Fundamentals of CNC machining of lathe

Lathe numerical control machining foundation

1 rapid and high-precision tool alignment method of outer diameter end cutter of numerical control lathe

traditional lathes mainly adjust the tool by trial cutting the workpiece, that is, turning the workpiece, accurately measuring the size of the turning position, calculating the difference between the measured value and the target value, and advancing or retreating the tool according to the size and positive and negative of the difference. For CNC lathes, except for a few equipped with tool setting function, tool setting instrument, tool setting block or trial cutting workpiece are mainly used for tool setting. Using a special tool setting instrument for tool setting outside the machine, although the accuracy is high, the tool must be aligned together with the tool holder. The knife clip is generally heavy, and it is difficult to disassemble. Especially when only replacing the blade, using this method is slower than using trial cutting to set the knife. The accuracy of tool setting is not high due to the influence of various errors. Therefore, at present, most CNC lathes still use trial cutting workpiece for tool setting. The first three steps of the step are the same as the traditional tool setting of the lathe, except that the tool compensation value is input with the button instead of the rocker to watch the scale advance and retreat

the advantages of tool setting of trial cutting workpiece are low cost and high precision; The disadvantage is that it takes time, and some cutters (such as oil groove cutter) are difficult to set with this method. Therefore, a fast and high-precision tool setting method suitable for external warp, end face cutter or similar oil groove cutter is explored in practice. This is a manual tool setting method without trial cutting. This method can shorten the time of trial cutting and tool setting by 60% without tool setting instrument, tool setting block or tool setting standard parts. This method can maintain the advantages of trial cutting and knife setting and overcome the disadvantages of trial cutting and knife setting

(1) principle. The outer diameter of the chuck can be used as a ready-made benchmark for horizontal (X-direction) tool setting, and the outer end face of the positioning block is an excellent benchmark for longitudinal (Z-direction) tool setting. The dimension obtained from the precise measurement of the outer diameter of the chuck is a constant value. The z-direction origin of the program is often on the outer end face of the positioning block, so the routine tool setting procedures of first trial cutting, then precise measurement, and finally calculating the compensation value of the tool before entering are avoided in both directions. Especially in the longitudinal direction, because it is not affected by the measurement error of the test cut, the tool setting accuracy is higher than that of the test cut method; Since it is not affected by the installation accuracy, its tool setting accuracy is higher than that of the standard tool setting method

(2) method. Since the numerical control devices of lathes are divided into two categories, the methods should be described separately in two ways

① for NC lathe with absolute position detector,

horizontal tool setting steps: a clear the x-direction compensation value of the corresponding compensation number; B accurately measure the outer diameter near the chuck ring hole, and record the D1 value (this step is only done once when changing the chuck, and the recorded D1 value can be directly used later); C turn the chuck by hand to the lifting eye hole and face the direction of the knife tip; Put a newspaper between the tip of the knife and the chuck with your left hand and pull it continuously. Use manual operation with your right hand to quickly and slowly approach the tip of the knife to the outside diameter of the chuck until the newspaper cannot be pulled. Set the x-direction display value on this time screen as D2; D if the subsequent processing takes a small amount of knife, the amount of knife can be ignored. Subtracting the chuck diameter from the light screen display value and then subtracting twice the newspaper thickness is the supplementary value of the knife. The average thickness of the newspaper is 0.08mm and 0.05mm after local compression Therefore, the tool compensation value in X direction =d2, d1-0.1. Input the calculated value into the x position of the corresponding compensation number of this cutter. If the cutting amount of later processing is large, the above value should be subtracted from the experience to enter the cutting amount

longitudinal tool setting steps: a clear the z-direction compensation value of the corresponding compensation number; B turn the chuck to the positioning block by hand and face the knife tip; C place a newspaper between the tip of the knife and the end face of the positioning block with your left hand and pull it continuously. With the right hand, use manual operation to approach the end face of the knife tip positioning block quickly and slowly until the newspaper cannot be pulled. Set the z-direction display value on the time screen as Z1, then the z-direction knife compensation value =z.05. Then input the calculated value into the Z position of the corresponding compensation number of this cutter. If the cutting amount of later processing is large, the above value should be input after subtracting the experience cutting amount

