Machining Methods

Numerical control technology of horizontal milling and boring machining center

Numerical control technology of horizontal milling and boring machining center

Overview

The horizontal milling and boring machining center embodies the rapid development of domestic CNC machine tools, marking a new breakthrough in CNC technology in my country. The products range from small-size 300mm worktables to large-size 2500mm worktables, from single worktables to double exchange work; from ordinary to precision, high-speed type plus centers, etc. This time, the horizontal milling and boring cnc machining center is the focus of the discussion, because these products have been manufactured in my country for decades, and their manufacturing CNC technology is relatively mature. Generally, the specifications of machine tool worktables are below 2000mm.

Beginning in the 1980s, there were dozens of companies manufacturing the product from the first domestic companies to the present, and the technical level of the products has also made a qualitative leap. However, in the development process of more than tens of years, although the product has made continuous breakthroughs in technical performance, accuracy, spindle speed and coordinate moving speed, etc., the maximum in product specifications is only a 2000mm table. Large specifications and major forms of horizontal milling and boring machining centers have only been developed in recent years. Today, 2500mm or above worktables, heavy and large horizontal machining centers with exchange workbenches have created a precedent for the history of this type of products, and serve for China’s aviation, aerospace, military, power, shipbuilding, engineering machinery and other machinery manufacturing industries. Provided large key equipment.

Structural characteristics and numerical control analysis of the overall layout of the horizontal milling and boring machining center

This analysis only analyzes traditional planer and cross slide horizontal machining centers, excluding floor-type and five-axis machining centers.
The overall layout of the horizontal machining center products has column fixed and mobile structures; the main spindle box has positive hanging boxes and side hanging boxes; the main shaft has fixed and mobile types, and the mobile main shaft has boring bar, ram type, flat Rotary disc and other structures.

1. Column fixed structure

Machine tools that adopt a column-fixed structure have the following layouts:

  • 1) The column is fixed on the bed, the worktable moves in X direction and Z direction, and the spindle box moves up and down in Y direction. The spindle box can be in two forms: front hanging box and side hanging box. This type of machine tool is suitable for multi-process processing such as boring and milling of medium-sized complex parts.
  • 2) The fixed frame column structure, the spindle box moves in the X and Y directions, and the table moves in the Y direction. This type of machine tool is suitable for various processes such as boring and milling of small and medium-sized parts.
  • 3) The column is fixed on the bed, the spindle box is hung on the column, the spindle box moves in the Y and Z directions, and the table moves in the X direction. This type of machine tool is suitable for multi-process machining such as boring and milling of medium-sized parts.

2. Upright mobile structure

The characteristics of the column mobile machine tool are that the overall bed is mostly T-shaped layout, which includes several structural forms:

  • 1) The bed has a T-shaped layout and a table-top structure. The column moves on the longitudinal bed in the Z direction, and the workbench moves on the horizontal bed in the X direction. The main shaft box has two forms of front hanging box and side hanging box on the column, and moves in the Y direction. This type of machine tool is suitable for multi-process processing such as boring and milling of medium and large parts, especially long length parts.
  • 2) The bed has an inverted T-shaped layout structure, the column moves in the X direction on the horizontal bed, and the table moves in the Z direction on the vertical bed. The main shaft box has two forms of front hanging box and side hanging box on the column, and moves in the Y direction. This type of machine tool is suitable for multi-process machining such as boring and milling of medium and large parts.
  • 3) The bed has an inverted cross-shaped layout structure, the column moves in X and Z directions, the spindle box moves in the Y direction on the column, and the worktable is fixed on the front bed. This machine tool can be suitable for multi-process processing such as boring and milling of small and medium-sized complex parts

At present, most of the machine tool layouts of horizontal machining centers at home and abroad use a T-shaped structure, and the machine tool technology of this structure is relatively mature. From the above structural layout analysis, it can be seen that the general small and medium-sized machine tools use inverted T-shaped structure. This structure machine tool can be equipped with multiple worktables to achieve rapid exchange. The moving parts can also move at high speed and can be cut at high speed to improve work efficiency. The T-shaped planer table structure is suitable for large and heavy machine tools, and can be equipped with double worktables for exchange processing. While the machine tool is working, it can clamp the workpiece in the area to be processed to improve the machining efficiency of the machine tool. This structural layout can be used as a flexible unit, with automatic lines to form a flexible manufacturing system.

3. The structure analysis of the headstock box

The spindle box is a positive hanging box, that is, the spindle box body moves up and down along the column guide rail in the center of the gantry frame type thermally symmetrical column. Due to the positive hanging box structure, the main shaft is located in the symmetric center of the box body, and the temperature rise deformation of the box body caused by the operation of the machine tool has little effect on the displacement of the main shaft axis. Therefore, it is easier to ensure the cnc machining china accuracy of the machine tool when the spindle box is positively hung. The spindle box body is installed inside the column of the gantry frame, and its assembly process is complicated. It is necessary to have a special process and tooling to ensure the assembly of the spindle box and the gantry column. Machine tools of this structure increase the manufacturing cost of the process.

