What Is a Centerless Grinding Machine?

Posted on May 16, 2021

Centerless Grinding Machine

Depending on the interaction between the workpiece and the abrasive wheels and the intricacy of the required ground parts, the operation principles that are available on the centerless grinding machine can be divided into profile grinding, in-feed grinding, and thru-feed grinding.

A centerless grinding machine, also known as a centerless grinder, is a type of grinding machine without the machining centers that holds and rotates the workpieces to be ground by the abrasive wheels. It is the interval between the abrasive wheels on the centerless grinding machine that secures and provides the space for the grinding procedure. Without the center, this type of grinding machine can still provide smooth ground surfaces of the workpieces in optimal condition.

For the metal products that cover applications in a wide range of industries, the smoothness of the surfaces is one of the keys that determine the value and the practicality of the products. Take the cylindrical bearings in the component of the mechanism as an example,  it is used to reduce friction, which would be wrapped around the shaft that performs both axial and radial movements. With the rollers or rolling elements rotating in between the outer and inner rings, the bearing is able to handle against the axial and radial thrusts.
 

Cylindrical bearing explained

Since there are outer and inner rings on the cylindrical bearing, there is the outside diameter and inside diameter that determine the size of the bearing. Only when the surfaces of the outside diameter and inside diameter are smooth the shaft and other components attached to the bearing on the outside can be perfectly fitted to each other.

The production of a cylindrical roller bearing requires the configuration of the inside and outside diameters, which are achieved by creating a hole along the length of the cylinder with the turning process. After the hole is created, it has to undergo the refining of the surfaces, which requires the assistance of a grinding machine. With a grinding machine, the burrs or residues on the surfaces of the products can be removed after being ground with the abrasive wheels. This makes the significance of the grinding machine during the manufacturing processes.
 

:: Read More: Introduction to Cylindrical Grinding Machine
 

CNC System

To pursue optimal precision and accuracy in the manufacturing of metal products, most of the machining devices nowadays are combined with a computerized system, referred to as the CNC machining center. In addition to the control panel that is set beside the machine, this type of machine mainly consists of a headstock that holds and rotates the workpieces with a chuck and spindle, a worktable that supports the tool turret that is combined with an automatic tool change function. 

With the multi-functional features of the movable headstock and worktable, the CNC machining center is capable of performing more intricate machining techniques compared to the conventional unit. The same as the grinding machine, the functions of this machine are also compatible with the CNC system, which enables the abrasive wheel to grind on the intricate parts of the products, and ensures the maximum precision and accuracy on the ground parts.

With the advanced development of the machine design, another type of the CNC grinding machine comes in centerless construction. The centerless grinding machine is, as the name implies, without a headstock that supports and rotates the workpiece to be ground. Instead, the workpiece is secured in between the two abrasive wheels, the grinding wheel, and the regulating wheel, with an additional work rest. Considering the operation principle, the rotating parts on the centerless grinding machine are the two abrasive wheels, and this shows the variation between the conventional grinding machine and the centerless type.
 

The machine design

A centerless grinding machine consists of a vibration-damping base, a PLC interface, a grinding wheel, a regulating wheel, a work rest, and the hydraulic dressing units. Before digging into the specific design of the machine, let’s learn about the arrangement of the workpiece since this can be recognized as the most significant feature that differentiates the centerless form from the other with a center.

The two abrasive wheels, including the grinding wheel and the regulating wheel, are set parallel to each other. Within the distance between these two wheels, there is a work rest at the bottom, which allows the workpiece to rest in between the two wheels. Depending on the operation principles, the workpiece can be kept stationary or fed through the gap, which would be discussed in more detail later.
 

Vibration damping base

During the grinding process, when the regulating wheel pushes the workpiece against the grinding wheel, the vibration would be produced on the working site. The base on this machine is equipped with the feature of vibration damping ability, which helps reduce the stress given due to vibration.
 

PLC interface

The PLC stands for the programmable logic control, and the PLC interface allows for the numerical control and adjustment of the process. Besides, there is a digital screen and several switches on this interface, which enable the operators to conduct some manual adjustments.
 

Grinding wheel

The grinding wheel is one of the abrasive wheels on the centerless grinding machine. It is set static and receives the stress given as the regulating wheel pushes the workpiece against it.
 

Regulating wheel

The regulating wheel is the movable abrasive wheel, which conducts the main grinding function by pushing the workpiece toward the grinding wheel. As the abrasives come in contact with the workpiece, the roughness of the abrasive would cause the burrs on the workpiece to be removed.
 

Work rest

The work rest in conjunction with the grinding wheel and the regulating wheel make three-point support for the workpiece above, which is the additional equipment that the conventional form doesn't have.
 

Hydraulic dressing units

The hydraulic dressing units are arranged beside the grinding wheel and regulating wheel respectively. These dressing units are used for sharpening the two abrasive wheels, which keeps the optimal functions of the wheels and the maximum quality of the ground workpieces.
 

The operation principle

Depending on the interaction between the workpiece and the abrasive wheels and the intricacy of the required ground parts, the operation principles that are available on the centerless grinding machine can be divided into profile grinding, in-feed grinding, and thru-feed grinding.
 

profile grinding

Profile grinding is specialized in performing the most intricate grinding on the workpieces. The profiling function of this operation principle is capable of grinding with multiple diameters on the same part.
 

In-feed grinding

The in-feed grinding provides the secondary intricacy of the ground parts on the workpieces among the three operating principles. During in-feed grinding, the workpiece is kept stationary, and the regulating wheel is fed into the workpiece, which completes the grinding process.
 

Thru-feed grinding

The thru-feed grinding is the most efficient and common operation principle of grinding. The workpiece is fed through one side to another between the two abrasive wheels, and the wheels help create relatively simpler parts on the workpieces.
 

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