Lathe CNC machining basics

1 Rapid and high precision knife setting method for outer diameter end face cutter of CNC lathe

The traditional lathe is mainly used to test the workpiece by cutting the workpiece, that is, turning the workpiece, finely measuring the size of turning, calculating the difference between the measured value and the target value, according to the size of the difference and the positive and negative feed or retract. For CNC lathes, with the exception of a few equipped with tooling functions, tool setting tools, countersunk blocks, or trial cuts are used. Using a special tool setting tool for external tool setting, although the precision is high, the tool must be aligned with the tool holder. Can be generally relatively heavy knife, disassembly is more laborious. Especially when only replacing the blade, using this method is slower than using a test-cutting knife. With the knife block cutter, due to the influence of various errors, the accuracy of the knife is not high. Therefore, at present, most CNC lathes still use test-cutting workpieces. The first three steps of the procedure are the same as for the lathe's conventional knife, but instead of changing the dial to the tool, use the button to enter the tool compensation value.

The advantages of test piece cutting tools are the low cost and high precision; the disadvantage is time-consuming, and some tools (such as oil grooved knife) are difficult to use this method for knife. Therefore, in practice, a rapid and high-precision knife setting method suitable for the outer warp, face knives or similar oil grooved knives has been found. This is a manual tool setting method that does not require trial cutting. This method can reduce the trial cutting time by 60% without the use of a tool setting tool, a tool block, or a standard tool. This method can maintain the advantages of the test-cutting tool and overcome the shortcomings of the test-cutting tool.

(1) Principle. The outside diameter of the chuck can be used as a ready reference for the transverse (X-direction) tool setting, and the outer end face of the positioning block is an excellent reference for the longitudinal (Z-direction) tool setting. The size of the chuck outer diameter measured once is a constant value. The Z-origin of the program is often located on the outer end face of the positioning block, so the conventional tool setting procedures after the first try-cut and then the fine-measurement, and finally the tool compensation value are eliminated in both directions. Especially in the longitudinal direction, due to the influence of measurement error of the test piece, the accuracy of the tool setting is higher than that of the test cutting method. Since the accuracy of the mounting is not affected, the tool setting accuracy is higher than that of the standard tool setting method.

(2) Method. Because the numerical control devices of lathes are divided into two categories, the methods are divided into two categories.

1 pair of CNC lathes with absolute position detector

Horizontal knife setting procedure: a. Clear the X compensation value of the corresponding compensation number. b. Measure the outer diameter size of the chuck near the ring hole. Record the D1 value. (This step can be done only once when the chuck is replaced. (D1 value directly recorded); c the chuck hand to the ring hole facing the direction of the blade; the left hand will put a newspaper between the tip and the chuck and continue to pull, the right hand with manual operation first fast after slow The tip of the tool is approached to the outer diameter of the chuck until the paper is not moved. The X-direction display value on the light screen is D2; d If the amount of subsequent processing is small, the amount of the knife may not be considered. Subtracting the screen diameter from the screen display value and subtracting twice the newspaper thickness is the value of the knife. The average thickness of the newspaper is 0.08mm, and it is 0.05mm after partial compression. Therefore, the X-direction cutter compensation value = D2, a D1-0.1. Enter the calculated value into the X position of this knife's corresponding offset number. If the amount of knife to be processed in the future is large, the above value should be subtracted from the experience so that the amount of the knife can be input again.

Longitudinal knife setting procedure: a. Clear the Z compensation value of the corresponding compensation number; b. Turn the chuck by hand to the positioning block in the direction of the cutting edge; c. Place a newspaper in the left hand between the cutting edge and the end face of the positioning block. And keep pulling. The right hand uses the manual operation to quickly and slowly approach the end of the tool nose positioning block until the newspaper does not move. If the Z display value on the light screen is Z1, then the Z direction compensation value = Z1-0.05. Then enter the calculated value into the Z position of this knife's corresponding compensation number. If the amount of knife to be processed is large in the future, the above value should be subtracted after the experience to let the amount of the knife be input.

