The Centerless Grinders Are Unique

Posted on Aug 17, 2020

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Centerless Grinders

Centerless grinding uses specially designed centerless grinders. Such a machine always includes a grinding wheel, a regulating wheel (adjusting wheel), and work support. Modern machines may require computer numerical control to enable automation and improve precision.

What Are Centerless Grinders?

Centerless grinders are a type of grinding machine used specifically for finishing operations. They are employed to perform the finishing process for cylindrical parts such as shanks, rods, pistons, and shafts in particular. What makes the centerless grinders stand out from the typical grinders is that the workpieces are not held in place by any sort of fixtures during the grinding process. Instead, the workpieces are fed between two wheels that are positioned against each other radially. This method allows large volume production since the workpieces are fed constantly between the wheels. Such a process is known as centerless grinding.
 

Working Principle of Centerless Grinding

Placed on work support (or work rest), the workpieces are fed between two grinding wheels rotating in the same direction at different speeds during a centerless grinding process. One of the wheels is known as a grinding wheel. It sits on a fixed axis and rotates so that the force applied to the workpiece is directed downward onto the work rest. This wheel typically performs the grinding operation at a higher tangential speed than the workpiece at the point of contact. The second wheel, known as the adjuster wheel or the regulating wheel, is movable. It exerts lateral pressure on the workpiece and has a very rough, or rubber bonded, abrasive that traps the workpiece.
 

Grinding Wheel & Regulating Wheel

During grinding, the force of the grinding wheel pushes the workpiece against the regulating wheel and against the support. The control wheel determines the rotational speed of the workpiece. The grinding wheel and regulating wheel rotate at different speeds and enact the grinding process. The rotating speeds determine the removal rate. During operation, the workpiece rotates with the regulating wheel at the same linear speed at the point of contact and (preferably) without slippage. The grinding wheel turns faster, slipping past the surface of the workpiece at the point of contact and removing chips of material as it passes.
 

Types of Centerless Grinding

There are three types of centerless grinding, differing primarily in the method used to feed the workpiece through the machine. They are through-feed, in-feed, and end-feed grinding.

Through-feed Grinding

Through-feed grinding is the most typical type of centerless grinding. The term, through-feed, refers to how a workpiece enters and exits the two wheels. During a through-feed grinding process, the workpiece advances through the wheels from one end and passes through the wheels from the other. Through-feed grinding is only applicable to process workpieces with a simple surface design.

In-feed Grinding

The in-feed centerless grinders are capable of machining workpieces with a more complex surface design. Since the workpieces that in-feed grinder processes may come with a variety of surface designs, they cannot pass through the grinding wheels from one end to the other. They have to be fed between the wheels radially. In order to process workpieces with complex contours or profiles, the grinding wheel can be dressed.

End-feed Grinding

Just like in-feed grinding, end-feed grinding is another technique that makes processing complex workpieces possible. That said, end-feed grinding is necessary when workpieces with certain profiles cannot be processed with in-feed grinding. The key difference between these two centerless grinding methods is that end-feed grinding is used when machining only parts of a workpiece is required. With the end-feed grinding capability, a centerless grinder is able to deal with pieces with even more complex surfaces.
 

Construction of Centerless Grinders

Centerless grinding uses specially designed centerless grinders. Such a machine always includes a grinding wheel, a regulating wheel (adjusting wheel), and work support. Modern machines may require computer numerical control to enable automation and improve precision. The grinding wheels are interchangeable to allow for different grains and shapes. Machines designed for pass-through grinding operations will allow the angle of the regulating wheel to be adjusted to accommodate different sized parts.

:: Read More: Centerless Grinding and Precision Machining


Centerless Grinding Pros & Cons

Centerless grinding is critical in the production of many high-volume auto parts. These include valve sliders, control rods, camshafts, crankshafts, pistons, bushings, and rollers. In addition, centerless grinding is used to manufacture parts for the hydraulic and fluid control industries, the medical and aerospace industries - in fact, any industry where roundness and extreme accuracy of cylindrical surfaces are required.

Centerless grinding has several advantages. Since there is no need to place the part between centers or clamp it to a chuck, parts can be quickly loaded into the grinder for increased throughput. The workpiece is held securely between the wheels and the support rail, allowing grinding of long, thin pieces. And because the wheel adjustment is diametric, rather than radial - as is the case with cylindrical grinders - any infeed errors are halved, which increases precision.
 

Other Features of Centerless Grinders

Centerless grinders are often classified according to the inclination of the machine bed. The most popular are machines with horizontal beds, which provide easy access for wheel dressing. Angular and even vertically inclined beds are used for grinding heavy workpieces because of the potential for a greater grinding force and less abrading of the workpiece by the work support.

Though the concept of centerless grinding is less straightforward to most people, and it seems that grinding without a center decreases the overall controllability of the process, centerless grinding is actually able to achieve the high-level surface finish, roundness, and precision when set up properly. The key to a successful centerless grinding is to set the grinding wheel and the regulating wheel at the same centerline.

 

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