4. Structure analysis of the side hanging box of the spindle box

The side hanging box is that the spindle box is hung on the outside of the column and moves up and down along the column guide rail. The uprights generally adopt a closed rectangular box structure, which has strong resistance to bending, torsion and deformation. Because the spindle box is hung on the side of the column, the temperature rise of the box body caused by the operation of the machine tool or other hot shots will deform the box body and cause the spindle axis to shift, which affects the machining accuracy of the workpiece. The machine tool of this structure can bear a large cutting force, and it is relatively easy and simple to assemble the correct hanging box.
The machining center is a kind of high-precision mechanical processing equipment, with the premise of improving the machining accuracy of parts. Therefore, most of the horizontal machining centers of domestic and foreign enterprises adopt a positive hanging box structure.

5. Spindle component analysis

1) Structure of fixed spindle:

  • ● Mechanical spindle: The compact integrated spindle group structure is generally used today. It is driven by an independent servo motor and drives the spindle to rotate through a gear stepped transmission. Due to the use of gear speed reduction transmission, the spindle has a wide speed range, which can achieve high torque and heavy cutting processing requirements. In addition, there is a toothed belt synchronous transmission structure, which can realize the stepless speed regulation of the main shaft. No matter what kind of main shaft structure is used for transmission, there is a gap between the head position of the main shaft diameter and the box body. Generally, the box or spindle flange blue disk is designed as a labyrinth structure and protected by an air curtain to prevent penetration of cutting fluid and dust, etc., to ensure the accuracy and service life of the spindle.
  • ● Electric spindle: This type of spindle usually adopts a built-in motor spindle unit structure, and realizes high-speed rotation of the spindle with zero transmission. An encoder is installed inside the spindle, and the spindle operation is controlled by a servo device, which can complete the spindle quasi-stop, emergency stop and other functions. Because the motor is directly driven without a transmission chain, the spindle can reach tens of thousands of revolutions or higher speed, and can reduce the noise, heat, vibration and power loss of the machine tool. It is generally suitable for the processing of small cutting forces, thin walls, complex curved surfaces, and precision parts.

2) Mobile spindle structure:

The mobile spindle structure is generally used on medium and large machine tools. It overcomes the shortcomings caused by the processing of a fixed spindle with a long cutter bar, which easily deforms the cutter bar, and is usually used for deep hole boring or plane milling. When the boring bar or ram is extended, deflection errors will occur, which will affect the processing quality of the workpiece. Therefore, this is a more critical item for machine tools that use mobile spindles. Domestic and foreign companies continue to conduct in-depth research on this, adopt new materials, improve design and process, adopt spindle integration technology and other methods to increase the rigidity of moving parts, and use control and compensation technology to correct moving errors to ensure processing accuracy.

  • ● Boring bar type mobile spindle: This spindle structure can be driven by an independent servo motor to drive the ball screw to move the boring shaft, and the position of the boring shaft is monitored by the position controller. As a coordinate axis of the machine tool, it can independently or participate in the coordinate processing of machine tool coordinates. This axis is usually defined as the W axis. In addition, the hydraulic system is used as the power source, and the hydraulic cylinder moves the boring shaft for the actuator. There is no position monitoring for the movement process of this type of boring shaft, and it cannot be the coordinate axis of the machine tool.
  • ● Ram type mobile spindle: This spindle structure can process the workpiece with a large stroke of the ram, and it can process deeper holes or faces than the boring bar mobile structure. This is because the main shaft continues to move out of the ram on the basis of the ram, and the total stroke can generally reach more than 1000mm. Because the cross section of the ram is a rectangular structure, the clearance of the ram travel is similar to the rectangular guide rail of the machine tool. The gap is adjustable, ensuring high rigidity and repeatability in the movement of the ram. Therefore, its guiding performance and moving accuracy are better than pure boring bar mobile spindle structure.
  • ● Flat-spindle spindle: The flat-spindle can be divided into fixed type and detachable type. The fixed flat turntable is installed on the machine tool and cannot be removed, and the disassembly of the detachable flat turntable can be determined according to the needs of processing. The rotary motion of the horizontal turntable is completed by the main motor through the gear drive; the radial feed movement of the horizontal turntable slider is driven by the servo motor and completed by the gear planetary mechanism. The flat turntable can also be equipped with two sliders moving in the same direction or in the radial direction to achieve feed processing. This flat turntable structure is different from the flat turntable on ordinary machine tools.

The feed of the flat turntable slider is controlled by a servo motor and is called the U axis. The radial slider of the flat turntable is equipped with an automatic tool clamping device, which can realize the automatic exchange of tools, so it is called a numerical control flat turntable. It can realize the swiss turning and boring processing of the turning surface and groove of complex parts.

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