Milling Cutter Materials

Milling Cutter Materials
Points : Milling Cutter Materials, Tool Steels, Plain Carbon Tool Steel, Alloy Tool Steels or High Speed Steels, Cast-Tool Materials, Cemented Carbides, Stellite The function of the milling cutter is no different from that of the tool bits, drills, reamers, etc. used on other machines; that is the milling cutter must be able to remove metal efficiently and satisfactorily. Considering the wide range of materials that must he machined, the ideal milling cutter should have:
1. High Abrasion Resistance
2. Red Hardness
3. Edge Toughness

As no material can meet these requirements at maximum value in all situations, cutters are made from materials that are, by necessity, a compromise. Cutting tool materials may be grouped as follows:
1. Tool steels Carbon Tool Steel and High Speed Steel.
2. Cast Tool Materials-Cast High-Speed Steel and Cast nonferrous Tool Materials.
3. Sintered or Cemented Carbide Tool Materials.
Each of these groups will be briefly discussed. 1. Tool Steels The name tool steel has been given to all cutting materials which have iron as chief constituent. They consist of a mixture of various elements. When carbon is the only major element added to iron, the resulting product is called steel or carbon steel. The names alloy carbon tool steel and alloy tool steel, or high speed steel, are applied to those steels in which other elements, such as tungsten, cobalt, chromium, vanadium, etc. are present, in addition to carbon. Plain Carbon Tool Steel It is not widely used for milling cutters because of the rapid loss of hardness at temperatures above 400° F. Milling cutters made of this type of steel arc used for screw slotting and slitting, and for light work. This is especially true for those carbon tool steels of low carbon content, known as low-carbon steel. Plain carbon tool steel, with higher carbon content, when used in making milling cutters, is better material than the low-carbon steel. Carbon steels having a carbon content of 1.10 to 1.30 per cent are known as the high carbon steels. They are uses, as a rule,” for finishing cuts and for accurate form tools. Alloy Tool Steels or High Speed Steels Alloy tool steels form one of the most important and widely used groups of cutting tool materials..They are commonly known as high speed steels, since they can he operated at speeds of 2 ‘/2 times those of carbon tool steels. These steels when used as cutting tools may be operated to temperatures up to approximately 1100 F. High-speed steels consist of iron with various amounts of carbon, chromium, tungsten, molybdenum, and vanadium. Alloy steels have been named usually after the major alloying element; for example tungsten high-speed steel is so called because tungsten is the chief alloying element. 2. Cast-Tool Materials Cast high-speed steels and cast nonferrous materials belong to the group of cast-tool materials because the tools made are usually shaped by the use of a mould. Cast High-Speed Steels Cutters made of these steels can be operated at high cutting speeds and are used for machining such materials as armor plate and aluminum.
Cast Nonferrous Tool Materials
They are cast to the desired shape, are fully hardened after cooling to room temperature, and are finished to size by grinding. They are used for marching cast and malleable iron, semi-steel, cast and forged steel, stainless, and other alloy steels. Since cast nonferrous tool materials are brittle and cannot withstand shock, the cutter must not he stopped in the cut. 3. Cemented Carbides Tungsten Carbide is a cutting tool material composed of tungsten, carbon and cobalt. it is very expensive and eneral1y is used in the form of tips brazed to steel shanks which become the teeth of inserted tooth face milling cutters. Tungsten Carbide is used, for tipping the teeth of certain types of solid cutters where the diameter of the cutter makes inserted tooth design impractical. As it is comparatively brittle, the cutting edges of cutters must be backed up in the best possible manner. Cutters with Tungsten Carbide tips are used mostly on cast iron and on non-ferrous materials, in general these cutters can be operated at three to ten times faster than high speed steels cutters. Cemented Carbide cutters are excellent for long production runs and for milling materials with a scale like surface (cast iron, bronze, etc.). 4. Stellite Stellite is a non-ferrous alloy of varying percentages of chromium, cobalt and either molybdenum or tungsten. It cannot be forged or machined except by grinding, but can be cast readily. Cutters with cutting edges of this material retain their cutting quality at high temperature and can be used at higher peripheral speeds than cutters of high speed steels. Small cutters made of Stellite, are usually solid, while on larger cutters the teeth are clamped to a steel disk. Cutters with Stellite teeth are used satisfactorily for mass production such as for milling automobile engine castings and similar parts.