2 pairs of CNC lathes with relative position detector

Horizontal knife setting steps: a, b, c, d are the same as the above-mentioned CNC lathe with absolute position detector; e "locking" the mechanical part, and manually shifting the X display value of the light screen to (D1+) 0.10) The same value; f lift the above "mechanical lock", with manual operation, the knife holder to the lateral start position; g will be the X value in the program G50 program segment minus the screen display X value, this This is the tool offset value, which is entered in the X position of the knife's corresponding offset number. If the amount of knife to be processed in the future is large, the above value should be subtracted after the experience to let the amount of the knife be input.

Longitudinal knife setting steps: a, b, c Three steps are the same as those of the numerically controlled lathe with the absolute position detector described above; d “locking” the mechanical part, manually turning the Z display value on the light screen to +0.05; e lift The above "mechanical locking", manual operation to raise the knife holder to the longitudinal start position; f will be the value of the program in the G50 segment minus the Z value displayed on the screen, is the tool compensation value, enter it This knife can correspond to the Z position of the compensation number. If the amount of Z-cutting to be machined in the future is large, the above value should be subtracted from the experience to re-enter the amount of the knife.

(3) Precautions

1 If the origin of the program is located at Z from the end face of the positioning block, then the aforementioned Z-direction tool compensation value should be added with the Z value, both of which are the same.

2 If the tool tip cannot reach the end face of the positioning block due to the jaws, the Z-axis can use the chuck face to face the blade. At this time, the tool compensation value must be converted once.

2 Method of turning both sides of the turning center of a workpiece with a knife

Figure 8.1 is a schematic diagram of a flange used on a remote sensor to turn five faces A, B, C, D, and E. In addition to the A surface, the dimensional accuracy, position accuracy, and surface roughness of all other surfaces are higher. Blanks are forgings. In order to ensure the accuracy, it can be completed by roughing or finishing. Use installation 55. The outer cutter of the equilateral diamond blade is mounted on the knife table in the direction shown.

Turning method: If the conventional method is used, a knife is used for car A and B surfaces, and another knife is used for car C, D, and E surfaces. In this way, four tools are used for rough and fine cars, and they are processed by this method. It is difficult to make the dimensional error between the B and E faces not exceed the tolerance (0.02 ram) range. The use of a knife to turn both sides of the turning center of the work piece solved the above problem. This method uses a knife for the rough and fine cars respectively. The two knives are the same except for the arc of the tip. The route of the knife is the same. The following only describes the turning process of fine turning tools.

Let the tip quickly reach the point m'. When the workpiece rotates forward (M03), the tip of the tool will reach the cutting start point m, and the C, D, and E faces will be sequentially cut until point f. Then let the workpiece stop (M05) while letting the tool tip reach n'point, let the workpiece reverse (M04.) and let the tool tip reach the cutting start point n on the other side, cutting the B surface and the A surface in turn until the tool The tip reaches g. At this point, the cutting has been completed, withdrawing, stopping, and ending the program.

With this method, more than 10,000 pieces have been successfully machined and the effect is very good, which can be used for turning similar workpiece references.

3 CNC turning methods that do not allow burrs at corners

Some steel parts require the corners to be right-angled and can't have burrs. This can be done by CNC lathe machining.

The turning point of the turning tool is mostly arc-shaped. See Figure 8-2. K is the imaginary tool tip point, and E and F are the cutting point of the edge arc and the horizontal and vertical lines, respectively. If the cutting route is arranged as shown in Figure 8-3 and Figure 8-4, the burrs will be formed on the outer diameter and the corners of the end face respectively. As shown in Figure 8-5, the burrs on the workpiece after the car are basically the same as those shown in Figure 8-4. It can be seen that the above three conventional turning methods all produce burrs.

The common feature of these three types of turning: the cutting edge leaves the workpiece contour for a period of time, which gives the glitch a chance. According to Figure 8-5 turning this part of the program for

N4 G01 X100 F0.3:
N5 Z-50:

Just looking at the program, it seems that the tip of the tool is always on the contour of the workpiece, but the program dictates the position of the imaginary tip. From Fig. 8-5, it can be seen that in actual cutting, when the F point on the cutting edge moves from point A to point B on the workpiece and point E moves from point C to point A on the workpiece, the cutting edge leaves the contour of the workpiece.

