CNC machining must master the knowledge
Release time:
2019-08-23
At present, China's economic CNC lathes generally use ordinary three-phase asynchronous motors to achieve stepless speed change through frequency converters. If there is no mechanical deceleration, the spindle output torque is often insufficient at low speed. If the cutting load is too large, it is easy to be stuffy. However, some machine tools have gears to solve this problem.
1. Influence on cutting temperature: cutting speed, feed rate, back cutting amount;
Influence on cutting force: back cutting amount, feed rate, cutting speed;
Impact on tool durability: cutting speed, feed rate, back to eat the amount of the knife.
2. When the amount of back knife is doubled, the cutting force is doubled;
When the feed rate doubled, the cutting force increased by about 70%;
When the cutting speed is doubled, the cutting force is gradually reduced;
In other words, if you use G99, the cutting speed becomes larger, and the cutting force will not change much.
3. The cutting force can be judged according to the discharge of iron filings and whether the cutting temperature is within the normal range.
4. When the measured actual value X and the drawing diameter Y are greater than 0.8 when the concave arc of the car, the turning tool with a secondary angle of 52 degrees (that is, the turning tool with a common blade of 35 degrees and a primary angle of 93 degrees) may wipe the knife at the starting position.
5. The temperature represented by the color of iron filings:
White is less than 200 degrees
Yellow 220-240 degrees
Dark blue 290 degrees
Blue 320-350 degrees
Purple black is greater than 500 degrees
Red is greater than 800 degrees
6.FUNAC OI mtc General Default G Instruction:
G69: Cancel the G68 rotating coordinate system command
G21: Metric Size Input
G25: Spindle speed fluctuation detection disconnected
G80: Fixed cycle cancellation
G54: Coordinate System Default
G18:ZX plane selection
G96(G97): Constant Linear Speed Control
G99: per feed
G40: Nose compensation canceled (G41 G42)
G22: Storage travel detection ON
G67: Macro program modal call cancel
G64: It is the instruction of continuous path mode in the early Siemens system. Its function is roundness rounding with axial tolerance. G64 is the original instruction of G642 and CYCLE832 in the later period.
G13.1: Polar coordinate interpolation mode canceled
7. The external thread is generally 1.3P, and the internal thread is 1.08P.
8. Thread speed S1200/pitch * safety factor (generally 0.8).
9. Manual tool tip R compensation formula: chamfer from bottom to top: Z = R *(1-tan(a/2)) X = R(1-tan(a/2))* tan(a) chamfer from top to bottom to top.
Feed every increase in 0.05, the speed is reduced 50-80 this is because the lower speed means that the tool wear decreased, the cutting force increased more slowly, so as to make up for the increase in feed so that the cutting force increases, the temperature increases and the impact.
11. Cutting speed and cutting force are crucial to the impact of the cutting tool, cutting force is too large the main reason for the collapse of the machine.
The relationship between cutting speed and cutting force: the faster the cutting speed is, the slower the cutting force will decrease. At the same time, the faster the cutting speed will make the tool wear faster, making the cutting force bigger and bigger, and the temperature will be higher and higher. When the cutting force and internal stress are too large for the blade to bear, the knife will collapse (of course, there are also reasons such as the decrease of stress and hardness caused by temperature change).
12. In CNC lathe processing, the following points should be paid special attention:
(1) For the current economic CNC lathes in our country, ordinary three-phase asynchronous motors are generally used to realize stepless speed change through frequency converters. If there is no mechanical deceleration, the spindle output torque is often insufficient at low speed. If the cutting load is too large, it is easy to be stuffy. However, some machine tools have gear gears to solve this problem;
(2) As far as possible, the tool can complete the processing of a part or a work shift. Special attention should be paid to the finishing of large parts to avoid changing the tool in the middle to ensure that the tool can be processed at one time;
(3) When turning threads with CNC turning, high speed is used as much as possible to achieve high quality and efficient production;
(4) Use G96 whenever possible;
(5) The basic concept of high-speed machining is to make the feed exceed the heat conduction speed, so that the cutting heat is discharged with the iron filings to isolate the cutting heat from the workpiece and ensure that the workpiece does not heat up or heat up less. Therefore, high-speed machining is to select a very high cutting speed to match the high feed and select a smaller amount of back cutting;
(6) Pay attention to the compensation of the tip R.
13. Vibration and knife breakage are often generated when turning the groove:
The root cause of all this is that the cutting force becomes larger and the tool rigidity is not enough. The shorter the tool extension length, the smaller the rear angle, the larger the area of the blade, the better the rigidity, and the greater the cutting force, but the greater the width of the groove knife, the greater the cutting force it can bear, but its cutting force will also increase. On the contrary, the smaller the groove knife, the smaller the force it can bear, but its cutting force is.
14. Causes of vibration when the car trough:
(1) The extended length of the tool is too long, and the rigidity is reduced;
(2) The feed rate is too slow, which causes the unit cutting force to become larger, thus causing large-scale vibration. The formula is: P = F/back cutting amount * f P is the unit cutting force F is the cutting force, and the knife will vibrate if the rotating speed is too fast;
(3) The machine tool is not rigid enough, that is to say, the cutting tool can bear the cutting force, but the machine tool cannot bear it. To put it bluntly, the machine tool does not move. Generally, new beds will not have such problems. The beds with such problems are either old or often encounter machine tool killers.
