At present, the economic CNC lathes in my country 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 stall. However, some machine tools have gear gears to solve this problem well. 1. Influence on cutting temperature: cutting speed, feed rate, back cutting amount;
Influence on cutting force: back cutting amount, feed rate, cutting speed;
Influence on tool durability: cutting speed, feed rate, back cutting amount.
2. When the back cutting amount doubles, the cutting force doubles;
When the feed rate doubles, the cutting force increases by about 70%;
When the cutting speed doubles, the cutting force gradually decreases;
That is to say, if G99 is used, the cutting speed increases, and the cutting force will not change much.
3. The cutting force and cutting temperature can be judged based on the discharge of iron chips.
4. When the difference between the actual value X and the diameter Y on the drawing is greater than 0.8, when turning a concave arc, the R cut by a turning tool with a secondary deflection angle of 52 degrees (that is, a turning tool with a blade of 35 degrees and a main deflection angle of 93 degrees that we often use) may scratch the tool at the starting point.
5. Temperature represented by the color of iron chips:
White is less than 200 degrees
Yellow is 220-240 degrees
Dark blue is 290 degrees
Blue is 320-350 degrees
Purple is greater than 500 degrees
Red is greater than 800 degrees
6.FUNAC OI mtc generally defaults to G instructions:
G69: Cancel G68 rotation coordinate system instruction
G21: Metric dimension input
G25: Spindle speed fluctuation detection disconnected
G80: Fixed cycle canceled
G54: Coordinate system default
G18: ZX plane selection
G96 (G97): Constant line speed control
G99: Feed per revolution
G40: Tool tip compensation canceled (G41 G42)
G22: Stored stroke detection turned on
G67: Macro program modal call canceled
G64: It is an instruction of continuous path mode in the early Siemens system. Its function is 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. External thread is generally 1.3P, internal thread is 1.08P.
8. Thread speed S1200/pitch*safety factor (generally 0.8).
9. Manual tool tip R compensation formula: Chamfering from bottom to top: Z=R*(1-tan(a/2)) X=R(1-tan(a/2))*tan(a) Chamfering from top to bottom can be changed from minus to plus.
10. For every 0.05 increase in feed, the speed is reduced by 50-80 revolutions. This is because reducing the speed means that the tool wear decreases, and the cutting force increases more slowly, thereby compensating for the increase in cutting force and temperature caused by the increase in feed.
11. The influence of cutting speed and cutting force on the tool is crucial. Excessive cutting force is the main reason for the tool to break.
The relationship between cutting speed and cutting force: the faster the cutting speed, the constant feed, the slower the cutting force decreases, and the faster the cutting speed, the faster the tool wears, the greater the cutting force, and the higher the temperature. When the cutting force and internal stress are so great that the blade cannot bear it, the blade will collapse (of course, there are also reasons such as stress caused by temperature changes and a decrease in hardness).
12. When machining with CNC lathes, the following points should be paid special attention to:
(1) For the current economic CNC lathes in my country, ordinary three-phase asynchronous motors are generally used to achieve stepless speed change through frequency converters. If there is no mechanical deceleration, the spindle output torque is often insufficient at low speeds. If the cutting load is too large, it is easy to stall. However, some machine tools are equipped with gear gears to solve this problem well;
(2) Try to make the tool complete the processing of a part or a work shift. When finishing large parts, pay special attention to avoiding tool changes in the middle to ensure that the tool can complete the processing in one go;
(3) When turning threads with CNC lathes, use a higher speed as much as possible to achieve high-quality and efficient production;
(4) Use G96 as much as 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 chips to isolate the cutting heat from the workpiece, ensuring that the workpiece does not heat up or heats up less. Therefore, high-speed machining is to select a very high cutting speed to match the high feed and select a smaller back cutting amount;
(6) Pay attention to the compensation of the tool tip R. 13. Vibration and chipping often occur during slotting:
The root cause of all this is the increase in cutting force and insufficient rigidity of the tool. The shorter the tool extension length, the smaller the back angle, the larger the blade area and the better the rigidity, the greater the cutting force that can be borne. However, the larger the width of the slotting tool, the greater the cutting force that can be borne. On the contrary, the smaller the slotting tool, the smaller the force it can withstand, but its cutting force is also smaller.
14. Reasons for vibration during slotting:
(1) The tool extension length is too long, resulting in reduced rigidity;
(2) The feed rate is too slow, resulting in a large unit cutting force and causing large vibrations. The formula is: P=F/cutting depth*f P is the unit cutting force and F is the cutting force. In addition, too fast a speed will also cause vibration;
(3) The machine tool is not rigid enough, that is, the tool can withstand the cutting force, but the machine tool cannot. To put it bluntly, the machine tool cannot move. Generally, new machines will not have such problems. Machines that have such problems are either old or often encounter machine tool killers.
15. When turning a product, the dimensions were found to be good at the beginning, but after a few hours, the dimensions changed and became unstable. The reason may be that at the beginning, the cutting force was not very large because the tools were new, but after a period of time, the tools were worn and the cutting force became larger, causing the workpiece to shift on the chuck, so the dimensions kept shifting and unstable.