Take the outer diameter of the rear car as an example to see the process of the glitch. Figure 8-6 shows the condition when the tip is cut to the left and the E point on it approaches point A. At this time, the metal on the upper side of point A is pressed downward by the cutting edge, and is partially pushed to the outside of the already passed end face, and becomes a burr. The size of the burr is related to the sharpness of the edge. In order to avoid burrs on the workpiece, the cutting line shown in Figure 8-7 was used, and the program was changed accordingly.

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 a bit longer than Fig. 8-5, the overall distance of the tool tip movement is rather short, ie the cutting time is less than Fig. 8-5. Among them, in order to ensure that the corners of the work-piece are not burr-turned, precision-grade inserts should be selected before turning.

If programmed with an automatic programming machine, it will only program (inject) the routine of Figure 8-5, even if the continuous cutting at the end face and at the outer diameter is specified to the left. To avoid glitches, only make artificial changes to the output program: Change the value of the X command in the N4 segment to 96.8 and add the N44 segment.

To make the burr-free cutting of Fig. 8-7, strictly speaking, the function of the tool nose R compensation cannot be used here, that is, the C42 command cannot be used, and the following programming can be used:

N3G42 x45 Z0:
N4 G01 x100F0.5:
N5 Z-50:

The implementation will still follow Figure 8-5 and will not follow Figure 8-7. If the program before and after this program segment uses G42, and the programmer does not want to remove G42 here and recalculate the instruction values in many other places, the program can be programmed as follows:

N3G42 X45 Z0:
N4G01 X99.998 F0.3:
N44 G03 X100 Z-0.001 K-0.001:
N5 Z-50:

Do not look at only adding a radius of 1gm this tiny value, the arc does not affect the contour of the car, will follow the route of Figure 8-7, turning out the workpiece without burrs at the corner.

4 How to prevent sudden increase in tool load at the corner of the cutting recess

As shown in Fig. 8-8, finishing machining of the workpiece, the dotted line and the solid line in the figure are the contours before and after the machining respectively. It is mass-processed and requires no surface prints.

The end face outer diameter cutter with an 80° equilateral diamond-coated blade was selected. If turning on a single-spindle CNC lathe, if the first part of the car is near the C point, a very wide chip will appear, and the load on the blade on the left side of the blade will suddenly increase, which is unfavorable to the cutter and the machine tool. If this knife is about to come into contact with Part II, then the second part of the knife II will be: if it cuts down to point C first, then it will take at least 1.5mm to the right to retract the knife, so the cutting load is not It will suddenly rise, but there will be a knife mark on the outside diameter, which is not allowed. The same applies to the use of the first car II and the second car. It is possible to use the I and II units to resolve several vehicles back and forth. However, the cutting efficiency is reduced a lot. Small batch processing is also possible. Mass processing is not suitable. It is also possible to use a 35° equilateral diamond blade outer diameter knives for turning, so that the load at the end of the first knives does not increase too much, but the strength of 35° diamond knives is poor, and the effect is not good. Finally, the double-knife CNC lathes are solved by the following method. Two identical outer diameter knives with an 80° equilateral diamond-coated blade were used, one on the upper blade and the other on the lower blade. During processing, the two knives are turned to point C at the same time. Of course, they are also retracted. Through analysis, it can be seen that when the two knives are approaching point C at the same time, the cutting load will not have a large increase, and the actually cut chips will not be significantly widened. Instead, the chips will become narrower and narrower when cutting to point C.

