The turning center (also called the turning and milling machine, the turning and milling center) is developed from the CNC lathe. After the workpiece is finished on the CNC lathe, most of the turning process often has a small amount of milling or drilling. The process cannot be done on a CNC lathe and must be clamped to a special milling machine or drill press. This leads to problems such as increased workpiece errors and low processing efficiency. In order to solve this contradiction, a CNC lathe with a powered tool holder has been developed. The C-axis indexing of the power tool holder and the lathe spindle completes the machining of milling and drilling. This is the prototype of the turning center. The turning center generally adopts the process of completing the outer circle, the end surface, the drilling center hole, the boring and the twisting of the workpiece by the fixed knife seat, and the power tool seat on the power turret cooperates with the C axis function of the main shaft to complete the milling of the workpiece. Drilling, tapping and hobbing. For workpieces that require one-time clamping to complete the machining to ensure the accuracy of the workpiece, and the machining requirements are mainly for turning (60%~95%), the milling (such as 5%~40%) is especially suitable for machining on the turning center.
Classification of power tool holders
According to the structure and shape, the power tool holder can be divided into 0° (straight shank) tool holder, 90° (right angle) tool holder, right angle retracting (also called short position) tool holder and other special structure tool holders; Can be divided into: externally cooled tool holder and external cooling plus internal cooling (central cold) type of knife holder; according to the input and output speed ratio can be divided into constant speed knife seat, speed knife seat and speed reduction tool holder.
Power knife seat problem
Power tool holders often have low efficiency due to their lack of rigidity, low repeatability, and long adjustment time during process conversion. At the same time, the power tool holder can only be clamped with the ER spring chuck, and the machining accuracy of the tool holder is limited due to the error superimposed by the ER chuck. In addition, since the clamping force of the ER chuck is limited, the tool is easy to slip when the cutter bar of φ16 or more is clamped, and the blade tip is also relatively large. It is undoubtedly a very important bottleneck for tool life and machining efficiency.
Moreover, the type of tool clamped by the ER chuck is limited and can only be used for simple drilling and milling operations. Customers need to purchase a special face milling cutter power knife seat, etc., and the tool holder has a large investment. How to solve the problems brought by the ER chuck, expand the scope of use of the power tool holder, and achieve "one multi-energy" is the direction that the major power tool holders actively seek solutions.
Investigate and evaluate the indicators of the dynamic tool holder
Investigating and evaluating the power tool's indicators mainly include speed, torque, rigidity, accuracy, service life, temperature rise, noise and interface flexibility.
Among them, the rotation speed reflects the machining efficiency of the tool holder, and the torque mainly investigates the cutting force that the tool holder can carry. Affects milling depth, drilling and tapping diameter. The type of bearing used in the power tool holder has a large effect on the torque. Generally, angular contact ball bearings are used, and the overload resistance is poor, and it is easy to form a dead point on the surface of the ball, resulting in a decrease in the accuracy of the power tool holder. Nowadays, some manufacturers use double tapered roller bearings, their load capacity is greatly enhanced, but at the same time to solve the problem of speed and noise and temperature rise, it requires high precision and assembly precision of the power tool cavity, so as to ensure high speed and large. Simultaneous implementation of targets such as torque, temperature rise and noise control.
Rigidity is an important part of the entire tool chain system of the machine tool - turret - tool holder - tool holder - blade - workpiece, which directly determines the rigidity of the chain system. Accuracy includes two aspects, one is the accuracy of the tool holder itself, including axial runout, radial runout, position accuracy and parallelism of the mandrel, etc. Second, the positioning accuracy and repeat positioning accuracy of the tool holder on the turret are reflected separately. The accuracy of the tool holder at the turret installation position and the positioning accuracy after repeated disassembly and assembly affect the machining accuracy of the workpiece and the adjustment time of the machine tool.
The power tool holder is a very frequently used function on the turning center. Its service life is related to the manufacturing quality of the tool holder itself, the correct use method in the later stage and the reasonable maintenance method. Temperature rise refers to the degree of temperature rise when the tool holder is working, and the noise when the tool holder rotates reflects the rotational vibration of the mandrel and the bearing, which will affect the machining accuracy of the turning center. Finally, the flexibility of the toolholder interface means that in addition to the spring collet, the toolholder can have a variety of other types of adapter connection tools.
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