Milling cutters. Which ones are better.
Milling cutters. Which is better: quick-cut or hard alloy?
Without an axe — not a carpenter, without a needle — not a tailor, well, and without a cutter — not a milling cutter. There are a huge number of these cutters: different shapes, different contents, execution and purpose. A professional milling cutter dresses, a milling cutter shoes, so we must choose among this variety exactly the option that will meet our expectations. And the first thing to deal with is the material of the tool.
There are two main materials for the manufacture of monolithic milling cutters: high-speed steel (HSS) and hard alloy, and, of course, they have their advantages and disadvantages. Now in order.
Quick cut
High-speed steels contain from 0.7-1.5% carbon, up to 18% tungsten, and other elements. They are designated by the Russian letter "R" (P18, P6M5, etc.) or Latin HSS (High Speed Steel) + additional letters, indicates the included elements in the composition or certain manipulations in the production of the tool that enhance its properties. Быстрорез stronger and cheaper than hard alloy. Such cutters are easily and quickly re-sharpened (especially GOST) on a grinding machine. These advantages are still enough to choose in favor of a quick-cut, if, for example, we cut ordinary steel on an old universal machine, with low rpm, weak SPEED system. In general, if we work outside favorable conditions, at low speeds, with simple machine-building materials, and with a low budget, then we buy cutters of the GOST type.
The situation is different if we have new equipment, reversible, rigid: universal or CNC — not the point, if the materials remain structural, and the speeds are gentle up to 80-100m /min, then you can continue to use high-speed steel. But there is a nuance: it is better to take with a protective coating, cobalted and created using powder metallurgy technologies (HSS-E, HSS-E-PM, etc.). Productivity will increase, but the price of the milling cutter will also increase: it will approach the cost of a hard alloy. And since the processing speed and prices of our milling cutters are increasing, it's time to discuss the hard alloy.
Hard alloy
Hard alloys are alloys of refractory metal carbides with cobalt, which is a kind of binder. From the name it is clear that these alloys have high hardness, wear resistance and heat resistance up to 1000 degrees Celsius (quick cuts up to 650).
Hard alloys are obtained by powder metallurgy from micron, submicron substrates. Usually tungsten carbide with cobalt is used, often titanium carbide and tantalum carbide are mixed there (the well-known Soviet marking VK, TK, TTK).
Each manufacturer has its own import markings, since the composition of their tool, which pleases machine operators with resistance to a certain operation, is a competitive advantage and a trade secret. They are also improved by various combinations of PVD and CVD coatings that increase the wear resistance of the milling cutter. Such cutters are capable of processing at a speed of up to 500 m/min., the so-called hard-to-process materials of groups P, M, K, S, H, and non-ferrous metals (group N) are processed up to 2000 m/min.
But, of course, only the best equipment works in these modes. The hard alloy in tandem with a high-quality, high-speed and rigid machine gives greater accuracy, better quality of the treated surface, predictable tool life. This allows you to significantly increase productivity, which will more than pay off the high price tag of a solid-alloy monolithic milling cutter.
So, now we understand that the choice of a tool made of high-speed steel or a hard alloy depends on the conditions in which the milling cutter will work. But in addition to the material of the tool, there are other subtleties of choosing the right milling cutter for a particular operation. And as experienced classics say in such situations, this is a completely different story...