The remaining problem is how to make the upper and lower blades cut to point C at the same time. One method is to use fast forward to allow the upper and lower knives to reach points E and D respectively, and then start the process at the same time with the synchronous command. The feed command for each turn of the upper and lower knives is the same value. Another method is to wait for the upper knife to wait at point F. The lower knife starts cutting from point D to the left, and when it is cut to 32 mm from point C, the upper knife starts to work again with the synchronous command. The third method is to let the upper and lower knives reach points F and D, respectively, and then add a pause block (G04) in the upper blade program. In this pause block and the lower blade program, the process proceeds. In the segment, add the same synchronization instruction. If the pause time is properly selected through precise calculation, the upper and lower knife will also reach point C at the same time. Whichever method is used, its efficiency and effect are the same. However, if the upper and lower cutters use different feed rates, only the third method described above can be used.

Do not worry that the two knives will hit together at the same time cutting to point C. In fact, the upper and lower knives respectively cut the two different sides of the center of rotation of the workpiece.

5 How to shorten the process flow of batch workpiece turning

A sealing seat that requires a large number of turnings, the blank is a forging, and its cross-sectional shape after the completion of the vehicle is shown in dotted lines in Fig. 8-10. The original process flow was 3 roughing, 1 semi-finishing, 2 finishing, and 6 processes. Using C7620 hydraulic semi-automatic lathes and C7220 profiling lathes, the ellipticity of the outer diameter after processing may not reach the requirements of 0.12 mm in drawings.

Through analysis and trial and error, the process flow was shortened. Only three processes are used to complete all coarse and fine machining. The machining accuracy also meets the requirements of the drawings, and only one CNC lathe is used.

The first process is shown in Figure 8-9. The inner diameter of the card is small, and the C7620 semi-automatic lathe is used to turn A and B surfaces and C and D chamfers. The second process is shown in Figure 8-10, using a double-spindle CNC lathe, the outside diameter of the card has been roughed. Install two 80 on the upper blade. Equilateral diamond blade end face outer diameter blade, T1 edge length 16 blade, for F, E surface and K chamfer roughing machine, Figure 8-10 The second process edge length 12 blade, for this 3 Fine cars at the office. The lower tool holder is fitted with two self-made tool holders W1 and W2, and 55 are mounted on the respective heads. The outer diameter of the edge of the equilateral diamond blade is the same as that of the blade and the side length of the blade. Only the tip radius of the blade for the T3 is 1.6 mm, and the tip radius of the blade for the T4 is 1.2 mm. T3 and T4 are used for roughing and finishing of H, J and L, M, and N corners respectively, and after the corresponding NC machining programs are programmed, they can be turned. The third procedure, using the C7620 semi-automatic lathe, uses a spring fixture with a small internal diameter G, and uses the end face F to position, the finishing outside diameter A, the end face B, and the outside corner C.

Through the application of mass production practices, the above process has been used to shorten the process flow by half, which is successful.

6 Measures to improve ergonomics by balancing processing time

The use of double tool lathes to process the same workpiece, if using a different process, the efficiency will be a lot of difference. The core here is the balance of cycle time, ie processing time. Among them, one is the balance between the processing time between the front and the back of the two processes, and the second is the balancing of the processing time between the top and bottom tool carriers in each process. If the measures are reasonable, the ergonomics can be improved a lot.

As shown in Fig. 8-11 and Fig. 8-12, there are two processes before and after the bearing inner ring is turned. In the previous process, the T1 and T2 tools are mounted on the upper tool holder, and the T3 and T4 are installed on the lower tool holder. After the process, the T1, T2, and T3 tools are mounted on the upper tool holder, and the T4, T5, and T6 tools are installed on the lower tool holder. .

The original row process according to the conventional method, the previous process does not have the T3 knife in the figure, and there is a T7 knife (actually the previous process T3 knife moved over) in the subsequent process map, that is, the large rib 3 part of the rough car is placed on the process Turning. The cycle time of the previous process was 61s, and the cycle time of the later process was 89s. This workpiece is mass-processed, the former process is very loose, and the post-process time is very tight, which affects the processing efficiency. The first measure is to move a knife to the previous process after the process, as shown in the figure. The original process used 3 knives, namely, one knives installed two knives, and the other knives were equipped with a knives. No matter how arranged, the processing time of the upper and lower knives cannot be balanced. Now, after the two cutters are installed on the upper and lower cutters, the cutting path can be reasonably arranged so that both the upper and lower cutters can end cutting at the same time, and the cutter can be retracted at the same time. This reduces the cycle time of the previous process to 72 s. At this time, the cycle time of the subsequent process is 78 s.

