【正文】 vise. As you rotate the vise crank, you rotate a lead screw that, in turn, drives the movable jaw on the vise. By parison, a linear axis on a CNC machine tool is extremely precise. The number of revolutions of the axis drive motor precisely controls the amount of linear motion along the axis.How axis motion is manded understanding coordinate systemsIt would be infeasible for the CNC user to cause axis motion by trying to tell each axis drive motor how many times to rotate in order to mand a given linear motion amount4. (This would be like having to figure out how many turns of the handle on a table vise will cause the movable jaw to move exactly one inch!) Instead, all CNC controls allow axis motion to be manded in a much simpler and more logical way by utilizing some form of coordinate system. The two most popular coordinate systems used with CNC machines are the rectangular coordinate system and the polar coordinate system. By far, the more popular of these two is the rectangular coordinate system.The program zero point establishes the point of reference for motion mands in a CNC program. This allows the programmer to specify movements from a mon location. If program zero is chosen wisely, usually coordinates needed for the program can be taken directly from the print.With this technique, if the programmer wishes the tool to be sent to a position one inch to the right of the program zero point, is manded. If the programmer wishes the tool to move to a position one inch above the program zero point, is manded. The control will automatically determine how many times to rotate each axis drive motor and ball screw to make the axis reach the manded destination point . This lets the programmer mand axis motion in a very logical manner. Refer to , 3.All discussions to this point assume that the absolute mode of programming is used6. The most mon CNC word used to designate the absolute mode is G90. In the absolute mode, the end points for all motions will be specified from the program zero point. For beginners, this is usually the best and easiest method of specifying end points for motion mands. However, there is another way of specifying end points for axis motion.In the incremental mode (monly specified by G91), end points for motions are specified from the tool39。s current position, not from program zero. With this method of manding motion, the programmer must always be asking How far should I move the tool? While there are times when the incremental mode can be very helpful, generally speaking, this is the more cumbersome and difficult method of specifying motion and beginners should concentrate on using the absolute mode.Be careful when making motion mands. Beginners have the tendency to think incrementally. If working in the absolute mode (as beginners should), the programmer should always be asking To what position should the tool be moved? This position is relative to program zero, NOT from the tools current position.Aside from making it very easy to determine the current position for any mand, another benefit of working in the absolute mode has to do with mistakes made during motion mands. In the absolute mode, if a motion mistake is made in one mand of the program, only one movement will be incorrect. On the other hand, if a mistake is made during incremental movements, all motions from the point of the mistake will also be incorrect.Assigning program zeroKeep in mind that the CNC control must be told the location of the program zero point by one means or another. How this is done varies dramatically from one CNC machine and control to another8. One (older) method is to assign program zero in the program. With this method, the programmer tells the control how far it is from the program zero point to the starting position of the machine. This is monly done with a G92 (or G50) mand at least at the beginning of the program and possibly at the beginning of each tool.Another, newer and better way to assign program zero is through some form of offset. Refer to . Commonly machining center control manufacturers call offsets used to assign program zero fixture offsets. Turning center manufacturers monly call offsets used to assign program zero for each tool geometry offsets.Fig. 4 Flexible manufacturing cellsA flexible manufacturing cell (FMC) can be considered as a flexible manufacturing subsystem. The following differences exist between the FMC and the FMS:1. An FMC is not under the direct control of thecentral puter. Instead, instructions from the centralputer are passed to the cell controller.2. The cell is limited in the number of part families itcan manufacture.The following elements are normally found in an FMC:? Cell controller? Programmable logic controller (PLC)? More than one machine tool? A materials handling device (robot or pallet)The FMC executes fixed machining operations with parts flowing sequentially between operations. High speed machiningThe term High Speed Machining (HSM) monly refers to end milling at high rotational speeds and high surface feeds. For instance, the routing of pockets in aluminum airframe sections with a very high material removal rate1. Over the past 60 years, HSM has been applied to a wide range of metallic and nonmetallic workpiece materials, including the production of ponents with specific surface topography requirements and machining of materials with hardness of 50 HRC and above. With most steel ponents hardened to approximately 3242 HRC, machining options currently include: Rough machining and semifinishing of the material in its soft (annealed) condition heat treatment to achieve the final required hardness = 63 HRC machining of electrodes and Electrical Discharge Machining (EDM) of specific parts of dies and moulds (specifically small radii and deep cavities with limited accessibility for metal cutting tools) finishing and superfinishing of cylindrical/flat/cavity s