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Knowledge that must be mastered in CNC machining
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Knowledge that must be mastered in CNC machining

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2019-08-23 16:49
  • Views:15

(Summary description)For the current economic CNC lathes in China, the ordinary three-phase asynchronous motor is generally used to realize stepless speed change through the frequency converter. If there is...
(6) Pay atten

Knowledge that must be mastered in CNC machining

(Summary description)For the current economic CNC lathes in China, the ordinary three-phase asynchronous motor is generally used to realize stepless speed change through the frequency converter. If there is...
(6) Pay atten

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2019-08-23 16:49
  • Views:15
Information
For the current economic CNC lathes in China, the ordinary three-phase asynchronous motor is generally used to realize stepless speed change through the frequency converter. 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 boring. Some machine tools with gears solve this problem very well.
 
1. Influence on cutting temperature: cutting speed, feed rate, back-feeding amount;
 
Influence on cutting force: back-feeding amount, feed rate, cutting speed;
 
Impact on tool durability: cutting speed, feed rate, back-feeding.
 
2. When the amount of back-feeding knife is doubled, the cutting force is doubled;
 
When the feed rate is doubled, the cutting force is increased by about 70%;
 
When the cutting speed is doubled, the cutting force is gradually reduced;
 
That is to say, if G99 is used, the cutting speed becomes large, and the cutting force does not change much.
 
3. The cutting force can be judged based on the discharge of iron filings, and the cutting temperature is within the normal range.
 
4. When the measured actual value X and the diameter Y of the drawing are greater than 0.8, the concave arc of the car, the turning tool with the auxiliary declination of 52 degrees (that is, the commonly used blade is a blade with a main angle of 93 degrees of 35 degrees) The R that the car is out may be rubbed at the starting point.
 
5. The temperature represented by the 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 default G command:
 
G69: Cancel the G68 rotating coordinate system command
 
G21: Metric size input
 
G25: Spindle speed fluctuation detection disconnected
 
G80: Canned cycle cancellation
 
G54: coordinate system default
 
G18: ZX plane selection
 
G96 (G97): constant line speed control
 
G99: Feed per revolution
 
G40: Tool nose compensation cancel (G41 G42)
 
G22: Storage stroke detection is turned on
 
G67: Macro program modal call canceled
 
G64: It is the instruction of the continuous path mode in the early Siemens system. It functions as roundness rounding with axial tolerance. G64 is the original instruction of the later G642 and CYCLE832.
 
G13.1: Polar coordinate interpolation method canceled
 
7. The external thread is generally 1.3P and the internal thread is 1.08P.
 
8. Thread speed S1200 / pitch * safety factor (usually 0.8).
 
9. Manual tool nose R compensation formula: chamfering from bottom to top: Z=R*(1-tan(a/2)) X=R(1-tan(a/2))*tan(a) From The chamfer up and down will be reduced to plus.
 
10. For every 0.05 increase in feed, the speed is reduced by 50-80 rpm. This is because lowering the speed means that the tool wear is reduced, and the cutting force is increased more slowly, thereby making up for the increase of the cutting force and the temperature increase due to the increase of the feed. The impact.
 
11. The cutting speed and the influence of the cutting force on the tool are the main reasons why the cutting force is too large to cause the tool to collapse.
 
The relationship between cutting speed and cutting force: the faster the cutting speed, the constant the cutting force, the slower the cutting force, and the faster the cutting speed, the faster the tool wears, the larger the cutting force, the more the temperature will come. The higher the cutting force and the internal stress are so large that the blade cannot withstand the landslide knife (of course, there is also a drop in stress and hardness due to temperature changes).
 
12. When processing CNC machines, the following points should be specially noted:
 
(1) For the current economic CNC lathes in China, the ordinary three-phase asynchronous motor is generally used to realize stepless speed change through the frequency converter. 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. Car, but some gears with gears on the machine solve this problem well;
 
(2) As far as possible, the tool can complete the machining of one part or one work shift. In particular, the large-piece finishing should pay attention to avoiding the middle of the tool change to ensure that the tool can be processed once;
 
(3) When using CNC machine to turn the thread, use high speed 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 along with the iron filings to isolate the cutting heat from the workpiece, ensuring that the workpiece does not heat up or heat up. Therefore, high-speed machining is very high. The cutting speed is matched with the high feed while selecting a smaller amount of backing knife;
 
(6) Pay attention to the compensation of the tool nose R.
 
13. Vibration and chipping often occur in the trough:
 
The root cause of all this is that the cutting force becomes large and the tool rigidity is not enough. The shorter the tool extension length, the smaller the back angle, the larger the blade area, the better the rigidity, the larger the cutting force, but the width of the groove cutter. The larger the cutting force that can be withstood, the larger the cutting force will be, but the cutting force will increase. On the contrary, the small groove cutter can withstand less force, but its cutting force is also small.
 
