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What we must know about CNC machining

General operation steps of CNC machining

  • (1) Before writing or programming, you should first compile the processing program of the workpiece. If the processing program of the workpiece is longer and more complicated, it is best not to program on the machine tool. Instead, use a programming machine or computer programming to avoid occupying the machine time. , For short programs should also be written on the program list. It's best to try it out after editing to avoid unnecessary waste due to formal processing.
  • (2) Generally, the machine is turned on before the system is turned on when the machine is turned on. In some designs, the two are interlocked, and the machine cannot display information on the CRT without power on. In addition, as soon as the system is turned on, a problem is prone to occur when the program written before is started up and running, which may be potentially dangerous. It's like the car is igniting after it is in gear, which is very dangerous.
  • (3) Return to reference point For machine tools with incremental control systems (using incremental position detection components), this step must be executed first to establish the movement reference of each coordinate of the machine tool.
  • (4) Adjust the processing program. According to the storage medium of the program (paper tape or magnetic tape, disk), it can be input by paper tape reader, cassette tape machine, programming machine or serial communication. If it is a simple program, the keyboard can be directly used on the CNC control panel. If the program is very simple and only one piece is processed, there is no need to save the program. The MDI method can be used to input and process section by section. In addition, the workpiece origin, tool parameters, offsets, and various compensations used in the program must also be input before processing. Of course, most of us would not be able to process only one workpiece.
  • (5) Editing of the program If the inputted program needs to be modified, it must be edited. In the meantime, the machine must be tentatively set. At this time, place the mode selection switch in the edit position, and use the edit keys to add, delete, and change. For the editing method, see the corresponding manual.
  • (6) The machine is locked, and the program is run. This step is to check the program. If there is an error, it needs to be edited again.
  • (7) Manual incremental movement is adopted for loading the workpiece, aligning and tool setting, and continuous movement or the machine tool is moved by hand crank. Align the starting point to the beginning of the program, and set the tool benchmark.
  • (8) Starting coordinate feed for continuous processing generally uses the program in the memory for processing. This method has a lower failure rate than the program on paper tape. The feed speed during processing can be adjusted by the feedrate override switch. During processing, you can press the feed hold button to pause the feed movement, observe the processing conditions or perform manual measurement. Precision machining manufacturers press the cycle start button again to resume processing. To ensure that the program is correct, it should be rechecked before processing. In the milling process, for the plane curve workpiece, a pencil can be used instead of the cutter to set the contour of the workpiece on the paper, which is more intuitive. If the system has a tool path simulation function, it can be used to check the correctness of the program.
  • (9) Operation display Utilize the various screens of the CRT to display the position of the workbench or tool, the program and the state of the machine tool, so that the operator can monitor the processing conditions.
  • (10) After the program output processing, if it is necessary to save the program, it can be left in the CNC's memory. If the program is too long, the program in the memory can be output to an external device (such as a punching machine) in the punched tape (or Tape, disk, etc.).
  • (11) Generally, the machine tool should be shut down before shutting down the system.

Precautions during the operation of CNC machining

  • (l) Before starting each time, check whether the lubricating oil in the lubricating oil pump behind the milling machine is sufficient, whether the air compressor is turned on, and whether the mechanical oil used for the cutting fluid is sufficient, etc.
  • (2) When starting up, first turn on the main power supply, then press the start button in the CNC power supply, turn the emergency stop button clockwise, and wait for the milling machine to detect all functions (a row of red indicators on the lower operation panel goes out) , Press the button of the machine tool to reset the milling machine and put it on standby.
  • (3) During manual operation, you must always pay attention. Before moving in the X and Y directions, the Z-axis must be at the tool-raising position. In the process of moving, you can't just watch the change of the coordinate position on the CRT screen, but observe the movement of the tool. After the tool moves in place, look at the CRT screen to make fine adjustments.
  • (4) In the programming process, for beginners, try to use the G00 instruction as little as possible, especially in the X, Y, Z three-axis linkage, you should pay more attention. When emptying the knife, the movement of the Z axis should be carried out separately from the movement of the X and Y axes, that is, raise the knife more and insert less obliquely. Sometimes due to oblique insertion, the tool will hit the workpiece and the tool will be damaged.
  • (5) When using a computer for serial communication, do: first turn on the milling machine, then turn on the computer; turn off the computer first, then turn off the milling machine. Avoid impacting the computer due to the instantaneous change of current when the milling machine is switched on and off.
  • (6) When using the DNC (program transfer between computer and milling machine) function, pay attention to the memory capacity of the milling machine. Generally, the total number of bytes of the program transferred from the computer to the milling machine should be less than 23kB. If the program is relatively long, it must be processed by the computer while transmitting, but the block number must not exceed N9999. If the number of blocks exceeds 10,000, the block number can be cancelled with the help of the program editing function in MASTERCAM.