16. When using G71, the values of P and Q cannot exceed the sequence number of the entire program, otherwise an alarm will be issued: G71-G73 instruction format is incorrect, at least in FUANC.
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17. There are two formats for subroutines in the FANUC system:
(1) The first three digits of P000 0000 refer to the number of cycles, and the last four digits are the program number;
(2) The first four digits of P0000L000 are the program number, and the last three digits of L are the number of cycles.
18. The starting point of the arc remains unchanged, and the end point is offset by a mm in the Z direction, then the bottom diameter position of the arc is offset by a/2.
19. When drilling deep holes, the drill bit does not grind the cutting groove to facilitate chip removal.
20. If you use a tool holder to drill holes, you can rotate the drill bit to change the hole diameter.
21. When drilling the center hole of stainless steel, or when drilling stainless steel holes, the drill bit or the center of the center drill must be small, otherwise it cannot be drilled. When drilling with a cobalt drill, do not grind the groove to avoid annealing of the drill bit during the drilling process.
22. According to the process, there are generally three types of cutting materials: one material at a time, two materials at a time, and the whole bar material at a time.
23. When an ellipse appears during threading, it may be that the material is loose. Just use a tooth cutter to make a few more cuts.
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 to expand the hole, but the hole jumps a lot, a flat bottom drill can be used to expand the hole, but the twist drill must be short to increase rigidity.
26. If you use a drill bit to drill directly on a drilling machine, the hole diameter may deviate, but if you use a drilling machine to expand the hole size, it will generally not deviate. For example, if you use a 10MM drill bit to expand the hole on a drilling machine, the expanded hole diameter is generally around 3 wire tolerance.
27. When turning small holes (through holes), try to make the chips roll continuously and then discharge them from the tail. The key points of chip rolling are: 1. The position of the knife should be appropriately raised. 2. The appropriate blade inclination angle, cutting amount and feed amount. Remember that the knife should not be too low, otherwise it is easy to break the chip. If the secondary deflection angle of the knife is large, the knife rod will not be stuck even if the chip breaks. If the secondary deflection angle is too small, the chip will get stuck in the knife rod after breaking the chip, which is easy to cause danger.
28. The larger the cross-section of the knife rod in the hole, the less likely it is to vibrate the knife. You can also tie a strong rubber band on the knife rod, because the strong rubber band can play a certain role in absorbing vibration.
29. When turning copper holes, the tool tip R can be slightly larger (R0.4-R0.8), especially when turning tapers. Iron parts may not be affected, but copper parts will be stuck.
Tool compensation for machining centers and CNC milling machines
The CNC system of machining centers and CNC milling machines has tool compensation functions including tool radius compensation, angle compensation, and length compensation.
(1) Tool radius compensation (G41, G42, G40) The radius value of the tool is pre-stored in the memory HXX, where XX is the memory number. After executing tool radius compensation, the CNC system automatically calculates and makes the tool automatically compensate according to the calculation result. Tool radius left compensation (G41) refers to the tool deviation to the left of the programmed machining trajectory movement direction (as shown in Figure 1), and tool radius right compensation (G42) refers to the tool deviation to the right of the programmed machining trajectory movement direction. G40 is used to cancel tool radius compensation, and H00 can also be used to cancel tool radius compensation.
CNC technician training reminder: Note that when using: When establishing or canceling tool compensation, the program segment using G41, G42, or 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 interchangeable.
Tool radius compensation has two compensation forms: B function and C function. Since the B function tool radius compensation only calculates tool compensation based on the current program segment, it cannot solve the transition problem between program segments and requires the workpiece contour to be processed into a rounded transition. Therefore, the workpiece sharp corners have poor processability. The C function tool radius compensation can automatically handle the transfer of the tool center trajectory of the two program segments, and can be programmed completely according to the workpiece contour. Therefore, modern CNC machine tools almost all use the C function tool radius compensation. At this time, the subsequent two program segments that require the establishment of the tool radius compensation program segment must have displacement instructions (G00, G01, G02, G03, etc.) that specify the compensation plane, otherwise the correct tool compensation cannot be established.
(2) Angle compensation (G39) When two planes intersect at an angle, overcutting may occur, resulting in machining errors. Angle compensation (G39) can be used to solve this problem. When using the angle compensation (G39) command, please note that this command is non-modal and is only valid in the commanded program segment. It can only be used after the G41 and G42 commands.
(3) Tool length offset (G43, G44, G49) The tool length offset (G43, G44) command can be used to compensate for changes in tool length at any time without changing the program. The compensation amount is stored in the memory instructed by the H code. G43 means that the compensation amount in the memory is added to the end point coordinate value of the program instruction, and G44 means subtraction. The tool length offset can be canceled by using the G49 command or the H00 command. In the program segment N80 G43 Z56 H05, if the value in the 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 pre-stored in the memory using MDI or DPL, or the program segment instruction G10 P05 R16.0 can be used to indicate that the compensation amount in memory No. 05 is 16mm.
Post time: Mar-10-2025
