For the current economic CNC lathes in our 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 get boring. However, Some machine tools have gear gears that solve this problem very 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 engagement amount.
2. When the amount of back cutting is doubled, the cutting force is doubled;
When the feed rate is doubled, the cutting force increases by approximately 70%;
When the cutting speed doubles, the cutting force gradually decreases;
In other words, if G99 is used and the cutting speed becomes larger, the cutting force will not change much.
3. It can be judged based on the discharge of iron chips whether the cutting force and cutting temperature are within the normal range.
4. When the measured actual value ) The R you drove out may be scratched 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 generally defaults to G command:
G69: Cancel the G68 rotation coordinate system command
G21: Metric size input
G25: Spindle speed fluctuation detection disconnected
G80: Fixed cycle cancel
G54: Coordinate system default
G18: ZX plane selection
G96 (G97): constant linear speed control
G99: Feed per revolution
G40: Tool nose compensation cancel (G41 G42)
G22: Stored stroke detection is on
G67: Macro program modal call canceled
G64: It is the continuous path mode command in the early Siemens system. Its function is roundness rounding with axial tolerance. G64 is the original command of later G642 and CYCLE832.
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/thread 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) From Just change the chamfer from minus to plus when going up and down.
10. Every time the feed increases by 0.05, the rotational speed decreases by 50-80 rpm. This is because lowering the rotational speed means that the tool wear decreases, and the cutting force increases more slowly, thus making up for the increase in cutting force and temperature due to the increase in feed. impact.
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 collapse.
The relationship between cutting speed and cutting force: the faster the cutting speed, the feed remains unchanged and the cutting force decreases slowly. At the same time, the faster the cutting speed, the faster the tool wears, making the cutting force larger and larger, and the temperature will also increase. The higher it is, when the cutting force and internal stress are too great for the blade to withstand, the blade will collapse (of course there are also reasons such as stress caused by temperature changes and a decrease in hardness).
12. During CNC lathe processing, special attention should be paid to the following points:
(1) At present, economic CNC lathes in our 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 speeds. If the cutting load is too large, it is easy to get boring. However, some machine tools are equipped with gear gears to solve this problem;
(2) Try to enable the tool to complete the processing of one part or one work shift. Pay special attention to the finishing of large parts to avoid tool changes midway to ensure that the tool can be processed in one go;
(3) When turning threads with a CNC lathe, 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, thereby discharging the cutting heat with the iron chips to isolate the cutting heat from the workpiece to ensure that the workpiece does not heat up or heats up less. Therefore, high speed machining is to choose a high temperature. Match the cutting speed with high feed and select a smaller back cutting amount;
(6) Pay attention to the compensation of tool tip R.
13. Vibration and tool collapse often occur during turning:
The fundamental reason for all this is that the cutting force increases and the tool rigidity is insufficient. The shorter the tool extension length, the smaller the relief angle, the larger the blade area, the better the rigidity, and the greater the cutting force, but the width of the groove tool The larger the cutting force, the greater the cutting force it can withstand will increase accordingly, but its cutting force will also increase. On the contrary, the smaller the groove cutter, the less force it can withstand, but its cutting force will also be smaller.
14. Reasons for vibration during lathe turning:
(1) The extension length of the tool is too long, which reduces the rigidity;
(2) The feed rate is too slow, which will cause the unit cutting force to increase and cause large vibrations. The formula is: P=F/back cutting amount*f. P is the unit cutting force and F is the cutting force. In addition, the rotation speed is too fast. The knife will also vibrate;
(3) The machine tool is not rigid enough, which means that the cutting tool can withstand the cutting force, but the machine tool cannot. To put it bluntly, the machine tool does not move. Generally, new beds do not have this kind of problem. The beds that have this kind of problem are either very old. Or you often encounter machine tool killers.
