【正文】 four methords used to judge machinability are discussed below: 15 Tool life :Metals which can be cut without rapid tool wear are generally thought of as being quite machinble ,and vice versa .A workpiece material with many small hard inclusions many appear to have the same mechanical properties as a less abrasive metal .It may require no greater power consumption during cutting . Yet ,machinability of this material would be lower because its abrasive properties are responsible for rapid wear on the tool ,resulting in higher machining costs. Tool Force and Power Consumption :The use of tool force or power consumption as a criterion of machinability of the workpiece material es about fow two reasons .First ,the concept of machinability as the case with which a metal is cut ,imples that a metal through which a tool is easily pushed should have a good machinability rating .Second ,the more practical concept of machinability in terms of minimum cost per part machined , relates to forces and power consumption ,and the overhead cost of a machine of property capacity . Surface Finish ： The quality of the surface finish left on the workpiece during a cutting opeeration is sometimes useful in determining machinability rating of matel 。 7 Machinability Of Metals The condition and physical properties of the work materials have a direct influence on the machinability of a work various conditions and characteristics described as‘condition of work material’, individu ally And in binations,directly influence and determine the machinability. Ope rating conditions,toolmaterial and geo metry ,and workpiece requirements exercise indirect effects on machinability ang can offen be used to overe difficult conditions presented by the work the other hand ,they can create situations that increase machining difficulty if they are ignored .A thorough understanding of all of the factors affecting machinability and machining will help in selecting material ang woekpiece designs to achieve the optimum machining binations critical to maximum productivity. of Work Material The following eight factors determine the condition of the work material microstructure, grain size,heat treatmen,chemical, position ,fabri cation hardness , yield ,and tensile . Microstructure: The microstructure of a metal refers to its crystal or grain structure as shown through examination of etched and polished surface under a microscope .Metal whose microstructures are similar have like machining properties .But there can be variations in the mincrostructure of the same workpiece ,that will affect machinability. Grain Size :Grain size and structure of a metal serve as general indicators of its machinability .A metal with small undistorted grains tends to cut easily an finish easily .Such a metal is ductile ,but it is also ‘gummy’.Metal of an intermediate grain size represent a promise that permits both cutting and finishing machinability . Hardness of a metal must be correlated with grain size and it is generally used as an indicator of machinability. Heat Treatment:To provide desired properties in metals ,they are sometimes put through a series of heating and cooling opertions when in the solid state .A material may be treated to reduce brittleness ,remove stress ,to obtain hardness ,or to make other changes that 8 affect machinability. Chemical Composition :Chemical position of a metal is a major factor in determing its machinability .The effects of position though ,are not always clear ,because the elements that make up an alloy metal ,work both singly and collectively .Certain generalizations about chemical position of steels in relation to machinability can be made ,but nonferrous alloy are too numerous and varied to permit such generalizations. Fabrication: Whether a metal has been rolled ,cold rolled ,cold drawn,cast,or fed will affect its grain size ,ductility , hardness , structureand thereforeits machinability . The term‘wrought’refers to the hammering or forming of materials into permanfactured shapes which are readily altered into ponents or products using traditional manufacturing metals are defined as that group of materials which are mechanically shaped into bars,billets, rolls, sheets,plates or tubing. Casting involves pouring molten metal into a mold to arrive at a near pone nt shape which requires minimal,or in some cases no machining. Molds for these operations are made from sand ,plaster,metals and a variety of other materials. Hardness:The textbook definition of hardness is the tendency for a material to resist is offten measured using either the Brinel