1- Small oil groove cutting part and small outside diameter fine cut part; 2-Rope fine cut part; 3- Small end surface rough cut part; 4- Small outside diameter and raceway rough cut part; 5- Large oil groove cutting part ;6- Large rib cutting and end fine cutting.

At this point, the cutting time of upper and lower tool rests of the upper process is balanced, and the processing time of the front and rear processes is still unbalanced. It was observed that the time of the upper and lower tool post processing of the post process is one of early completion and one end of late is very different. Thus, in the following process 6, the three knives were mounted on the upper knives, and three on the premise of the lower knives. Four kinds of cutting programs were performed. After calculation and actual cutting, the present program was selected: The lower tool post basically ends cutting and retracting. The cycle time is also 72s. At this point, not only the processing time of the upper and lower turrets of the pre- and post-processes is balanced, but also the cycle time of the pre- and post-processes is balanced. a can also say that this is the best solution.

If the former and latter processes are combined into one production line, then the cycle time of this line will be reduced from the original 89s to the current 72s, shortening the processing time by 19% and significantly improving the work efficiency.

7 Problems to be aware of when cutting at constant line speed

Constant-line-speed cutting is also called fixed-line-speed cutting. Its meaning is that when turning non-cylindrical inner and outer diameters, the lathe spindle speed can be continuously changed to maintain constant (constant) cutting line speed at the real-time cutting position. CNC lathes above the mid-range generally have this function. Using this function not only improves ergonomics, but also improves the quality of the machined surface, that is, the uniformity of the surface roughness of the cut end face or cone surface is good. Here we use Figure 8-13 as an example to illustrate the issues that should be addressed when using this feature.

The trajectory of the tool (tip) in Fig. 8-13 indicates the rapid traverse, the solid line indicates the working feed, and the F point and its dimensions are added for the following description.

One is to pay attention to the maximum speed that should be limited before using this function. If the tool has to travel close to the center of rotation of the workpiece, then the maximum speed must be limited before the constant speed command, otherwise there will be a "speed". In this example, according to the instructions of our machine tool and the specific installation conditions, determine the maximum speed should not exceed 3000r/min. According to the workpiece material and the tool used, the cutting line speed decides to choose 200m/knin. The following program is the actual machining program for the part shown in figure a.

0123;
N1 G50 X to Z to T0100:
N2 G97G00Xa Za S1000 M04;
N3 Xb Zb S1061 T0101 M08;
N4 G50 S3000:
N5 G96G01Xc ZcF0.2$200;
N6 G97G00Zd$746;
N7Xe
N8 G96G01 Xg$200;
N9 G97 COO Xh ZhS1500 M09;
N10 G28 U0 W0 M05;
N11 M02:

Here, the speed limit of 3000 r/min is programmed into the N4 segment. This "G50S3000;" instruction can also advance to any position in front, in this case as long as the N5 segment can be. The result is that in the constant surface speed cutting process of the end face, the point F and the upper part thereof are cut at a constant linear velocity of $200, the rotational speed no longer increases from point F, that is, it is converted into a constant angular velocity (3000 r/min). Until G. If there is no speed limit command for the N4 segment, then the speed will continue to increase below point F, and theoretically it will reach 6366 r/min at G, which is very dangerous.

The second is to note that this function cannot normally be used in fast-forward (G00) blocks. In other words, the COO program segment cannot normally appear before and after the G96 program segment and before the G97 program segment. In this example, if the G96 in N6 is removed and the G96 in N8 is removed, although the taper and end faces can still be used for constant linear velocity cutting, the spindle will suddenly accelerate during the execution of N7, that is, the point quickly reaching from point D to point E. Rising from 530 r/min to 909 r/min. If the tool has reached point E and the spindle has not yet risen to 909 r/min, the tool waits at point E until the spindle rises to 909 r/min before cutting.

