CNC lathe is the abbreviation of a digital program-controlled lathe, which combines the characteristics of a universal lathe, a precision lathe with high processing accuracy, and a special lathe with high processing efficiency.
CNC lathe is mainly used for the processing of rotating body workpiece, generally can automatically complete internal and external cylindrical surface, internal and external conical surface, complex rotary internal and external surface, cylindrical-conical thread and other contour cutting, and can carry out grooves, drilling, reaming, broaching, tapping and other processing.
The most basic components of a CNC lathe include 11 parts: spindle box, feed box, tailstock, bed, lead screw, smooth bar, slide box, wheel frame, tool rest, carriage, and control lever.
Main Parts of CNC Lathe
1. Spindle Box
The spindle box is fixed on the upper left of the lathe. It transmits the rotary motion of the motor to the main axis and drives the workpiece to rotate together through the jig. By changing the position of the handle outside the box, the spindle can obtain a variety of different speeds of forward and reverse.
2. Feeding Box
The feeding box is fixed on the left front and lower side of the lathe and the rotating motion of the main shaft is transmitted to the lead screw or smooth bar through the hanging wheel.
3. Carriage Apron
The carriage apron is fixed on the front side of the saddle and reciprocates longitudinally on the guide rail of the CNC lathe together with the saddle. Through it, the rotary motion of the lead screw or the smooth rod is changed into the feeding motion of the saddle and the middle sliding plate.
4. Change Gear Plate
The change gear plate is installed on the left side of the CNC lathe. It is equipped with an exchange gear (change gear), which transmits the rotational motion of the main shaft to the feed box. Adjust the gears on the hanger frame and cooperate with the feed box to turn threads with different pitches.
5. Knife Rest
The tool rest is fixed on the small carriage for mounting the spare turning tool.
The carriage includes 4 parts: saddle, middle slide, turntable, and small slide. The saddle is mounted on the outer guide rails of the bed, and can move longitudinally along the guide rails of the CNC lathe; the middle slide plate can move laterally along the dovetail guide rails on the upper part of the saddle; the small slide plate can move longitudinally along the dovetail guide rails on the upper part of the turntable. After the turntable is rotated by an angle, the small slide plate can drive the knife to move obliquely to turn the short inner and outer conical surfaces.
The tailstock is mounted on the guide rails in the CNC lathe and can move longitudinally along the guide rails of the lathe. The tip, drill, reamer, tap, and other knives and auxiliary tools can be installed in the sleeve taper hole on the tailstock to support the workpiece, drilling, reaming, tapping, etc.
8. Lathe Bed
The bed is the supporting element of the lathe. It is fixed on the left and right lathe legs to support the main parts of the lathe and keep them in an inexact relative position during work.
9. Screw Rod
The screw rod is one of the main precision parts on the lathe, which is mainly used for turning threads. In order to maintain the accuracy of the screw rod for a long time, the screw rod is generally not used for automatic feeding.
10. Light Lever
The light lever transmits the motion of the feeding box to the sliding box so that the saddle and the middle sliding plate are automatically fed vertically and horizontally.
11. Control Lever
The control lever is one of the main parts of the CNC lathe control mechanism. The left end of the control lever and the right side of the slide box are respectively provided with a control handle. The operator can easily and freely manipulate the handle to control the forward turn, reverse turn, or stop of the lathe spindle.
8 Characteristics of the Mechanical Structure of CNC Machine Tools
1. Has High Static and Dynamic Stiffness and Good Shock Resistance
The stiffness of the machine tool reflects the ability of the machine tool mechanism to resist deformation. The error caused by the deformation of the machine tool is usually difficult to be completely solved by adjusting and compensating. In order to meet the requirements of high efficiency, high precision, high reliability, and automation of CNC machine tools, compared with ordinary machine tools, CNC machine tools should have higher precision and rigidity. In addition, in order to give full play to the efficiency of the machine tool and increase the amount of cutting, it is also necessary to improve the vibration resistance of the machine tool to avoid resonance and chatter during cutting. And improving the dynamic stiffness of the mechanism is the basic way to improve the shock resistance of the machine tool.
