difference in its performance and sump life. Most manufacturers of cutting fluids will perform the necessary water testing to determine exactly what minerals are dissolved in your water and make a fluid recommendation based on the results.
The third question – “What are you using now?” – helps narrow the range of choices. When coupled with an objective analysis of the strengths and weaknesses of the current fluid, the answer to this question can quickly point you toward a relatively small number of competitive alternatives that have the attributes required to meet your cutting needs. Many cutting fluids are in use today simply because they were in use yesterday. It is a hard reality of today’s marketplace that if one isn’t constantly striving to improve, they will certainly be overtaken by a competitor who is. What Are Your Options? The fourth question – “What are your options?” – leads to the final selection of a cutting fluid. Cutting fluids can be divided into four general groups, based on their chemistry. They are:
The final decision in this case would have to be made based on the detailed economics of the shop where the fluids were to be used, and on the owner’s individual preferences. Soluble Oils Soluble oils are oils that disperse in water when emulsifiers are added. They are generally suitable for moderate- to heavy-duty machining and grinding of all non-ferrous metals, carbon and cast steels, and in applications where dissimilar metals such as aluminum and steel are present. They can also be used in turning, drilling, tapping, reaming, gear cutting, broaching, as well as internal and centerless types of grinding operations. Soluble oils provide excellent aluminum and copper corrosion control; good rancidity control, which extends fluid for long-lasting, trouble-free performance; and good concentrate and mix stability, making it ideal for mixing in water with a minimal amount of agitation. An example of this is Valenite’s VNT®-650 premium heavy-duty soluble oil. Synthetics Synthetics are completely oil-free solutions made of polymers, organic and inorganic materials that are mixed with water. These clear, low-foaming and bio-stable coolants are ideal for machining and grinding of ferrous materials, carbon steels or cast iron. Their complex lubricant packages make synthetics well-suited for tough-to-machine materials such as stainless steels and high-temperature alloys. Certain synthetics are specifically designed to address the primary failure modes of flank wear and nose wear. Although there are many benefits, some synthetics may cause staining of non-ferrous materials. Semi-Synthetics Semi-synthetic fluids are a mixture of oils, synthetic emulsifiers and water. They were primarily developed for the aircraft, nuclear and related industries. Consequently, they work extremely well on all non-ferrous metals, such as titanium, aluminum, copper, brass, bronze and stainless steel, in both machining and grinding. Semi-synthetics can be used on ferrous metals, too. They are chlorine-free to reduce bi-metallic corrosion and staining of metals. They should be used at a 5-8% dilution with water, depending on the severity of the operation. Hybrids Hybrids are cutting fluids custom engineered to solve a particular problem. For example, Valenite’s VNT®-800 was developed to be very clean in the machining and grinding of cast iron. It provides better stability in hard water and rejects tramp oil very well, which adds to its bio-stable chemistry. Hybrids work extremely well on all metals in both machining and grinding. They should be mixed at a 5-7% dilution with water, depending on the condition of the water. What Do You Prefer?
Choosing the right fluid today is easier than ever, as the system approach to metal-cutting productivity continues to grow in acceptance. The day is not far off when choosing a complete solution will be as easy as choosing the right insert and chip-breaker today. The answers are available, and the results will more than justify the time you spend choosing the right metal-cutting fluid.
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he metal-cutting industry today is well into the age
of system solutions. What used to be the art of insert selection has been
simplified and codified to the point where it can honestly be called a
technology, if not a science. Grades, coatings and chip-breakers are all
engineered to work together to perform more efficiently over an
increasingly specific range of applications and workpiece materials.
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