The third is to calculate the spindle speed at the starting point of G96, and then divide the speed change amount into the previous COO program segment. In this example, the rotational speeds at points B and E can be calculated as 1061 r/min and 909 r/min, respectively. It can be seen that the rotational speed change before point B is 1061 r/min. Since the distance from the starting point to point A is long, the variation of 1000r/'rain is arranged before point A, leaving only a change of 61r/min between A and B. This S value in the N2 segment is more accurate, and can be calculated based on the ratio of the above distance to the distance between A and B. In addition, C can be calculated as 530r/min, so that the rotational speed variation between C and E is 379r/min. Since the length ratio of CD to DE is about 4:3, we arrange CD to increase 216r/min. DE The rise between 163r/min, this can reduce or even eliminate the wait time of the tool, thereby improving the processing efficiency.

8 round chamfering CNC turning tips

There are generally three types of round chamfers for parts. Figure 8-14 is the most common one. The broken lines in the figure are blank outline surfaces. The specific part drawing will give a, b, and R dimensions. 80 is preferred for processing. Equilateral diamond blade outer diameter knives, blade tip arc radius r can be selected according to processing conditions. Here, the imaginary tool tip point on the left side of the blade is the representative point of the knife T.

Turning solutions are now discussed. Assume that the front face of the car and the outer diameter of the rear car. From point A,


Workers cut the end face downwards. After cutting the end face, let the tool reach point B quickly, and then cut it to point C with counterclockwise circular interpolation, and then work to the left to cut the outer diameter. According to the a, b, R values to find the order of B points relative to the coordinates of the O point: first calculate the coordinates of the center of the H point, and then use r to go through the M point transition to calculate the coordinates of the B point. According to the calculated H point coordinate, the coordinates of N point can be obtained, and then the coordinate of point C comes out. One of the advantages of this processing method is that it saves time, the end face does not have to cut down and then eat a small amount of pull a knife, and the second is simple programming: I in the circle interpolation G03 segment is zero (can be omitted), K is negative ( R+r) value, do not have to do geometric calculations. If it is changed to the front end of the car and the end face of the car, it can also be turned using similar methods as above.

The second type of round chamfer is shown in Figure 8-15. In the figure, the values of the outlets a, b, R, a, and β, and the radius of the cutting edge arc r are selected by the process. To see clearly, the outline of the blank is not shown in the figure. Here choose the first car rear car outside diameter. From point A outside the blank, cut the end face down and let the tool quickly reach point B. The distance L from point B to the end face can be customized. The trick for this scenario is to add a transition line that is a distance from end face L. The tool moves from B to C, and then counterclockwise circular interpolation goes to D, and then works to E, and finally - cuts the outer diameter to the left. The coordinate values of B, C, D, E with respect to point 0 in the figure can be determined by 6 known numbers, and will not be described in detail here.

The third type of round chamfer is to add rounded corners to the end face and outer diameter, as shown in Figure 8-16.

If the precision requirements are general, use an ordinary blade to machine the method shown on the left. Start at point A of the outside diameter of the blank and cut the end face down to B. Leave a small amount between AB and 0C, such as 0.05mm or 0.1mm. Then use a small feed to cut to C, pull the work up to D, cut the fillet to E, and then cut the outside diameter to the left. If the accuracy of the fillet is high, the accuracy level of the blade should be increased accordingly. If the accuracy of this round chamfer is not high enough, it can be processed as shown in the figure to the right. The technique here is to make some technical corrections to the relative positions of the end face and the rounded corners so that the end faces do not have to be turned twice. The specific cutting procedure is: starting from point A outside the outside diameter of the blank, after cutting down the end face, quickly retreat to D, then cut the arc to E, and then cut the outside diameter to the left. Pay attention to the selection of correction L. As long as the face is not pulled back when reversing after turning the end face, the L value should be as small as possible. This mainly depends on the clearance of the machine tool guide and the rigidity of the tool holder. The specific value can be determined by test cutting.