② for CNC lathes with relative position detectors,

horizontal tool setting steps: step a, B, C, D are the same as the above CNC lathes with absolute position detectors; E "lock" the mechanical part, and manually shake the X display value of the light screen to the same value as (d1+0.10); F release the above "mechanical locking" and manually raise the tool holder to the horizontal starting position; G subtract the x value displayed on this time screen from the x value in the G50 program section in the program, which is the tool compensation value. Enter it into the x position of the corresponding compensation number of this tool. If the cutting amount of later processing is large, the above value should be input after subtracting the experience cutting amount

longitudinal tool setting steps: steps a, B and C are the same as the above-mentioned CNC lathe with absolute position detector; D "lock" the mechanical part, and manually shake the Z display value on the light screen to +0.05; E remove the above "mechanical locking" and raise the tool rest to the longitudinal starting position by manual operation; F subtract the Z value displayed on the screen from the Z value in the G50 program section in the program, which is the tool compensation value. Enter it into the Z position of the corresponding compensation number of the tool. If the z-direction cutting amount of later processing is large, the above value should be subtracted from the experience to enter the cutting amount

(3) precautions

① if the program origin is located at z from the end face of the positioning block, then the z-direction tool compensation value mentioned above should be added with the Z value, which is the case for both types

② if the technical index information of nearly 1million products from more than 800 enterprises around the world and more than 46000 UL yellow card information are collected, the knife tip cannot reach the end face of the positioning block due to the claw, the Z direction can be adjusted with the chuck end face. At this time, the knife compensation value should be converted once

2 method of turning both sides of the workpiece rotation center with a knife

figure 8-1 is a schematic diagram of a flange used on a remote sensor, which needs to turn five surfaces a, B, C, D and E. Except for side a, the requirements for dimensional accuracy, position accuracy and surface roughness of other sides are relatively high. Blanks are forgings. In order to ensure accuracy, it is completed by rough turning and fine turning. Use installation 55. The cylindrical knife with equilateral rhombic blade is installed on the cutter table in the direction shown in the figure

turning method: for example, according to the conventional method, one knife is used for turning surfaces a and B, and another knife is used for turning surfaces C, D and E. in this way, four knives are used for rough turning and fine turning. Moreover, it is difficult to make the dimensional error between surfaces B and e not exceed the tolerance (0.02ram) with this method. The above problems are solved by turning both sides of the workpiece rotation center with a knife. This method is to use a knife for rough turning and fine turning respectively. Except for the different arc of the knife tip, the other two knives are the same, even the path of walking the knife is the same. The following only introduces the turning process of the knife, which has become an important factor in the performance of the safety belt

first make the tool tip quickly reach the M 'point, while making the workpiece rotate forward (M03), then make the tool tip reach the cutting starting point m, and cut surfaces C, D, E in turn until point F. Then stop the workpiece (M05), and make the tool tip reach the n 'point. While reversing the workpiece (m04.), make the tool tip reach the cutting starting point n on the other side, and cut surface B and surface a successively until the tool tip reaches the G point. So far, the cutting has been completed, and the tool withdrawal, stop and end procedures

with this method, more than 10000 pieces have been successfully processed, and the effect is very good, which can be used as a reference for turning similar workpieces