When the milling machine has an alarm, it is necessary to find the cause according to the alarm number and clear the alarm in time. Do not turn off the machine, otherwise it will still be in the alarm state after turning on the machine. Using edge finder to set the knife, the detailed steps are as follows:

X and Y tool setting

  • ①The workpiece is mounted on the worktable of the machine tool through the fixture. When clamping, the measuring position of the edge finder should be reserved on the four sides of the precision part.
  • ②Quickly move the worktable and spindle so that the edge finder probe is close to the left side of the workpiece;
  • ③Use the fine-tuning operation to slowly touch the probe to the left side of the workpiece until the edge finder glows, and write down the X coordinate value in the machine coordinate system at this time, such as -310.300;
  • ④Lift the edge finder to the upper surface of the workpiece, quickly move the worktable and spindle, and make the probe close to the right side of the workpiece;
  • ⑤ Change to fine-tuning operation, let the probe slowly touch the left side of the workpiece until the edge finder glows, and write down the X coordinate value in the mechanical coordinate system at this time, such as -200.300;
  • ⑥ If the probe diameter is 10mm, the workpiece length is -200.300-(-310.300)-10=100, based on this, the X coordinate value of the workpiece coordinate system origin W in the machine tool coordinate system is -310.300+100/2+ 5= -255.300;
  • ⑦ Similarly, the Y coordinate value of the workpiece coordinate system origin W in the machine coordinate system can be measured.

 Z-direction tool setting

  • ①Remove the edge finder, and install the tool used for processing on the spindle;
  • ②Place the Z axis setter (or the tool setting block with a fixed height, the same below) on the upper plane of the workpiece;
  • ③Quickly move the spindle so that the tool end face is close to the upper surface of the Z axis setter;
  • ④ Change to fine-tuning operation, let the tool end face slowly touch the upper surface of the Z-axis setter until the pointer indicates the zero position;
  • ⑤Write down the Z value in the machine coordinate system at this time, such as -250.800;
  • ⑥ If the height of the Z axis setter is 50mm, the Z coordinate value of the workpiece coordinate system origin W in the machine coordinate system is -250.800-50-(30-20)=-310.800.

Input the measured X, Y, Z values ​​into the storage address of the machine tool workpiece coordinate system (usually use G54-G59 codes to store tool setting parameters).

Matters needing attention 

The following issues should be paid attention to during the tool setting operation:

  • (1) Use correct tool setting tools according to processing requirements to control tool setting errors;
  • (2) In the process of tool setting, the precision of tool setting can be improved by changing the fine-tuning feed;
  • (3) When setting the knife, please operate carefully, especially pay attention to the moving direction to avoid the danger of collision;
  • (4) The tool setting data must be stored in the storage address corresponding to the program to prevent serious consequences due to call errors. 2. Input and modification of tool compensation value According to the actual size and position of the tool, input the tool radius compensation value and tool length compensation value to the storage location corresponding to the program. It should be noted that the correctness of the compensated data, the correctness of the symbols and the correctness of the address where the data is located will threaten the processing, leading to the danger of collision or the processing scrap.

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