An Introduction to High Speed Steel

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  • Topic: Machining, Reamer, Drilling
  • Pages : 14 (4997 words )
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  • Published : March 28, 2011
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High Speed Steel
* High Speed Steel (HSS) refers to any of a variety of steel alloys that engineers primarily use to construct machine tool bits and blades and drill bits for industrial power tools. Materials scientists can infuse this steel with differing percentages of elements to form a variety of HSS manufacturing alloy types. While all of these different types exhibit HSS's characteristic resistance to high-temperature, the properties of each alloy will vary depending on the percentage of other elements the alloy contains. Physical Composition

* High Speed Steel is a multi-component alloy carbon-based steel and, as such, steel mills manufacture HSS according to the Fe-C-X system (Iron-Carbon-X). In this system, "X" can represent one or more other elements, most commonly Tungsten plus chromium, molybdenum, vanadium, or cobalt. Generally, the final proportions of total weight of non-ferrous elements used to manufacture HSS range from .65 to .80% carbon, .10 to .40% manganese, .20 to .40% silicon, 3.75 to 4.0% chromium, no more than .30% nickel, 17.25 to 18.75% tungsten, .90 to 1.30% vanadium, no more than .25% copper, .03% phosphorous, or .03% sulfur. Strength

* High Speed Steel exhibits a density of 8.67x1000 kg/m3 (kilograms per meters-cubed). This high density affords it incredible durability and hardness (even at high temperatures) and shock and vibration resistance while still allowing for its machinability into tools and drill bits. Once formed, the low carbon percentage gives it a very high melting point (ranges vary depending on the alloy). Its strength also leads to greater durability in tools even when used in conditions of mechanical and thermal stress. A greater percentage of chromium in HSS alloys will increase its strength, while vanadium increases will improve the cutting quality and sharpness of tools and drill bits made with HSS. Alloys containing higher percentages of molybdenum will also display increased hardness. Thermal Properties

* When used in tools, High Speed Steel operates at a very low thermal expansion rate of 9.7 microns per meter per degree Celsius. It also conducts heat at a very low rate. Both of these properties enable HSS tools to cut faster (hence the name, "high speed") and to be used for longer periods. Because of this low thermal conductivity, technicians using HSS manufactured tools can also use a wide variety of lubricants for the tools. As a general rule, the higher the percentage of carbon in HSS, the lower the melting point of the steel, which will lessen its thermal properties as well. Alloys containing cobalt demonstrate an improved hardness at high temperatures and greater durability.

Turning

Turning is the process whereby a single point cutting tool is parallel to the surface. It can be done manually, in a traditional form of lathe, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of machine tool is referred to as having computer numerical control, better known as CNC. and is commonly used with many other types of machine tool besides the lathe. When turning, a piece of material (wood, metal, plastic, or stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise diameters and depths. Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various geometries. Although now quite rare, early lathes could even be used to produce complex geometric figures, even the platonic solids; although until the advent of CNC it had become unusual to use one for this purpose for the last three quarters of the twentieth century. It is said that the lathe is the only machine tool that can reproduce itself. The turning processes are typically carried out on a lathe, considered to be the oldest machine tools, and can be of four different types such as straight turning, taper...
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