15. When the car was loaded, the size was found to be fine at the beginning, but after several hours of work, it was found that the size changed and the size was unstable. The reason may be that the cutting force was not very large at the beginning because the knives were new. However, after a period of time, the cutting tool was worn and the cutting force became larger, causing the workpiece to shift on the chuck, so the size was always running and unstable.
16. When using G71, the values of P and Q cannot exceed the sequence number of the whole program, otherwise an alarm will occur: the G71-G73 instruction format is incorrect, at least in FUANC.
17. There are two formats for subroutines in the FANUC system:
(1) The first three digits of the P000 0000 refer to the number of cycles, and the last four digits are the program number;
(2) The first four digits of the P0000L000 are the program number, and the three digits after L are the number of cycles.
18. If the starting point of the arc remains unchanged and the ending point is offset by a mm in the Z direction, the bottom diameter of the arc will be offset by a/2.
19. When drilling deep holes, the drill does not grind the cutting groove to facilitate the drill chip removal.
20. If the tool holder is used to drill holes, the drill bit can be rotated to change the hole diameter.
21. When drilling the stainless steel center hole or the stainless steel hole, the drill bit or the center of the center drill must be small, otherwise it cannot be drilled. When drilling with cobalt drill, the groove shall not be ground to avoid annealing of the drill bit during drilling.
22. According to the process, there are generally three types of material: one material, two goods, and the whole bar.
23. When an ellipse appears during threading, the material may be loose. Just use a dental knife to manage a few more knives.
24. In some systems that can input macro programs, macro programs can be used instead of subroutine loops, which can save program numbers and avoid a lot of trouble.
25. If a drill is used for reaming, but the hole has a large runout, a flat bottom drill can be used for reaming, but the twist drill must be short to increase rigidity.
26. If the drill is directly used to drill holes on the drilling machine, the hole diameter may be deviated. However, if the reaming size is generally not run on the drilling machine, for example, if the reaming size is carried out on the drilling machine with a 10MM drill bit, the expanded hole diameter is generally about 3-wire tolerance.
27. When making small holes (through holes) in the car, try to make the chips roll continuously and then discharge them from the tail. The main points of chip rolling are as follows: First, the position of the knife should be properly raised; Second, the knife should be properly inclined, the amount of knife eaten and the amount of feed. Remember that the knife should not be too low or it will easily break chips. If the minor deflection angle of the knife is too large, even the chip will not stuck, if the chips are broken, the chips will jam the tool bar and cause danger.
28. The larger the cross section of the knife bar in the hole, the less likely it is to vibrate the knife. There is also a strong rubber band that can be tied to the knife bar, because the strong rubber band can play a certain role in absorbing vibration.
29. When the car copper hole, the tip R of the knife can be appropriately larger (R0.4-R0.8), especially when the taper is under the car, the iron piece may be nothing, and the copper piece will be very stuck.
Machining center, CNC milling machine tool compensation
Machining center, CNC milling machine CNC system, tool compensation functions include tool radius compensation, angle compensation and length compensation and other tool compensation functions.
(1) Tool radius compensation (G41, G42, G40) The radius value of the tool is stored in the memory HXX in advance, and XX is the memory number. After the tool radius compensation is performed, the numerical control system automatically calculates and makes the tool automatically compensate according to the calculation result. Tool radius left compensation (G41) means that the tool is biased to the left of the programmed machining trajectory (as shown in Figure 1), and tool radius right compensation (G42) means that the tool is biased to the right of the programmed machining trajectory. Cancel tool radius compensation with G40, cancel tool radius compensation can also be used H00.
CNC mechanic training reminder: attention should be paid during use: when tool compensation is established and canceled, that is, the program segment using G41, G42 and G40 instructions must use G00 or G01 instructions, and G02 or G03 are not allowed. when tool radius compensation takes a negative value, the functions of G41 and G42 are interchanged.
Tool radius compensation has B function and C function of two forms of compensation. Since the B function tool radius compensation only calculates the tool compensation according to this section of the program, it cannot solve the transition problem between the program sections and requires the workpiece contour to be processed into rounded corners. Therefore, the manufacturability at the sharp corners of the workpiece is not good. The C function tool radius compensation can automatically process the switching of the tool center trajectory of the two program sections and can be programmed completely according to the workpiece contour. Therefore, modern CNC machine tools almost all use C function tool radius compensation. At this time, it is required that the following two program segments of the tool radius compensation program segment must have displacement instructions (G00, G01,G02, G03, etc.) specifying the compensation plane, otherwise the correct tool compensation cannot be established.
(2) Angle compensation (G39) The intersection of two planes is an angle, which may cause over-range over-cutting and lead to processing errors, which can be solved by angle compensation (G39). When using the included angle compensation (G39) instruction, it should be noted that this instruction is non-modal and is only valid within the program segment of the instruction, and can only be used after the G41 and G42 instructions.
(3) Tool length offset (G43, G44, G49) The tool length offset (G43, G44) instruction can compensate for 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 instruction. G43 indicates that the compensation amount in the memory is added to the end coordinate value of the program instruction, G44 indicates subtraction, and the G49 instruction or H00 instruction can be used to cancel the tool length offset. In the program segment N80 G43 Z56 H05 and middle, if the value in 05 memory is 16, it means that the end point coordinate value is 72mm.
The value of the compensation amount in the memory can be stored in the memory in advance by 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.
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