Materials Used in Milling Cutters

The milling cutter may be made of high-speed steel, Super high-speed steel; Nonferrous cast alloys or cemented carbide tipped. The high-speed steel cutters are the most widely used cutters in general workshop. The cutters are successfully used for plain milling or slotting operations where the chip thickness is small. The cast alloy or cemented carbide tips are used as inserted blades or tips are brazed on tool steel shanks. The milling cutters must be able to remove metal efficiently and satisfactory. To discharge its function the cutter must be stronger and harder than the material being cut. The main materials being used are summarized below.

Tool Steel

It contains carbon in amounts ranging from 0.80 to 1.5 %. Disadvantages of tool steels are that they comparatively low heat and wear resistance. Cutters made of tool steel are comparatively cheap, easy to forge and simple to harden.

Alloy Steel

It is the most important and widely used group of cutting tool material. They are commonly known as high speed steels since they can be operated at high speed of two and half times more than those used as a carbon tool steel and retain their hardness up to about 900⁰C. These are the general type of high speed steels, high tungsten, high molybdenum and high cobalt. The steel containing 18 % tungsten 4 % chromium and 1 % vanadium is considered to be one of the best of all-purpose tool steel. In some steels of similar composition the percentage of vanadium is slightly increased to obtain better result in heavy-duty work. This steel containing 6 % molybdenum 6 % tungsten 4 % chromium and 2 % vanadium have excellent toughness and cutting ability. Cobalt high-speed steel called super high speed steel. Cobalt is added from 2-15 % to increase hot hardness and wear resistance. One alloy of this steel contains 20 % tungsten 4 % chromium 20 % vanadium and 12 % cobalt.

Stellites

It is the trade name of non-ferrous cast alloy composed of 40- 80 % cobalt, 30-35 % chromium and 12-19 % tungsten. In addition to one or more carbide forming elements, carbon is added in amounts of 1.8 to 2.5 % stellites preserve hardness up to 1000⁰C and can be operated on steel at high speed two times higher than for high-speed steel.

Cemented Carbides

These are composed principally of carbon mixed with other elements. The basic ingredients of most cemented carbides are tungsten carbide which is extremely hard. Carbide tools are made by brazing or silver soldering the formed inserts on the ends of commercial steel holders. The most important properties of cemented carbides are their very high heat and wear resistance. Cemented carbide tipped cutters can machine metal even when their cutting elements are heated to a temperature of 1000⁰C. They can withstand cutting speed for more than six times higher than tools of high-speed steel. Cemented carbide is the hardest manufactured material and has an extremely high compressive strength; however it is very brittle, low resistance to shock.

Ceramics

Ceramics are the latest development in the metal cutting tools uses Aluminium oxide, generally referred to as ceramics. Compacting aluminium oxide power in a mould makes ceramic cutters. The ceramic cutters are made in the form of tips and are to be clamped on metal shanks.