14. Reasons for vibration during the trough:
 
(1) The length of the tool extension is too long, and the rigidity is reduced;
 
(2) The feed rate is too slow, causing the unit cutting force to increase and causing large vibration. The formula is: P=F/back knife amount *f P is the unit cutting force F is the cutting force, and the rotation speed is too fast. Will also vibrate the knife;
 
(3) The rigidity of the machine tool is not enough, that is to say, the tool can bear the cutting force, but the machine tool can't bear it. To put it plainly, the machine tool car does not move. Generally, the new bed will not have such problems. The bed with such problems is either old. Either the machine killer is often encountered.
 
15. When the car was in a shipment, the size was found to be good at the beginning, but after several hours, the size was changed and the size was unstable. It may be because the knife was new at the beginning, so the cutting force was It is not very big, but after a period of time, the tool wears and the cutting force becomes large, causing the workpiece to shift on the chuck, so the size is old 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 occur: the G71-G73 instruction format is incorrect, at least in FUANC.
 
17. The subroutine in the FANUC system has two formats:
 
(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 loops.
 
18. The starting point of the arc is unchanged, and the end Z direction is offset by a mm, and the arc bottom diameter is offset by a/2.
 
19. The drill does not grind the cutting groove when drilling deep holes to facilitate the chip removal.
 
20. If you are using a tool holder for the tooling, you can turn the drill bit to change the aperture.
 
21. When hitting the stainless steel center eye or the stainless steel eye, the drill bit or the center drill center must be small, otherwise it can't be moved. When using the cobalt drill, the groove is not ground to avoid the bit annealing during the drilling process.
 
22. According to the process, there are generally three kinds of materials: one material, two goods, and the whole bar.
 
23. When the ellipse appears in the thread of the thread, it may be loose, and a few knives with a dental knife will do.
 
24. In some systems where macro programs can be input, macro program charging can be used instead of subroutine loops, which saves the program number and avoids a lot of trouble.
 
25. If the drill is used for reaming, but the runout of the hole is large, the flat hole drill can be used for reaming, but the twist drill must be short to increase the rigidity.
 
26. If the drill hole is directly drilled with a drill bit, the hole diameter may be deviated, but if the reaming size of the drill press is generally not run, for example, using a 10MM drill bit to ream the drill bed, the expanded aperture is generally Around 3 wire tolerances.
 
27. In the small hole (through hole) of the car, try to make the scraps continuously and then discharge from the tail. The main points of the coil: First, the position of the knife should be properly raised. Second, the appropriate blade inclination angle, the amount of knife And the feed rate, remember that the knife can not be too low or it is easy to break the chip. If the secondary declination of the knife is large, the cutter bar will not be stuck even if the chip breaking is broken. If the secondary declination is too small, the chip will catch the knife after the chip breaking. The rod is prone to danger.
 
28. The larger the cross section of the arbor in the hole, the less likely it is to vibrate the knives. It is also possible to attach a strong rubber band to the arbor, because the strong rubber band can play a certain role of absorbing vibration.
 
29. In the copper hole of the car, the tip R of the knife can be appropriately large (R0.4-R0.8), especially when the car is taper, the iron piece may be nothing, and the copper piece will be very chipped.
 
Machining center, CNC milling machine tool compensation
 
For CNC centers of machining centers and CNC milling machines, the tool compensation functions include tool compensation functions such as tool radius compensation, angle compensation and length compensation.
 
(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 executed, the CNC system automatically calculates and automatically compensates the tool according to the calculation result. Tool radius left compensation (G41) refers to the left side of the tool direction of the programmed machining path (as shown in Figure 1), and the tool radius right compensation (G42) refers to the tool to the right of the programmed machining path. Cancel G40 for tool radius compensation and H00 for tool radius compensation.
 
CNC mechanic training reminder: In use, please pay attention: when establishing or canceling the tool compensation, the block using G41, G42, G40 command must use G00 or G01 command, and G02 or G03 should not be used. When the tool radius compensation takes negative value, The functions of G41 and G42 are interchangeable.
 
The tool radius compensation has two compensation modes: B function and C function. Since the B function tool radius compensation is only calculated according to the program in this paragraph, the transition problem between the blocks cannot be solved, and the workpiece contour is required to be processed into a rounded transition. Therefore, the workability of the workpiece corner is not good, and the C function tool radius is not good. The compensation can automatically handle the transfer of the tool center trajectory of the two blocks, which can be programmed according to the workpiece contour. Therefore, the modern CNC CNC machine tool almost adopts the C function tool radius compensation. At this time, it is required that the subsequent two blocks of the tool radius compensation block must have the displacement command (G00, G01, G02, G03, etc.) of the specified compensation plane. Otherwise, the correct tool compensation cannot be established.
 
(2) Angle compensation (G39) The intersection of the two planes is an angle, which may cause over-cutting and over-cutting, which may cause machining errors, which can be solved by the angle compensation (G39). Note that when using the angle compensation (G39) command, this command is non-modal and valid only in the block of the command. 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 without changing the program. The compensation amount is stored in the memory of the H code command. G43 indicates that the compensation amount in the memory is added to the end point coordinate value of the program command, G44 indicates the subtraction, and canceling the tool length offset can be performed by the G49 command or the H00 command. In the block N80 G43 Z56 H05 and 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 by MDI or DPL, or the compensation amount in the memory No. 05 can be 16mm by the block instruction G10 P05 R16.0.

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