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Posted on Feb 18, 20190
In modern machine tool industry, a spindle is a rotational axis of the machine, which usually designed with a shaft at its center. The shaft itself is named a spindle, but also, in the market slang, the referring term (phrase) is often used metonymically to point at the entire rotating unit, including not only the shaft itself, but also its bearings and anything around (or attached to) to it (such as chuck, cylinder, etc.).
In modern machine tool industry, a spindle is a rotational axis of the machine, which usually designed with a shaft at its center. The shaft itself is named a spindle, but also, in the market slang, the referring term (phrase) is often used metonymically to point at the entire rotating unit, including not only the shaft itself, but also its bearings and anything around (or attached to) to it (such as chuck, cylinder, etc.). In this point of view, a built-in spindle is one of the top-classed one that is self-motorized due to its electric-driven nature and is designed with the power unit close with the spindle case box.
A machine tool may be installed with several different spindles, such as the headstock and tailstock spindles on a bench lathe, or primary spindle and secondary spindle on machining centers. The main spindle is usually the biggest one installed at the primary machining unit. In the market, references to "the spindle" without further qualification indicate the main spindle only.
Some machine tools that specialize in mass production model have a group of four, five, or even six more main spindles. These are called multi-spindle machine tools. For example, gang drills and many screw machines are multi-spindle machines that can process simultaneously. Although a bench lathe has more than one spindle, it is not called a multi-spindle machine.
If it is on a lathe machine (both woodworking lathe and metalworking lathe), the spindle is the center of the headstock case. Moreover, in rotating-cutter metalworking machine tools (such as milling machines and tapping machines), the spindle unit is the shaft to which the machining tool (i.e. a drill bit or milling cutter) is attached to. There are varieties of spindles, including electric spindles, grinding spindles, machine tool spindles, low-speed spindles, high speed spindles, just to name a few.
Regarding the speed, the RPM and the range classification is vague. Normally, high speed spindles are used strictly in machines, like CNC mills, which are designed for metalworking sector. There are two types of high speed spindles, each with different designs:
- The belt-driven spindle, which is consisted of spindle and bearing shafts held within the spindle housing. The belt-driven spindle is powered by an external motor connected via a belt-pulley system.
- External Motor source: This design can be changed to create higher power and torque maximum speeds range from 12,000 RPM to 15,000 RPM. The advantage is agile in speed switch and cost effective. Meanwhile, the disadvantage is limited maximum speed that would eventually limits the machinery applications.
- Integrated motor spindle: Within this design, a main component of this spindle is the motor, which is stored internally inside the body, and the internal motor grants limited power and torque due to the restricted space within the spindle housing, so that the frame design confines the machining capability.
For built-in spindles (motorized spindles), the primary applications are not in heavy duty machining but mostly on the high end processing, such as 3C consumable processing, work piece finishing, aerospace propeller cuttings, engine cylinder machining, sedan chassis processing, transmission joint grinding, just to name of few here. For these applications the manufacturers demand a common feature that is to be quick and agile during machining process. Therefore, this critical key determines most of the application field that motorized spindle, or say, electric spindle, to be exploited.
Electric spindle, when compared with other spindle models, can achieve good processing quality with high speed RPM and fast speed switch between models. Moreover, its torque performance, though not to be compared with direct drive spindle, is much stable and stronger than belt-drive spindle models averagely. For example, conventional CNC turning machine may be installed with belt-driven spindles, but with higher processing demands, such as turn-mill centers (turning centers), the spindle would normally be electric spindles since work pieces fixed on the chuck and clamped by the cylinders may be more rigid regarding its toughness, so that if the spindle is driven by belt, the teeth on the belt are more likely to encounter mistakes with the gears, rendering unfavorable results.
For machining centers, most of the machining centers on the market are installed with electric spindles for the multi-tasking processing sake. With the built-in motor inside the spindle case, the multi-axis heads are thus able to rotate more freely and work in a more swift way, which means a lot of curved machining and complicated cutting.
Vertical machining centers, horizontal machining centers, double column machining centers, and moving column machining centers are thus installed with motorized spindle more than with other types of spindle models in order to make the best use of their structural design and process in an efficient way.