Currently, most economical CNC lathes in my country use ordinary three-phase asynchronous motors with frequency converters to achieve stepless speed regulation. Without mechanical reduction, the spindle output torque is often insufficient at low speeds. If the cutting load is too large, the machine is prone to stalling. However, some machine tools have gear shifting, which solves this problem well.
Here are some CNC machining tips you absolutely need to know!
1. Effects on cutting temperature: cutting speed, feed rate, depth of cut;
Effects on cutting forces: depth of cut, feed rate, cutting speed;
Impact on tool durability: cutting speed, feed rate, depth of cut.
2. When the depth of cut doubles, the cutting force doubles.
When the feed rate is doubled, the cutting force increases by approximately 70%.
When the cutting speed is doubled, the cutting force gradually decreases;
In other words, if G99 is used, the cutting speed increases but the cutting force does not change significantly.
3. The cutting force and cutting temperature can be determined from the condition of the metal chips being discharged.
4. When the actual measured value X is greater than 0.8 compared to the diameter Y on the drawing, the R cut by a cutting tool with a secondary cutting edge angle of 52 degrees (that is, a cutting tool with a cutting edge angle of 93 degrees and a cutting edge angle of 35 degrees that we commonly use) may rub against the tool at the starting position when turning a concave arc.
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 greater than 500 degrees
Red greater than 800 degrees
6. FUNACOImtc generally defaults to the G command:
G69: Not sure.
G21: Metric dimension input
G25: Spindle speed fluctuation detection disconnected
G80: Fixed loop cancellation
G54: Default coordinate system
G18: ZX Plane Selection
G96 (G97): Constant linear velocity control
G99: Feed per revolution
G40: Edge compensation canceled (G41G42)
G22: Storage trip detection enabled
G67: Cancel macro program modal call
G64: Not sure
G13.1: Polar coordinate interpolation mode canceled
7. External threads are generally 1.3P, and internal threads are 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) Chamfering from top to bottom, simply change the subtraction to addition.
10. For every 0.05 increase in feed, the spindle speed decreases by 50-80 rpm. This is because a decrease in spindle speed means less tool wear and a slower increase in cutting force, thus compensating for the increased cutting force and temperature caused by the increase in feed.
11. Cutting speed and cutting force have a crucial impact on cutting tools. Excessive cutting force is a major cause of tool breakage. The relationship between cutting speed and cutting force: When the cutting speed is faster and the feed rate remains constant, the cutting force decreases slowly. At the same time, faster cutting speeds cause faster tool wear, leading to increasingly larger cutting forces and higher temperatures. When the cutting force and internal stress become too great for the cutting tool to withstand, tool breakage will occur (of course, this is also due to factors such as stress caused by temperature changes and a decrease in hardness).
12. When machining on a CNC lathe, the following points should be paid special attention to:
(1) For the current economic CNC lathes in my country, the ordinary three-phase asynchronous motor is generally used to achieve stepless speed change through frequency converter. Without mechanical deceleration, the spindle output torque is often insufficient at low speed. If the cutting load is too large, the machine is prone to stalling. However, some machine tools have gear shifting, which solves this problem well.
(2) Make the tool complete the machining of one part or one shift as much as possible. For large parts finishing, pay special attention to avoid changing the tool in the middle to ensure that the tool can complete the machining in one go.
(3) When turning threads with a CNC lathe, a higher speed should be used 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 as to discharge the cutting heat with the chips and isolate the cutting heat from the workpiece, ensuring that the workpiece does not heat up or heats up less. Therefore, high-speed machining is to select a very high cutting speed and a high feed while selecting a small depth of cut.
(6) Pay attention to the compensation of the blade tip R.
13. Vibration and tool breakage often occur during grooving. The root cause of all this is the increased cutting force and insufficient tool rigidity. The shorter the tool extension length, the smaller the clearance angle, the larger the insert area and the better the rigidity, the greater the cutting force it can withstand. However, the wider the grooving tool, the greater the cutting force it can withstand, but its cutting force will also increase. Conversely, the smaller the grooving tool, the less force it can withstand, but its cutting force is also smaller.
14. The cause of vibration during the turning of the wheel:
(1) The excessive extension length of the cutter reduces its rigidity;
(2) If the feed rate is too slow, the unit cutting force will increase, which will cause large vibration. The formula is: P=F/depth of cut * f, where P is the unit cutting force and F is the cutting force. In addition, excessively fast rotation speed will also cause the tool to vibrate.
(3) The machine tool is not rigid enough. In other words, the cutting tool can withstand the cutting force, but the machine tool cannot. To put it bluntly, the machine tool cannot move. Generally, new machines will not have this problem. Machines that have this problem are either old or have frequently encountered machine tool killers.
15. When machining a workpiece, the dimensions were initially found to be fine, but after several hours, the dimensions changed and became unstable. The reason may be that at the beginning, the cutting tools were new, so the cutting force was not very large. However, after machining for a period of time, the cutting tools wore out, the cutting force increased, and the workpiece shifted on the chuck, so the dimensions kept changing and became unstable.
16. When using G71, the values of P and Q cannot exceed the number of sequences in the entire program, otherwise an alarm will occur: G71-G73 instruction format is incorrect, at least in FUANC.
17. Subroutines in the FANUC system have two formats:
(1) The first three digits of P0000000 indicate the number of loops, 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 loops.
18. If the starting point of the arc remains unchanged, and the ending point is offset by a mm in the Z direction, then the position of the bottom diameter of the arc will be offset by a/2.
19. When drilling deep holes, the drill bit is not ground with cutting grooves to facilitate chip removal.
20. If you are using a tool holder to drill holes, you can rotate the drill bit to change the diameter of the hole.
21. When drilling a center hole in stainless steel, the drill bit or center drill must be small, otherwise it will not be able to drill. When using a cobalt drill, do not grind grooves to avoid annealing of the drill bit during the drilling process.
22. According to the process, there are generally three types of material cutting: one piece per cut, two pieces per cut, and the whole bar per cut.
23. If an oval shape appears when threading, it may be due to loose material. Simply use a thread cutter to smooth it out a few times.
24. In some systems that allow input of macro programs, macro programs can be used to replace subroutine loops, which can save program numbers and avoid a lot of trouble.
25. If you are using a drill bit to enlarge a hole, but the hole runs out a lot, you can use a flat-bottom drill to enlarge the hole. However, the twist drill must be short to increase rigidity.
26. If you drill directly with a drill bit on a drilling machine, the hole diameter may deviate. However, if you enlarge the hole on a drilling machine, the size will generally not deviate. For example, if you enlarge the hole with a 10mm drill bit on a drilling machine, the enlarged hole diameter will generally be within a tolerance of about 3 mils.
27. When machining small holes (through holes), try to make the chips continuously roll up and then exit from the tail. Key points for chip rolling: First, the tool position should be appropriately high. Second, the appropriate cutting edge angle, depth of cut, and feed rate. Remember that the tool should not be too low, otherwise the chips will easily break. If the secondary cutting edge angle of the tool is large, even if the chips break, the tool holder will not get stuck. If the secondary cutting edge angle is too small, the chips will get stuck on the tool holder after chip breaking, which can be dangerous.
28. The larger the cross-section of the tool holder in the hole, the less likely it is to vibrate. Also, a strong rubber band can be tied to the tool holder, as the strong rubber band can absorb vibration to a certain extent.
29. When machining copper holes, the cutting edge radius (R) can be appropriately larger (R0.4-R0.8), especially when machining the lower taper. It may not be a problem for iron parts, but it will cause a lot of chipping on copper parts.
