Tool compensation in the most popular NC machining

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Tool compensation in NC machining

[ader] 1. The proposal of tool compensation

machining a workpiece on a NC machine tool with an end milling cutter, it can be clearly seen that the tool center motion gauge does not coincide with the workpiece contour, because the workpiece contour is formed by the motion envelope of the end milling cutter. The center of the end milling cutter is called the tool position of the cutter (4 and 5 coordinate CNC machine tools are called the tool position vector), and the motion track of the tool position represents the motion track of the cutter. In NC machining, whether to program according to the outline dimension of the workpiece or the moving track dimension of the tool location should be handled according to the specific situation

NC machine tool end mill machining

in the full-function NC machine tool, the NC system has a tool compensation function, which can be programmed according to the workpiece outline size. After the tool compensation is established and executed, the NC system automatically calculates and the tool position is automatically adjusted to the tool motion path. Directly using the workpiece size to compile the machining program, the tool wear, change the machining program unchanged, so it is simple and convenient to use

economical CNC machine tools have simple structure, low price and certain ownership in manufacturing enterprises. In the economical NC machine tool system, if there is no tool compensation function, the machining program can only be compiled according to the motion path size of the tool location, which requires that the path size of the tool location should be calculated first according to the workpiece outline size and tool diameter. Therefore, the calculation is large and complex, and the tool wear and replacement need to recalculate the path size of the tool location and re compile the machining program

2. Tool compensation in the full-function CNC machine tool system

1. compensation for the tool table and piston adapter of CNC lathe

the tool compensation function of CNC lathe includes two aspects: tool position compensation and tool arc radius compensation. Use the t function to specify in the machining program. The first two XX in Txxxx are tool numbers, and the last two XX are tool compensation numbers, such as T0202. If the tool compensation number is 00, it means that the tool compensation is cancelled

(1) tool position compensation tool wear or tool position change caused by tool reinstallation. After tool position compensation is established and executed, its processing program does not need to be re compiled. The method is to measure the position of each tool and input it into the specified memory. After the program executes the tool compensation command, the actual position of the tool will replace the original position

as shown in Figure 2, if there is no tool compensation, the tool moves from point 0 to point 1, and the corresponding program segment is N60 G00 C45 X93 t0200. If the tool compensation is x=+3, z=+4, and is stored in the corresponding compensation memory, the tool will move from point 0 to point 2 instead of point 1, and the corresponding program segment is N60 G00 x45 z93 T0202

(2) tool arc radius compensation when compiling the NC lathe processing program, the turning tool tip is regarded as a point (imaginary tool tip P point), but in fact, in order to improve the service life of the tool and reduce the surface roughness of the workpiece, the turning tool tip is ground into an arc with a small radius (tool tip AB arc), as shown in Figure 3, which will inevitably produce the shape error of the workpiece. On the other hand, the position of the tool tip arc and the shape of the turning tool will also have an impact on the workpiece processing, which can be solved by tool arc radius compensation. The shape and position parameters of the turning tool are called the tool tip orientation, as shown in Figure 4, and are represented by parameters 0 ~ 9. Point P is the theoretical tool tip

(3) tool compensation parameters each tool compensation number corresponds to a total of 4 parameters: tool position compensation (x and Z values) and tool arc radius compensation (R and T values), which are input into the corresponding memory before machining. The display on CRT is as shown in Figure 5. In the process of automatic execution, the CNC system automatically corrects the position error of the tool and automatically compensates the arc radius of the tool tip according to the values of X, Z, R and T in the memory

2. tool compensation of machining center and NC milling machine

the NC system of machining center and NC milling machine. The tool compensation function includes tool radius compensation, included angle compensation, length compensation and other tool compensation functions

(1) tool radius compensation (G41, G42, G40) the tool radius value is stored in memory hxx in advance, and XX is the memory number. After the tool radius compensation is performed, the CNC system automatically calculates and makes the tool automatically compensate according to the calculation results. Tool radius left compensation (G41) means that the tool deviates to the left of the movement direction of the programmed machining path (as shown in Figure 1), and tool radius right compensation (G42) means that the tool deviates to the right of the movement direction of the programmed machining path. G40 is used to cancel tool radius compensation, and H00 is also used to cancel tool radius compensation

note during use: when creating or canceling tool compensation, that is, the program segment using G41, G42, and G40 commands must use G00 or G01 commands, not G02 or G03. When the tool radius compensation takes a negative value, the functions of G41 and G42 are interchanged

tool radius compensation has two compensation forms: B function and C function. Because the B-function tool radius compensation is only calculated according to the program of this section, it can not solve the transition problem between program sections, and it is required to process the workpiece contour into fillet transition, so the processability of the sharp corners of the workpiece is not good. The C-function tool radius compensation can automatically process the transfer of the tool center path of the two program sections, and can be programmed completely according to the workpiece contour. Therefore, almost all modern CNC machine tools use C-function tool radius compensation. At this time, it is required that the next two program segments that establish the tool radius compensation program segment must have the displacement instructions (G00, G01, G02, G03, etc.) that specify the compensation plane. "Shenjiahong of BASF China Co., Ltd. told the reporter, otherwise, the correct tool compensation cannot be established

(2) included angle compensation (g39) the intersection of two planes is an included angle, which may cause over travel and over cutting, resulting in machining errors. Included angle compensation (g39) can be used to solve this problem. When using the included angle compensation (g39) command, it should be noted that this command is non modal, only valid in the program section of the command, and can only be used after G41 and G42 commands

(3) tool length offset (G43, g44, G49) the tool length offset (G43, g44) command can be used to compensate the change of tool length at any time without changing the program, and the compensation amount is stored in the memory of the H code command. G43 indicates that the compensation amount in the memory is added to the end coordinate value of the program instruction, g44 indicates subtraction, and G49 or H00 can be used to cancel the tool length offset. In procedure segment N80 G43 z56, the carbon content of 42CrMoA or B7 adopted for cold heading hexagon bolt is high at 0 45 in the range H05 and H05, if the value in the 05 memory is 16, it means that the end coordinate value is 72mm

the value of the compensation amount in the memory can be pre stored in the memory with MDI or DPL, or the program segment instruction G10 P05 r16.0 can be used to indicate that the compensation amount in the 05 memory is 16mm

III. Calculation of tool path in economical CNC machine tools


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