Knowledge of CNC machining that professionals in the CNC machine tool industry must know
Regarding the current economic CNC lathes in our country, a general three-phase asynchronous motor is generally used to achieve stepless speed change through a frequency converter. If there is no mechanical reduction, the output torque of the spindle is often insufficient at low speeds. If the cutting load is too large, it is easy to get stuck. However, some machine tools have gears that effectively handle this problem.
The following CNC machining knowledge is something you need to know!
1. The impact on cutting temperature: cutting speed, feed rate, back cutting amount;
The impact on cutting force: back feed, feed rate, cutting speed;
The impact on tool durability: cutting speed, feed rate, and back cutting amount.
When the back cutting amount doubles, the cutting force doubles;
When the feed rate doubles, the cutting force increases by approximately 70%;
As the cutting speed doubles, the cutting force gradually decreases;
That is to say, if G99 is used, the cutting speed will increase and the cutting force will not be significantly changed.
3. Able to determine the cutting force and whether the cutting temperature is within the normal range based on the condition of iron filings being discharged.
When the actual value X measured is greater than 0.8 compared to the diameter Y on the drawing, the concave arc of the car may rub against the R produced by the turning tool with a secondary deviation angle of 52 degrees (which is the commonly used turning tool with a main deviation angle of 35 degrees and 93 degrees) at the starting position.
5. The temperature represented by the color of iron filings:
White less than 200 degrees
Yellow 220-240 degrees
Dark blue 290 degrees
Blue 320-350 degrees
Purple black is greater than 500 degrees Celsius
Red color greater than 800 degrees
6. FUNACOIMtc generally acquiesces to the G instruction:
G69: Not very clear
G21: Metric scale input
G25: Spindle speed fluctuation detection disconnected
G80: Fixed loop revocation
G54: Coordinate system tacit consent
G18: ZX plane selection
G96 (G97): Constant linear speed control
G99: Feed per revolution
G40: Knife tip compensation cancellation (G41G42)
G22: Store Travel Detection On
G67: Macro Program Modal Call Revocation
G64: Not very clear
G13.1: Revocation of Polar Interpolation Method
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 tip R compensation formula: Chamfer from bottom to top: Z=R * (1-tan (a/2)) X=R (1-tan (a/2)) * tan (a)) Chamfer from top to bottom by changing the subtract to add.
10. For every 0.05 increase in feed, the rotational speed decreases by 50-80 rpm. This is because a decrease in rotational speed means a decrease in tool wear, and the increase in cutting force is relatively slow. Then, compensation is made for the impact caused by the increase in feed, which increases cutting force and temperature.
11. The influence of cutting speed and cutting force on the tool is crucial, and excessive cutting force is the main cause of tool collapse. The relationship between cutting speed and cutting force: When the cutting speed is faster, the feed remains unchanged, and the cutting force slowly decreases. The faster the cutting speed, the faster the tool wear, resulting in greater cutting force and higher temperature. When the cutting force and internal stress are too high for the blade to accept, the tool will collapse (of course, there are also reasons such as stress and hardness decrease caused by temperature changes).
During CNC machining, special attention should be paid to the following points.
(1) Regarding the current economic CNC lathes in our country, a general three-phase asynchronous motor is generally used to achieve stepless speed change through a frequency converter. If there is no mechanical reduction, the output torque of the spindle is often insufficient at low speeds. If the cutting load is too large, it is easy to get stuck. However, some machine tools have gears that effectively handle this problem;
(2) Try to ensure that the tool can complete the machining operation of a part or a work shift as much as possible, and pay special attention to the center to prevent changing the tool halfway during large precision machining to ensure that the tool can be completed in one go;
(3) When using CNC lathe to turn threads, it is advisable to choose 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, and then discharge the cutting heat along with the iron filings to block the cutting heat from the workpiece, ensuring that the workpiece does not heat up or heats up less. Therefore, high-speed machining selects a 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. When turning the groove, oscillation and tool breakage often occur, and all the fundamental reasons are that the cutting force increases and the tool rigidity is not good. The shorter the tool extension length and the smaller the back angle, the larger the blade area and the better the rigidity, which can adapt to the larger cutting force. However, the larger the width of the groove tool, the more cutting force it can accept, but its cutting force will also increase. On the contrary, when the groove tool is small, it can accept less force, but its cutting force is also small.
14. The reason for oscillation during the car slot.
(1) The extended length of the cutting tool is too long, which leads to a decrease in rigidity;
(2) If the feed rate is too slow, it will increase the unit cutting force and cause significant oscillation. The formula is: P=F/back cutting amount * fP is the unit cutting force F is the cutting force. Other speeds that are too fast will also cause tool vibration;
(3) The rigidity of the machine tool is not good, which means that the cutting tool can bear cutting force, but the machine tool cannot accept it. In other words, the machine tool cannot move. Generally, new beds do not have such problems. Beds that have such problems are either old or often encounter machine tool killers.
15. When driving a cargo, it was initially found that the scale was good, but after a few hours of operation, it was found that the scale had changed and the scale was unstable. The reason may be that the cutting force was not very large at the beginning because the knives were all new. However, after driving for a period of time, the cutting tool worn out and the cutting force increased, causing the workpiece to shift on the chuck, resulting in an old and unstable scale.
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 instruction pattern is incorrect, at least in FUANC.
There are two patterns of subroutines in the FANUC system.
(1) The first three digits of P0000000 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. If the starting point of the arc remains unchanged and the ending Z direction is offset by a mm, then the bottom diameter direction 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.
If using a tool holder to drill holes, the drill bit can be rotated and the hole diameter can be modified.
21. When drilling stainless steel center holes, it is necessary to make the drill bit or center hole smaller, otherwise it cannot be moved. When drilling with cobalt drill, do not grind the groove to avoid annealing of the drill bit during the drilling process.
According to the process, cutting is generally divided into three types: one material per batch, two goods per batch, and the entire bar material per batch.
23. When the thread appears elliptical during threading, it may be due to loose material. Use a tooth cutter to make a few more cuts.
In some systems that can input macro programs, macro programs can be used to replace subroutine loops, which can save program numbers and prevent a lot of trouble.
25. If the drill bit is used for reaming, but the hole has a large bounce, the flat bottom drill can be used for reaming, but the Fried Dough Twists drill needs to be short to increase rigidity.
26. If a drill bit is directly used to drill holes on a drilling machine, the aperture may show deviation. However, if the hole is enlarged on a drilling machine, the scale generally does not run. For example, if a 10mm drill bit is used to enlarge the hole on a drilling machine, the expanded aperture is generally around 3 threads
27. When in the small hole (through hole) of the car, try to curl the chips one by one and then discharge them from the tail. The key to curling the chips is
(1) The position of the knife should be appropriately raised,
(2) The appropriate blade inclination angle, cutting amount, and feed rate should be kept in mind, and the tool should not be too low to avoid simple chip breakage. If the secondary deviation angle of the tool is large, even if the chip is broken, the tool holder will not get stuck. If the secondary deviation angle is too small, the chips will get stuck on the tool holder after chip breakage, which is a simple risk.
28. The larger the cross-sectional area of the tool holder in the hole, the more difficult it is to vibrate the tool. Additionally, a strong rubber band can be attached to the tool holder, as the strong rubber band can have a certain adsorption and oscillation effect.