2. Has Good Thermal Stability
The thermal denaturation of the machine tool is one of the main factors affecting the machining accuracy of the machine tool.
Since the spindle speed and rapid feed of CNC machine tools are far higher than those of ordinary machine tools, and the machine tools are in a continuous working state for a long time, the heating of motors, lead screws, bearings, and guide rails are relatively serious, and the influence of chips generated by high-speed cutting, that the thermal denaturation effect of CNC machine tools is much more serious than that of ordinary machine tools. Although the advanced numerical control system has the thermal denaturation compensation function, it cannot completely eliminate the influence of thermal denaturation on machining accuracy. Necessary measures should be taken on the numerical control machine tool to reduce the thermal denaturation of the machine tool as much as possible.
3. The Mechanical Structure of the Transmission System is Simplified
The servo feed system is used to replace the feed system of the ordinary machine tool, and the spindle can be automatically shifted through the spindle speed control system. The motor can be directly connected to the main shaft and the ball screw, and the number of gears, shaft parts, and bearings is greatly reduced; therefore, in terms of mechanical structure, the structure of the main spindle and feed gearbox of CNC machine tools is generally very simple. In operation, it is not like ordinary machine tools, which require the operator to adjust and change speed through the handle, and the operating mechanism is much simpler than that of ordinary machine tools.
4. High Transmission Efficiency and Backlash-Free Transmission
The CNC machine tool performs high-speed and high-precision machining, and while simplifying the mechanical structure, it also puts forward higher requirements for the mechanical transmission and components. Such as ball screw pair, plastic sliding guide, hydrostatic guide, linear rolling guide, and other high-efficiency executive components, not only can reduce the frictional resistance of the feeding system, and improve the transmission efficiency; but also can make the movement smooth and obtain high positioning accuracy.
5. Adopt Guide Rails with Low Friction Factor
In order to allow the machine tool pallet to move in the specified direction (parallel or perpendicular to the direction of the spindle axis) (triangular guide rail “orientation”), and to carry the cutting resistance during cutting (rectangular guide rail “bearing”).
6. The worktable realizes a variety of movement modes, which can meet various requirements of parts processing.
7. The tool magazine and automatic tool changer realize continuous processing, reduce tool change time and workpiece loading and unloading times, and improve production efficiency.
8. Auxiliary device to protect the machine tool and improve the quality of the workpiece.
Common Tools and Selection of CNC Lathes
1. Common Tools for CNC Lathes
The tools used on CNC lathes include cylindrical turning tools, drills, boring tools, cutting tools, threading tools, etc. Among them, cylindrical turning tools, boring tools, and drills are the most commonly used.
The turning tools, boring tools, cutting tools, and threading tools used in CNC lathes are divided into welding types and machine-clamping types. Except for economical CNC lathes, machine-clamping turning tools have been widely used. The blade and the blade pressing system are composed of three parts, among which the blade generally uses a carbide-coated blade.
2. Tool Selection
In actual production, the CNC turning tool is mainly determined from the tool sample according to the tool installation size, workpiece material, processing type, processing requirements, and processing conditions of the CNC lathe rotary tool holder. The steps are roughly as follows:
1) Determine workpiece material and machining type (external, hole, or thread);
2) Determine the grade and geometry of the insert according to the roughing and finishing requirements and processing conditions;
3) Choose a holder based on holder size, blade type, and size.
3. Tool Installation
After selecting the appropriate blade and knife back, first, install the blade on the shank, and then install the shank on the rotary tool holder in turn, and then check the tool installation size through the tool interference diagram and the machining stroke diagram.
4. Matters Needing Attention
In the process of tool installation, the following issues should be paid attention to:
- Before installation, ensure that the tool holder and blade positioning surface are clean and without damage;
- When installing the knife back on the tool holder, ensure that the direction of the tool holder is correct;
- When installing the tool, ensure that the tool point is higher than the rotary center of the spindle.
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