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Flexible use of several coordinate instructions of machining center

generally, when machining operations are carried out with machining centers, it is hoped that machining operations will be carried out in a unified machining coordinate system, but in some cases, using some coordinate transformation skills, combined with subroutine call instructions, can make machining programming more concise and easy. The author has been engaged in NC machining for many years, and has summarized some solutions to various problems in actual machining. All instructions in this paper refer to Okuma CNC system, which is somewhat different from other CNC systems in the format of coordinate selection instructions, coordinate translation (rotation) and spatial coordinate conversion instructions

I. common coordinate instructions of machining center

there are the following kinds of coordinate related instructions commonly used by the CNC system of machining center (various CNC systems have some differences in the definition of individual function instructions and the command codes used, but the functions are the same):

G15 - coordinate system selection

g90 - absolute coordinate programming mode

g91 - relative coordinate programming mode

g92 - coordinate system translation function

g11, G10 - coordinate system translation and rotation, G11 is the coordinate system translation and rotation command, G10 is the cancellation command of G11

g69, g68 - space coordinate system conversion function, g68 is the coordinate system conversion instruction, g68 is the g69 cancellation instruction

the g11/g10 command can translate and rotate the current machining coordinate system in the selected machining plane to generate a local coordinate system

g69/g68 instructions are often used in numerical control of equipment equipped with coordinate conversion function, such as five sided machining centers. It is used to program the machining parts on the plane other than the X-Y plane. With this instruction, the machining plane in any direction can be transformed into the positive direction of the X-Y plane, which solves the complex and error prone problem in the machining change of the plane in any direction

g91 instruction is carried out in incremental mode during machining calculation. The G92 command can change the position of the current coordinate system in the program, causing the coordinate origin to shift. These two instructions should be used with caution, especially G92. Careless use may cause the loss of machining coordinate system and the loss of benchmark for all machining. However, if used properly, it can achieve the effect that other instructions are difficult to achieve

g91 instruction is carried out in absolute mode in machining calculation, that is, all machining instruction values are referenced to the current workpiece coordinate system or local coordinate system. This is a modal command to compare the hardness and softness of the tested material with the local plastic deformation of the material surface

second, the use of coordinate instructions

Figure 1

Figure 1 is a virtual part schematic diagram. We can use the machining program of this box model to explain several uses of coordinate instructions. Suppose that the parts in Figure 1 need to process the following parts:

milling the top surface of two square window planes, the processing dimensions of the two planes are the same, and the tool used is a face milling cutter

mill the front two hole end faces, and use the cutter as the face milling cutter

drill two groups of four holes on the flange end face of the front two holes. The array mode of each group of holes is the same, and the tool is fried dough twist drill

finish boring the front two holes, and the tool is a fine boring tool

the coordinate system o in Figure 2 is the machining coordinate system of the workpiece, and the coordinate system number is 1. Because there is surface turning content in the processing part of the workpiece, we assume that the equipment used is a five sided machining center

figure 2

of course, these processes can be programmed in the workpiece coordinate system o using the most direct method

(1) for the processing of the top window, in G91 mode, use the absolute command value to write the processing procedures for processing two planes

(2) for the previous processing parts, the processing here is in the z-x plane. First select the z-x plane, and then write the processing procedures of the two processing parts in the selected plane. It should be noted that the first coordinate axis at this time is the Z axis rather than the X axis, which is very important in fixed cycle instructions and some mathematical calculation functions. Special attention should be paid to it, otherwise it will be wrong

here we do not use the above methods, but use several coordinate transformation methods to deal with these processing contents, and see if it is more convenient than using the above methods. The following is a brief description of the programming method used for each processing part:

(1) milling the front two hole end faces, using the cutter as the face milling cutter. First, the processing part is located in the z-x plane, and consider first using the coordinate system conversion command to convert this processing plane to the X-Y plane, as shown in Figure 2, the setting system O1 is more in line with the operation and programming habits. Coordinate conversion can be written into subroutines, which can be called when programming all other machining parts of the same face. G68/g69 instructions are used here

milling two flange end faces, the processing contents of the two places are similar, and subroutines can be considered. Because the two machined surfaces are not at the same height, incremental programming can be used to solve this problem

(2) drill two groups of four holes on the flange end face of the first two holes. The array mode of each group of holes is the same. The tool is fried dough twist drill. Both groups of holes are in the z-x plane, so the coordinate conversion subroutine can be called. The two groups of holes are arrayed in the same way, so the same hole location subroutine can be used. The inconsistency of array center can be solved by G11 and G10 coordinate translation instructions

(3) for fine boring the first two holes, the tool is a fine boring tool, and the coordinate conversion subroutine is also used. The processing programming is carried out in the coordinate system O1. G76 fine boring cycle command is required for fine boring two holes. In this command, the hole bottom tool yield parameters: I, J, K, corresponding to the X, y, Z coordinate axis directions respectively. The specific axis direction of the boring tool depends on the direction of the boring tool tip. Here, if the coordinate conversion instruction is not used and the programming is still carried out in the workpiece coordinate system o, the machining plane is the negative direction of the z-x plane, the tool parameter addresses in the fine boring cycle should be K and I, and the feed axis is Y axis, so the programming is easy to make mistakes. Now, after calling the coordinate system conversion program, the machining plane and the feeding direction are converted to the familiar direction of general machining, that is, the positive direction of the X-Y plane is the machining plane, and in the fine boring cycle, the tool parameter addresses are I and j, and the negative direction of the Z axis is the feeding direction, so programming is much easier. This is one of the benefits of using coordinate system conversion instructions

