Numerical control often encountered 30 problems and solutions

Mon Jul 04 14:10:05 CST 2022

CNC machining often encounter some problems, master the 30 points, I believe that will help your machining work:

1. The influence of cutting temperature: cutting speed, feed rate, back draft.

Influence on cutting force: backdraft, feed rate, cutting speed.

Influence on cutting tool durability: cutting speed, feed rate, backdraft.

2. When the amount of back draft is doubled, the cutting force is doubled.

When the feed rate is doubled, the cutting force increases about 70%.

When the cutting speed is doubled, the cutting force decreases gradually.

In other words, if using G99, the cutting speed increases, the cutting force will not change much.

3. According to the discharge of iron filings, we can judge whether the cutting force and cutting temperature are in the normal range.

4. When the actual value X measured and the diameter Y of the drawing is greater than 0.8 of the concave arc of the car, the turning tool with the auxiliary Angle of 52 degrees (that is, the turning tool with the main Angle of 93 degrees of the commonly used blade of 35 degrees) may wipe the tool at the starting position.

5. 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 over 500 degrees

Red is greater than 800 degrees

6.FUNAC OI MTC generally default G instruction

G21: Metric size input

G25: Spindle speed fluctuation detection is disconnected

G80: Fixed loop cancelled

G54: Coordinate system default

G18: ZX plane selection

G96 (G97) : Constant linear speed control

G99: Every turn feed

G40: Tool tip compensation cancelled (G41 G42)

G22: Storage travel detection is connected

G67: Macro program modal call cancellation

G13.1: Polar interpolation is cancelled

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 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. feed each increase 0.05, speed reduced 50~80 RPM this is because reduce the speed means tool wear decline, the cutting force increase is slower, so as to make up for the feed increase the cutting force increase, temperature increase and bring about the impact.

11. cutting speed and cutting tool force on the impact of the tool is very important, too much cutting force is the main cause of tool collapse.

Relationship between cutting speed and cutting force: Feed unchanged when cutting speed faster, slow cutting force is reduced, and the faster cutting speed will make the faster tool wear, the cutting force is more and more big, the temperature will be higher and higher, when the cutting force and internal stress to the blade can't bear, will collapse knife (of course there is the change in temperature stress generated by and drop in hardness, etc).

12. in CNC machining, the following points should be paid special attention to:

(1) for the current our country's economic CNC lathe usually USES is ordinary three-phase asynchronous motor by frequency converter to realize stepless speed change, if there is no mechanical reduction, often at low speed output shaft torque is insufficient, if cutting load is too large, easy to stuffy car, but some machine tool with a pinion gear on the very good solve the problem.

(2) as far as possible to make the tool can complete a part or a work shift of processing work, large finishing especially to pay attention to the middle to avoid changing the tool to ensure that the tool can be processed at a time.

(3) with CNC turning thread should be used as high speed as possible, in order to achieve high quality, efficient production.

(4) Use G96 whenever possible.

(5) The basic concept of high speed processing is to make the feed exceed the heat conduction velocity, so that the cutting heat with the iron chip discharge cutting heat and workpiece isolation, to ensure that the workpiece is not heating up or less heating up, therefore, high speed processing is to select a high cutting speed and high feed matching at the same time select a small back draft.

(6) Pay attention to the compensation of tool tip R.

13. Some common forms:

Grading table of machinability of workpiece materials

Commonly used thread cutting times and back tool table

Commonly used geometric figure calculation formula

Inch to millimeter conversion table

14. Often generates vibration and collapse in car slot insert, all of which the root cause is rigid enough variable cutting force and cutting tool, cutting tool out of the shorter length, the Angle is smaller, the area of the insert is larger, the better rigidity, produce the bigger the cutting force, but the width of the slot cutter can withstand the greater the cutting force will increase, but its cutting force also increases, On the contrary, the groove insert is small, but its cutting force is also small.

15. Causes of vibration in grooves:

(1) The tool extension length is too long, resulting in the reduction of rigidity.

(2) the feed rate is too slow, resulting in large unit cutting force resulting in large vibration, the formula is: P=F/ back tool * F P is the unit cutting force F is the cutting force, and the speed is too fast will also vibrate the tool.

(3) machine rigidity is not enough, that is to say, the cutting tool can bear the cutting force, and the machine tool can not bear, to put it bluntly, the machine tool car is not moving, the general new bed will not appear this kind of problem, the bed with this kind of problem is either old, or is often encountered machine tool killer.

16. In the car when a goods, found that size is also good at first, but made a few hours later found size changed and size in unstable because may be the beginning of a insert is new, so the cutting force is not big, but after a period of time, tool wear, cutting force, led to the workpiece on the chuck shift, so the size run and unstable.

17. When using G71, the values of P and Q cannot exceed the sequence number of the entire program or an alarm will appear: G71~G73 instructions are not formatted correctly, at least in FUANC.

18. Subroutines in FANUC system have two formats :(1) P000 0000, the first three digits refer to the number of cycles, and the last four digits refer to 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.

19. If the starting point of the arc remains unchanged and the end point of the arc is offset by a mm in the Z direction, the bottom diameter of the arc will be offset by A /2.

20. When drilling deep holes, the bit does not grind the cutting groove to facilitate chip removal.

21. If the tool holder is used for drilling, the drill bit can be rotated to change the aperture.

22. In the stainless steel center hole, or stainless steel hole when the drill or the center of the drill center must be small, or it can not move, in the use of cobalt drilling without grinding groove so as to avoid the drill annealing in the process of drilling.

23. According to the process, the material is generally divided into three kinds: one material, two goods and the whole bar material.

24. in the car thread ellipse may be loose material, with a tooth insert more than a few insert on the line.

25.In some systems where macros can be input, they can be used instead of subroutine loops. This saves the program number and saves a lot of trouble.

26. If the drill bit is used for reaming, but the hole has a large jump, then the flat bottom drill can be used for reaming, but the twist drill must be short to increase rigidity.

27. In the drill press if directly drilled with drill, the aperture can appear deviation, but if in the drill press for reaming size generally will not run, such as with 10mm drill in the drill press for reaming, the aperture is generally expanded in 3 tolerance.

28 in the car hole (through hole) as far as possible to make the chip child continuous chip and then discharge from the tail.

Rolling points:

(1) The position of the insert should be properly raised.

(2) The appropriate Angle of the blade, the amount of cutting tool and feeding, remember that the insert can not be too low or easy to chip, if the auxiliary Angle of the insert is large, even if the chip will not stick the insert rod, if the auxiliary Angle is too small, the chip will be stuck after the chip rod is easy to danger.

29. The larger the cross section of the insert rod in the hole, the more difficult it is to vibrate the insert. And the strong rubber band can be tied to the insert rod, because the strong rubber band can play a certain role in absorbing vibration.

30. When the copper hole is in the car, the tip R of the insert can be appropriately large (R0.4~R0.8), especially when the taper is under the car, the iron parts may be nothing, and the copper parts will be very chip.