In a metal working machine, the spindle is the rotating axis of the machine. The spindle is usually a combined unit containing a mandrel. This rotating unit includes a mandrel, a sleeve, a tool holder or a work piece holder device, bearings, cutting fluid and a coolant circuit, etc. It can be seen that the built-in motor spindle has the most complicated spindle structure. Its power unit- spindle motor is built into the spindle sleeve, so it can supply power by itself.
The spindle can have various names according to its characteristics, including electric spindle, grinding spindle, machine tool spindle, low speed spindle, high speed spindle, high torque spindle and many other variants. This category of spindle is generally called electric spindle or motorized spindle, but in this article, we call it a built-in motor spindle.
Multiple spindles can often be seen on the machine tool, such as the headstock and tailstock spindles on a bench lathe, or primary spindle and secondary spindle on machining centers.
Some machine tools dedicated to mass production will be equipped with a set of four, five or even six spindles. These machines are called multi-spindle machines. For example, row drills and many screw machines are multi-spindle machines that can perform multiple tasks simultaneously.
Some machine tools are equipped with multiple spindles, but depending on the purpose of each spindle, it cannot be called a multi-spindle machine because it cannot perform multiple tasks at the same time. For example, bench lathes.
The spindle on the lathe is usually fixed in the center of the headstock or tailstock to hold the work piece; the spindle on the milling machine is used to hold the rotating tool and move along each axis to cut the work piece.
The term “Revolutions per minute (rpm)” is the measurement unit for spindle speed. The so-called high speed and low speed classification is not very clear, but in general, high speed spindles are considered to be used for high-end machining centers such as CNC milling machines. In addition to the built-in motor spindle, the field of high speed spindles also includes two other types:
The first is the belt driven spindle. As the name implies, a belt is installed in its structure. The belt driven spindle transmits the movement of the external spindle motor to the spindle through the belt.
The second is the direct driven spindle. The spindle motor is placed above the spindle. The motor and spindle are connected by a high rigidity coupling. The movement of the motor is transmitted to the spindle via the coupling.
The types of spindles using external motors mentioned above, such as belt driven and direct driven spindles, have a max. speed of approximately 12,000 rpm to 15,000 rpm. The advantage of this type of spindle is that the speed can be switched quickly and the cost of the spindle is lower, but due to their limited speed, they cannot be used for many complex machining centers or high-profit machining tasks.
In contrast, in the integrated motor spindle, the spindle motor is placed in the spindle sleeve. It makes appearance very simple, and can meet the high speed requirements such as 30,000 rpm. The disadvantage of this type of spindle is the low torque, so it is not suitable for heavy cutting tasks.
Just like other mechanical parts, the spindle can also be customized. The customized built-in motor spindle is mainly used for high-end machining, which is commonly seen in 3C wearing parts machining, work piece finishing, aircraft propeller cutting, engine cylinder machining, car chassis machining, gearbox joint grinding, etc.
In the field of machining centers, most machining centers on the market are equipped with electric spindles for multi-task machining. The motor is installed in the spindle sleeve, so the spindle can rotate and move in each axial direction, the machining efficiency is higher, and various curved machining and complex cutting can be performed.
Therefore, compared with spindle driven by other ways, built-in motor spindles are more often installed in complex machine tools such as vertical machining centers, horizontal machining centers, double column machining centers, and moving column machining centers.
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