(4) because the two square window planes on the milling surface have the same size, it is considered to compile a unified milling subroutine and simplify the processing program by calling it into the program. Although the two machining surfaces here are in the same direction, they are not in the same plane, so coordinate translation cannot be used, and there is no problem of surface rotation, so coordinate conversion function cannot be used

here we can use G92 coordinate translation command to realize the conversion of two machined surfaces. Because the G92 command needs to change the position of the current workpiece coordinate system in the machine coordinate system, you must be careful when using it. The specific method is to first command the tool to move to a specific position relative to the target machining surface in the main program, and then call the surface machining subroutine

the content of the subroutine is: first use the G15 coordinate system selection instruction to select a coordinate system with another number (and so on. These standards you'd better understand in advance that this coordinate system is not used for other purposes in this program), and then use the G92 instruction to set the current point as a specific point in the new coordinate system, so as to complete the translation of the machining coordinate system. The remaining milling program can be compiled in this coordinate system. After finishing the milling action program, you must first return to the original machining coordinate system, and then exit the milling subroutine

by calling this milling subroutine repeatedly in the same way, multiple identical machining can be completed

III. example of processing program

here, we can write the above processing content as the following processing program:

o0001 (example program of using cod command) N10 (facing T1) milling program T1 tool adjustment command M6 tool change command G15 H1 select the coordinate system of No. 1 workpiece as the current processing coordinate system call ob vc20 = 2 vc10 = 1 call the coordinate conversion subroutine ob, Use the coordinate system o1modin OFAC to call the subroutine OFAC: this instruction calls the subroutine once every time a group of coordinate values are encountered and the tool moves this point. The subroutine call ends. X X1 y y1x x2 y y2modoutcall ocan calls the coordinate conversion cancellation subroutine N20 (drilling T2) drilling program T2 tool adjustment instruction M6 tool change instruction call ob vc20=2 vc10=2 calls the coordinate conversion subroutine ob, uses the coordinate system o1ncyl g81 Z Z1 r R1 F100 S350 drilling fixation cycle, and does not execute the G11 x X1 Y Y1 coordinate system translation instruction at the current point, Shift the origin to the center of 1 hole call OP4 call the hole location subroutine G10 coordinate system translation end G11 x x2 y Y2 coordinate system translation instruction, shift the origin to the center of 2 holes call OP call the hole location subroutine G10 coordinate system translation end g80 end the fixed cycle call ocan call the coordinate conversion cancellation subroutine N30 (finish boring T3) fine boring program T3 tool adjustment instruction M6 tool change instruction call ob vc20=2 vc10=2 call the coordinate conversion subroutine ob, Use the coordinate system O1 ncyl G76 Z ZZ R rl 5 F60 S300 fine boring cycle, the negative direction of X axis is the tool withdrawal direction X X1 y y1x x2 y y2g80 fine boring cycle ends, call ocan call coordinate conversion cancel subroutine N40 (manufacturing top side T4) top milling program T4 tool adjustment instruction M6 tool change instruction g15h1 selects the No. 1 coordinate system as the current workpiece coordinate system g56 Z H place water with different temperatures in the cooling water tank in sections 4 add tool length compensation in the Z direction go x XA x Ya Z Za tool fast forward to 100mm above the center of the first rectangular machining surface call oft call rectangular face milling subroutine go x XB x Yb Z ZB tool fast forward to 100mm above the center of the second rectangular machining surface call off call rectangular face milling subroutine M2 main program end subroutine (subrogram)

/ocan coordinate conversion cancellation subroutine go z360 m5g68 coordinate conversion cancellation once g68 coordinate conversion cancellation twice G334 cancellation of accessory head compensation (five side machining center) RTs/ob front coordinate system conversion subroutine g333 pac=90 pat=vc20 h=vc10 five side machining center accessory head turns to the front machining surface, At the same time, add the tool length compensation and accessory head compensation go y... X... Z... Run the tool to the position suitable for conversion g69 x... Y... Z... R90 coordinate system conversion instruction: convert the processing coordinate system from O to o1go XO yo Z100, send the tool to the tool preparation position RTS return/ofac (FAC Jinan new era Gold Testing Instrument Co., Ltd. has a strong reputation in the country ing round) The flange milling subroutine go Z Z2 sends the tool to the machining depth S500, the spindle speed G91 G1 Y-A F100 m3 changes to the incremental mode, the tool cuts into the machining part G2 JA arc interpolation, the flange milling subroutine G1 ya f500 tool exits the machining part G90 go Z100 M5 returns to the absolute mode, the tool returns to the preparation position RTS return/OP4 (position of 4 holes) hole position subroutine BHC XO yo I R1 J45 K4 calculates the hole position with a mathematical formula; Circular array, the center is the coordinate origin, the radius is R1, and the starting angle is 45 degrees, A total of 4 holes RTS return/oft (machining square) milling rectangle subroutine g15h5 calls the No. 5 coordinate system as the current machining coordinate system (temporary) G92 x0y0z100 sets the current point as the (0, 0100) point of the current machining coordinate system g0z0 rectangular surface machining process program... (milling surface machining instruction)..... Go Z100 tool exits G15 H1 returns the current machining coordinate system to the No. 1 coordinate system RTS return

use the subroutine call method to process similar machining content, It can make the program of machining center easy to read and reduce the possibility of error. When dealing with this kind of problem, we should first find out the similarities and differences of different parts to be processed. The common subroutine reflects the difference

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