电子教案统一模板(数控)Unit5.ppt

Unit 5 NC Programming,5.1 Lesson 9 Basic Requirements of NC Machine Control,To control a machine, it is necessary to begin by defining the coordinate of the tool motion. It is necessary to specify whether the motion is a positioning motion (rapid traverse) or a feed motion (cutting). The feed motion includes linear motion and circular motion. These control functions and data requirements are summarized in what follows: Preparatory functions the words specify which unit, which interpolator, absolute or incremental programming, which circular interpolation plane, cutter compensation, and so on., Coordinates define three dimensional (and three rotational) axes. Machining parameters specify feed and speed. Tool control specifies tool diameter, next tool number, tool change, and so on. Cycle functions specify drill cycle, ream cycle, born cycle, mill cycle, and clearance plane. Coolant control specify the coolant condition, that is, coolant on/off, flood, and mist. Miscellaneous control specifies all other control, spindle on/off, spindle rotation direction, pallet change, clamp control, and so on. Interpolators linear, circular interpolation, circle center, and so on.,These control functions are programmed through program words (codes). G-code The G-code is also called preparatory code or word. It is used to prepare the MCU for control functions. Modal functions are those that do not change after they have been specified once, such as unit selection. Non-modal functions are active in the block where they are specified F-code The F-code specifies the feed speed of the tool motion. It is the relative speed between the cutting tool and the work-piece. Feed speed can be changed frequently in a program, as needed. When an F-code is present in a block, it takes effect immediately., S-code The S-code is the cutting speed code. Cutting speed is the specification of the relative surface speed of the cutting edge with respect to the work-piece. It is the result of the tool rotation. Therefore, it is programmed in rpm. The Machine Ability Data Handbook gives these values in surface feet per minute (sfpm), and conversion is required before programming is done.1 The S-code is specified before the spindle is turned on. The S-code does not turn on the spindle. The spindle is turned on by an M-code. To specify a 1000 rpm spindle speed, the program block is：N0010 S1000 M03., T-code The T-code is used to specify the tool number. It is used only when an automatic tool changer is present. It specifies the slot number on the tool magazine in which the next tool is located. Actual tool change does not occur until a tool change M-code is specified. R-code The R-code is used for cycle parameters. When a drill cycle is specified, one must give a clearance height. M-code The M-code is called the miscellaneous word and is used to control miscellaneous functions of the machine. Such functions include turn the spindle on/off, start/stop the machine, turn on/off the coolant, change the tool (Table 5-1).,5.2 Lesson 10 Interpolation Commands of CNC Lathes,Interpolation commands include linear, circular interpolation, circle center interpolation, and so on. Linear interpolation commands For CNC lathes, linear interpolation involves moving the tool along a straight line programmed at the specified feed rate.1 Linear interpolation is used to execute such operations as turning, facing, taper turning, and taper boring.2 In the discussion to follow it is assumed that the center of tool nose radius is programmed.,General syntax G01 X1 Z1 Fn X2 Z2 X3 Z3 Xn Zn In which G01 Specifies the linear interpolation modes. X1 and Z1 specify the absolute coordinates of the center of the tool nose radius at the end of the first line cut, second line cut, third line cut, and so on.,Fn specifies the feed rate of the tool. If not programmed, the system will use the last feed rate programmed. If not specified at the beginning of the program, the system will issue an alarm.3 Circular interpolation commands Circular interpolation for lathe operations involves cutting a circular arc in either a clockwise or a counterclockwise direction. The commands are similar to those used in milling. Assume, again, that the center of the tool nose is programmed. General syntax G02 Xn Zn In Kn Fn,In which G02 specifies circular interpolation in the clockwise direction. Xn and Zn specify the X and Z absolute coordinates of the center of the tool nose radius at the end of the arc cut. In and Kn specify the incremental X and Z distances with or direction from the center of the tool nose radius at the start of the arc to the center of the arc.4 Fn specifies the feed rate of the tool. If not programmed, the system will use the last programmed feed rate.,5.3 Reading Materials 9 Setup Procedure,The setup operation can begin after the fixtures, tooling, program tape, setup sheets, and part blank arrive at the CNC machine. Usually the setup person starts by securing the cutting tools in the tool holders. The tooling assemblies are loaded into the tool magazine according to the order outlined in the setup sheet. The work-holding device is put in place on the machine table.,The part blank is located into the work-holding device as requested by the programmer. After loading the program into the MCU, the setup person then proceeds to enter another important piece of information left blank by the programmer: the location of the part origin or part Xo Yo with respect to machine home. The machine home position or machine zero is a location set once by the machine manufacturer. The CNC machine is homed at the start of the part program setup. When homed, the machine retracts the spindle to its maximum height above the table (machine Zo) and moves the table to a preset machine zero position (machine Xo Yo).,The part origin is the（0，0，0）location of the part XYZ coordinate system. In absolute coordinate programming all tool movements are taken with respect to this origin. See Figure 5-1 for an illustration of these positions. The point from which dimensions are taken on the part print is usual1y considered the part origin. This could be the center of a hole, the edge of the part or a certain predetermined distance from the edge. The setup person must determine the XYZ locations of the part origin from machine home. This is accomplished by placing an edge finder or end mill with known diameter in the spindle and using the MCU s jog buttons to move or “tram” the edge finder probe from machine home to the part edge or hole center. See Figure 5-2.,There are two main methods of programming this location into the MCU. The first is called the fixture offset method. This involves using the MCU keypad to enter the XYZ values directly into the MCU unit. The MLU s fixture offset storage area is opened and the values are placed here. Later, when the part program is run, a fixture offset code in the program directs the MCU to use the XYZ values previously placed in its offset storage area.,5.4 Reading Materials 10 Debugging the Program,The debugging process begins after the part program has been successfully loaded. First, the setup person locks the machine and runs the program using only the output from the MCU. This is done to check if the controller recognizes all the codes in the program. If this test is successful, the program can be run with the machine Z-axis locked. This will guard against any possible collisions between the tool and the work holding or part itself. Next is the so-called “dry” run with the part removed.,During this test the setup person slows down the rapid feeds and speeds up the actual feeds. These tests will indicate whether the program runs and if there are any extraordinary moves which could cause a collision of the work and/or work holding wit