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Home > Haisen Blog > Basic knowledge of CNC milling machine

  • (1) Features of CNC milling machine

    The CNC milling machine was developed on the basis of a general milling machine. The processing technology of the two is basically the same, and the structure is somewhat similar, but the CNC milling machine is an automatic processing machine controlled by a program, so its structure is also very different from the ordinary milling machine. The CNC milling machine is generally composed of a CNC system, a main drive system, a feed servo system, a cooling and lubricating system, etc.:

    1: The spindle box includes the spindle box body and the spindle drive system, which is used to clamp the tool and drive the tool to rotate. The spindle speed range and output torque have a direct impact on processing.

    2: The feed servo system is composed of a feed motor and a feed actuator. The relative motion between the tool and the workpiece is realized according to the feed speed set by the program, including linear feed motion and rotary motion.

    3: Control system CNC milling machine motion control center, execute CNC machining program to control the machine tool for processing

    4: Auxiliary devices such as hydraulic, pneumatic, lubrication, cooling system and chip removal, protection and other devices.

    5: Machine tool basic parts usually refer to the base, column, beam, etc., which are the foundation and frame of the entire machine tool.

    (2) The working principle of CNC milling machine

    1: According to the technical requirements of the part shape, size, precision and surface roughness, make the processing technology and select the processing parameters. Input the compiled processing program to the controller through manual programming or automatic programming with CAM  software. After the controller processes the processing program, it sends instructions to the servo device. The servo device sends a control signal to the servo motor. The spindle motor rotates the tool, and the X, Y  and Z-direction servo motors control the relative movement of the tool and the workpiece according to a certain path, so as to realize the cutting of the workpiece.

    The CNC milling machine is mainly composed of a bed, a milling head, a longitudinal table, a transverse saddle, a lifting table, and an electrical control system. It can complete basic milling, boring, drilling, tapping and automatic working cycles, and can process various cams, templates and mold parts with complex shapes. The bed of the CNC milling machine is fixed on the base for installation and various parts of the machine tool. The console has a color LCD display, machine operation buttons, various switches and indicators. The longitudinal table and the horizontal slide are installed on the lifting platform, and the feed of X, Y, Z coordinates is completed by the drive of the longitudinal feed servo motor, the lateral feed servo motor and the vertical lift feed servo motor. The electrical cabinet is installed behind the column of the bed, and the electrical control part is installed in it.

    2: Performance indicators of CNC milling machine

    3: Point position control function can realize the processing that requires high mutual position accuracy.

    4: The continuous contour control function can realize the interpolation function of straight line and circular arc and the processing of non-circular curve.

    5: The tool radius compensation function can be programmed according to the marked size of the part drawing, without considering the actual radius size of the tool used, thereby reducing the complicated numerical calculation during programming.

    6: The tool degree compensation function can automatically compensate the length of the tool to meet the requirements for the adjustment of the tool length during processing.

    7: Proportion and mirroring processing function, the proportion function can change the coordinate value of the processing program according to the specified proportion to execute. Mirror processing is also called axisymmetric processing. If the shape of a part is symmetrical about the coordinate axis, only one or two quadrants can be programmed, and the contours of the remaining quadrants can be realized by mirror processing.

    8: Rotation function can execute the edited processing program by rotating it at any angle in the processing plane.

    9: Subroutine call function. Some parts need to repeatedly process the same contour shape at different positions. Use a contour shape processing program as a subroutine and call it repeatedly at the required position to complete the processing of the part.

    10: Macro program function can use a general instruction to represent a series of instructions to achieve a certain function, and can operate on variables, making the program more flexible and convenient.

    (3) Coordinate system of CNC milling machine

    1: The relative movement of the milling machine is stipulated. On the machine tool, the workpiece is always considered to be stationary while the tool is moving. In this way, programmers can determine the machining process of the machine tool based on the part drawing without considering the specific movement of the workpiece and the tool on the machine tool.

