|
The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often considered as a pair because of their combined effect on the cutting process. Each, however, can also be considered and analyzed in its own right. ''Cutting speed'' (also called ''surface speed'' or simply ''speed'') is the speed difference (relative velocity) between the cutting tool and the surface of the workpiece it is operating on. It is expressed in units of distance along the workpiece surface per unit of time, typically surface feet per minute (sfm) or meters per minute (m/min). ''Feed rate'' (also often styled as a solid compound, ''feedrate'', or called simply ''feed'') is the relative velocity at which the cutter is advanced along the workpiece; its vector is perpendicular to the vector of cutting speed. Feed rate units depend on the motion of the tool and workpiece; when the workpiece rotates (''e.g.'', in turning and boring), the units are almost always distance per spindle revolution (inches per revolution (or ipr ) or millimeters per revolution ()). When the workpiece does not rotate (''e.g.'', in milling), the units are typically distance per time (inches per minute (or ipm ) or millimeters per minute ()), although distance per revolution or per cutter tooth are also sometimes used. If variables such as cutter geometry and the rigidity of the machine tool and its tooling setup could be ideally maximized (and reduced to negligible constants), then only a lack of power (that is, kilowatts or horsepower) available to the spindle would prevent the use of the maximum possible speeds and feeds for any given workpiece material and cutter material. Of course, in reality those other variables are dynamic and not negligible; but there is still a correlation between power available and feeds and speeds employed. In practice, lack of rigidity is usually the limiting constraint. The phrases "speeds and feeds" or "feeds and speeds" have sometimes been used metaphorically to refer to the execution details of a plan, which only skilled technicians (as opposed to designers or managers) would know. == Cutting speed == Cutting speed (also called ''surface speed'' or simply ''speed'') may be defined as the rate (or speed) that the material moves past the cutting edge of the tool, irrespective of the machining operation used. A cutting speed for mild steel, of 100 ft/min (or approx 30 meters/min) is the same whether it is the speed of the (stationary) cutter passing over the (moving) workpiece, such as in a turning operation, or the speed of the (rotating) cutter moving past a (stationary) workpiece, such as in a milling operation. What will affect the value of this surface speed for mild steel, is the cutting conditions: For a given material there will be an optimum cutting speed for a certain set of machining conditions, and from this speed the spindle speed (RPM) can be calculated. Factors affecting the calculation of cutting speed are: * The material being machined (steel, brass, tool steel, plastic, wood) (see table below) * The material the cutter is made from (Carbon steel, high speed steel (HSS), carbide, ceramics) * The economical life of the cutter (the cost to regrind or purchase new, compared to the quantity of parts produced) Cutting speeds are calculated on the assumption that optimum cutting conditions exist, these include: * Metal removal rate (finishing cuts that remove a small amount of material may be run at increased speeds) * Full and constant flow of cutting fluid (adequate cooling and chip flushing) * Rigidity of the machine and tooling setup (reduction in vibration or chatter) * Continuity of cut (as compared to an ''interrupted cut'', such as machining square section material in a lathe) * Condition of material (mill scale, hard spots due to white cast iron forming in castings) The cutting ''speed'' is given as a set of constants that are available from the material manufacturer or supplier, the most common materials are available in reference books, or charts but will always be subject to adjustment depending on the cutting conditions. The following table gives the cutting speeds for a selection of common materials under one set of conditions. The conditions are a tool life of 1 hour, dry cutting (no coolant) and at medium feeds so they may appear to be incorrect depending on circumstances. These cutting speeds may change if, for instance, adequate coolant is available or an improved grade of HSS is used (such as one that includes cobalt). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「speeds and feeds」の詳細全文を読む スポンサード リンク
|