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The role of tools in CNC machining
Influence on cutting force: amount of back cut, feed rate, cutting speed;
Influence on tool durability: cutting speed, feed rate, back engagement
2. When the amount of back-engagement is doubled, the cutting force is doubled;
When the feed rate is doubled, the cutting force increases by about 70%;
When the cutting speed is doubled, the cutting force gradually decreases;
That is to say, if G99 is used, the cutting speed will increase, and the cutting force will not change much.
3. According to the discharge of iron chips, it can be judged whether the cutting force and cutting temperature are within the normal range.
4. The temperature represented by the color of the iron filings: when the actual value X measured and the diameter Y of the drawing are greater than 0.8, when the concave arc of the car is turned, the turning tool with a secondary declination angle of 52 degrees (that is, our commonly used blade is 35 degrees) Turning tool with a main declination angle of 93 degrees) may wipe the tool at the starting point of the R drawn.
White is less than 200 degrees
Yellow 220-240 degrees
dark blue 290 degrees
Blue 320-350 degrees
Purple and black greater than 500 degrees
Red is greater than 800 degrees
5. FUNAC OI mtc generally defaults to the G command:
G69: Coordinate rotation cancel
G21: Metric dimension input
G25: Spindle speed fluctuation detection disconnected
G80: Canned cycle cancellation
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 ON
G67: Cancel macro program modal call
G64: Not so sure
G13.1: Cancel coordinate interpolation mode
6. The external thread is generally 1.3P, and the internal thread is 1.08P.
7. Thread speed S1200/pitch*coefficient (usually 0.8).
8. Manual tool nose R compensation formula: Chamfer from bottom to top: Z=R*(1-tan(a/2)) X=R(1-tan(a/2))*tan(a) From When going up and down, the chamfer can be changed from minus to plus.
9. Every time the feed increases by 0.05, the speed decreases by 50-80 rpm. This is because reducing the speed means that the tool wear decreases, and the cutting force increases slowly, thereby making up for the increase in cutting force and temperature due to the increase in feed. impact to come.
10. The influence of cutting speed and cutting force on the tool is very important. Excessive cutting force is the main reason for the collapse of the tool. The relationship between cutting speed and cutting force: when the cutting speed is faster, the feed remains unchanged, and the cutting force decreases slowly. The higher it is, when the cutting force and internal stress are too large for the blade to withstand, the tool will collapse (of course, there are also reasons such as stress and hardness reduction caused by temperature changes).
11. During CNC lathe processing, the following points should be paid special attention:
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 output torque of the spindle is often insufficient at low speeds. If the cutting load is too large, it is easy to get bored. , but some machine tools with gears can solve this problem very well;
2) As far as possible, the tool can complete the processing of one part or one work shift, especially in the finishing of large pieces, it is necessary 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, 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 filings to isolate the cutting heat from the workpiece and ensure that the workpiece does not heat up or heats up less. Therefore, high-speed machining is to select a high cutting temperature. Match the speed with the high feed and select a small amount of back cutting;
6) Pay attention to the compensation of tool nose R.
12. Vibration and chipping often occur during grooving. The root cause of all these is that the cutting force increases and the rigidity of the tool is not enough. The shorter the extension length of the tool, the smaller the clearance angle, the larger the area of the blade, the better the rigidity. It can increase with the larger cutting force, but the larger the width of the grooving knife, the cutting force that it can withstand will increase accordingly, but its cutting force will also increase. Cutting force is also small.
13. Reasons for vibration when troughing:
1) The extension 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 become larger and cause large vibration. The formula is: P=F/back cutting amount*f P is the unit cutting force F is the cutting force, and the speed is too fast. will vibrate
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 cannot bear it. To put it bluntly, the machine tool does not move. Generally, new beds do not have such problems. The beds with such problems are either old, or Is often encountered machine tool killer.