15. When carving a product, I found that the dimensions were fine at first, but after a few hours I found that the dimensions had changed and the dimensions were unstable. The reason may be that the knives were all new at the beginning, so the cutting force was too low. It’s not very big, but after turning for a period of time, the tool wears and the cutting force increases, causing the workpiece to shift on the chuck, so the dimensions are often off 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 appear: The G71-G73 command format is incorrect, at least in FUANC.
17. There are two formats of 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 three digits after L are the number of cycles.
18. If the starting point of the arc remains unchanged and the end point is offset by a mm in the Z direction, the arc bottom diameter position will be offset by a/2.
19. When drilling deep holes, the drill bit does not grind the cutting groove to facilitate chip removal by the drill bit.
20. If you are using a tool holder to drill holes for tooling, you can rotate the drill bit to change the hole diameter.
21. When drilling stainless steel center holes or stainless steel holes, the center of the drill bit or center drill must be small, otherwise it will not be drilled. When drilling holes 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: cutting one piece, cutting two pieces, and cutting the whole bar.
23. When an ellipse appears during threading, it may be that the material is loose. Just use a dental knife to clean it a few times.
24. In some systems that can input macro programs, macro programs can be used instead of subroutine loops. This can save program numbers and avoid a lot of trouble.
25. If you use a drill bit to ream the hole, but the hole has a large runout, you can use a flat-bottom drill to ream the hole, but the twist drill must be short to increase the rigidity.
26. If you directly use a drill bit to drill holes on a drilling machine, the hole diameter may deviate. However, if you expand the hole on a drilling machine, the size will generally not change. For example, if you use a 10MM drill bit to expand the hole on the drilling machine, the enlarged hole diameter will generally be the same. The tolerance is around 3 wires.
27. When carving small holes (through holes), try to roll the chips continuously and then discharge them from the tail. Key points for rolling chips: 1. The position of the knife should be appropriately high. 2. The appropriate blade inclination angle and the amount of cutting. As well as the feed rate, remember that the knife cannot be too low otherwise it will be easy to break chips. If the secondary deflection angle of the knife is large, the chips will not get stuck in the tool bar even if the chips are broken. If the secondary deflection angle is too small, the chips will get stuck in the tool after the chips are broken. The pole is prone to danger.
28. The larger the cross-section of the tool holder in the hole, the less likely it is for the tool to vibrate. You can also tie a strong rubber band on the tool holder, because the strong rubber band can absorb vibration to a certain extent.
29. When turning copper holes, the tip R of the knife can be appropriately larger (R0.4-R0.8). Especially when turning the taper, the iron parts may be fine, but the copper parts will get stuck.
Machining center, CNC milling machine tool compensation
For CNC systems of machining centers and CNC milling machines, the tool compensation functions include tool radius compensation, angle compensation, 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, 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 results. Tool radius left compensation (G41) means that the tool deviates to the left of the movement direction of the programmed machining path (as shown in Figure 1), and tool radius right compensation (G42) means that the tool deviates to the right of the movement direction of the programmed machining path. Use G40 to cancel tool radius compensation, and H00 to cancel tool radius compensation.
CNC technician training reminder: Please pay attention during use: when establishing or canceling tool compensation, that is, the program segment using G41, G42, and 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.
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There are two compensation forms of tool radius compensation: B function and C function. Since the B function tool radius compensation only performs tool compensation calculations based on this section of the program, it cannot solve the transition problem between program sections and requires the workpiece contour to be processed into a rounded transition. Therefore, the workpiece’s sharp corners have poor processability, and the C function tool radius compensation The 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, almost all modern CNC machine tools use C function tool radius compensation. At this time, it is required that the subsequent two blocks of the tool radius compensation block 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) When two planes intersect at an included angle, over-travel and 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 within the command block. 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 commanded by the H code. G43 means the addition of the compensation amount in the memory and the end point coordinate value commanded by the program, and G44 means the subtraction. To cancel the tool length offset, you can use the G49 command or the H00 command. Program segment N80 G43 Z56 H05 is in the middle. 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 stored in the memory in advance 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: Nov-06-2023
