In the field of metal grinding, the centerless grinder is a processing procedure that uses abrasive cutting to remove material from the work piece during the whole process. The operation difference between centerless grinding and centering grinding is that no spindle or fixture is used to position and fix the work piece, and the work piece is only fixed between the two rotating grinding wheels, but their rotation relative to determines the efficiency of material removal.
In short, a grinding machine is used to shape the outer, inner, or surface side of a work pieces through the continuous grinding mechanism that is using multiple cutting methods. The centerless grinding usually takes action preferentially over other grinding processes. On-site operators in the production line have to process many parts in a short time.
In the grinding machine, each grain of abrasive on the surface of the grinding wheel gradually cuts out small pieces from the workpiece by the shear deformation method, while flowing continuously in a very fast process. Due to the difference in purpose and application, the types of grinding machines are huge and the classification is complicated. Each grinding type will have different corresponding grinding wheels, or say tools. Regarding the grinding machine types, some are easy to recognize, such as belt grinders, bench grinders, cylindrical grinders, surface grinders, tool, and cutter grinders, jig grinders, gear grinders, die grinders, angle grinders, and roller grinders.
For centerless grinding (some may use the term as center-less grinding), the workpiece is clamped between two grinding wheels, rotating at different speeds in the same direction, and a work-holding platform like a magnetic chuck. A grinding wheel rotates on a fixed axis and applies a downward force on the workpiece, against the work holding platform.
The design purpose of the specific grinding wheel is usually to perform the grinding by having a higher tangential speed than the workpiece in terms of contact time and sides. The other wheel, which is called the regulating wheel, is designed to be movable. This wheel is positioned to apply lateral pressure to the workpiece, and the grinding wheel usually has a very rough or rubber-bonded abrasive to trap the workpiece. The speed of the two wheels relative to each other provides the grinding effect and determines the rate at which material is removed from the workpiece. During the centerless grinding operation, the workpiece rotates with the regulating wheel, has the same linear velocity at the contact point, and there is no further slip. Therefore, the grinding wheel rotates faster, slips over the surface of the workpiece at the contact point, and eventually removes material chips as it passes by.
The centerless grinding mechanism is different from the ordinary grinding process. It uses a purpose-built centerless grinder. Such a machine will always contain some of the critical components that are very specific and exclusive to this type of grinding process. For example, grinding wheels, relating wheels, and some means that are used for supporting the intended workpieces.
Moreover, modern grinders may involve computer numerical control (CNC) to allow automation and improve accuracy. The grinding wheels are interchangeable for the operators, so the design goal is to allow different grit and shape according to the task. Machines designed to feed grinding operations will allow adjustment of the angle of the regulating wheel to accommodate parts of different sizes and materials, all under the control system of the CNC system.
Regarding the end-feed centerless grinding, the workpiece component is fed axially into the machine in one direction and comes to rest against an end stop. The grinding operation is performed this way and then the workpiece is fed on the other side, and the opposite direction in order to exit the machine. To sum up, the end-feed grinding is best for tapered workpieces. On the contrary, the in-feed centerless grinding is applied to grind workpieces that are with relatively complex profiles and shapes, such as hourglass shapes, curved cylinders, bent-like tubes, etc. Before the process begins, the workpiece is loaded by workers manually onto the grinding machine.
In short, the centerless grinders are designed for specific workpiece shape, because no spindle or fixture is used to locate and fix the workpiece during the grinding process, and the workpiece is only fixed between the two rotating grinding wheels and will be based on each other's rotation speed determines the rate at which material is removed from the workpiece. This type of grinders serves manufacturers for their industrial purposes and works centerless processes. Because of the functionality it can bring to workpieces, it will never be considered an old technology.
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