Grinding Spindles

Spindle application is an important topic in machine tool field, and grinding spindle is one of the items that are often concerned about. As one of the important components of modern machine tools, there are many types of spindles, which can be divided into belt driven, gear driven, motor built-in, and direct driven, etc. according to the spindle driven mechanism. Direct driven spindles usually have greater torque and can be applied to large machining areas. Because the above functions are less needed in the grinding machining, and more attention is paid to the vibration resistance and high precision of the spindle, most of them adopt belt driven and motor built-in mechanism.

Grinding can be defined as the rapid removal of material from the work piece surface to the target size, or the removal of irregularities from the surface. The grinding wheel or grinding tool usually rotates at a high speed, and covered by coarser abrasive grains on its appearance. The higher precision grinding is lapping and polishing, which is characterized by the finer abrasives. The amount of these materials removed can be precisely and minutely controlled, especially in the nano-level range.
Many different types of spindles can be used as grinder spindles for equipping grinding wheels. Common applications include motorized spindles that equip traditional grinding wheels for grinding tasks, traditional grinders that equip CBN grinding wheels, or CNC controlled motorized spindles.


Grinding wheel

To complete grinding tasks, the spindle on machine needs to be equipped with a proper grinding wheel. Below we will have an overview of grinding wheel.
Grinding wheels are wheels composed of abrasive materials used for various grinding tasks. This type of grinding wheel is used for grinding machines. Grinding wheels are usually made of composite materials, which are composed of pressed coarse-grained aggregates and are bonded together by a cemented matrix to form a solid and circular shape. Depending on the intended use of the wheel, various profiles and cross-sections can be used. They can also be made of solid steel or aluminum discs with particles attached to their surfaces. The history of grinding wheel materials began with natural composite stones. Today most grinding wheels are made of artificial composite materials made of artificial aggregates.
The production of grinding wheels is highly precise. The design of the grinding wheel must be able to withstand the high pressure of the rotating disk while maintaining the function of uniform rotation. Obviously, the design, development and production of grinding wheels and grinding wheel spindles is a highly complex process that requires the experience and engineering knowledge of manufacturers in various fields.


Grinding speeds

The speed of the grinding spindle determines the grinding speed. The grinding speed is not the higher the better. It needs to be determined according to the characteristics of the work piece material and the size of the grinding wheel.
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.


Power source of spindles

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.


Wider applications

In the latest machinery technology, a machine tool can equip multiple spindles, such as the headstock spindle and tailstock spindle of a bench lathe. Other machine tools dedicated to mass production may also have 2, 3 or more spindles. These are called multi-spindle machine tools, such as gang drills and screw machines.
Some spindles are specially designed for certain machine tool types and functions, such as turning spindles, milling spindles, drilling spindles, etc. Within grinding spindles, you will find like surface grinding spindle, internal grinding spindle, tool cutter spindle, etc. These spindles usually needed to equip with different tool (cutter or grinding wheel) to perform their designed functions. Only when the correct spindle is installed can the machine tool perform its functions accurately.

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