The tool turret is also called the CNC lathe machine tool turret or a turret head. The tool turret is one of the components in a CNC turning center where the tooling is mounted. The tools are all mounted onto the integral disc, the tool turret disc, of a turret head. A servo turret is the tool turret that has the motion capability. The servo turrets are turned or moved by the AC, sometimes DC, servo motor or a compatible AC servo driver. Typically speaking, the clamping and de-clamping of the servo turret heads are done by a hydraulic or pneumatic power system. A tool turret usually has a single axis motion capability while in some CNC turning centers the turret head is equipped with multi axes movement by the motors in the CNC machine.
The computer numerical control machines control operating tools and the movable parts by converting instructions into action. That is, when the codes are entered in a CNC system, the movements of the parts on a CNC turning center will be initiated. There is a tool turret head on the CNC spindles where the cutting tools are attached. The tooling includes laser cutters, drill bits, and routers. In order to grant the CNC tool turrets with certain motion capability, two major types of motor are used: the stepper motors and the servo motors.
The name stepper derives from the steps that are made by the motor with the signal pulse. This type of motor is simple to function. They are inexpensive compared to the servo motors. With the signal pulses to manage the function, a stepper motor has a higher accuracy as well. The stepper motor usually comes with low speed torque which enables the use of a pulley reduction and timing belt. This makes it possible to drive the loads of tools without gearing.
However, a stepper motor has a lower efficiency than a servo motor. The servo turrets are more efficient in changing the tooling as a result. Also, the low speed torque leads to the slow acceleration of the loads. In addition, a stepper motor is resonance prone, which means it makes louder noise when operating at high performance. The stepper motors usually give a lower power output due to the limitation of its size and weight.
In a servo motor, the closed loop circuit is used to transfer information to the CNC turret head. The servo motors are connected to an encoder with a sensor so that they have high accuracy and resolution. Unlike a stepper motor, the higher torque to inertia ratio generates by a servo motor enables the rapid load acceleration. The lighter the loads are, the more efficient the servo turret head is.
The key disadvantage of the servo turret is that it is more costly than the stepper motor turret head. The servo turret is less simple to operate as well. The peak operating power is produced only at high speed and this easily leads to the contamination of the ventilation system. As a result, the servo motor can be easily damaged by overheating and overloading.
The servo turret head is a platform to mount various types of CNC tooling on a turning center. With a servo turret head, the tooling can be versatile to meet the requirements of particular machining operations. In addition to the conventional drill bits or cutting tools, other types of CNC tools can be mounted to a servo turret head such as CNC routers, laser cutters, plasma cutter, etc.
The CNC routers are used to cut wood, plastic, and sheet metal on a three axes motion basis with the servo turret. The CNC routers are made for larger scale products and the power output is essential in a larger scale operation. Therefore, the servo turret is preferred. The CNC routers are typically capable of only three dimensional routing; yet, there are also routers that are capable of more axes routing which are more efficient. The setup and loading time of the routers can be reduced with a servo turret.
The laser cutters and the plasma cutters are the non-conventional CNC cutting tools. When cutting some types of materials that a conventional metal drill bit cannot cut through, these types of cutter are used. They remove the parts from a work piece by meaning of burning, melting, and evaporating instead of cutting. They are also able to deal with the cutting operations where complicated shapes or cutting angles are involved.
The first advantage of the turret is that it is flexible. Due to the higher power output, a servo turret has a higher capacity of tool stations. In a regular machining operation, there are four to eight tool stations on a turret head while in a larger scale CNC machining operation, there can to up to twelve or even more tools stations on a servo turret.
On the tool stations of the turret head, there are pieces of tool holders on the turret disc. The turret head is able to deal with larger diameter parts. Some of the tool stations on a turret disc allow multiple tool holders and this means more cutting tools can be mounted onto a turret head. With the tooling turret, the CNC machine can accommodate with more machining operations on more axes. Consequently, the turrets have gradually become a must on larger CNC turning centers and other types of multifunction machines.
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