    2: The regulation of machine tool coordinate system, the mutual relationship of X, Y, Z coordinate axes in the standard machine tool coordinate system is determined by the right-hand Cartesian coordinate system. On a CNC machine tool, the motion of the machine tool is controlled by a numerical control device. In order to determine the forming motion and auxiliary motion on the CNC machine tool, the displacement and direction of the motion on the machine tool must be determined first, which needs to be realized through the coordinate system. This coordinate system is called the machine coordinate system.

    3: Z coordinate. The movement direction of Z coordinate is determined by the spindle that transmits cutting power, that is, the coordinate axis parallel to the spindle axis is the Z coordinate, and the positive direction of the Z coordinate is the direction in which the tool leaves the workpiece.

    4: X coordinate, X coordinate is parallel to the clamping plane of the workpiece, generally in the horizontal plane. If the workpiece rotates, the direction of the tool leaving the workpiece is the positive direction of the X coordinate.

    If the tool is rotating, it can be divided into two situations:

    1) When the Z coordinate is horizontal, when the observer looks at the workpiece along the tool spindle, the +X movement direction points to the right.

    2) When the Z coordinate is vertical, when the observer faces the tool spindle and looks toward the column, the +X movement direction points to the right.

    5: Y coordinate. After determining the positive direction of the X and Z coordinates, you can use the direction of the X and Z coordinates to determine the direction of the Y coordinate according to the right-hand rectangular coordinate system.

    (4) Features and composition of CNC milling machine

    1: CNC vertical milling machine, vertical CNC milling machine, the main body is mainly composed of base, column, saddle, worktable, headstock and other components. The five major parts of the main body are made of high-strength high-quality castings and resin sand modeling, with stable organization , To ensure that the whole machine has good rigidity and precision retention. The three-axis guide rail pairs all adopt high-frequency hardening and plasticized guide rail combination to ensure the accuracy of the machine tool and reduce friction resistance and loss. The three-axis transmission system is composed of precision ball screws and servo system motors, and is equipped with an automatic lubrication device.

    All three axes of the machine tool adopt stainless steel guide rail telescopic cover, which has good protection performance. The whole machine is fully closed guard, doors and windows are larger, and the appearance is neat and beautiful. The operation control box is placed in the front right of the machine tool, and it can be rotated, and the operation is convenient. It can perform various milling, boring, rigid tapping and other processing, and is cost-effective. It is an ideal equipment for high-quality, high-precision, and high-efficiency machinery manufacturing industry.

    2: Horizontal CNC milling machine, the same as the general horizontal milling machine, its spindle axis is parallel to the horizontal plane. In order to expand the processing range and expand the functions, the horizontal CNC milling machine usually adopts the addition of a CNC turntable or a universal CNC turntable to realize 4, 5 coordinate processing. In this way, not only the continuous revolving contour on the side of the workpiece can be processed, but also in one installation, the station can be changed by the turntable to perform "four-sided processing"

    3: Vertical and horizontal CNC milling machines. At present, this type of CNC milling machine is rare. Because the spindle direction of this type of milling machine can be changed, it can achieve both vertical and horizontal processing on a machine tool. , And has the functions of the above two types of machine tools at the same time, its use range is wider, the function is more complete, the room for selecting the processing object is larger, and it brings a lot of convenience to the user. Especially when the production batch is small, the variety is large, and the vertical and horizontal processing are required, the user only needs to buy one such machine tool.

    4: CNC milling machines are classified by structure:

    ①Worktable lifting type CNC milling machine, this type of CNC milling machine adopts the way that the worktable moves and lifts, while the spindle does not move. Small CNC milling machines generally use this method

    ②Spindle head lift type CNC milling machine, this type of CNC milling machine uses the worktable to move longitudinally and horizontally, and the spindle moves up and down along the vertical slide; the spindle head lift type CNC milling machine has many advantages in terms of accuracy maintenance, weight bearing, system configuration, etc. , Has become the mainstream of CNC milling machines.

    ③Gantry type CNC milling machine, this type of CNC milling machine spindle can move on the horizontal and vertical slides of the gantry, and the gantry moves longitudinally along the bed. Large-scale CNC milling machines often use gantry movable type because they have to take into account the problems of expanding the stroke, reducing the area and rigidity.
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