29 CNC machining tips compiled by veterans-no need to elaborate, just take a look.
1. Impacts on cutting temperature: cutting speed, feed rate, and back-cut; Impacts on cutting force: back-cut, feed rate, and cutting speed; Impacts on tool life: cutting speed, feed rate, and back-cut.
2. When back-cut doubles, cutting force doubles; when feed rate doubles, cutting force increases by approximately 70%; when cutting speed doubles, cutting force gradually decreases. In other words, if you use G99, increasing cutting speed won't significantly change cutting force.
3. You can determine whether the cutting force and cutting temperature are within normal ranges based on chip discharge.
4. When turning a concave arc with a ratio of the measured value (X) to the diameter (Y) on the drawing being greater than 0.8, a turning tool with a 52-degree secondary rake angle (commonly used with a 35-degree blade and a 93-degree primary rake angle) may scrape the tool at the starting point.
5. Temperature represented by the color of the iron filings:
White: less than 200°C;
Yellow: 220-240°C;
Dark blue: 290°C;
Blue: 320-350°C;
Purple-black: greater than 500°C;
Red: greater than 800°C.
6. FUNAC OI MTC generally uses the following default G commands:
G69: Unknown;
G21: Metric dimension input;
G25: Spindle speed fluctuation detection disabled;
G80: Canned cycle canceled;
G54: Default coordinate system;
G18: Z/X plane selection;
G96 (G97): Constant linear speed control;
G99: Feed per revolution;
G40: Tool nose compensation canceled (G41 G42);
G22: Stored stroke detection enabled;
G67: Macro program modal call canceled;
G64: Unknown;
G13.1: Polar coordinate interpolation mode canceled.
7. External threads are generally 1.3P, internal threads 1.08P.
8. Thread speed S1200/pitch * safety factor (generally 0.8).
9. Manual tool tip R compensation formula: For chamfering from bottom to top: Z = R * {1-tan(a/2)} X = R {1-tan(a/2)} * tan(a). For chamfering from top to bottom, simply add instead of subtract.
10. For every 0.05 increase in feed, reduce the rotational speed by 50-80 rpm. This is because reducing the rotational speed means less tool wear and a slower increase in cutting force, thus compensating for the increased cutting force and temperature caused by the increased feed.
11. Cutting speed and cutting force have a crucial impact on tool performance. Excessive cutting force is the primary cause of tool breakage. The relationship between cutting speed and cutting force: faster cutting speeds, while keeping the feed constant, gradually reduce cutting force. At the same time, faster cutting speeds lead to faster tool wear, increasing cutting force and temperature. When the cutting force and internal stress become too great for the insert to withstand, it will break (of course, this is also due to stress caused by temperature changes and a decrease in hardness).
12. When machining with CNC lathes, the following points should be paid special attention to:
(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 spindle output torque is often insufficient at low speeds. If the cutting load is too large, it is easy to stall. However, some machine tools are equipped with gear gears to solve this problem very well;
(2) As much as possible, the tool can complete the processing of a part or a work shift. When finishing large parts, it is especially important to avoid changing the tool in the middle to ensure that the tool can complete the processing in one go;
(3) When turning threads with CNC lathes, it is best to use a higher speed 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 chips and the cutting heat is isolated 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 to match the high feed and select a smaller back cutting amount;
(6) Pay attention to the compensation of the tool tip R.
13. During grooving, vibration and chipping often occur. The root cause of all this is the increase in cutting force and insufficient tool rigidity. The shorter the tool extension length, the smaller the back angle, the larger the blade area and the better the rigidity, the greater the cutting force it can withstand. However, the wider the groove cutter, the greater the cutting force it can withstand, but its cutting force will also increase. On the contrary, the smaller the groove cutter, the smaller the force it can withstand, but its cutting force is also smaller.
14. Reasons for vibration during grooving:
(1) The tool extension length is too long, resulting in reduced rigidity;
(2) The feed rate is too slow, resulting in a larger unit cutting force and causing large-scale vibration. The formula is: P=F/back cutting depth*f, P is the unit cutting force, F is the cutting force, and too fast a speed will also cause vibration;
(3) The machine tool is not rigid enough, that is, the 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 kind of problem. Machines that have this kind of problem are either old or often encounter machine tool killers.
15. When turning a product, the dimensions were all good at the beginning, but after a few hours, the dimensions changed and became unstable. The reason may be that at the beginning, the cutting force was not very large because the tools were new. However, after turning for a period of time, the tools wore out and the cutting force became larger, causing the workpiece to shift on the chuck, so the dimensions kept changing and became unstable.
16. When using G71, the values of P and Q cannot exceed the sequence number of the entire program, otherwise an alarm will be displayed: G71-G73 instruction format is incorrect, at least in FUANC.
17. There are two formats for subroutines in the FANUC system:
(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 refer to the program number, and the last three digits of L refer to the number of cycles.
18. If the starting point of the arc remains unchanged and the end point is offset by a mm in the Z direction, the bottom diameter position of the arc will be offset by a/2.
19. When drilling deep holes, do not grind cutting grooves on the drill bit to facilitate chip removal.
20. If drilling with a tool holder, you can rotate the drill bit to change the hole diameter.
21. When drilling a center hole in stainless steel, or when drilling holes in stainless steel, the drill bit or center drill must be small, otherwise it will not be able to drill. When drilling with a cobalt drill, do not grind cutting grooves to avoid annealing the drill bit during the drilling process.
22. Based on the process, there are generally three types of cutting: one piece of material at a time, two pieces at a time, and the entire bar at a time.
23. If an ellipse appears when threading, it may be due to loose material. A few more cuts with a threading cutter will correct the problem.
24. In some systems that support macro programming, macros can be used instead of subroutine loops, saving program numbers and avoiding a lot of trouble.
25. If you are using a drill to enlarge a hole, but the hole runout is large, 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 drill press, the hole diameter may vary. However, if you enlarge the hole on a drill press, the size generally remains within a tolerance of 3 mm. For example, using a 10mm drill bit on a drill press will generally result in a hole diameter within a tolerance of approximately 3 mm.
27. When turning small holes (through holes), try to ensure that the chips are continuously coiled and discharged from the rear end. Key points for chip coiling: 1. Position the tool appropriately high. 2. Maintain an appropriate rake angle, cutting depth, and feed rate. Remember not to lower the tool too low, as this will easily break the chip. A large rake angle will prevent chip breakage without causing the tool to become stuck. A small rake angle can lead to chip jamming after breaking, potentially creating a dangerous situation.
28. The larger the cross-section of the tool bar in the hole, the less likely the tool will vibrate. You can also tie a strong rubber band to the tool bar, as this can absorb vibration.
29. When turning copper holes, the R of the tool tip can be slightly larger (R0.4~R0.8), especially when turning the taper. Iron parts may not be affected, but copper parts will be easily chipped.