3 NC turning method without burr at the corner

some steel workpieces require that the corner is right angle and there should be no burr. This can be achieved by using NC lathe processing

the turning tool tip is mostly circular arc when enlarged, as shown in Figure 8-2. K is the imaginary tip point, and E and F are the tangent points between the cutting edge arc and the horizontal and vertical lines respectively. If the cutting route is arranged according to figure 8-3 and figure 8-4, burrs will appear at the outer diameter and end face corners respectively. As arranged in Figure 8-5, the burrs on the workpiece after turning are basically the same as those in the figure. It can be seen that the above three conventional turning methods all produce burrs

the common feature of these three kinds of turning: the cutting edge leaves the workpiece contour for a period of time, which provides an opportunity for burring. According to figure 8-5, the program for turning this part is

n4 G01 X100 f0.3:

n5 z-50:

looking at the program, it seems that the tool tip is always on the contour line of the workpiece, but what is instructed in the program is the position of the imaginary tool tip. It can be seen from figure 8-5 that in actual cutting, when point F on the blade moves between points a to B on the workpiece and point e between points c to a on the workpiece, the cutting edge leaves the contour line of the workpiece

take turning the end face first and then the outer diameter as an example to see the process of burring. The figure shows the condition when the tool tip cuts to the left and the e point on it is close to the a point. At this time, the metal on the upper side of point a is squeezed downward by the cutting edge, and part of it is squeezed to the outside of the turned end face, which becomes a burr. The size of the burr is related to the sharpness of the cutting edge. In order not to Burr the workpiece, the cutting route shown in the figure is adopted, and the program is correspondingly changed to

n4g01 x96.8 f0.3

n44g03 X100 z-1.6 k-1.6:

n5 z-50:

in this way, there will be no burrs on both sides of the corner after cutting. Although the program is longer than the figure, the total distance of tool tip movement is shorter, that is, the cutting time is less than the figure. Among them, in order to ensure the good effect of turning without burrs at the corners of the workpiece, precision blades should be selected before turning

if the automatic programming machine is used for programming, even if the continuous cutting at the end face up and the outer diameter left is specified, it only compiles (outputs) the program of drawing route. If you want to avoid burrs, you can only make artificial modifications to the output program: change the X instruction value in N4 segment to 96.8, and add N44 segment

for burr free cutting to be plotted, strictly speaking, the tool tip r compensation function cannot be used here, that is, C42 command cannot be used. The following programming can be used:

n3g42 x45 z0:

n4 G01 x100f0.5:

n5 z-50:

when executing, it still follows the diagram rather than the diagram. For example, G42 is used in the programs before and after this program segment, and the programmer does not want to remove G42 here and recalculate the command values in many other places. The following program can be programmed:

n3g42 x45 z0:

n4g01 x99.998 f0.3:

n44 G03 X100 z-0.001 k-0.001:

n5 z-50:

don't look at the arc with a small radius of 1gm and no impact on the contour of the car, it will be executed as shown in the figure.Take the route of, Turn the workpiece without burr at the corner

4 method to prevent sudden rise of tool load at the corner of cutting concave

the finish machining of the workpiece is shown in the figure. The dotted line and solid line in the figure are the contours before and after machining respectively. It is mass processing, and the surface is required to be free of knife contact marks

select the end outer diameter knife with 80 ° equilateral diamond coated blade. If turning on a single table CNC lathe, if part I is turned first, a wide chip will appear when it finally approaches point C, and the load on the left edge of the blade will rise sharply, which is detrimental to both the tool and the machine tool. If this knife ends when it is about to contact part II, then the second knife turning part II must be turned like this: cut down to point C first, and then walk at least 1.5mm to the right to withdraw the knife, so that the cutting load will not rise abruptly, but there is a tool receiving mark on the outer diameter, which is not allowed. The same is true when using car II first and then car I. It can be solved by turning parts I and II back and forth several times, but in this way, the cutting efficiency is reduced a lot. Small batch processing is OK, and large batch processing is not suitable. The outer diameter knife of 35 ° equilateral diamond blade can also be used for turning, so that the load at the end of the first knife does not increase too much, but the strength of 35 ° diamond blade is poor, and the effect is not good. Finally, it is solved by the following methods on the double turret CNC lathe. Use two identical 80 ° equilateral diamond coated blades