Tool compensation in the processing of the hottest

Tool compensation in NC machine tool machining

tool compensation in NC machine tool machining:

first, the proposal of tool compensation:

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

NC machine tool end mill machining

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

economical CNC machine tools have simple structure and low price, and have a certain amount of 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 according to the workpiece outline size and tool diameter first. Therefore, the calculation is large and complex, and the tool wear and replacement need to recalculate the trace size of the tool location and re compile the processing program

II. Tool compensation in full-function CNC machine tool system:

1. NC lathe tool compensation

NC lathe tool compensation function includes tool position compensation and tool arc radius compensation. Use the t function to specify in the processing program. The first two XX in t***x 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 changes caused by reinstallation of the tool, after the establishment and implementation of tool position compensation, 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 stored in the corresponding compensation memory, after performing tool compensation, the tool will move from point 0 to point 2, not point 1, and the corresponding program segment is N60 G00 x45 z93 T0202

Fig. 2 a processing state

(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 Fig. 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, expressed by parameters 0 ~ 9, and point P is the theoretical tool tip

Figure 3 tip arc

Figure 4 tip side grasp the project reserve position

(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, and the CRT display is 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

Figure 5 contents displayed by CRT

2. Tool compensation of machining center and NC milling machine

NC system of machining center and NC milling machine, tool compensation functions include tool radius compensation, included angle compensation, length compensation and other tool compensation functions

(1) tool radius compensation (G41, G42, G40) the radius value of the tool is stored in memory hxx in advance, and XX is the memory number. After the implementation of tool half diameter compensation, 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 movement direction of the programmed machining path. At this time, the system displays "C0" to the left (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 in use: when establishing and canceling tool compensation, that is, the program segment using G41, G42, G40 instructions must use G00 or G01 instructions, and G02 or G03 must not be used. 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 only calculates the tool compensation according to the program of this section, it cannot solve the transition problem between program sections, and it is required to treat the workpiece contour as fillet transition, so the processability of the sharp corner 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 it 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, 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, which can be solved by included angle compensation (g39). When using the included angle compensation (g39) command, it should be noted that this command is non modal, valid only in the program segment of the command, and can only be used after G41 and G42 commands

(3) tool length offset (G43, g44, G49) according to American media reports, 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 instruction or H00 instruction can be used to cancel the tool length offset. In program segment N80 G43 z56 H05 and, if the median value of 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 memory 05 is 16mm

III. Calculation of tool path in economic CNC machine tools:

Economic CNC machine tool system, if there is no tool compensation command, can only calculate the motion path size of the tool location, and then program according to this, or carry out local compensation processing

1. calculation of tool center (tool location)

in the numerical control system that needs to calculate the tool center trajectory, it is necessary to calculate the coordinates of the base point and node on the tool center corresponding to the base point and node of the part contour. Figure 1 shows the use of φ 8. The movement track of the tool center when the end milling cutter processes the workpiece curve. It can be seen that the tool path is the isometric line of the part contour, which can be obtained from the part contour and the tool radius

isometric equation of straight line:

when the calculated isometric line is on the upper side of the original straight line, take the "+" sign, otherwise take the "-" sign

equation of isometric line of circle:

when the calculated isometric line is an outer isometric line, take "+" sign, otherwise take "－" sign

to solve the coordinates of the base point on the isometric line, only the relevant isometric line equations need to be solved simultaneously. For example, calculate the coordinates of 3 ', 2 points (40, 85) and 3 points (70105)

a=y2-y3=-20

b=x3-x2=30

c=x3y2-ybx2=1750

calculate the center coordinate as (85105)

two equidistant line equations are simultaneous:

-20x+30y=1750+144.222

(x-85) + (y-105) = (15+4)

solve x=66.134 y=107.231

that is, the coordinate of 3 'point is (66.34107.231). The coordinates of other base points or nodes on the tool center path can be calculated in the same way, and then program according to this

2. Calculation of the offset of the imaginary tool tip of NC lathe

in NC turning, for the convenience of tool setting, the tool is often set with the imaginary tool tip P point. If there is no tip arc radius compensation, undercutting will occur when turning conical surfaces or arcs. When the accuracy of the part is high and there is a cone or arc, the solution is to calculate the size of the center track of the tool tip arc, and then compile the product according to this, and calculate the local compensation

Figure 3 shows the tool position compensation caused by the arc radius r of the tool tip when turning the dimensional surface. When the tool position compensation is carried out at the same time in the Z direction and X direction, the actual contact point a between the blade and the workpiece moves to the tip set point P during programming, and the compensation amount of R can be calculated according to the following formula:

when programming the conical surface of the workpiece, its base point coordinate is the base point coordinate of the workpiece contour (Z and x) plus the compensation amount of the tip arc radius R (DZ and DX), which solves the problem of no tip arc radius compensation

IV. conclusion:

in NC machining, because the tool tip has an arc and the workpiece contour is formed by the tool motion envelope, the motion trajectory of the tool location does not coincide with the contour of the workpiece. In the full-function CNC system, the tool compensation instruction can be applied to program and process conveniently according to the contour dimension of the workpiece. In the economical numerical control system, the motion path of the tool location can be calculated according to the contour dimension of the workpiece and the tool, and it can be programmed according to this method, or it can be solved according to the method of local compensation